Winter attic ventilation

[SailFan]

I have a couple of questions regarding attic ventilation and ice dam prevention:

My house is a cape cod style, which presents a challenge. In the upper attic there is plenty of loose insulation, but it is right up against the roofing at the edges. I know I need to pull this back and put those foam air channels in. BUT, what about the area between my attic floor and the bottom edge of the roof (10-12 feet, probably)? I am not sure yet whether there is any chance for air to travel this path. I have no access to this area other than by tearing out walls or the roof. Gah!

I am looking at installing a powered gable vent. I have a continuous ridge vent now. If I can establish air flow from the soffits to the attic, it would seem that I should block the ridge vent so that the powered gable vent pulls air up under the roof? Also - the powered gable vents I saw at Menards/Lowes/Home Depot are thermostat controlled. They go off at the set temperature. These thermometers only go down to 50 or 60 degrees F. That seems too warm to me - in the winter it would seem that I would want the fan to go off at a much lower temp. Am I missing something here?

Thanks for any advice!

Matt

[Speedy Jim]

Had a similar situation. Actually there are 2 winter problems: warm roof causing ice dams and lack of ventilation, causing condensation on rafters/roof deck and resulting in mold growth.

I put a gable vent fan in and a louvered intake at the opposite gable. Thermostat is bypassed in winter and the fan runs under manual control from a speed control ("dimmer" for motors). If I set it so the fan is barely spinning, that's enough to keep the roof cold AND prevent condensation.

In your case, give it a try without blocking the ridge vents; it may work just as well.

Jim

[trader4]

" am looking at installing a powered gable vent. I have a continuous ridge vent now. If I can establish air flow from the soffits to the attic, it would seem that I should block the ridge vent so that the powered gable vent pulls air up under the roof?"

If you have a ridge vent and decent soffit vents, that is widely recognized as one of the best solutions, so why fool around with a powered gable vent?

[Joseph Meehan]

I can't figure out what you are talking about.

/\\ / \\ / a \\ /___\\ / | | \\ / | b | c \\ _______ | | | | | |

I am sure many of you will not be able to see the ASCI art as I do but maybe you can figure out what I am trying to do.

What areas are you talking about being a problem? A,B or C??

[barry]

The overall concept is simple:

1. contain heat below, from transmission through walls and ceiling. Seal off these cavities from above. Vapor barrier at inner surface.
2. allow moisture entering insulation, and entering attic via leaks, means of escape. Simple enough through exterior walls. In attic, by means of venting attic, like with vents in soffit and ridge- sounds like you're short the soffit vents, which should admit air over all insulation. Basic physics will cause airflow to occur. This airflow, if vents are of adequate size for situation, will keep roof skin from melting snow.

Powered gable vent is for summer cooling, and shouldn't be necessary if you effect soffit venting to match the ridge vent.

HTH, J

[SailFan]

In the ascii drawing above the area that concerns me is "C". I can take care of "A", but I am anticipating trouble getting airflow from eaves up into the attic through "C". It is all area I can't easily inspect.

Matt

[Joseph Meehan]

I thought that might be what you were talking about. Sorry I don't have any answers. The only home I have had with this situation was when I was a kid (1950's) and we did have access to those areas, we even used them for storage, but I don't know what we did about ventilation. A had a gable vent at each end and B was a bedroom for me and my brother. I am going to guess C was vented from B, but I really don't remember.

Personally I would not put powered vents in. I would look for non powered vents as low as possible in the gables and let the ridge vents pull the air.

[SailFan]

Thanks, Joseph!

Looks like I need to do some exploratory work this weekend and see what I can discover about "C". I'm hoping the proper air space was incorporated into the construction, but not counting on it.

Looking at my soffits: The soffit is wood (rough-sawn cedar). I'd like to get a continuous vent in the whole length of the eave. Right now there are maybe 6 vents along a 60 foot length of eave.

Wish me luck...

Matt

[Joseph Meehan]

I can say that many contractors are very creative about finding answer to problems like this. You may want to check with a roofing contractor, pick an older guy who has had lot of experience.

[PHILIPWOLF]

Hi, Matt. I'm working on the same problem... but I'm sorry I have access to "C". I'm laying down insulation on the ceiling joists( my house was severely under insulated). Last year, I had severe ice damming it even leaked INSIDE one of my window frames. I hate to think about what this did to my inside walls and behind the aluminum siding. This year I've decided to eliminate this problem. Here are two sugestions in addition to the ones mentioned. Try a roof rake. It comes in many styles but the one I bought this year (and haven't tried yet) is a flat piec of aluminum about 20" wide with small rollers to lift it off of the shingles. I don't know if this will fit your home but i installed small vents on each side of the wall. I don't have safettes so I don't have a choice. I have to vent from somewhere. I tried to place the vents so that they are in alignment and hopefully will cross ventilate. Kinda like peak vents but farther down the wall.

phil