Sealing attic kneewall


Old 12-11-16, 04:47 PM
Thread Starter
Join Date: Dec 2015
Posts: 11
Sealing attic kneewall


I posted earlier about mold and ventilation issues, and our house finally has a ridge vent and soffit vents (before only had ONE gable vent )

The drama continues, as the roofer installed the soffit vents, but as we have an attic kneewalll (its a cape), the air is now flowing into the kneewall and through the two access holes, into the house. I could smell my neighbors woodsmoke in my house the other day. So now our kneewalls are leaky.

We have a NEW roofer coming to install baffles in the next few weeks. The knee wall is insulated from the inside along the roof decking and I believe within the floor. So the kneewall is "inside" if that makes sense. Its not cold like an attic (looks like right side of photo below)
Name:  6a.gif
Views: 1406
Size:  21.4 KB

There is insulation along the roof decking and the knee wall and in the floor. So its insulated from the outside, as opposed to the house insulated from the crawlspace.

we still have elevated mold levels in the attic, and i had an ah ha moment when i climbed up there and saw that insulation is flush against the wall in the corner like this: (not a photo of my attic)
Name:  index.jpg
Views: 575
Size:  5.9 KB

So air is not venting up into the attic, but, the soffits are leaking into the kneewall, and in the back of two closets we have these access points:
Name:  IMG_0769.jpg
Views: 370
Size:  40.6 KB

I am attempting to seal these access points off. Obviously its a bad air leak, but because of the mold problem we are wondering if that is why the room still has elevated levels. IE not properly ventilated still and sending spores right into the bedroom.

I have found a lot of ideas for making a access "door" but since it is in a closet, it doesn't have to be fancy. I have several inch thick insulation foam and plywood to use.

Not sure the best way to to this to get the best seal.

1. Cut the foam to fit directly into the hole, and line with weather stripping. have it attatched to a larger piece of plywood that is larger than the hole.
con: how do i ensure i tight seal?

2. Have my foam attatched to plywood, and angle it into the crawlspace, and pull it flush against the access hole, and use eyehooks and a latch to pull it tight.

Any help would be appreciated. I'm pretty upset that the person who installed out soffit vents did not ensure they were flowing into the attic. The access holes into the kneewall always just had a piece of plywood resting against them, so bad in terms of energy efficiency. So my first steps are fixing the venting issue, and sealing off these points. I just made an attic hatch with plywood and insulation foam and weather stripping (before it was just a piece of plywood).
Sponsored Links
Old 12-16-16, 08:39 PM
Join Date: Nov 2013
Location: United States
Posts: 165
Fellow cape owner so I feel your pain. Although we have no soffits or baffles at all.
If you aren't concerned about looks there are a multitude of ways to seal it. One pretty easy one if the opening allows it is:

1. Cut the foam and plywood larger than the opening by a couple inches
2. Take some scrap plywood strips and make a simple frame on the back of the foam so that the frame is the same size as the inside of the opening
3. Lay it all down so it's (from bottom up): playwood, foam, frame
4. Drill some holes in equally around the frame through all 3 layers. Enlarge the plywood holes.
5. Push some bolts through the frame and foam
6. Install inside the cavity
7. Put the plywood over it and line up the bolts through the holes
8. Tighten with wingnuts and washers
This would sandwich it together and is a pretty simple and quick approach. You can also add some weather stripping to the plywood that would contact the drywall overlap.

But again, there's a number of ways to seal a hole if looks aren't important
Old 03-07-17, 03:29 PM
Thread Starter
Join Date: Dec 2015
Posts: 11
Thanks...I had trouble logging on for a bit but I found this post again.

My first attempt I'm not that happy with it, it was good in a pinch. The big problem I have is the floor is not framed out (the sides are), so I am going to install a piece of 2x4 along the floor and seal any gaps with foam. Right now I made the plywood a bit larger than hole and cut the foam to fit in, so I push it in...but I'm still getting air leaks.

I think I'll cut a piece of plywood a bit larger than the hole like you said, and angle it into the kneewall, then weatherstrip the inside wall and pull the plywood (with foam on back) tight against the it and secure with eyehooks to get a tight seal. Hope that works.
Old 03-07-17, 05:32 PM
Join Date: Nov 2013
Location: United States
Posts: 165
Glad to see you back - easy to forget about something like this until next winter. Your plan sounds good - you may be able to use turnbuckles.
Old 03-07-17, 05:39 PM
Join Date: Nov 2013
Location: United States
Posts: 165
Also you may be able to keep your current setup if the plywood has enough overhang of the opening frame.

1. Get some hanger bolts
2. Drill some holes through the plywood and just enough into the frame to know where they are (size based on bolt)
3. Drill a smaller hole into the frame the depth of the threads on screw end of bolt. Just to make screwing the bolt in easier and prevent splitting
4. Install threaded end into frame
5. Add some of that door weatherstripping to the plywood where it will touch the frame
6. Install the plywood, lining up the holes and bolts
7. Tighten with wingnuts or nuts

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Thread Tools
Search this Thread
Display Modes