insulating a garage

[Stephen]

Hello,

I have a garage constructed of a single brick skin with a leaky roof (see flat roof post). I am thinking about insulating it with some Kingspan or Celotex. Would a 50mm thick sheet be sufficient if I fix it to all three walls and the ceiling or should I use a thicker sheet? Or is it a waste of time, after all, the fourth wall is not a wall at all but a door. Is any saving made by the Kingspan on three walls going to be lost due to heat loss through the door?

Do I have to leave a gap between the kingspan and the brick? I thought I read on this group that I should leave an air gap? Would a gap of one or two inches be sufficient? Is this just to stop condensation on the bricks?

I presume an air gap alone is not sufficient and that the gap requires to be ventilated? Would having it open at the eaves be sufficient?

If I cover the Kingspan with plywood, would 12mm ply be sufficient to withstand knocks and would it support shelves, or would I be best to use 18mm?

Thanks.

[John Rumm]

I did my workshop (similar construction to your garage by the sounds of it) with 50mm foil faced PIR foam, and 12mm ply lining. I used a combination of squirty foam, and some 5 & 1/4" screws through the lot into holes drilled into the brick / blockwork - you only need about 4 screws per sheet. No air gaps required. The result is plenty strong enough to take shelves or anything else you want to mount.

[NoSpam]

I did my garage/workshop by covering the walls with DPM plastic sheeting, fixing 2x2 treated battens vertically with 1400 gaps, 8x4 sheets of 50mm polystyrene in the gaps and then 8x4 18mm shuttering ply screwed to the battens (I trimmed the polystyrene slightly so it was narrower than the ply). The thicker ply means I can screw almost anything to it, almost any where. I cut thinner celotex to fit the panels in the steel doors and stuck them directly to the steel. A rubber wiping strip on the bottom of the doors and some bits of rubber up the sides stop most of the draft. I also cut polystyrene to fit between the rafters and just wedged them in (but you need to fix your leaks first!). I also put the boiler and DHW tank in the back of the garage, together with a small radiator to heat the work area when needed.

So far it's been through one or two winters and has been successful

Dave

[Rob G]

If you are converting a garage, please do make sure that you have a good emergency exit - not an up-and-over door. My father didn't and he died.

Rob

[Stephen]

Thanks. I was confused about the air gap. I understand you need an air gap when you insulate a loft space because there are timbers that need ventilation but there are no timbers when insulating the garage walls, so I wasn't sure if one was needed. I doubt I'll ever get the car in there - there's too much junk in the way - but if I could lose the air gap and use 12mm ply instead of 18mm, then that would maximise the space. Thanks again.

[Stephen]

Sorry, I am bit unsure why did you need to use DPM?

I notice you used polystyrene rather than kingspan/celotex. I thought realise that polystyrene is very much cheaper than celotex but I thought it was a much poorer insulator? 50mm of polystyrene would be equivalent to how much celotex? I won't have the advantage of a boiler and water tank, so I wonder whether I might notice the difference? Should I pay more for the celotex?

Polystyrene is also more flammable, so is that another good reason not to use it?

John seems to be able to screw anything to the 12mm ply he used, so I hope to use 12mm rather than 18mm, just to help keep the cost down. Do you think that would work as well as your 18mm ply?

Thanks again.

[Stephen]

I am very sorry to hear this.

I am not converting it as such, it was a garage before and will be a garage after, just hopefully it won't get as cold so that the tins won't freeze and the metal things won't get covered in condensation and rust.

[John Rumm]

Yup, in a loft you not only have the timbers, but also the possibility of water ingress should a tile slip or break. A garage wall is a much simpler proposition.

Yup, know that feeling!

12mm seems adequate for quite reasonable loads. Give a paint with some light coloured emulsion as well and it makes the whole space much lighter and more inviting.

[NoSpam]

To reduce the moisture entering the workshop

You need to get the thermal conductivity figures and do the sums to decide whether the cost is worth the performance. I stumbled over a pea processing factory that was being dismantled so the polystyrene sheets were free.

I tested it and it appeared to have a flame retardent in it, it burnt slightly but then went out. It's down to cost-benefit again

Obviously it depends what you might want to fix to it and how it will be fixed to the wall.

[Stephen]

Shelves, shelves, and more shelves!

[Stephen]

I thought that would be a simple exercise so I went away to look for a web site listing u values. I've now got a headache!

I've seen sheets of polystrene, kingspan, and celotex for sale in places like Wickes and B&Q. You would think they might include u-values in the product descriptions on their web sites but they don't.

I visited the celotex and kingspan websites and became bewildered with the variety of sheets they sell.

I think 50mm polystyrene has a u-value of 0.48 W/m^2K but I wasn't sure what the difference was between expanded, blown, and extruded polystyrenes.

I think, but I'm really not sure, that 50mm celotex has a u-value of

0.30 W/m^2K and 25mm has a u-value of 0.45 W/m^2K, in which case celotex packs as much insulation into half the thickness.

Does 50mm Kingspan have a u-value of 0.28 W/m^2K? None of the web ites I found made it simple to look these figures up.

I suppose I'll have to go away and work out what this all means. I need to work out the area of my wall but then what? Select a temperature difference and from that I can calculate a heating requirement?

I'm confused!

[Tim Lamb]

In message , Stephen writes

The Celotex site has a calculator. You need to sign up and then remove most of your security but it will give a printed result suitable for presenting to building control.

regards

[John Rumm]

Any use:

[mike]

You'll probably get more for your money here:

've been mentioned on here several times, and I've used them and found them fine.