Flat roof

Alec

Is it possible to roof over a tar and gravel roof after removing the gravel? I am in the process of getting quotes for a commercial roof and a roofer said i could just remove the gravel and torch down a cap sheet over the old roof. Any suggestions would be appreciated.

Thanks
Alec

1985gt

You can do this, but its not ideal. Is just just putting a cap sheet on? How many layers of roofing are on it now? Did he spec any insualtion board? Add a few pictures if you can.

Don Smith

If your not worried about the extra weight sweep off as much loose gravel screw insulation and a base sheet down torch down roofing. I would tear it off inspect the deck install tapered insulation for positive drainage and single ply roofing

OldNBroken

Don wins the teddy bear on this one.

1985gt

I didnt see any pictures?

Grumpy

Depending on the number of layers that would be the first determination if youc an go over. Often local code limits the number of layers of roofing that can be installed. furthermore sweeping the gravel and torching over should be considered a temporary roof covering at best. Would it work? For a short time. Certainly there woould be adhesion problems because of all the old dirt on the roof and the rock that couldn't be swept. If you were set on this, I'd first prime the surface though it wouldn't help all that much and I suspect if you want to go over, you want cheap and priming would just add to the cost.

Another concern if you can install a new flat roof over the existing is if there is any trapped moisture. Any moisture in the existing roof assembly will have a negative affect on the new roof. You can find out by performing a series of core cuts 10' on center or hiring a professional to perform an infra red roof scan. If there are wet areas these would first need to be fixed.

If I were to go over I would screw down some kind of cover board, assuming you have a metal gypsum or wood substrate. I would then install a thermoplastic single ply such as TPO or PVC. EPDM is also a good choice and modified bitumen is adequate. It is my practice to always ventilate the top layer of roofing when I install a lay over. This is incase there is any trapped moisture I may have missed or any moisture migrates through the roof assembly in the future since some single ply acts very well as a vapor barrier and we want to let any vapor out. Notice that I said cover board, not insulation earlier, insulating and ventilating is often silly.

Preferrably when ever logistics and budget allow I want to tear off. There are numrous reasons to tear off the roof, weight is a factor sometimes, but being able to identify if there are any problems with the substrate is the main concern. The budget seldom allows now-a-days however and I have to compete against hacks willing to add a 3rd or 4th or 5th layer with no regard for code nor weight.

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-Grumpy

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Sometimes the savings that comes from doing it yourself can be blown away with one mistake.

The information found in this post is not to be considered legal advice. All information should be considered relative, not specific. Never attempt any repairs you are not comfortable with. Always maintain safety! The author of this post takes no responsibility for any losses that occur. Use at your own risk.

Don Smith

I would like to see a roofer remove all the gravel clean enough to do a torch down. we have done this but the labor is I mean alot. If anyone has spudded a tie in knows and that might only be a foot wide. Best to sweep all the loose grave lay a 1/2 inch fasten down or some sort of tapered system then choose your roofing system depending on funds

Grumpy

That brings up a good point. I have spoken with some manufacture reps who actually prefer not to sweep anything. Their reasoning is that the gravel often accumulates in any low spots and in sweeping it off the roof will reveal those spots and create puddles in the new roof. having said that I really prefer to sweep.

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-Grumpy

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Sometimes the savings that comes from doing it yourself can be blown away with one mistake.

The information found in this post is not to be considered legal advice. All information should be considered relative, not specific. Never attempt any repairs you are not comfortable with. Always maintain safety! The author of this post takes no responsibility for any losses that occur. Use at your own risk.

Don Smith

Yeah because roofers seem to over gravel sometimes if they have extra gravel they would just as soon fan it out on your roof then take it back and that's alot of extra weight. And in a snow area that weight is trapped between layers of roofing

1985gt

Any time you screw insulation down over a gravel roof there will high and low spots. No matter how hard you try. One could always use a rotory spudder and then 1/2 coverboard with what ever system you prefer. We have done a few of these and mopped new layers on, I would guess though that if you tore off and put 1 1/2 iso down and EPDM would be about the same cost as spudding, 1/2 coverboard and 3ply with gravel. 3ply with gravel is a better roof then EPDM, but you still have the moisture issue and uneven spots to deal with, even spudding smooth wont help a poorly designed roof.

Don Smith

I agree BUR is better but you will never sell that to the single ply guys. I been on hot tar roofs that were 50 yrs old and don't leak. It was pitch but that a whole new thread.Been on alot of really long lasting asphalt roof but is all about drainage and ponding water

1985gt

Very true, seen some pitch roofs 80+ years, the more water they ponded the better off they were. No you will never sell them to single ply guys as I belive most are scared of them . Every roofing type has its place, wait scratch that not spray foam it has no place being on a roof, but it seems Burs are dead, or atleast getting there.

Don Smith

Yeah lol the only foam i want to see is on my beer then not much there either

1985gt

anything over 1 1/2 inches is a waste of glass space!

Don Smith

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