Increasing Roof Rafter Depth For Insulation

Advised i need 50mm air gap for ventilation therefore need to increase depth of rafter by min.

Increasing roof rafter depth for insulation.

Use cleats the same length as the width of the. 12 inches r38. 9 inches r30. 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.

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. Figure the rafter depth needed to provide the desired r value. It works well to increase the r value and furring strips and then drywall can be applied. This gives you a total joist height of 13 inches which.

Multiply the appropriate r value times. Install a timber stop batten across the rafters as shown in position c with the batten equalling the thickness of the quinn therm insulation. For future reference here is the cavity depth you need for some common insulation r values. So we extended our rafters with some two by fours giving us the space to increase our ceiling insulation to r30.

In any case you will not be able to use your present roofsystem. Attach 1 2 inch wood cleats to both sides of the existing rafter. Rafters are 83mm deep x 63mm wide at 425mm centres. After a bit more destruction and dust it is time to look at how we increased the rafter depth in preparation for the insulation.

Measure the depth of the existing insulation. 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. 6 inches r19.

Almost there with the old fo. I want to insulate with 50mm celotex or similar then plasterbd skim over. 3 5 inches r13.