Hi,
During the fall we had our slate roof repaired, and added new attic insulation. (the old stuff didn’t seem to be adequate). Last week, after our first snowstorm (Maine) I went into the attic to check on how things were holding up. In previous rainstorms I had gone up there and not seen a drop.
Anyway, as I looked down toward the eaves, the sheathing had a wet sheen to it, runnig horizontally across the roof. Later when I went outside, I saw that there was still snow on the roof in this area.
Last year, the snow quickly fell off the roof, while this year, it is staying on the roof, except for the one area that has direct sun. Our house is the south side of a duplex which has a main ridge and two hips. So our roof faces, east, west, and south.
I think the sheathing is wet due to the snow still being on the roof, which is partly caused by the increase in insulation in the attic. As I said, last year the snow would quickly fall off the roof, which I am chalking up to the attic being warmer.
Can someone tell me if: a) this is normal for a slate roof, b) if I have some kind of ice dam forming, and c) how I can go about fixing this issue, if it is an issue.
Thanks,
David
Replies
David,
Where in Maine are you located?
It's hard to tell what you have going on without seeing it.
If it is ice damming and subsequent leakage from it ,then several solutions come to mind.
Aprons on the lowest 3 ' of the roof after removing those courses of slate will let no water from backup into the house.
Also Grace ice and water shield laid on the roof deck after slate removal-then relaying the slate also has success.
More info on snow depth,icicle formation,etc. would be helpful.
Have you also got proper ventilation?
The thing that has changed is the added insulation, so you would expect the attic to be colder and the roof to keep the snow on.
you don't say whether you have venting in that atic, or vapour barrier between living space and the insulation.
You probably have enough warm damp air from the house getting to the sheathing and condensing
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Thanks for the responses. We live in Bath.
The soffit does not have any ventilation, and as I understand it, slate roofs are considered breathable already and do not require ventilation.
When I put the batt insulation in, I may not have allowed for enough airflow in every bay, but certainly a majority of them. Also, the snow buildup is only on the bottom third of the roof, the top part is clear and there is no condensation on the roof sheathing. That is why I thought the condensation issue had to do with the snow sticking to the roof.
It is interesting that the wet sheathing starts from the hip ridge as 6 boards wide, and as you move to the center of the house, the wet sheathing lessens to only 2 boards wide. Why would that occur?
I didn't place a vapor barrier down when I added the insulation. There was already 2 layers of old kraft faced insulation that I thought was adequate.
The thing we keep trying to figure out is why last year without the new insulation would the snow always fall off the roof, and now this year the snow is staying on the roof and we are seeing this problem. It seems like that since we removed the 'warmth' from the attic we caused this issue.
In terms of the icicles, we had quite a few originally but they have since fallen off. We no longer have icicles but could attribute that to the cold weather. Also, we do not have gutters.
Thanks for the help so far.
David
Where is the insulation? In the joists bays (floor level) or in the rafter bays?You say that you think slate is "breathable". I don't know anything specific regarding this, but many slate roof as installed on skip sheathing (1x3 up to 1x6's boards spaced 1/2 to several inches apart) so maybe this is why you heard that.While the combination of slate and skip sheathing could certainly assist ventilation you still need a place for the air to come in. Since you have no soffit vents you can never create a loop of ventilation.Why does your condensation problem grow as you near the hips? I have no idea on this one. Maybe there are some localized conditions that are causing the difference? Is there any correlation with bathrooms in the house?
Jon Blakemore RappahannockINC.com Fredericksburg, VA
Before you start adding ventilation to the roof, start by learning about vapour diffusion, air leakage, air sealing and attic moisture. Installing a better vapour barrier (unsealed) will only affect/stop 1% of the moisture getting to the attic from the house. To try and seal this vapour barrier will be a hassle so.......leave it out and air seal the attic at the ceiling level. Air leakage from the house below is responsible for about 99% of the attic condensation.
Control the moisture:
1) Clean up any moisture sources in the house- dry the basement up, don't dry clothes indoors, vent the dryer, don't have too many plants (good ones too), aquariums etc.
2) vent the baths and kitchen
3) airseal the attic. By this time your attic moisture may have disappeared except for a bit in the colder weather. This is not a problem since it will disappear by evaporation before its warm enough to start causing mould, etc.
4) add a bit of ventilation at the eaves.
See a paper at http://www.cmhc.ca titled "Attic Venting, Attic Moisture and Ice Dams". Just search for "attic venting" and it will come up. Some shocking but true statements in the paper.
Edited 12/15/2005 7:04 am ET by experienced