energy... I stand to be corrected.

[Big Neil]

I bet she pronounces February Feb-u-ary!!!

[Big Jimbo]

1 hour ago, Big Neil said:

 

Probably too busy day dreaming abut dancing about in her fields of corn!!!

Big Neil. I am going to struggle to get you that job of housing minister.?

[Crofter]

Going back to the original question...

The OP mentioned the embodied energy of solar panels. I can't find it right now but we had quite an enlightening discussion on that point recently on BuildHub. I think it was @Ed Davies who pointed out that you can do a very simple bit of arithmetic involving the cost of energy in China vs the wholesale cost of solar panels, which proves that they are very much energy positive over their lifespan. I.e. if they used more energy to make, they would have to be sold at a much higher cost.

 

On a different note, one subject that I think does not get enough attention is that standards like PassivHaus, or EPC ratings, etc, are always about energy cost per unit area or volume. Not about usage per person, or per dwelling. So we are incentivised to build bigger houses which use less energy per square metre- not to reduce our actual total energy usage.

 

We don't sell cars like this, do we? "The new Range Rover uses less energy per tonne than a Fiat 500, making it the eco friendly choice!" No, we look at absolute energy consumption, because that's what actually matters.

[Ed Davies]

6 hours ago, Ferdinand said:

"Meets the Building Regs" is often translated into "Build to the latest environmental standards" in the literature.

 

When “meets the Building Regs” should be translated as “not quite bad enough that the state would ultimately be willing to use violence to prevent”.

[Ed Davies]

Something really weird happens on the first page of this thread. @JSHarris has a post starting “It's worth looking in a bit of detail at just how great the emissions are from some of the building materials used”. Two posts below @Big Jimbo quotes this (I assume, maybe he's quoting from somewhere else) but the text is significantly different. @JSHarris did you edit that post? If so, why is it not marked as edited? Was it because you edited it with your moderator superpowers or something?

 

Whatever, even the revised version seems low to me. “so taking our concrete slab as an example, that uses around 25 tonnes of concrete, plus around another 120 tonnes in our retaining wall (!), plus another 10 tonnes for the garage slab, so a total of around 155 tonnes of concrete” … “and for all the concrete in our build (which is a lot more than average, because of the big retaining wall) it looks like the CO2 figure is around 11 tonnes”.

 

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

 

says: “The carbon dioxide CO2 produced for the manufacture of structural concrete (using ~14% cement) is estimated at 410 kg/m³ (~180 kg/tonne @ density of 2.3 g/cm³) (reduced to 290 kg/m³ with 30% fly ash replacement of cement)” so that would be 155 tonnes x 180 kg/tonne = 29.14 tonnes (so about 2½ times as much).

 

The 120 tonne retaining wall is a bit atypical, though. Counting just the 35 tonnes in the house and garage slabs it would come out to 6.3 tonnes of CO₂. That's for a house which is otherwise regarded as a pretty much pure timber frame. Of course, the timber frame will be sequestering some carbon at the same time. Still, I think we could do better.

 

For example, my house is built on concrete pads which came in one mixer load, 6.75 m³ IIRC (could find the slip in my invoices box but I'm reasonably sure it was close to that) so that's 2.7 tonnes of CO₂.

 

I mentioned this thought before on here but it didn't get any attention: could the typical passive slab be built in the normal way with blinding, DPC, EPS but then, instead of concrete, use CLT (big kids plywood) to sequester carbon instead of emit it?

Edited March 7, 2019 by Ed Davies

[Big Jimbo]

Ed Davies. I like the idea of Concrete pads. I did find some things online which are basically steel plates, with basically steel poles through them at angles, like spider legs. They hold up all sorts of things, and i think they could replace concrete pads. you could then join them with a timber ring beam, and build off them. No digging, and no concrete in the ground.

[Jeremy Harris]

I made a cockup, @Ed Davies!  I used a document published by the Readmix concrete people to get the CO₂ produced from making concrete, and then spotted later that it was seriously optimistic, as it didn't include the CO₂ emissions from manufacturing the cement - not sure how on earth they thought that made sense.  Your Wiki link looks as if it might be more accurate, as I worked back from the mass of cement in the mix using the densities and volume mix ratios), tried to guesstimate the mass of water in the mix (that ends up becoming part of the set concrete) and ended up with what I thought was about the right CO₂ produced (which it seems it wasn't).

 

PS: when I edit stuff it doesn't show as being edited unless I remember to select the "show this message has been edited" box.

Edited March 7, 2019 by JSHarris
Added a PS

[Big Neil]

@JSHarris. To further look at your concrete use as described above. Do you know if the company you used had any measure of GGBS or Fly ash in the mix. I don't have the document to had which quotes the figures but if I remember correctly GGBS, in a state such that is can be directly compared to OPC for immediate addition  to a cement mix, saves something like 800kg of CO2 per tonne of the product. One supplier I spoke to - think it was CEMEX - said they often use up to 50% substitute for OPC in smaller domestic projects.

[PeterW]

The worry about using GGBS is that the strength is unknown due to its composition so whilst it may be ok for garage footings or non structural elements, I would want a BS known mix for anything such as a ground bearing slab or structural work. 

[Jeremy Harris]

31 minutes ago, Big Neil said:

@JSHarris. To further look at your concrete use as described above. Do you know if the company you used had any measure of GGBS or Fly ash in the mix. I don't have the document to had which quotes the figures but if I remember correctly GGBS, in a state such that is can be directly compared to OPC for immediate addition  to a cement mix, saves something like 800kg of CO2 per tonne of the product. One supplier I spoke to - think it was CEMEX - said they often use up to 50% substitute for OPC in smaller domestic projects.

 

I just used a document published by BRE (what used to be the Building Research Establishment), so it wasn't referring to a specific concrete company.  The cement data came from the widely used figures that a tonne of cement produces between 750kg and 950kg of CO_2. I'm not sure how that tallies with the data in that Wiki article though, as it doesn't seem to match very well.  The mix ratios of concrete are volumetric, plus there is a fair mass of water added, much of which ends up being incorporated into the cured concrete.  I used SGs of 3.11 for cement and 2.65 for the fine stuff and aggregate, and 1 for the water content, then just used the volumetric ratios of each to try and estimate the amount of CO₂ from the cement manufacture that ended up in the final mix.

[Crofter]

Another point raised by the OP is sourcing of locally produce/manufactured goods.

I'd be interested to put some figures behind this, but IMHO it's a bit of a red herring. Global transport is really quite efficient- you can ship a whole container from China to the UK for a few thousand pounds, which puts an upper bound on how much energy it must take. So sourcing more energy efficient windows that have to be transported some distance is, IMHO, very likely to work out as beneficial over the lifespan of the building.

[Jeremy Harris]

10 minutes ago, Crofter said:

Another point raised by the OP is sourcing of locally produce/manufactured goods.

I'd be interested to put some figures behind this, but IMHO it's a bit of a red herring. Global transport is really quite efficient- you can ship a whole container from China to the UK for a few thousand pounds, which puts an upper bound on how much energy it must take. So sourcing more energy efficient windows that have to be transported some distance is, IMHO, very likely to work out as beneficial over the lifespan of the building.

 

It's a good pint, as although we used locally grown (as in ~6 miles away) larch trees for our cladding, and had them milled at a place about halfway between us and the estate that grew the trees, the transport footprint was pretty dire as were the 1930 saws and machines in the sawmill.  The logs were taken out piecemeal on a big trailer behind an old Landrover, towed to the mill cut to size then transported back to us on the same trailer, in maybe 10 loads.  They may have only come a short distance, but being transported on pretty dirty forms of transport, several times, added a fair bit to the environmental impact.

[Big Jimbo]

That's the thing. None of us know, or are able to really find out what the true carbon costs of our properties are. Also, we all have to work to a budget, so the £20 jumber made in England, or the £6 jumper made in Bangladesh. When we have already paid tax 20 times on our income we have to make a choice. I'm defo going to consider the Hippie idea.

[Jeremy Harris]

Back on to concrete, then working from the assumption that the volumetric mix will be 1:3:3 (cement, sand, coarse aggregate), that gives a mix by weight of about 3.11:7.95:7.95. plus the mass of water that gets included in the cured mix (probably around 1/5th by mass)

 

Working back to mass percentages, then I reckon that cement is around 14% of the total mix for a typical RC35 grade concrete, which matches the Wiki article reasonably well.  For our total of around 155 tonne of concrete, and assuming that the concrete would be offset by the energy saving in the the house running cost, it looks like the crossover point would be around 24 years,  Ignoring the big retaining wall, and only looking at the house and garage changes things a lot, and makes the "repayment time" around 5 1/2 years (so it's just about paid of the CO₂ from pouring that concrete for the house and garage by the end of this year).

 

[Tom]

Also worth noting that cement will absorb CO2 back from the atmosphere in a process called carbonation - so it's carbon footprint could potentially be a lot less than calculated simply from the manufacturing process.

[jack]

16 hours ago, Bitpipe said:

Based on my brief doorstep chat with her, she's not big into listening ....

 

She has voice reproduction circuitry but I'm not sure she has sound receiving capacity. Maybe with her next upgrade?

[Bitpipe]

23 minutes ago, jack said:

 

She has voice reproduction circuitry but I'm not sure she has sound receiving capacity. Maybe with her next upgrade?

 

I think she runs Windows '95 on an Intel 486 so is no longer a supported product.

 

Will be interesting to see what happens to her in the next few months. Whatever the outcome, it's inevitable she'll be deposed as leader and I would't be surprised if she stood down as our MP. Not convinced the tories would still be a shoe-in, I think TIG would do quite well here as the LibDems traditionally come in second but were beaten by Labour in the last election.  

 

I will obviously be voting for Lord Buckethead and pledging my undying loyalty to his galatic empire.

[Jeremy Harris]

2 hours ago, Tom said:

Also worth noting that cement will absorb CO2 back from the atmosphere in a process called carbonation - so it's carbon footprint could potentially be a lot less than calculated simply from the manufacturing process.

 

 

Good point, I've just been trying to dig out some numbers (not at all easy) and it looks as if concrete may absorb about 40% of the CO2 released during its production over the first couple of decades after being poured, with more being absorbed through life as the deeper layers carbonate.  It's a non-linear process, with the shallower depths from surface (even when buried in aerobic conditions) absorbing CO₂ fairly quickly, and then the process slowing down for the deeper regions (typically greater than ~100mm from a surface).  It seems reasonable to assume that a floor slab may absorb around 25% of it's manufacturers CO₂ in the first 10 years, which reduces the total that needs to be offset from our house (excluding the retaining wall) to around 3.7 tonnes, and over the same 10 years the house will have avoided having to produce 9 tonnes of CO₂, so will definitely be carbon neutral before them.

 

[Big Neil]

3 hours ago, Bitpipe said:

o longer a supported product.

 

[Big Neil]

15 hours ago, PeterW said:

The worry about using GGBS is that the strength is unknown due to its composition so whilst it may be ok for garage footings or non structural elements, I would want a BS known mix for anything such as a ground bearing slab or structural work. 

 

Check these chaps out. I haven't looked at any of their docs for a while but I think it was somewhere near bedford they used this for a development of small houses, the foundations that is.

 

https://dbgholdings.com/cemfree/

 

The laymans description they gave to me was something like - 'You just use GGBS entirely instead of Cement and use the CEmfree product which does the magic inbetween'.

 

I know nothing about the Chemistry (cue @JSHarris) but in principal sounds interesting

[TerryE]

On 07/03/2019 at 22:42, Big Jimbo said:

None of us know, or are able to really find out what the true carbon costs of our properties are. Also, we all have to work to a budget, so the £20 jumber made in England, or the £6 jumper made in Bangladesh.

 

Jim, all you need to do is a bit of research.  Wikipedia is a good starting point for most uses, but always be willing to look at the debate on the associated talk pages or point check quoted sources if the topic is controversial. 

 

Take costs for global movement of goods, googling "shipping costs per tonne km" gives Wikipedia:Freight rate as its first link, so for example "bulk coal long-distance rates in America are approximately 1 cent/ton-mile" and the reference is a US Energy Information Administration article so this is going to pretty accurate.  Bulk and container shipping costs are almost an order of magnitude cheaper: a fraction of a cent per tonne km, thanks to automation and scale of international shipping, so take your jumper example, another link gave this 2018 Overseas Cargo & Freight Costs From The UK reference, which gives the cost of moving a standard 40ft container from Bangladesh (Chittagong) to the UK as $1,874.  Divide that by the number of jumpers you can fit in a standard container: 10s of cents.  If you don't believe me then the sources are there for you to come up with your own figure.  That's why everything is global these days; the shipping costs are in the noise.

 

We have a passive-class house.  The timber is Finnish grown CLS and OSB3, the skin is locally quarried stone, so no inner concrete block leaf and no bricks.  Yes we have a raft slab, but the total concrete @ 10 m³ isn't much more than would have been used in conventional trench footings.  Our LPA prevented us using PV, so I can't claim any 7-year payback period, but what is more relevant is the point at which the gross carbon cost falls below that of an equivalent conventional build and that is already true at day 0.

 

 

Edited March 10, 2019 by TerryE
Mindfart over weights vs volumes