Increasing Roof Rafter Depth For Insulation

In any case you will not be able to use your present roofsystem.

Increasing roof rafter depth for insulation.

Figure the rafter depth needed to provide the desired r value. Advised i need 50mm air gap for ventilation therefore need to increase depth of rafter by min. 6 inches r19. Multiply the appropriate r value times.

I want to insulate with 50mm celotex or similar then plasterbd skim over. So we extended our rafters with some two by fours giving us the space to increase our ceiling insulation to r30. It works well to increase the r value and furring strips and then drywall can be applied. Install a timber stop batten across the rafters as shown in position c with the batten equalling the thickness of the quinn therm insulation.

Rafters are 83mm deep x 63mm wide at 425mm centres. For instance if the roof has 2 by 6 rafters and. Lay quinn therm qr insulation boards above the rafters butted tightly against the stop batten and supported on both sides by the rafters. Measure the depth of the existing insulation.

Almost there with the old fo. Use cleats the same length as the width of the. 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 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.

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. 12 inches r38. 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. For future reference here is the cavity depth you need for some common insulation r values.

Attach 1 2 inch wood cleats to both sides of the existing rafter. 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.