Add fan for circulation WITHIN attic?


N

Nexus7

I've come across a situation that seems unlike any I've seen discussed
here, but this is probably common in 30-40 year old houses. This is an
approx 20x80 sq ft raised ranch (a basement and 1 floor of living
space) with a hip roof. The attic has loose fill fiber, about 4", but
it's pretty uneven and dusty (30 years will do that). In addition,
insulation has settled deep into the bathroom and kitchen walls, so
that if the vanity cabinet in the bathroom is removed, the bathroom
wall is open to the attic. There's a ridge vent running along the
middle 2/3 of the length of the ridge, and 3-4 passive vents halfway
down the roof. While adding some batts seems an obvious way to increase
the efficiency of the roof, there are two problems.
- the hip roof overhangs about 3 ft in the front of the house, and this
is the only place where there are 2 soffit vents
- with the lack of soffit vents along the other 3 sides, air may short
circuit between the ridge and passive vents

I was wondering if, after adding another 8" of batts, it makes sense to
have a small (6 or 8") fan going at low speed, at around half the
height of the attic. This could circulate the air enough that moisture
(and heat in the summer) would circulate with the outside air through
the vents.

Also wondering if laying some Tyvek before laying down the batts where
the roof is open to the walls of the living space would be advisable.
 
S

SQLit

Nexus7 said:
I've come across a situation that seems unlike any I've seen discussed
here, but this is probably common in 30-40 year old houses. This is an
approx 20x80 sq ft raised ranch (a basement and 1 floor of living
space) with a hip roof. The attic has loose fill fiber, about 4", but
it's pretty uneven and dusty (30 years will do that). In addition,
insulation has settled deep into the bathroom and kitchen walls, so
that if the vanity cabinet in the bathroom is removed, the bathroom
wall is open to the attic. There's a ridge vent running along the
middle 2/3 of the length of the ridge, and 3-4 passive vents halfway
down the roof. While adding some batts seems an obvious way to increase
the efficiency of the roof, there are two problems.
- the hip roof overhangs about 3 ft in the front of the house, and this
is the only place where there are 2 soffit vents
- with the lack of soffit vents along the other 3 sides, air may short
circuit between the ridge and passive vents

I was wondering if, after adding another 8" of batts, it makes sense to
have a small (6 or 8") fan going at low speed, at around half the
height of the attic. This could circulate the air enough that moisture
(and heat in the summer) would circulate with the outside air through
the vents.

Also wondering if laying some Tyvek before laying down the batts where
the roof is open to the walls of the living space would be advisable.

Google for R values for your area then you might be able to make some
decisions.

I just added R-30 of blown to a 1977 home. A/c bill dropped in half the
next month.
According to the FEDS, My home needs, either R-30, R-38 or R-43. I elected
to go toward the top and not the bottom. New homes here come with R-30.

Circulation of the air in the attic seems like a dumb idea to me. You have a
ridge vent, so as long as you have enough sq inches of supply air the ridge
vent should do the rest for ya.
 
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B

Bob

Nexus7 said:
I've come across a situation that seems unlike any I've seen discussed
here, but this is probably common in 30-40 year old houses. This is an
approx 20x80 sq ft raised ranch (a basement and 1 floor of living
space) with a hip roof. The attic has loose fill fiber, about 4", but
it's pretty uneven and dusty (30 years will do that). In addition,
insulation has settled deep into the bathroom and kitchen walls, so
that if the vanity cabinet in the bathroom is removed, the bathroom
wall is open to the attic. There's a ridge vent running along the
middle 2/3 of the length of the ridge, and 3-4 passive vents halfway
down the roof. While adding some batts seems an obvious way to increase
the efficiency of the roof, there are two problems.
- the hip roof overhangs about 3 ft in the front of the house, and this
is the only place where there are 2 soffit vents
- with the lack of soffit vents along the other 3 sides, air may short
circuit between the ridge and passive vents

I was wondering if, after adding another 8" of batts, it makes sense to
have a small (6 or 8") fan going at low speed, at around half the
height of the attic. This could circulate the air enough that moisture
(and heat in the summer) would circulate with the outside air through
the vents.
I suspect this would just kill any natural ventilation which would occur.
Also wondering if laying some Tyvek before laying down the batts where
the roof is open to the walls of the living space would be advisable.
Plastic maybe. Not Tyvek. Tyvek allows moisture to pass into the insulation.

Bob
 
M

m Ransley

There are rigid foam baffles you staple to the roof deck at the
overhang that are designed for adding more insulation without stoping
the airflow in from the soffit vents, cheap and easy to instal.

A fan will do nothing, forget it.

R values are minimums for code. 4 of what you have + 8 will be apx R
42. Optimal anywhere cooling or heating is needed as a major cost yearly
is R 60+. Insulation settles, I put in R 100 a few years ago, now it is
apx R-80. Once you are doing the work the exrtra insulation is cheap. I
am zone 5 to - 20f.
 
N

Nexus7

SQLit said:
Google for R values for your area then you might be able to make some
decisions.
Depending on the conditions and source, anywhere from R-38 to R-49.
I just added R-30 of blown to a 1977 home. A/c bill dropped in half the
next month.
Seeing a show I have 4-5" of very old and patchy fill, adding R-25 or
more would probably make a big difference; but the devil's in the
details.
Circulation of the air in the attic seems like a dumb idea to me. You have a
ridge vent, so as long as you have enough sq inches of supply air the ridge
vent should do the rest for ya.
Well, there are no soffit on 3 sides, so the fan was to utilize the
combination of ridge and the 2 existing soffit vents better. However
the roof has come through for two years as it is, so perhaps it is best
to leave well alone.
 
N

Nexus7

Bob said:
Plastic maybe. Not Tyvek. Tyvek allows moisture to pass into the insulation.
Very little of the living space is open to the roof, so I could add
plastic only there, and the rest of the space doesn't have any vapor
barrier. Since it was finished 30-35 years ago, there are imperfections
due to remodels, repairs in the intervening years, and so instead of
sealing the interior, I was thinking of providing a way to escape for
the moisture which will make it's way into the walls and roof.
 
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N

Nexus7

m said:
There are rigid foam baffles you staple to the roof deck at the
overhang that are designed for adding more insulation without stoping
the airflow in from the soffit vents, cheap and easy to instal.
The problem is that there are only 2 1x2 sq ft soffit vents in the
front, and no vents on the other 3 sides. The roof has no overhang, so
there isn't any space to retrofit soffit vents.
is R 60+. Insulation settles, I put in R 100 a few years ago, now it is
apx R-80. Once you are doing the work the exrtra insulation is cheap. I
am zone 5 to - 20f.
Was this fiberglass or cellulose? I was thinking of batts, then after
reading some, I was leaning towards cellulose and Home Depot's rental
blower. Only worried that the moisture from cracks, etc. in the old
walsl and ceiling would saturate the cellulose.
 
N

Nexus7

Joseph said:
Same goes for venting. It appears you need improved venting. I can't
see those "3-4 passive vents halfway down the roof." but they sound like
they should be closed up as they are likely short circuiting the proper air
flow. It also sounds like you need a lot more effective soffit venting.
The roof has no overhang on 3 sides, so no soffit vents can be added. I
can clear up the two at the front, but something else would be needed
for the other 3 sides. On the other hand, the roof components are in
good shape, so whatever is there isn't too bad to begin with. The
suggestion fo the fan was to mitigate the short-circuiting of the ridge
and passive vents.
While you may be able to do all or some of this yourself, I am going to
suggest a local professional.
They're suggesting new batts all around and that's it. Given that the
roof made it all these years, maybe that is the best course of action.
 
B

Bob

Nexus7 said:
The roof has no overhang on 3 sides, so no soffit vents can be added. I
can clear up the two at the front, but something else would be needed
for the other 3 sides. On the other hand, the roof components are in
good shape, so whatever is there isn't too bad to begin with. The
suggestion fo the fan was to mitigate the short-circuiting of the ridge
and passive vents.


They're suggesting new batts all around and that's it. Given that the
roof made it all these years, maybe that is the best course of action.
I just added lots of fiberglass batts, and it made a huge difference in my house. The more the better, I'm sure. I did
plug the tops of some walls that opened into the attic with plastic bags stuffed with scraps of insulation.

I have thought about adding plastic or something to the underside of the rafters in my attic. It would go from low in
the attic (but open at the bottom) to the top, thus forming a natural convection path to the ridge vent which would be
fed by sun heat on the roof. There would be guaranteed air flow under the roof deck in the areas where this is done.

Opinions?

Bob
 
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G

Goedjn

The roof has no overhang on 3 sides, so no soffit vents can be added. I
can clear up the two at the front, but something else would be needed
for the other 3 sides. On the other hand, the roof components are in
good shape, so whatever is there isn't too bad to begin with. The
suggestion fo the fan was to mitigate the short-circuiting of the ridge
and passive vents.


They're suggesting new batts all around and that's it. Given that the
roof made it all these years, maybe that is the best course of action.
If you can't conveniently vent the eaves/soffits (because there
aren't any) and you're not willing to give up on vents entirely,
which is what I'd do, then you do need to mechanically drive outside
air into the the attic somewhere.

Is there some reason why one can't lay PVC drain-tile around the
perimeter, and use a high-volume fan to force air from any convenient
source through it? Would one have to run a grounding-wire inside
the pipe, or is that just when you're using it for dust-collection?
 

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