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
So..... any suggestions? Will either the fan or additional insulation
make a significant difference in bedroom comfort? Any advice would be
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)...
Tom covered this very well.
First make sure you have enough vents for the area and that they
are clear and working.
I have never had much luck with fans, but they can help at times.
It sort of depends on the area where you live.
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
Check for window leaks, etc.....
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.
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
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...
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.
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.
Before you get too "bent" on going out and adding more insulation to
an attic that is already insulated, you might want to get the facts.
The biggest change in your heat loss through the attic is going from
0" of insulation to 3". After that, its really not that big of a
change in btu loss. Dont believe me?
Have a Right J load calculation done on your house and plug in the
correct amount of insulation you currently have ( 3", 6" etc.?)
Now take that same exact calculation and change it to 12" or 18" or
whatever you wish. Now look at the btu loss difference. Its not that
great so now you have to figure is it worth spending $1000 etc to save
very few btu's. Its your money and your figurin.
So Bubba, since we're talking about gaining heat, not heat/cooling loss,
how much heat is being gained?
How did you arrive at a $1000 amount to insulate?
It would be utterly foolish to attempt fixing an insulation problem, by
adjusting and wasting BTU's.
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.
What do you mean by an attic fan? A fan blowing out, in the roof or
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
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.
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.
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