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bp21901
How to increase attic ventilation on one side

I'm trying to figure out how to increase the ventilation that comes from the soffit vents to the roof peak on the north side of the house and need some ideas. I am getting moisture above the air channels on that side only. I can see where the black mold is starting from just above the air channels to the peak. There is no black mold on the roof deck that is covered by the air channel which leads me to believe the air flow there is sufficient to keep it dry.

The front side is fine, I believe because it catches sun most of the day and that side also has a deck which warms considerably and I believe promotes the flow of air up through the soffit.

Both sides are insulated the same and there is no difference in room moisture below which is why I am thinking it is a north - south thing. I am thinking about placing 1/2" foil faced foam board across the roof rafters to enclose the bays and see if that encourages the air flow to keep them dry. Any other better ideas?

canuk
Re: How to increase attic ventilation on one side

Hmmm --- interesting.
Could it be a North / South exposure thing --- I guess it's possible.

Is there snow cover on the roof ? If so , is it roughly the same on both sides?

It may also be the South side venting is stronger than the North causing an imbablance of intake.
You could do what you propose though you may not know if it's really working.
Unless there is noticable frost build up on the underside of the roof deck. That might be a visual indication if your idea is working or not.

...... scratches head .... rubbing chin .... have to think more on this.:)

Sombreuil_mongrel
Re: How to increase attic ventilation on one side

A question I would pursue is where is the moisture coming from in the first place? The moisture that is causing the mold. If it wasn't getting into the attic in the first place, it wouldn't need to be got rid of.
That said, You can do two things to increase the ventilation. Adding larger area of soffit vent on the north side, or adding a fan to expel air/draws more air through. Perhaps both need to be done.
S_M

canuk
Re: How to increase attic ventilation on one side
Sombreuil_mongrel wrote:

A question I would pursue is where is the moisture coming from in the first place? The moisture that is causing the mold. If it wasn't getting into the attic in the first place, it wouldn't need to be got rid of.
That said, You can do two things to increase the ventilation. Adding larger area of soffit vent on the north side, or adding a fan to expel air/draws more air through. Perhaps both need to be done.
S_M

That's really the number 1 issue that should always be considered before any insulation is done.
However, moisture can also be coming from outside into the attic.

bp21901
Re: How to increase attic ventilation on one side

At this point I believe the moisture is coming in from outside. I've really been checking this out the last few days to try to see what is going on and I have come up with a theory...let me know what you think...(like you people would be shy about sharing an opinion! :) )

The north side does not get the sun exposure like the south side. For instance we had about 8" of snow last Sat and yesterday there was still some on the north side down by the eaves, but the south side had melted off by Monday. We had about 2" more last night and it is all off the south side by afternoon since there was strong sun today, but there is still some on the north side down by the eaves. The north side roof deck remains cold, cold enough to keep snow on it, compared to the south side. I think the south side air from the eave vents is warm enough and contains enough moisture to condense on the cold north side roof deck inside the attic.

This is what I think is going from being in the attic space and actually feeling the warm draft on the south side air channels.

I am not sure yet what would fix it though. I think by putting the 1/2" foam panels on the north side rafters it may keep the warm air from condensing on the plywood roof deck. I'm not sure a fan would solve the issue unless the extra airflow would either warm the north side roof deck quick enough to not condense the moisture or dry it out before it caused the mold. But I am thinking the fan would draw more warm air from the south side and may not have the desired effect.

Timothy Miller
Re: How to increase attic ventilation on one side

Howdy is the bathroom under the north side of the roof? you may be getting moisture in the attic from the interior of the home and then condensation on the colder northern roof decking. are the baths equipped with exhaust fans and are ya running them during and after showers. the dryer vent clogged? just ideas from past insurance claims handling.? The first time i saw this it was from the builder exhausting the bath fan into the attic instead of out the roof....

RJordan
Re: How to increase attic ventilation on one side

Your first supposition is probably correct. The sun on the south side heats the roof and moisture doesn't condense. It does condense on the cold north side. If the moisture is coming from the outside air, it would be colder than inside the attic and therefore wouldn't condense on the underside of the roof. Moisture problems usually are from internal sources. Is the humidity level high in the house? Hot air rises and carries moisture through the many penetrations in the ceiling into the attic. The ceiling needs to be air sealed, which can be challenging. Probably left to an experienced air sealer. Better yet, spray foam the underside of the roof deck. The spray foam will be warm and there will be no condensation problems. It will also save you a ton of money on heating bills and get rid of ice dams.

Powered ventilation is a terrible idea. What gets exhausted has to be made up by incoming air. Some of that air is likely to be drawn from inside the house. Air you paid to heat. If either theory about the source of the moisture is correct, you would be bringing more moisture laden air in from either the house or the outside by using powered ventilation.

canuk
Re: How to increase attic ventilation on one side

Just about forgot about this thread ---

What living space is under this side of the attic and which direction are the dominant winds from ?

Second thought I should just come down for a visit during the winter and see for my self :D

bp21901
Re: How to increase attic ventilation on one side

There are bedrooms and a hallway under it. Other side is bedrooms, but no hallway. This is an addition to the original part of the house and makes the structure an L shape. The prevailing winds run W to E parallel to the ridge of the addition where the moisture is on the N side of the roof. There is a noticeable temp difference on the underside of the roof deck, I was up there the other day, its still damp-ish on the N side. There is about 4 to 5 inches of snow still on the roof on the N side and no snow on the S side from the sun hitting it. I had hung a box fan up in the rafters and have it on low trying to dry out the roof decking. I want to dry it out as much as possible before trying the foam board. Like you mentioned before, the issue is I won't be able to see the effect since the foam board will be in place.

C'mon down, we still have about 6-8" of snow, some bare patches where the sun hits regularly. Too early here for golf yet, although I have the putting green cleared off for practice. I'd post a pic if I could, showing the green with the piles of snow all around it!

Timothy Miller
Re: How to increase attic ventilation on one side

Howdy, again re read you post an questions now. Is there a ridge cap vent or gable end wall vents or roof vents look like Darth Vader helmet located near the peak of the roof? i Ask because maybe the exit venting is not enough to allow the moister to exhaust out of the attic. How old is the roof? Type shingle? Last time roof inspected for holes above the wet area?

bp21901
Re: How to increase attic ventilation on one side

There is a ridge vent/vented eaves the length of the roof, roof deck cut back equidistant on each side of ridge board. The roof is about 10 years old, no leaks, archy asphalt shingles.

Apparently enough ventilation on S side of roof, but not on N side of roof.

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