Increasing Roof Rafter Depth For Insulation

This gives you a total joist height of 13 inches which.

Increasing roof rafter depth for insulation.

Almost there with the old fo. 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. In any case you will not be able to use your present roofsystem. Multiply the appropriate r value times.

Figure the rafter depth needed to provide the desired r value. Lay quinn therm qr insulation boards above the rafters butted tightly against the stop batten and supported on both sides by the rafters. 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. 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.

I want to insulate with 50mm celotex or similar then plasterbd skim over. 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. 9 inches r30.

Use cleats the same length as the width of the. 12 inches r38. Rafters are 83mm deep x 63mm wide at 425mm centres. 3 5 inches r13.

Advised i need 50mm air gap for ventilation therefore need to increase depth of rafter by min. How to increase rafters for insulation step 1. Attach 1 2 inch wood cleats to both sides of the existing rafter. Measure the depth of the existing insulation.

After a bit more destruction and dust it is time to look at how we increased the rafter depth in preparation for the 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. For instance if the roof has 2 by 6 rafters and.