Plywood-over-Asphalt Shingles Question
frank1492
proposing to lay down 3/8" plywood before reshingling.
This is on an old garage. If the job lasts 20 years, that
is enough.
I am really not looking for a purist's solution here. I
realize that the only one of those would be remove all the
old shingles and start over. I am looking for something
that will work and look REASONABLY well while developing
virtually nothing to dispose of.
I have been told that condensation and excessive
weight might be problems with my proposed solution. The weight
I know will not be an issue, but I don't know about the condensation.
That's why I'm here- to have your overall opinion.
Thanks very much for your help!
Frank
Chip
"frank1492" <fran...@worldnet.att.net> wrote in message
news:lm3eju04oo2ttn6om...@4ax.com...
: As the underlying asphalt is somewhat irregular, I am
an unconventional approach, but i have seen this done when we tore roofs
off...cant answer about the condensation...without seeing it, i would say to
just re-roof over the existing, if you *butt* the new shingles into the
existing, instead of *bridging* the existing, you can make the new roof look
as though there is just a single layer, without any humps in it...just need
to nail down any large bubbles/humps...your starter and first course are the
only ones that take any cutting material, then you just butt the new into
the old...maybe a little more to it than that, but thats the basics...
putting the ply over the existing sounds too much like work for the end
result, myself i would tear off the old...if you're set on doing this idea,
a large drip edge around the whole perimeter will hide the old shingle also,
i would make sure my ply edges, end up on a rafter and that you nail into
all rafters, and not just through the existing sheathing...
chip
frank1492
I had planned to use the "butt" method anyway, but you
would have to see this roof to understand why that would only
be a partial solution. These shingles were put on in the forties
(yep that's right) and they are a double-thick shingle that have
bumps and warped areas too numerous to count. I had thought
about trying to grind the bumps off but that that would be a
pretty time-consuing task with questionable results. The same
would be true if I tried to flatten the humps down with nails.
I think somebody should design a shingle grinder, much like
a drum sander for floors, that could be used in this kind of
situation.
I did think about the drip edge too. As for nailing into the
rafters, good idea but I would think that would be tricky. We're
talking about a good foundation of 3/4 tongue-and-groove
boards here. I'd consider using deck screws as well.
Dealing with 4x8 plywood sheets, what would be the
suggested locations/spacing of the nails/screws to achieve
best results?
(Thank you so much for your time on this!)
Frank
Chip
: Thank you Chip. Everything you have said makes sense.
: I had planned to use the "butt" method anyway, but you
: would have to see this roof to understand why that would only
: be a partial solution. These shingles were put on in the forties
: (yep that's right) and they are a double-thick shingle that have
: bumps and warped areas too numerous to count. I had thought
: about trying to grind the bumps off but that that would be a
: pretty time-consuing task with questionable results. The same
: would be true if I tried to flatten the humps down with nails.
: I think somebody should design a shingle grinder, much like
: a drum sander for floors, that could be used in this kind of
: situation.
: I did think about the drip edge too. As for nailing into the
: rafters, good idea but I would think that would be tricky. We're
: talking about a good foundation of 3/4 tongue-and-groove
: boards here. I'd consider using deck screws as well.
: Dealing with 4x8 plywood sheets, what would be the
: suggested locations/spacing of the nails/screws to achieve
: best results?
: (Thank you so much for your time on this!)
: Frank
i would fasten every 6" on edges, and every 12" in the field, if you're not
using the rafters to nail to, i would still go every 24" or 16" apart (thats
a whole bunch of screws if you decide to screw it in)... i know about those
shingles from the 40's, run into old wrappers when we tear off, seems a
popular style was called *thick butt*, i had to chuckle the first time i
seen that, had to be one heck of a shingle...
chip
frank1492
into the rafters. Is there a quick trick to knowing where the
rafters are when you're on the roof??? (Would a stud finder
work?)
These were reputed to be Bird "double butts." They were
put on the roof right after the '44 hurricane which hit Cape Cod
really bad. (This house is on a bay. The roof on the house is
still in pretty good shape, as is one side of the garage. The
problem is on the side of the garage that faces south into
most of the weather.)
I do not expect the new shingles to last as well!
I look at it this way. The shingles and plywood for
a 12 X24' area will run me under $400. I'm on vacation so
I have the time to do it. What's the worst thing that could
happen?
Seems to me it's worth a try!
I would use 1/4" plywood, but the local yard only carries
3/8" and up. Do you think 1/4" would be thick enough.
Frank
Chip
: Thank you again. I probably won't be using screws if I can get
: into the rafters. Is there a quick trick to knowing where the
: rafters are when you're on the roof??? (Would a stud finder
: work?)
: These were reputed to be Bird "double butts." They were
: put on the roof right after the '44 hurricane which hit Cape Cod
: really bad. (This house is on a bay. The roof on the house is
: still in pretty good shape, as is one side of the garage. The
: problem is on the side of the garage that faces south into
: most of the weather.)
: I do not expect the new shingles to last as well!
: I look at it this way. The shingles and plywood for
: a 12 X24' area will run me under $400. I'm on vacation so
: I have the time to do it. What's the worst thing that could
: happen?
: Seems to me it's worth a try!
: I would use 1/4" plywood, but the local yard only carries
: 3/8" and up. Do you think 1/4" would be thick enough.
: Frank
i would stick with the 3/8"...to find the rafters, tap with a hammer, will
sound more solid, you only need to find one, or look from inside the garage,
run a screw up along side a rafter from the inside, then just come back 3/4"
for your center (unless you have true 2x material,then come back 1" for the
center) measure from outside, then do your 16 or 24 on centers, however far
your rafters are spaced...keep in mind, securing the edges of the ply would
be the important part in this application, especially if you use 1 & 1/4"
roofing nails, the sheathing will be nailed down secure from the roofing
nails penetrating into the existing sheathing...use 8's to nail the edges of
ply...and you're right, the new shingles probably wont last as long...Bird
was bought by Certainteed, no doubt those old shingles were organic, which
seem to last forever...
chip
John Willis
<fran...@worldnet.att.net> scribbled this interesting note:
>As the underlying asphalt is somewhat irregular, I am
>proposing to lay down 3/8" plywood before reshingling.
>This is on an old garage. If the job lasts 20 years, that
>is enough.
Unless your garage is rather larger than average, you won't really be
saving any time with this proposal. It does not take all that long to
tear shingles off a garage. If you are careful with your trash
management, clean up is also easy (we put down dropcloths around the
perimeter of the houses we work on to help in this regard). A side
benefit to tearing off the old roof is you get to check the top side
of the existing decking for damage, cracks, etc. that may not be
apparant from underneath.
If a customer of mine suggested this unconventional approach to
re-roofing a garage, I'd try to direct that customer towards a simple
tear-off and re-roof, even though, in my opinion, your proposal would
generate a higher priced job because of the added expense of materials
and installation.
Just my $0.02
--
John Willis