Increasing Roof Rafter Depth For Insulation

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.

Increasing roof rafter depth for insulation.

Use cleats the same length as the width of the. Rafters are 83mm deep x 63mm wide at 425mm centres. Attach 1 2 inch wood cleats to both sides of the existing rafter. 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.

Measure the depth of the existing insulation. Install a timber stop batten across the rafters as shown in position c with the batten equalling the thickness of the quinn therm 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.

3 5 inches r13. How to increase rafters for insulation step 1. 9 inches r30. 6 inches r19.

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. For instance if the roof has 2 by 6 rafters and. Advised i need 50mm air gap for ventilation therefore need to increase depth of rafter by min.

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. After a bit more destruction and dust it is time to look at how we increased the rafter depth in preparation for the insulation. This gives you a total joist height of 13 inches which.

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. 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.