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Old 07-07-2011, 01:33 PM   #1
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Oh God.. no ventilation


So, I was recently married and now am, the 'proud owner' of a rental property that was previously my late mother-in-law's place, built in 1936, one of thousands of those "Mile-High" bungalow-style homes to be found in Denver built duiring that era. Since we want this teensy little 800 sq. ft. place to be as 'energy-efficient' as possible (good luck to me...), I began examining EVERY possible way of keeping this place cool in our scorching summer temps, only to find out that there is absolutely ZERO ventilation in the attic. No gable vents, no soffits (or eaves at all), and no ridge venting... and now I know why this place was always an oven in the summer.
So - how does one get 'adequate' ventilation throughout this attic using what I believe may be my only option: arguably, a continuous ridge vent and one or more gable vents? If I use this method, I believe I can achieve the 'necessary' venting of some 750 sq. in. of 'free vent area' (5.8 sq. ft. if my math is correct for our area).
As I said, this place has no eaves, so there are no soffits to use as ventilation, and my only 'access' would be through the gables and of course the ridge peak. But, is this sufficient?
The 'layout' of the home is a simple little rectangle-shape, roughly 24' X 33' and I believe I may have no other options with this type of construction.
"Power ventilation" (or 'evacuation' of the space by a powered fan) in the attic does not really appeal to me as I had read a report about how this seldom 'pays for itself' considering the electrical power required to achieve much true ventilation (even if I don't quite believe or understand this...).
So here I am searching for some input on how I can get this stuffy little box to 'breathe' a bit.
As an alternative, I'd also like to consider a small 'whole-house fan' that I saw at Home Depot that is affordable and easily installed, and 'lends itself' very well to cooling this place once the daytime heat diminishes (thank God for 'Mile High' cooling once the sun goes down - those who know understand that it can fall almost 40 degrees at night around here most often). But this fan 'requires' something like 1440 sq. in. of 'FVA' (free vent area) for 'proper operation' - so that just doubled my 'FVA' requirements, right?
Or - maybe not. Since this WHF would do the same thing as a 'power vent', arguably this is NOT the case... eh?
But are simple gable vents and a ridge vent 'sufficient'? Not a lot of capacity to vent much other than the 'central area' of this attic like this... But as I am always accused of 'over-engineering' everything I do (personal fault) I might be 'guilty' of this same thing here....
Input?

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Old 07-15-2011, 04:02 PM   #2
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Oh God.. no ventilation


I think I can almost picture your building, but a photo or two would help.

If you install a ridge vent, it needs an equivalent input vent at the BOTTOM of the roof, where eaves should have been. Gable-end vents will just act as short-circuit input vents for the ridge-vent's output, so most of the attic will be effectively unvented still, AND you will be drawing air IN through a gable vent that was intended/designed as an output vent. You risk pulling rain, snow, and dust into your attic.

A power vent needs the same thing - input air. If it can't get it from proper low-lying vents at the lower edges of the roof, then it'll suck air through whatever gaps exist between house and attic. This depressurizes the house and causes the house to suck in air at every gap, pulling in hot outdoor air. Pulling air from the house into the attic also pulls moisture from cooking and bathing, which gets into your insulation, or at night (with that drastic temperature drop) condenses it on the underside of the roof, precipitating mold. Don't use big suction (a power vent) if you don't have proper lower inlets. If you DO manage to install some sort of "soffit" level inlets, then you've got what a ridge vent (or mushroom vents, less effectively) needs and you don't need power venting anyway. Not a great situation you are in. But you knew that... sorry.

Is there no drip edge at all, where the tops of your walls meet the roof? Not even a little overhang?

If there's flashing there, you might be able to use a product from Air Vent for that purpose. Check their website.

- kevin

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