We used salvaged four inch XPS boards under the roof joists in the attic. Because salvaged material is rarely perfect around the edges, I was left with gaps where the boards meet.
Edit: The described insulation assembly does not comply with important building science principles. For more information read the following post: Do-over dilemma
These gaps needed sealing to prevent warm air and moisture from migrating into the insulation assembly. The associated energy loss — and even more so the wetting of the roof assembly — would be counterproductive or even dangerous.
Taping over those gaps didn’t seem feasible. I thought about using spray foam cans to fill the gaps. That would would be a big and expensive job.
Sealing the seams with closed cell SPF, however, is relatively straight forward, particularly with our installer and his attention to detail.
During the SPF installation, the installer “over sprayed” the top of the wall to properly seal the interface between the XPS boards and the masonry wall. From there he moved on to the ceiling, and sealed the joints between the boards with foam.
I got the gaps between the boards closed up. But it doesn’t entirely solve the problem of air or moisture from migrating into the roof assembly. There will always be some imperfections, leaving small pathways. My plan to manage that moisture is a good subject for another blog post.
- 2nd floor closed cell installation
- Blower door test – before insulation
- 2nd floor insulation strategy
- Shrinking a long to do list
- Insulation preps – plugging the 3” gap
- Insulation preps – 3” thermal break
- Insulation update
- The insulation riddle is back
- Following the control layers
- Insulation riddle resolved
- Insulation – how much is needed
- Insulation – which material cuts it
- Insulation – starts with moisture management
- Insulation – lots of conflicts
- Insulation – how it started