This home was completed in late 1965 and originally had a gravel roof I
was able to keep painted white. Insurance required replacing roof so now
it is 30-year asphalt shingle. Old A/C having a hard time keeping up with
heat load so I'm thinking of installing 2 inch foil backed polystyrene
between the "rafter" portion of the trusses. This foam would be installed
flush with the bottom side of the "rafters" leaving an airspace of one and
one half inches between the upper surface of the foam and the lower
surface of the roof planks/sheathing.

The new roof has a ridge vent and there are vented soffits along both of
the lower roof portions. This looks to me like it would provide adequate
venting of the heat built up during our sunny days. I'm wondering if the 2
inches of foam, along with the foil as a radiant barrier, will do enough
to reduce the heat load in the attic to allow the A/C ductwork to operate
more efficiently thereby keeping the living space more comfortable. The
ceiling has original blown-in fiberglass at three and a half inches. Not
great but that's all the space we have to insulate. Also, I am tempted to
install this foam with the radiant barrier up since there will be a 1 &
1/2 inch airspace above for it to work. Any thoughts would be welcome.

--

On Tuesday, June 2, 2015 at 10:44:05 PM UTC-4, William wrote:
This home was completed in late 1965 and originally had a gravel roof I
was able to keep painted white. Insurance required replacing roof so now
it is 30-year asphalt shingle. Old A/C having a hard time keeping up with
heat load so I'm thinking of installing 2 inch foil backed polystyrene
between the "rafter" portion of the trusses. This foam would be installed
flush with the bottom side of the "rafters" leaving an airspace of one and
one half inches between the upper surface of the foam and the lower
surface of the roof planks/sheathing.

The new roof has a ridge vent and there are vented soffits along both of
the lower roof portions. This looks to me like it would provide adequate
venting of the heat built up during our sunny days. I'm wondering if the 2
inches of foam, along with the foil as a radiant barrier, will do enough
to reduce the heat load in the attic to allow the A/C ductwork to operate
more efficiently thereby keeping the living space more comfortable. The
ceiling has original blown-in fiberglass at three and a half inches. Not
great but that's all the space we have to insulate. Also, I am tempted to
install this foam with the radiant barrier up since there will be a 1 &
1/2 inch airspace above for it to work. Any thoughts would be welcome.

--

Why I can't you get more than 3 1/2" of insulation between the
living space and the attic? THAT is the main problem. What you're
proposing would help, but the real and bigger problem is the lack
of proper insulation where it belongs. The other issue is that
if you do what you're proposing, it leaves the core of the attic
unventilated, because air will flow from soffits to ridge inside
the new insulation system. I guess you'd probably still have enough
air flow in the rest of the attic that moisture wouldn't be a problem,
but without knowing the details, IDK.

Hi William,

This home was completed in late 1965 and originally had a gravel roof
I was able to keep painted white. Insurance required replacing roof so
now it is 30-year asphalt shingle.

Can you describe the roof structure in more detail?

I always think of a gravel roof as a flat or low slope roof. If that's
the case, asphalt shingles aren't really made for low slopes. Wind blown
rain can easily back up under shingles on low slopes. I hope an ice and
water membrane was installed under the shingles.

Old A/C having a hard time keeping up with heat load so I'm thinking
of installing 2 inch foil backed polystyrene between the "rafter"
portion of the trusses. This foam would be installed flush with the
bottom side of the "rafters" leaving an airspace of one and one half
inches between the upper surface of the foam and the lower surface
of the roof planks/sheathing.
The new roof has a ridge vent and there are vented soffits along both
of the lower roof portions. This looks to me like it would provide
adequate venting of the heat built up during our sunny days. I'm
wondering if the 2 inches of foam, along with the foil as a radiant
barrier, will do enough to reduce the heat load in the attic to allow
the A/C ductwork to operate more efficiently thereby keeping the
living space more comfortable. The ceiling has original blown-in
fiberglass at three and a half inches. Not great but that's all the
space we have to insulate. Also, I am tempted to install this foam
with the radiant barrier up since there will be a 1 & 1/2 inch
airspace above for it to work. Any thoughts would be welcome.

If you have room to get in and install the foam, you should be able to
add more blown-in insulation instead. The standard solution is to install
foam baffles in each rafter bay so you don't block the air flow when you
add more insulation.

That will be easier, cheaper, and more effective than adding foam boards
to the trusses.

Good luck,

Anthony Watson
www.mountainsoftware.com
www.watsondiy.com

On Wed, 3 Jun 2015 15:29:31 +0000 (UTC), HerHusband
wrote:

Can you describe the roof structure in more detail?

Since this is another OLD thread brought back from the past, no one will
explain the structure.

On Wed, 03 Jun 2015 13:21:38 -0500, wrote:

On Wed, 3 Jun 2015 15:29:31 +0000 (UTC), HerHusband
wrote:

Can you describe the roof structure in more detail?

Since this is another OLD thread brought back from the past, no one will
explain the structure.

And you know this exactly _how_, Home Guy!

I'm not buying it.

On Wed, 03 Jun 2015 02:44:02 +0000, William
wrote:

This home was completed in late 1965 and originally had a gravel roof I
was able to keep painted white. Insurance required replacing roof so now
it is 30-year asphalt shingle. Old A/C having a hard time keeping up with

Is that because the old roof was white and the new roof isn't?

heat load so I'm thinking of installing 2 inch foil backed polystyrene
between the "rafter" portion of the trusses. This foam would be installed
flush with the bottom side of the "rafters" leaving an airspace of one and
one half inches between the upper surface of the foam and the lower
surface of the roof planks/sheathing.

On Wednesday, June 3, 2015 at 11:30:49 AM UTC-4, HerHusband wrote:
Hi William,

This home was completed in late 1965 and originally had a gravel roof
I was able to keep painted white. Insurance required replacing roof so
now it is 30-year asphalt shingle.

Can you describe the roof structure in more detail?

I always think of a gravel roof as a flat or low slope roof. If that's
the case, asphalt shingles aren't really made for low slopes. Wind blown
rain can easily back up under shingles on low slopes. I hope an ice and
water membrane was installed under the shingles.


Good catch. I missed that. I agree, going from a
from a gravel roof on a house to shingles doesn't add up.

replying to trader_4 , William wrote:
trader4 wrote:

Why I can't you get more than 3 1/2" of insulation between the
living space and the attic? THAT is the main problem. What you're
proposing would help, but the real and bigger problem is the lack
of proper insulation where it belongs. The other issue is that
if you do what you're proposing, it leaves the core of the attic
unventilated, because air will flow from soffits to ridge inside
the new insulation system. I guess you'd probably still have enough
air flow in the rest of the attic that moisture wouldn't be a problem,
but without knowing the details, IDK.


Thank you for your input trader4. The trusses are 2X4 so without raising
the attic floor I don't see how I could get more than 3 1/2" of insulation
between the living space and the attic. I have been supplementing the
original blown-in insulation with bats where needed but not any more than
3 1/2 inches in thickness. As for ventilation, I intend to leave open
space between the foam pieces at the ridge line (about 4 or 5 inches
between them) so that the attic air space will be ventilated through the
ridge vent. My main concern with the attic right now is to try to keep the
sun-sourced heat buildup to a minimum during the daytime hours. I'm
thinking that the 1 1/2 inch space between the top of the foam and the
underside of the roofing planks will aid the radiant barrier at the top of
the foam while also allowing the heat to escape through the ridge vent,
along with whatever heat builds up inside the attic space during the day
(through the ridge vent). The insulating properties of the foam, I am
assuming, will slow the transfer of heat from that 1 1/2 inch air space
above the foam to the attic air space below the foam. I just don't have
any experience with this type of application so I don't know if 1) it will
work at all, 2) it might work some or 3) the benefit will outweigh the
cost. I am willing to do the work myself so labor cost will be minimal and
the square foot area of the roof is only about 2,000 sq. ft. so I'm
guessing the material cost will be easily handled as well.

I estimate the roof to be about a three-twelve pitch (maybe four-twelve)
and the asphalt shingles have held up well for over three years (no
leaking) and during that time there have been a few wind-blown rains
during that time so I'm not particularly concerned about the water
tightness of the roofing. The shingles are "white" but not as reflective
as the roof coating I had applied to the gravel roof so the net effect has
been that the A/C has had to work harder to try to keep the living space
cool and it has not been able to keep up with it. We also have poor
windows and a generally inefficient home in terms of
insulation/emissivity. This attempt to slow the heat transfer through the
roofing is the first step in getting this home to be more efficient.
Thanks for your concern.

--

William,

The trusses are 2X4 so without raising the attic floor I don't see
how I could get more than 3 1/2" of insulation between the living
space and the attic.

There is no problem covering the bottom chord of the truss. That is
standard practice. Wood isn't the greatest insulator so it's actually
beneficial to cover that bottom chord with insulation.

Just add baffles in each rafter bay so the ventilation isn't restricted,
then add as much insulation as you want. If the attic is tall enough to
allow ventilation, you can easily add 12" or more of insulation.

Blown in would probably be easiest, but you can also layer batt insulation
too. Just make sure your batts do not have a vapor barrier attached, and
ideally run each layer at right angles to cover the gaps of the previous
layer (You're trying to minimize air flow between the batts).

the insulating properties of the foam, I am assuming,
will slow the transfer of heat

Foam insulation is expensive and difficult to install. Batts or blown
insulation will be easier and cost less.

I estimate the roof to be about a three-twelve pitch (maybe
four-twelve) and the asphalt shingles have held up well for over three
years (no leaking)

3/12 is about the minimum slope for shingles, but it's doable if you have
an ice and water membrane, or a double coverage of roofing felt.

Good luck,

Anthony Watson
www.mountainsoftware.com
www.watsondiy.com

On Friday, June 5, 2015 at 1:31:01 AM UTC-4, HerHusband wrote:
William,

The trusses are 2X4 so without raising the attic floor I don't see
how I could get more than 3 1/2" of insulation between the living
space and the attic.

There is no problem covering the bottom chord of the truss. That is
standard practice. Wood isn't the greatest insulator so it's actually
beneficial to cover that bottom chord with insulation.


I've never seen 2x4 trusses used for the bottom of the attic/ceiling
of the living space. But if that's what's there, then I agree with
the above observation. Only problem is he said the attic has a floor
and depending on how much of it has floor, how many nails were used,
etc., it could be some trouble removing plywood to get the insulation
in.

replying to HerHusband , William wrote:
unknown wrote:

Hi William,
Can you describe the roof structure in more detail?
I always think of a gravel roof as a flat or low slope roof. If that's
the case, asphalt shingles aren't really made for low slopes. Wind blown
rain can easily back up under shingles on low slopes. I hope an ice and
water membrane was installed under the shingles.
If you have room to get in and install the foam, you should be able to
add more blown-in insulation instead. The standard solution is to install
foam baffles in each rafter bay so you don't block the air flow when you
add more insulation.
That will be easier, cheaper, and more effective than adding foam boards
to the trusses.
Good luck,
Anthony Watson
www.mountainsoftware.com
www.watsondiy.com


Anthony, thank you, as well, for your reply. Please see the reply to
trader_4 above for details on roof structure. The original roof material
looked like tar with embedded gravel and was about 1 inch thick. Gravel
stop was used along the fascia so it looked to me like a gravel roof;
apparently common in this area of Florida during the time this home was
built (1960s). I'll take a look at your suggested method of blown-in with
foam baffles. Thanks for your input.

--

I've never seen 2x4 trusses used for the bottom of the attic/ceiling
of the living space.

Trusses are almost always built with 2x4's, except for specialized trusses
like attic trusses.

Only problem is he said the attic has a floor and depending on how
much of it has floor, how many nails were used, etc., it could be
some trouble removing plywood to get the insulation in.

Did he mention an attic floor? I must have missed that.

If that's true, adding insulation will be problematic. Also, as you said,
the bottom 2x4 chords won't carry any significant weight, certainly not for
a living area in the attic.

Anthony Watson
www.mountainsoftware.com
www.watsondiy.com

On Friday, June 5, 2015 at 12:55:42 PM UTC-4, HerHusband wrote:
I've never seen 2x4 trusses used for the bottom of the attic/ceiling
of the living space.

Trusses are almost always built with 2x4's, except for specialized trusses
like attic trusses.

Only problem is he said the attic has a floor and depending on how
much of it has floor, how many nails were used, etc., it could be
some trouble removing plywood to get the insulation in.

Did he mention an attic floor? I must have missed that.

IDK what WTF exactly he has, because the description hasn't
been clear. gravel roof? shingles? trusses? If you don't
have an attic, then how are you doing what he proposes,
unless you're tearing out the ceiling of the living space?

HerHusband wrote:
I've never seen 2x4 trusses used for the bottom of the attic/ceiling
of the living space.

Trusses are almost always built with 2x4's, except for specialized
trusses like attic trusses.

Only problem is he said the attic has a floor and depending on how
much of it has floor, how many nails were used, etc., it could be
some trouble removing plywood to get the insulation in.

Did he mention an attic floor? I must have missed that.

If that's true, adding insulation will be problematic. Also, as you
said, the bottom 2x4 chords won't carry any significant weight,
certainly not for a living area in the attic.


I saw nothing about floors in the O.P. and highly doubt floors would be
installed in a truss roof.

Does anyone do that?

On Friday, June 5, 2015 at 2:28:07 PM UTC-4, Bob F wrote:
HerHusband wrote:
I've never seen 2x4 trusses used for the bottom of the attic/ceiling
of the living space.

Trusses are almost always built with 2x4's, except for specialized
trusses like attic trusses.

Only problem is he said the attic has a floor and depending on how
much of it has floor, how many nails were used, etc., it could be
some trouble removing plywood to get the insulation in.

Did he mention an attic floor? I must have missed that.

If that's true, adding insulation will be problematic. Also, as you
said, the bottom 2x4 chords won't carry any significant weight,
certainly not for a living area in the attic.


I saw nothing about floors in the O.P. and highly doubt floors would be
installed in a truss roof.

Does anyone do that?

Not in the first post, but in his second:

"The trusses are 2X4 so without raising
the attic floor I don't see how I could get more than 3 1/2" of insulation
between the living space and the attic. I have been supplementing the
original blown-in insulation with bats where needed but not any more than
3 1/2 inches in thickness. "

Which is why I said we still don't know what he actually has.
If the attic doesn't have a floor, then why can't he install
more than 3 1/2" on insulation? It was a gravel roof, now
it's shingle? In any case, I've said from my first post that
his real problem is that he only has 3 1/2" of insulation
between the attic and the living space and that is what he
should focus on fixing.