Insulating a single skin wall

Batten out, insulate with 50mm kingspan and board with duplex plasterboard.

You will need a heat source in there - insulation does provide heat, but merely slows down its escape.

 

"You will need a heat source in there - insulation does NOT provide heat, but merely slows down its escape."

 

You should use a breather membrane on the outer surface of the insulation and also a vapour check membrane on the inner face of the insulation, especially if you are heating the garage and it has an access door into the house. Heating the air inside the garage raises the dew point of the air and if that air permeates through the insulation then it will condense out on the cold side (intersticial condensation). Don't forget the ceiling. Hot air rises so insulating the ceiling is even more important.
Celotex have some useful application sheets for this on their web site:
http://www.celotex.co.uk/Applications/Conversions/Garage-conversions
As it's being used as a utility room you don't have to comply with the minmum requirements for U-Value though.
Cheers,
Nick
http://buildingplans.web.officelive.com

 

I keep reading various posts on here about insulating garage walls and most ( including this one ) refer to breather and/or vapour control membranes.

As this is a job I intend to do in my own garage very soon, I'd be grateful if someone could please just clarify for me what form these take ie is the breather membrane simply the stuff on a roll as used by roofers or does it come in sheets, like DPM?

Hope that makes sense.

 

No need for a dpm if using duplex board!

A breather membrane is of limited use too - theres no air gap!

 

There is if you leave the residual cavity you're supposed to between the liner wall and the outer skin.

 

Theres no need for a cavity! What purpose does it serve?

 

Ok. Thanks for that. So duplex board takes care of the warm side.

Now, on the off chance that I end up with a cavity behind the 50mm Kingspan, a breathable membrane is presumably required, so what would I use? Rolls of roofing membrane or can it be bought in sheets, say 3m wide, which would obviously be more appropriate for this kind of application?

 

"Theres no need for a cavity! What purpose does it serve?"

Serious question?

 

What do you need a cavity for?

Another way of doing this is to dot and dab insulated plasterboard to the walls - no cavity and no breather membrane there!

The breather membrane on, say, a timber frame house is to allow moistire from the timber frame to evaporate into the cavity.

Now if, instead of a timber frame, you just have battens with all the space between them with kingspan - where can any moisture exist? There isn't any room for it! The foil on the plasterboard stops any moisure from the room entering too.

This is a technique i have used many times - and always with a BCO looking on.

 

So what prevents moisture tracking across the 100mm wall you've got your boards fixed to?

 

Those nice people at Celotex have a downloadable .pdf on garage conversions, which details how walls, floors and roofs should be insulated.

Now they dont mention leaving a cavity but they do say that if its a single skin wall, you should install a breather membrane.

I believe I may have asked this before, but does breather membrane come in big sheets or just rolls?

 

So what prevents moisture tracking across the 100mm wall you've got your boards fixed to?

The fact that kingspan is waterproof.

 

There's your problem. Kingspan is moisture resistant, not waterproof. That's why it's fixed to the face of the inner skin in a cavity wall and why it's always positioned above the dpm in a solid floor. If it's continually damp it will decay and fail.

 

There's your problem. Kingspan is moisture resistant, not waterproof. That's why it's fixed to the face of the inner skin in a cavity wall and why it's always positioned above the dpm in a solid floor. If it's continually damp it will decay and fail.

Kingspan rots? You sure?

I will forward your concerns on to kingspan and i am sure they will change their specs.

 

They probably won't have to do anything, as they probably don't have any specifications that suggest it should be installed in that way.

Might also be worth pointing your BCO in the direction of something called Approved Document C, he might like to read it.

 

If you don't mind i won't fall out with my inspector - if its ok with you!

I assume that you realise that the building regs are over ridden by other legislation?

You may want to look at kingspans website yourself. I did just to prove myself right.

http://www.insulation.kingspan.com/uk/pdf/k18.pdf

 

I admire your persistance. I agree that that technique can be used in certain circumstances. However, its all dependant on the type and thickness of the wall as well as the level of weather exposure. I suspect that if you locate the BBA cert for this product it'll make reference to Regulation C2 and perhaps some british/european standards, if not, those standards will be identified within ADC.

The guidance in ADC isnt't compulsary, but you still need to demonstrate you've achieved, one way or another, that minimum standard. There's nothing to sugest a 100mm common brick wall (which is what we have in this sitution) will satisfy the regulation. Perhaps thats why the wall in the Kingspan literature is depicted much thicker than 100mm.