Garage Conversion Insulation

[blastedfury]

Hi, I'm after a bit of advice regarding PIR boards.

I've got an existing garage conversion which was converted before we moved into the house. The room is almost unusable in the winter as it is so cold.

I know from having many people round to look at it that there is no cavity. I've now decided to sort it out myself so I thought I would use Ecotherm pir board (only because i can easily get it from local building supplier). Now the easiest was to do this would be to attach 1x2 battens and then attach the EcoTherm Eco Liner to the battens, skim, job done. The only thing is that they are really expensive.

So i then thought about using 2x3 battens and putting 75mm Eco-Versal pir board in between each batten, then cover with plasterboard and skim. Would this be an acceptable way of doing it and would it give the same amount of insulation as thermal plasterboard. This would be my preferred option cause it will be much cheaper.

 

[jeds]

The Eco-Versal is fine and will give you a good U-value for walls. The construction wouldn't pass a condensation analysis though because of cold bridging through the battens. you'd be better off with smaller battens, a thinner layer between and a continuous layer over. You should also include a vapour barrier between the insulation and the plasterboard.

 

[blastedfury]

That sounds like quite an expensive way of doing it isn't it? I would need to get double the amount of board all be it a thinner version? If i went this way how would i attach the plasterboard?

I thought these boards had a vapour control layer on them already? Isn't that what the foil is for?

Also can the boards be butted directly to the wall or does there need to be a small gap for air to circulate?

Sorry for all the questions. I've read so much stuff on these boards and i'm still confused about them. Maybe it would just be easier for me to use thermal plasterboard...

 

[jeds]

The board can be tight to the wall.

The vapour will travel through the joints - particularly when you have battens between boards. If you do nothing else you should have a vapour barrier. Not having one is asking for problems.

By not covering the battens you run the risk of mold growth forming on the cold bridging. Look up pattern staining for examples.

Outside of what is regulation it's all about risk. Doing it your way might be allright. But it might not.

 

[^woody^]

Tape the joints with foil or duct tape

 

[ajrobb]

So i then thought about using 2x3 battens and putting 75mm Eco-Versal pir board in between each batten, then cover with plasterboard and skim. Would this be an acceptable way of doing it and would it give the same amount of insulation as thermal plasterboard. This would be my preferred option cause it will be much cheaper.

A quick look at Eco-Versal. Like other PIR boards, it has vapour-proof foil facing to retain the insulating blowing agent for a few years. Being aluminium, this foil is also low-emissivity so gives some extra insulation (R value up to 0.6) next to a 20mm cavity.

So my choice is treated 19mm thick battens at 400mm centres on the outside wall with a full layer of PIR sealed with aluminium tape. More 19mm battens (untreated), forming a service cavity then ordinary tapered edge plasterboard. Finish with a couple of coats of drywall sealer and then decorated. The 2 cavities have a total thickness of 38mm and may be as good as an additional 30mm of PIR insulation.

 

[Deluks]

Tape the joints with foil or duct tape

Don't use duct tape

It can break down and lose it's 'airtightness'

http://www.bukisa.com/articles/31120_recipe-for-disaster-do-not-use-duct-tape-on-ducts

 

[blastedfury]

Thanks for the reply ajrobb. How would you fix the battens to the PIR board and would i need the vapour barrier?

 

[ajrobb]

Thanks for the reply ajrobb. How would you fix the battens to the PIR board and would i need the vapour barrier?

Have a look at the Celotex application guide. The vapour proof foil on the PIR when sealed with aluminium tape is a good enough VPL.