Common sources of air leakage, Part 3

Rim joists & sill plates:  These are often significant sources of air leakage as air escapes through the framing and into the home.
1.  Sill plates.  Sill seal is not an effective air block. This applies to all homes, but is particularly important for slab models.

• Consider using a continuous seal on the exterior between the foundation and the framing.  


• Alternatively, sealant on the inside should be carefully and liberally applied.  Sill seal must be trimmed out of the way.

2.  Rim joists.  

• Both the top and bottom of the rim joist should be sealed to the framing.  Typically this is done with sealant on the interior.
• Rim joists on all levels should be addressed.  In platform-framed, two-story home, this includes the basement rim joists and the rim joists at the second floor platform.
• All penetrations through the rim joists must be sealed.  These are often hidden by insulation batts.  Like many air sealing problems they can be created by mechanical trades drilling holes to the exterior after the air sealing.

Note that sealant was not applied on the bottom joint.

Foam missed the lower joint and is incomplete at the top.

Walls:  Typically we try to prevent unconditioned air from getting into the walls.  Air is often observed coming out of the electrical devices, but this is a symptom, not the cause.
1.  Rim joists, doors and windows, see above, see above and previous post.
2.  Penetrations to the exterior should be sealed.
3.  Penetrations through the top plates to unconditioned spaces (attics, basements) should be sealed.
4.  Walls adjacent to unconditioned floor space.

• These require blocking in the floor joist space.

5.  Attached roofs.

• Sheathing between the roof and the wall should be complete.

 
Basements & Crawlspaces:  
1.  Rim joists, sill plates, doors and windows, see above and previous post.
2.  Penetrations through the wall.
3.  Penetrations through the floor slab.  While typically less air leaks through a hole cut in the slab, this is often a source of air flow into the home.  For a tight home, seal around penetrations and fill larger cuts with concrete.
 
Slabs:  
1.  When wall framing rests on a slab, it is critical that these be sealed well.  All too often these are done sloppily and sealant does not completely seal.  Dirt and debris and protruding sill seal should be removed first.  A heavy bead of caulk is generally more effective than spray foam.  Tool the caulk to ensure good adhesion to both surfaces.

Insufficient caulk does a poor job stopping air flow.

We hope these tips were helpful to you.  Please let us know if you have questions.