Insulating a pebbledash solid wall and damp concerns

[saveasteading]

1 hour ago, Roger440 said:

The answer to your opening line is number 3.  

My answer is, your wall is wet. It shouldn't be. 

Thanks. I put option 3 in especially for you.

I should emphasise that the wall is wet now because bits of roof are missing and there are no doors or windows, no gutters or pipes, and no drainage.

There is an open central courtyard which likewise has no drainage....and rain leaks in on both sides.   well we have just stripped of the decades of cow 'sludge' and found clean sand, and so that is now 'draining' too.

If it wasn't for the ground being porous sand for 15m depth, and on a hill, I think the building would be long gone.

 

(for those interested, we have 17seconds/mm soakage rate.....which couldn't be better.) So an inch of rain is gone in 10 minutes. The  first site I have had with no puddles or mud.

 

We will fix the roof and put in doors and windows, gutters pipes and drains to soakaways far away. Walls will be repaired, pointed and rendered.

 

So the water will only be from driving rain, plus of course dampness from the air.

Most of the stone is granite which is impermeable, Of course the mortar is lime and can absorb water.

The wall will no longer be wet.

 

You will gather that I still see some merit in encasing the wall on the inside only at the very bottom, where any dampness will be at its highest. The front face can vent and so can the remaining 2-3m on the inside.

I have seen that this is a recommended detail for steadings in Aberdeenshire, for near identical construction. Does it have any issues?....no idea.

 

Meanwhile another Highland contributor has been made to put lots of vents in through the wall, so all thermal benefit from the masonry (which is significant) is lost in the created draught.

Does this detail work?   no idea.

 

Yet another blogger has said that their cross walls carry draught from one side of the house to the other, and there is no need for any forced ventilation.

 

They cant all be right, and the solutions are mutually exclusive.

 

Hence my proposed compromise, made safer by the superb ground properties. . There shouldn't be much dampness and it should not condense....the time it takes for any water to permeate through 600mm should be enough for a change in weather and the air to draw it back outside. what does stay in may drift downwards through the core, where we will contain it until it wither dribbles out to ground or evaporates outwards.

 

would 1/2m work better? or 250mm?  at some height the risk or benefit of a liner becomes  minimal.

 

SimonD       Also, is the ventilation between the suspended floor and iwi cavity a continuous gap along the junction, similarly at the ceiling?

Yes it will be, all the way to the roof where there are timber sarking boards with gaps. I don't want to put holes in the walls to force this draught as I believe that there will always be some air gaps and movement. 

Ideally there could be a moisture and temperature  sensor in the cavity and vents would open and close as necessary....opening an a nice sunny or breezy day, and shutting when miserable. But that won't happen.

 

I should also emphasise that the area has low rainfall around 700mm pa.

 

I still welcome hunches as well as approved detailing and especially any proven successes or failures.

 

Thanks for the interest....and  really  am listening.

 

[Roger440]

33 minutes ago, saveasteading said:

Thanks. I put option 3 in especially for you.

I should emphasise that the wall is wet now because bits of roof are missing and there are no doors or windows, no gutters or pipes, and no drainage.

There is an open central courtyard which likewise has no drainage....and rain leaks in on both sides.   well we have just stripped of the decades of cow 'sludge' and found clean sand, and so that is now 'draining' too.

If it wasn't for the ground being porous sand for 15m depth, and on a hill, I think the building would be long gone.

 

(for those interested, we have 17seconds/mm soakage rate.....which couldn't be better.) So an inch of rain is gone in 10 minutes. The  first site I have had with no puddles or mud.

 

We will fix the roof and put in doors and windows, gutters pipes and drains to soakaways far away. Walls will be repaired, pointed and rendered.

 

So the water will only be from driving rain, plus of course dampness from the air.

Most of the stone is granite which is impermeable, Of course the mortar is lime and can absorb water.

The wall will no longer be wet.

 

You will gather that I still see some merit in encasing the wall on the inside only at the very bottom, where any dampness will be at its highest. The front face can vent and so can the remaining 2-3m on the inside.

I have seen that this is a recommended detail for steadings in Aberdeenshire, for near identical construction. Does it have any issues?....no idea.

 

Meanwhile another Highland contributor has been made to put lots of vents in through the wall, so all thermal benefit from the masonry (which is significant) is lost in the created draught.

Does this detail work?   no idea.

 

Yet another blogger has said that their cross walls carry draught from one side of the house to the other, and there is no need for any forced ventilation.

 

They cant all be right, and the solutions are mutually exclusive.

 

Hence my proposed compromise, made safer by the superb ground properties. . There shouldn't be much dampness and it should not condense....the time it takes for any water to permeate through 600mm should be enough for a change in weather and the air to draw it back outside. what does stay in may drift downwards through the core, where we will contain it until it wither dribbles out to ground or evaporates outwards.

 

would 1/2m work better? or 250mm?  at some height the risk or benefit of a liner becomes  minimal.

 

SimonD       Also, is the ventilation between the suspended floor and iwi cavity a continuous gap along the junction, similarly at the ceiling?

Yes it will be, all the way to the roof where there are timber sarking boards with gaps. I don't want to put holes in the walls to force this draught as I believe that there will always be some air gaps and movement. 

Ideally there could be a moisture and temperature  sensor in the cavity and vents would open and close as necessary....opening an a nice sunny or breezy day, and shutting when miserable. But that won't happen.

 

I should also emphasise that the area has low rainfall around 700mm pa.

 

I still welcome hunches as well as approved detailing and especially any proven successes or failures.

 

Thanks for the interest....and  really  am listening.

 

 

The bit about no roof was a key detail i think you left out!

 

But, never mind.

 

If you say it will be dry, why do you want to line it? I dont understand this.

 

You also, correctrly, mention losing the thermal benefit of the masonary. Your proposed scheme does exactly doesnt it? So you will surely need more insulation thickness that you could otherwise reduce.

 

Once the wall is dry and repointed propely, driving rain isnt likely to penetrate 600m. If conditions are that bad, render it.

 

I dont follow your thought process here. 

 

 

 

[saveasteading]

18 hours ago, Roger440 said:

I don't follow your thought process here. 

neither do I perhaps.

Thanks for testing me on this.

 

If you say it will be dry, why do you want to line it? I don't understand this.

 

Because we have one chance, it is a recommended 'solution' and it seems a better one than making deliberate air holes in the wall.

And because it is consistent with that drawing showing dampness to the base only.

 

You also, correctly, mention losing the thermal benefit of the masonry. Your proposed scheme does exactly doesnt it? So you will surely need more insulation thickness that you could otherwise reduce.

My proposed construction leaves the masonry intact, does not put holes in it, then has a necessary gap (I don't think anyone doesn't do this). Then an inner wall of 6 x 2 with breather barrier outside and airtight barrier inside, stuffed with insulation.

The thermal effect of 600mm wall has been proven to be much more than the design programs acknowledge, hence not making holes in it and creating an air stream out of the gap.

The wings of the building are narrow, so keeping wall lining skinny is an aim.

My original plan was to use cavity batt hard against the masonry but I think the innovation would trouble building control, and the wall is so rough that it would be all over the place,

 

Once the wall is dry and repointed properly, driving rain isn't likely to penetrate 600m. If conditions are that bad, render it.

? They aren't that bad, and a lot of it is rendered already. We will expose some of the prettiest areas for reasons of style and interest., and cross fingers.

Render casts more of the water off immediately, but still gets and stays damp. At some stage we regard the risk as acceptable.

 

As nobody has chipped in to say that they recognise the bitumen liner detail, perhaps it was only used in one area. Perhaps it isn't any longer. I cannot find the original source whch was a very useful blog, but didn't quite go to completion.

 

The perimeter will be 120m so the cost saving without bitumen tanking would be £1,500 plus labour. a useful saving but not the end of the world in this important context, esp if avoiding the hole drilling.

 

 

 

[SimonD]

30 minutes ago, saveasteading said:

As nobody has chipped in to say that they recognise the bitumen liner detail, perhaps it was only used in one area. Perhaps it isn't any longer. I cannot find the original source whch was a very useful blog, but didn't quite go to completion.

 

The perimeter will be 120m so the cost saving without bitumen tanking would be £1,500 plus labour. a useful saving but not the end of the world in this important context, esp if avoiding the hole drilling.

 

I'm sure you've done extensive research on this and may already have consulted this stuff, but generally speaking SPAB recommends the removal of all impervious materials used on wall in old buildings. Interestingly, in the linked technical advice by SPAB, it mentions damp rising up a wall due to this kind of material;

 

Quote

Figure 10: Strong cement-based render has been used to
replace plaster affected by dampness on the lower part of
these massive walls. As a result the dampness has risen higher
in the wall and has now affected the old plaster that had
remained sound.

 

https://www.spab.org.uk/sites/default/files/SPAB Technical advice note-Need for old buildings to breathe.pdf

 

I think your ventilation strategy using an independent inner wall is the sensible choice as it will allow the wall to have its full breathing space without the bitumen. I can't think of why the bitumen needs to be there - what useful purpose does it serve other than to create a barrier against which the wall cannot breathe?

 

Interestingly SPAB has introduced some guidance to the opposite effect where they suggest using capillary materials:

 

Quote

in particular circumstances, at the base of the wall or if it is particularly porous or exposed, for example, there may also be a need for the insulating material to provide hygroscopic buffering and/or to promote the capillary movement of water, as these may also be mechanisms by which the wall remains reasonably ‘dry’.

 

https://www.spab.org.uk/advice/breathability-and-old-buildings

 

I also don't think you need any holes in the wall, you just need to give it potentially a few years to dry out.

 

 

[Roger440]

3 hours ago, saveasteading said:

neither do I perhaps.

Thanks for testing me on this.

 

If you say it will be dry, why do you want to line it? I don't understand this.

 

Because we have one chance, it is a recommended 'solution' and it seems a better one than making deliberate air holes in the wall.

And because it is consistent with that drawing showing dampness to the base only.

 

You also, correctly, mention losing the thermal benefit of the masonry. Your proposed scheme does exactly doesnt it? So you will surely need more insulation thickness that you could otherwise reduce.

My proposed construction leaves the masonry intact, does not put holes in it, then has a necessary gap (I don't think anyone doesn't do this). Then an inner wall of 6 x 2 with breather barrier outside and airtight barrier inside, stuffed with insulation.

The thermal effect of 600mm wall has been proven to be much more than the design programs acknowledge, hence not making holes in it and creating an air stream out of the gap.

The wings of the building are narrow, so keeping wall lining skinny is an aim.

My original plan was to use cavity batt hard against the masonry but I think the innovation would trouble building control, and the wall is so rough that it would be all over the place,

 

Once the wall is dry and repointed properly, driving rain isn't likely to penetrate 600m. If conditions are that bad, render it.

? They aren't that bad, and a lot of it is rendered already. We will expose some of the prettiest areas for reasons of style and interest., and cross fingers.

Render casts more of the water off immediately, but still gets and stays damp. At some stage we regard the risk as acceptable.

 

As nobody has chipped in to say that they recognise the bitumen liner detail, perhaps it was only used in one area. Perhaps it isn't any longer. I cannot find the original source whch was a very useful blog, but didn't quite go to completion.

 

The perimeter will be 120m so the cost saving without bitumen tanking would be £1,500 plus labour. a useful saving but not the end of the world in this important context, esp if avoiding the hole drilling.

 

 

 

 

Im unclear why you need any holes? Once the building is complete, and you have stopped the source of water ingress, why do you need to do anything else. Im at a loss as to why you need "holes".

 

As i explained in my earlier post, i too had wet walls. I dont now. There are no holes.  Still dont understand.

 

And what is it you have "one chance of doing"?

 

With my solution you will add NO thickess to the wall. Do nothing, apart from reistate a roof etc and let it dry out.

 

IF you want insulation, and ask yourself if you really do in this instance, then the usual lime product supliers all offer IWI systems that DONT leave an air gap. Why are you simply not using one of these? Some are LABC approved. No air gap, less added thickness. Completely breathable. Problem fixed.

 

Ive chosen NOT to insulate, just lime plaster internally. That decision however is primarily driven by the fact that i am flood prone, and all of the options use various natural materials such as woold, woodfibre, cork etc. These are unlikely to cope well with flood conditions. Lime plaster will likely be fine given such flood events are very short duration.

 

Were i not in this position id be investgating the various IWI optins and selecting accordingly.

 

As Simon said, adding bitumen, realistically, is only likey to add problems. Its the go to solution by builders who are ignorant of how to deal with older buildings. Its plenty common enough. My neighbours did it.

 

 

[saveasteading]

1 hour ago, Roger440 said:

I'm unclear why you need any holes?

I know that another Buildhub correspondent was made to add holes at 1m cc all around the base. That was Highland region too. I don't want to.

 

1 hour ago, Roger440 said:

"one chance of doing"?

We plan to build an inner wall which provides insulation and damp-proofing. I don't know of another solution, and the existing wall will not be available.

 

1 hour ago, Roger440 said:

IF you want insulation, and ask yourself if you really do in this instance,

Yes : it will be  a house and needs serious insulation.

 

1 hour ago, Roger440 said:

Ive chosen NOT to insulate, just lime plaster internally.

U value?

 

1 hour ago, Roger440 said:

builders who are ignorant of how to deal with older buildings.

And Architects and building inspectors?

I'm only contemplating it because I have seen it required elsewhere. I thought it was quite clever, and I do understand damp, and that many people don't.

[saveasteading]

4 hours ago, SimonD said:

SPAB recommends the removal of all impervious materials

Thanks for that link. Looks good and I will read it in detail.

 

I have read, only today, that cement mortar carries moisture rather than being impervious.   Will re-read that part.

The document is splendid and deserves detailed study https://issuu.com/hspubs/docs/guide_for_practitioners_1_-_rural_b

Rural Buildings of the Lothians: Conservation and Conversion, A guide for Practitioners.

The main difference re geography is the stone type.

 

We don't seem to have any cement where it shouldn't be. All lime.

 

4 hours ago, SimonD said:

 

I also don't think you need any holes in the wall, you just need to give it potentially a few years to dry out.

 

If the Building Officer decides to ask for holes I will need some proof. 

 

Ahhh. We have to move faster than that. However, when the roof and gutters are done, the wind that whips through the openings will dry it quite fast....and then there will be the scorching Highland summer.

 

Many thanks.

[Adsibob]

1 minute ago, saveasteading said:

and then there will be the scorching Highland summer.

this made me chuckle

[SimonD]

9 hours ago, saveasteading said:

I have read, only today, that cement mortar carries moisture rather than being impervious. 

 

That is true. Impervious is a bit of an exaggeration with cement mortar. It's similar to the popular belief that gypsum plaster isn't breathable where particularly recent research shows that it is both vapour permeable and hygroscopic and more so that lime plaster. As such it performs better as a moisture buffer and allows the whole house to breathe (with the right buildup). I suspect that the historical problems we see are more down to material compatibility within a building system and the common use of other layers that are for all intents and purposes impervious. For example, the airtighness liquid membrane Soudatight LQ I'm using has an Sd value of just under 11m, my primer for porous materials for clay paint Sd value is 10cm. I wonder whether at some point we might eventually see the equivalent to an Sd value for wall buildups and their respective layers.

Edited February 10, 2022 by SimonD

[saveasteading]

6 hours ago, SimonD said:

Impervious is a bit of an exaggeration with cement mortar.

That document you referenced from SPAB is excellent, and recommended reading for anyone with an old property. It is short and well explained, and I have learnt more than I expected. (esp how water gets in through cement but not out again).

https://www.spab.org.uk/advice/breathability-and-old-buildings

[Roger440]

22 hours ago, saveasteading said:

I know that another Buildhub correspondent was made to add holes at 1m cc all around the base. That was Highland region too. I don't want to.

 

We plan to build an inner wall which provides insulation and damp-proofing. I don't know of another solution, and the existing wall will not be available.

 

Yes : it will be  a house and needs serious insulation.

 

U value?

 

And Architects and building inspectors?

I'm only contemplating it because I have seen it required elsewhere. I thought it was quite clever, and I do understand damp, and that many people don't.

Im not bright enough to do multiquote, so take these in order

 

1. I agree. Ludicrous idea.

2. You dont need an inner wall if its not damp. We are going round in circles here. The insulation i discussed in my previous post. What do you mean the existing wall will "not be available".?

3. In which case, the various solutions available would seem to make more sense, and applied to a dry wall.

4. Who cares? It is what it is. Its 2 walls only at ground floor level only. There is nothing i can do about it, especially in light of the flood risk. Any solutions that will survive flood, beyong straight lime plaster, are not compatible with keeping the wall dry long term.

5. Dont tell them? Lie? Thats what i did. BCO adds nothing to the process other than likely trying to impose inappropiate solutions. Which will potentially cost YOU money when they dont work. Frankly i have NO time for the process. I have a suite of certificates for bits of the house generally. NONE of the jobs comply with the regs. All signed off though. Totally and utterly pointless system. Architects? Mostly i suspect, dont really understand. For every 50 jobs, they probably get one where its an issue. Its not a surprise unless you find a specialist one. You would take a transit to a VW specialirt to get it fixed would you?

6, Ive said all there is to say.

 

 

Edited February 10, 2022 by Roger440

[Roger440]

12 hours ago, SimonD said:

 

That is true. Impervious is a bit of an exaggeration with cement mortar. It's similar to the popular belief that gypsum plaster isn't breathable where particularly recent research shows that it is both vapour permeable and hygroscopic and more so that lime plaster. As such it performs better as a moisture buffer and allows the whole house to breathe (with the right buildup). I suspect that the historical problems we see are more down to material compatibility within a building system and the common use of other layers that are for all intents and purposes impervious. For example, the airtighness liquid membrane Soudatight LQ I'm using has an Sd value of just under 11m, my primer for porous materials for clay paint Sd value is 10cm. I wonder whether at some point we might eventually see the equivalent to an Sd value for wall buildups and their respective layers.

 

The evidence on the ground says plaster doesnt breathe.

 

Do you have a link tosomething that says it does?

 

Though im inclined to believe the evidence of my own eys.

[SimonD]

32 minutes ago, Roger440 said:

 

The evidence on the ground says plaster doesnt breathe.

 

Do you have a link tosomething that says it does?

 

Though im inclined to believe the evidence of my own eys.

 

Interestingly gypsum plaster has been used on the ground in places like Italy since Roman times for its moisture buffering capabilities which demonstrates properties of breathability. I now believe that gypsum has been blamed in many cases incorrectly and that it was more the full wall buildup that caused the problem, for example the common use of PVA and also an incorrect categorisation of all gypsum plaster being the same. However, it's also important to understand how gypsum plaster may absorb more moisture following wet-dry cycles due to a change in its structure, whereas lime reduces sorption rate following the same cycle. This points to using the materials where appropriate and in the right environment  as well as evaluating materials according to their compatibility with each other as part of a buildup - hence why you might not want to use gypsum plaster directly on a solid damp granite wall that's subject to wind driven rain, but as an internal layer which is removed from this wet/dry cyclicle damp it may very well possess useful moisture buffering properties that benefit air quality within the home and still allow the building to 'breathe.'

 

These are some of the reasons I don't feel the term 'breathable' is particularly helpful.

 

Here are a couple of links to full downloadable PHD theses on the subject:

 

Understanding moisture buffering effects in the indoor environment:

https://researchportal.bath.ac.uk/en/studentTheses/understanding-moisture-buffering-effects-in-the-indoor-environmen

 

Measurement and modelling moisture transport processes within porous construction materials:

https://uobrep.aws.openrepository.com/handle/10547/622114

[bighouseproblems]

Just posted about internal insulation looking for advice and noticed this post. there goes my entire evening reading everything now thanks everyone. 

 

 

[saveasteading]

Can you summarise for us all please?

[bighouseproblems]

23 hours ago, saveasteading said:

Can you summarise for us all please?

ha lots of words is all I have. On a seperate note I have come across a study which has been quite informative. check out ribuild.eu if you go to the case studies it details maybe around 30 buildings of various construction types and varying types of insulation used they go on to take many different measurements in joists wall cavity temps etc etc.

Just spent the day reading the report has helped me quite abit.

https://static1.squarespace.com/static/5e8c2889b5462512e400d1e2/t/5e9db87943530a16d2f414eb/1587394701972/RIBuild_D3.2_v1.0.pdf

[Ben Weston]

For anyone who's interested (and I think everyone must have lost interest by now, including me ?), the working plans have been submitted. We've gone with building the new extensions with traditional cavity walls and marrying up to the solid walls that will have EWI with a small overlap to the cavity. The EWI itself will be a build-up of rockwool and a mineral-based breathable render, with lime render internally. We won't be injecting a DPC in the old solid walls.

 

I've highlighted the EWI on the attached plan.

 

I realise there are many opinions on this subject and I'm sure some will disagree with this approach.

 

 

[saveasteading]

5 minutes ago, Ben Weston said:

For anyone who's interested

Of course some of us are still interested. Thanks.

 

On 17/02/2022 at 18:06, bighouseproblems said:

On a separate note I have come across a study which has been quite informative.

Thanks for this.

It is not easy reading, and I have had to read some of the recommendations more than once.

Only 2 buildings in UK and one in Ireland, but the variation  of circumstances might be informative....I have only read the intro properly.

 

I like it as I think it is mostly good news for our project, I think.

 

But the Executive Summary is perhaps all we need to know. (My Executive Executive Summary is...keep the rain out, but let it evaporate back out if it does get in.)

 

Here it is, if interested.....mostly seems obvious (or accurate).

 

In general, the following conclusions and recommendations can be derived about the hygrothermal performance from the measurement and simulation results in the present case study report:

 The thinner the existing wall, the lower is the possible damage-risk free thermal resistance resp. thickness of the added insulation system. A thin wall increases the condensation risk and the impact of driving rain on the construction.

 The lower the driving rain load (driving rain protection of façade or low driving rain load at the specific location), the more insulation systems are possible to use.

 The dryer and warmer the indoor air, the more insulation systems are possible to use. Especially the performance of capillary active systems (aka. condensate-tolerating systems) improves as these show a strong interaction with the indoor climate. Opposed to this, the behaviour of vapour-tight insulation systems (aka. condensate-preventing systems) (e.g. VIP) is only marginally depending on indoor climate conditions.

 A humidification potential from one side of the construction (e.g. moist indoor air or driving rain) requires an equivalent drying potential on, at least, the opposite side of the construction. This could be provided with a condensate-tolerating internal insulation system or avoided with a reduction of the moisture load (improved driving rain protection).

 The higher the built-in moisture, the higher is the required drying potential of the construction. Insulation systems with a high build-in moisture should therefore at the best be vapour-open and capillary active.

 The more vapour tight the insulation systems are, the more caution should be paid on proper workmanship at constructive details, connection jointing etc.

 

 

 

[fletcher5555]

I just wanted to thank everybody who contributed to this incredibly useful thread. This is what community is all about and it informs new projects significantly. Thank you