I just read your column on low sloped roof and would like your opinion
on proposals to re-roof my house with a low sloped, 2:12 roof. It is a
one storey with a simple gable roof of 3000 square feet. It currently
has 2 roofs: an asphalt and gravel (installed in 1972) over 1 X 6
planks. And, a second roof of 30 year dimensional shingles over the
first roof (installed in 1993). I am replacing the roof because of
leaks from the current solar system that was installed on the west
side half of the roof. It has 72 screws through the roof to hold the
panels in place (installed in 1993)
(Jon)Duane thanks for reading. You have several problems. A 2/12 is the minimum slope for composition roofs, and I mean minimum.
1) You should have removed the built up roof (asphalt and gravel) or at least remove the gravel. If the plane of the roof is not completely smooth, you might lose the 2/12, thereby leak.
2) The cheaper three tab shingles will work better because they lay flatter and you’re paying extra for a 30 year you can’t see.
3) Plank decks tend to crack and cup, causing a loss of pitch and/or leaking.
Let’s review the bid.
1. Tear off both roofs, replace any deteriorated 1 X 6 and add 7/16"
OSB over the 1 X 6 planks. Install 3" stand-offs on the rafters for
new Sealed Air panels on the west side of the roof and flash with 12"
X 12". Ridged solar panels will be mounted off the roof on steel
stringers bolted to the 3" standoffs. Install two layers of 15 pound
felt. Install 30 year Certain Teed Landmark shingles (Certain Teed said
they will warrant the shingles if installed per their specifications
and roofer will follow them).
Jon: Pretty good so far. The only thing different I’d do is either pulls off the plank deck and install radiant barrier OSB with edge support, “H” clips. If you put a deck over a deck it is my understanding it is best to separate them with rosin paper or felt but since the existing deck is plank the issue is lessened than if it were plywood. You can leave the deck and install furring strips every two feet, with edge support, prior to installing the radiant barrier deck. I recommend Techshield. The aluminum seems more difficult to damage than on Solar Board, but it too is a good product.
If freezing and torrential rains are not an issue then “WinterGuard” is not necessary. Otherwise I’d put it at least on the roof penetrations.
2. Same as 1, above, except use 3-tab shingles: Either Malarkey Durra-
Seal 25 year or Malarkey Alaskan 35 year shingles.
Jon: Forget Malarkey. They do not respond to complaints easily. I cannot believe the level of either corruption or ineptness to which they have handled the roof complaints I’ve had with them or others I’ve heard about. Stick with Certainteed. They have all the products you could ever need to choose from.
3. Tear off both roofs, replace any deteriorated 1 X 6 and install a
traditional built up roof with number 3 granite gravel. Option is to
add 1/2" fiberboard instead of base layer. Solar panels to be
installed as noted above, off the roof. With fiberboard this would be
the most expensive roof.
Jon: I’d go with this one but I’m a roofer. Don’t forget to make sure the solar panels are not installed to insulation. The weight will cause them to sink. After removing everything, and inspecting the deck and insulation, decide. At this time, as the deck is so close to the ceiling, especially on the outside perimeter, you could install foil faced insulation, with the foil up.
Do you have no attic? No discussion of ventilation was made
I am sure that you are very busy but any response would be greatly
Ventura, California (6 miles from the coast and 60 miles north of Los
Angeles where we seldom get freezing temperatures and average about 16
inches of rain a year)