attic stair insulation

I wanted to know if anyone has actual experience building an insulation box for pull down attic stairs? I see the sticky note at the top of this forum but the link seems totally useless and is just a government energy website.I plan to just build a rectangular box out of 2 inch rigid foil faced foam board, and then using Tyvek tape to seal around all the edges.I just wanted to know if there is a specific caulk that would be best to use with the tape between the seams.
I saw one guy used two or three small bungee cords to hold down the box to the stair opening once he was done using it .
So as long as the rigid board has straight edges all the way around, the bungee cords would seal any gaps.Hopefully someone sees this question to answer it because this forum does not look very busy to me. thank you for the response.

 

Hi Dale, actually, the number of energy related questions peaks in the fall before the cold weather and then declines throughout the winter, especially with the lower energy costs. They usually post under basements or attics, although this is a good title.

But, to your question. The best solution is a permanent box around the opening as the depth of the insulation should be well over a foot. A coffer dam so to speak around the opening made out of plywood will be insulated on the sides by the existing insulation, Then your 2 or 4" of rigid over the top. I like a 2" piece that fits tight inside the plywood frame, glued to a larger 2" piece that fits over the entire frame.

Air sealing is a high priority as exfiltration pressures are highest at the ceiling.

Bud

 

Bud, how would you have insulation a foot deep around the framing. Existing attic batts sit between the joists whereas a plywood built box frame would sit on top of the joists so you would have about two foot thick total insulation surrounding the box to the top? Secondly, it seems like a lot of work to build the walls out of plywood because you would need complete framing inside of it to keep it from warping with extreme attic temps. Why is my idea of making a complete movable box out of rigid foam board not a good one in your opinion? If its because the R value of two inches is not enough, then ill make a 4" thick box both sides and top. I don't like the idea of having permanent fixed walls because my wife and I will have 6-12 inches to step over when going up in the attic which is a nice jump from the last ladder step. We do only access it about once or twice a month however.

 

NJ has a code minimum of about r-40 so more would be better. Batts do not present the same problem as blown in cellulose, which if you add more I would strongly suggest. Fiberglass insulation loses r-value as it gets cold and it permits all of the cold ventilation to filter all the way down to the ceiling below, not good. Wild guess would be your 6" (assuming) of fiberglass insulation (rated r-19). between bridging and poor thermal performance is acting at less than r-10. Adding more over the top covers the thermal bridging and if you use cellulose it improves the performance of the fiberglass below.

2x2's in the corners hold the frame together and angled screws through the plywood secure it to the joists.

But, there is really nothing wrong with your approach, just offering a more permanent solution, which would allow cellulose to be added at some point in the future.

As attics get really filled with insulation, any hope of using them, or even getting around up there, is lost. When I have audited homes with 16 to 24 inches of insulation and all I can do without doing more harm than good is look around from the access opening.

Go for it,
Bud