insulation question for a Hanson workshop

[Jobe1972]

Hi all looking for some guidance as I have looked all over google and answers vary I have a 20ft by 8ft workshop sectional concrete that I had installed in November last year I lined it with 18mm plywood on 3x2 studs .. I was waiting for better weather and the concrete to dry out before using 40mm PIR insulation which I will be doing in a month or two when weather improves but I need to know the correct way to do it

My thinking is take the boards off add the PIR to the concrete sections they have a dip in them and raised at the centre and edges which will allow for airflow then use foil tape to cover the edges next to the studs and expanding foam for any gaps I miss.

Now do I need a vapour barrier this is where I have seen mixed answers some say yes but others say the foil covered PIR boards will themselves act as a vapour barrier and then I will the 18mm plywood back

 

[Lorenzl]

I would think the boards would be OK with tape covering the gaps in the boards. That is what I have done in my attic and it passed building regs.

 

[Lorenzl]

I should add I have solid brick walls and I have battened them for mounting the insulation using treated roof battens and plastic between the wall and the battens.
If you check the insulation manufactures website they can have examples of installation. Example the Kingspan brochure

 

[Cabinetman]

As the exterior isn’t timber I don’t think you need a vapour barrier or a ventilation gap, but I would try to get as much insulation in there as possible (that your pocket allows) and obviously pile it thick in the roof.

 

[meccarroll]

If you look up TIMBER FRAMED HOUSING that should give you an idea about construction details.

It would look something like: From the inside: Plasterboard, vapour barrier, sheathing ply, insulation between studwork, sheething ply, cavity, external brickwork.

What you need to do is use enough insulation to stop the temperature dropping rapidly between the internal surface and external surface. If the temperature drops too rapidly you could get interstitial condensation forming in the built up fabric which can lead to rotting.

The vapour barrier is there to prevent (vapour/moisture) passing through the fabric and is placed on the warm side of the wall.

I have worked on sites where taping the joints of foil backed insulation boards has been used but also where a vapour barrier has been added on top.

Check with the manufacurers of the insulation and obtain any literature that has recommended guidance. You can normally obtain guidance from the technical department of the manufacturer.

Mark