Increasing Roof Rafter Depth For Insulation

Measure the depth of the existing insulation.

Increasing roof rafter depth for insulation.

Advised i need 50mm air gap for ventilation therefore need to increase depth of rafter by min. It works well to increase the r value and furring strips and then drywall can be applied. Rafters are 83mm deep x 63mm wide at 425mm centres. In any case you will not be able to use your present roofsystem.

3 5 inches r13. After a bit more destruction and dust it is time to look at how we increased the rafter depth in preparation for the insulation. Multiply the appropriate r value times. Each inch of batt type insulation provides an r value of 3 1 to 3 5 and loose insulation provides 2 9 to 3 7.

Lay quinn therm qr insulation boards above the rafters butted tightly against the stop batten and supported on both sides by the rafters. For example if the existing joists are two by eights which are 7 5 inches deep you can add two by six boards which are 5 5 inches deep. I want to insulate with 50mm celotex or similar then plasterbd skim over. How to increase rafters for insulation step 1.

You may want to consider applying a rigid polyisocyanurate insulation typically r7 to 8 per inch on the bottom of the rafters after installing baffles continuous from eave to peak and batt insulation between the rafters. Figure the rafter depth needed to provide the desired r value. Use cleats the same length as the width of the. Attach 1 2 inch wood cleats to both sides of the existing rafter.

Increase the rafter depth with an i joist deep enough to accommodate appropriate insulation insulate to required r value probably r40 strap the roof for ventilation or go solid eps or spray. For instance if the roof has 2 by 6 rafters and. Install a timber stop batten across the rafters as shown in position c with the batten equalling the thickness of the quinn therm insulation. 6 inches r19.

This gives you a total joist height of 13 inches which. For future reference here is the cavity depth you need for some common insulation r values. Almost there with the old fo.