How do I test for adequate attic ventilation?

I was looking at this sight and got curious about my attic ventilation.
http://www.airvent.com/homeowner/pro...of-specs.shtml

I was looking at the roof vents and there are only three for a 2500 sqft
single story house. The vents that I have looks like these
http://www.airvent.com/homeowner/pro...ts-sqMetal.jpg

I estimate the free area at 190 sqin free area total for the three. There
are no ridgevents or gable vents to help out. There is a continuous soffit
vent around the eave of the house and I calculate the area as 2000 sqin
total. More than enough

I suspect the there is inadequate ventilation on the roof vent side and I'd
like to test for this.

Is temperature the big deternining factor.

This is in Houston, TX where HEAT is a big problem.

mook Johnson wrote:
How do I test for adequate attic ventilation?

I was looking at this sight and got curious about my attic ventilation.
http://www.airvent.com/homeowner/pro...of-specs.shtml

I was looking at the roof vents and there are only three for a 2500 sqft
single story house. The vents that I have looks like these
http://www.airvent.com/homeowner/pro...ts-sqMetal.jpg

I estimate the free area at 190 sqin free area total for the three. There
are no ridgevents or gable vents to help out. There is a continuous soffit
vent around the eave of the house and I calculate the area as 2000 sqin
total. More than enough

I suspect the there is inadequate ventilation on the roof vent side and I'd
like to test for this.

Is temperature the big deternining factor.

This is in Houston, TX where HEAT is a big problem.


Hi,
Stick your head in there and see how hot/cool in there.

"Tony Hwang" wrote in message news:nuGKg.499695

Hi,
Stick your head in there and see how hot/cool in there.


OK its HOT. How hot should it be if the outside temp is 90 degreesF?

The house is not shaded.

mook Johnson wrote:

How do I test for adequate attic ventilation?

I was looking at this sight and got curious about my attic ventilation.
http://www.airvent.com/homeowner/pro...of-specs.shtml

Ask to see the "federal guidelines" they rely on.


I was looking at the roof vents and there are only three for a 2500 sqft
single story house. The vents that I have looks like these
http://www.airvent.com/homeowner/pro...ts-sqMetal.jpg

I estimate the free area at 190 sqin free area total for the three. There
are no ridgevents or gable vents to help out. There is a continuous soffit
vent around the eave of the house and I calculate the area as 2000 sqin
total. More than enough

I suspect the there is inadequate ventilation on the roof vent side and I'd
like to test for this.

Is temperature the big deternining factor.

This is in Houston, TX where HEAT is a big problem.




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mook Johnson wrote:

I was looking at the roof vents and there are only three for a 2500 sqft
single story house... at 190 sqin free area total... There is a continuous
soffit vent around the eave of the house... 2000 sqin total.

I suspect the there is inadequate ventilation on the roof vent side and I'd
like to test for this.

Is temperature the big deternining factor.

This is in Houston, TX where HEAT is a big problem.

The average daily max temp is 92.7 F in July in Houston. On a still sunny day,
a square foot of light-colored south shingles might absorb 0.2x250 = 50 Btu/h
and lose heat to outdoor air with a 2 Btu/h-F conductance, which makes the
equivalent shingle temp 92.7+50/2 = 118 F, so we might have something like
this, with attic air temp T (F), viewed in a fixed font:

T
0.5 | R1 | -----
-----www-------www------| -- |---|
| | -----
| 118 inside I
---
-
|
-

If 1250(118-T)/1.5 Btu/h that flows into the attic equals I that flows out
and I = 16.6Asqrt(H)(T-93)^1.5, with lesser vent area A ft^2 and height diff
H in feet, A = 190/144 = 1.3 ft^2 and H = 8' make T = 118-(T-93)^(2/3)/13.5
= 117.4 F, after 2 iterations. With A = 8 ft^2 (eg 2 2'x2' gable vents),
T = 114.5. Not a big difference, esp since the larger soffit area will add
about 40% to the flow in the first case, which isn't counted above.

A radiant barrier can help by increasing the R1 above.

Nick

With inadequate venting your beams and deck would mold and rot.