Insulation Between Roof Joists

The main difference between the two is the location of the insulation.

Insulation between roof joists. Where the insulation does not fill the total rafter depth the low emissivity foil facings can gain additional thermal benefit from the air spaces they face. It creates a breeding ground for mold and mildew and ruins the air trapping pockets that block heat flow. Good question theoretically when building a warm roof the vaper control layer goes on the warm side of the insulation. Other benefits of roof insulation include.

A warm roof is where it is above and between the rafters so the rafters are kept warm. Install batting between the attic s floor joists. Once up at roof level the between rafter boards can be cut accurately to fit the rafter spacings. You can also add rigid foam insulation under the rafters which adds r value and eliminates thermal bridging through wood rafters.

Look for water stains on the roof sheathing or damp or moldy spots on attic joists and existing insulation as a clue to where leaks might be. Convenience polyurethane or polystyrene spray foams can provide thorough coverage to roof rafters and attic walls in much less time than is needed for other materials. A vent baffle should be installed between the insulation and the roof decking to maintain the ventilation channel. This will depend on the construction on your roof and if it is a refurbishment whether the roof tiles are going to be removed.

The batting material must be faced and at least as thick as the joists are wide so the batting is nearly flush with the top of the joists. Being lightweight they do not impose significant additional loads on existing structures. Uneven or sloppy application however can make the insulation ineffective and unsealed open cell insulation can absorb moisture causing the roof to rot or leak. If you put insulation under the decking and between the joists you lower the temperature of the decking and lower the due point thus bringing it closer to the danger point of being in the building.

Insulation between the joists keeps warmth in your living space below and creates a cold loft while insulation in the rafters allows you to keep warmth in the roof space as well. Water is insulation s enemy. When you use solid insulation board to create a warm loft the key thing to remember is ventilation you must keep a 50mm gap between the roof and the rigid insulation board. Improving your home s energy efficiency rating.

We would always recommend having a breathable membrane in place between the tiles and the rafters too to allow the roof to breathe. Increasing your home s value. Consider using high density r 30 batts which are as thick as r 25 batts but fit into 2x10 framing.