Some Roof Slope Factors to Consider

Some Slope Factors to Consider
. Safety. Again (and I can’t stress this enough)
neither you, nor workers you hire should have to
risk life and limb to work on your roof. Roofs
steeper than 6:12 are increasingly dangerous.
. Degree of Difficulty. Your roof should be
relatively simple to work on. I’m not saying it
should be easy, but it shouldn’t require scaffolding,
mechanical lifts or mountain-climbing equipment to
access your roof. Again roofs above 6:12 in slope
are the most problematic.
. Drainage. Your roof should not pond water as
dead-flat roofs do. Ponding causes leaks and
premature roof failure. Building codes, warranties
and good roofing practice all require positive
drainage. Tapered systems can correct slope
deficiency, but they are labor-intensive and pricey.
 Do-it-Yourself Friendly. If you desire (or
finances dictate) that you do the roofing work
yourself, your roof should accommodate you.
Roofs that are too low or too steep are both
troublesome for the handyman. A slope of 4:12 to
6:12 is just right.. Curb-appeal. Roofs that are too steep tend to
make a home look top-heavy. (Except for Aframes,
which look great!) Roofs that are too low
tend to make a home look boxy or bottom-heavy.
Many manufactured homes have this problem.
Again 4:12 to 6:12 just looks right.
. Quantity of Material Required. The steeper
the slope, the more framing, sheathing and roofing
needed. For example a roof with a 12:12 slope
uses 30% more material than a 5:12 slope.
. Quantity of Labor Required. The steeper the
roof, the more labor required. Not only is there
more material to be installed, but it is much slower
working on steep roofs. A 12:12 slope can take
twice as long to shingle as a 5:12. A near-vertical
mansard can take four times as long.
. Compatibility. Roofing systems are designed
to function properly within a certain range of slope.
Violating these requirements invites roof failure,
and can void your warranty.
For example: “Steep-slope” roofing systems such
as asphalt shingles require at least 2:12. Many
architectural metal roofs require at least 3:12.
“Low-Slope” roofing systems such as built-up roofs
single-ply and modified bitumen are typically used
below 2:12. But quality low-sloped roofing systems
cost about double what steep-slope systems
cost… and may not last as long!
. Special Requirements. Some roofing systems
require special considerations for marginal
applications. Asphalt shingles for example, may
require a two-ply underlayment on roofs less than
4:12. That can be a pricey little add on, especially
if you’re using one of the new premium
underlayments.
. Contractor Interest. The best roofers (which
are the only kind you want) often have all the work
they want. They can afford to pass on dangerous
jobs. They don’t want to risk injuries on steep roofs
if they don’t have to.
If they bid a steep roof at all, you can expect high
prices, because they probably don’t really want the
job. However, roofing projects that fall in the 4:12
to 6:12 range are highly desirable.
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