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Heating & Air Conditioning Home Repair

Attic ventilation

3 years ago

last modified: 3 years ago

I live in Houston, TX. My attic gets very hot during the summer. When its 90F outside, its 115 in the attic. My ac unit is trying to cool the inside but it can't get the inside below 80F. I have been reading about different solutions, including radiant barrier, attic insulation and powered attic vents. I have attic insulation but I probably have to add more. Should I add radiant barrier or powered attic vents? Are they worthwhile?

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Comments (3)

kathyg_in_mi
3 years ago
Maybe it's the AC?
PRO
Austin Air Companie
3 years ago
last modified: 3 years ago
Attic ventilation is a science just as much as air conditioning is.

In order to vent properly, you need air in to get air out.

It's much better to use 'natural ventilation practices'. Powered vents tend to make matters worse, not better. Plus powered vents will burn up in the heat.

What is natural ventilation? cold air falls, hot air rises. Follow that principle to cool the attic. You're limited by the design of the home, foolishness of the builder or in some cases the foolishness of the former owner or whoever was last hired to replace the roof and in some cases who insulated the attic (if it was re-insulated). So depending on that you could be looking at major expense to cool (vent) that attic properly.

In terms of your air conditioner not cooling below 80F, this may be more of a problem of the air conditioner. Did someone tell you this?

I service the Katy, Texas area.
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Well, idmd, this is just my opinion...I grew up in a one-storey ranch house built in 1958, the roof was hipped but fairly shallow and my dad put insulation batts in the attic, but I'm pretty sure it wasn't up to modern code. This was back in '61 when we moved in, and lived there until '87. We never had moisture problems and had no ridge vent and I don't recall any soffit vents either, although the crawlspace had sliding louvers every six feet or so. My current house is a 1908 two and a half storey frame house with a steep pitched hipped roof with three dormers and two chimneys. It has box gutters, so no soffit vents, and no ridge vent either. There is not one sign of moisture damage in the attic, which is a finished single room which takes up all the territory except for about 5 feet per side for storage under the rafters. The roof is skip-sheathed which meant original roof was slate, but is now asphalt shingles. My guess is that if it has lasted this long without vents, it will last another 100+ years. Old houses, even ones built in the 50s were not so hermetically sealed that moisture was a problem. The biggest problem with moisture from our ranch house was in winter, when ice formed on the aluminum window frames and the marble sills. We tended to put towels on them to catch the water as it melted--this was in the bedrooms, at the far end of the house from the furnace. :)
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Well, here's a link with a good explanation of how ventilation plays a part... But a previous answer recommending proper insulation and possibly a radiant barrier is key. But if you already have these, better ventilation will help. My neighbor's thermostat controlled fan would run all day before he added eyebrow vents and soffit vents; now it comes on only in the late afternoon. Also, if you re-roof, a light colored shingle will help a lot, if you can stand the look. I just went from wood shake to a black asphalt and my attic is now almost degrees hotter. Here is a link that might be useful: Summer Heat Build-up
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The 4" hole will not be completely open. Look at a piece of vented soffit. It only has perforations, so there is still a lot of material that would block the 4" hole you went to the trouble to drill out, instead of just removing the wood entirely. There will also probably be blocking/bridging that might interfere with some of the soffit panels (which would further reduce your plan of 2-1-2-1), not even getting into whether you have insulation baffles or anything. Code calls out 150/300 as a minimum calculation, but this is not an exact science. The best situation for an attic is to have the air in the space be exactly the same as outside, with airflow to remove moisture, but obviously we can't ever achieve this because we need to enclose the space for weather protection. So more air is better. Code also references where you want more intake (at the eave) than exhaust (at the ridge). This helps insure the balance of cool/warm air and high/low air pressures remain to function low-in and high-out air movement.
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Hi, Warm air can carry more moisture than cold air. When warm air hits a cold window it has to loose it's moisture. That is also the reason you see your breath on a cold day. Your roof and attic are fine. Remember in Southern Cal this will pass. Good Luck Woodbutcher
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mike_home
3 years ago
When was the last time the AC was serviced? You could be low on refrigerant. Have it checked out if has been more than a year.

How much insulation is currently in the attic? If it is less than R-30 then you should spend money to upgrade it. A temperature of 115F during a hot sunny day is not unusual. What is the temperature at 10pm? If it is still over 100F degrees then you need better attic ventilation. You can't add a power attic fan if there are not enough air intakes. If you do you potentially make the problem worse.

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