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

[joe90]

I do think that there are so many variables (construction, orientation, ground conditions, etc etc) that no one answer is correct for every situation. 

[SteamyTea]

1 hour ago, joe90 said:

I do think that there are so many variables (construction, orientation, ground conditions, etc etc) that no one answer is correct for every situation. 

This is how science works.

Something is observed, a hypothesis (tentative explanation about a phenomenon) to explain it, then an experiment is created to either, and this is very important, falsify the hypothesis, and be able to repeatably test it.  The falsification is the really important bit as that is where the statistical data comes in.  All falsification does is reject the hypothesis, it never proves and alternative (which is where we are at in this discussion).

This may seem like a binary choice, but it is by reducing a problem to either, yes or no, that the truth is found.

 

This area of science has allowed us to delve incredibly deeply into problems, while also getting rid of the rubbish.

Hypothesis are often referred to by lay people as guesses, this is very much not the case, they are based on existing knowledge i.e. which is more porous cement or lime render, how much liquid water, as a fraction of existing mass, can the materials absorb, is the render applied correctly.

 

Once a Hypothesise is has passed the above tests to the desired significance, it becomes a theory.

If there are no known exceptions, then it comes a scientific law.

This is where science and mathematics diverge, in science, you can have a theory that holds true only 80% of the time as it is considered 'good enough for most cases', medical work is at this level, Physics works to a much higher standard, usually 1 in 35 million that it is not chance.

Mathematics has to hold true, with no exceptions, in all cases, no matter what.

[saveasteading]

1 hour ago, SteamyTea said:

Physics works to a much higher standard, usually 1 in 35 million that it is not chance.

Explain please? Where does that very small number come from?

 

Structural Engineering is physics, isn't it? We add 20% ish contingency just in case, although some of that is weather and quality.  So more like your medicine figure.

 

1 hour ago, SteamyTea said:

Hypothesis are often referred to by lay people as guesses

It so annoys me when lay people (the polite term) argue that ' scientists don't  even agree on'  ....climate change, viruses, etc.

 

It's science until 100% proven at which stage it becomes fact and stops being science?

[SteamyTea]

18 minutes ago, saveasteading said:

1 hour ago, SteamyTea said:

Physics works to a much higher standard, usually 1 in 35 million that it is not chance.

Explain please? Where does that very small number come from?

It is the 5 sigma on the normal distribution chart.

It is the point where Physists agree that the change it is something else is so small that it is if no consequence.

20 minutes ago, saveasteading said:

Structural Engineering is physics, isn't it?

There is Physics, the rest is stamp collecting.

It used physical attributes of materials, just at a lower level, probably around 3 sigma. So 99.7% your designs are correct.

That does not mean that if you build 1000 columns and beams, 3 will fail. Just that you can be confident that the chance if failure over a design life is too small to worry about i.e if you design for a 60 year life, and your materials are good for 100 years, you won't have a failure.

27 minutes ago, saveasteading said:

 

It's science until 100% proven at which stage it becomes fact and stops being science

Not really, there are still proper scientist trying to find holes in well established theories.

It is often said that a Doctor of Philosophy spends 4 years proving something, then a lifetime trying to disprove it.

 

(I am just doing a little experiment to see if something I think will not work, may work. Much of it is to do with my own bias, but I may uncover something useful)

[Roger440]

11 hours ago, SimonD said:

 

 

You still haven't read the paper have you?

 

You said it was a fact that Lime was breathable, or whatever.

 

The paper quite rightly highlights that the materials behave differently due to their pore structure. As a result, gypsum is both hygroscopic and vapour permeable whilst lime is only vapour permeable.

 

I merely corrected you to highlight the facts are more nuanced and that the term breathable is meaningless.

 

From any perspective of building, you need to select the correct materials for the job. In some instances, due to the behaviour of the materials, it may be better to select one material over another and it's down to the local context. Therefore, clearly lime may be better in some circumstances than gypsum, and in other gypsum will be more preferrable to lime.

 

However, there is also the fact that there are many buildings without a DPC that perform absolutely fine without damp problems so for me it remains the question that the priority is to investigate the excess moisture first and then, if not practicable, take measures that mitigate against the excess moisture.

 

Unfortunately, I get to see many older buildings suffering from damp that have used lime where the lime plaster is also cracking and peeling off the wall due to long term exposure to excess damp, even far up the wall. But then we get back to the issue of layers such as paint, or even wallpaper and the effects they have on the ability of a wall to regulate moisture content. But even in cases where these layers do not contribute, it has been shown that it still takes years for walls to shed excess moisture following remedial works and if there is a continuous supply of moisture the dampness will remain. The only way a wall will be drier is if you remove the supply of moisture and provide it with adequate time to dry out.

 

This is one of the reasons why @SteamyTea 's point about numbers and measures is so important because otherwise you end up going round in circles in conversations because the reference points are unclear and ambiguous, not really helping anybody - what are we referring to specifically here when we speak of a damp wall? How damp?

 

I have, but it seems to be looking at a different problem, ie moisture buffering for indoor comfort/humidity etc. Im sure thats all very interesting to some, but is not the same as what im talking about, which nothing to do with "moisture buffering". But what im calling moisture "shedding". Sure, theres common factors, but its not the same thing as far as i can see.

 

I agree the term breathable is largely pointless

 

But really, it not that relevant is it.

 

Yes, of course, some buildings without DPC will be fine. And? Some are not.

 

No one is going to conduct extensive investigations into an old wall(s) to determine exactly how wet it might be at any given point in time. At different times it will be different.

 

The fundamental problem, is there is no DPC. I note you didnt offer a practical solution to that issue.

 

So, faced with a house that has "some" damp in the walls, you need to decide what to do. I could read some reports, like those posted, but does that help me decide what to do? No.

 

I know, however, that if i do it in lime, it has the best chance possible of not having a problem going forward (assuming of course ive done all the obvious things to reduce moisture getting into the wall, im taken that as a given). Were i to do it in something less "breathable" then i increase the risk of a problem.

 

I say again, i might be fine. I may be able to put foil faced PIR in front of it, and a vapour barrier over, effectively reducing moisture movement to zero. And still be fine.

 

But it might not. So back in the real world, one has a choice to make. Unless someone else is offering to pay for rectification if there is a problem, then, when spending your own money, go with the lowest risk option. Maybe you would do different, but i cant afford doing it twice.

 

 There is no practical testing available to homeowners to allow such decisions to be made, even if one wanted too.

 

So the default option is lime, because its the most likely to work given a damp wall. I emphasise likely.

 

Just to add of course, is that with a moderately damp wall, it can take years, maybe decades to manifest itself, visually. So walls you "think" are ok, maybe anything but.

 

 

[Roger440]

12 hours ago, Gone West said:

So presumably an insulated lime based plaster should be ok, such as hempcrete? Would there be a difference in the effects on the wall, of different types of insulating materials in the plaster, such as hemp or expanded glass beads.

 

That is the generally considered view.

 

However, the usual warning is not to make it too good, as you will drop the wall temp, which "may" lead to a dew point in the exsisting wall. You dont want that.

 

As always, this will vary wildly from house to house.

 

And the key point is, ALL the long term risk is yours. No one will guarantee a solution that wont see the return of damp at some point. Despite the chat in this thread, no one is going to test your house and make/draw up a plan.

 

The last point being a major consideration for me at least, when deciding what to do with my money.

[SteamyTea]

8 minutes ago, Roger440 said:

So the default option is lime, because its the most likely to work given a damp wall. I emphasise likely.

Who you agree that a cement based product, with the same properties as a lime based one would work just as well?

[Roger440]

1 minute ago, SteamyTea said:

Who you agree that a cement based product, with the same properties as a lime based one would work just as well?

 

Based on logic, yes. 

 

But no such thing seems to exsist. If it does on paper, either no one has found it, made it, or it doesnt work in practice.

 

For me, at least, it working in practice is rather important.

[Gone West]

24 minutes ago, Roger440 said:

And the key point is, ALL the long term risk is yours. No one will guarantee a solution that wont see the return of damp at some point.

Which is exactly why I started this thread. To find out as much as I can. There is no discernable damp in the wall, which has been the same for the last 50 years. Although I would like to insulate it I don't want to end up with a wall that deteriorates as a result.

[Roger440]

10 minutes ago, Gone West said:

Which is exactly why I started this thread. To find out as much as I can. There is no discernable damp in the wall, which has been the same for the last 50 years. Although I would like to insulate it I don't want to end up with a wall that deteriorates as a result.

 

You said its not damp now, but didnt say, what, if any covering is on it now. If what you want to fit is no less permeable than whats on it now, then id suggest the risks are low.

 

On the other hand if its a bare wall, or just lime plaster, then risks are much higher.

 

As i already suggested, no one will give you a definitve answer. It will come down to judgement and your appetite for risk.

 

With absolute respect to those on this forum, there are other places with much more practical experience of older buildings than is available here, this being pretty focussed on new build.

 

Warning though, some can be hardcore limeists! Believing its the answer to everything, or just open the windows to ventilate!!!

 

PS. As im sure you have read what i did to dry my last house out, however my neighbours took their traditional modern builders approach and put a DPC a meter up the wall and boarded over it. Looks nice, and is is damp free. However, im pretty confident, indeed, can see, that the walls are damp. And im sure, just like mine used to be, if i drilled into them, slurry paste would come out, not dust. Sadly, this is the industry standard for damp walls. 

[Mike]

11 hours ago, SteamyTea said:

12 hours ago, Gone West said:

So presumably an insulated lime based plaster should be ok, such as hempcrete

You would need to find out the fraction of moisture it can absorb

According to a study of 3 hempcretes*, 'liquid transfer appears negligible for relative humidity lower than 80%', it has a moisture buffer value of 'excellent' or 'nearly excellent' on the Nordtest classification (from 1.94 to 2.15 g/(m2 %RH) depending on the composition), and high water vapour permeability. Which is pretty good.

 

*Florence Collet, Julien Chamoin, Sylvie Prétot, Christophe Lanos. Comparison of the hygric behaviour of three hemp concretes. Energy and Buildings, 2013, 62, pp.294-303.  10.1016/j.enbuild.2013.03.010 hal-00810372.

 

 

[SteamyTea]

7 hours ago, Mike said:

According to a study of 3 hempcretes

That seems to be one of the most useful papers I have seen on the subject.

Thanks

 

(not that it addresses the original question here, with is about insulation and thermal inertia) 

[Alan Ambrose]

>>> not that it addresses the original question here

 

Banish the thought. Anyone? Is it related to this question below or are they totally different? Does ‘comfort’ (in the original question) imply lack of temperature variation?

 

“What's the target for phase shift / decrement delay?

 

I can't decide whether the optimum is 12h based on the idea of 'cancelling out' some of the dailytemperature swing or 'very large' on the basis that the interior temperature swing will be super low?”

[Gone West]

10 hours ago, Roger440 said:

You said its not damp now, but didnt say, what, if any covering is on it now. If what you want to fit is no less permeable than whats on it now, then id suggest the risks are low.

 

There has never been any visual indication that the wall is damp in the three years we have lived here, and as far as we have been able to find out, the wall structure has not changed in the last 50 years. When we moved in, the house had been empty for a year and felt damp. As humidity is generally quite high around here we assumed the structure had just absorbed moisture from the air. Our solution was to heat the building to 23C and ventilate in the summer. It took the best part of a year before we felt the house was ok. We had moved from a Passivhaus where the humidity and temperature was more or less constant all the time, so we may have been more sensitive to the situation here.

As I said previously, the wall is hard plastered, which was done in the 1970s. From what has been said it seems that removing the hard plaster and replastering with Hempcrete may be the best solution for increased insulation without greatly affecting 'thermal mass' and the feeling of comfort.

[SimonD]

35 minutes ago, Alan Ambrose said:

Does ‘comfort’ (in the original question) imply lack of temperature variation?

 

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!

[SteamyTea]

27 minutes ago, Alan Ambrose said:

Does ‘comfort’ (in the original question) imply lack of temperature variation?

Possibly.

But energy storage has no time units connected to it, remember that 1 kWh is really 3.6 MJ.

Thermal resistivity, which is insulation, does have time units.  The absolute thermal resistivity has the units K/W, where K is temperature difference and W is watts, which is J/s.

So just having energy stored in mass does not, in itself, have anything to do with the rate that energy is delivered (think of a car with a half full tank of fuel, but you don't know what the upcoming journey is going to be).

So if you want thermal stability, you have to add insulation because that is what governs the rate that energy is delivered.  It is independent of the amount of energy stored (at any give temperature).

35 minutes ago, Alan Ambrose said:

I can't decide whether the optimum is 12h based on the idea of 'cancelling out' some of the daily temperature swing or 'very large' on the basis that the interior temperature swing will be super low

12 hours would be useful if we lived an exact 12 hour lifestyle i.e. 12 hours daylight, 12 night time, known temperature regimes i.e. 22°C during daylight, 16°C night time, known other energy inputs i.e. heating, cooking, showering, number of people etc.

The UK (and most Northern Hemisphere places) do not have any of the above, so using mass, especially the built in mass of a building, is not really going to help greatly with stability.

As I mentioned early on in this thread, wine cellars built into caves are often quoted as 'proof' that much mass created stability.  They are relatively stable compared to the ambient temperature, but at a lower mean temperature, or to put it another way, if you want to keep your house cold, fill it with rubble.

 

Now here is an experiment that anyone can do, it is simple and only requires a bucket full of water and a thermometer.

 

Fill bucket from the cold tap, place somewhere out of the way (just to save knocking it over).

Write down the date and time, take a temperature reading of the air inside and outside the house, then take the water temperature.

Do this as often as you like, but at least 3 times a day.

Chart the temperatures.

Draw your conclusions.

[SteamyTea]

4 minutes ago, SimonD said:

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!

I have just bought an old banger of a car, trip up to my Mother's and it averaged (mean) 70 MPG (0DP).

Now I am going to look at a blue sky by the sea.

[Gone West]

48 minutes ago, Alan Ambrose said:

Does ‘comfort’ (in the original question) imply lack of temperature variation?

 

 

2 minutes ago, SimonD said:

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!

 

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.

[SteamyTea]

2 minutes ago, Gone West said:

As I said, we moved from a Passivhaus

I can't remember what the construction was.

What were the wall, floor, roof build up.

No need to have actual values, but was the insulation inboard or outboard of the main structure and what was that structure.

It may also have been a combination of inboard and outboard insulation and low mass structure.

 

Granite has a k-value of between 2.1 and 3.5 W/m.K

Brick is ~300 W/m.K

Polyurethane foam 0.03 W/m.K

 

So polyurethane foam retards the thermal losses by a factor of between 70 and 117.

Uninsulated stone will just draw all the energy you put into heating your inside air outside in now time.

 

If 'thermal mass' was so brilliant, why do we need to insulate all our old housing stock?  Most of them are brick and stone.

 

 

[saveasteading]

8 minutes ago, SteamyTea said:

why do we need to insulate all our old housing

Because there is only thermal mass and no insulation.

However, that works in hot climates, absorbing the sun on the outside, shedding the heat at night.

[SteamyTea]

7 minutes ago, saveasteading said:

However, that works in hot climates, absorbing the sun on the outside, shedding the heat at night.

I am not sure it does (if you mean heavyweight housing in the tropics).

The main driver of concrete housing in the developing countries was cheapness and speed of construction.

All the places we lived in apart from 2 (Seria and Pin de Galle, both a few metres from the sea) had air conditioning and no insulation.  Was a shock moving to The Netherlands where there was no insulation apart from rugs hanging on the walls, but lots of town gas to burn.

 

Just having a quick look at the EPC register and the house we lived in when we got moved to the UK has an EPC of D, as did the one we moved to, and the one after that.  My recent places seem to be Cs (have to look at the neighbours as the EPC was not invented when I last moved).

 

So apart from two places, all our 'tropical' homes where of heavyweight construction.

[Gone West]

29 minutes ago, SteamyTea said:

What were the wall, floor, roof build up.

No need to have actual values, but was the insulation inboard or outboard of the main structure and what was that structure.

It was a timber I-beam portal frame with 350mm Icynene insulation between the I-beams and 50mm Rockwool outside of the 15mm OSB3 racking, so walls and roof were the same except for the rain screen, U 0.095 W/m2K. Floor was 200mm concrete on 300mm EPS with 200mm upstand, overall U=0.1W/m2K.

[SteamyTea]

3 minutes ago, Gone West said:

Floor was 200mm concrete on 300mm EPS with 200mm upstand, overall U=0.1W/m2K.

As that was the only significant mass, it was thermally isolated from the 'world'.

Was the place stable in the non heating season?  This assumes you did not cool the slab.

 

Rather pointing to insulation keeps the temperature stable more than mass.

[Iceverge]

Definitions.

 

Thermal Mass: Sales term used by concrete salesmen to dupe customers with poor scientific understanding. 

Breathability: Sales term used to confuse customers who want "eco" products or have old houses. 

 

 

[SteamyTea]

7 minutes ago, Iceverge said:

Definitions.

You can always tell when a sales person is lying, their lips move.