What's more important for comfort U value or 'thermal mass'

[Iceverge]

Back to the point. 

 

One of those Scottish heritage studies measured the in situ U-Values of old stone and lime walls. (I think I linked it in one of @saveasteadings earliest threads).

The U-Value correlated with the moisture content in the wall. Damp Wall = Bad U-Value. 

More importantly moisture in a structure that wasn't designed to be damp causes decay, through mould, fungus, frost action and physical water erosion.  

 

My understanding  of the issue is as follows. 

 

This moisture gets into walls because of:

 

A. Bulk water ingress. Solved by (but not limited to) 

1. Unblocking drains and gutters
2. Repointing externally
3. Adding roof overhangs/flashings
4. External brick creams,
5. French drains to lower the local water table.
6. Fixing leaking pipes and showers enclosures. 
7. Water proof external render or paint

B. Condensation from humid internal air. Solved by (but not limited to)

1. Managing internal humidity with adequate heating and ventilation. 
2. Entirely blocking air paths through the wall to prevent air "carrying" moisture to a part of the wall below the dew point. 
3. Keeping the entire structure above the dew point. Normally with insulation, thermal Bridges must be managed!!!!

 

 

Now that's all fine in theory, but unless you build your house in a laboratory that's impossible to achieve. In any case, there'll be some construction moisture in the walls anyway. You need to allow your wall to dry. 

 

 

To deal with this you need to the moisture to leave the wall via evaporation. 

 

This can be achieved by (but not limited to)

1. Keeping the wall warm through heating, limiting IWI or fitting EWI.
2. Keeping internal humidity low. 
3. Not trapping moisture between materials of too low vapour permeability. (This is nuanced, more later....)

 

Alternatively for some construction types moisture is acceptable (e.g. foundations) but you'll need to build  it out of permanently moisture tolerant materials like concrete, stainless steel and plastic. 

 

 

 

 

 

 

 

 

                                        

 

[SteamyTea]

5 minutes ago, Iceverge said:

Damp Wall = Bad U-Value

Generally true of all insulation.

Water had a k-value of 0.6 W/m.K

Air is 0.026 W/m.K.

 

9 minutes ago, Iceverge said:

Managing internal humidity with adequate heating and ventilation. 

I think this is probably the easiest way to deal with it once the obvious external ones are dealt with.

By limiting the amount of water that can condense, most of the problem goes away.

Airtightness can also be worked on.

If the internal air is dryer than the external air, vapour migration will take place, further reducing the problem.

Basically what dehumidifiers do.

[Iceverge]

1 minute ago, Iceverge said:

Not trapping moisture between materials of too low vapour permeability. (This is nuanced, more later....)

 

To quote myself, this needs more digging as it's the root of most debate here I think.

 

Every material has a different permeability. Something like aluminium foil over PIR has a very low vapour permeability, practically impervious for the purpose of building (as long as there's no holes!) A fabric wall hung drape is very permeable, almost all the vapour gets through. 

 

Gypsum plaster, Cement plaster, Lime plaster, Woodfiber, EPS, OSB, plywood, are all somewhere in the middle. 

 

Now lets move to the real world. Every house is different with different occupants, different heating habits, different standards of construction. Each house goes through daily, weekly and annual cycles of accumulating and loosing moisture in the structure via vapour. What we are aiming for is to make sure that the walls can dry out on average faster than they are being wetted. This is a case by case basis for every house. 

 

A house with poor airtightness and IWI will see lots of damp air make it's way into the walls and condensate there. However if it can dry outwards in the long term no great damage will be done. However if it's drying is restricted by say cement external render, the moisture will build up and there's trouble. 

 

Similarly a house with terrible airtightness but a cosy layer of continuous EWI could survive with terrible ventilation and airtightness as the wall would always be too warm to condensate the vapour.  ( It wouldn't be healthy or comfortable through) 

 

 

Some forum examples here to discuss. 

 

@jayc89 has done I suspect a pucker job of their house, they PIR is taped and foamed diligently and all thermal bridges are taken care of from the inside out. Then there's proper internal ventilation and heating. Outside is properly pointed (and maybe brick creamed?) Not lightly to see any issues. Perhaps so good that if there had been external render then that might have even been ok as there was so little moisture getting into the wall initially. Good airtightness to prevent vapour reaching the joist ends would be my only concern. 

 

Suppose a typical builder had under taken the same issue, badly applied insulated plasterboard, air gaps and thermal bridges galore, noisy bathroom fans that would never be used. The same wall would probably ended up sodden for most of the year. 

 

 

@Roger440 maybe had some issues, maybe from a high water table pushing water up through the walls. The low permeability cement render was enough to cause moisture to build up faster than it could dry, hence problems. Reapplying lime render with its greater vapour permeability instead was enough to tip the balance in favour of more drying than wetting and - hey presto, problem solved. Maybe a dehumidifier in the room, or a fire or a French drain would have had the same benefit. Hard to say or maybe they were not practically possible. 

 

@Gone West Peter your first house had no internal "vapour control layer". Just plasterboard over open cell spray foam. As this is a relatively permeable material, one could have worried that the backside of the  colder OSB sheathing ( which was less permeable) may have accumulated moisture.  However your airtightness was so good (<0.6ACH) that no air leaks got to take internal humid air to the sheathing. This approach is very acceptable in the US but not so much here.

 

@IanR I know specced a foil backed plasterboard for his house with it's external airtightness layer as vapour control measure. However I don't think this was needed as the superb airtightness (0.11ACH I think, hurray for cellulose!!) would never allow enough vapour to escape into the walls to be a problem. Similarly the MDF sheathing with it's high vapour permeability could probably have been replaced with OSB or something cheaper. ( It does help thermal bridging in his case thought.)  

 

A mate of mine built a house recently from Hempcrete blocks, TF with hemp batts insulation, more hemp blocks and lime render both sides. There's a single MVHR unit inside but I'm unsure as to the level of airtightness. The house will ok with diligent occupants. However if there's under ventilation and under heating  at any stage I would worry about the moisture content in the walls caused by air leaks despite them being of a very high vapour permeability.

 

@Gone West back to (some of) your original problem. You simply need to establish can your walls dry faster than they can accumulate moisture. Very important in this case as the colder wall will be condense vapour more readily.  If you can absolutely bullet proof an internal PIR install, with no chance of air leaking via gaps, or sockets, or by the walls or ceiling and you can completely eliminate thermal bridges then I would be happy to do it. The wall will still dry (slowly) via the cement render externally but so long as it's not getting vapour from the inside it'll be ok. As an added complication, insulation giving higher internal temperatures makes the air more vapour laden, so unless you're really on top of ventilation as well it'll increase the risk further.   

 

Maybe if you're less sure of the ability to seal the PIR completely use an internal soft backed woodfiber layer with lime render. It can still readily dry inwards and airtightness isn't so vital. From a practical point of view I'm far more in favour of flexible IWI like wool batts or sprayfoam. Then at least if you get a puncture the risk is very localised to one spot. Puncture a PIR sheet or insulated plasterboard poorly foamed in, and you could expose a whole wall to internal vapour via air leaks. 

 

 

If you really want to be sure, EWI is almost completely fool proof from a moisture risk position as the whole structure is above the dew point.  

 

 

 

 

TLDR:

 

Anything can work so long as it can dry faster than it gets wet. 

 

 

 

 

  

 

 

[Iceverge]

1 hour ago, SteamyTea said:

If the internal air is dryer than the external air

 

Almost never the case though assuming the house is habited. 

 

1 hour ago, SteamyTea said:

I think this is probably the easiest way to deal with it once the obvious external ones are dealt with.

 

The MEV unit I installed in my parents completely uninsulated house has had a really positive effect on the comfort. Everything is dryer. Also the mould is gone from under the stairs.  

[Gone West]

2 hours ago, SteamyTea said:

Was the place stable in the non heating season?

There was no active cooling and in the summer with long sunny days the inside temperature went up to 26C IIRC. Cooling took place in the evening by opening an outside door and the roof window in the bathroom.

[SteamyTea]

2 minutes ago, Gone West said:

26C

Lovely.

That is about the right temperature for humans to do nothing by laze about.

Happens to be the mean temperature in the parts of Kenya where humanins initially developed.

[Iceverge]

@Gone West

 

Original question. 

 

Comfort I think is simply the temperature we feel on our skin. Nothing really to do with U-Values really.  

 

Hence we like the sun on our face, hate cold tiles on our feet, like sitting on a radiator (briefly!) and hate a breeze when getting out of the shower as the evaporative heat losses of the water really cool our skin. 

 

For a comfort we need to manage 3 things, the old faithful trio Convection Conduction and Radiation. 

1. Convection or Drafts. Solved by airtightness and eliminating different internal temperatures that cause convection currents. Insulate cold surfaces similarly.  Slow and steady heating is better then intermittent blasts, heating all the rooms equally is better than just one or two. This may not always be possible or economical. 
2. Conduction. Getting rid of cold things you touch or replace them with materials of lower thermal conductivity. Tiles for example are worse than Lino. Fit UFH. Wear slippers. Keep humidity under control, a damper carpet feels colder.  
3. Radiation. Keep you skin covered, even a light shirt will reduce the amount of energy you "shine" away. Cover windows and cold walls with curtains to reduce the amount of energy they soak up through radiation. Fit 3G windows and add insulation to cold surfaces. Add an IR heater to bathrooms to heat your skin directly after a shower. 

 

In short I think you should insulate the wall but only after tacking the airtightness and ventilation of the house first.

 

Then you can then decide on your preferred build up based on (but not limited to):

• Cost
• Risks of low permeability materials and poor workmanship
• Contribution to airtightness
• Mitigation of thermal bridges
• Floor space loss
• Ease of construction

 

[SimonD]

5 hours ago, Gone West said:

As I said, we moved from a Passivhaus, so we were used to very little temperature or humidity variation. It is not that simple though, as we thought the reason it felt uncomfortable was because the temperature, and possibly humidity, changed as you moved closer to the wall, even though the room temperature away from the wall was as expected. After months of heat being pumped into the house the walls warmed up and it felt more comfortable. At the time @SteamyTea explained about the large amount of energy required to remove water from the wall.

 

As I think @SteamyTea is alluding to, I don't think you have a problem with moisture, or moisture in the wall per se. It's just that the wall is sucking too much heat out of the space, and will continue to conduct heat even after a long period of acclimatisation. Due to the nature of the wall itself, you'll always experience it as being cooler than the surrounding air - a very pleasant property during a heat wave,not so much in the depths of a cold winter.

 

I have heard some people suggesting that the interior finish has a great impact on the experience of thermal comfort in the home, some of which has come from those selling woodfibre IWI, for example. I've heard it said that this is because of how the material bounces infrared from its surface and apparently woodfibre returns these to the body to make it feel warmer - I suspect this is a brilliant example @Iceverge's definitions above and could be added to those. Why do I suspect this? Because downstairs in my house I have masonry walls with just a gypsum parge coat internally (my 140mm woodfibre insulation is EWI so not relevant to the IR claims) and upstairs I still have mostly OSB. Neither feels more or less comfortable than the other with the temperature and humidity remaining the same. The only time there's a difference is during very hot weather and downstairs remains beautifully cool for days during heatwaves.

 

Now in your instance, you will also have your wall contributing to your RH, even if it isn't wet or damp. If you use ventilation to try to reduce humidity, the wall will simply give it back to the room. If you had a wall lined with PIR, this wouldn't happen and you would see a reduction from extract ventilation (see paper I linked to above which measures this process).

 

I'm sure I'm not new in suggesting the solution is to insulate, but then the question remains as to how.

 

Generally the concensus is now verging to using a buildup of materials that largely behave in the same way as the wall material and this doesn't require a ventilation gap between the wall and the insulation layer.

 

So your options could be to use just a thin layer of insulating plaster which can be lime based, or even lime and cork like SecilTek ecoCork, for example, which is then finished using a lime render. Alternatively, you could look at IWI in cork, woodfibre, or even sheeps wool (sheeps wool recommending a breather membrane against the wall between the insulation and wall). Each of these will have different buildups with the cork and woodfibre generally being stuck to the wall and then plastered. The sheepswool is installed between battens followed by vapour control/airtightness layer, then plasterboard and skim if you want to.

 

If you wanted to try ecoCork, and your wall areas isn't too big, I have about 33 bags of it surplus to requirements that I'd be happy to let you have - I just don't know the expiry date on these and hope they's still be okay as they've been stored for a couple of years now. This is just covered with a Seciltek render to finish.

 

Then there's the hempcrete spoken about earlier.

 

There are then those that are quite happy to put PIR on the wall, but generally this is now only recommended with a ventilation gap between the wall and insulation.

 

TBH, I don't envy you, I once loved the period property thing and having bumped along a rocky road with these types of buildings, I've found the road is paved with a lot of snake oil and its salesmen. Even some reputable suppliers and designers make things up as they go so buyer beware.

Edited January 16 by SimonD
It seems @Iceverge was busy posting while I was half distracted in draft model so repeated some of what he's already said.

[Adrian Walker]

Have a look at https://adaptavate.com/ they have a range breathable and insulated plasters made in Bristol. 

[Gone West]

3 hours ago, SteamyTea said:

Lovely.

I agree, but without cooling the house down in the evenings, it would have just got hotter day by day. We like a warm house and I don't feel comfortable sitting down, unless the temperature is at least 23C.

[Gone West]

1 hour ago, SimonD said:

If you wanted to try ecoCork, and your wall areas isn't too big, I have about 33 bags of it surplus to requirements that I'd be happy to let you have - I just don't know the expiry date on these and hope they's still be okay as they've been stored for a couple of years now.

Thanks for the offer, but I have just looked at the data sheet for ecoCORK and it says shelf-life is 12 months.

[SteamyTea]

3 minutes ago, Gone West said:

looked at the data sheet for ecoCORK and it says shelf-life is 12 months

Perfect excuse for @Pocster's shirkers thread

[Roger440]

11 hours ago, SimonD said:

 

Now you're opening up an even more contentious can of worms, which in todays world are the binary a) uniform temperature, b) temperature variation.

 

In camp a there is the suggestion a la passivhaus/mvhr etc/ fervents that it's the uniformity that matters mosts as clearly that's implicit in the designs

 

In camp b is a growing vocal cadre of building and human 'experts' suggestion that temperature variation is both more natural, more healthy, and more comfortable than uniformity.

 

I think it's a difficult one, made all the more difficult when comfort is so subjective.

 

Ideally we want to know what @Gone West really means by comfort and then in the BH fashion, we can answer by going completely off topic!

 

Possibly slightly on a tangent, but when i had the dubiuos priviege of looking after a fleet of trains, we always had lots of complaints about cold carriges in winter, and to a lesser degree too hot in summer.

 

Investigation usually revealed all was working as intended. ie, the system was controlling the internal temp to 21c as expected.

 

However, humans being fickle, this wasnt the answer. So we ran an test one year, to increase the target temp to 23 for winter, and 19 for summer. Being rekleativelt simple, this involved a manual adjustment twice a year. The results were better than expected. complaints dropped to a fraction of the previous levels.

 

Illogical? Maybe.  But its the reality. Having stood on a freezing cold platform for 15mins, you wanted it warm when you boarded. 21c didnt fulfil that criteria. I confess, it applies very much to me in that circumstance. Like wise in summer when its 27c outside. Getting on, 19c is great.

 

 Im the same at home. Despite the fact the living room is at 21, im layered up. In the summer, it would be just a t shirt. At the same temp. Maybe im odd. 

[SimonD]

On 16/01/2024 at 22:16, Roger440 said:

 

Possibly slightly on a tangent, but when i had the dubiuos priviege of looking after a fleet of trains, we always had lots of complaints about cold carriges in winter, and to a lesser degree too hot in summer.

 

Investigation usually revealed all was working as intended. ie, the system was controlling the internal temp to 21c as expected.

 

However, humans being fickle, this wasnt the answer. So we ran an test one year, to increase the target temp to 23 for winter, and 19 for summer. Being rekleativelt simple, this involved a manual adjustment twice a year. The results were better than expected. complaints dropped to a fraction of the previous levels.

 

Illogical? Maybe.  But its the reality. Having stood on a freezing cold platform for 15mins, you wanted it warm when you boarded. 21c didnt fulfil that criteria. I confess, it applies very much to me in that circumstance. Like wise in summer when its 27c outside. Getting on, 19c is great.

 

 Im the same at home. Despite the fact the living room is at 21, im layered up. In the summer, it would be just a t shirt. At the same temp. Maybe im odd. 

 

I think we're all illogical when it comes to temperature and almost everything else behavioural 😊, but I was just talking to a customer about this the other day. I'm exactly the same, with the heating cranked up even when it shows a health 21C in the house. Our system has a cold weather boost where it increases target temp by 3C during cold periods, which is supposed to be for draught ridden uninsulated properties, but seems to be the perfect solution for us right now!

[SteamyTea]

On 16/01/2024 at 22:16, Roger440 said:

Possibly slightly on a tangent, but when i had the dubiuos priviege of looking after a fleet of trains, we always had lots of complaints about cold carriges in winter, and to a lesser degree too hot in summer.

 

27 minutes ago, SimonD said:

I think we're all illogical when it comes to temperature and almost everything else behavioural

I am not so sure.

During a cold, grey winters day, or more so at night, there is no extra, direct energy received from the body from the sun.

This tends not to be the case in the summer, even when a bit cloudy.

But you may have noticed that even in the summer, you can feel quite chilled when the sun sets and darkness comes.

I have spent the last 30 years going to see the sun set at Land's End, 15 minutes before sunset it can feel quite warm, come the moment, and most people are shivering.

[Iceverge]

On 16/01/2024 at 22:16, Roger440 said:

Illogical? Maybe.  But its the reality. Having stood on a freezing cold platform for 15mins, you wanted it warm when you boarded. 21c didnt fulfil that criteria. I confess, it applies very much to me in that circumstance. Like wise in summer when its 27c outside. Getting on, 19c is great.

 

 

Its the air temperature in the train at 23deg. Everything else will be colder so your bodies conduction and radiation losses will be greater than in summer. 

 

 

 

[SimonD]

3 hours ago, SteamyTea said:

 

I am not so sure.

During a cold, grey winters day, or more so at night, there is no extra, direct energy received from the body from the sun.

This tends not to be the case in the summer, even when a bit cloudy.

But you may have noticed that even in the summer, you can feel quite chilled when the sun sets and darkness comes.

I have spent the last 30 years going to see the sun set at Land's End, 15 minutes before sunset it can feel quite warm, come the moment, and most people are shivering.

 

I didn't really mean the scientific explanation of the experience of temperatures, I was more referring to how human beings tend towards illogical behaviour when it comes to how they deal with their experience. E.g. walking around in shorts and a t-shirt in the middle of winter in the house and saying it's chilly and ramping up the thermostat instead of just putting on some trackies.

 

Likewise we see the same thing in studies around heating and ventilation systems. For example, some large scale studies found that the monitoring systems were showing abnormal behaviour in MVHR systems being studied, looked everywhere they could to try and find a problem, but it wasn't until they asked the residents when they found out they were all opening their bedroom windows at night - a relic of the country'culture. We see the same thing with heat pumps where the users don't bother to find out about how the system works, instead expecting that the system behaves as they've always done using bursts of high heat twice a day. You also just need to look at the surge in wood burning stove installations when gas prices rocketed, without much consideration to how that might impact solid fuel prices and the logistics of keeping the stove, sotring the fuel, etc. etc. and that it really isn't any cheaper than gas at all.

 

The other day I read that scientists are finally realising that a lot of the problems we're experiencing with climate breakdown, consumption and environmental damage has to do with people's behaviour and that we need purposeful behaviour modification, however sinister that might sound!

 

 

[SteamyTea]

23 minutes ago, SimonD said:

The other day I read that scientists are finally realising that a lot of the problems we're experiencing with climate breakdown, consumption and environmental damage has to do with people's behaviour

Hardly recent, this has been known about all my life.

[SimonD]

12 minutes ago, SteamyTea said:

Hardly recent, this has been known about all my life.

 

Quote

Record heat, record emissions, record fossil fuel consumption. One month out from Cop28, the world is further than ever from reaching its collective climate goals. At the root of all these problems, according to recent research, is the human “behavioural crisis”, a term coined by an interdisciplinary team of scientists.

 

https://www.theguardian.com/environment/2024/jan/13/human-behavioural-crisis-at-root-of-climate-breakdown-say-scientists

 

You might wonder what's taken them so long 🤷‍♂️

 

 

[saveasteading]

This is displayed in a Spanish bank and applies to all offices and retail buildings.

Very sensible say I and it must save huge amounts of energy. It is an Act of Parliament.

Corporates won't be running the cooling at shirt sleeve temperatures in winter, just because they can. 

Staff won't be arguing that the temperature is too high and too low at the same time. 19 isn't high enough that people open windows.

Jumper industy benefits too.

 

To summarise. Heating can only be used below 19C.

Cooling can only be used sbove 27C.

Doors must be closed. Electric signs are turned off at night.

Would we have to change the numbers for UK use?

[SteamyTea]

3 hours ago, saveasteading said:

Staff won't be arguing that the temperature is too high and too low at the same time.

Maybe, maybe not.

 

 

 

[saveasteading]

4 minutes ago, SteamyTea said:

Maybe, maybe not.

But management can pass the responsibility on to the king, as it  is a  royal decree.

I think this was introduced about 10 years ago during a recession  or fuel shortage along with reducing speed limits. The speed limits reverted but temperatures not, and no fuss as far as I'm aware.

[Iceverge]

Just put up the cost of gas. 

 

People would figure it out themselves. 

[SteamyTea]

26 minutes ago, Iceverge said:

Just put up the cost of gas.

Yes.

And not a small amount either.

Price shock the market to force change.

 

[Iceverge]

6 hours ago, SimonD said:

You also just need to look at the surge in wood burning stove installations when gas prices rocketed

And Solar PV, ASHPs and EV's. 

 

 

 

 

 

Edited January 19 by Iceverge