Attic temperatures

[JackOfDiamonds]

I'm in Southern Idaho, Climate zone 5B. We have dry summers over 100F, cold winters down into the teens, low humidity, and less than 12 inches per year of precipitation. Lots of sun, pretty big temperature swings between day and night.

I built an addition, and I'm not sure the attic venting is correct. The eaves have plenty of venting...continuously vented soffit panels and full soffit baffles. For the ridge, there's a continuous ridge vent. I'm told this is supposed to be sufficient or even optimal, but the attic gets very hot, and when you are in the attic, you can't "feel" any airflow.

I put a temperature sensor in the attic, and it goes up to 150F during the day in the summer. Even on days it's only 80F outside, it will be 120F in the attic. There is plenty of cellulose insulation, so climate control in the addition is fine, but I might want to store some items in this attic, and there's not much you can store in a space that gets up to 150F. I'd like to moderate the temperature, if not for energy reasons, to make the attic more usable for storage, and so a person won't literally die if you need to go up there in the summer.

• Is there something wrong with my venting? Is continuous soffit vents and ridge vent not enough? Do you sometimes need even more venting?
• Are these normal attic temperatures, or higher than expected?
• If I install an attic fan, what type is best? I have electrical feed available in the attic to power it.

 

[pcmeiners]

is there something wrong with my venting? Is continuous soffit vents and ridge vent not enough? Do you sometimes need even more venting?

Sounds about normal for ventilation. My ranch attic stays about a couple degrees above ambient because I have a back wall open, air comes in by an over hang soffit which is equivalent of approx 144sqft opening plus the soffit and ridge vent. If possible get as much ventilation as possible, the advantage is my roof is 46 years old and good for years to come and AC cost are low.

 

[fitter30]

The solar heat gain from shingles outside temp 100°is 150-180° surface temp. Square foot attic X .7= cfm needed to drop temp 60°. Plus would need 1 sq ft for ever 300 cfm ventilation. With a powered ventilator.

 

[billconner]

What color is your roof? That has a much larger effect on attic temperature than venting. And the purpose of the race and ridge vents is to get moist air out in cold weather.

 

[aggie113]

I think my attic space started out properly vented with a grilled opening on the east side wall, but when additional insulation was blown in they likely covered up the soffit air flow. When the roof was replaced I asked for a ridge vent. They installed the metal part for the venting but never put any cuts in the decking! So still hot as balls in the attic.