New Roof

November 12, 2008 8:40 PM

FLAT ROOF tear-off/replacement question: What is the difference between using HOT tar versus WARM tar? Also, if a roof needs replacement, how cold can the outdoor temperature be before it is inadvisable to do a roof tear-off job? (Is November or December in Chicago a bad time to do this job?, we would like to do it before it snows)
posted by Lylo to home & garden (7 comments total)

Flat roof? The only thing you want to put on one of those is a rubber membrane.
posted by caddis at 8:42 PM on November 12, 2008

tar should not be used at all?
posted by Lylo at 8:48 PM on November 12, 2008

Flat roof? The only thing you want to put on one of those is a rubber membrane.

No. Built-up bituminous roofing (AKA tar) is perfectly acceptable, and in fact is recommended to clients by my firm over any other roofing system, and all we do is flat roofs. Also, let's please all understand that unless a builder is severly brain-damaged there is no such thing as a perfectly flat roof -- even flat roofs have a slope to them, which is typically about 2%. And if you're going to be throwing out "rubber", at least define what you're talking about -- EPDM? TPO? Something else?

I've never heard of a difference between hot and warm tar for roofing though. It might be a difference between a coal-tar product or asphaltic hot-mop coating. I'm in California, where it's always okay to intall tar roofing. I'd guess that if your roofing installer is guaranteeing their work, you can hold them to that regardless of what type of installation they do or how cold it is. They should be guaranteeing their work for a certain number of years.
posted by LionIndex at 9:44 PM on November 12, 2008

Tar may be fine in CA, but if your roof gets cold, like say below freezing, then tar cracks over time, at least as far as I know. Interview a bunch of roofers and ask lots of questions. Membranes are superior and more expensive, so look for the long term cost. Remember, leaks suck.
posted by caddis at 10:09 PM on November 12, 2008

Membranes are superior and more expensive, so look for the long term cost. Remember, leaks suck.

Maybe the membrane itself is more expensive, but installation costs are waaaaaay lower for single-ply roofing than for built-up. That's the whole point of their existence. Why install five layers of roofing when you can just install one? But once that one layer is compromised...
posted by LionIndex at 10:39 PM on November 12, 2008

We saw someone in my old office replacing the membrane roof with a new membrane roof (in NW Ontario, i.e. really frickin' cold, so I'd vote against tar, with its cracky-tendency), and we wondered:

Why do the membrane, dump rocks, etc. deal, when, unless it's a HUGE roof, put truss rafters on, sheet and shingle, for less mess, less chance of membrane puncture, and (likely) cheaper? Temperature doesn't matter, and shingles are WAY cheaper to replace down the road (especially if you put good 20-year ones on to start).

Just a thought.
posted by liquado at 10:07 PM on November 13, 2008

liquado writes "Why do the membrane, dump rocks, etc. deal, when, unless it's a HUGE roof, put truss rafters on, sheet and shingle, for less mess, less chance of membrane puncture, and (likely) cheaper?"

I can think of a few reasons even if it was cheaper:

• Makes the house taller, maybe illegally so
• Changes the appearance of the house
• Doesn't work with all architectural styles (Art Deco/Modern, Greek Revival, Spanish Colonial Revival, etc.)
• May not be allowed by HOA/Strata rules

posted by Mitheral at 9:16 PM on December 8, 2008