Reply to Best way to insulate 100 year old unfinished attic ceiling?

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[quote=Anonymous][quote=Anonymous]I (OP here) really appreciate the discussion.  From what I saw in the article and read online, it is still very hard to know what to do.

We have an 18x10 space in a semi detached house.  100 years old.  No vents.  Typical DC semi detached - brick, front slope of roof covered in terracotta tile, rest of roof is flat with a 10 year old membrane on it.

We have a HVAC unit that provides AC to our upstairs located in the attic.  The attic is totally unfinished with no signs of moisture.  There is no insulation and two 27x38 inch windows facing south.

There is electrical for one light and the HVAC.  We don't have knob and tube up there.

ALSO:  When we redid our bathroom last year, the ceiling went up to the flat part of our roof where there is no crawlspace.  This was loaded with old insulation that looked to be like finely shredded paper.  There were a lot of moths in there and moth larvae on the exposed rafters. The contractor removed the insulation.  We think it might have been original to the house as there were generally very few updates throughout.

Is blown in cellulose the way to go?  Put it in the rafters, put the drywall over it and move on?  Or is this a disaster?
[/quote]

If you read the linked articles, you know that the issue is moisture management. Specifically, how to prevent moisture from inside the building from condensing when it hits a cold surface in the attic. There are two approaches, and they aren't really complementary. The traditional approach is to have ventilation between the insulation and the roof to allow moisture to dissipate. Usually the ventilated area was quite large -- the floor of the attic was insulated, and everything between the floor and the roof was ventilated. But code allows the ventilated area to be as thin as 1", so long as it is unobstructed from the eave to the peak. If you can put in a baffle from eave to peak you can put pretty much any kind of insulation below it.

The other approach is to use an insulation that is impermeable, so that moisture cannot get through to the roof. Usually this means closed cell spray foam. If your house does not have existing vents at the eaves and peak and there's no easy way to add them, this is pretty much your only option.

Having your HVAC equipment outside of the insulation, as you do now, is bad. You're essentially heating and cooling the outdoors. The equipment can get damaged by freezing as well. [/quote]

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