Roofing - Tear Off or Overlay
|The question often comes up about whether an
existing composition shingle roof should be torn off or if an overlay (or
recover) is possible. Overlays save on time, labor, and disposal costs. If
the existing roof has only one layer, lays flat, and there aren’t any
problems with the roof deck, removal is not necessary.
whether you overlay or tear off, you should properly ventilate your attic.
In almost all cases, continuous soffit and ridge vents will provide maximum
cross ventilation. For more information on ventilation, visit
If any of the following are true, a complete tear-off of the existing
roof system(s) should be considered.
- Too many layers – If a roof has more than one layer of roofing, the
roof should be torn off. In most cases this is a code requirement. Codes
rarely permit more than two layers of roofing. To determine this, all
you need to do is contact your local building inspections department.
- Bad decking - if spongy areas are noticed when walking on a roof, or
if you see sags between the rafters or trusses, there's a chance that
some of the roof deck may be deteriorating or be damaged. Deterioration
can be attributed to dry rot or delamination of the plies in the plywood
due to glue failure. Dry rot is wood rot caused by certain types of
fungi and if it isn't taken care of, it can spread. If there is
suspicion of bad decking, then a full tear off should seriously be
- Ice dams - ice dams can be a big problem. In areas where there the
average January temperature can be below 30° F, and no ice and water
protection membrane is present on a roof, then a full tear off should be
considered. Twenty year old buildings with no ice and water protection
and no prior problems, can suddenly experience thousands of dollars in
damage when a freak cold front hits. For more information on ice dams,
- Incompatible shingles - if a heavy weight architectural style shingle
is used to cover a light weight strip shingle such as 3-tabs, then the
roof will look good. However, if a light weight shingle is used to cover
a heavy weight shingle, the light weight shingles have a tendency to
show all the bumps and ridges (called telegraphing) and won't look good.
- Existing roof is in poor condition - if the existing roof is in really
poor shape, such as tabs being severely curled or if the rows are
crooked, then complete tear off and replacment should be considered.
- Shorter Life Span - There is no known documented research, but most
roofing professionals agree that with an overlay, the average lifespan
of the shingles will be shortened by about 10%-20%.