Hi, on my house I've got a flat roof covered with tarpaper. The top layer
is cracked "alligatored" and needs another layer of paper on top of it. How
many layers of paper can a flat roof take? At what point do all of the
layers need to be torn off?
What about city codes limiting the number of layers of paper for houses in
baltimore City, MD?
I think you are asking the wrong question. tarpaper is an underlayment
used under a layer of either shingles or roll roofing. It is not,
itself, a roof covering. Is what you have, roll roofing? If so, you
never want more than two layers. Anything more than one layer shortens
the lifespan of added layers. Two is the maximum before you need to
tear off and start over. By that time, there is usually decking and
flashing that needs to be uncovered and repaired anyway.
Flat roofs with roll roofing last about 10 years before they start
failing. Sometimes they can go a few more years than that, but that's
about the average for a properly installed roll roof. If you own the
building, you really should investigate either a builtup roof, or as
someone else suggests, building a pitched roof over what's there. You
may get 25 years out of a built up roof or a pitched roof withy
shingles. There are no real shortcuts. When you compare the cost of
different options, compare them against years of service. Re-doing a
roll roof every 10 years gets expensive and annoying. If a 25-30 year
solution costs 3 times as much as a 10 year solution it's a no
brainer. Just do it. Even at 4 times the cost it's got a lot of
advantages. Heck, with adding a pitched roof, you have an opportunity
to add a lot of insulation, too.
Not entirely true.
For a hot tar roof, the crew often puts down 90 lb tar paper, and then
hot mops tar over it. The tarpaper is then part of the roofing layer
and you could count the layers by counting how many layers of tarpaper
you tear through as you take it off.
If you can't build a pitched roof, you might still be able to improve
things by re-roofing with a built up composite, or a torch down
membrane, both of which will be more expensive initially than roll
roofing, but will last much longer. Worth getting some comparative
estimates, and talking to some roofers about it. Roll roofing is
really the low end of roofing materials. It's the northern equivelent
of a thatched roof made from palm fronds and grass. <g>
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