maximum attic temperature, Middle Tennessee?
August 9, 2015 12:26 PM   Subscribe

Are there guidelines for appropriate attic temps by region?

I am clearing up an estate by selling a house, 2 years old, that was built with energy efficiency in mind. I am not familiar with the details of the home but I do know that the crawl space is conditioned and the attic has soffit and ridge vents.

The inspection says that the attic temperature of 132 is excessive and recommends replacing the ridge vents with box vents. The temperature that day was sunny, upper 90's. This is a hot, humid climate, Middle-Tennessee.

Are there guidelines for appropriate attic temps by region?

My research suggests that the attic is appropriately vented and that changing the ventilation could cause more problems than are solved.
posted by egk to Home & Garden (8 answers total) 1 user marked this as a favorite
The issue with having such high attic temperatures register (regardless of region) is that the HVAC system will have to work harder to keep the rest of the house cool. I, too live in middle Tennessee, and I just went up to our attic to do a temperature reading. Our attic is currently 98 degrees F. Our vent fans were both running; they are temperature controlled and come on when the attic is over 85 degrees. I have to agree that 132 degrees is excessively hot, so much so that I would say do your own reading if that is possible. I would also encourage looking into whether it is possible to add vent fans, not just passive ventilation.
posted by dawg-proud at 1:07 PM on August 9, 2015

Though, not everyone agrees powered vent fans are a good idea energy-wise, so definitely a question to ask.
posted by dawg-proud at 1:13 PM on August 9, 2015

There are a few issues with high attic temperatures. One is increasing the cooling load of the house, particularly if the ceiling is leaky, poorly insulated, or there is HVAC equipment in the attic (is there?). The other is possibly shortening the lifespan of the shingles with higher temperatures, but I'm not sure this is well understood as to how big the effect is.

It does sound like additional venting would not be a bad idea idea in your case. Have you measured how much venting you currently have? I'm not sure why you'd replace the ridge vent. Why not just add more venting?

What problems do you think adding more venting will cause?
posted by ssg at 1:53 PM on August 9, 2015

Response by poster: The inspection report suggested the change in vents, that is to remove the ridge vent and install box vents.

The house is only 2 years old, so I am not sure why the roof isn't adequate as it is.

There is some ducting in the unfinished space that services a finished room on the upper level that was used as a "conditioned attic." It was not considered a room, there are no windows.
posted by egk at 6:15 AM on August 10, 2015

Response by poster: Another category of problems caused by attic venting occurs in hot, humid climates. In their ASHRAE Journal article, Rose and TenWolde wrote, “No scientific claims have ever been made that attic ventilation is needed for moisture control in hot, humid climates. In these climates, the outside air tends to be much more humid than the inside air. … In such climates, attic venting tends to increase rather than reduce moisture levels in the attic.”
posted by egk at 6:17 AM on August 10, 2015

Regarding your quote above, I think you may be misunderstanding. The article is about the difference between a vented attic and a unvented attic. They are entirely different beasts, with different designs.

What you have is apparently a vented attic that isn't venting very well. That's not the same as an unvented attic at all. It is an either / or choice and since you have a vented attic you need to make sure the venting is sufficient. In other words, the take away is not the less venting the better. The point is that you can design attics in two entirely different ways. In between is not a good place to be.

The house is only 2 years old, so I am not sure why the roof isn't adequate as it is.

Construction practices are very often less than ideal.
posted by ssg at 11:17 AM on August 10, 2015 [1 favorite]

Response by poster: ahh, ok; I am sure that the amount of mis-understanding I am doing is considerable.

3 roofers came by to look, one of them would add box vents. None suggested they be removed; they strongly disagreed with the inspector that point. One of them said that the attic fan in his home is set to come on at 170 degrees.

I've got one more coming and then I'm going to call it a day.
posted by egk at 12:27 PM on August 10, 2015

Response by poster: 4 roofers, all agreed - keep the ridge vent. One said box vents could be added, no one suggested this was needed. The inspector also thought the hvac wasn't working, so I had a service call that found nothing wrong. This inspector has cost me a lot of time from work and the service call expense.

Thanks all, apparently there isn't a guideline for temperatures in attics.
posted by egk at 10:06 AM on August 16, 2015

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