Scenario: 100 + yr old house in New England, large gabled colonial 10(ish)/12 roof w/ slate roofing, old cedar claps covered in vinyl. Off of back gable wall is 14’X12′ bump out kitchen single story 8′ ceiling with 2-3/12 shed style roof coming off of gable wall. Asphalt roll roofing leaks during storms w/ strong winds, we will be replacing w/ EPDM as part of kitchen remodel. Ceiling and walls of kitchen had been insulated w/ old blown in rock wool or other nasty dusty material…but no venting for roof existed. There is a small soffit (~8″) that was wrapped w/ vinyl. We are trying to decide on the insulation/ventilation details that would be most appropriate and cost effective. Option 1. Hot Roof, no ventilation, spray foam on underside of roof deck, and 1 1/2″ foam bd. on top of roll roofing covered by EPDM…problem is cost of foam and access is made difficult/limited by 1″ boards that were installed on top of 2X8 ceiling joists (w/ linoleum laid over). There is a 20″ space above the ceiling that decreases to 10-12″ at the outer wall. Option 2. Cellulose in 2X8″ ceiling joists and foam board under EPDM roofing. To vent or not to vent? How? Ridge vent at roof-sidewall w/ soffit vents cut into rafter bays…labor intensive and does low pitch of roof present a situation where water/snow/ice could make its way into ridge vent?
Any thoughts out there?
Replies
Take a look at the details on a vent meant for your shed roof connection. Being in your location, I suppose there'd be a question about snow buildup at the wall and that low slope of roof. Worth a look maybe.
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Well if you put insulation down under the roofing, no sense in venting. I'd vote for non vented commercial style roof. Put the insulation where you want it ... in the ceiling joists and/or on the roof deck. On the deck will help eliminate thermal bridging ... but make sure you insulate all the way up the wall to the roof deck (i.e. above the wall plate.
I agree w/ the other poster ... the roof/wall connection and venting may pose a problem w/ e.g. snow. I assume your range hood/venting will be improved to control moisture generation in the kitchen.
I'll tell you one thing I wouldn't do: EPDM membrane with closed cell foam sprayed against the roof sheathing. I have taken apart a lot of roofs over the years, and one thing you can be fairly sure of is that some day, all roofs leak. With the closed cell foam, there is no drying capacity and to make matters worse, leaks can disguised. I've endured many a sales pitch from spray foam salesman, and it definitely has it's place, but against a flat roof isn't one of them IMHO.
If it was mine, I'd install cardboard or even OSB chutes from the soffit right up to the sidewall and blast the whole thing full of dense pack cellulose. I'd cut the sheathing back at the sidewall and install a strip of cobra ridge vent, covering it with coil stock or something. Or maybe if there was room, I'd create a tiny attic and install some can vents. Or even some gable type vents.
The company I work for has one house out there with a flat EPDM roof with spray foam against the decking and no ventilation. You can literally feel the heat radiating off of the ceiling in the upstairs on a hot summer day.
I'm sure I'll get tons of flack for saying this but... Technically you do NOT need attic venting in cooler regions if you have a darn near perfect VB on your cieling.. The attic ventilation in these areas is to release moisture drawn into attics via the natural stack effect in a home.. Now, I'm not saying that we can just do away with attic ventilation altogether. And in fact in my area (now Western Kentucky) attic ventilation is rather important to decreas solar gains from the roof. However, in your situation, since you're remodeling anyways, I'd redo the VB in that area, and don't forget to seal all those pesky holes drilled by plumbers and electricians in wall top plates.. I have done this exact thing in Alaska because venting would have been a real pain in the butt. And to make sure we didn't screw up in doing so, we installed a temporary humidity detector(the real name is lost in the back of my mind at the time) and when we went back to check it about a month later, everything was fine...
I'm sure I'll get tons of flack for saying this but... Technically you do NOT need attic venting in cooler regions if you have a darn near perfect VB on your cieling.. The attic ventilation in these areas is to release moisture drawn into attics via the natural stack effect in a home.. Now, I'm not saying that we can just do away with attic ventilation altogether. And in fact in my area (now Western Kentucky) attic ventilation is rather important to decreas solar gains from the roof. However, in your situation, since you're remodeling anyways, I'd redo the VB in that area, and don't forget to seal all those pesky holes drilled by plumbers and electricians in wall top plates.. I have done this exact thing in Alaska because venting would have been a real pain in the butt. And to make sure we didn't screw up in doing so, we installed a temporary humidity detector(the real name is lost in the back of my mind at the time) and when we went back to check it about a month later, everything was fine...
Skip the vents. In your situation likely to cause more trouble than good. OF course you will have to get codes approval, but in my area If I can get it to R-38 they don't care if it's a hot roof.
Option 1 or 2 sounds fine to me. Important no matter what: make sure you have a good air seal at the thermal boundary. That's the beauty of spray foam. If the ceiling is going to be open you might consider a couple inches of foam on the underside of the roof deck, then close the ceiling and pump the rest of the space full of cellulose.
Steve