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Posted by kio.ami on June 30, 2007, 12:07 pm
I did a lot of googling to try and come up with an answer, but I
couldn't find anything addressing my situation.
I have a standard early 1980s suburban house in Texas with a vented
roof. The A/C unit ductwork is in the attic, but only the attic floor
is insulated (blown fiberglass). Obviously, this isn't an efficient
use of the A/C unit since the attic heats up the cool air in the
ductwork before it reaches us. However, we have a very good A/C unit
(home's original owner was an HVAC engineer) with a fully programmable
thermostat and smart home layout (only 2 windows face west), so our
electric bill never gets beyond $250 even in the nastiest summer.
Even so, I'd like to improve the attic temperature so the A/C won't
have to work as hard.
I've researched local insulation companies, and they push the spray on
radiant barrier (cost ~$2500) that's applied to the roof deck. We
can't use the foil radiant barrier because it would block our TV
signal (antenna in attic space) & cell reception (no land line). I
don't mind the price, but anecdotes that I've found range from "didn't
do anything" to "dropped my attic temp 30degrees". The one
insulation installer who came and looked at our house admitted that
radiant barrier wouldn't have a great ROI for us -- it'd probably take
~7-9yrs to fully pay for itself.
However, I've been looking at open cell spray-on foam insulation for
the roof deck -- specifically Sealection 500 -- and every review I've
seen said that it works beautifully. Ideally, it's supposed to be
used with an unvented attic, but I was wondering if it'd buy you
anything in a vented attic. My semi-educated guess is yes, but I'd be
interested in hearing educated opinions.
TIA,
ami
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Posted by Rick Blaine on June 30, 2007, 12:26 pm
kio.ami@gmail.com wrote:
show/hide quoted text
>I have a standard early 1980s suburban house in Texas with a vented
>roof. The A/C unit ductwork is in the attic, but only the attic floor
>is insulated (blown fiberglass). Obviously, this isn't an efficient
>use of the A/C unit since the attic heats up the cool air in the
>ductwork before it reaches us.
Assuming the blown in insulation is up to spec, I'd bet you get a far better
payback by making sure all the ac ducts are sealed and insulated and that the
attic is well ventilated. Look into things like a ridge vent with lots more
soffit vents. Worse case, you could put a power vent in there as well, but you
still will need lots of soffit vents.
show/hide quoted text
>However, I've been looking at open cell spray-on foam insulation for
>the roof deck -- specifically Sealection 500 -- and every review I've
>seen said that it works beautifully. Ideally, it's supposed to be
>used with an unvented attic, but I was wondering if it'd buy you
>anything in a vented attic. My semi-educated guess is yes, but I'd be
>interested in hearing educated opinions.
If you insist on spraying foam, you could look at this:
http://www.tigerfoam.com/ but I suspect you will be wasting money at best and
creating a bigger problem worse case.
"Tell me what I should do, Annie."
"Stay. Here. Forever." - Life On Mars
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Posted by ransley on June 30, 2007, 12:48 pm
show/hide quoted text
> kio....@gmail.com wrote:
> >I have a standard early 1980s suburban house in Texas with a vented
> >roof. The A/C unit ductwork is in the attic, but only the attic floor
> >is insulated (blown fiberglass). Obviously, this isn't an efficient
> >use of the A/C unit since the attic heats up the cool air in the
> >ductwork before it reaches us.
> Assuming the blown in insulation is up to spec, I'd bet you get a far better
> payback by making sure all the ac ducts are sealed and insulated and that the
> attic is well ventilated. Look into things like a ridge vent with lots more
> soffit vents. Worse case, you could put a power vent in there as well, but you
> still will need lots of soffit vents.
> >However, I've been looking at open cell spray-on foam insulation for
> >the roof deck -- specifically Sealection 500 -- and every review I've
> >seen said that it works beautifully. Ideally, it's supposed to be
> >used with an unvented attic, but I was wondering if it'd buy you
> >anything in a vented attic. My semi-educated guess is yes, but I'd be
> >interested in hearing educated opinions.
> If you insist on spraying foam, you could look at
this:http://www.tigerfoam.com/but I suspect you will be wasting money at best and
show/hide quoted text
> creating a bigger problem worse case.
> --
> "Tell me what I should do, Annie."
> "Stay. Here. Forever." - Life On Mars
The attic is vented, unheated, the floor is what needs more
insulation, foams go to R7.5, some are only R 4
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Posted by Joseph Meehan on June 30, 2007, 1:02 pm
kio.ami@gmail.com wrote:
show/hide quoted text
> I did a lot of googling to try and come up with an answer, but I
> couldn't find anything addressing my situation.
> I have a standard early 1980s suburban house in Texas with a vented
> roof. The A/C unit ductwork is in the attic, but only the attic floor
> is insulated (blown fiberglass). Obviously, this isn't an efficient
> use of the A/C unit since the attic heats up the cool air in the
> ductwork before it reaches us. However, we have a very good A/C unit
> (home's original owner was an HVAC engineer) with a fully programmable
> thermostat and smart home layout (only 2 windows face west), so our
> electric bill never gets beyond $250 even in the nastiest summer.
> Even so, I'd like to improve the attic temperature so the A/C won't
> have to work as hard.
> I've researched local insulation companies, and they push the spray on
> radiant barrier (cost ~$2500) that's applied to the roof deck. We
> can't use the foil radiant barrier because it would block our TV
> signal (antenna in attic space) & cell reception (no land line). I
> don't mind the price, but anecdotes that I've found range from "didn't
> do anything" to "dropped my attic temp 30degrees". The one
> insulation installer who came and looked at our house admitted that
> radiant barrier wouldn't have a great ROI for us -- it'd probably take
> ~7-9yrs to fully pay for itself.
> However, I've been looking at open cell spray-on foam insulation for
> the roof deck -- specifically Sealection 500 -- and every review I've
> seen said that it works beautifully. Ideally, it's supposed to be
> used with an unvented attic, but I was wondering if it'd buy you
> anything in a vented attic. My semi-educated guess is yes, but I'd be
> interested in hearing educated opinions.
> TIA,
> ami
No. You don't want to insulate the roof deck. Doing so may shorten the
life of your roof. The problem is the lack of or insufficient quality of
insulation on the ducts. You also want to add insulation to the attic
floor as I am sure the standards of the 1980's were not what they are today.
Insulate the ducts first and the attic floor next. Make sure you have
at least minimum current code venting for the attic as well.
--
Joseph Meehan
Dia 's Muire duit
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Posted by CJT on June 30, 2007, 4:12 pm
Joseph Meehan wrote:
show/hide quoted text
> kio.ami@gmail.com wrote:
>
>>I did a lot of googling to try and come up with an answer, but I
>>couldn't find anything addressing my situation.
>>I have a standard early 1980s suburban house in Texas with a vented
>>roof. The A/C unit ductwork is in the attic, but only the attic floor
>>is insulated (blown fiberglass). Obviously, this isn't an efficient
>>use of the A/C unit since the attic heats up the cool air in the
>>ductwork before it reaches us. However, we have a very good A/C unit
>>(home's original owner was an HVAC engineer) with a fully programmable
>>thermostat and smart home layout (only 2 windows face west), so our
>>electric bill never gets beyond $250 even in the nastiest summer.
>>Even so, I'd like to improve the attic temperature so the A/C won't
>>have to work as hard.
>>I've researched local insulation companies, and they push the spray on
>>radiant barrier (cost ~$2500) that's applied to the roof deck. We
>>can't use the foil radiant barrier because it would block our TV
>>signal (antenna in attic space) & cell reception (no land line). I
>>don't mind the price, but anecdotes that I've found range from "didn't
>>do anything" to "dropped my attic temp 30degrees". The one
>>insulation installer who came and looked at our house admitted that
>>radiant barrier wouldn't have a great ROI for us -- it'd probably take
>>~7-9yrs to fully pay for itself.
>>However, I've been looking at open cell spray-on foam insulation for
>>the roof deck -- specifically Sealection 500 -- and every review I've
>>seen said that it works beautifully. Ideally, it's supposed to be
>>used with an unvented attic, but I was wondering if it'd buy you
>>anything in a vented attic. My semi-educated guess is yes, but I'd be
>>interested in hearing educated opinions.
>>TIA,
>>ami
>
>
> No. You don't want to insulate the roof deck. Doing so may shorten the
> life of your roof.
There is a lot of conflicting information on that. I seriously doubt
it's true.
The problem is the lack of or insufficient quality of
show/hide quoted text
> insulation on the ducts. You also want to add insulation to the attic
> floor as I am sure the standards of the 1980's were not what they are today.
>
> Insulate the ducts first and the attic floor next. Make sure you have
> at least minimum current code venting for the attic as well.
>
>
--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form che...@prodigy.net.
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>roof. The A/C unit ductwork is in the attic, but only the attic floor
>is insulated (blown fiberglass). Obviously, this isn't an efficient
>use of the A/C unit since the attic heats up the cool air in the
>ductwork before it reaches us.