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Community and Q&A

Retrofiting third story one-sided shed dormer during roof replacement

Stefwef | Posted in Energy Efficiency and Durability on

We are in a second/third story condo near Boston, MA and in the process of hiring roofers. We have a 1.25:12 low-slope shed dormer with rubber roof, sharing a ridge with a steeper side that has a shingled roof. Under the dormer are bedrooms and a bathroom, and under the steeper side are mostly closets, but also one tall dormer with a skylight (at top of stairs) and shingle roof. The dormer side wall has windows all along that are facing south and sunny all year-round. The front (main) bedroom under dormer has a skylight as well. There are soffit vents all along both the low and the steep undersides. At top ridge of roof, we currently have a ridge vent open on both sides. The front and back gables of house have grids that look like they used to be vents, now closed (we presume/hope).

I attach a drawing from 2000 remodel when they put in the dormers.

The problem(s)
• In the summer, it gets incredibly hot on third floor.  [When the heat is working, it does not get cold on the third floor. We have not experienced any draft there either.] We use AC window units from early May to early October, and we hate it.
• We are experiencing lots of rain leaks throughout. However, we do not believe we have a mold problem (I’m extremely sensitive to mold so my nose would tell me).
• We don’t know what the roof deck looks like. We are hoping it was a properly installed in 2000 as a cold roof (with insulation against the lower roof deck allowing ventilation above it from soffits to ridge). However, roofers tell us they often see bad installations with too much insulation blocking the way.
• It’s possible water is entering ridge vent on the dormer side because it’s very flat (1.25/12).
• We are getting ice dams on the dormer roof, causing leaks.
• The chimney, skylights, and vent openings are also likely causing leaks.

The desired outcome
• We would like to redo the roof in a way that fixes the leaks, addresses the heat, and does not create humidity issues.
• We will be placing solar panels all along the dormer side (also this spring).
• We will be losing the skylight over the main bedroom in order to add more panels.
• We will be replacing the skylight above the stairs (the smaller, tall dormer).
• Eventually we plan to add heat pumps to cool the third floor in summer.

I thought it would be an easy process to screen and pick a contractor, but the wide range of proposals is overwhelming:
• Redo the roof exactly as it is. If it ain’t broke don’t fix it. Make sure the gable grids are closed.
• Redo the roof exactly as is, but don’t cut open the dormer side ridge vent so that water won’t get in.
• Redo the roof exactly as is, but add a 1″ baffle all along the dormer-side ridge vent to make sure water does not leak in.
• Add a thick ISO board on dormer roof side only, to add insulation. We worry this would not solve the problem as cold air may still circulate underneath, but perhaps there’s a way to do it properly where you also insulate around the vents on either side – but them we worry about humidity collecting.
• Add a thick wedge ISO-board on the dormer side only, to both add insulation and to increase the steepness of the flat roof. Same worry as above, plus how would this affect venting at ridge as presumably it would make peak higher?
• Blow foam insulation through the ceiling to insulate the dormer side and block ventilation on that side (turning our cold roof into a warm roof). We worry this would shift the dew point to below the decking and cause humidity problems. We’re also not sure how that would pair with the steeper cold roof.
• Remove ridge vent altogether, and re-enable the front and back gable vents, adding two solar-powered fans. We really like this roofer, but worry his solution would cause unnecessary energy use, add something that will break, create perfect nests for squirrels, and actually lower our ventilation, causing an even hotter roof.  We also worry the “attic triangle” area would become pressurized and pull air from inside the home (so losing heated air in winter and cooled air in summer, though our house is likely too leaky for this scenario) — or worst, dangerously push furnace exhaust into the home.
• Add box vents on the dormer side. We’re not crazy about this as we hear they leak a lot.
• Pull and replace most of/entire roof deck to make sure insulation is adequate and not blocking ventilation, and perhaps add baffles. This is a lot more costly so we’d like to avoid it if not totally necessary.
• The heat problem is more to do with our rows of windows, so upgrade all the windows.

I’d be super grateful for any advice. Thanks!

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