roof venting and attic insulation
I have read articles on various websites on roofing and venting that most homes in the US have inadequate roof venting which creates major problems in attics. Unfortunately, my roof was blown off during a major storm and the roofer did not know anything about venting and simply replaced what was originally installed. I would like to install some sort of venting but would not particularly like to install the typical vents originally installed (I’m afraid there would be significant damage done by workmen crawling around on the new shingles). I have seen a vent that is installed at the peak that runs the length of the roof peak but in Minnesota with blowing snow in winter, these peak vents allow snow to blow in which eventually melts and ruins the insulation. Are there powered vents that can be installed in each end of the house up near the roof peaks? Speaking of insulation, the insulation in the crawl space (this is a single level home) between the rafters is the old “blown in” stuff; would it be practical to have this vacuumed out and replaced by a spray-in product? Many thanks.
Replies
Since you are in MN, you may actually be in an area that actually benefits from attic ventilation, as it provides some protection from ice dams (the area where any benefit accrues is realy quite small).
You might want to add buildingscience.com to your reading list, it can be quite interesting (even if the site map is a bit obtuse).
Now, generally, I'm always in favor of removing that "gravity: insulation laid on attics (which are not generally air sealed in any meaningful way). Moving the insualtion plane to the underside of the roof makes for so many more benefits that it's near reflex.
However, you are in a place where keeping air circulatin under the roof deck has benefits (IIRC), so that needs preserving. Now, that could be as easy as installing rigid foam sheets on the bottom of the rafters, sealing the edges with spray foam. Two plies might be neater work in an attic, for that matter. Then Coravent or a similar product could be used to get air in and out under the roof deck. Your local AHJ (authority having jurisdiction) will be able to tell you if foam has to be covered with a non-combustable material in that application. They will also tell you what R value they will insist upon, too,
Oh, and for perspective, my attic, which is ventilated, only reached 109º today (but, that was for 3 hours, over 95º for 9 hours, though. That air ventilating the attic went from 89% RH down to a paltry 62%, but that was at 109º . . .
We've had ridge vents for about 20 years now, and no problems from snow blowing in. Southern MN.
IMO ridge vents are the only way to go.
As to your insulation, first install more eave vents and chutes, then crawl around and seal penetrations, then get about a foot of new cellulose added. No need to remove the old.