On Sun, 09 Dec 2007 18:03:03 GMT, (Una) wrote:

I am considering alternatives re how to repair an old, leaking roof.

The roof has a shallow pitch (4 in 12?) and a single layer of asphalt
shingles in bad condition. They are not curling much but they are
badly weathered and missing many edges. And there are plenty of leaks.
I don't know how long the roof has been leaking; it leaked already
when we bought the house last year. (We factored the cost of a new
roof into the purchase price.)

Part of the roof is over an attic. Under the shingles is tar paper
over sheathing. From inside the attic (crawl space) in many spots
the sheathing is cracked or broken. The roof has an 18" overhang
and neither soffits nor ridge are vented. The attic has gable ends
with vents but at one end the vent is covered with siding.

Another part of the roof is over an addition with a ceiling of
exposed rafters and tongue&groove boards. I don't know what lies
between the asphalt shingles and the ceiling. Probably not much,
because the addition gets very cold in winter and hot in summer.

The house is in very sunny and dry New Mexico at 7000' elevation
(so nights are cold). It has no AC nor a swamp cooler but is cool
in summer thanks to deciduous trees that overhang the west side
of the house (blocking afternoon sun) and good cross ventilation.
The climate is "high desert", so heavy snows, monsoon rains, and
significant hail storms are normal.

A recommended local roofer proposes to strip the old shingles then
install new shingles. I anticipate once the old shingles are off
I will hear that the sheathing needs repairs and the roof needs to
be vented. Should I go with stripping the old shingles? Should I
plan to replace the sheathing?

Una

Remove shingles and tar paper, do necessary repairs, add vents. Should
last 20 years, maybe more. Layering over old shingles might over
burden your roof when it needs that strength to hold the snow.