Attic cooling

[Painter]

Just moved to Houston TX this week to an inherited house. Wonderfully hot place this early in the year. AC runs 24 hrs, we're already afraid of the first electric bill. No wonder they wanted a $400 deposit.

Our attic has an 8" thermo-type roof exhaust fan that is set to come on at

140F. My wife says this usually happens about 11AM. Even with the AC on and set to 74F, she says the house is unbearably hot during the day, never getting below 84F.

From what I've been told after asking around, this house is what some call "Dutch construction," meaning there are no soffit vents of any kind (among other things). There are no attic vents other than a triangular louvre at one end of the house - the end closest to the exhaust fan.

The attic is about 1700 SF. I have no idea what the RPM/CFM exhaust of the attic roof fan is, and there is no legible mfr ID on the fan.

The attic insulation seems to be the cellulose type stuff at a depth of about

2".

My question is, what do I do to cool us further? Would adding some sidewall vents farther away from the fan help the airflow? Small vents, like the 6x8 panels at Lowe's/HD? Or is a very large additonal exhaust fan in order? Should I add more insulation? I'm really just stabbing in the dark here...

Painter

[donald girod]

You absolutely need to

1) add insulation in the attic--bring it up to at least 6"-8". More cellulose is ok, or you could place unfaced fiberglass batts on top of the existing stuff.

2) cool the attic off

If your AC is running as you describe, you are going to really bleed.

Now, if you increase insulation without more ventilation, attic temps are going to really shoot up. Right now much of that heat is coming down into the house to be air-conditioned away. You probably can't add soffit vents unless you have eave overhangs--do you? If so, then put in soffit vents and vents in the roof itself near the ridge. The best venting is continuous ridge venting but unless you are replacing the roof, it is cheaper and less work to put in the kind with a hood over them that just require you to cut a hole in the roof here and there. You would need about 4 or 5 of these vents I'm guessing, spaced along the ridge or ridges. A well-ventilated attic won't go much above 100 degrees no matter what. I'm guessing you have attic temps of 160 plus on hot days, or you will once you add insulation.

If soffit vents are not an option, then at least put a good-sized vent in each gable end. If you can put some lower down (you mentioned sidewalls), that would be good. A combination of vents in the gable ends and vents along the ridge should help attic temperatures quite a bit. A bigger fan would also help--8" is pretty insignificant.

This project will definitely pay for itself in a few years thru decreased utility bills (and increased comfort).

[Default]

If the attic is 1700 sf, then you need a minimum ventilation area of around 6 square feet of ventilation area, evenly split between intake air and exhaust air for passive venting but I don't know how that changes for powered vents. In any case, if you only have the exhaust port, and no intake vents, then the attic is probably sucking cooled air out of your living spaces to replace that blasted out the power-vent. So yes, you need sidewall vents, or soffit vents, or something. The other thing you need is about 10 more inches of insulation on top of the existing 2" cellulose.

[jim]

if you can get to the inside of the attic and have the room i would tear out two large holes on each side of the house and put in two power vents with louvers about 24 inches wide/high each... and keep the two fans running most of the day and that will get rid of the heat.......... when you can get up in the attic and not get toasted with the 148 deg. temp. you have satisfied the ventilation problem....

[Jim Mc Namara]

Welcome to Houston - wait until August! LOL!

Insulate! Your best defense against this mess is insulation. Blow in

10-12" of the stuff - ventilate your attic - and tint your windows. Build yourself a barrier between the cold and the hot - live in the cold side.

Jim Mc Namara

[ROBMURR]

Your need a ton more insulation in there! You also need more air ventilation. The little power vent on my did not last long and pulled almost no air out... a fan at the louver end of the house with a Thermostat is the way to go.