How to seal a flat roof?

Question

I have a southwest style house with a low pitch roof and parapets, commonly referred to as a flat roof. I have a quote for $6500 to redo the entire 1500 SqFt, but I think I can lay a coat of sealant for about $500. Do I have to strip all the old rooffing off or would simple spreading a new coat on top of the old roof seal it tight? Looking for advice from someone who has tried what I am talking about. How did it work for you?

Answer 1

We did one flat roof with a seam-welded membrane cover that is still waterproof after 5 years. The hardest part is to get the membrane UP on the roof, since it's huge and heavy, and really difficult to move around. Then you have to cover it with something, since it degrades in sunlight. We put large potato-sized rocks on it, about 4 inches deep all over... And a floating edge all around to hold the rock on, but let the water run off. We connected wooden 4x4s all along the edge with steel cables that go both longitudinally and latitudinally across the roof. It's not a good place to try put up a lawn chair and read anymore, but it doesn't leak! It wasn't expensive to do (400 dollars) but would have been really expensive to pay for labor.. And you have to have a scaffolding and a really strong winch. The vents and tubes were a pain. I hope this helps, and good luck!

Answer 2

I think that the best solution for low pitched or flat roofs is to remove all existing roofing down to the sheathing, make sure that there is nothing sticking up, no nails, nothing.  Put down a layer of insulating roof board and then a membrane that is either one piece or solvent welded together at the seams.  The edges will have to have coping and flashing installed correctly as well as any vents or pipes that penetrate the roof deck, without stetching the membrane.

I've tried sealing and resealing old flat roofs and they have only lasted a year or so at best.  Good luck  

Answer 3

we tried quite a few different ways to seal our roof.  we finally broke down and had a professional reseal it.  he guaranteed his work for three years.  paid about $4000 for a 50 x 60 foot area.

Answer 4

That’s a pretty expensive quote. I would recommend calling a couple of commercial roofing contractors and seeing if any of them are slow right now, or if any of them may be inclined to do a small job like this ‘on the side’ The commercial roofing market is more equipped for this type of installation- most industrial / commercial buildings are 'flat' or low sloped. Products like EPDM, TPO, or PVC would be ideal for a re-cover of the existing roof. If you do go the route of re-covering be sure to get a warranty from the material manufacturer- and if you can I would ‘write into the contract’ that the roof be inspected by an independent 3rd party or the material manufacturer.

Sealants certainly are an option as long as you now what type of roof you currently have and are trying to seal. An asphaltic based sealer (like black jack) will destroy Rubber, PVC and TPO, an acrylic based sealer will work with EPDM (Rubber) but wont 'stick' to PVC or TPO, and will work about like a coat of thin paint on asphaltic systems.... You would need to identify your roof first- but overall, sealers can be expected to last about a year and a half... they just don’t take extreme temperature changes very well (winter to summer) they crack. And no, you don’t want to remove the existing roof prior to their installation, you do want to make sure the roof is clean and dry though.

If you’re the DIY type, there are commercial roofing products available to the public, check out ABC Supply Co. or Bradco Distribution- I personally would recommend a 10' pre-taped EPDM sheet- it’s an easy to use product- but overall I would rank re-roofing as a 9.5 / 10 in the difficulty scale... Where is your building located- that will play a large roll in what type of roof product you might want.