In order to ensure attachment for siding and trim, you should frame all windows, doors, and corners to meet the thickness of your InSoFast panel. The EX 2.5 panel is 2½” thick. There are many ways to accomplish this task.
Here, the contractor chose to install a 1″ thick extruded insulation board directly onto the sheathing around the openings to maintain the thermal barrier. He framed the openings with 2x6s, nailing through the insulation board and sheathing into the structural wall. Housewrap was installed over the wall and frames to complete the air and moisture barriers. Lastly, the InSoFast panels were installed, sometimes trimmed in order to align with the pre-exisiting structural framing.
The dew point is the temperature at which water vapor held in air begins to condense. It is extremely important that your rigid foam is thick enough to keep the sheathing above the dew point during winter. This will protect the plywood or OSB materials from water damage. To determine the minimum R-Value of the rigid foam see Calculating the Minimum Thickness of Rigid Foam Sheathing
The R-value shown on polyisocyanurate labels is usually equivalent to R-6 or R-6.5 per inch. However, the actual performance of polyiso decreases dramatically at cold temperatures. Concerns about the cold-temperature performance of polyiso are serious enough that GBA recommends that cold-climate builders use extreme caution when choosing a rigid foam meant to keep wall sheathing above the dew point. Either EPS or XPS would be safer choices for this purpose than polyiso. For more information on this issue, see In Cold Climates, R-5 Foam Beats R-6.
With 2×4 construction, InSoFast EX panels exceed the minimum R-Value code requirements in most climate zones and add the benefit of moisture control channels that allow a wall to dry outward. For 2×6 construction in zones 6-8, see information about InSoFast PLUS or give us a call.
The following is essential information that applies to foam-sheathed walls. More information can be found on the Department of Energy website.
|Climate Zone||Minimum R-Value of Rigid Foam Sheathing for 2×4 and 2×6 walls|
|Marine Zone 4||R-2.5 (2×4 walls)||R-3.75 (2×6 walls)|
|Zone 5||R-5 (2×4 walls)||R-7.5 (2×6 walls)|
|Zone 6||R-7.5 (2×4 walls)||R-11.25 (2×6 walls)|
|Zone 7 and 8||R-10 (2×4 walls)||R-15 (2×6 walls)|