Posted in Architects
Decompress on Energy Trusses
The evolution of energy codes over the past several years has resulted in an increased demand for insulation as a means of achieving greater efficiency. More and more, builders are faced with the need to incorporate design changes to meet prescriptive requirements. Energy trusses, or raised-heel trusses, can help.
An energy truss is one that has been designed with a small vertical truss element or “heel” at the bearing locations of the truss—where the bottom chord intersects with the perimeter wall plate—that raises the top chord of the truss. This vertical element creates a space between the top and bottom chords, providing room for uncompressed, wall-to-wall insulation along the attic floor, which allows builders to meet the prescriptive requirements outlined in section R402.2 of the 2012 International Energy Conservation Code (IECC).
The 2012 IECC states that ceilings with attic spaces requiring R-38 insulation must also have the full height of uncompressed R-30 insulation extended over the top wall plate at the eaves. Climate zones that require R-49 insulation must have the full height of uncompressed R-38 insulation extend over the top wall plate at the eaves.
An energy truss can place the roof sheathing above the top wall plates by as much as 24 inches, allowing room for the uncompressed insulation. According to APA System Report SR-103, a standard 2x4 or 2x6 is insufficient to provide lateral support for the truss. Because the raised heel of the truss aligns with the outside surface of the wall framing, there is an opportunity for the use of structural panel wall sheathing such as oriented strand board (OSB) to resist the lateral load accompanying the energy trusses.
A number of building codes in wind zones require extensive blocking for energy trusses to prevent uplift. Using a longer panel like LP® LongLength™ OSB Sheathing can cover both the wall height and the raised heel, which may help eliminate the need for blocking and satisfy uplift requirements through the use of one continuous panel.
The benefits of energy trusses go beyond meeting prescriptive code requirements for uncompressed insulation as they help increase overall efficiency of a home.
With proper attic ventilation designed to help regulate temperature and pressure differences between the attic and living space, uncompressed wall-to-wall insulation on the attic floor reduces heat loss around the perimeter, which can prevent ice damming in cooler climates as well as thermal transfer (or heat loss) between the attic and conditioned space.
The resulting effect is that a home’s HVAC system may not have to work as hard to heat or cool the home, perhaps allowing builders to downsize its capacity.
For a quick snapshot on energy trusses, check out our infographic here.
Longer length OSB panels can also help builders meet the stricter mandatory air leakage requirements found in section R402.4 of the 2012 IECC. Builders can install panels vertically, reducing seams and ultimately reducing air leakage
Additionally, vertical installation of longer length panels can reduce the need for additional cutting, blocking and filler strips. These panels also provide resistance to shear and wind uplift in certain wind zones. Plus the use of one continuous panel may eliminate the need for extensive strapping.
This information and the websites identified above are provided solely as a convenience to the reader. They are not intended to state or imply that the editors of Engineered Wood or LP Building Products sponsor, recommend, endorse or are affiliated or associated with the companies or products listed.