I have a lack of insulation in my roof behind drywall I really do not want to tear out. The house is a cape with half walls and drywall installed on the bottom side of the roof rafters. Here is the catch the rafters are 24 – 30 inches on center on a 6-12 or better pitch. (I guess that is why it handles the snow load up here) I have access at both the top and bottom of the cavities so I intend on sealing the bottom of the cavity with rigid insulation and blowing cellulose in from the top. Now my concern, I want to make sure I have ventilation from the bottom of the cavity at the side attic to the top attic and plan on sliding foam vent protectors (the ones usually used at the edge of attics to prevent insulation from blocking eave vents) down the cavity and stapling them to the underside of the sheathing. Now here is the question. Do I need to make the venting the full 24-30 “wide or can I run a 16†vent up each cavity and call it good???
Discussion Forum
Discussion Forum
Up Next
Video Shorts
Featured Story
Learn how to fight wood-boring beetles and prevent home infestations with expert advice from Richard D. Kramer, an authority in pest control.
Highlights
"I have learned so much thanks to the searchable articles on the FHB website. I can confidently say that I expect to be a life-long subscriber." - M.K.
Replies
Ideally, you should provide full width ventilation channels in each rafter bay. This is especially important considering the climate where you are located.
Polystyrene vent panels aren't particularly stiff, though; I have my doubts as to whether they would just collapse flat against the underside of the sheathing when you blow in that cellulose. It seems to me you'd be safer doing it right with 2x2s and homosote panels...but that means ripping out the drywall.
The other option is to insulate on the outside. If you see yourself re-roofing anyway sometime in the next five to ten years, this is the way to go as you will kill two birds with one stone.
Dinosaur
How now, Mighty Sauron, that thou art not brought
low by this? For thine evil pales before that which
foolish men call Justice....
Slide sheets of rigid insulation. With a 6:12 pitch, they should still hug the drywall leaving a venting space between the top of the rigid insulation and the bottom of the roof sheathing for venting.
There is growing view that one need not ventilate, at least if certain conditions are met.
The subect has been much discussed and the search function should help locate the threads.
The "War on Terrorism" has failed - in part by narrowing our options to only the option of last resort.
I propose we start a worldwide Partnership Against Terror, in which the reasonable people of the world work together to oppose terrorism and the conditions which lead people to that desperate condition.
"We hold these truths to be self-evident, that all people are created equal, that they are endowed by their Creator with certain unalienable rights, that among these are life, liberty and the pursuit of happiness."