To get the target r value from the product you chose use the number of bags your calculations showed that you needed to insulate your attic never fewer.
Insulating your roof space.
The technically correct approach depends on a number of factors.
Flat roof insulation always requires professional insulation and damp roofs require professional assessment before work can be carried out.
Before fitting any insulation to the sides of a pitched roof space any repairs to the roof should be completed once the insulation is in place it will be harder to spot any leaks inside the roof and any leaks will soak the insulation itself.
Pipes water tank and loft hatch.
Before insulating seal any air leaks and make roof and other necessary repairs.
Whether or not there is an inner roof lining and the total thickness of the roof structure.
Insulate and air seal any knee walls vertical walls with attic space directly behind them in your home as well.
If it is located in a conditioned part of the house also remember to insulate and air seal your attic access.
That means insulating the attic floor only not the walls and having vents in the roof.
If you ve reached your target depth but still have a few bags left over keep adding the material at an even depth throughout the space until all the bags your calculations called for are empty.
How to insulate a finished attic.
A finished attic should be insulated much like the rest of the house with insulation in the walls and ceiling.