It creates a breeding ground for mold and mildew and ruins the air trapping pockets that block heat flow.
Insulation between roof trusses.
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.
Consider using high density r 30 batts which are as thick as r 25 batts but fit into 2x10 framing.
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.
You can also add rigid foam insulation under the rafters which adds r value and eliminates thermal bridging through wood rafters.
With a regular roof insulation isn t a problem.
To insulate the underside of the ceiling between rafters you ll want to add insulation to the exterior portion of the finished ceiling.
The benefits of insulating a building around the outside protecting the structure and effectively creating a tea cosy effect are well publicised.
Improving your home s energy efficiency rating.
The bigger issue comes around when you are dealing with a roof that has exposed trusses cathedral ceilings or specialty open ceilings.
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.
Increasing your home s value.
Water is insulation s enemy.
A vent baffle should be installed between the insulation and the roof decking to maintain the ventilation channel.
Other benefits of roof insulation include.