Replies

1. Expert Member
   DCcontrarian | Oct 04, 2023 04:11pm | #1

   Is it leaking or condensation?

2. 
   onslow | Oct 05, 2023 05:49pm | #2

   555jjb,

   Your description raises questions. What size are the beams? Are they solid or laminated? What is the spacing between the beams? What exactly do you mean by high R sheathing? Are you sure about the roof stack up above the beams? Did you just lay on the high R sheathing?

   What you described as the original roofing makes no sense unless you meant roll roofing instead of tarpaper. As you note, that doesn't make a whole lot of sense either, especially the gravel part. Homesote is certainly an odd choice, but in its defense my father's garage was completely clad in it and it lasted over 40 years. It was one of the post war wonder materials.

   If by high R sheathing you mean something like R-12 Zip panels, then condensation could still occur during winter lows. Homesote and gravel are vapor open, so any interior moisture will pass through and collect on the first cold barrier. That would have been the roll roofing material (if) that was used before. Insufficient foam panel thickness under the current metal roof could still leave the roll roofing cold enough to condense intruding warm air.

   There are other avenues to explore if your timbers are milled logs that extend through the wall line to support the roof overhang. A friend of mine has 8x10 timber roof supports that extend in this manner, which has resulted in a leak problem not from condensation, but rain intrusion. The timbers have cracked over time as most milled logs do. Driving rains manage to enter the cracks at the end of the timber and track inside. A very poor flashing job was also allowing the top of the beam to get additional rain introduced on the tops of the beam tips. Perhaps you need to look at the perimeter flashing in the high side of your slope and see if you can spot avenues for rain intrusion.

   You have not mentioned if there is any pattern to the leaks presentation beyond the chimney being one potential culprit. Now that it is gone, have the leak patterns changed? Do you see more damage over high moisture areas like kitchen or bath? If the leaks only appear near the beam edges it suggests a tracking leak. If the overall homesote ceiling is damp, discolored or breaking down it may well be a more generalized condensation issue. I would think that a roof as you described would present such high heat losses that condensation would not be a concern if you were keeping yourself warm. Would snow even remain on the old roof?

   If you took any photos of the chimney opening that shows the layers old and new, it might help me or others to suggest better paths forward. Photos of the current high side of the new metal roof edge would be helpful too.

3. Expert Member
   Michael Maines | Oct 06, 2023 12:45pm | #3

   It sounds like a "Deck-House" style of construction. The beams are probably 3-4' o.c. and extend out to support the roof overhangs. Over the beams there are probably 2x6 tongue and groove softwood planks as sheathing. Over that sounds like a typical balasted built-up roof (tar paper, tar, tar paper, tar, gravel). That roof system actually works pretty well as long as it can drain. The Homosote might be original or might have been added in an attempt to get a little insulation value.

   It's a structurally efficient system but not a good one for cold climates, because there is not enough insulation to keep the ceiling warm, resulting in condensation. You probably added a few inches of polyiso foam on the exterior which would help a lot but where the beams pass through the wall they will still be cold and create condensation.

   Photos would be helpful.

4. 
   user-5946022 | Oct 07, 2023 07:14pm | #4

   Post photos so we can help.
   If you have photos taken during the roof work, right before they put the new roof system on, that will also be helpful.