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I have a question concerning proper roof ventilation for an addition I built onto my house.I am now insulating the ceiling of the addition. The roof has a 6/12 pitch with a clipped roof peak, and was built with 16″ parallel chord roof trusses. The peak of the roof has a continuous ridge vent, and I have installed ventilation chutes on the underside of the roof sheathing from the soffits to the ridge vent, between the roof trusses. My problem is with the clipped roof section. Because of the roof truss design, I can only fully ventilate about half of the roof. For a majority of the rest of the roof, I can only install the chutes so they are vented at the bottom end, but not the top end. (due to the roof truss framing blocking the ventilation chutes.) Also,there is about a 5’x5’x6′ triangle shaped section at the top end of the clipped roof peak that I could not ventilate at all because of the framing. I live in Minnesota, and am insulating the roof with fiberglass batts to a value of R-44. Can I ventilate the roof as described, without incurring condensation problems in the future because of the lack of proper roof venting? In the triangle area with no venting, should I install the chutes to space the insulation away from the roof sheathing,or should I install the insulation tight to the deck there? How do you recommend I deal with this? –Matt in Minnesota
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Wrong place to ask, which is probably why no recent responses. Check archives, including the energy one, as this has been a years long debate here. Many here don't know why you need to vent, except on the Internet. Example: your last paragraph -- what condensation if you don't let any moisture into that area in the first place?
*Matt,Steve the ex-Minnesotan here. Venting in the hipped area can be accomplished by putting a ridge vent on the hips as well, but there are many here who will ask you why you would want to do such a thing.The short answer is that if you have a well-sealed ceiling and you have your moisture sources under control, you shouldn't have to worry too much about condensation.But again, go to the archives for a more involved history of the arguments for and against.Steve
*Steve, thanks for the reply. I researched the archives, and still didn't find enough information to answer my questions, given my circumstances. Do you (or anyone else) have any advise for the questions raised in my last paragraph of my initial em-ail? Other information of interest: (1) the addition is for a 4 season porch, with 3 walls that are essentially all glass. (2) there are no excessive moisture sources for this room (like a kitchen or bathroom would have.) (3) the only ceiling penetrations are for a ceiling fan and an exhaust fan. (4) I question how well I will be able to seal the walls and ceiling, because it will be finished with tongue and groove cedar, not sheet rock. (5) all the exterior work is already completed.I am new to this discussion forum, please be patient with me if I ask questions that some may be tired of answering. --thanks, Matt in Minnesota
*Matt, to seal the room you may have to hang and finish drywall as you will not probably get a complete seal with a t&g bd ceiling. And also, where is that exhaust fan going to vent to?
*Matt,Is the ceiling a flat ceiling (not cathedral)?If so, I would just install the ridge vent, maybe with a wider than normal channel cut at the ridge, vent the entire length of the soffits, and insulate at the ceiling plane, not the rafter plane. I too would add a layer of something more air-tight under that t&g. What about a layer of Poly-iso board and tape the seams? Then blow cells two feet thick on top of that.Steve
*Calvin, I was planning on installing 1/2" plywood on the underside of the roof trusses before I installed the t&g cedar, so I wouldn't have to deal with the 24" spacing when I nail the cedar in place.(I was planning on nailing the cedar directly to the wall studs (after installing a vapor barrier.) I question how good the vapor barrier will be, after all the nail holes from installing the cedar. Also, at this point it would be difficult to deal with trying to sheet rock walls too, before installing the cedar, (although I agree fully sheet rocking walls & ceiling first, would certainly give a much better seal) --because one of the walls has an arched transom window which would have to be furred out for the added wall thickness. The exhaust fan is installed in the ceiling, close to the peak, and exhausts through the roof through a 4" vent. Any further comments or suggestions? --Matt
*Steve, The ceiling is vaulted, the framing is done with 16" parallel chord trusses. Please refer to my original message(s) for more details. I appreciate your input. --Matt in Minnesota
*I have not received any responses lately. Can I PLEASE get some input from some of the experienced carpenters and contractors out there? Please refer back to my earlier messages. --thanks! Matt in Minnesota
*Matt, your better off checking http://WWW.weatherization.com Nobody here is going to touch this one.
*Matt, For what it's worth, I did a lot of research on this and it seems to vary a lot depending on where you're at. Here in Minnesota we need to do a great job on the vapor barrier. The rest of it seems to work out O.K. if you put fiberglass insulation in and don't pack it down, then the normal settling will provide the air path. Remember in the winter air here can be dryer then the desert. The summer is another matter though and that's where dark shingles seem to offer an advantage. The heat that's generated under the shingles apparently increases the venturi effect. (remember hot air rises) That venturi effect will help evacuate the chambers formed when the roof trusses form bays. Just remember to provide a air path at the eves. (and make sure there is clear air space above the insulation. The Basic rule of thumb seems to be the total of the air outlet (at the ridge) must be greater then the total of the air inlet (at the eves). I've gotten so much contradicting advice that whatever you select you'll get a differant opionon. If you're saying that one corner is butted up agaisnt plywood or something, see if you can cut some larger holes in it to provide some air path, anything is better then nothing.
*Ever think of a house fan?
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I have a question concerning proper roof ventilation for an addition I built onto my house.I am now insulating the ceiling of the addition. The roof has a 6/12 pitch with a clipped roof peak, and was built with 16" parallel chord roof trusses. The peak of the roof has a continuous ridge vent, and I have installed ventilation chutes on the underside of the roof sheathing from the soffits to the ridge vent, between the roof trusses. My problem is with the clipped roof section. Because of the roof truss design, I can only fully ventilate about half of the roof. For a majority of the rest of the roof, I can only install the chutes so they are vented at the bottom end, but not the top end. (due to the roof truss framing blocking the ventilation chutes.) Also,there is about a 5'x5'x6' triangle shaped section at the top end of the clipped roof peak that I could not ventilate at all because of the framing. I live in Minnesota, and am insulating the roof with fiberglass batts to a value of R-44. Can I ventilate the roof as described, without incurring condensation problems in the future because of the lack of proper roof venting? In the triangle area with no venting, should I install the chutes to space the insulation away from the roof sheathing,or should I install the insulation tight to the deck there? How do you recommend I deal with this? --Matt in Minnesota