This article discusses the question of exactly where to locate the outer edge of a wood-framed double wall for super-insulated building construction.

Added details discuss structural load capability of an offset wood framed wall, and insulation and vapor barrier placement on a wood framed wall.

Sketch at page top and accompanying text are reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss.

Double-Wall Houses: Framing Details

The text below paraphrases, quotes-from, updates, and comments an original article from Solar Age Magazine and written by Steven Bliss.

Four Detailed Questions & Answers About Double Wall Framing

1. What is the exact placement of the double wood framed exterior wall with respect to the ends of the floor joists?
2. How does the offset in a double-wall framed exterior wall affect the load bearing capabilities of the joists?
3. What thickness foundation wall is used for double-wall wood framed buildings?
4. What changes are needed to double-wall framed houses when a brick exterior veneer wall is used?

The questions above referred to "Double-Wall Houses," in Solar Age Magazine, December 1982 and were answered the next April. The questions and the detailed answers by Steven Bliss remain current today. Readers should also refer to the wood framed double wall details in the sketch below.

In the Hughes double-wall wood frame structure design, the double wall overhangs the floor platform, bringing the outside surface of the exterior wall sheathing in line with the outside of the building's foundation wall below. (See sketch at left.)

The floor framing is set back from the outer edge of the foundation wall by 3 1/2 to 4 inches. The overhanging section of the double wall is supported by short 2x4's (red in the sketch) toenailed between the top of the foundation sill plate and the bottom of the plywood plate (green in the sketch).

Setting the load-bearing (inner wall) back from the band joist (rim joist) a few inches will, in most cases, not affect the sizing (nor load bearing ability) of the joists (and structure).

Hughes uses a treated-wood foundation system, ordinarily framing with 2x6 lumber for one story and 2x8 lumber for two-story construction.

A brick veneer would need to be supported by an additional thickness of foundation, whether the wall itself is wood or masonry. This section of the building foundation is often offset so that the brick wythe veneer can be carried down to or below grade.

(Don't forget termite shields where appropriate and don't forget to provide weep openings in the veneer wall).

This double wall framing system allows the air/vapor barrier to run continuously between floors - around band joists and sill plates, reducing building air leakage and simplifying building sealing. The spaces outside the band joists are filled with insulation, keeping the vapor barrier towards the warm side of the insulation.

Here we include solar energy, solar heating, solar hot water, and related building energy efficiency improvement articles reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss.

Original article:

• Double Wall Details: Double Wall House Framing Details Q&A - PDF version, use your browser's back button to return to this page (original article - also see text below)

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