Vapour Control Layer Required?

[Gizzers]

Afternoon,

Looking for some expert advice as I am a DIY beginner hoping to build a garden workshop. The concrete slab is existing and has a dpm.

Floor construction on top of concrete slab is proposed as follows:-

50x50mm timber battens.
50mm Celotex GA4000 insulation between battens.
22mm chipboard.

My question is do I need some type of vapour control layer for the installation?
Also if so what type of vcl is recommended and where should it be located?

Any advice on the above is very much appreciated.

Many thanks in advance to any comments.

 

[Notch7]

Personally I would use 75mm foil tape and tape over every joist so there is a continuous layer of foil over the whole floor.

If you want to, you can also put down a VCL onto that.

Then put flooring on top.

Tip for cutting insulation:

1. Cut insulation first, then put in place as you put in joists.

Or

2. Measure gaps very carefully -don't measure in middle where joists could be bowed, measure at ends.... and cut insulation accurately. For a snug fit cut so the insulation is tapered, i.e. Narrower underneath.

Alternatively do it about 8mm narrower then foam all joints using a metal foam gun with the pressure turned right down.

 

[Gizzers]

Thanks. Once I now use the foil tape as you suggested is the VCL a must do or is the foil tape sufficient do you think?