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

[saveasteading]

44 minutes ago, SimonD said:

Excess moisture isn't good for any structure, so deal with the moisture

Fix the roof rather than changing the bucket.

I may have a look for the excellent explanatory sketch of moisture in a masonry wall...but I think I said that a week ago.

[SteamyTea]

6 hours ago, SimonD said:

Excess moisture isn't good for any structure, so deal with the moisture.

Which is a point I made earlier as well.

 

Hopefully, tomorrow, I shall have a proper read of that PhD paper.

[saveasteading]

4 minutes ago, SteamyTea said:

proper read of that PhD paper.

I started but didn't get far. Looking forward to your summary.

[SteamyTea]

8 minutes ago, saveasteading said:

Looking forward to your summary.

I am reading with the assumption that there is no intrinsic difference in the materials.

But seems from what @JamesPa quoted, gypsum is better than lime.

Will just have to see where OPC mixes fit in.

[Mike]

On 08/01/2024 at 16:09, Gone West said:

I am trying to work out if adding a thin layer of insulated plasterboard, say 25mm PIR, will improve comfort levels. Alternatively if I just plaster skim the wall, will the comfort level be better because of the thermal mass effect.

In a traditional building that is subject to some moisture, one option I'd consider is adding hempcrete to the inner face of the wall, improving the U-value and maintaining breathability without isolating the interior from the 'thermal mass' of the wall.

 

There's an example here: https://lowcarbonbuildings.wordpress.com/2019/09/15/a-domestic-insulation-project-chapter-3-weeks-of-weetabix-walls/

[SteamyTea]

2 minutes ago, Mike said:

There's an example here: https://lowcarbonbuildings.wordpress.com/2019/09/15/a-domestic-insulation-project-chapter-3-weeks-of-weetabix-walls/

I hate to say it, but seems more like hopium than a solution.

Is there any proper research as to the long term performance.

[Mike]

55 minutes ago, SteamyTea said:

59 minutes ago, Mike said:

There's an example here:

I hate to say it, but seems more like hopium than a solution.

Is there any proper research as to the long term performance.

 

Yes. The French Réhafutur 1 research project (http://www.rehafutur.fr/) was the initial research project, a collaboration between the housing association Maisons et Cités and the University of Artois, with support from the regional Eco-business Creation and Development Association (CD2E), the French Building Federation, the Federation of Construction Employers Cooperatives, and others. It's 60 miles inland from Calais, south of Lille, so a similar climate to southern UK.

 

The 4 elevations were insulated with different materials:

• 300mm hempcrete blocks in thin-bed lime mortar, with the gap against the brick wall filled with hemp fibre (so functionally similar to the in-situ hempcrete linked to above)
• 350mm blown-in cellulose fibre
• 350mm flax wool
• 360mm sheep wool

There's some brief info here in English - https://www.isohemp.com/en/hemp-solution-heritage-renovation and a video of the insulation here in French: https://www.youtube.com/watch?v=QkR4WATzp0Q

 

The building was monitored by the regional Civil Engineering & géo-Environnement Laboratory (LGCgE) using 80 probes, measuring temperature & heat flow (on the internal surfaces, external surfaces, and boundary between insulation and structure of the external envelope), temperature & hygrometery (in the centre of the insulation), ventilation air flow & internal air quality. Energy use was logged and the external weather measured. Various metrics were calculated including actual -v- predicted U-values, thermal inertia and thermal decoupling; plus acoustic performance, materials wastage, embodied energy, cost effectiveness, environmental life cycle analysis, etc.

 

The outcome of this (and a subsequent pilot) was that the hempcrete was judged the optimal solution for wall insulation. As a result an initial 50 houses were insulated with hempcrete in Pecquencourt a couple of years ago (to be increased to 115), with a plan to expand that to 1,000 by around 2026, and eventually more as the local production capacity and knowledge are developed. There's some info on these plans in English here: https://batinfo.com/en/actuality/le-bailleur-maisonscites-lance-lexperimentation-pecquenchanvre_19931 and a video in French here: https://www.youtube.com/watch?v=7u8gxdJP_pU

 

 

Edited January 13 by Mike

[SteamyTea]

@Mike

Save me reading it, where in France?

The climate regime may be very different from ours.

The UK has quite a unique climate.

[Mike]

6 minutes ago, SteamyTea said:

Save me reading it, where in France?

 

10 minutes ago, Mike said:

It's 60 miles inland from Calais, south of Lille, so a similar climate to southern UK.

 

[SimonD]

1 hour ago, SteamyTea said:

I hate to say it, but seems more like hopium than a solution.

Is there any proper research as to the long term performance.

 

Have you visited the Centre for Alternative Technology and the Wise building? Wall mainly insulated with Hempcrete - https://cat.org.uk/info-resources/free-information-service/building/the-wise-building/

 

If I had the opportunity again I'd seriously consider it for a build myself.

 

1 hour ago, SteamyTea said:

But seems from what @JamesPa quoted, gypsum is better than lime.

 

I think that might have been me. From the standpoint of that research, then if you want both vapour permeability and moisture buffering, then gypsum would be preferable to Lime, yes, and gypsum plaster would be preferable to plasterboard on the basis of the more dynamic tests conducted as part of the thesis. 

Quote

In the full-scale testing, gypsum was the better
performing material, as it presented higher moisture adsorption (88.63 g/m2), whilst
lime exhibited the lowest capacity (33.56 g/m2). Plasterboard had lower values than
gypsum (76.16 g/m2) and similarly to the laboratory testing the material presented a
plateau.

 

With that being said, we also have to keep in mind that as per the discussion part of the paper, the behaviour of these materials and the building aren't static. For example the moisture buffering behaviour of gypsum (with micro-pore structure) increased in variable temperature scenarios but sinusoidal RH variations reduced the moisture buffering behaviour of all materials.

 

The whole research provides some very interesting data, but also throws up alot of questions, particularly about the overall behavour in real world scenarios of indoor and outdoor environments.

 

To me what is interesting is that the concrete wall performed almost as well as the woodfibre in buffering moisture.

[saveasteading]

7 minutes ago, SimonD said:

If I  had the opportunity again I'd seriously consider it for a build myself

I'd consider it with someone else's money.

I've seen this and other continental materials promoted in UK, but you'd want a uni or the old unbiased bre to test it for real.

1 hour ago, Mike said:

2 hours ago, Mike said:

similar climate to southern UK.

 

Drier by a distance I think.

[Mike]

2 hours ago, SimonD said:

Have you visited the Centre for Alternative Technology and the Wise building? Wall mainly insulated with Hempcrete - https://cat.org.uk/info-resources/free-information-service/building/the-wise-building/

I visited the CAT, but when it was regarded as a strange hippy commune and eco-anything was generally treated as a joke. So long before the WISE building was built. I must get back there some day.

 

2 hours ago, saveasteading said:

Drier by a distance I think.

Depending on the time of year: Compare the Climate and Weather in Lille and Winchester - Weather Spark

 

2 hours ago, saveasteading said:

you'd want a uni .... to test it for real.

The LGCgE is a University - or, rather, a collaboration by 4 regional universities - so it's already been extensively tested 'for real'.

 

2 hours ago, saveasteading said:

I've seen this and other continental materials promoted in UK, but you'd want ... the old unbiased bre to test it....

You may not have too long to wait. IndiNature are already producing & selling UK hemp-based insulation (though not yet hempcrete blocks) and have applied for their first BBA certificate.

 

Edited January 14 by Mike
Clarity

[Mike]

3 hours ago, saveasteading said:

you'd want ... the old unbiased bre to test it for real.

Turns out they have: Yates T. (2002). Final report on the construction of the hemp houses at Haverhill, Suffolk, client report 209-717 Rev2, BRE, Watford, 2002.

 

I don't have a copy, but the CAT mention key findings in a report: https://www.votehemp.com/wp-content/uploads/2018/09/building_with_hemp_and_lime.pdf

 

Short version - two houses were built, sponsored by the Suffolk Housing Society in collaboration with BRE, who performed a full assessment. Despite having higher U-values (Hemp homes 0.58 w/m2.K Control Homes 0.35 w/m2/k) they performed as well as the standard construction, occupied or unoccupied. This may be partly explained by hempcrete's 'thermal mass', low thermal bridging & airtightness.

 

 

 

[MikeSharp01]

Have just read this whole thread - very interesting and some excellent academic work cited and deployed. No real consensus on 'Thermal Mass's existence as a 'thing' although thinking deeper it must exist as a thing or we would not be talking about it. Boy do we talk about it - 526 mentions in various threads since BH was started! I do agree in some ways with @SteamyTea about not getting the units, and terms EG Mass, confused as it makes life difficult but on the other hand if an idea is easy to conceive of for people less used to 'units' then the challenge is to get the same conception in everybody's head so we are all talking about the same thing. After all not everything can be expressed in SI units - if you want an example try 'Love' - a word bandied about universally which everybody sort of understands but is devoid of units.

 

I am, however, not yet sure we have got to the bottom of the OP in the comfort area. I am in my study at Millstone manor in Sevenoaks,  it is 15.2 deg in here but I am comfortable reading and typing away. I will have to go and light a fire downstairs shortly so the core of house, currently at 18.5 will stay around that. I dimly recall attending a 'comfort' seminar with the Passive House Trust which, IIRCC, intimated, in the end, that comfort is, in a range, what you get used to.

 

All of which gets @Gone West not much further. Still a great thread though.

[Gone West]

3 minutes ago, MikeSharp01 said:

comfort is, in a range, what you get used to

I think it is also linked to age and fitness/health.

[Gone West]

12 hours ago, Mike said:

The outcome of this (and a subsequent pilot) was that the hempcrete was judged the optimal solution for wall insulation.

Many thanks, hempcrete is something I shall be looking into. I have seen it used on buildings featured on TV programmes but I had forgotten about it, old age 😟.

[SteamyTea]

19 minutes ago, MikeSharp01 said:

it is 15.2 deg in here but I am comfortable reading and typing away.

I assume you have some clothing on.

So the insulation value of your clothes is keeping you comfortable.

As an experiment, how about covering yourself in thick mud, letting it dry, and see how comfortable you feel.

Get pictures posted up.

 

As for evidence of love, love without evidence is stalking.

 

[SimonD]

10 hours ago, Mike said:

I visited the CAT, but when it was regarded as a strange hippy commune and eco-anything was generally treated as a joke. So long before the WISE building was built. I must get back there some day.

 

I think it's worth a visit. I attended a self-build project management course there before starting my build and stayed at the centre. We also had the time to walk around the whole site and get a proper lowdown of all the experimental builds they've done, including all the pros, cons, and the odd disaster of the various builds techniques - but at least they're honest about them. We also got out to the site on a current build out in the countryside somewhere to have look. We had a discussion about the hempcrete with, IIRC, the only major learning point that they got a lot of movement/shrinkage of thus gaps at a few joints which needed to be dealt with. The question is whether this movement was down to the hempcrete or the timber frame as it settled.

[Roger440]

On 13/01/2024 at 12:26, SimonD said:

 

This is exactly mine and @SteamyTea 's point - the term 'breathable' is actually completely meaningless and shouldn't really be used at all. But with respect to the facts about gypsum v lime you should read the paper I linked but the TL;DR is:

 

 

But the fundamental problem you're talking about hasn't really got anything to do with lime or gypsum, it's down to excess moisture. Excess moisture isn't good for any structure, so deal with the moisture.

 

I cant argue with the logic.

 

But as i said earlier, on a house without a DPC and likely less than optimal construction, how? Aside from demolition.

 

Theres a few million homeowers would love to know...............................

 

In the meantime, until you come up with a PRACTICAL solution, ill work on the basis of shedding that moisture.

[Roger440]

Im no scientist, but it remains, that stick gypsum over a damp wall, it will resist, for a while. Eventually, salts will appear on the surface, and if bad enough, the plaster will become detached from the wall. By which time the damp will be the best part of a meter up the wall.

 

This is VERY common to see in older, non DPC houses. 

 

Stick lime plaster over the same wall, and nothing much happens to it. Yes, moisture will enter the room, but the wall will be unaffected. And it will be drier IN the wall.

[Gone West]

9 hours ago, Roger440 said:

Stick lime plaster over the same wall, and nothing much happens to it.

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.

[jayc89]

I've been living in this minefield for the last couple of years having bought an 1850's house. A couple of points;

- There's certainly something in "thermal mass" we have 2 rooms of similar size, both have 2x external walls, one room has 2x 220mm external walls, the other has 2x 330mm external walls (it's almost like a solid brick wall using cheap reds and then a single leaf facade of nicer cream bricks in front of it, and I haven't found anywhere it's tied in yet...) the room with the thicker walls was always the warmer of the two before any insulation.

- Because of the external looks of the property, EWI was a no go for us, we couldn't hide the original brickwork. We opted for IWI, having spent months researching "breathable" solutions we couldn't justify either the cost of additional build up. For the most part we opted for PIR adhered direct to the existing lime plaster, mechanically fixed battens through it and PB finish, which BCO was happy about. We came to the conclusion that moisture does get into "traditional" brickwork and the best remedy is two-fold - fix the source of moisture; so ensure gutters, ground levels, etc are sound and if moisture gets in, it has to be able to get out again, so at least one side of the wall needs to be permeable; so lime mortar/render on the exterior, no cement.

 

2 years in and it's worked well for us, we did have a damp patch showing on an external wall last year which was caused by a cracked drain near it, we fixed that and the damp patch is slowly going away again, so the logic we built to, seems, to hold...

 

There are so many horror stories out there, but they come without full context. We were pretty OCD about foaming and taping all gaps, to avoid condensation, we also have MVHR so internal humidity should be managed well, both of which likely contribute to our (early) success. 

[SteamyTea]

20 minutes 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.

You don't want to be putting a damp sponge on your wall.

 

19 minutes ago, jayc89 said:

There's certainly something in "thermal mass" we have 2 rooms of similar size, both have 2x external walls, one room has 2x 220mm external walls, the other has 2x 330mm external walls (it's almost like a solid brick wall using cheap reds and then a single leaf facade of nicer cream bricks in front of it, and I haven't found anywhere it's tied in yet...) the room with the thicker walls was always the warmer of the two before any insulation.

Are they at the same orientation to South?

What are the respective wall areas?

Is the window to wall area, with respect to floor area, identical?

Is one room used more than the other?

What size heat emitters are in each room.

 

And regardless of that, a greater thickness of any material will transmit less energy though it.  So your 2 x 330mm wall will have a lower U-Value than the 2 x 220mm one.  So it is a better insulated room.

 

[SimonD]

10 hours ago, Roger440 said:

I cant argue with the logic.

 

But as i said earlier, on a house without a DPC and likely less than optimal construction, how? Aside from demolition.

 

Theres a few million homeowers would love to know...............................

 

In the meantime, until you come up with a PRACTICAL solution, ill work on the basis of shedding that moisture.

 

10 hours ago, Roger440 said:

Im no scientist, but it remains, that stick gypsum over a damp wall, it will resist, for a while. Eventually, salts will appear on the surface, and if bad enough, the plaster will become detached from the wall. By which time the damp will be the best part of a meter up the wall.

 

This is VERY common to see in older, non DPC houses. 

 

Stick lime plaster over the same wall, and nothing much happens to it. Yes, moisture will enter the room, but the wall will be unaffected. And it will be drier IN the wall.

 

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?

[SteamyTea]

58 minutes ago, SimonD said:

what are we referring to specifically here when we speak of a damp wall? How damp?

And the depth of the damp into the wall.