Increasing Roof Rafter Depth For Insulation

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.

Increasing roof rafter depth for 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. For future reference here is the cavity depth you need for some common insulation r values. Rafters are 83mm deep x 63mm wide at 425mm centres. Advised i need 50mm air gap for ventilation therefore need to increase depth of rafter by min.

Attach 1 2 inch wood cleats to both sides of the existing rafter. 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. It works well to increase the r value and furring strips and then drywall can be applied. In any case you will not be able to use your present roofsystem.

How to increase rafters for insulation step 1. Measure the depth of the existing insulation. This gives you a total joist height of 13 inches which. 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.

I want to insulate with 50mm celotex or similar then plasterbd skim over. Install a timber stop batten across the rafters as shown in position c with the batten equalling the thickness of the quinn therm insulation. So we extended our rafters with some two by fours giving us the space to increase our ceiling insulation to r30. 9 inches r30.

Multiply the appropriate r value times. Use cleats the same length as the width of the. 6 inches r19. 12 inches r38.

Almost there with the old fo. 3 5 inches r13. 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.