In this case the rigid foam can be thinner than when it s used alone.
Roxul for roof rafters.
Rafters are commonly spaced about 24 inches 61 cm apart.
Other relevant factors include the type of wood being used for the rafters the size of the rafters and the load that the rafters need to support.
Visit the roof framing page for more information on cutting roof rafters and visit the roof pitch calculator for determining rafter lengths based on rise and run.
All roof rafters should be identical so follow the same steps to measure the plumb cut tail cut and birdsmouth cut.
Rigid foam on roof sheathing with air permeable insulation between the rafters.
The higher the r value the greater the insulation performance.
Exceptional dimensional stability and rated for extreme hail rockwool stone wool insulation roof boards have meet both the fm severe hail and the ul 2218a standard for impact resistance.
The spacing between rafters in a given building is part of the engineering calculations that determine the required structure of the roof.
The number of rafters needed will be determined by the length of your roof.
Rafter span tables use these tables to determine lengths sizes and spacing of rafters based on a variety of factors such as species load grade spacing and pitch.
R value measures how well certain building insulation materials can resist heat.
Not only do we withstand hail damage but our roof boards maintain their bond to the roof membrane lowering the likelihood of a catastrophic roof failure.
Rigid foam also can be installed above the roof sheathing in tandem with air permeable insulation between the rafters.
Code specifies the minimum r value of the rigid foam layer.