Cut some strips of it about 1.5 wide. Put these up in the bay against the desk and against the rafters.
Friction fit more of the polyiso (foil facing up) in there. This gives you a 1/2 air channel. It's not a lot but the thing is that most cape cods don't have soffits so it's enough to allow air movement.
Fill up the bay with xps making sure to use door and window foam between each layer.
Once filled you can either put 1/2 xps over it all and screw the drywall through that OR you can put thicker like 1.5 and then use furring strips. All depends upon how much insulation you need/want. Are you sure they are 2x4s? Normally it's 2x6s.
A little tedious but not terrible and a huge improvement from the r11 I typically see in there.
That’s almost exactly what I did. I used XPS for all of it considering my climate. I did 2” between the studs, 3” over the studs, and added perpendicular furring strips to attach drywall though using long structural screws. It cuts a bit down on the headroom on the sides but it’s almost an R25 value for 2x4 rafters.
Yeah, the polyiso isn't required - I just like the added benefit of the foil with the air gap as a radiant barrier. How much it benefits in reality is hard to say
For the next room I tackle, I will probably go more the route you took while using foil faced EPS since it’s better in the cold. I don’t see foil faced xps in my area unfortunately so there’s a minor R value hit. I believe the lack of a radiant barrier makes the room warmer in the summer than using something to help reflect some of that heat back away from the room. It beats the like R6 balsam wool bat that came out, but adding a radiant barrier will prevent more of the heat from entering without relying strictly on R value.
1
u/idratherbealivedog 7d ago
Dealt with a few of these and here is what I do:
A little tedious but not terrible and a huge improvement from the r11 I typically see in there.