Insulation & Breathability

[wobs]

As someone who is far from being an expert in this subject, I thought the following links would be of interest to people here, and anyone more knowledgeable than me could comment (most here probably are).

First up is Kingspan's comments on the importance of breathability in buildings:
http://www.kingspaninsulation.co.uk/Knowledge-Base/Breathability-1.aspx
It includes a study into the subject, claiming that over 95% of a building's vapour escapes via ventilation, and the idea of breathable walls etc. is a red herring. Guess I could be a bit devil's advocate here.

Also, is a pdf regarding breathable insulation systems:
https://www.lime.org.uk/directlinkdownloads/10209Ty-Mawr_insulation.pdf
None appear to be as effective insulators as celotex of course, but certainly some interesting products.

Again, some comments from our more experienced members would be valued.

The idea of breathability has always been a regular point on this board, but I never really understood why old buildings need it more than modern buildings. In fact I have some friends who live in a modern house (less than 30 years old) who struggle with moisture build up. They probably need more ventilation of course, although they have no gas central heating so this could be a factor.

 

[malcolm]

If you have a non-breathable external wall covering such as cement render it will be brilliant for the first few years, then as soon as it gets a crack it will allow water in but not out again, so your 17th century timber frame that had previously been doing very well with breathable materials gets eaten by beetles.

Modern buildings need to last for 10 years until the insurance runs out and then they don't matter, so all manner of non-breathable materials are fine for modern buildings. Who knows, they might even last for 50 years. At that point lack of maintainability will mean it is more economic to knock them down and start again.

For houses that have been knocking around for 400 years already 50 years seems a very short target. I would go for an air tight construction where possible but use breathable materials. When the air tightness fails (which it will) the breathable insulation will allow the walls to dry out a bit. Where I have used non-breathable insulation the outside face is well ventilated so any water that will run down the back once the air tight seal gives way can hopefully evaporate away.

Take care with the manufacturer's claims. They like to make non-breathable stuff, but the market is slowly cottoning on that non-breathable will make their house fall down. Some manufacturers of insulation and paints are making much the same stuff but are now insisting it is breathable. Others seem to be denying the importance of breathability.

Just about all of the problems I have needed to fix have been due to modern practices and poor breathability - stuff getting wet and not being able to dry out again after something fails.

 

[DavidB]

Wobs, I am not an expert in anything, but just prior to reading your post I watched this video on YouTube about mould in modern buildings. https://youtu.be/g0TTqAQ6ybI

I have lived in a modern house that suffered from condensation and on the other hand apparently the couple who owned my property before us were told that the cement skim that they bought for the 18C cottage was breathable. So I think you have to critically assess any advice particularly from manufacturers. That said many old buildings seem to have been badly repaired I.e. non sympathetic materials, but those repairs were probably in response to failing original materials. So traditional building materials don't last forever and do need repair and maintenance. Last point. My previous house was a brand new building - the bricks were stated to have an expected life of 20 years...

 

[88v8]

Kingspan... well they would say that, wouldn't they.

Buildings with no dpc nor dpm need breathable materials so as to dissipate the inevitable damp. So do those with leaky constructional joints such as half-timber, unless they are tile-clad or weatherboarded.

As Malcolm says, putting an impermeable cement skin on something is no sort of long-term solution.

More modern buildings benefit from breathability in the form of ventilation, and I do rather cringe when I see threads about draught-stripping where folk are aiming to block up the dispersed, one could almost say natural, ventilation around door and window perimeters.
Even an open fireplace does not create ventilation if there is nowhere for air to get in !!

As I sit here, I can look into our bedroom and see the rather 'draughty' window where I have deliberately left one edge unstripped. The west front door has no draught strip down the hinge edge, of an early morning one can see the sun shining in through the gap. The kitchen windows seal where they touch. The sitting room windows are the original (whatever that means) Crittal. All these 'draughts' add up to a steady air ingress that does not create an actual draught anywhere, and in conjunction with the dampers of the woodburners being always open, and the kitchen extractor, guarantee a certain amount of air throughput.
Even so, I still need to go round and vacuum the windows every morning, although less so now the weather is warming, and on the wall plate of the C17 extension, there is the winter's crop of mould to remove. I hate to think how it would be if the place were sealed up like a modern house.

Mind you, some materials are best when non-breathable. Glass for example.

Ivor

 

[malcolm]

Mind you, some materials are best when non-breathable. Glass for example.
Ivor

Surely if glass were breathable you wouldn't need to vacuum up the water that condenses on it every day.

 

[88v8]

Mind you, some materials are best when non-breathable. Glass for example.
Ivor

Surely if glass were breathable you wouldn't need to vacuum up the water that condenses on it every day.

Good point

So, where can I buy some horn sheet?

Ivor

 

[MatthewC]

....The idea of breathability has always been a regular point on this board, but I never really understood why old buildings need it more than modern buildings. In fact I have some friends who live in a modern house (less than 30 years old) who struggle with moisture build up. They probably need more ventilation of course, although they have no gas central heating so this could be a factor.

The point is that modern buildings and old buildings are built to entirely different principles. A modern building is effectively a sealed watertight box, whereas an old building was built with a different set of materials, typically limestone or sandstone and lime mortar. The principle difference is that these materials do something that modern (i.e. cement based) materials do not: they EXPAND and CONTRACT, because they are significantly more porous and have a much greater coefficient of thermal expansion. This is why it is utterly pointless, and even damaging, to re-point or render with cement on a lime-based building - the lime mortar and limestone will expand and contract whereas the cement pointing will not expand much if at all; thus it is inevitable that the two will part company in time.

Consequently you have to manage the moisture in an old building more than in a new one. In a modern building the only main issue is with ventilation to allow water vapour (e.g. from people, cooking and bathrooms) to escape, or else you get mould. However, in an old one you need to make sure that the walls are working as originally intended, and that moisture is able to escape and, moreover, that continual excessive moisture is avoided (e.g. leaking downpipes and gutters, or high ground up to the wall). Lime does not like being continually damp (unless it's very old or hydraulic lime, perhaps).

Somone has built a small house near here using (apparently) limestone but clearly (from the rate at which it went up) using cement mortar. In five or ten years time they will probably find their stone is spalling as moisture that gets into the stone will be retained and the surface will slowly disintegrate. If they has used reconstituted stone they would have avoided that, as (I believe) it contains cement. Moral: don't mix old and new!

Matthew

 

[plasticpigeon]

I'd largely agree. Even in an old building I'd imagine most vapour escapes via ventilation. In fact how could any vapour given off from something inside the building (people, showers, baths, cooking, permeable floors etc) escape other than through ventilation? Very little will get through the walls even if they are of some slightly porous material. I understand porous stuff on the inside can act as a moisture buffer, but not really as a conduit to the outside. I am happy with modern materials internally in my Edwardian brick house with a slate damp proof course. I believe that so long as nothing stupid such as broken drains or gutters, and stupidly high ground levels which cause a constantly high level of damp that can soak from outside in, that "breathable" internal surfaces are not needed in my house. The one place i didn't risk modern materials was on an internal wall with no dpc which I lime plastered. Unfortunately some people who live in wet areas with driving rain find that old construction using lime and slightly porous masonry just doesn't work.

I am absolutely convinced that it is necessary to use a soft mortar on old buildings, as any hard mortar will cause the masonry to fail in the event of water trapped between masonry and mortar freezing, thermal expansion and contraction or structural movement, and it is always better to have the mortar sacrificial to the masonry. I also agree that an impervious render outside is also very bad, as water will get in through cracks or gaps round apertures, or just plain shoddy workmanship, which will then soak the masonry which won't be able to dry out as has already been said.

 

[andrew gayton]

Hello,

I can't find the linky at the moment, but the BRE have recently produced a paper on the issue of retrofitting insulation to walling .... well worth a read .... and probably why the red herring from kingspan came into being.

personally, I am firmly of the opinion that solid walling must be as permeable as when originally built. I have doubts about the permeability of the insulating / render carrying boards that are commonly available, as well as the nhl based insulating renders.

90% of the problems I encounter with historic buildings - or those built pre industrialism - is to do with inappropriate intervention with impermeable (or less permeable than the primary build) materials.

 

[andrew gayton]

link to bre report at the bottom of this page.

http://ihbconline.co.uk/newsachive/?p=12485

 

[tobydog]

When we talk about the ability of bricks, fibre boards or renders to be breathable, are we really talking about their ability to absorb? My understanding of breathability was that excess moisture inside a building is absorbed into the brick, board or render and will be released back into the building when the equilibrium is regained. Should the excess moisture overwhelm the brick, board or render then this is wicked (absorbed) away to the outer surface where a lower RH or wind action dries the surface and encourages further wicking. By its very nature, this is going to be a slow process and therefore draughts or ventilation are always going to be more effective in the short term.

My house is timber framed and cement rendered but, despite having heavy condensation in the winter on very thin crown glass, the house never feels damp or musty. Would having the house lime rendered with breathable wall insulation make a big enough difference to justify the cost? I am conscious of condensation on the inner cement render and its effect on the frame but my inspections to date suggest this isn't a problem, probably mainly due to so many gaps for air to flow where the top of the gypsum boarding disappears into the frame.

 

[andrew gayton]

each case will be site specific and dependant on how a building is heated, ventilated and how it is used by the inhabitant/s. impermeable coated walling will have a better chance if the house is lived in by a single person, who doesn't boil food, shower twice a day, dry washing indoors and keep the windows shut. ensuring multiple air changes (see kingspan blurb) wasn't a necessity when historic buildings were constructed because of contemporary usage and construction methods. my current project includes timber frame, clay lump, shuttered clay, red brick and flint work .... all of it sighed a sigh of relief, started drying and stopped condensating when the s+c all came off. it is all a balance.

 

[wobs]

....The idea of breathability has always been a regular point on this board, but I never really understood why old buildings need it more than modern buildings. In fact I have some friends who live in a modern house (less than 30 years old) who struggle with moisture build up. They probably need more ventilation of course, although they have no gas central heating so this could be a factor.

The point is that modern buildings and old buildings are built to entirely different principles. A modern building is effectively a sealed watertight box, whereas an old building was built with a different set of materials, typically limestone or sandstone and lime mortar. The principle difference is that these materials do something that modern (i.e. cement based) materials do not: they EXPAND and CONTRACT, because they are significantly more porous and have a much greater coefficient of thermal expansion. This is why it is utterly pointless, and even damaging, to re-point or render with cement on a lime-based building - the lime mortar and limestone will expand and contract whereas the cement pointing will not expand much if at all; thus it is inevitable that the two will part company in time.

Consequently you have to manage the moisture in an old building more than in a new one. In a modern building the only main issue is with ventilation to allow water vapour (e.g. from people, cooking and bathrooms) to escape, or else you get mould. However, in an old one you need to make sure that the walls are working as originally intended, and that moisture is able to escape and, moreover, that continual excessive moisture is avoided (e.g. leaking downpipes and gutters, or high ground up to the wall). Lime does not like being continually damp (unless it's very old or hydraulic lime, perhaps).

Somone has built a small house near here using (apparently) limestone but clearly (from the rate at which it went up) using cement mortar. In five or ten years time they will probably find their stone is spalling as moisture that gets into the stone will be retained and the surface will slowly disintegrate. If they has used reconstituted stone they would have avoided that, as (I believe) it contains cement. Moral: don't mix old and new!

Matthew

Some great points so far, and this post clarifies some points. I am aware of the different rates of expansion of modern cements compared to say lime mortar.

The importance of the right materials on external surfaces is something I have been aware of, but eg. in our rear bedroom, our Edwardian brick house still has lime plaster, but no doubt has modern wallpaper, and emulsion on it, so it almost certainly is not a breathable wall, and the window is a single glazed with little ventilation, and yet we don't see a build up of moisture, so I'm wondering if I should be worried about this when we come to make this room warmer through a new window, and review what we do with the walls.

A local builder has a similar house to ours and fitted celotex attached to metal brackets on most walls on his house to give a cavity. It seems to make it much warmer of course, but could he just ensure there is enough ventilation to avoid problems with condensation?

 

[malcolm]

A lot of modern construction is waterproof inside and outside. At some point there will be a failure of the waterproofing and water will be able to get in but not get out. The 1970s bungalows near here have terrible damp problems - I think they are nearing end of life. For me modern construction is part of our disposable society.

Older breathable houses can continue to function even after failure. The builders expected failure - for example the oak frame would shrink very soon after building and would leave cracks. It didn't really matter as the lime render would suck up water and allow it to escape. Perhaps the difference is these days the failure is 30 years after building rather than 1 year and has become less of a thing to worry about.

 

[jocelyn plummer]

In fact I have some friends who live in a modern house (less than 30 years old) who struggle with moisture build up. They probably need more ventilation of course, although they have no gas central heating so this could be a factor.

Well now I can really identify with that comment Wobs. I have never lived in a modern house until now.-our Georgian properties have been warm , cosy and DRY, thanks to their lovely ill fitting wooden windows, doors, floors, cosily insulated with thick curtains, blinds and luxurious carpets in natural fibres

Our, now forever, downsize was built in 1986--just on that 30 year mark that you mention--over time, the wooden windows were replaced with PVC, and as a cheap build there are solid floors on the ground floor, breezeblock walls---after only 14 months here I have never felt so cold and am very aware of moisture build up from domestic vapour lurking around--DESPITE having windows open, an Aga City 60 in the kitchen, running 24/7, and a log burner in the 'living' room------it's AWFUL. moisture build up is a real problem when you bear in mind the number of domestic appliances, showers etc in use all the time, but I have ever been so aware of it as I am these days!

In short, instead of living with squeaky floorboards and draughty windows I am living with aching fingers and toes!

 

[Roger H]

-after only 14 months here I have never felt so cold!

[/quote]

Jocelyn,

I wonder if your building has had its cavity filled with blown insulation and that this might now be wet? If so, potentially wicking massive ammounts of heat out of the building.

 

[tobydog]

My first house was built in 1985 and I bought it in 1995. I never got round to changing the original single glazed windows but I did have the wall cavity filled with Rockwool under an incentive programme. Can't say that it made much difference at all. The contractor dropped a long length of brush between me and next door so the filling didn't migrate, however, that didn't stop half of it blowing up the cavity and into the loft :roll: . I was told the house did take all the filling it was supposed to but I'm sure there were air pockets. No doubt, over time, the filling would have dropped and compressed so the gaps are probably much larger now.

This product, along with the fluffy insulation batts that builders put in cavities, is a one time only option. With the Rockwool, now that it's in the cavity there's not much that can be done when it fails. Also, the insulation batts (as I know from their use between our 1640's studs) does desiccate and shrink over time with it's efficacy severely impaired. I can take mine out (with hassle) but not in a new build. This only leaves cost and space expensive internal or external cladding. Let's not forget the lovely expanding foam sitting in the cavities of thousands of 30's houses from when it was injected in the 70's. Aside from the apparent toxic fumes at the time, could this prove to be a better long term solution for those houses that have never had their cavities filled? Technically it's no different to Celotex.

 

[malcolm]

I don't think any filling is a good idea in cavity walls - I won't fill mine. If you must fill them then something easy to extract when it causes trouble would have to be the answer. Polystyrene beads that can be vacuumed out maybe?

Jocelyn - condensation will tend to form on surfaces that are cold. Does yours form on walls, ceilings or windows? I saved about 40% on heating bills just by insulating the loft, and the mould in the shower room no longer forms on the ceiling - instead it forms on the top of the walls (I want to move the shower before fixing ventilation in there).

 

[jocelyn plummer]

I wonder if your building has had its cavity filled with blown insulation and that this might now be wet? If so, potentially wicking massive ammounts of heat out of the building.

Blimey--how on earth do I find that out?

Jocelyn - condensation will tend to form on surfaces that are cold. Does yours form on walls, ceilings or windows? I saved about 40% on heating bills just by insulating the loft, and the mould in the shower room no longer forms on the ceiling - instead it forms on the top of the walls (I want to move the shower before fixing ventilation in there).

The damp chill just seems to hang around in the atmosphere--no visible mould or moisture anywhere------the loft is insulated. Oddly, the bathroom and landing now seem better since the revolting artex has been removed from the ceilings and plastered. We still have to do the bedrooms and the living room. Also, something simple like hanging the freshly ironed bed linen on the bannisters takes ages to really dry off despite the rising warmth from the Aga in the kitchen below. Honestly, I feel such a numptie not having the first idea about how a 20thc house functions-give me back my period house any day--easy to understand! (This time, it was not possible to find our required price bracket for a period home in Chelsea by the Sea) so, we are really lucky to have what we have, located in our favourite part of NN!)

Would the river frontage play a part in all this do you think?

 

[malcolm]

Central heating would probably be a fix. It takes a fair bit of insulation to run a house without central heating, and 1980s houses tend to be poorly insulated. 300mm loft instlation is fairly cheap to install if you don't have it already.