Drylining an old house - what thickness insulation?

sarkozy

We're soon to begin renovating our 1900's redbrick mid-terrace house (87 sq/m). Walls are solid/do not have a cavity.

The question of drylining/external wall insulation has come up.

We have drawings specifying 62.5mm Kingspan Kooltherm 17 insulated plasterboard for the external walls. We were told that this is too thin and not worth the money, that we should go for at least 82.5mm.

The problem is the rooms aren't big (e.g. the sitting room is 3.5m square max.) and we're worried about losing space - e.g. our sofa and TV wouldn't fit where they currently are.

So we're left wondering what the right thing to do is given our utter lack of technical knowledge. We have lived in old houses that have been insulated with what we believed were 62.5mm insulation and found them very toasty with little need to use the heating.

A second question is, given that external walls are solid, would we need a drylining with some kind of vapour barrier (if K17 doesn't have one) to prevent problems?

DOCARCH

Dry lining solid brick external walls with a conventional internal dry lining 'system' is never a great idea...can lead to problems with the brick over time.

sarkozy

Thanks, but no option but to insulate internally. What are the options and their cost-effectiveness, and how to they relate to my questions?

DOCARCH

You need to investigate a breathable dry lining system/allow the wall breath...rather than prevent it from breathing.

sarkozy

Such as? What options are available? We have done what research we can and still can't figure anything out. No professional we spoke to can explain any of this to us. Our house is old, but not protected. It's currently in more or less the same state it's been in since it got some wallpapering and a lick of paint in the 1960s.

We want to try to do the right thing, but, as always, budget is a major factor.

DOCARCH

Some others on here may be able to better advise what you should be considering to use.

All I know is that brick is a pourous material, by it's nature, it gets wet and soaks up water...they way (solid) brick houses 'work' is that the internal heat from the house, passing through the wall, over time drives that moisture out. By dry lining/insulating internally, with the wrong product, you cut off/remove that driving force and over time you end up with permanently damp/wet brick which can cause it's own problems in the long run and be pretty much detrimental to the brick.

You obvioulsy have yet to speak to the right professional?

Even though your house is not a protected structure, consider speaking with an architect with conservation accreditation.

kkelliher

To be honest it really does come down to the loss of space internally as you want to go as thickness is what its all about. There are not hugh options on internal insulation as there is little between the different products. You could batten a vapour barrier to wall insulate between the battens and the put as thick a board as you can. Breathable options (gutex and calsatherm boards) are very expensive at plus 100 per m2

DOCARCH

kkelliher wrote: »

Breathable options (gutex and calsatherm boards) are very expensive at plus 100 per m2

...but for a solid brick house/external wall it's these that you really need to consider using.

Just didn't have these names on the tip of my tounge with my weekend head on! There are other breathable systems too, but, they do take up space.

kkelliher

DOCARCH wrote: »

...but for a solid brick house/external wall it's these that you really need to consider using.

Just didn't have these names on the tip of my tounge with my weekend head on! There are other breathable systems too, but, they do take up space.

Agreed but if you implement breathable membranes you can work a cheaper system

MicktheMan

OP, have you considered external wall insulation (ewi)?

If you are considering internal insulation then perhaps have a read of this first.

sarkozy

Gutex is €100 per sq/m? Jeez. If that's the the board itself, then I'm guesstimating that would be €1,500, then you're paying for the extras and labour. TBH, I'm not sure how that compares to typical drylining. We would like to insulate the best way for the house without losing too much floor space and it's just so unfortunate these breathable methods are so prohibitively expensive.

We also asked previously about Spacetherm/Aerogel as a way to get good insulation and creating a cavity for services, evaporation/ventilation, etc, but, again, hardly anybody knows about it and, we're told, the Spacetherm rep in Ireland said we shouldn't even think about using it as it's basically illegal due to building regs (which strikes me as a bizarre thing to say).

I did discuss this with my architect at length and he said he was sure the dew point would be somewhere inside the wall and therefore not a problem for us, but I've no idea.

Looking at something 'standard' but breathable might be a way to go, but I know nothing.

MicktheMan: external just isn't an option, as I said, our house is a 100+ year-old mid-terrace redbrick.

I've read that article and, TBH, it's double-Dutch to me.

MicktheMan

sarkozy wrote: »

I did discuss this with my architect at length and he said he was sure the dew point would be somewhere inside the wall and therefore not a problem for us, but I've no idea.

How did your architect come to this conclusion? Did he/she model the wall build-up and show you the results?

MicktheMan

sarkozy wrote: »

MicktheMan: external just isn't an option, as I said, our house is a 100+ year-old mid-terrace redbrick.

Why not?

MicktheMan

sarkozy wrote: »

I've read that article and, TBH, it's double-Dutch to me.

Perhaps, find someone (your architect) to explain / summarise it for you.

4Sticks

If you over insulate with dry lining you will cause trapped condensation to form to such and extent that it will never dry out but rather will accumulate over time.
The article linked to which you don't care to read suggest that limiting the U Value is much more important than the material specification in managing this risk.

So rather then increasing from 62.5 to 82.5 step back to 50mm (37.5 +12.5) boards. Also make sure that the brickworks joints are all sound , that all roof overhangs and gutters are in good condition that all DPC's and flashing are present and correct. Because excessive external rain penetration will certainly heighten the risk a creating a permanently damp wall.

I would use this system myself for reasons best explained in the video

sarkozy

4Sticks: if you read what I said, I did read that article. I'm not versed in this stuff was my point, and we had paid a professional to make these decisions for us, but due to various reasons, we're now having to make them ourselves with absolutely no knowledge or experience. Not an ideal situation I know, but here we are.

But I will pass this article on to our contractor and I am seeking other opinions.

From what I've been reading (e.g. on www.superhomes.org.uk), it does make sense that reducing u values to slow down heat and moisture transfer only such that the dew point is unlikely to regularly be between the wall and drylining is the way to go. Or, as I understand it, it's important to allow the solid brick wall to be a little warmed by internal air.

This should be combined adequate ventilation to reduce relative humidity inside the house and a vapour barrier on the warm/room-side and no foil backing. There seems to be mixed views on whether a small cavity between the PIH foam and external solid wall - some say it allows moisture to evaporate, others say it defeats the purpose of the insulation.

In order to reduce internal humidity, it also seems sensible, when insulating under out suspended timber floor, to lay a vapour barrier below the boards and ensure good cross ventilation beneath.

I came across one article on the Superhomes site which makes the point that millions of old solid-wall dwellings in France have been internally insulated with Kingspan (and similar) with no apparent problems and that the important thing is the quality of installation.

One question I have is: would open fireplaces qualify as adequate ventilation in old house that have been drylined? We'll be installing new sash windows, so those can be used for additional ad hoc venting. Perhaps installing additional brick vents (traditional style which the house was built with) in upper bedrooms would work (though the bedrooms have functioning (though closed) fireplaces.

4Sticks

If you read what I said I offered you simple advice. Take / leave it.

sarkozy

Look, you were a bit presumptuous in your opening remarks, but your remarks were helpful, and I'm looking into this Isover system, too. Everything is on the table for now.

You see, even though I thought I understood what you said, perhaps I'm misinterpreting. I do find this stuff very difficult to understand and no one person I've managed to find so far can explain the reality/options to me and I do need to move quickly on this.

Busted Flat.

Put 100mm polyurethane plaster board on the inside and do not listen about the bull$hit.

4Sticks

There you go op. Beauty of the internet in all its glory.

sarkozy

Indeed.

BryanF

Busted Flat. wrote: »

Put 100mm polyurethane plaster board on the inside and do not listen about the bull$hit.

banned

Bubbling

I have specified "RemmersUK iQtherm" insulation system for a project I am currently working on - with a 600mm solid masonry wall construction.

This is thermal insulation which allow humidity regulation.

sarkozy

Another one on the list. How do the costs of materials and installation compare to, e.g. your usual Kingspan rigid drylining?

Bubbling

Really, Kingspan insulation and other similar foil backed insulations (that form a vapour barrier) are not suitable for dry lining a masonry wall that needs to 'breath'. Vapour permeable insulations are more expensive, but it is the most appropriate solution - there is no point in going for a cheap solution, when what you should be looking for is the solution that will add value.

read the forum charter before posting again

Jabba Da Putt

Sarkozy, I've looked into this for my own house which is solid brick. Im getting prices on the the Gutex boards, Calsitherm boards and Isover system at the moment as they all seem to thick the most boxes to address the problems mentioned in the articles which were a bit double dutch to me too!!

Gutex seems like a good product but seems pricey, not sure if its airtight though. <snip>

The Isover video is good, kind of thing you could nearly do yourself as its dry and there's good info on the Isover IAB <snip> about it too. Its got continous vapour control and airtightness membrane too so no leaky joints which is where most dry lining products fall down.

People rave about Calsitherm boards because of there good breathability but they dont seem to get as low U-values as the rest with the boards only 30mm & 50mm thick, needs to be plastered onto the wall and plastered over so seems messy.
<snip>

I can understand your point about the space but in a few months time you won't notice the space but will notice the heat.

sarkozy

Hi Jabba, can you PM me with more details about your job and the kind of prices you're coming in with, please?

I know what you mean about losing space, but our house is so small.

Bubbling

Sorry BryanF. I didn't mean to break the rules!.

antiskeptic

MicktheMan wrote: »

Why not?

If you have to ask then you probably won't appreciate the answer

4Sticks

If you have to answer a question not directed at you you probably don't understand the question.

antiskeptic

Possible cheaper and cheerful-er? By all means open fire!

The problem appears to stem from a) brick/mortar joints being porous and b) Ireland being a rainy old place. The traditional ways in which a solid brick wall dried was a) heat loss through the wall accelerating the rate of evaporation generally b) the brick having two faces to evaporate from: outside face evaporating to outside and inside face evaporating to inside, the draughty, fireplace-ridden nature of houses eliminating internal damp issues. Adding an insulated, impermeable layer to one side cuts the legs of the rate of evaporation (but not rate of soaking) and so the wall stays wet.

Let's suppose we install plain old insulated, vapour-barrier backed plasterboard using the dab n' slab method to an external, rain-exposed wall. And let's suppose we employ the (sound) practice of running a band of board adhesive around the extreme perimeter of the each wall we're sticking the boards to by way of fire retardation. We'd now have a sealed cavity between the back of insulated plasterboard 'leaf' and the brick leaf. We can make this cavity somewhat wider than usual by increasing the thickness of the dabs if we like.

What happens if we now vent that cavity space by installing some external vents in this brick wall - say one or two down low and one or two up high and diagonally opposed (using something that's not too noticeable). Wouldn't the air flowing through the cavity from outside provide a means of keeping the humidity in the cavity down such as to keep the inside face of the brick wall dry? I'm thinking of the kind of passive, low-flow ventilation that keeps the space under old floor dry even though the ground is plain old earth and so subject to becoming sodden if not vented.

Naturally, you'd have to pay attention to penetrations such a electrical sockets, windows and the like (I'd not put sockets on an external wall anyway) but all doable with a decent contractor.

sarkozy

That seems to make sense, but I've also read that this cavity would eliminate the benefit of insulation altogether and provides a means for moist, potentially fungus-laden air to spread around the house interstitially or into the interior of the home?

antiskeptic

sarkozy wrote: »

That seems to make sense, but I've also read that this cavity would eliminate the benefit of insulation altogether and provides a means for moist, potentially fungus-laden air to spread around the house interstitially or into the interior of the home?

On the hunt, as I am, for a period doer-upper and not impressed by conservation-nazis encouragement to but don extra garments, I thought to fiddle with the idea of more pragmatic solutions

I can't envisage the means whereby you'd lose the benefit of insulation since the cold air venting the cavity is contacting the cold side of the insulation - which is precisely what it does with external insulation. Certainly, you'd want to ensure you've a continuous unbroken band of adhesive around the perimeter of each boarded wall (and around socket holes and window opes) to prevent draughts into the house. But that's certainly doable.

As each wall is closed off from the rest of the house by said perimeter band, air isn't going to go anywhere other than out through another vent in the same banded space. I don't suppose the air to be moist as such, since the cavity is continuously vented and so any water penetrating the brickwork is being dealt with straight away by airflow through the space, preventing the air in the cavity becoming damp.

Indeed, there doesn't appear to be any difference with the way the moisture is being dealt with as suggested and the way it is dealt with in the original, uninsulated house. In the original house, the 'cavity' was the full internal space and it was draughts through windows / floorboards /up chimneys which swept away penetrating moisture evaporating off the internal surface of the wall. The only difference with what I'm suggesting (it appears) is the internal cavity is somewhat less than room-sized.

sarkozy

I came across this link which suggests it may be a bad idea with a gap or not - it clearly explains how having foil backing or a vapour barrier on the cold side of the insulation makes everything worse, too.

http://www.superhomes.org.uk/resources/interstitial-condensation-3/

On the other hand, it does seem to make sense, provided the board is fully sealed, to make a gap by attaching insulating battens (e.g. wood) but, the point of insulation is for things to be airtight, otherwise things don't work properly.

And in houses designed to breathe, this seems to not work so well. Or, as the French experience is, not really a problem. But that's only assuming France has the same climate as ours, which not all of it does.

Obviously each house has to be looked at as unique and it's the whole system that matters. Perhaps, in a relatively well-built, dry house with chimneys that gets lots of sun on certain sides, condensation will be kept under control, especially with any additional vents added in, especially bedrooms, and a good extractor fan in bathrooms and kitchens, bog standard drylining might be OK. Here, I assume that any moisture also coming from below (evaporating through the floor from the ground below and from rising damp, must also be taken into account and stopped.

So there are a number of issues - managing insulation and vapour from below, managing ordinary rising damp through evaporation or tanking and drylining with ventilation.

Clearly, then, it would be extremely bad for a house that has some normal rising damp at the lower part of walls to have that moisture effectively trapped by the fact that the wall never gets warm enough to force the moisture out slowly over time. On the other hand, perhaps the house would be fine as the dampness is only on the outer side of the solid wall and there is little to no moisture on the inner side to worry about.

So, then, would it be good in this case to either apply waterproof plaster to seal the room, or install an injected chemical damp-proof course into the wall from the inside and then slab it, eliminating a main source of interstitial dampness?

All very technical questions and none that I understand.

antiskeptic

sarkozy wrote: »

I came across this link which suggests it may be a bad idea with a gap or not - it clearly explains how having foil backing or a vapour barrier on the cold side of the insulation makes everything worse, too.

http://www.superhomes.org.uk/resources/interstitial-condensation-3/

This article appears to be dealing with interstitial condensation (a function of the movement of water vapour from inside the house - and a potential issue with dry lining). What is being dealt with in my suggestion however is penetrating moisture.

On the other hand, it does seem to make sense, provided the board is fully sealed, to make a gap by attaching insulating battens (e.g. wood) but, the point of insulation is for things to be airtight, otherwise things don't work properly.

The gap suggested would be made from a band of adhesive using dab and slab method of fixing. That would be able to provide for air tightness at a level above wooden batten (plus, battening likely to introduce undulations due to variations in the wood and uneveness in the wall surface you're battening to.) It's not like it would be the end of the world if absolute air tightness wasn't achieved since a house does need ventilation but for the purposes of evaluating my suggestion, we could suppose effective airtightness.

Obviously each house has to be looked at as unique and it's the whole system that matters. Perhaps, in a relatively well-built, dry house with chimneys that gets lots of sun on certain sides, condensation will be kept under control, especially with any additional vents added in, especially bedrooms, and a good extractor fan in bathrooms and kitchens, bog standard drylining might be OK.

I wouldn't be worried about penetrating damp on walls that don't face into the weather. It's those walls which get seriously wet that need attending to. But every house is different indeed. It could be that a wall facing into the weather isn't worth dry lining at all if the area involved includes lots of openings (such as my own front wall)

Here, I assume that any moisture also coming from below (evaporating through the floor from the ground below and from rising damp, must also be taken into account and stopped.

Or let it rise and evaporate in a vented cavity between wall and insulated boards..

redrummed

What system did you choose in the end sarkozy. I like your idea of the vented cavity antiskeptic. I am in a similar predicament at the moment. Thinking of slab K18 62.5mm slab on treated battens backed with strips of dpc. The gap between the floor boards and the wall will serve as the vent you proposed. (suspended floor vent) and ensure as much air-tightness as possible on the warm side of the insulated slab.

antiskeptic

redrummed wrote: »

I like your idea of the vented cavity antiskeptic. I am in a similar predicament at the moment. Thinking of slab K18 62.5mm slab on treated battens backed with strips of dpc. The gap between the floor boards and the wall will serve as the vent you proposed. (suspended floor vent) and ensure as much air-tightness as possible on the warm side of the insulated slab.

Any possibility of venting the wall to outside at high level at a couple of points to encourage flow over the moist inner surface of the wall? Your underfloor space will normally be vented at front and rear of building to achieve that same effect. If no flow over the surface then the damp air just sits there for want of something to move it along preventing further evaporation. I don't suppose the holes need be big since you'd have permanent ventilation - maybe a discrete series of holes through the mortar line at high level if a brick facade?

For the same reason I'd avoid continuous battens, floor to ceiling as they'd tend to produce isolated vertical "strips" of damp wall, each strip requiring successful ventilation up top if wanting flow from under floor, up the wall and out the vent, over each strip. It's be better to interconnect the vertical strips somewhat, perhaps by "castellating" the battens after they've been fitted (removing say 2" long sections of batten to 1/2 batten depth, every couple of feet of length or so, so as to allow for air movement across vertical section - easy and quick to achieve with a skillsaw to cut to depth then remove the bits with hammer and chisel). You could also stop the battens a foot short of the horizontal cross batten being fitted (presumably) at ceiling level- that's the height your vents would be located be, so achieving minimum restriction to air movement between strips. You've enough to be fixing the slab to even with this foot of batten missing.

Dab n' slab achieves that kind of result too - with a continuous sealing strip around the perimeter except at bottom.

Then what? Tape the slab to floorboard? And trim the floorboards back level with the rear of the slab for max air flow? Perhaps use thicker battens to, to open up the cavity.

I'd be less worried at sheltered sides of the building especially if the outside surface is well rendered.