I started working on the details for our attic hatchway a few months ago. The internet is fairly void of super-insulated air-tight attic hatchways. I found this curious considering all the net zero and Passivhaus work going on to date.
The problem is how to insulate and air seal the attic access to the same standards as the rest of the ceiling. Our ceiling will be insulated with 24 inches of loose cellulose (R-75), so I wanted to make sure the hatchway was at least equal in R value and air tight. The trick was to find a way to achieve this and still be able to open and close the hatchway with relative ease.
Our solution is nicknamed the ‘cork’. Essentially it’s a 24″ deep hatchway filled with 2 insulated components. The first component is air sealed to the interior drywall. It is a piece of plywood screwed to the ceiling within a gasket and 8″ of left over rigid insulation (R-40) glued to the top of it. This is a fairly standard approach to sealing the attic hatch. The second component (the cork) is 14″ of rigid insulation (approx. R-70) held in place by a hinged top plate.
To gain access to the attic we will first remove the lower panel from inside the house, then we pop the top barrier out into the attic. To close the access we reverse the process.
The total insulated value is R-110, but that is misleading. Due to inefficiencies of sealing the insulation to the hatchway, air can circulate inside the hatchway in tiny gaps at the edges and between the two insulated components, so I just tried to cram as much insulation as possible into the hatchway as tightly as possible but still be able to pop the cork to gain access to the attic. Only an inferred camera will tell if my efforts have been successful.
I hope this is helpful to others out there building super insulated houses with attic access from the inside. If you have a simpler detail, please don’t tell me. I feel silly enough spending 2 days building the cork. But please do post your solution to make it easier for the next person.
One last word, the code requires attics be accessible, but I don’t believe it specifies whether it has to be from the inside or outside of the house. Assuming you have an attic that needs access and your local code allows outside access, I would recommend exterior access based on my experience building a super-insulated air-tight attic access hatchway. Interior access can be done, but it’s a lot of tedious work.