The coolers work awesome except some foams and caulks eat styrofoam so some testing needs to take place before you head into the attic. If you have to deal with codes and an inspector ask his opinion first. There are covers available that can be caulked in place and are treated so they won't burn and aren't quite as easy to find, are more of a pain to work with and to some are expensive if you have a dozen to do. One other option is a 'sealed' trim that goes on the inside. I think these are great if installed and caulked in place so they truly are sealed but then painting can be a challenge later. They come with a flakey stick on gasket which is still much better than a cheap trim but still is far from perfect without caulk. I have purchased the trims from Ebay much cheaper than home depot or lowes and I did use caulk and caulked the tiny slots in the top of the trim and at the ring to sheetrock contact area. Doing the rings inside the house still does not spare you from sealing the wires and pipes that enter into the attic which are huge leaks also. Most people blow off the recessed light sealing and they can be the largest hole into your attic and cause the most comfort/allergy issues. I have 14 and on an energy audit we tested the cfm or cubic feet per minute of air at each vent and register and also tested each recessed light on a day with light wind. I had an average leakage of 5 cfm from each light which doesn't seem like much until you do the math per hour and per day. 70cfm per minute for 14 lights 4,200 cfm per hour 100,800 cfm per day. I don't even remember the numbers when we fanned the doors but they went all over the place negative and positive which pulls nice clean air out of your attic and cellulose fibers or fiberglass fibers in for the owner to live in. I highly recommend paying someone to shoot your house inside and out with a thermal imaging camera before you jump in too far so you can develop a game plan. I also highly recommend a blower door test with the thermal camera and cfm testing ducts and such. I had less than 150cfm total of actual return air going through my registers on a 1200cfm system because I was sucking air out of the attic and basement for return air. I would have never known the severity of the issue without the test. Get the testing done and pay for it get photos of the results. I would pay for the testing and any other services I would wait on until you digest the information and figure the best way to attack the issues. I hope I get to read your findings and what approach you decide on. You are on track to keep money in your wallet and be more comfortable in the process.

I will tell you what i did in the same situation you have, roof trusses on 24" centers. moved into the house the attic door had no insulation just trim holding a piece of drywall up. So i took down the trim. The hole was already framed to the ceiling. I took 1 x 4 boards framed them around the edge of the ceiling drywall. picture framed the 1 x 4 with the same trim as the door trim. Cut a 2' x 2' piece of birch plywood 1/2" thick to fit on top of the 1 x4's. Painted everything. Got some 3/4" wide self stick foam weatherstripping and put it on the top of the 1 x 4's. Had a 4 x 8' sheet of blue styrofoam and cut it to the same dimensions as the plywood. glued as many pieces as I could get out of the sheet to the plywood after the plywood was in the attic. Also cut a piece of R-25 fiberglass insulation to fit on top of the plywood and foam board. I figure it insulates well enough. Also installed 2 hooks and eyes to hold the plywood tight to the weatherstripping. I could have used foil faced board at R-7 per inch like I did at the previous house we owned. When I remodeled that house,when I gutted rooms I put 1/2" foil faced board on the interior of the exterior walls, so I had plenty of scrap. I had at least 8" of foil board on the 2 attic doors.

I'm glad to come across this thread because I'm also trying to figure out whether/how to add blown-in insulation to our attic, and possibly radiant foil. I hope I'm not derailing the thread by tacking on. Our home is a roughly 120 year old Victorian, and it also has a sprinkling of old insulation in the (sealed) attic, but nothing more. And when I say attic, I should clarify--we actually have a finished attic/third floor but the very peak of the attic, above the ceiling of the finished area, is unfinished. It's like a capital A, where the lower half is the finished portion and the upper half is unfinished. I'm sure there's proper terminology for that but I don't know what it's correctly called. We use the finished portion regularly, or at least we would if it didn't get very hot up there in both the winter and the summer. In the winter, we can counteract this by closing the HVAC vents so the attic is only heated by the hot air rising through the house, and that works well enough. But in the summer, we add two window units in addition to the house AC (to cool a space that's probably 400 sqft)--the window units are kind of a mixed bag because with the way they're installed, they let in a good portion of hot outside air around them through the window. We're contemplating replacing the window units with a minisplit system in the attic alone, but I feel like it's worth exploring all the various possible ideas to try to keep summer heat out of the finished portion of the attic before installing a whole new additional system. Any thoughts or ideas for me?

Currently it is fiberglass batts, and it’s from 1963 and has been damaged. I haven’t personally been up there to look yet. My husband and the house inspector have been up there. Nothing urgent, but something we think should be done on our to do list. No we will not have living space up there, joists are not sufficient for that and there is very little headroom with the hip roof and square hour style anyway. The attic will never be “conditioned” as we do not have A/C and live in a climate in which is is not at all necessary to have A/C for comfort, and heat only runs at night for 3-4 months of the year. Our windows are open most of the day all year round. I am sure that the attic heats up a lot due to solar heat gain, though - so it does seem sensible that lining the roof with a radiant barrier to reduce solar heat gain into the attic would be more effective than insulating the floor of the attic as it is, to reduce heat gain into the house on those days that it does get uncomfortable. We have a new (one year old) energy-star roof. I understand what you are saying about the “envelope” and I assume that it would be necessary to ensure that insulation and any vapor barrier on the attic floor was removed in order to avoid trapped moisture? I know double layers of waterproofing can be risky in that way but if they are separate spaces maybe not an issue. what about the sound insulation issue - both external sound (road noise and neighbors) and room to room? I can only guess insulation on the attic floor does more for the latter.