Insulating behind plasterboard

ScottishDanny

I am working on insulating a bedroom in a 1940s house. I have been using 35mm insulated plasterboard screwed onto wooden laths into the existing plaster/masonry, but now I have a wall with a window and the combined thickness of the board and lath exceeds the depth of the window sill so it won't look right. I'm thinking of using the stuff that looks like silver bubble wrap (can't remember the name)with wooden laths and standard plasterboard over the top of it. Does anyone have any experience of this material? I've seen it in B&Q for €35 a roll. It is supposed to have the same thermal qualities as 120mm polystyrene. Any advice on how to use, condensation issues etc would be appreciated. (Or where to get it cheaper) Thanks

patrido

search in the archives for actis and xfoil. not sure what the b&q stuff is, but i think it's similar to these products. there's lots of controversy over it's effectiveness. in any event, i think you need an air gap both sides of the foil for it to be effective.

why not just put in a bigger window sill?

ScottishDanny

I got new uPVC 'Oak effect' frames with matching sills put in last summer and I don't want to wreck them by pulling them out. I've seen stuff called reflectix on the web which looks like what I'm after.

rooferPete

Hi,

Looks like a memorable moment patrido and I are in agreement

There are local Authorities in the UK who approved similar products only now to be withdrawing their approval because of the lack of certification (basically prove the figures) from the manufacturers.

I did make enquiries about the product when it came on the market here around (I think) 1995 my question to the agent was if the product is that good why not send it for approval by the Irish Agrement Board ?

I had the contact who would carry out the research for about half the cost charged by IAB and it would be accepted because he carries out work for them, when the agent still refused to send the product for testing I lost interest.

I could be wrong but I am almost sure that there must be an air space left between the insulation and the plaster slab if that's any help.

.

GreeBo

Im kinda in the same boat as the OP.
I have a ~15 year old house thats cavity block built so I cant just pump in insulation as I would like.

The house is pretty cold and has tasty draughts around light fittings/sockets etc.

The construction appears to be
[]|$+P
[]|$+P
[]|$+P
[]|$+P

[] cavity block
| timber laths
$ fibreglass insulation
+ vapour barrier
P plasterboard

I have cut the vapour barrier (accidentally) while doing some other work and the wind coming from it is unreal.

I aim to investigate lean to roofs etc to see if I cant block off some of this draught but I also want to increase the insulation (if possible) especially in regard to these new House Insulation regulations...

My question is (finally!) if I strip the wall down to the block work and then fix on insulated plasterboard (Ive seen some good looking stuff in Heiton's about 250mm of foamy stuff stuck to plasterboard) , what does this do for my vapour barrier?
I assume the plasterboard will have one between itself and the insulation, but where I join sheets together there will naturally be a gap.
I guess this is bad or is there a solution?

Many thanks!

ScottishDanny

Hi Pete,
Thanks for the input, I reckon the air gap will be provided by the thickness of the timber batten (20mm).
So it would be constructed like this
Wall => Shiny Bubblewrap => [20mm air gap] => 20mm batten => plasterboard

ifah

Why not just laminate an oak slip onto the front of the window sill ? You'll have to trim off the bullnose but you should be able to get a capable carpenter to cut it clean and attach the new trimmer.

derekcfoley

Hi, I've used this as my property is timber based sectional stud walls.

The product I've used is Airtec double, from screwfix its much cheaper if you need a large amount in terms of per square meter. I'd say only go for the B&Q stuff if you need to cover a small area.

http://www.screwfix.com/prods/50913/Building/Roofing-Insulation/Airtec-Double-Insulation-1-5m-x-25m

I've noticed the key to using this stuff is overlapping joins by 40mm and sealing the two sheets with silicone where you have to make joins - effectively gluing it together - where it ends, say against a post, again seal with silicone, overlapping plenty of silicone behind the airtec on the seam and over the front face, this makes an airtight (draughtproof join).

The alumninum foil tape you're "supposed to use" tends to lift with draughts and external air pressure over a couple of days - well it did in my home as it has all the properties of a "shed" so its not a good long term solution if you have a lot of airflow behind it like I do with rubershield (a breathable membrane) and weatherboards on the outside.

Stapling is good for fixing - get an electric staplegun in my case I put the airtec onto the stud wall on the inside of the building.

Air gaps are essential to reduce condensation on the "cold side" - although I've ended up having an air gap behind and in front of it - as I found 22mm battens are useful for attaching on top of the airtec for the final plasterboard layer.

The specs say its as good as 55mm of kingspan/celotex - so as my walls are only 3 inches thick, this was a perfect solution coupled with 60mm of kingspan between the stud posts, as there wasn't much I could do. Basically the airtec on the inside acts in 2 ways, 1) as a barrier reflecting the inside heat back into the room and 2) stopping the wind getting in from the outside if you get the joins right.

Its made a massive difference to my home, I've used it everywhere, below the floors, on the flat roof. It means I need a lot less heat to warm the home, and I manage to heat an entire 3 bed bungalow with a couple of electric panel heaters during the winter.

Brilliant stuff, although in my case its a combination of kingspan and airtec, I can though judge how one performs without the other, because I installed the kingspan first, and before I put the layer of airtec on the inside, it was freezing in the house, this made a massive difference - so I definately recommend it.

In my case I have a US style 18" crawlspace under the floor, so I draped it over each floor joist and used kingspan between the joists to reduce heat loss through the floor too.

kodak

GreeBo wrote: »

Im kinda in the same boat as the OP.
I have a ~15 year old house thats cavity block built so I cant just pump in insulation as I would like.

The house is pretty cold and has tasty draughts around light fittings/sockets etc.

The construction appears to be
[]|$+P
[]|$+P
[]|$+P
[]|$+P

[] cavity block
| timber laths
$ fibreglass insulation
+ vapour barrier
P plasterboard

I have cut the vapour barrier (accidentally) while doing some other work and the wind coming from it is unreal.

I aim to investigate lean to roofs etc to see if I cant block off some of this draught but I also want to increase the insulation (if possible) especially in regard to these new House Insulation regulations...

My question is (finally!) if I strip the wall down to the block work and then fix on insulated plasterboard (Ive seen some good looking stuff in Heiton's about 250mm of foamy stuff stuck to plasterboard) , what does this do for my vapour barrier?
I assume the plasterboard will have one between itself and the insulation, but where I join sheets together there will naturally be a gap.
I guess this is bad or is there a solution?

Many thanks!

I've pretty much the same project coming up!!

I'm planning on studing it out, cavity block, 100 mm stud with rockwool, 50mm horizontal stud with rockwool and services, vapour barrier, 12.5mm plasterboard with skim. (u value of .27 for the wall)

I think the main problem is intersistial condensation

I looked into using the insulated plasterboard but i've read varying reviews.. Would be interested in any help given!


To the op, Surely a new window sill is cheaper than the thin insulation??