What to do? Insulating and covering up the roof hatch

Update: Here’s the finished solution if you want to see how we solved this problem.

Things are nearly ready to reveal on the upstairs sleeping porch, but the last major remaining item (other than installing the light fixtures and fan on the ceiling and casing the windows) is figuring out how to insulate and cover the roof access over one of the closets. And once again, I turn to the internet for suggestions. How should we go about best insulating the thing?

Roof access hatch and wall

The access was rebuilt when we did the roof, so it’s theoretically sealed from air by at least the membrane flashed up and over the framing, though the new 2×12 framing that composes the frame that sits on top of the roof doesn’t sit totally flush and there are gaps around it, which you might be able to see in that first photo. While there is 2″ polyisocyanurate sheathing insulation under the actual roof surface (same as this stuff I used under the attic floor), I don’t believe that they put any on top of the hatch, making the hatch a veritable chimney for air leakage.

Ideas for insulating the hatch

Idea #1

My first idea for insulating the hatch was to cut up rectangles of polysio sheathing and stacking them on top of a hatch cover that would overlap the framing a little bit on the bottom. The sheathing would fit fairly snug in the opening and sit in a stack on the hatch cover, and then the hatch would be locked in place with a couple sliding bolts or something to that effect that would be mounted on the trim. (There’s going to be 1×4 or 1×5 flat trim around the opening)

You can see my first thought at this in this photo, stacked up on the closet. I happened to have a big panel of sheathing down in the basement, so I measured the opening and cut it up to see how this would work.

And yes, I did that illustration myself and I am available by the hour and half hour.

Attic hatch insulation

The biggest issues with this solution are: the stack becomes quite heavy, meaning that there’s no way that Rachel can open the hatch by herself that easily. The sheathing doesn’t fit as snug as I like, which means that there’s still lots of gaps around the edges and room for air to move around. It looks DIY, in a really bad way, and in the kind of way I’ve been criticizing while undoing decades of it in the house for the last year and a half.

So I think I can scrap this ill-advised plan. Apparently this “idea” was the spawn too little sleep.

Attic Hatch

There’s the attic opening as I painted the ceiling last weekend.

Idea #2

My only other idea at this point is to insulate around the inside of the opening and the top hatch with 2″ sheathing.

I’d recut that sheathing, cover the inside of the top hatch all the way to the edges where the hatch sits on top of the framing, lay pieces vertically all around the sides of the opening all the way up to the piece on the top, put one 2″ piece on top of the inside hatch, cover everything with drywall, and then just have the lower hatch cover it all up and still be locked with some bolts attached to the trim like I was originally planning.

The only drawbacks I can think of are: 2″ of sheathing isn’t a lot of R-value. Maybe around R-13 to R-15 for two inches. And then there’s the issue that there’s still this giant air cavity inside the access with what amounts to 2″ on the lower hatch, and 2″ on the top hatch. Still seems like it’s not enough to me, but I’m definitely no insulation expert. And there will certainly be gaps and holes for air flow around the hatch cover, and potentially on the top cover as well.

Is there something I’m not thinking of, or a better product I should use other than the sheathing? What about a span of thick fiberglass batt on top of the hatch to fill some of the area? Worth it?

Thanks, smart people out there who might be able to help.

Update: one photo I remembered that I had that might show the hatch a little better. Here’s the view from the roof.

New roof hatch

 

UpdateHere’s the finished solution if you want to see how we solved this problem.

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