Built Up Roof (BUR) vs Modified Bitumen Roof (Torch Down)

Old 01-16-10, 10:12 AM
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Built Up Roof (BUR) vs Modified Bitumen Roof (Torch Down)

I need some advice and/or opinions about these types of roofs. I have a flat section of roof on my house that needs to redone. I had this roof completely torn off and redone (BUR) approx 11 years ago. I spent a whole lot of money with a LICENSED contractor on this roof wanting not to have to deal with it again for a long time. Apparently it wasn't done correctly according to the roofers that have come out and bid the job. I was told that they didn't prime the edge metal correctly and this caused the edge to lift up/de-lam and water to wick in. It has destroyed all of the fascia on this part of the roof and some of the sheathing underneath. Other than the edges lifting up/ de-laming, the roof is still in relatively good shape. This is a FLAT roof with less than 1/4" per foot fall. Some of the guys bidding have suggested modified bitumen (torch down) as the way to go and some say that the BUR is the way to go. Which would provide me with the better roof? Which would last longer? Is it better to go with a 4ply (base, 2 11 lb. plys, granulated cap sheet) or a 5ply (base,3 11 lb. plys, granulated cap sheet)BUR? What about a 2 ply modified bitumen vs. a 3ply modified bitumen? I live So Cal. and we don't get a ton of rain. I would like this roof to last at least 10-15 year min. Thanks in advance for any advice or suggestions!
Old 01-16-10, 11:13 AM
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At least in my climate (Chicago) IMO the best alternative would be a tear-off , followed by installing a properly sloped deck, and then mod bit.

If you want to keep the "nearly flat" deck, consider one of the PVC roof membranes, some of these are *highly* resistant to standing water - you will probably need to find a commercial roofer to install it though, most residential roofers don't work with this material, and some manufacturers don't warranty it in residential use.

The bottom line however is that if you have significant ponding water it may be heavy enough to gradually compact or defect the decking and supporting structure.... which increased the ponding... which increases the weight... which increased the ponding...
Old 01-16-10, 02:35 PM
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both the BUR and Torch down applications are both great roofs when installed correctly. but i must agree with michael nothing beats a nice pvc or tpo.

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