My house is one half of a prefab duplex from the 80's. Last week I went
into the attic and found mold covering the roof sheathing. It had not
been there a few weeks earlier. The attic is supposed to be vented by
soffit vents and ridge vent, but I found that the air is not flowing up
from the soffit to the ridge like it should. The only moving air in the
attic is the air blowing in from the ridge vent. The soffits are
blocked by fiberglass batts and an additional layer of blown in
insulation. So there's practically no ventilation.
Now here's the problem: the roof pitch is something like 2/12 and the
rafters (except those at the soffit vent) run parallel to the ridge.
The pitch is so shallow that I can't get any closer than maybe 10 feet
away from the soffit vent from inside the attic. I can't clear out the
insulation blocking the vents. Plus, if I did remove the insulation,
the ceilings of the rooms below would be exposed and uninsulated for a
couple of feet from the outside wall.
I'm considering buying an electric attic fan and just forgetting the
soffit vent. Any ideas?
Yes. Fan will be very effective. Get a variable speed control
("dimmer" for motors) while you're doing it. The fan will
only need to run slowly in winter.
Purists will say to fix the venting problem, but clearly
that's not practical here.
Shawn: Congratulations on your very clear explanation of the problem.
It just proves what has frequently been considered and referred to, by
some, as 'just a theory'.
i.e. That it is important to ventilate the attic roof space.
We have even had those who have asked "Is it OK if their dryer vent (
i.e. hot air loaded with moisture) can vent into their attic". Strewth!
Many building standards not only mention percentages of vents in
relation to the area to be ventilated they also importantly say
something along the lines 'arranged to permit cross ventilation'.
Based on what you have described I think you are on the right track
proposing an electric fan to exhaust damp air, both summer and winter
as a practical solution. Cost of the fan and a bit of electricity minor
compared to replacing a roof and more!
But as someone mentions you may be able to run fan slower at times to
avoid negative pressure up there sucking warm air out of the house?
Anybody here have a number for how often the air up there should be
Use a tool, like a rake. I forget the name of the rake with an iron
part at the end with tines perpendicular to the handle. That might
work better than a leaf rake. Or make a tool from an old broom handle
and 2x10" piece of plywood.
Don't remove it that far.
First scrape away the blown insulation. That might be the only
problem**. For those vents that are still obstructed, move the batts
back 2 to 6 inches. Even with a low pitch, an inch or two will likely
be enough to let air from the soffit vents circulate through the
attic. It doesn't have to be a big opening. An inch from the roof is
If the batts run perp to the edge of the roof, you may be able to stay
where you are and pull them towards you an inch or two or whatever it
takes. If this leaves some of the ceiling uncovered, you can push
back some of the blown in.
**Because the guy who put down the batts was probably careful, since
you didn't have mold from the 80's until a few weeks ago. But blown
insulation is harder to control and I would guess can move even when
no one is there. So I suspect the blown-in is the only problem.
I don't understand which direction thiis fan is going to blow, or why
the ridge vent should be closed. Closing that will close everything,
it seems, so you'll just be blwoing the air around inside, no?
Can you remove the sofit vents from the outside? If so you could
move the insulation away and add propa vents. These are 4' long "air
shoots". The insulation should hold up the shoot, but it would be good
to get a few staples in it from the inside.
What size sofit vents do you have? You should have at least a
6"x12". You could have a 4", which will not alow enough air to move.
Since there was no mold on the roof deck "a few weeks ago",
The problem may well be lack of vapor retarder at the ceiling level.
It's possible the cool deck has led to condensation and mold growth.
By force venting the attic space, you will be drawing in air from
perhaps the house.
Yes, if it will work, it's worth a try. They sell these chute type
widgets you are referring to at building supply/home centers. They get
stapled to the underside of the roof sheathing, between the rafters.
But in this case, he might be able to work them in by sliding them
after using a rake or similar to try to clear the end of the channel.
If that doesn't work, then I'd probably consider gable end vents on
both ends. That together with the ridge might be enough. I'd go with
a power fan as the last solution, because it uses power and without air
intake somewhere, it's going to either not work very well or suck air
from the living space. If you get a fan, you obviously need one that
goes on with humidity as well as temp.
Yeah, I tried the rake. But, because the roof rafters and the ceiling
joists run _parallel_ to the roof ridge, there's only about a 4 inch
space between rafter and joist at the farthest point I can reach. And
that's at least 3 or 4 feet away from the outside wall. (I hope you can
picture this, I've never seen a house with rafters and joists run this
way. Seems stupid.) So I can't really get in there with a rake.
I tried those Owens-Corning Raft-R-Mate polystyrene things, but they
crushed, snagged on roof nails, and fell apart when I tried pushing
The electric attic fan I'm considering is one of the type that goes
through the roof near the ridge. The soffit vents aren't completely
choked off, just not open enough to allow the ridge vent to work as
it's supposed to, so I'm hoping that the fan would draw most of the air
through the vents and not the house. I assumed the ridge vent should be
blocked because otherwise the fan would only draw in air from the ridge
and not move any other air in the attic.
Thanks for the help, folks,
Attic fan is ambiguous. Do you mean a fan in the roof blowing out, or
a fan in the floor of the attic blowing into the attic, or a fan
within the attic. **
If you're talking about a roof fan, I've supported those in many of my
posts. If you mean a whole-house fan, I don't know of any one here
who has recommended that for a humid attic.
If you mean the third, let us know what you mean.
**I don't take hot showers, so I never have much humidity in my attic.
But you can have a humidistat or a manual switch to turn it on when
you want it in the winter. The attic fan vents at the ridge rail,
which may or may not be close enough to the outside. Check yours.
If you can't move the insulation with a rake, how about a vacuum
cleaner or a shop vac? Borrow extra extensions to the wand, don't
use any end except the wand, and put some window screen over the wand
so it only grabs the insualtion and holds it, but doesn't suck it in.
Also you can put a solid piece of cardboard or something over part of
the wand opening to lower the suction, and make the hole smaller so
that it will just hold things and won'pt suck them in.
If it does suck some in anyhow, if you've cleaned the vacuum before
using it, you cnn just get the insulation out of the vacuum and use it
Or hire a midget or a child to go in there and do the work up close.
I'm not kidding. AIUI, quite a few burglars have used children
because they fit in places that other people don't. Use some temp
pieces of wood over the joists so the person doesn't fall through the
ceiling. He should wear an approriate mask so he doesn't breathe the
fiberglass. You should too. I always do, even when I don't really
disturb the fiberglass. You could vacuum the air first and get rid of
most of what is NOW floating in the air. I've never actually checked
if the stuff is in the air.
If you can get to the eaves, can you take the caps off the
vent-holes, and shove a rolled up tube of tarpaper up
through the insulation, and then stick the grates back on?
If you end up going with a fan, use duct work to force the air
go to/from where you want it to.
Can you tackle this problem from the soffets? If you can pull down
the softet cover, move the insulation back, and slide a rigid rafter
baffle you might succeed.
As for a fan, you need to ensure there is an inlet for air, and will
cost you money to operate.
Just a guess....
tom @ www.BlankHelp.com
Since you cannot clear the soffits from your attic, can you use a powerful
leaf blower to blow through the screens of the soffit vents from the
outside? This may dislodge the battens, which you can afterwards push back
partially. It would certainly clear the blown-in insulation material from
the soffit vents.
might try a shop vac with small long wand, made from like 1 inch pvc
pipe to suck the loose fill insulation from the vents.
have you tried accessing it from outside? might be able to vacuum from
outside too, or blow topwards inside
if you install a fan with open ridge vents it wouldnt do much sucking
air from nearby ridge vents.
if you choose fan have ridge vent removed from above, tar paper over
the holes and replace shingles
i would try getting the soffit vents open
Buy cardboard or styrofoam "chimneys" that attach to the underside of
the roof. Buy a chimney for every space between the rafters. Pull
away the insulation, tack up the chimney (I used a staple gun), and
put the insulation back in place, against the chimney. Use a pole or
broom handle, dust mask, long sleeves, protective clothing. Now is a
good time to do this task, before the attic summer heat. You might
consider adding more soffet vents too. Attic fans work, but these
can be noisy, add to your energy usage.
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.