plaster backed insulation on inside of walls

iplogger1

What are folks thoughts on the effectiveness of adding dry lining
insulation (not sure what the technical term is) on the inside of
walls which face the outside in a standard cavity wall block built
house ?

For what it's worth I will be putting in UFH and I've heard some
general recommendations to add insulation on inside walls.
I know I lose space and inner window cills need to be dimensioned
larger (are there other dimensioning side effects?)

My understanding is that by installing this type of insulation one
gets a faster heat up time in the room compared to the norm and
faster cool down (basically cancelling a certain amount of the
thermal mass effect of the block walls). How does this play out
with UFH ? UFH is going to require longer time to warm up and
most folks seem to recommend running it 24x7 in the cold seasons
with setback controls for best efficiency and better room warm
up response.

Has anyone an idea on the extra cost (say per meter squared)
of installing this on the perimeter walls in a house ?
Who makes this ? (kingspan/extratherm ?)

~ipl

optiplexgx270

We got that in a few weeks ago. TBH its after winter so i havent noticed the diff in heat yet. Give brooks in sandyford a call thats where we got the stuff. Instalation was 300€ polish style for 2 bedroom walls

johnny_adidas

when u say u have a standard cavity wall. is this wall already insulated in the cavity?
dry lining can be done in a number of ways and wouldnt be down to one specific manufacturer.
basically what it consists of is timber battens / metal studs fixed to the inside of your wall. rigid insulation is then fitted between the studs, then u get your foil backed plasterboard fixed to the battens and skin over. you could quite easily do all the work except the plaster skimming yourself or you could just tape the joints in the plasterboard and paint if you didnt want the expense of getting a plasterer in. u need to remember your gona have to move rads and sockets etc if there are any on the walls. and other than the width of the battens(generally 40-75mm) and plasterboard (15mm max) that is what u will lose off the size of the room.
your room will heat up quicker because the heat will reach the insulation layer of the wall sooner instead of having to heat the block as was its first layer.
the better quality of insulation u use, will obviously decrease the loss of heat so this should be included in pricing factors. id say kingspan prob do some kind of composite system with the plaster bonded to the insulation but the way i have suggested would almost certainly be cheaper.

iplogger1

johnny_adidas wrote:

when u say u have a standard cavity wall. is this wall already insulated in the cavity?

Yes. Whatever the standard is nowadays for cavity insulation.
The internal wall insulation would be to supplement the cavity
insulation although I'm wondering if there is a partial cancelling
effect which renders the cavity insulation less useful if
walls inside the building have insulation added on.

dry lining can be done in a number of ways and wouldnt be down to one specific manufacturer.
basically what it consists of is timber battens / metal studs fixed to the inside of your wall. rigid insulation is then fitted between the studs, then u get your foil backed plasterboard fixed to the battens and skin over. you could quite easily do all the work except the plaster skimming yourself or you could just tape the joints in the plasterboard and paint if you didnt want the expense of getting a plasterer in.

u need to remember your gona have to move rads and sockets etc if there are any on the walls. and other than the width of the battens(generally 40-75mm) and plasterboard (15mm max) that is what u will lose off the size of the room.

Rads will be underfloor and sockets I imagine would be installed *after*
the insulation is added to the walls in the case of a new house
build.. or am I off the mark there ?

your room will heat up quicker because the heat will reach the insulation layer of the wall sooner instead of having to heat the block as was its first layer.
the better quality of insulation u use, will obviously decrease the loss of heat so this should be included in pricing factors. id say kingspan prob do some kind of composite system with the plaster bonded to the insulation but the way i have suggested would almost certainly be cheaper.

johnny_adidas

well to be honest i was assuming you were talking about upgrading an existing house, either way, we have always fitted recessed sockets so these need to be first fixed before the insulation is put in place. and the insulation and plasterboard is then cut to fit around the socket. havent come across anyone who has done both in a house before so cant comment on the effect it would have. generally cavity wall insulation is sufficient. when was the house built?

tribesman

I dry-lined the external walls of our house even though we had insulated the cavity. There was 60mm polyiso in the cavity and we added 25mm polyiso (Xtratherm) on the inside.

The combination of the two is the best way of eliminating thermal bridges. If you go with dry-lining alone then you have no insulation where the internal walls meet the external walls or where floors meet the external walls. If you just use cavity insulation then you will have thermal bridges at cavity closers and often at window cills also.

Similarly I used 25mm insulated plasterboard for the upstairs ceilings as well as the insulation between the joists because otherwise you have thermal bridge through the joists.

This probably seems like overkill but its easy to put the insulation in as you are building. It's difficult to put a figure on the payback time for the extra expense of dry-lining but here's an ideas of our running costs.

We're just over a year in the house now so I added up my ESB bills which includes the heating since we have a Geothermal Heat Pump. It came to EUR 1050 total (heating and lighting). I'm not sure how much of it is down to the efficiency of Geothermal or down to the extra insulation.

iplogger1

Tribesman - thanks for the details and also for the update on your
geothermal/GSHP electricity usage figures.

If I recall from a previous post your house is 2500sq ft or thereabouts
living area is that about right (and block built not timber-frame)?
1100 Euros for 12 mths including lighting is not bad at all for that
size of house and I imagine that includes the standing charges
for the night rate meter in there as well. Also I've heard that
the first years geothermal electricity bill will be a certain amount
higher because of the screed drying cycles in the first few weeks
where it is on constant.

Do you make light use of clothes washer/dryer and dishwasher?

Who was your heat pump/collector supplier if you don't mind me
asking ?

~ipl

johnny_adidas

just wana pick you up on 2 things there, in all new houses there is insulation(25mm) turned up at the edges of the floor slab for the cold bridge at that point. u wont get a cold bridge where the internal and external walls meet as the internal walls only start at the internal leaf so the insulation just continues past in the cavity outside. similarly the one at the joists shudnt be a problem as the joists are either hung on the inside of the inner face of the wall or built onto the internal leaf, so again the insulation will just pass up by them in the cavity. the thermal bridge at the cavity closer will as u say always be one which is difficult to detail and when done incorrectly gives you that ugly staining on your ceiling.
in theory if the house is properly detailed and built as such, you shud have no thermal bridges. however in reality this may not be the case. i would say doing both seems excessive, but if your current construction is not meeting your needs, then obviously this it the easiest method to improve the u-value of your walls.

just at tribemans - what we have in a couple of our houses has been people running the heat pump off solar energy, basically leaving the ESB to deal with the lighting/appliances of the house, obviously though this does mean a larger initial outlay. cudnt tell you what the savings etc are but i seem to remember someone saying the cost of esb to the house was somewhere around 400 euro for the year but i thought this seems excessively low so i may have picked this up wrong.

tribesman

I don't disagree with you.

johnny_adidas wrote:

just wana pick you up on 2 things there, in all new houses there is insulation(25mm) turned up at the edges of the floor slab for the cold bridge at that point. u wont get a cold bridge where the internal and external walls meet as the internal walls only start at the internal leaf so the insulation just continues past in the cavity outside. similarly the one at the joists shudnt be a problem as the joists are either hung on the inside of the inner face of the wall or built onto the internal leaf, so again the insulation will just pass up by them in the cavity.

True. What I meant is that you get a cold bridge in these situations if you have dry-lining only. No cavity insulation.

johnny_adidas wrote:

the thermal bridge at the cavity closer will as u say always be one which is difficult to detail and when done incorrectly gives you that ugly staining on your ceiling.

This is where that advantage of having both comes in.

johnny_adidas

apologies, just read your post again a little slower this time!!

karltimber

johnny_adidas wrote:

basically what it consists of is timber battens / metal studs fixed to the inside of your wall. rigid insulation is then fitted between the studs, then u get your foil backed plasterboard fixed to the battens and skin over. you could quite easily do all the work except the plaster skimming yourself or you could just tape the joints in the plasterboard and paint if you didnt want the expense of getting a plasterer in. .

Hi Johnny,
outside of price difference -- would I get the same effect by putting up battens and then screwing on insulated pb - in a new double 4" cavity wall extension. Or if by your way --do you need to put up plastic between battens/insulation and pb or does the foil eliminate the plastic.
What type of rigid insulation are you refering to ?

thx
Karl.

Viking House

Hi guys

It is impossible to build partial fill cavity walls correctly, you always end up with Thermal Looping which cuts the effect of the insulation in half. 70% of these houses fail the Thermal Imaging test.

Kingspan drylining causes condensation/fungus at the dewpoint between the insulation and the wall and causes offgasing. It is not breathable and you are sealing up the inside of your house with plastic.

The best place to put the insulation is outside the wall. Use breathable insulation with an insulating block like Poroton.

With Polysterene (White) or Polyeurethene (Kingspan, Polyiso, the yellow stuff) the U-value is high but these materials don't have any capacity to hold onto heat like Rockwool or Woodfibre insulation. You get what is commonly known as the "Caravan effect", on a hot summer day your caravan gets as hot as an oven because the heat passes through the insulation very quickly.
The same happens in reverse.

FrankGrimes

Interesting thread lads.

I've just done major renovations on my house and have now started an extension. Your opinions on what I've done/intend to do in terms of insulation would be appreciated.

For the existing house which was built in 1949 (solid block walls which seem to be 12 inches thick in total though I have found a bit of a cavity) I have put foam backed slab (i.e. plasterboard with 40mm of rigid insulation on the back) on all external walls. I applied this by blobbing the boards with bonding compound. I'm expecting yis to say I'm gonna have a problem with the lack of a vapour barrier though I'd like to understand more.

I put 100mm fibreglass in the space in the attic joists and am putting chipboards over that - I really need to floor the attic to get the storage space.

I put acoustic fibreglass in all internal partition walls and in the ceiling between ground and first floor - cuts down noise and means if I want to heat a room next to an unoccupied room I heat one room, not both.

Single storey Extension: using cavity walls and am insulating the cavity with rigid kingpsan insulation (think this is 50mm). I put in 50mm rigid insulation below the concrete floor before I poured it (currently up to finished floor level). Planning on just using normal plasterboards directly blobbed onto the internal walls - foam backed slab is pricey and a pain to work with and I will have the cavity insulated.

Going to use 100mm rigid insulation in the rafters of the extension and cover the rafters with the aluminium style bubblewrap - should break thermal bridge and provide vapour barrier.

Overall, what marks out of ten would you give this approach? I see a lot of talk about thermal bridges above but just how much of a difference do they make - is it a case of them only making a slight differnce or can it negate most of the good work done elsewhere? If its an exponential increase in price and hassle to get what amounts to a small improvement I'll leave it, but if theres something drastically wrong with my plans I'd consider changing them. Thanks

whosedaddy?

hi,
just joining in with some more questions.
Just started upgrading first two rooms in 195x house.
In one room I found thin woodboards over white polystyrene underneath the wallpaper. Insulation 1970s style I guess. However, this was not done in the other room - even though both outside walls are same side of the house.

As we want to paint the rooms we need to skim the walls. Assuming the skim won't stick to the wood - and there are better insulation masterials about these days, I wonder what is the best way to upgrade that wall insulation?

I have been reading up on the different options. The quickest would be dry-lining with insulated plasterboard right.

But what about condensation as mentioned by Viking House?

No idea what the external walls are made of.

karltimber

FrankGrimes wrote:

foam backed slab is pricey and a pain to work with and I will have the cavity insulated.

. Thanks

Hi frank,

I was thinking along thise line for my similar ext - but by putting battons up first and then screwing the insluated pb onto them.
why do you say it's a pian to work with -just cuious :rolleyes:

thx
karl.

FrankGrimes

I'd say using the battens is probably best practice as you could put a moisture barrier behind them but blobbing defo seems to be what most lads are doing out there.

Combined width of the battens and foam backed slab means you're losing a fair bit of space - if you have it to lose then its the best option, I don't have that space to lose on top of the additional space I gave to having a cavity wall.

Would love to see estimates of the difference in these approaches in terms of percentage of heat lost etc.

Dunno, I just dont like working with foam backed slab as its more awkward to put into place and you have to cut it with a handsaw. Normal slab can just be cut with a stanley blade and thrown into place in no time. Foam backed also has a higher tendency to warp (more of a factor if you're blobbing rather than screwing to battens which will bend it back straight) if stored on its side for a while (so store it on its flat).

patrido

frank, kingspan say you do not need a seperate vapour barrier, while xtratherm say you do need one. both products have a foil vapour layer. my own view is that xtratherm are taking a belt and braces approach so i would hope that you should not have any problems with condensation, even if you've used xtratherm.

you say that insulated slabs are expensive, but they are worth the investment. if anything your insulation is very slightly underspecced... i would have put 60mm in the floor, 60mm in the cavity.

unless you're making sure to have an air gap on BOTH sides of the foil under the rafters, your money would be better spent on a small layer of insulated pb under the rafters. overall a few small increases would make your extension B energy rated... i'd expect it to be just short of B at the moment.

whosedaddy,
i don't agree with Viking house about the condensation problem. There is an integral vapour layer between the plasterboard and the insulation. if you are concerned, you can put in a seperate vapour layer (500 gauge polythene). these will prevent any vapour from reaching the dew point and condensing.

FrankGrimes

thanks patrido.

I checked and the cavity wall insulation is actually 60mm.

Not sure I understand what your suggesting for the rafters. I'm planning on putting the 100mm foam between the rafters and then putting the bubblewrap on the underside of this and then putting plasterboard under this. would putting bubblewrap on both sides of the foam help much?

Viking House

All that plastic Polysterene, Polythene, Bubblewrap, Polyeurethene, Plastic windows. how can your house breathe? Its like putting your head into a plastic bag. No wonder Irish kids have so many allergies.
Ireland is full of bad building practices, they would laugh at you in Scandinavia if you put polysterene backed plasterboard inside the house and I am not pointing the finger at anybody, I'm blaming the regulations.
There is so many insulation materials available why pick the plastic ones?

renedescartes

Hi great thread, Iam new to this, Viking could you say if putting Aluminium foil on the rafters is cost effective? (radient heat and solar gain?0
Michael

Mellor

where abouts on the rafters? above or below insulation, hpw is it fixed