Do it Yourself: [DIY] Roofing insulation redux

02 March 2013

[DIY] Roofing insulation redux

After a month of pretty intensive research we
are focusing in to make a decision to insulate
our flat 1x8 tongue and groove roof on 10' centers
of 4x8 open beams//circa somewhere in the early '60s
without a ounce of insulation in the walls either!

Thanks again for all the public and private input
we have received, so we are back again for final thoughts
before we launch the project.

Our latest design we may go with is an R12 4x8x2 inch foam
board at about $30 a sheet with white roll asphalt
over and 3" flashing all around...we have about a 1500 sq
ft roof and plan to use 20 sq of roofing for about a 30%
overlap seal between rows covering the foam board.

We are stuck on how to fasten it to the existing roof..we
are thinking of 2 1/2 nails or screws with a 3/4 washer
and driving through both the asphalt and the foam board
into the roof boards without penetrating the roof boards
of course. The foam board can take 20psi so walking on it
is no problem.. foam board is not backed by OSB to reduce
cost by 10 bucks a sheet. Cost is about $1600 for the
foamboards, 1000 for the roll asphalt, 750 for roof
sealant, nails, tool rental,etc total job w/o labor
comes in about $4000. Contractor estimates we have
received are in the range of $18,500 to 22,700
so this DIY project has potential to save big bucks
(I am retired so no problem...labor is free...LOL)..

Any thoughts on the efficacy of this plan? THe fasteners
need some input?

Thanks,

Rich and Kate,
San Diego,Ca 20 miles inland so it gets HOT! buts cools
off at night nicely...used to have $500 a month A/C costs.