It's Hot Upstairs More Insulation or Attic Fan?

[Tom in PA]

Hi!

We have a two-story home in Flagstaff, AZ. It's normally cool enough around here that, without using our central air, the downstairs stays pretty comfortable during the day if we open things up at night to cool the house down. But the bedrooms upstairs get pretty toasty. The attic gets very toasty, naturally. I'm thinking about either adding insulation in the attic to keep that heat out of the bedrooms or putting in an attic fan. The house is two years old.

Each bedroom has two walls and of course the ceiling that are adjacent to the attic, so I can add insulation to both walls and ceiling. Currently, the walls have fiberglass insulation between 2x6s and the ceiling has roughly 6" of blown-in insulation. There are three gable vents in the attic and a good number of 3-4" diameter vents on the eaves.

So..... any suggestions? Will either the fan or additional insulation make a significant difference in bedroom comfort? Any advice would be appreciated!

Thanks!

Tom

[dpb]

Tom in PA wrote: ...

Additional insulation may help, yes.

Attic fan could aid when is cooler in evenings to hasten the cooldown by drawing in cooler air more quickly.

I'd look first, however, at whether there is adequate are movement through the attic -- what's the area of soffet venting and are they free and open (not blocked w/ insulation or otherwise)...

--

[hallerb]

do both but make CERTAIN all the vents are open, often they get covered with blown in insulation

[Tony Hwang]

Hi, Improve attic vent and if insulation is not enough increase it. I saw attic fan lifting insulation from ceiling due to lack of vents.

[Oren]

What floor is the thermostat on?

Is your attic scuttle access panel leaking cool air from the house up into the attic, the top floor never really stays cool?

Add more insulation in the attic would be my choice; instead of a fan.

I would also check the T-stat (even look behind it for a larger than necessary hole for the wire) and patch the hole up. Hot air from inside the walls can cause the T-stat to work poorly.

Seal around the attic scuttle panel with painters caulk to prevent energy loss.

Check for window leaks, etc.....

[Tony Hwang]

Hi, Actually the panel should have insulation to. I glued a piece of think styrofoam block. Here that is code.

[Oren]

Must be the most violated code in NV. Of four homes I've owned here, none of the panels were backed with any form of insulation. The panels are simple 5/8 sheet rock. Caulked with painters caulk (easy to cut for access later).

A firend here found out two upper bed rooms were missing attic insulation and a portion of the hall.

Noted: your foam backing, good idea with blown insulation.

[ransley]

We cant know anything complete about your home or situation , even from what you poorly describe in relationship to code and your homes "energy envelope" .

Hire out a complete energy evaluation , a blower door test and a load calc write up, or you are just guessing as to what you are doing. Spend the 600+ and do it right

[John Grabowski]

Since the house is only two years old there is probably quite a bit of insulation up there already. I vote for an attic fan which should also help with long term roof and sheathing preservation. According to my rooftop ampacity adjustment chart Flagstaff has an outdoor design temperature of 85 degrees compared to Phoenix which is 110.

[aemeijers]

Good idea if there IS anyone locally that does that. Not all cities have one (including here). I've been looking for years, including asking the utility companies. There is no 'This Old House' style insulation company around here with thermal cameras, blower doors, etc. Just some coots in old trucks, doing it the way they were taught when they were the youngest guy on the crew. None of them are inclined to tell you that you DON'T need the services they offer. Lacking actual numbers, I have been slowly improving things based on guesswork and 'best practices', and have plucked most of the low-hanging fruit. (like redoing the window glazing putty and blacksmithing the storms, plus another six inches insulation in attic.) The undone big items are new windows and redoing the wall insulation, neither of which are likely to pay back in the 5-6 years I plan to keep the place.

If OP's house has 2x6 walls, it is likely less than 25 years old, so the walls are probably insulated okay. And absent water damage, the windows are probably okay, and hopefully double-glazed. I'd recommend making sure the attic is well vented, and adding another 8-12 inches of insulation in the attic, as the common-sense steps to take, along with insulating the access hole. (that alone made a noticeable difference here.) I've ben to Flagstaff- it can still be nasty winter up there in the mountains, when people 20 miles away but downhill are in T-shirts.

-- aem sends, resignedly...

[Ollie N.]

.

Without knowing the type of insulation blown in the attic, it appears you have an R value in the attic of approx R-24...... When you should have R-49. Again, this depends on the type of insulation you have in the attic.

Here's a few links to help you out.

[Oren]

I would summon the builder; before my court, and that's my rulin'!

Builder fixes........ and that's my rulin'! Two years makes him a rookie. Already ruled on.

[Wayne Boatwright]

On Sat 05 Jul 2008 12:20:37p, Tom in PA told us...

I live in East Mesa, but I do know the Flagstaff climate well. If you're trying to avoid using the a/c, I'd probably do both the additional insulation and a temperature activated attic exhaust fan. On your hotter days, the fan will get rid the attic of superheated air. As the outside air cools down later in the day, it will cool off the attic. That's about as good as it gets without a/c.

Another option would be a ceiling mounted whole house fan mounted in the

2nd floor ceiling. Running this at night with open windows will pull the cool night air all through the house. Whole house fans are closed off when not in use by shutters. Some models open the shutters using a small motor. Other models rely on the suction of air moving up through the fan to hold the shutters open.

[mm]

What do you mean by an attic fan? A fan blowing out, in the roof or the gable?

Or a fan blowing in, from the second floor? I'm not going to deal with that one.

I'm in Baltimore where it's not nearly as hot I presume, but I love my roof fan. I have a townhouse with a full width ridge vent and full width soffitt vents on both the front and back of the house. Despite that, since I don't use AC, when I got home from work all summer the first year, it was too hot to go upstairs so I would sleep in the basement and go upstairs for a change of clothes in the morning.

Once I put in the fan, I could sleep up here every night.

Even if you use AC, it will take a similar load off the AC.

Also, my soffitt screens have to have a layer of lint or plant seeds removed every 10 years, probably quicker than otherwise because of all the stuff sucked up because air flow is greater than with passive ventialtion. But I don't think every area has that problem.

I gather they also recommend more insulation than either you or I have. I have some fiber, and one layer of batt.

[Tony Hwang]

Hi, Up here I see lot of roof turbine(whirly bird) on roofs.

[tnom]

Neither of your choices will do much to remedy your situation.

You say that downstairs stays cool enough that you don't use the central air. This means that there is no forced air circulation during these time periods. Since heat rises it would be normal for the upper floors to be considerably warmer than the lower floors Since heat rises the heat in the attic will have little effect on the floor below. Most all of the heat on the upper floor is from lack of circulation. Do not let stagnate air laminate into temperature layers.

[mm]

If that were true, why did putting the roof fan lower the temperature of my second floor by more than 10 degrees? When the attic fan is out of service, and the motor only lasts between 3 years and 10 years**, so it's out of service for a couple days when it breaks, and I stand on a chair and put my hands near the ceiling, it's terribly hot. If I were to do that when the fan is working, it would only be a little hotter than at the 4 foot level. (I have 8 foot ceilings.)

Now maybe I could benefit from more insulation in the attic (i have one or two inches of cellulose plus one batt) but it's still not ture that because heat risess, the heat in the attic will have little effect on the floor below.

**It's amazing to me that some motors lasted only 3 years and others 7 to 10. I first sent away to the fan maker, but now I just buy new ones at the motor shop in town.

My comparisons are drawn with no AC in both situations. The only difference is whether the fan in the roof is running or not.

[aemeijers]

You are correct, especially after dark. That big mass of superheated air and building materials called an attic, radiates heat back into the 2nd floor until well after dark. Keeping attic vented, and adding insulation to provide a thermal barrier, does a lot to keep the 2nd floor cooler. Even in this one-story house, I noticed a big difference after adding more attic insulation and improving the attic venting. I don't have to immediately set the a/c on full when I get home from work anymore, and ceiling is no longer warmer than walls to the touch.

-- aem sends...

[PerryOne]

Tom, the fact is that fiberglass is useless as an insulation as, the heat/air move through it too easily. What is needed is a closed cell polystyrene insulation sprayed/poured between the joists in the attic A five inch thick layer of polystyrene or similar poured between the joist will spread into every gap and seal all the holes that are letting the heat in. Perry.

[Tony Hwang]

Hmmm. Not useless! All insulating material is per it's R value. Nothing in this world is 100% insulator, whether it's heat or eletricity. Also you have to consider cost per R value. I still say first thing is to have proper attic ventilation. Soffit, roof vents, proper baffles under the eave between roof trusses. Insulation material shouldn't block air flow for proper venitilation. I often see covered baffles by blown in insulation deafeating the purpose of baffles.