Insulating workshop roof. Spray foam. Thughts?

[Roger440]

I need to insulate the roof of my workshop.

Its a touch over 2000 sq/ft. Roof of Fibre cement board on steel frame and purlins.

Ive looked at every concievable option.

Surprisingly, spray foam came in much better than i thought. With the advantage that i dont need to do it.

However. The roof has some minor leaks. In normal conditions, it doesnt, but today we had a moonsoon. And 4 monor leaks. 2 are clealy cracks in the panel, 2 are weeping around the sceews.

All the spray foam peole will tell you, it fine, it will seal it up. But is it? Really?

Anyone have an experience of this in a commercial building setting or similar.

Pic of roof

 

[Bornfree]

How does spray foam stand up to grinding sparks?

 

[Roger440]

How does spray foam stand up to grinding sparks?

They have specified classE fire retatdant foam.

But its only the roof, noit walls. And it over 5 mtrs up.

Most if not all grinding will be in an enclosed roof for the purpose.

 

[Beanwood]

Does it make any difference to insurance or resale value? I vaguely recall some problems but never checked what exactly.

 

[Brad93]

That's a lovely barn

 

[gaz1]

spray foam will burn

spray foam causes damp on metal and wood thats why many roofs need the whole lot taken off and replaced if you get or have a water leak as you cannot see the damage until its to late

metal roofs do expand and contract so the do break free from foam and your left with a foam structure as it does seperate

spray foam is not a uk thing so any risks that you do can cost you more in the long run

 

[More Amps]

First question would be how long are you planning to be there? Personally I wouldn't be too confident long term in relying on sealing the roof from underneath - water will find any gaps or cracks and if the temp drops to freezing, any cracks will only grow. I would prefer to replace the defectice sheets before spray insulation. Also need to bear in mind the age of the roof - are the sheets of an age where they're reaching the end of their life or has the damage been caused by falling branches?

Whatever you decide, I''m still jealous of a shed that size!

 

[Blobber]

I wouldnt use foam, there are plenty systems on the market to put another skin over the top of the existing roof which causes no disruption inside

 

[Roger440]

I wouldnt use foam, there are plenty systems on the market to put another skin over the top of the existing roof which causes no disruption inside

There is indeed. But cost effective its not!

Ive got the added issue that thec roof extends a further 1000sq ft as a canopy, and another 500 or so over the office/kitchen etc. So in ends up rather closer to 3500 if i do outside. Or i have weird steps in the roof, but that will look awful.

Spray foam will be under £10k all in. Over roofing over £30k. Complete new composite roof, nearer £40k. Which is of course the best answer. But £40k!!!!!

 

[Roger440]

First question would be how long are you planning to be there? Personally I wouldn't be too confident long term in relying on sealing the roof from underneath - water will find any gaps or cracks and if the temp drops to freezing, any cracks will only grow. I would prefer to replace the defectice sheets before spray insulation. Also need to bear in mind the age of the roof - are the sheets of an age where they're reaching the end of their life or has the damage been caused by falling branches?

Whatever you decide, I''m still jealous of a shed that size!

25 years maybe?

The building was put up in 2001, so they are not that old. Certainly not end of life.

Replacing the sheets is no easy task. And certainly not one i can do myself.

Move to wales. Then you too can have a massive shed!

 

[Roger440]

Does it make any difference to insurance or resale value? I vaguely recall some problems but never checked what exactly.

Thats more of a domestic thing where timber structures are involved. No wood in this roof at all.

 

[Wildefalcon]

If the steel is sound then apply corrosion protection first?

 

[Morrisman]

All the spray foam peole will tell you, it fine, it will seal it up. But is it? Really?

The company that did spray foam in my dads house swore it would seal the old tiles, stop them leaking, stop them blowing off, and gave a 30 years guarantee.... except after he died and we came to sell the house the company didn't exist any more....

We had to get a roof specialist to come in and say there was nothing wrong with the foam etc, before the sale could proceed.

 

[More Amps]

25 years maybe?

The building was put up in 2001, so they are not that old. Certainly not end of life.

Replacing the sheets is no easy task. And certainly not one i can do myself.

Move to wales. Then you too can have a massive shed!

From memory those sheets have a (claimed) life expectancy of around 50-60 years, so they should see you out. If you're set on spray insulation, then I would get a roofer to seal any leaks from the top first - fill the cracks with bitumen, stick on a patch and then bitumen around the edges of the patch (but if he's doing all that, then it might be better to just get him to replace the split sheets!)

 

[Roger440]

From memory those sheets have a (claimed) life expectancy of around 50-60 years, so they should see you out. If you're set on spray insulation, then I would get a roofer to seal any leaks from the top first - fill the cracks with bitumen, stick on a patch and then bitumen around the edges of the patch (but if he's doing all that, then it might be better to just get him to replace the split sheets!)

Im certainly not "set on it". I think its bloody awful stuff and to look at.

But the alternatives are bonkers money, or do it myself options. But those involve installing something, on the inside with all the attendant risks of working 5 meters up with sheets of whatever. And dont solve the leak issue.

Just been looking at replacing or repairing the defective ones as you suggest.

Finding a roofer, is a challenge. Finding one that will actually create a completely leak free roof is another entirely. Especially out here. Its farming territory, and minor leaks like these are normally of no concern in a farming environment.

I see the sheets themselves are cheap enough. And a suitable cherry picker would get me up there. Not sure how i physically handle a 2.5m sheet whilst staying in the basket though?

 

[James1979]

Have you looked at overpainting the outside with bitumen paint, like blackjack?

It sort of finds and seals small holes.

Used it quite a bit over the years on various wriggly tin roofs that have got ‘tired’ around the nails. I have a pot waiting to go on here.

You won’t get the insulation of foam but none of the grief either.

Just thoughts…..

 

[magnet]

Could you live with the leak and build a shed within the main shed to protect things that are environmentally sensitive.

 

[Onoff]

CT1 over the cracks.

 

[More Amps]

Im certainly not "set on it". I think its bloody awful stuff and to look at.

But the alternatives are bonkers money, or do it myself options. But those involve installing something, on the inside with all the attendant risks of working 5 meters up with sheets of whatever. And dont solve the leak issue.

Just been looking at replacing or repairing the defective ones as you suggest.

Finding a roofer, is a challenge. Finding one that will actually create a completely leak free roof is another entirely. Especially out here. Its farming territory, and minor leaks like these are normally of no concern in a farming environment.

I see the sheets themselves are cheap enough. And a suitable cherry picker would get me up there. Not sure how i physically handle a 2.5m sheet whilst staying in the basket though?

I'd phone round the local agri-shed people and see if anyone has a job coming up near you and could then fit you in when its convenient for them. I wouldn't volunteer to be at the wrong end of a cherry picker with a roofing sheet while praying the wind doesn't get up....

 

[Gareth J]

A quick fix for split sheets is to cut a valley (or two/three/whatever is required) from a skylight sheet and tuck them over the next lower sheet to move the water downhill. Done without going onto the roof and effective.

How does battoning over the purlins and sheeting compare cost-wise? Plasterboard would be cheapest?

The airgap will help a lot with heat retention, even with no actual insulation. Though you could tuck rockwool above.

Don't go onto the roof without either crawling boards that span X3 purlins. Or nets underneath. I know it's fairly new but it's a long way down. Seriously, don't.