Chimney chase condensation
Classic problem I believe.
I have a wood framed chimney chase which houses two 8″ insulated, stainless steel metalbestos wood stove pipes and my main DWV stack. On certain days, when the inside/ outside temps, and the relative humidity are just right, I have condensation build-up and dripping from the underside of my chimney chase roof.
6×10 timber rafters 36″ (on center)
2 x 6 rough sawn decking (not T&G)
3 layers of 3″ Polyiso foam board
2×6 Sleepers 36″ (on center, screwed to rafters below)
3/4″ T&G OSB decking
Grace Ice & Water over entire roof
Standing Seam metal roof
Chase Construction built on top of roof (with exception of metal roof)
2×4 and 2×6 construction
3/4″ OSB wall sheathing
Sheet Flashed around perimeter
Grace ice & water over exterior walls (which I think is best to remove at this point)
1 – 2″ Closed cell spray foam on interior chase walls
3/4″ plywood cap w/ ice & water
Stainless Steel Chase cap (3 penetrations)
The condensation is dripping only from the exposed underside of the stainless steel cap. This is where the manufactures clearances from combustibles (2 inches) dictate the wood hole be 4″ larger than pipe.
So my question is:
1. Should I turn the chase into a vented, uninsulated air space by continuing insulating across/ at the roof line (or maybe even below to the attic floor) and cut vent strips/ holes in the chase wall?
The concern I have with this option is will the relatively warm pipe still cause condensation even when vented?
2. Or should I continue insulation on the underside of the chimney chase cap with a combination of fire resistant spray foam and rock wool?
My concern here is of course the lack of venting directly under the cap.
I lean towards option 1 but would appreciate any further input.
Thanks a bunch,
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