Garage roof

[srobrien]

Hi all, I have just ordered a new steel box profile roof to replace my leaky old corrugated concrete one. (BTW I am aware of the asbestos issue).

I am concerned about condensation on the inside so have thought about laying OSB sheeting with felt on top under the sheets but I am not sure what would be the best sort of felt to use?

 

Has anyone any experience of this?

 

Cheers

 

R

[leonk]

Only a thought....

 

Why not counter batten it and use a breathable membrane?

[ATTAK Z]

Condensation will occur only if inside temp is significantly higher than outside temp ... so my question is, is the garage heated ?

[Neilp]

Condensation will occur only if inside temp is significantly higher than outside temp ... so my question is, is the garage heated ?

You are correct in sense but when outside temps drop below freezing you will almost always get condensation no matter as the inside air moisture content will condense on the cold surface regardless of whether it is heated or not. As soon as the outdoor ambient temps drop the inside air will most likely reach it's dew point and form condensation.

 

I have this problem in my garage. Insulate the steel and make sure you have sufficient ventilation gaps.

[ATTAK Z]

Condensation will occur only if inside temp is significantly higher than outside temp ... so my question is, is the garage heated ?

You are correct in sense but when outside temps drop below freezing you will almost always get condensation no matter as the inside air moisture content will condense on the cold surface regardless of whether it is heated or not. As soon as the outdoor ambient temps drop the inside air will most likely reach it's dew point and form condensation.

 

I have this problem in my garage. Insulate the steel and make sure you have sufficient ventilation gaps.

As stated by Neil, good ventilation is the key

[srobrien]

Thanks lads so what about my idea of laying it ontop of OSB and felt? Surely because the bottom of the tin is not in contact with the inside of the garage it should be more or less the same as the ambient temp? Any idea on what felt is best and where to get it?

[Stew]

You can do my sisters afterwards Ross!

 

My mate erects a lot of 'sheds' in the farming sense of the word so if you are looking for material we can pilfer his yard for a casher I'm sure!

[Grantmitchell]

You can do my sisters afterwards Ross!

 

 

You can do mine after that too - whole new career for you

[leonk]

As above, excellent advice, but if you are starting from scratch it might be worth considering a breathable underlay onto roof joists, then battens and then fix your sheets to the battens. Any condensation forming on the underside of your sheets will be prevented from entering the garage by the beathable membrane.

 

Again only a thought ( based on nearly thirty years in the construction industry )

[leonk]

Plus you are creating an air gap between the two.

[Grantmitchell]

As above, excellent advice, but if you are starting from scratch it might be worth considering a breathable underlay onto roof joists, then battens and then fix your sheets to the battens. Any condensation forming on the underside of your sheets will be prevented from entering the garage by the beathable membrane.

 

Again only a thought ( based on nearly thirty years in the construction industry )

 

Come to Aberdeen and there are 3 roofs for you to do

 

When I did my dads garage roof thats how we did it, still water tight now and no condensation

[srobrien]

As above, excellent advice, but if you are starting from scratch it might be worth considering a breathable underlay onto roof joists, then battens and then fix your sheets to the battens. Any condensation forming on the underside of your sheets will be prevented from entering the garage by the beathable membrane.

 

Again only a thought ( based on nearly thirty years in the construction industry )

 

Thanks leon, would i just attach the membrane straight to the top of the purlins?

R

[leonk]

"Purlins" are the big joists that support smaller roof spars or joists.

 

So felt first then spacer battens on top of felt and spars then your metal roof cladding. 50mm tanalised battens should be enough.

Just google " breathable roof membrane "

 

If you want i can pm you my mobile and I'll talk you through it.

[srobrien]

"Purlins" are the big joists that support smaller roof spars or joists.

 

So felt first then spacer battens on top of felt and spars then your metal roof cladding. 50mm tanalised battens should be enough.

Just google " breathable roof membrane "

 

If you want i can pm you my mobile and I'll talk you through it.

 

 

Hi sorry forgot to mention it is a flat roof with a pitch from front to back so only has purlins...ala this:

 

 

R

[leonk]

Thought as much, various ways of doing it. Will PM you my mobile, just give me a ring and I'll advise. All F.O.C to club members.

 

If it's medical advice or kitchen fitting DoogyRev is your man.

[srobrien]

Thought as much, various ways of doing it. Will PM you my mobile, just give me a ring and I'll advise. All F.O.C to club members.

 

If it's medical advice or kitchen fitting DoogyRev is your man.

 

 

Thanks very much, got your PM. Will give you a call when I get stuck haha.

 

R