Fix 1.5 story roof insulation/venting
Hi all, quick background: 1925 craftsman home. 1.5 stories. Climate zone 4a mixed humid. Closets built into the “wings” of the 1.5 story space.
Two of three closets are getting demoed due to unrepairable damage to the plaster from a bad roof install and chimney flashing, since fixed. The roofer put in a ridge vent.
When we demoed the closet, all of the cavities were packed with blown in, and there were some old school rockwool batts here and there. But that’s mostly gone now.
Some photos for reference here:
https://imgur.com/a/p9tg5Gt
1. Can I reasonably expect to get a solution here that vents adequately? There is currently no air path between the addition’s attic and the original attics. They built the addition on top of the old roof without cutting the eaves off and the original roof was not vented. So the addition has soffit vents but no ridge, and the ridge has no soffits feeding it air. I had thought to sawzall/drill some big openings between these two roof spaces while I have this closet demoed. Worth it or folly?
Some previous discussion of the addition roof situation here: https://www.greenbuildingadvisor.com/question/soffit-vents-but-no-ridge-vent#
At that point in time I was not fully understanding the added complication of the “lower” and “upper” existing attic spaces created by the 1.5 story design.
2. Is there a way to get some insulation in the ceiling of this closet with a vented assembly without rotting my roof deck? (Roof is decked with osb over the top of the old solid wood decking.) The roof is 4X construction so there’s not a lot of depth to work with.
3. The walls of the rooms upstairs have their double top plates notched into the roof 2x4s. I assume to move them as far outboard as possible. This leaves very little room for airflow. I could possibly bridge the spaces with 1″ pvc pipes jammed through to keep some clear airflow. Currently old blown in is definitely hampering any flow.
A photo of the above notched top plate situation here: https://imgur.com/a/Vmyuj12
The house would have been a perfect candidate for insulation above the roof. But I didn’t know any better a year and a half ago and had a brand new, pricey standard roof with a ridge vent put on.
Thanks,
Nathan
Replies
You can generally dense pack short sloped ceiling sections. Provided the mini attic above and bellow is vented, any moisture can move through the cellulose and dry to the other sections.
Looking at your picture, you can install some gable vents into your siding for the rest of the attic spaces. Do your best to seal up the ceiling there, more important to fix the air leaks than to get perfect venting.
You mean the ceilings inside the house, to keep moist air inside right?
I had an engineer out and he recommended gable vents as well. He also recommended adding vents up under the gable to each of the lower attic spaces. I had thought gable vents weren't thought well of anymore.
Would it be prudent to do a thin layer of xps spaced 1" from the roofline above the dense pack to leave a clear air channel? That seems relatively easy to do.
Would rockwool bats be considered appropriate as dense pack? Or does it need to be something blown in tight.
Thanks!
Nathan
Gable vents work, there is nothing wrong with using one. As long as you size the free area based on the sqft and slope of the roof it serves, you should have no issues.
Provided there is some reasonable amount of venting, most roof issues are caused by house air leaks, important to deal with those first.
Normally you dense pack the sloped section to not have to remove the ceiling. If the ceiling is off, you can go with batts. Adding a vent space is even better. With older real 2x4s I have used the acoustic insulation batts before for vent space as they are slightly thinner than the regular batts. This gives you a 1" vent space, no need for any fancy baffles. If you are going to make some baffles, make sure it is out of unfaced foam. You don't want the baffle to be a vapour barrier.
Got it. It's totally demoed at the moment. Aside from the limited space the world is my oyster so to speak.
I like mineral wool in general because it doesn't hold water like fiberglass.
The house had terrible air sealing at the second floor attic. I built a new attic access with full weatherstripping etc to help address that. I'm having all the electrical boxes etc replaced concurrently with this work so I should have ample opportunity to seal all the ceiling boxes up.
One other followup, is unfaced rockwool a reasonable solution for the exterior wall? It looks to me like there is some kind of foam board under the siding outside the original wood sheathing.
My biggest concern is causing rot with insulation that traps moisture where it shouldn't be!