Perhaps the most striking
visual aspect , and in fact a defining feature of contemporary homes is the
low pitched roof, often less than 2:12. The most common original roofing
material is tar and gravel. A tar and gravel roof consists of layers of
asphalt and tar paper (or newer, more sophisticated materials) adhered with
applications of molten asphalt. The laminated layers get a top finish of
gravel, some of which becomes embedded in the hot asphalt, and some of which
lays loose on the surface of the roof. The purpose of the gravel is to
shield the asphalt from the damaging effect of sun exposure. It also
provides a nice finished appearance if well maintained. The life expectancy
of such a roof is 20 years.
The complexities arise
when doing repair or replacement, or addressing poorly done past repairs.
Homes that are 30 to 50 years old will certainly have had some roof work
done. In many cases, multiple generations of tar and gravel will have been
applied. This is problematic for a number of reasons-- primarily that tar
and gravel does not do well with multiple layers. The process for
subsequent layers of roofing is to sweep the loose gravel from the roof and
apply new layers of tar paper and hot asphalt. Okay in theory, but in
practice, the rough and sharp gravel surface of the original layer/s puts
the new layer at risk of damage. If the new roof is walked on (to maintain
the gravel, clean gutters and skylights, remove redwood debris) the new roof
membrane is likely to be punctured underfoot. Once the membrane has a hole,
even a tiny one, moisture can get between the layers of roofing, expand in
the heat causing a separation between layers, called a blister. In cold
weather particularly, the blisters become extremely brittle and exposed to
much greater damage by foot traffic. If a blister is broken, a large
water retaining pocket is opened up, increasing the chance of leaks. A second or third generation tar and
gravel roof has a life expectancy of only eight or ten years, but most
roofers recommend against doing secondary generations at all.
So what are the
alternatives? Removal of the existing roofing material is virtually
mandatory for whatever steps will follow. Removal is a substantial item,
both in terms of labor and disposal fee expenses. As an example, when the
three layers of tar and gravel were removed from this project, it took a crew of
six men two days, and the weight of the refuse was 20 tons!
The low pitch largely
defines the roofing materials that can be used. Manufacturers of
composition shingles, the most common and affordable roofing material for
general use, will not warrantee their materials on roofs with a pitch of less
than 2:12, which rules out its use on many modern homes. Certainly a new
tar and gravel roof is a possibility, though many roofers consider other
newer alternatives to be better. Torch-down is essential the same material
as in composition shingles but in roll form, with a layer of asphalt on the
back. That layer is heated with a gas torch to liquefy it and then it is
laid onto a substrate ply which has been tacked to the roof. Another
option is a combination of built up tar and substrate plies, topped with a
cap sheet that resembles composition shingle material in roll form, applied
to the roof with a layer of hot mopped asphalt. Each of these – and other
roof types—have their distinct advantages and supporters. Best to consult
with several roofing contractors to get a variety of viewpoints, and then
select based on your own specific criteria.
Many roofs, in particular
those over open beam ceilings, will have a layer of fiberboard (Firtex)
insulation, perhaps several layers, and probably only over the living areas
of the house. The old roof material will probably separate nicely from the
Firtex, so the Firtex layers can be left in tact. In homes with open beam
ceilings, leaving the Firtex in place has the advantage of limiting the
amount of filtration of dust and dirt and asphalt particles through the
roof planks and into the home interior during the reroof project. (In
areas where Firtex is not present, be prepared for a huge and filthy mess
caused by filtration). Areas covered by layers of Firtex once roofed over,
will be visibly higher than areas with no Firtex—potentially creating an odd
stepped appearance to the plane of the roof.
On homes with open beam
ceilings, electrical wires for any ceiling mounted devices will typically be
run on the exterior of the roof, under the roofing material. The wires may
be embedded under the Firtex or in grooves cut into the top of the Firtex,
or just laying on top of the Firtex, then covered over with the roofing
material. This suggest a few things:
the existing roofing material must be removed carefully to avoid damaging
the roof is removed, there is a rare opportunity to add or change wiring
for ceiling mounted devices;
when the new roof is applied, depending on material, a trace of the wire
paths may be visible.
One last word of advice:
if you’re buying a home with a tar and gravel roof, unless you are given
documentation of a recent roof removal and replacement, be skeptical of any
report that indicates that the roof is in good condition. Conscientious
roofers and roof inspectors consider tar and gravel roofs to be very
difficult to inspect and determine condition with any degree of certainty.
Unless you can personally observe the roof performing in a downpour, assume
major roof work to be imminent.
Removing the old roof material is a laborious task, scraping it up
and lifting it off with shovels.
roofing material has been removed, exposing the 2x8 tongue and groove roof
planking over the carport and garage. Firtex insulation over the living
areas is visible in the foreground. Note that the three layers of original
firtex insulation is stepped to minimize an abrupt elevation change in the
surface of the roof.
asphalt kettle transforms our driveway into the smoldering gates of hell
while D the hot-moppers do their thing top side.
E Rolls of
the first ply have been attached to the roof deck with hot asphalt. Note
electrical wires exposed on surface of roof deck being covered by the new
roof material. Again, the layers of original Firtex insulation are stepped
toward the edge of roof to minimize an abrupt elevation change.
plies have been applied. A skylight has been temporarily removed to allow
roofing material to be carefully wrapped up the surrounding curb.
G The final
cap sheet has been applied. Asphalt seeping out from the seams looks black
and shiny now, but will mellow with age. New filon skylight material is
fitted over the openings in the carport. Wiggle molding matches the
corrugated profile of the filon.