Less Can Be More With Insulated Headers and Corners

Insulated Headers

Wood frame houses offer many opportunities to replace non-structural wood, which allows rapid heat loss, with insulation. In the Northwest, this practice is known as “advanced framing.”

If you sheath exterior walls with foam boards, you’re already getting some additional insulating value at headers. Some is better than none. However, the R-value of headers should be equal (or at least close) to the rest of the wall. That’s generally not difficult to do. But since space is tight, you should use some type of rigid insulation to pack in lots of insulating value. By installing 2-1⁄2 in. of polyisocyanurate—at R-7.2 per in.—you would have R-18.

While headers are usually structurally necessary (except below the gable end of a roof), they may be over-built. Caution is admirable, but by sizing headers, you can size headers for ample strength and still have room left for insulation. To size headers consult the appropriate span tables or enlist the services of an architect or building engineer.

Much of a header’s strength comes from its vertical dimension, instead of its thickness. That comes in handy when you decide to insulate headers, because increasing the vertical dimension allows you to get adequate structural strength, while reducing the thickness of wood. Now more insulation will fit. Taller headers won’t work in some cases, because there isn’t enough distance between the top of the opening and the top plate of the wall.

For shorter spans, you may be able to use a single 2x. Most builders nail or glue insulation on the inside of the header. For larger openings and heavier building loads, you probably already gang 2x’s. Instead of nailing them together to make one thick header, try sandwiching the insulation between them. In a 2x6 wall, there’s room for 2-1⁄2 in. of insulation. This approach is popular with builders, because it puts wood on the outside for nailing siding and on the inside for attaching drywall and drapery hardware.

Lumber may also be eliminated from header supports. Headers transfer building loads from the wall or roof framing above to wall studs on both sides of the opening. Each side carries half the load of the header. Typically, there are two, three or even four studs on each side of an opening. Depending on the loads, fewer studs may be needed. Often, only one stud is necessary. If this is so, a simple framing connector can allow the king stud to carry the header load. That eliminates the support stud.

Insulated Corners

By eliminating non-structural lumber from exterior corners, you can make room for more insulation. A 2x6 stud has an R-value of 6.8, while the insulated cavity can easily have an R-value as high as 21. By removing nailer studs, you make room to install the full level of wall insulation all the way to the corner. Of course, something has to support the drywall.

Instead of nailers, try corner-back fasteners that allow two sheets of drywall to be supported by the same stud. These clever devices are stamped and folded from a single piece of flat metal. Part of the clip forms a slot that slips over the edge of the drywall, holding it tightly. The other part forms a strap with two holes for nails or screws.

Here’s how to use them. First, look at the corner to decide which sheet will have no lumber backing. That sheet must go up first. Slip three clips onto the four foot end of the sheet. Position the sheet against the wall and drive screws or nails into the wall studs. At the corner, drive a nail through one hole on each fastener. Now hang the sheet on the other wall as you normally would, attaching it to the structural stud that’s exposed.

In addition to making room for more insulation, the fasteners save money. Six fasteners at 12¢ each replace one eight-foot stud, for a total cost of 72¢ per corner. Fasteners also eliminate the labor to install that stud. Multiply these savings by all the corners in your typical house plan and you should be impressed by the econonics.

Framers will be happy that they don’t have to think about installing nailers for drywallers. And drywallers will be happy, because they’re no longer at the mercy of the framers for backing.
Although drywallers often resist the idea of using fasteners at first, most eventually embrace the idea. Because the drywaller can adjust the backing, corners tend to be a bit straighter. There are also fewer cracks in the corners, because both sheets of drywall hang from the same stud. Corner-back fasteners are available through most drywall supply outlets. One manufacturer is Prest-On.

Standard corners often have one or more non-structural studs for drywall backing. Unless there’s a point load on the corner, each corner stud carries only half as much building load as a wall stud.
A two-stud corner eliminates the extra stud that serves only to hold up the drywall. Instead, “corner-back fasteners” hold the sheet that would normally be nailed to the non-structural stud.
For the less adventurous, a three-stud corner can be modified by turning the non-structural stud 90 degrees. This allows insulation to be squeezed into the corner, but cuts the R-value by about 20 percent.

This article appeared in Energy Source Builder #19, February 1992,
©Copyright 2008 Iris Communications, Inc.