Insulating a Timber Shed

FreeBear

fifthofwhisky said: I have a shed base which is constructed of 27mm x 47mm (approx) with T&G over. Would there be any benefit in terms of improved insulation to put Celotex or similar between the 27mm x 47mm floor supports? 

If you have already done the walls & roof, then yes, insulating the floor is a very good idea. It will reduce heat loss through the floor.

fifthofwhisky

FreeBear said:

fifthofwhisky said: I have a shed base which is constructed of 27mm x 47mm (approx) with T&G over. Would there be any benefit in terms of improved insulation to put Celotex or similar between the 27mm x 47mm floor supports? 

If you have already done the walls & roof, then yes, insulating the floor is a very good idea. It will reduce heat loss through the floor.

Thanks. I plan to do the walls and roof, so might as well start with the floor (since I'll have to take the shed down and repair damaged timbers). If the floor joists are 47mm what thickness insulation should I use? Would it contact the T&G or the base or where to leave air gap? Any vapour barrier needed?

FreeBear

I'd go for 50mm foil faced Kingspan/Celotex type sheets. A couple of millimetres gap between the concrete base (assuming you have one of course) and timbers of the floor will help to stop them from rotting.

fifthofwhisky

That's a helpful suggestion, thank you. The base is made of a few concrete slabs which have shifted so I doubt I can use 50 all over (might need to sub 25mm in places). It might be worth looking into those plastic screw floor height adjusters to overcome the problem (even though it would increase shed height approx 5cm).

I was reading about the vapour membrane as raised by the OP. Some are saying that if you use Celotex (or foil backed insulation) and then (after filling gaps) tape up with aluminium tape that is probably sufficient for a shed (making a vapour control membrane superfluous). That might be OK for the floor and verticals but not sure it would cover the gaps/forms in the roof space.

Speaking of roof, is there any merit to putting a membrane under the roofing felt (which in my case will sit on T&G), or indeed is there a better option than roofing felt for exterior coverage?

Huggy_Bear

Morning all - I'm back to insulating my shed/workshop.

The framing I have is 63mm so can someone advise on the best thickness for the insulation boards like celotex.

Should I go with a 12mm air gap and 50mm thick boards or 30mm boards with a larger air gap. I'm working out my budget and think I need about 10 boards.

Floor and ceiling will be done another time as my budget doesn't allow that in one go

Thank you

FreeBear

More insulation is better. Go for 50mm.

Get yourself a foam gun and run a bead of expanding foam around the edges - A gun allows you to control the amount of foam much better than a hand held can (there are cheaper sources than Screwfix for guns). A bread knife or other serrated kitchen knife is good for cutting the insulation boards. A hand saw leaves a very rough edge, a kitchen knife gives a nice smooth cut.

Huggy_Bear

FreeBear said:

More insulation is better. Go for 50mm.

So this will mean I have a 12mm air gap is that ok - good tips on the foam gun and cutting thank you.

I'm cladding parts of the walls with pallet wood which will have gaps as they are uneven - will that matter?

FreeBear

Huggy_Bear said: I'm cladding parts of the walls with pallet wood which will have gaps as they are uneven - will that matter?

It's only a bleedin' shed... If you like the "rustic" look of pallet wood, go for it. Gaps, knot holes, and other defects are not going to make the slightest difference.

Huggy_Bear

FreeBear said:

Huggy_Bear said: I'm cladding parts of the walls with pallet wood which will have gaps as they are uneven - will that matter?

It's only a bleedin' shed... If you like the "rustic" look of pallet wood, go for it. Gaps, knot holes, and other defects are not going to make the slightest difference.

sorry I mean the gaps are going to allow air to hit the celotex behind it and wondered if over time it might cause damp etc.

I make things to sell from pallets so I'm all for the rustic look

FreeBear

Huggy_Bear said: I mean the gaps are going to allow air to hit the celotex behind it and wondered if over time it might cause damp etc.

For internal cladding, gaps between the slats are not going to make any difference to condensation/damp. Externally, you'd want to shiplap to ensure water runs off freely.