Firstly is the choice of insulation material.
How to insulate a cold pitched roof.
While warm pitched roofs are insulated over under or between the rafters providing a protective insulation layer for the space under the rafters like a loft cold pitched roof is insulated at the ceiling level which implies that any space above the insulation is left uninsulated.
A cold roof is where the insulation is between and below the rafters and the rafters remain cold.
Safety precautions and mistakes to avoid during garage roof insulation.
Install underlay above the rafters.
How to insulate a pitched roof at rafter level a warm roof is where it is above and between the rafters so the rafters are kept warm.
Kingspan with a flat roof this issue does not arise but the u value constraint and the amount of insulation needed is just the same.
For an un ventilated roof construction a vapour open underlay or breather.
This is why warm pitched roof insulation is probably a better option if you want to seal and heat your loft or attic space.
The bottom of the insulated plasterboard should meet the floor level of the roof space.
Stagger the horizontal joins.
For a ventilated roof fix battens on the inside of the rafters 50mm from the underlay to leave vented air spaces.
Measure the space between the rafters where the insulation.
In the case of a cold roof structure the insulation is placed between or between and under the rafters or at ceiling joist level and the roof is ventilated by leaving a 50mm gap above the insulation which vents air to the outside.
On new build or replacement pitched roofs the ideal build up would be insulation fitted over and then between the rafters giving a big boost for airtightness image credit.
After cutting the plasterboard to width so that it fits between horizontal centres of rafters screw the insulated plasterboard to the rafters.
If making a warm pitched roof construction you should opt for some type of rigid insulation boards such as kingspan k7 pitched roof board orcelotex xr4000 pir insulation boards which can be installed both between and over the rafters and offers a level of fire resistance if important and applicable.
One solution is to use hooks and rot proof nylon string but it may be easier to use polystyrene urethane or another rigid product in which case insulating the pitched roof is probably going to.
Traditionally pitched roofs are insulated by nailing or attaching insulation boards to the floor of the attic space keeping the cold air in the loft room and preventing it from penetrating down into the rest of the property unless a door is opened or air sweeps through between the panels.