I am converting an existing attic with a dormers to a master suite. There is old blown- in insulation between the floor joists. Of course we will be insulating between the rafters now that the “thermal envelope” is changing. The question is whether we must remove the existing blown-in? Also, is it best to carry the insulation up the rafters outside the knee walls, or to insulate across the floor in the eaves areas and then turn up the knee walls to the rafters? Any advise welcome!
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Billy,
How much insulation is present? If you can deck over the the ceiling joists with the insulation in place then the answer is no, you don't have to remove the insulation and it will serve to some degree as a sound barrier between floors.
Is the attic vented? If so, how? What part of the country? If you are in a snowy/colder part of the world, venting the attic is critcal to prevent condensation on the underside of the roof decking and to the prevention of ice dams.
I would insulate both the roof rafters, allowing for a baffle or 1" air space to ventilate (add soffit and ridge vents if not existing), and the knee walls. There has been a lot of information posted on insulating and venting cathedral ceilings, which is basically what you going to end up with.
Thanks for the advice. The house is in the DC area and about 50 yrs old. There are no soffit vents, but there gable vents on either end. I had planned on using baffles and batt insulation up the rafters. Should I plan on venting the soffit then? If so, then probably button vents would be the best way to avoid having to remove the entire soffit and redo it.