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Old 10-24-2009, 10:51 AM   #1
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condensation/ventilation/insulation question


We had a new standing seam roof put on a few weeks ago, replacing asphalt shingles. We think it looks great, but we have a problem with condensation in one of the attics. This attic is directly over a wood stove.

The roofer says that it can't possibly be his fault. I think he is *probably* correct, but a) I want to know if it is his fault and 2) I want to know the best way to fix it.

Pictures of the part of the roof I am asking about are here:
http://picasaweb.google.com/mcorner/Roof#

The condensation is visible on the underside of the ridge cap and the plywood seems very damp (there is a layer of sheathing boards under most of the plywood as well). It is pretty humid up there 70% or so, even though it isn't humid here right now.

Ventilation:

This is a very old house (parts of it from 1790), so adding ventilation was challenging. There was a ridge vent and he replaced that with a metal ridge cap. There were 1-2" button vents in the soffits, but I know that they are clogged up with insulation. It isn't as simple as unclogging them (although I haven't done that yet), because there is a beam that almost entirely blocks the path from the soffits to the ridge. See pictures.

Insulation:

This attic has 5-6" inches of cellulose, which is a totally inadequate R15 (New England). I didn't really notice this until now.

So the options I see (or combinations):

1) Try and make these soffit vents work. Clean them out, and possibly replace with a continuous strip. The roof is built so that the plywood/sheathing boards contact the beam, blocking the airflow. Should I shave a bit off the edge of the beam to get air going? Is there a better way to do this?

2) Add a gable vent of some kind. This is an end of the house without another end for cross-flow ventilation, but we could put square vents lower down (on each side of the chimney) and get airflow from there to the ridge vent.

3) Add a lot of insulation. My roofer suggested doing this with no ventilation. At R-15 we need more insulation anyway (he said R-60!). Pink bats or more cellulose? If we try and get the soffits working, we will need foam baffles or something to keep the insulation out of the soffits.

Sorry for being long-winded, I want to get you all of the relevant information.

Thanks,
-Mark

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Old 10-25-2009, 07:08 PM   #2
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condensation/ventilation/insulation question


I would check whether there is poly moisture barrier first before adding more insulation and ventilation. In my area (Winnipeg), the standard attic insulation is R50.

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Old 10-25-2009, 07:58 PM   #3
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condensation/ventilation/insulation question


Your location would help to determine the amount of insulation that you would need. Anything up north would need R-50. Also, without a ridge vent, soffit vents are useless and according to studies gable vents only vent the first 4 feet in. You have warm moist air escaping and hitting a cold surface to create the condensation. You need to add a ridge vent and soffit vents to allow the moisture to escape and also add more insulation and seal any leaks with spray foam to prevent heat loss. The roofer should have included a ridge vent or at least given you that option.
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Old 10-26-2009, 07:57 AM   #4
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condensation/ventilation/insulation question


Removing the ridge cap and replacing it with a vented ridge is as simple as drilling out his rivets, pulling and saving the cap, then cutting the steel pans back from the ridge to allow for air movement, and finally, setting a ridge vent material in place and re-installing the ridge cap. I have always found that vented ridge cap on a system like yours works best with an alignment plate placed under the actual cap. This gives me something to rivet to and it helps add rigidity and structure.
Short of adding ridge vent, your best bet would be to ventilate toward another part of the attic adjacent to that area.
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