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-   -   Gable fan? Powered roof vent? (http://www.diychatroom.com/f9/gable-fan-powered-roof-vent-49364/)

idahojoec 07-21-2009 06:46 PM

Gable fan? Powered roof vent?
 
Here is my situation.
House built in around 1970. Location SW Idaho. Roof pitch 12/12 (very steep). The second floor living space is in the attic such that the top 1/3 of the walls are pitched like the roof. The result is 3 triangular "attic" spaces; between the 1st floor ceiling, the roof, and the 2nd story wall on each side and one above the middle of the second story living area along the ridge line. I don't think air gets from the soffet to the ridge line. The house is in the shape of a T with the top about 45' running north south and the long part of the T running east west about 75'. The attic is about 8' +/- wide and 5' +/- high. There are 3 gable vents, one at each end.

Problem: The upstairs gets very hot as does the attic. Hard to cool the second floor.

I have 4 square plastic ridge vents that are cracking and need replacing. I was thinking about replacing them with powered vents, turbines, or solar vents. I have decided that perhaps a gable fan would be a better solution, and just replace the square vents with metal vents. Someday I will likely install a whole house fan. I have heard the powered vents don't help and increase AC costs.

Questions:
1) Is a gable fan a good idea?
2) Do I need more than 1? Should I put it on the long end of the T?
3) Is one or more roof vent fans a better solution?
4) If I go with a gable fan, Do I suck the hot air out of the attic? Or draw in the cooler outside air and blow the hot air out the roof vents?

Suggestions, corrections, ideas, all appreciated.

thanks,
Joe

Ed the Roofer 07-21-2009 06:55 PM

The proper answer will depend on if you know if the insulation in between the drywall and the roof deck sheathing has a clear and free flowing air space of a minimum of 1" to 1 1/2" on the top side of the insulation.

If the insulation is installed packed tight, then air flow is stifled and you have other concerns.

A powered attic ventilator would then be pulling the interior, paid for, conditioned air through air passage ways and leak points in the building envelope and you would increase your costs dramatically to cool the upstairs living quarters.

When you stated that you don't think that air gets in through the soffits, is that because of being blocked by the insulation, or because there is not continuous soffit vents installed in the overhangs?

Also, just for the discussion, how old is the current roof and when would you be considering replacing it? Because, the answer may generate some other additional possibilities for the solution.

Ed

idahojoec 07-25-2009 02:06 PM

Ed, Thanks for the response. I don't know the exact age of the house. The house is about 30+ years old and the roof has been replaced. It looks in good shape.

I went and checked and there seems to be insulation stuffed between roof and drywall. I am not sure "packed tight" would be right but there is not an inch of free space either. I have siding on the soffits and I don't see any venting holes but my original statement was based upon the insulation blocking airflow.

We have owned this house for 10 years. Last I was in the attic I did not notice any evidence of moisture, we have not been having any ice damming issues. We do not have any bathrooms or anything else venting into the attic.

Joe


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