Insulate Cathedral Ceilings with PlastiSpan or DuroFoam

Written By: Melissa Carruthers

Let’s talk about your roof…

The roof area can be the area of highest heat loss in buildings. In order to conserve energy and to make buildings more comfortable, building codes stipulate higher R-value  for the roof area compared to other building components. On traditional cathedral ceilings where tongue and groove timber is exposed on the inside and is used as an architectural feature, PlastiSpan or DuroFoam Insulation is ideal for both single and double layered applications.

The detail below is what the two layer application should look like.

Step 1: First layer of insulation
Use nailers the same thickness as the first layer of insulation. Starting at the bottom of the roof slope lay first row of nailers horizontally across the roof slope, then insulation working your way up the slope of the roof with all joints tightly butted. Fasten nailers to the roof deck as work proceeds.

Step 2: Second Layer of Insulation
Lay a second layer of insulation perpendicular to the first layer. Lay insulation with joints tightly butted. Lay nailers over insulation spaced to support roof sheathing.

Step 3: Fastening Layers of Insulation*
Fasten the second layer nailer to the first layer nailer where they intersect. If the thermal resistance requires extra layers of insulation, add layers to the bottom of the system changing the nailer direction as required so that the top nailer runs vertically up the roof slope.

*Multiple Layers: if the thermal resistance required extra layers of insulation, add layers to the bottom of the system changing the nailer direction as required. The top nailer must always run from the bottom of the roof slope to the ridge.

Step 4: Finish
Nail rood sheathing to nailers taking care that air movement is unobstructed in ventilation space.

Step 5: Roofing cover
Install roofing cover in accordance with manufacturer’s instructions. Adequate ventilation must be insured using an acceptable method to the applicable building code and/or local regulations.

For additional information on Cathedral ceilings, visit

Stay tuned for the next Plasti-Fab Blog coming in August!

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