Earth Advantage. Better Buildings Now
Login Contact

Move Your Window Headers to the Rim for Better Thermal Performance

Window headers have always been a weak point in the thermal performance of a building shell, and the most common solution is to face the header with rigid foam. Even with a foil-faced polyisocyanurate rigid foam product, such as R-Max, headers typically have less than half the insulation R value of the rest of the wall cavity in a 2X6 wall with blown insulation.  Even worse, large window openings frequently have a full depth header that is a substantial source of thermal bridging.

So, how can we build better?  One option is to move the window header up to the rim joist whenever you can – typically a workable solution on all but the top floors. This technique allows for full insulation values in all wall areas, since the thicker header at the rim joist can still be insulated to the same R value as the rest of the rim joist. This also allows for more options with window height and placement as windows can be placed all the way up to the top plate. The headers in the rim are most commonly Laminated Veneer Lumber (LVL), and are carried by full-height jack studs.

Does it cost more? According to the builder on this project, Bill Hughes, “the cost difference is basically a wash. But the wall framing probably goes a little faster with the headers in the rim.”

What are the trade-offs, or down-sides of this strategy? Typically, the I-joists over window and door openings will need joist hangers at the rim rather than being back nailed to the rim from outside with this approach, since the structural rim joist could be too thick to nail from outside and it could be too thick for the top plate to allow the minimum 1.5” of bearing space required for joists. Also, this requires a custom engineering calculation rather than prescriptive. These are not necessarily significant barriers, however, as both of these practices are already common.

With prior planning, it’s possible to prevent poor thermal performance of window and door headers with minimal increase in build costs.

Article photo is of a WA Hughes Construction home. 
Find a Better Builder
Search for high performance builders or remodelers that work with Earth Advantage.
What makes a builder better?
Find an Accredited Professional
Accredited high-performance experts
The Benefits of Certification
Certified high-performance buildings are healthier, more efficient and show a documented increase in value.
Certified buildings are better buildings