Hello from London

[AdamJ]

Hi Buildhub, 

 

Given that I've been thinking about self-building for years, I'm amazed that I haven't noticed this forum before now.  It seems like a really active and friendly place, with a lot of knowledgeable members. 

 

I've got an option on a site in south-east London (which took a lot of searching and negotiating to get), and now that I have the option my second step is figuring out what construction method to use. 

 

My goal with this house is for it to be net zero carbon, and to begin with I'm trying to do a comparison between ICFs and SIPs. I know that any construction method can be used to create a high performance, energy efficient building fabric, but both of these methods have a reputation for achieving good performance levels relatively 'easily'. 

 

I'm doing some simulations of energy in use (using a trial of Designbuilder I downloaded last week) and calculations of embodied carbon (in an Excel spreadsheet, using the ICE database) to get an idea of whether the higher embodied carbon of the concrete could be justified with lower energy in-use.  I'd love to share these with you guys and get your thoughts when they are done. What is the best sub-forum to post in? New House and Self Build Design? 

[SteamyTea]

Welcome.

Decide on the foundation system first, it is where it all starts.

Then go the timber frame route, things are much better when they are build in a factory.

[ProDave]

Hi and welcome.

 

Before you decide on construction methods, research "decrement delay"  There is more to insulation than just the U values and the performance of the "same" walls with PIR / PUR insulation (like you get in most SIP panels) and the "same" wall in say a timber frame using mineral wool or wood fibre insulation.

 

Take a look at this thread recently

 

Here he posted an analysis of 2 roof constructions that both had the same U value, but look how much quicker heat passes through the PUR one compared to the mineral wool / wood fibre one.

[SteamyTea]

7 minutes ago, ProDave said:

Before you decide on construction methods, research "decrement delay" 

Or Thermal Time Constant (the time it takes to drop or rise 1°C).

Or just do it properly:

https://en.wikipedia.org/wiki/Thermal_effusivity

 

And never, ever us the common term.

 

[Iceverge]

Welcome Adam

 

I assume the desire for Net Carbon Zero is an environmental aspiration.

 

It might be worth getting a handle on some figures. 

 

Concrete emits about 375kg CO2 per m3.  EPS is about 66kg/m3. So assuming a passive standard ICF wall is 200mm eps /150mm concrete/50mm eps thats 0.15m3 concrete/m3 and 0.25m3 eps or about 73kg CO2 per area eternal wall excluding finishes or for 200m2 of wall area about 15 tonnes CO2 emitted all in one big bang at the time of building the house.

 

Compare that to an equivalent twin wall timber frame 300mm cellulose built wall. 

 

OSB stores about 1 tonne co2/m2 - 200kg co2 to manafacture = 800kg Net negative co2/m3. 

Timber is also net negative, about -500kg/m3

Cellulose is also about -80kg/m2

 

Twin wall construction 10mm OSB 300mm cellulose 7% timber 10mm OSB  works out at

-16kg/Co2/m2 (OSB)

- 22.5kg/CO2/m2 (Cellulose)

-10.5kg/CO2/m2 (timber)

 

Total Nett negative 48kg/CO2/M2 or about 10 tonnes of carbon stored in the house for the duration of it lifetime. 

 

Total Difference of about 25 tonnes CO2 

 

Next build to passivhaus standards at 170m2 floor area and buy electricity from the grid at about 250gCo2/Kwh run it through a heat pump with an average COP of 3 and your carbon savings from change of construction type would heat your house for 116 years. 

 

Thats before you add solar PV, 

Decarbonise your foundations and roof structures, 

Consider the lowering carbon intensity of grid generation and consider improvements in heat pumps. 

 

The reality is that the concrete house will start the race over a century behind and never catch up. 

 

 

 

 

 

 

 

 

[AdamJ]

Thanks for the warm welcome and the initial thoughts guys!

 

18 hours ago, SteamyTea said:

Welcome.

Decide on the foundation system first, it is where it all starts.

Then go the timber frame route, things are much better when they are build in a factory.

Steamy Tea, do you mean timber frame in contrast to SIPs?  

 

15 hours ago, ProDave said:

Hi and welcome.

 

Before you decide on construction methods, research "decrement delay"  There is more to insulation than just the U values and the performance of the "same" walls with PIR / PUR insulation (like you get in most SIP panels) and the "same" wall in say a timber frame using mineral wool or wood fibre insulation.

 

Take a look at this thread recently

 

Here he posted an analysis of 2 roof constructions that both had the same U value, but look how much quicker heat passes through the PUR one compared to the mineral wool / wood fibre one.

Prodave, thanks for the tip on UKBAKUS. I've inputted the two walls I have been comparing and contrasting - both perform well, but the ICF wall is better from a decrement delay point of view, given the much higher mass of the concrete. 

 

12 hours ago, Iceverge said:

Welcome Adam

 

I assume the desire for Net Carbon Zero is an environmental aspiration.

 

It might be worth getting a handle on some figures. 

 

Concrete emits about 375kg CO2 per m3.  EPS is about 66kg/m3. So assuming a passive standard ICF wall is 200mm eps /150mm concrete/50mm eps thats 0.15m3 concrete/m3 and 0.25m3 eps or about 73kg CO2 per area eternal wall excluding finishes or for 200m2 of wall area about 15 tonnes CO2 emitted all in one big bang at the time of building the house.

 

Compare that to an equivalent twin wall timber frame 300mm cellulose built wall. 

 

OSB stores about 1 tonne co2/m2 - 200kg co2 to manafacture = 800kg Net negative co2/m3. 

Timber is also net negative, about -500kg/m3

Cellulose is also about -80kg/m2

 

Twin wall construction 10mm OSB 300mm cellulose 7% timber 10mm OSB  works out at

-16kg/Co2/m2 (OSB)

- 22.5kg/CO2/m2 (Cellulose)

-10.5kg/CO2/m2 (timber)

 

Total Nett negative 48kg/CO2/M2 or about 10 tonnes of carbon stored in the house for the duration of it lifetime. 

 

Total Difference of about 25 tonnes CO2 

 

Next build to passivhaus standards at 170m2 floor area and buy electricity from the grid at about 250gCo2/Kwh run it through a heat pump with an average COP of 3 and your carbon savings from change of construction type would heat your house for 116 years. 

 

Thats before you add solar PV, 

Decarbonise your foundations and roof structures, 

Consider the lowering carbon intensity of grid generation and consider improvements in heat pumps. 

 

The reality is that the concrete house will start the race over a century behind and never catch up. 

 

 

 

 

 

 

 

 

Iceverge, you're right that I'm coming at this with environmental aspirations.  I share your sentiments on getting a handle on the figures, which is why I wanted to compare the energy/carbon in use and embodied carbon for the two methods (what has taken me days to figure out you have summarised in a short forum post!).   It does look like the concrete house starts a century behind (more even) before cost is taken into account - something I haven't looked at yet but need to, and there are some other wrinkles I would like to talk to you guys about. 

 

Seeing as we've started the conversation here in this thread, I may as well continue! 

 

The house

The house is a simple three-storey box with pitched roof.  It sits at the southern end of a terrace, with the front door on the south or west elevation, and a garden to the east, with windows on the west, south, and east elevations. (The picture is the house model in Designbuildder - the windows were placed automatically by the software. I will move them around and resize them a bit at a later stage, but for now it shows pretty much the right amount of glazing). 

 

Floor area is approx 180-190 sqm GIA depending on wall thickness.  

 

I've assumed it would be heated with an ASHP with a COP of 3, with MVHR.  I've also assumed the windows would be triple-glazed with a U-value of 0.6, fitted with with shutters.  

 

In use

I haven't looked at energy use that would be the same in both house for lighting and applicances. 

 

ICF

I've assumed an ICF system with insulation to the outside only, like Nudura One, to expose the thermal mass of the concrete to the inside air, as well as concrete floors with no additional finish on top, which also increases the thermal mass.  For internal stud walls, I thought I could recycle the plywood shuttering from the Nudura One, and treat it with a fire retardant, instead of using plasterboard.  I've assumed the same SIPS roof to both houses. 

 

The Designbuilder simulation, using the weather data for Gatwick, shows that the house would require 320 kWh annually to heat using electricity from the grid.  

On winter design day, with -5 degrees air outside, the heating load is 2.8kW 

Overheating doesn't appear to be a problem. Opening the windows will provide good cross ventilation to cool the house at night, which I have put into the model. The worst case room is a bedroom on the first floor, which has 58 hours over 25 degrees each year, which I think is very low.  If I did want to add cooling (not really needed, but as a test) with a set point of 25 degrees, it would require a further 12kWh energy use annually. 

 

I also used a future forecast weather file produced by University of Exeter for the year 2080, which assumes 'business as usual' global carbon emissions as a worst case climate change scenario.  In this scenario, the energy needed to heat the building goes down to only 78kWh annually.  Overheating does become a problem though, with that worst case bedroom experiencing 1667 hours at 25 degrees or more.  Turning on cooling during the summer with a setpoint of 25 degrees brings the number of hours down to 914 at a cost of 1658kWh of electricity.  Maybe there are more advanced ways to set up shutters in the model that would reduce overheating but I've kept everything very simple for these comparisons.   This is really about getting simple answers to the basic questions, or getting a handle on the numbers as Iceverge said. 

 

Designbuilder does use the materials to model the effects of thermal mass, and you can see there is slightly less daily fluctuation in temperature throughout the year, and on the hottest days (using the current climate) the concrete does seem to contribute to up to 5 degrees of 'cooling'. 

 

SIPS

I've assumed the SIPS house would also have a concrete ground floor, with timber intermediate floors.  It would be clad in timber as well. 

 

The SIPS house performs very similarly in terms of heating, with 350kWh needed annually to heat, and a winter design day load of 2.65kW.  It is also cool enough in summer, though slightly warmer than the ICFs, with the worst case room experiencing 144 hours over 25 degrees.  If I turn on cooling with the same setpoint, it would use 148 kWh of electricity. 

 

In the future climate change scenario, the SIPS house uses 175kWh to heat, and the worst case room overheats 1810 hours a year. Turning on cooling would use 2440kWh annually. 

 

Carbon in use 

Using 234 gCO2/kwH (which is the current carbon intensity estimate for London), the ICF house would 'produce' 77.7kg of carbon to heat and cool in the current climate.  The SIPs house would produce 116.5kg.   

 

In the future scenario, the ICF house would produce 174kg of carbon to heat and cool, and the SIPs house 261kg, assuming the grid decarbonises to 100gCO2/kWh.  Interpolating the heating, cooling and decarbonisation (big assumptions, I know), shows that over the 60 year period between today and 2080, the ICF house would have 'saved' around 3500kg of carbon compared to the SIPs house.  

 

Embodied carbon

I used the ICE database for embodied carbon values. I haven't looked at the embodied carbon in elements that would be the same in both houses - windows / doors, kitchen, appliances, light fittings, sanitaryware, staircase etc. This is just about the difference between the two. 

 

ICF

I've assumed I could use a Cemfree, rather than regular cement, which I think reduces the embodied carbon of the concrete from 283kg carbon per m3 concrete to 63kg per m3. 

 

The embodied carbon in the ICF house, including the concrete, the reinforcement, the EPS and the EPDM on the roof, adds up to around 15680kg.  The sequestered carbon from the internal timber stud walls and the OSB in the SIPs roof adds up to around 4210kg, so the net embodied carbon is around 11470kg. 

 

SIPS

For the SIPS house, surprisingly to me, the embodied carbon from the various insulations, the concrete ground floor, and the floor finishes is not far off the ICF house at 12600kg. The sequestered carbon in the OSB and the timber studs, battens and cladding is much higher though, at 13400kg, so the net embodied carbon is -800kg. 

 

The difference between the two construction methods is 12270kg, which is 3.5 times the amount saved in use by the ICF house over 60 years. 

 

I don't really know how to think about the sequestered carbon.   If I halved the spacing between studs, which I would have said is a waste of material, the studwork would sequester twice the carbon.  Does that mean its a good idea?  If I added enough extra timber to the ICF house, it could net out the same as the SIPs house, which is a strange thought.  

 

Unknowns / further investigation

I also want to look at whether there is a lower carbon alternative to steel or glass fibre reinforcement for the concrete, find out the embodied carbon in the acrylic render I've assumed I would use to finish the exterior of the ICF house (which will increase its embodied carbon) and embodied carbon in the fire retardant (which would have a bigger increase in the SIPS house than the ICF one).

 

If one method is a lot cheaper than the other, I could use the money saved to offset carbon (paying for trees to be planted somewhere, for instance) which makes more sense to me than  adding unnecessary timber into the building.   I think my next step should be to get a rough cost estimate of the two houses and try and do the carbon offset calculation as well.  

 

TLDR:

Simulation shows both houses perform well in the current climate, though the ICF house seems to perform slightly better due to the thermal mass. The thermal mass of the ICF house is a greater advantage the warmer the climate gets.  Given the decarbonising grid, however, those savings in use seem to be outweighed by the sequestered carbon in the SIPS house.  If there is a big cost difference between the two, that might swing it because savings could be used to pay for carbon offsets. 

 

Am I thinking about this the wrong way? 

Adam_J_ICF_Wall_1.pdf Adam_J_SIPS_Wall_1.pdf

[SteamyTea]

Yes, timber frame, with cellulose insulation.

 

Not got the time at the moment to look at all the charts.

 

Couple of thoughts, reducing East/West window area may reduce overheating.  Reflective films will also help.

Adding PV will also reduce overheating.

 

The Exeter climate model does not take into account changes in cloud cover (as far as I know, it didn't when I was there), so not the ultimate guide.

 

And, just a little bugbear with some of us, tell us the SI units for 'Thermal Mass', or use the proper term.

[AdamJ]

8 hours ago, SteamyTea said:

Yes, timber frame, with cellulose insulation.

 

Not got the time at the moment to look at all the charts.

 

Couple of thoughts, reducing East/West window area may reduce overheating.  Reflective films will also help.

Adding PV will also reduce overheating.

 

The Exeter climate model does not take into account changes in cloud cover (as far as I know, it didn't when I was there), so not the ultimate guide.

 

And, just a little bugbear with some of us, tell us the SI units for 'Thermal Mass', or use the proper term.

Thanks for the design thoughts SteamyTea. 

 

Are there timber frame suppliers that you or Buildhub members recommend?  I haven't thought about cellulose insulation before. From quick googling it looks like it is usually (always?) loose fibres blown between the studs.  Wouldn't an additional layer of insulation in the form of a rigid board be needed on either the inside or outside to prevent thermal bridging?  The only mention I could find of a cellulose board is of a research project from Washington State University: Cellulose rigid foam board Insulation, environmentally-friendly styrofoam alternative - Ecohome

 

I didn't expect the charts to show up big like that! Its turned into a massive wall of images, but I can't edit the post to put in a summary PDF instead.  

 

For my own benefit I've summarised the differences between the two construction methods (with all my previous assumptions, no design changes yet) in a table. I forgot to add in the embodied carbon of the SIPs roof to the ICF house, so the ICF embodied carbon is even worse than I thought:

 

In-use
	ICF		SIPS
Annual energy used for heating - current climate	320	kWh	350	kWh
Annual energy used for cooling - current climate	12	kWh	148	kWh
Energy load for heating - winter design day	2.8	kW	2.65	kW
Overheating hours (assuming no cooling) - current climate	58	hours	144	hours
Annual energy used for heating - 2080 forecast climate	78	kWh	175	kWh
Annual energy used for cooling - 2080 forecast climate	1658	kWh	2440	kWh
Carbon produced with grid electricity for heating/cooling 2020	77.7	kgCO2e	116.5	kgCO2e
Carbon produced with grid electricity for heating/cooling 2080	173.6	kgCO2e	261.5	kgCO2e
Carbon produced over 60 year period	6983	kgCO2e	10509.7	kgCO2e
Difference between alternative method	-3526.7	kgCO2e	3526.7	kgCO2e
Embodied
	ICF		SIPS
Concrete (using Cemfree)	4251.5	kgCO2e	575.9	kgCO2e
GFRP reinforcement	5574.4	kgCO2e	606	kgCO2e
EPS insulation	5308	kgCO2e	759.5	kgCO2e
Growing medium	60	kgCO2e	60	kgCO2e
EPDM	489.5	kgCO2e	489.5	kgCO2e
PIR/PUR Insulation (Internal board)	426.9	kgCO2e	1626.4	kgCO2e
PIR/PUR Insulation (SIPS Core)	1912.6	kgCO2e	7286.3	kgCO2e
Mineral wool insulation			128.4	kgCO2e
Resilient layer floor insulation			73.4	kgCO2e
Screedboard floor			1003.2	kgCO2e
Fire retardant - unknown embodied carbon at this point
Acrylic render - unknown embodied carbon at this point
Total embodied	18022.9	kgCO2e	12608.6	kgCO2e
Plywood	-1804.9	kgCO2e
Timber studs (internal walls)	-650.5	kgCO2e	-2063.9	kgCO2e
OSB	-1748.2	kgCO2e	-8236.6	kgCO2e
Timber battens (service void)	-8	kgCO2e	-424.9	kgCO2e
Timber battens (rainscreen)			-469.7	kgCO2e
Timber floor I-joists			-507.6	kgCO2e
Timber siding			-1703.8	kgCO2e
Total sequestered	-4211.6	kgCO2e	-13406.5	kgCO2e
Net embodied	13811.3	kgCO2e	-797.9	kgCO2e
Difference between alternative method	14609.2	kgCO2e	-14609.2	kgCO2e

 

[ProDave]

Just for a heads up, if you fit some solar PV then you will have plenty of generation in the summer, so you can pretty much ignore energy consumption in the summer for cooling as that will be free.

[Iceverge]

Hi @AdamJ,

 

Excellent posts. You're well on the route to building an excellent house the way you're thinking. 

 

FWIW I started my journey at ICF too and ended up with a wide cavity wall after considering almost everything. (If I was to do it again I'd opt for timberframe)

 

 

A couple of points I noted from your posts. 0.6W/m2K is probably a bit optimistic for whole window performance including frames. I'd put 0.8 to 1w/m2K probably.

 

 

Overheating seems to be your prime differentiation for energy use with the different build methods. It can be all but eliminated at design phase. I'll try to summarise.

 

 

Heat added internally (body heat, cooking, radiators etc) and is either fixed or easily controllable ( assuming you don't do anything silly like install an AGA!) 

 

Heat added externally is from the Sun and enters through the windows or soaks through the walls/roof. ( more on this later) 

 

Windows transfer the bulk of the sun's energy and this can be limited when we don't want it via external shading. This is easy to do on the south as overhangs or brise soleil just sit there passively and block the high midsummers sun while letting the low winter sun in. East and West is more of an issue as the low morning and evening sun can't be shaded without blocking views. Motorised blinds can take care of this but are expensive and require manual intervention or complex software. @tonyshouse has a great blog and discusses his I think. As mentioned solar glass can be used but the real trick is to limit the size of E-W openings.

 

The wall and especially roof buildups can in certain circumstances cause overheating problems and I think this is what is causing your SIPS house to overheat. 

There are a few names for it but phase-shift and decrement delay are two of the most correct ( i think! ) .

In layman's terms it's the amount of time a change of temperature on one face of a wall/roof takes to be noticed on the other face.

 

A hot roof could be above 60deg in the sun and in a lightweight construction like SIPs will transfer heat to the inner surface quickly as there is not much energy taken up to heat the insulation itself. The inside of your roof will then be radiating heat into your house causing overheating.

With a high decrement delay roof, by the time the heat had soaked through to the inside it would be nighttime and the heat flow would have already reversed due to the drop in outside temperature therefore never allowing the interior to be exposed to the extreme summer heat.

Decrement Delay should be over 12hrs. More doesn't make any difference. 150mm concrete with external insulation to 400mm concrete with external insulation perform identically in heat protection. 

 

Overheating is taken care of in the following ways but they have issues. Its better and cheaper not to have it in the first place. 

1. Ventilation - Requires manual intervention, creates a security risk with open window, bugs can get in, noise and dust are issues. Only effective when the outside temperature is less than the internal. Relies on air as the cooling medium and it is pretty lousy at transferring heat. 

2. Active cooling via aircon - Extra plant required to be installed although can be relatively cheap and if the unit is correct can be used for efficient heating in winter.  Low ability to cool large volumes of air unless very large unit installed. Can be run for free from solar PV  as @ProDave said.

3. Active cooling via UFH- Niche idea in the mainsteam althought several buildhubbers have used it to great effect. Effective way of cooling quickly and if you're planning UFH not much cost involved either. 

 

Finally there is the heat storage capacity of a house. It is the amount of heat you have to add or take away to alter the temperature of the house internals. A house of high heat storage capacity or specific capacity will take much more energy to heat up the structure and will slow the temperature rise but also slow the temperature fall later on. Having a house of very heavy construction (high specific capacity) will do nothing to remove heat, only dampen its onset and retreat. It will help to level peaks during variable weather but do little during a prolonged heatwave.  Remember all the other items in your house like furniture, books, floor coverings etc add to this specific capability too. Low specific capacity is never the primary reason for overheating. 

 

TLDR.

 

Solve overheating at the design phase by

1. Adjust window sizes to reduce East and West glazed areas and add shading to the south. 

2. Build the walls and roof from a material with high Decrement Delay (Phase Shift) ( woodfiber, cellulose, concrete are examples)

3. Don't get hung up on adding too much mass to the interior. It'll only help buffer heat swings, not solve overheating. 

4. Allow for provision to add active cooling via solar PV if you think it's needed. 

 

 

Separately on the carbon issue look up MBC timberframes twinwall package with blown cellulose insulation. It is a good example of low/negative carbon construction but many are available. 

 

 

 

 

[SteamyTea]

What @Iceverge says, sums it up nicely.

 

Heat capacity is both mass, or volume, and the intrinsic properties of the material.

It is not just the mass or volume.

[AdamJ]

On 31/12/2020 at 16:56, ProDave said:

Just for a heads up, if you fit some solar PV then you will have plenty of generation in the summer, so you can pretty much ignore energy consumption in the summer for cooling as that will be free.

Good point ProDave.  I had thought to leave out the energy generation side to simplify the decision around construction method, but it does make sense to allow for it as it is essentially another way of investing carbon now to save it in the long run, which is what I've been trying to figure out.  

 

PV

The Designbuilder simulation shows that the SIPS house would use 3.76 kWh of energy to heat on a cold winters day (24 hour period) in the current climate (worst case scenario for heating), and 21.6 kWh for cooling on a hot summer day in the 2080 climate (worst case scenario for cooling). It seems like both of those could be met with a 6kWp solar PV array, which would have 15360 kg CO2e embodied carbon. 

 

Given that the heating / cooling differences in energy use between the two houses are essentially eliminated by the solar array, that leaves the embodied carbon of the construction method vs cost question as the likely decisive factor.  If the higher embodied energy house (ICF) is lower cost to the extent that the differences could be more than offset with the leftover money, then from an carbon point of view that would seem to be the best choice.  If the SIPS house is lower cost then that would be the best choice. 

 

Carbon offsetting

Looking at the price of carbon offsetting by creating new woodland, it seems incredibly cheap compared to the embodied carbon and the energy-in-use carbon figures I've been looking at.  For £10, forestcarbon.co.uk will plant 4 trees in a new woodland in the UK, which they say will offset 1 tonne of CO2e. 

 

Using those figures, the 14 tonne difference between the embodied CO2e of the ICF and the SIPS house could be offset with only 58 trees, for £140.  Presumably this considered to be offset in perpetuity, but in reality accumulates over time as the trees grow. An environmental drawback therefore could be that CO2 is emitted in the present day to build the house but is only sequestered over a period of many years (I don't know at what point the 1 tonne mark is considered to have been met - in some other non-UK forestation/sequestration projects I was looking at the lifetime is 20 years).

 

Carbonpirates.org say that a newly planted tree will absorb 5.9kg of CO2 in a year, and a 10 year old tree will absorb 22kg in a year.   With that in mind I could make my carbon offset payment when I get planning permission, with say a two year timeline from that point to moving in. Using the more conservative figure for a newly planted tree I would need 1238 saplings to absorb the 14 tonnes of CO2 by time I move in, which would cost around £3100.  Over the lifetime of the house those 1238 trees would absorb 309 tonnes of CO2e. 

 

Maybe I'm missing something, but I don't see how this is different from using sequestered carbon within the timber parts of the building to balance out embodied carbon in the insulation, ground floor slab etc. Or even using sequestered carbon in a timber building product to balance out the carbon generated by the extraction and processing of the tree into that building product in the first place. 

 

20 hours ago, Iceverge said:

Hi @AdamJ,

 

Excellent posts. You're well on the route to building an excellent house the way you're thinking. 

 

FWIW I started my journey at ICF too and ended up with a wide cavity wall after considering almost everything. (If I was to do it again I'd opt for timberframe)

 

 

A couple of points I noted from your posts. 0.6W/m2K is probably a bit optimistic for whole window performance including frames. I'd put 0.8 to 1w/m2K probably.

 

 

Overheating seems to be your prime differentiation for energy use with the different build methods. It can be all but eliminated at design phase. I'll try to summarise.

 

 

Heat added internally (body heat, cooking, radiators etc) and is either fixed or easily controllable ( assuming you don't do anything silly like install an AGA!) 

 

Heat added externally is from the Sun and enters through the windows or soaks through the walls/roof. ( more on this later) 

 

Windows transfer the bulk of the sun's energy and this can be limited when we don't want it via external shading. This is easy to do on the south as overhangs or brise soleil just sit there passively and block the high midsummers sun while letting the low winter sun in. East and West is more of an issue as the low morning and evening sun can't be shaded without blocking views. Motorised blinds can take care of this but are expensive and require manual intervention or complex software. @tonyshouse has a great blog and discusses his I think. As mentioned solar glass can be used but the real trick is to limit the size of E-W openings.

 

The wall and especially roof buildups can in certain circumstances cause overheating problems and I think this is what is causing your SIPS house to overheat. 

There are a few names for it but phase-shift and decrement delay are two of the most correct ( i think! ) .

In layman's terms it's the amount of time a change of temperature on one face of a wall/roof takes to be noticed on the other face.

 

A hot roof could be above 60deg in the sun and in a lightweight construction like SIPs will transfer heat to the inner surface quickly as there is not much energy taken up to heat the insulation itself. The inside of your roof will then be radiating heat into your house causing overheating.

With a high decrement delay roof, by the time the heat had soaked through to the inside it would be nighttime and the heat flow would have already reversed due to the drop in outside temperature therefore never allowing the interior to be exposed to the extreme summer heat.

Decrement Delay should be over 12hrs. More doesn't make any difference. 150mm concrete with external insulation to 400mm concrete with external insulation perform identically in heat protection. 

 

Overheating is taken care of in the following ways but they have issues. Its better and cheaper not to have it in the first place. 

1. Ventilation - Requires manual intervention, creates a security risk with open window, bugs can get in, noise and dust are issues. Only effective when the outside temperature is less than the internal. Relies on air as the cooling medium and it is pretty lousy at transferring heat. 

2. Active cooling via aircon - Extra plant required to be installed although can be relatively cheap and if the unit is correct can be used for efficient heating in winter.  Low ability to cool large volumes of air unless very large unit installed. Can be run for free from solar PV  as @ProDave said.

3. Active cooling via UFH- Niche idea in the mainsteam althought several buildhubbers have used it to great effect. Effective way of cooling quickly and if you're planning UFH not much cost involved either. 

 

Finally there is the heat storage capacity of a house. It is the amount of heat you have to add or take away to alter the temperature of the house internals. A house of high heat storage capacity or specific capacity will take much more energy to heat up the structure and will slow the temperature rise but also slow the temperature fall later on. Having a house of very heavy construction (high specific capacity) will do nothing to remove heat, only dampen its onset and retreat. It will help to level peaks during variable weather but do little during a prolonged heatwave.  Remember all the other items in your house like furniture, books, floor coverings etc add to this specific capability too. Low specific capacity is never the primary reason for overheating. 

 

TLDR.

 

Solve overheating at the design phase by

1. Adjust window sizes to reduce East and West glazed areas and add shading to the south. 

2. Build the walls and roof from a material with high Decrement Delay (Phase Shift) ( woodfiber, cellulose, concrete are examples)

3. Don't get hung up on adding too much mass to the interior. It'll only help buffer heat swings, not solve overheating. 

4. Allow for provision to add active cooling via solar PV if you think it's needed. 

 

 

Separately on the carbon issue look up MBC timberframes twinwall package with blown cellulose insulation. It is a good example of low/negative carbon construction but many are available. 

 

 

 

 

 

Thanks for the brilliant and helpful post @Iceverge

 

Why did you shift from ICF to wide cavity wall, and why would you now go for timber frame if you were doing it again? 

 

I've messaged @tonyshouse and asked him to point me to his blog post so I can read up on brise soleil vs blinds. 

 

Based on your suggestion I ran another couple of tests in Designbuilder. 

 

Firstly on the roof: I had previously assumed a SIPs roof with a layer of growing medium on top to allow for plants, and I think the heat capacity of the growing medium meant the decrement delay/phase shift was already quite good. The ubakus calculator said the phase shift period would be 15.2 hours. Adam_J_SIPS_Roof__Growing_Medium (1).pdf  Switching to a concrete roof (which has even better heat protection characteristics) Adam_J_Concrete_Green_Roof.pdfhad a negligible impact on overheating hours.

 

Adding louvres to the south-facing windows and halving the size of the east and west-facing windows reduced overheating hours in my worst-case room by 16%. With cooling on, on the typical hot summer day 24 hour cooling energy use was reduced from 21.6 kWh to 9.5kWh, which would allow me to downsize the PV array to a 3kWp system to deal with heating and cooling (and reduce the embodied energy in that).  

 

I'm sure there is more that I could do on solar control to bring those numbers down further. I'm drawn to the idea of shutters (either internal or external) with louvres with adjustable angles, rather than a fixed brise soleil, which should allow a huge amount of control over the solar gain.  I wouldn't even need to shrink the windows on the east or west side then - on an overheating day just fully shutter one half of the window for most of the same benefit (or shutter the whole thing if no one is in the room). I know its not exactly the same, as the U-values of the window + shutter are not as low as the wall would be.  It seems complex to set it up right in Designbuilder though to test it properly. 

 

Your TLDR is a very good summary   

 

I will look more into timber frame twin wall / cellulose insulation options, based your and SteamyTea's suggestions. I expect performance will be somewhere between the SIPs and ICF.  MBC have some useful information on their site - thanks for dropping their name.  

 

Given what I've found about carbon in use vs embodied carbon vs carbon offsetting, I think price is going to be the key factor and I need to get some rough ideas of prices for IFC, SIPS and the timber-frame option. It's likely the cheapest one will be the best from a carbon point of view because it will allow for the greatest amount of offsetting.  If prices are similar enough then perhaps the deciding factor will be how easy it is to get the construction right and achieve the performance target. 

[SteamyTea]

Roof integrated PV can work out cheaper than tiling, and it reduces the thermal energy by up to 20%.

 

A mate of mine did a report about 15 years ago about carbon sequestration schemes though forestation.  Found out that many were double counting i.e. the reforestation was going to happen anyway, so no net gain, and a few were just scams.

The best way to reforest is to let nature do it i.e. just put a area aside and the trees will appear.  Now that the UK has left the CAP, only time will tell if all the new environmental schemes will actually happen (pulse fishing has been banned already, but this may lead to over fishing).

I am always dubious about the tonnes CO₂ stored by trees, one has to be careful as there are different methods of measurement used around the world.

 

How everyone decided trees will save the planet – and why they won’t

Everyone seems to agree trees are a major solution to climate change, but there is a danger that mass reforestation could see us to continue pumping carbon into the atmosphere

 

EARTH 26 February 2020

By Adam Vaughan

De Agostini editorial/Getty Images

TREE planting doesn’t usually feature in US presidents’ speeches, UK general election battles or the business pitches of oil companies. Yet in the past year, pledges to embark on reforestation efforts have become a popular way to show you are committed to fighting climate change. There are several initiatives to plant or protect a trillion trees, to add to the 3 trillion we have today.

So how did we get here, with humble tree planting taking centre stage among the tools to stave off extreme warming? Can we really plant the numbers needed to lock up enough carbon to make a difference? Perhaps most importantly, is all this talk of trees just a big distraction?

“Fossil fuel industries can say they are harnessing nature to address their emissions”

 

 

 

“Suddenly, this last year there’s been an explosion of interest,” says Fred Stolle at Global Forest Watch, a US initiative from the University of Maryland and other groups. Rising public concerns seem to be making governments and corporations realise they need to do more on climate action, or at least be seen to do more.

“I think there’s massive concern about climate change now and people genuinely want to do something about it. I think they are reaching for what are easy solutions,” says Joanna House, a lead author of a UN Intergovernmental Panel on Climate Change (IPCC) report on land use published last year. Planting trees is popular, usually uncontroversial and brings benefits beyond storing carbon, from our mental well-being to habitats for wildlife. “People love trees,” says House.

The spotlight on tree planting may have its roots in the 2015 Paris agreement, in which governments committed to try to hold global temperature rises to 1.5°C, rather than the 2°C many had expected.

This led to a 2018 IPCC report, which made it clear that to hit 1.5°C, global greenhouse gas emissions need to fall to net zero by 2050. There was much debate about “negative emissions” technology, such as machines to capture carbon dioxide from the air. But with these in their infancy, the focus fell on trees as the only proven option.

“I think a lot of the talk around the new ambition for 1.5°C was one of the biggest driving forces for putting negative emissions – and particularly nature-based negative emissions – on the stage,” says Stephanie Roe at the University of Virginia.

But tree mania accelerated last year, when Tom Crowther at ETH Zurich in Switzerland and his colleagues published a paper that said Earth has room for nearly a billion hectares of extra trees, which could lock up several years’ worth of humanity’s carbon emissions. The research has been criticised as an overestimate, but was influential and made global headlines. “I think that played a key role in re-legitimising reforestation,” says Mark Hirons at the University of Oxford.

A few months later, political parties campaigning in the run up to the UK general election competed on who promised to plant the most trees. Last month marked peak tree planting fever, when the World Economic Forum launched 1t.org, a plan to plant a trillion trees (other plans launched three years ago). Even US president Donald Trump, who has withdrawn the US from the Paris agreement, backed the initiative.

Douglas Gimesy/Getty Images

But even if we start planting vast areas tomorrow, can trees store enough carbon to buy us time to act on climate change?

The Crowther paper said 0.9 billion hectares could lock up 205 gigatonnes of CO₂. Including land-use change, such as forests being cleared for farming, humanity’s annual emissions are about 41 gigatonnes. But House says many researchers were shocked by the paper. “It’s quite harmful because it makes it seem like trees can do more than they can,” she says.

Several experts took to scientific journals to explain why they felt it exaggerated the amount of usable land and how much carbon could be stored. In response, Crowther says a lot of the criticism is well-founded, but it is important to get a global perspective on what it is possible, in order to set meaningful restoration targets.

Based on Roe’s review of the literature, reforestation has the potential to lock up between 1 and 10 gigatonnes of CO₂ a year. “In terms of what is feasible, we came to 3 to 4 gigatonnes [a year],” she says.

More research is under way on calculating the carbon storage potential of tree planting. In the meantime, it seems large enough to be attracting big business. Last year, Shell announced that it would spend $300 million over three years on reforestation projects to generate carbon credits for itself and others.

On Crowther’s analysis, Duncan van Bergen at Shell says: “Even those people who have challenged it, have not challenged the fact that it is really, really big. It’s on the margins between really big and huge.” He says the numbers presented “resonated” with Shell’s own researchers.

Such interest in reforestation from oil companies has set alarm bells ringing in some quarters. “Fossil-fuel industries can say they’re harnessing nature to address their emissions, which is dubious I think, in terms of the scientific case for this significantly having an impact on climate change,” says Hirons.

There is a risk that we plant trillions of trees without firms and countries also deeply cutting their emissions. Shell says that isn’t the case. “We are definitely not doing this instead of other tough things and changes we need to make. This very much comes on top,” says van Bergen.

Even if mass reforestation happens in parallel with decarbonisation of economies, Stolle warns that trees must be planted at the right place and time. As well as picking suitable species for the climate and the soil where they are planted, it will be crucial to plant trees that help rather than hinder biodiversity.

Biodiversity warning

Take the UK, where the government’s climate advisers have called for a tripling of tree planting to hit carbon goals. Jane Memmott at the British Ecological Society says there are huge differences in biodiversity levels between trees you might pick for the UK. “Something like oak and birch is fantastic – there are literally hundreds of species associated with them, whereas something like sycamore has pretty much a single aphid on it,” she says.

Then there are the people who live in and around the places where reforestation might take place, often in developing countries. Restored forests won’t thrive or remain intact long enough to lock up CO₂ for centuries if local people aren’t invested in them, says Stolle. “In developing countries, people very much understand the value of trees,” he says, but only when they play a role in deciding when and where they are planted.

Hirons fears that the urgency of tackling climate change could see the wishes of local communities being ignored. “I think there’s a massive risk of social harm being caused by widespread reforestation. There is an idea that there is lots of underused land, which is a myth.”

While there are international guidelines on how best to do reforestation, set by the Society for Ecological Restoration, there is no requirement to follow them.

Lastly, if the CO₂ locked away is to be counted properly, we will need to monitor reforestation for a long time. That is surprisingly tricky. Deforestation is easy to spot – satellites show areas turning from green to brown. But they find it hard to detect new trees, which for the first few years will be tiny saplings hard to discern from space. Higher resolution images may help.

Perhaps the biggest thing missing from today’s focus on reforestation is the great number of trees being lost to deforestation, which is getting worse. The world lost forests the size of the UK every year between 2014 and 2018. Deforestation in the Amazon rainforest has spiralled to the highest level in a decade. Recent bushfires in Australia burned 64,000 square kilometres in Victoria and New South Wales, most of it forests.

“It’s an eternal debate,” says Stolle. “Is [reforestation] a distraction because we really need to stop deforestation? On the other hand, if you look at the IPCC, we need those negative emissions. We can’t wait until we’ve done one before we do the other.”

Revenge of the tree-hugger

Trees have long been at the heart of environmental issues. Three centuries ago, in a bid to stop local trees being cleared, villagers in India put themselves in front of loggers’ axes, with some literally hugging the trees. Several were brutally killed, says Alice Bell at UK climate charity Possible, who is writing a book on the history of climate change.

The actual term “tree-hugger” wasn’t coined until the 1960s, though, she says, and became pejorative in the 1970s.

Bell says the “save the trees” movements of the 1990s and 2000s weren’t dissimilar to today’s debate. “It was about climate change but without mentioning it. Now it’s climate first,” she says.

[Iceverge]

Please read this independent of ecological considerations, habitat loss, species extinction etc. That's an different topic. 

 

I considered the Carbon offsetting and have come to the notion that it's bogus and an excuse to continue the status quo. In @SteamyTeas article the $300 million over 3 years spent by Shell is only 0.028% of their revenue per year (2019). $1 out of every $3450 that goes through the company. They don't care, it's literally half of what they spend on ads.  

 

Climate change is a result of us digging up coal, oil, gas, peat and burning it. 

 

We are considering the idea of carbon sequestration as a way to reverse this but the process involves sucking carbon (CO2) form the atmosphere. Plants and trees and algae etc do this and over their lifespans die and fall to the forest/ocean floor. Some of the carbon they contain gets trapped in the earth but much gets released into the atmosphere again as greenhouse gasses. Left to it's own devices this process would eventually trap all the carbon we have released in the last 300 years into oil coal gas and peat again but it would take millions and millions of years. It's an incredibly inefficient process as only a fraction of the dead living thing gets permanently trapped in the ground and helps to slow climate change.

 

The tree you plant today will only make a useful immediate difference to capturing any carbon if you cut it down and dry store it permanently. If you let it fall and rot on the forest floor only a small fraction gets permanently trapped. That's assuming that the land isn't turned back to farmland in a hundred years and the carbon ploughed out again from the top layers. 

 

To this end, purely in terms of capturing carbon, you'd be as well off investing in commercial forestry and finding somewhere to store the lumber (like a house!).

 

There is nothing and I mean absolutely nothing which slows carbon caused climate change more than leaving fossil fuels in the bloody ground! Anything else misses the mark by orders of magnitude. 

 

To this end if you really want to build low carbon

1.Keep embedded energy low. Despite what the concrete+oil industry says you don't need energy intensive materials to have a superbly performing house.  

2.Don't use oil based products ( ICF and SIPS have plenty). Leave them in the ground.

3.Lock up as much carbon as possible using plant based building materials. 

 

You can't control bought in energy, so reduce your use as much as possible. Generate as much onsite via solar as you can and send the excess back to the grid to offset someone else's fossil fuel use. 

 

 

I went off ICF because of the cost. That and ICF is the Dime bar of wall construction when what you want is an Armadillo! The soft bit on the inside!

 

 

 

Timber is massively nicer to work with and does away with concrete which creates 99% of the suffering and mess on a build. I chased the walls of ours with a 9" grinder. It is the worst job I've ever done. I'm timber framing the garage myself and enjoying every moment.

 

It was difficult to find a builder comfortable with anything other than cavity walls. The common builders manual is full of pictures like this.

 

I suppose the reality is climate change is a generational thing, I'm mid thirties and I say the right words and believe the problem but I'm probably too selfish and lazy to really do much about it. 

 

I didn't really understand the issues and still don't with many. Until I learned to calculate the numbers myself I haven't appreciated how much BS there is put out by manufacturers of various products. There is an absolute sea of it. 

 

With the external blind option consider whether you want

1:half a window you can see out all the time or

2:all of a window you can see out half the time.

 

It will cost quadruple, need triple maintenance, and loose twice as much heat.  

 

I'd be interested to see where your table comes back when you add a timber frame option to the list along with the sips and the ICF. 

 

Jonathan

 

Edited January 2, 2021 by Iceverge
Clarity

[AdamJ]

Thanks for the thoughtful comments @SteamyTea and @Iceverge.   

 

Its the first time I'm looking into carbon offsetting so I am an ignoramus wading into waters that others have already mapped out quite well, but even after reading your posts and SteamyTea's article and other critical articles, I don't see how carbon offseting, if done by planting trees, is fundamentally different from using timber in construction and counting that as sequestered carbon. 

 

Here is my thought process, and I may have (probably have) misunderstood things:

• The production of timber building products uses energy and produces emissions. According to the ICE database, ignoring the sequestration, OSB produces 0.455 kgCO2e/kg of material. With carbon sequestration its net -1.05kgCO2e/kg.   
• As the ICE database notes, carbon storage can only be claimed for sustainably sourced timber, and the actual amount in reality will depend on what happens to the timber at the end of its life in the building (incineration/landfill/recycling).   The stored carbon was sucked out of the atmosphere during the lifetime of the tree, the net negative value we attribute to it is because in a sustainably managed forest a new tree will be planted to replace the harvested one which will again absorb carbon from the atmosphere. 
• In the newly planted carbon-offset forest, each tree will eventually die and release carbon back into the atmosphere, but new trees will grow and replace the dead ones. As long as the forest is not cleared away, it will settle into a state of equilibrium and function as a long-term average carbon store.   

If I double the number timber studs in a wall it will have taken more energy and produced more emissions to create that wall, but its overall embodied carbon goes down because (if it was sustainably sourced) more new trees have been planted to replace the ones that were harvested to make the timber.   

 

On the carbon offseting pitfalls raised in SteamyTea's article, the forestcarbon.co.uk website I looked at does address most of them: The projects are in the UK, they adhere to Woodland Carbon Code devised by the Forestry Commission, which assures 'additionality' (that the carbon would not have been captured without the intervention of the buyer ie. no double counting) and permanence. Every 5 years the projects are re-certified and the amount of carbon stored is verified.  

 

Having said all that, if we ignore carbon storage (either in the timber in the building or in new forests) then it seems clear that using less material, or less energy intensive material, is beneficial.

 

I've been looking at the performance of the twin wall timber frame with cellulose insulation as per MBC, and also a 'perfect wall' timber frame, which I saw some youtube videos about. The 'perfect wall' that I saw had, from inside to outside:

1. Studs to form structure, left open to the internal space

2. Timber boards

3. OSB

4. Air/Vapour proof membrane (in the example it was a bitumen-based sheet membrane) stuck onto the OSB

5. Insulation (in the example it was PIR, I think) 

6. Cladding 

 

I like the idea that the structure is the innermost layer, and that the insulation is outside the vapour barrier. I also like that the studs were left open and could be usable internal space, for shelving for example.  The insulation can't be cellulose, because it needs to be rigid, but it could be something like Pavatex, which is made from waste sawdust.  The timber boards have some benefit with the lightweight insulation because it slightly increases the phase shift time, but not with Pavatex, so in that scenario it could be a single OSB sheet layer.  I would prefer to replace cladding with render directly applied to the insulation, to save on wall thickness. 

 

Performance wise, there are a lot of similarities between all the walls I've looked at. The simulated house performs very well in today's climate, with very low heating energy use and no need for any cooling with all of the walls.  All the timber walls (including the SIPS) perform pretty similar to each other in the 2080 climate, with the ICF doing better in keeping the inside cool for less energy.  

 

I also looked at whether omitting the concrete upper floors from the ICF option in favour of timber floors had much of an impact. It made heating slightly easier and cooling slightly harder. 

 

	ICF		ICF + Timber floors		SIPS		TF: Twin wall + Cellulose		TF: Perfect wall + EPS		TF: Perfect wall + Woodfibre
Wall performance (from ubakus)
Wall thickness	373	mm			275	mm	395	mm	416	mm	454	mm
Un-usable wall thicknes	373	mm			275	mm	395	mm	268	mm	306	mm
U-value	0.15	W/m2K			0.15	W/m2K	0.14	W/m2K	0.14	W/m2K	0.14	W/m2K
Phase shift	non relevant				9.5	hours	14	hours	6.3	hours	non relevant
Thermal capacity inside	328	kJ/m2K			28	kJ/m2K	36	kJ/m2K	35	kJ/m2K	60	kJ/m2K
Simulated energy in use (from designbuilder)
Annual energy used for heating - current climate	320	kWh	261	kWh	350	kWh	315	kWh	350	kWh	314	kWh
Annual energy used for cooling - current climate	12	kWh	52.9	kWh	148	kWh	117	kWh	145	kWh	127	kWh
Energy load for heating - winter design day	2.8	kW	2.76	kW	2.65	kW	2.4	kW	2.6	kW	2.6	kW
Overheating hours (assuming no cooling) - current climate	58	hours	74.5	hours	144	hours	139.5	hours	142.5	hours	95	hours
Annual energy used for heating - 2080 forecast climate	183	kWh	176	kWh	175	kWh	159	kWh	169	kWh	165	kWh
Annual energy used for cooling - 2080 forecast climate	1629	kWh	1713	kWh	2440	kWh	2142	kWh	2405	kWh	2242	kWh
Hot summer day cooling energy - 2080 forecast climate	14.6	kWh	15.3	kWh	21.6	kWh	19.7	kWh	21.3	kWh	20.0	kWh
PV array spec to deal with 2080 cooling	4	kWp	4	kWp	6	kWp	5	kWp	6	kWp	5	kWp

 

This was based off the initial model geometry, rather than the one with the smaller windows and the brise soleil, to make comparison with my first table easier.  I assume that any design changes like that will have an effect regardless of the wall buildup, so I can consider them more fully later, after having bottomed out construction method. 

 

I haven't looked at the embodied energy of the newer options yet - it takes more time for me to work that out than run the simulations! 

 

@Iceverge, what did you mean about costing quadruple, need triple maintenance etc?  Were you talking about a shutter compared to a brise soleil? 

 

Adam_J_Timber_Frame_perfect_wall_w_pavawall.pdf Adam_J_Timber_Frame_perfect_wall_w_EPS.pdf Adam_J_Timber_Frame_twin_wall_cellulose.pdf Adam_J_ICF_Wall_1.pdf Adam_J_SIPS_Wall_1.pdf

 

 

Edited January 3, 2021 by AdamJ

[ZacP]

Not wishing to throw another complication into the mix @AdamJ but have you discovered/considered woodcrete ICF? Products such as durisol, istotex etc? Rather then being made of eps they use recycled chipped timber. This might help sequester carbon in the fabric? I don’t know much about it, but the thought crossed my mind! 
Good luck!

[NickK]

On ‎30‎/‎12‎/‎2020 at 12:04, Iceverge said:

The reality is that the concrete house will start the race over a century behind and never catch up. 

 

@Iceverge I am rubbish at this sort of stuff so won't even attempt to work it out myself so here it goes....how much would this be reduced by if you went down the isotex/durisol route? Thanks

[ZacP]

Great minds @NickK!

[Iceverge]

3 hours ago, NickK said:

 

@Iceverge I am rubbish at this sort of stuff so won't even attempt to work it out myself so here it goes....how much would this be reduced by if you went down the isotex/durisol route? Thanks

I had a look on their website but I couldn't find any info about the embodied energybof wood crete other than the usual "eco" and "green" and other platitudes. 

 

The total product contains PIR insulation, cement and crucially a concrete core so it will have a worse climate change effect than a timber frame with organic insulation. 

 

FWIW I do like the durisol and other woodcrete ICF systems. 

[SteamyTea]

4 minutes ago, Iceverge said:

I had a look on their website

Is there data in the ICE from Bath?

If not, email Steve Jones, he is very approachable.

[ZacP]

It’s obviously an approximation, and I have no idea what this means (but I’d be very interested to know!) in terms of carbon, but it might be a half way house between EPS ICF and timber frame.

 

• An average 3-bed semi-detached house built from Durisol will have 10 tonnes of recycled wood in the product. This wood is made up of old pallets and offcuts which would have been destined for landfill and consequently would have released carbon back into the atmosphere.
• Once the waste wood is mineralised and encased in cement, it won’t rot or burn. In effect, the embedded carbon is permanently captured and locked in.

 

Edited January 4, 2021 by ZacP

[SteamyTea]

3 minutes ago, ZacP said:

destined for landfill and consequently would have released carbon back into the atmosphere

But most would have gone to an incinerator to make electricity, possibly.

And there is a bit of a myth that all timber eventually rots to CO₂.  Not the case, much is left as soil.

[ZacP]

25 minutes ago, SteamyTea said:

But most would have gone to an incinerator to make electricity, possibly.

And there is a bit of a myth that all timber eventually rots to CO₂.  Not the case, much is left as soil.

Yes, I’m sure, but it’s an interesting comparison and relevant to consider in my opinion. 

[Iceverge]

I couldn't find it on the ICE database @SteamyTea. I won't bother that chap as our house is nearly finished. 

 

I had a look and couldn't find what % of organic carbon matter gets trapped permanently. Where can I find that out? For instance in a crop of hemp grown and processed for insulation I imagine almost all of the carbon would remain out of circulation. What % would that equate to if it was just left to rot?

 

@adamj

 

I was comparing a large window with moveable blinds Vs a window half its size with no shading devices. Apologies for the absolutist tone. I was guesstimating to convey my point. 

[keith65]

Hi I have gone for Isotex as some wood products is used in the makeup, most construction timber used in the UK is imported has to be kilned dried and a preserver applied to stop rot is this all taken into account in the carbon foot print and end of life.