insulating a sectional concrete garage

[lizzy]

We've moved into a house with a double sectional concrete garage. Structurally it is sound, it needs a new roof, its ugly and it sweats like hell. We had a price for knocking down and rebuilding in brick but we can't really afford it and it is ages before we can be fitted in. So I'm thinking about re-roofing in EPDM, insulating the roof and walls with celotex and then cladding the outside in wood.

I understand about leaving an air gap between the celotex and the underside of the roof, but the wall insulation is confusing me regarding whether to do internal or external wall insulation and whether we need a vapour barrier or not. Anyone able to offer any advice?

 

[^woody^]

Insulating a garage is a complete waste of time, you dont need any air gaps between insualtion and roof, and a vapour barrier is not required

 

[Ian H]

How much would you save compared to paying for the brick built one?

 

[lizzy]

Insulating a garage is a complete waste of time, you dont need any air gaps between insualtion and roof, and a vapour barrier is not required

So how do you suggest I stop it sweating?

 

[lizzy]

How much would you save compared to paying for the brick built one?

It will be half the price, but it will be done a lot quicker meaning we can get on with the groundwork and landscaping this year rather than waiting until September for the garage.

 

[John D v2.0]

External wall insulation is generally considered to be better if you can, same goes for warm roof. Your problem is going to be isolating the floor from the walls. When you say insulate, what are you going to use it for? If it's a workshop/potting shed for short time use in 3 seasons you don't need too much, 50mm eps would be plenty.

 

[lizzy]

External wall insulation is generally considered to be better if you can, same goes for warm roof. Your problem is going to be isolating the floor from the walls. When you say insulate, what are you going to use it for? If it's a workshop/potting shed for short time use in 3 seasons you don't need too much, 50mm eps would be plenty.

Yes, bit of a workshop and general storage. Just want to stop stuff from rusting mostly and make it a nicer place to be with a little heater for colder periods. At the minute the condensation can drip off the underside of the cement roof. What do you mean about isolating the floor from the walls?

 

[John D v2.0]

You didn't mention insulating the floor, but even if you did, the walls are connected pretty well to the ground so you might end up with cold coming in with external insulation. But since you're only trying to make a bad situation better I think it's not worth worrying.
Keeping things dry would need some background heating or dehumidification I think.

 

[lizzy]

to minimise the floor isolation problem, I guess internal insulation may be better? but then you lose any effect of thermal mass from the walls.

 

[lizzy]

Thought I'd report back on how this went and the experience so far. Despite the naysayers claiming this was a waste of time I went ahead anyway as it seemed to make sense to me. So I did a new warm roof using 50mm PIR and insulated the outside of the concrete panels with 25mm PIR along with the inside of the garage doors. Walls then had a breather membrane, small air gap and were clad in softwood. I also clad the inside of the walls in OSB for what its worth. Windows are now double glazed and I used draught excluders around the doors where possible to reduce the draughts, but there is still some airflow around the door. But I see this as my version of a trickle vent! I'm happy to report it is a million times better than what it was like last winter. No condensation and no more rusty tools! It is now usable without any heating in there but I reckon if the temperature outside was sub-zero a little fan heater would be adequate if I wanted to spend a prolonged period in there. All-in-all it has cost a few £, but it is a lot cheaper than starting again.

 

[John D v2.0]

Sounds like a pretty solid job there. Glad you're satisfied with the result