Desired Outcome:
Properly align thermal boundary and air barrier between the conditioned and unconditioned space
SWS Detail: Subtopic 4.0401 Rim/Band Joist
Author: Brenna
Before
Uninsulated rim joist
After
Insulated rim joist
Steps
- Follow work order for air-sealing sill
Sill should be air-sealed at seams and corners with adhesive or foam prior to insulating
See the Air seal Basement or Crawl Walls when air sealing is called for.
2. Install insulation
Install one of the following insulation types
2a. Fiberglass batts
Select batt insulation that has a class II vapor retarder facing and that has a flame spread and smoke development index of 25/450 or less
Cut batt to fit sill with no gaps up against the framing.
Insulation must maintain full contact to ensure a continuous thermal boundary.
Do not compress batt insulation
2b. 2-part foam
Install 2-part foam up to 3 1/4" thick. may also be used for air-sealing and insulation.
See SDS material safety for restrictions of use.
The Sill is the one location on a home where foam plastics can be installed without an ignition barrier but shall meet the conditions of 4.0401.1f.
Foam is not thicker than 3 1/4" thick, listed as either ASTM E84 or UL 723, Flame spread of 25 or less and Smoke Developed Index of 450 or less.
2c. Pin and drape
Folding foundation insulation to insulate sill.
Fiberglass blanket can be notched and folded into sill, attach to joists with staples.
Edges of blanket must be sealed ensuring no insulation is exposed.
2d. Rigid foam
Use non-corroding materials to seal the seams around the insulation with adhesive.
3. Worst Case Draft Test
Conduct a worst case draft test to verify Category I, II, and III appliances are venting before leaving the job for the day.
Testing shall be recorded using the Utah WAP Worst Case Draft Test form.
4. Install Insulation Certificate
A dated insulation certificate signed by the installer will be posted on a wall in the space where the furnace is located, a utility room or an approved location inside the building.
The certificate must include:
Installed insulation type
Coverage area
Installed thickness
Installed R-value
Manufacturer product name
Manufacturer supplied material density
Flame Spread rate
Smoke Development index