That s because it s easier for the contractor to spray than clean up existing insulation deal with any can lights or venting etc.
Should you insulate attic roof rafters.
In order to avoid damage to the roof deck you should insulate ceilings to create an air barrier between the living space and an unfinished attic or airspace underneath the roof deck.
You can add insulation to the floor.
Install ventilation baffles into the space between the rafters before you install the insulation usually by stapling into place.
If you do not use the attic much it is pointless heating this area.
Make sure it is flush against the wood as also a 1 inch gap can create a 20 percent heating loss.
Air movement is critical in the attic so.
You can use rigid foam panels or do as tom silva does with nearly all houses these days.
When choosing unfaced batting insulation for rafters you must staple sheets of plastic over the batting to accomplish the necessary moisture barrier.
Insulating between rafters will do no good because the attic should be ventilated and the rafter insulation would be between two unheated spaces.
Consumers are often told by spray foam contractors to do the rafters.
If you have vents in the walls of the attic or in the roof ridge then the insulation can go all the way to the roof.
If you live in the south you should consider putting in a radiant barrier in the attic.
But the best solution is actually to insulate both the attic floor and the underside of the roof.
If your attic is going to be converted into livable space then you will need to insulate the roof rafters.
In this way you prevent the heat from the rooms below escaping to the attic rooms above.
This will have the best return on investment if you live in an area with more than 2000 cooling degree days.
If you re using the attic for living space then you need to insulate the rafters.
Insulating the attic floor.
However if you super insulate your attic ie r 30 or better then it becomes redundent.
The idea is to allow some air to circulate through some part of the attic under the roof but outside the insulation to prevent moisture build up.
If you re not do the attic floor.
Hire a pro to install spray foam insulation.
For rolled insulation location it in between roof covering rafters.
Usually you will certainly fill the insulation blower with the insulation and blow it between the attic floor joists.
At the same time the areas below the roof benefit from increased comfort both during the winter and the summer.