I do think from your description that the failure of the drywall ceiling is a result of lack of venting between the top of the insulation material and the underside of the roof.

For starters, I would poke around and see if you have pre-formed (often pink, but possibly blue) foam pieces with ridges tucked up under the roof. These are installed between the rafters in cathedral ceilings (which is technically what you have from an insulation point of view, no matter how garrett-y your rooms feel). If not, then that's your problem (or problems) in a nut shell.

You can research this on the Owens-Corning website which has lots of instructions about venting cathedral-style roofs. And you can look over these pieces at any Home Depot/Lowes. It will make sense when you see them.

You may need to remove, install roof venting and replace the wall/ceiling surfaces. The plaster may be damaged more from aggressive removal of adjacent surfaces than from roof deflection, but one can't tell without studying it.

And you may also need additional venting on the kneewalls now that the attic has been converted into living space which generates a good deal of moisture. You can cut down on this by installing proper vent fans for the kitchenette and bathroom areas, but you will still need under-roof ventilation, if not soffit vents, as well.

It sounds as though the attic work was done by DIY amateurs.

And that brings me to the most serious point that occurred to me: is it possible your attic has been converted into living space on the QT, and without benefit of building inspections, permits, (and unfortunately, increased property taxes) etc.?

It may seem like a persnickety issue, but the chief risk in my opinion is that your attic living space - if done sub-rosa -might not have sufficient, legal, means of egress in an emergency. If you never have an emergency, it might not matter, but in the case of fire, inadequate escape routes can lead to the death of occupants and firefighters attempting a rescue. This is a very serious risk, and not one I'd care to undertake; it has the potential for devastating financial, legal, and even criminal consequences.

While you noodle on that risk, you can research the catherdral ceiling vent issues on line. If you think structural compromise might be the reason for the plaster cracking, then an old-house friendly structural engineer (and many are not) would be the one you need. Consultations with roofers, insulation contractors and plasterers will not resolve the central issues and may lead to unnecessary, off-point work at this stage.

Aside from permitting issues, however it doesn't sound that dire, though ripping and venting and replacing the wall and ceiling surfaces won't be any fun in the heat of the summer.

HTH,

Molly~

Molly,

Thanks for the detailed response. First, let me reassure you that the attic apartment goes back at least 50 years and is completely legal as far as building code and fire safety are concerned. (The fact that it's a third apartment in what is zoned as a two-family house ... well, that's a different conversation.) The previous owners were just trying to weather-tighten the existing apartment.

I talked to my carpenter about the roof situation, and he said the same thing you did. He called them baffles. They are essentially channels that push the insulation out of the way and allow air to circulate behind the walls. It looks like I'll be doing more drywall work in the attic than I'd planned.

Thanks again for your help.
Katie

katie
my thoughts were what molly has stated. So there is a way for a person to get out of the attic?

Also, 3 layers of shingles on the roof is against what any roofer or builder would recommend - The framing may not be designed to support the weight and that may indeed be the culprit.

I cut & pasted this - it's from a building inspector, who responded to a homeowner's ? about 3 layers of roofing

It is very possible that your roofÂs internal structure (joists or trusses) was not designed to carry the load of multiple layers of roofing materials. The maximum allowed in most locations is two layers, but I donÂt even like to see that. The excess weight may cause the trusses to bow, crack or even break. Saving a few hundred dollars by not tearing the old roof off only shortens the lifespan of the layer on top. Also, some insurance companies will not cover a home with multiple shingle layers.

Anyone replacing the roof on their home should insist on having the current roofing materials removed. This is also an excellent time (and relatively cheap time) to improve the ventilation for the roof, and replace all the flashing materials. Doing so will cost a little bit more, but doing things right in the first place usually pays off in the end.

I would rec finding a good home inspector in your area to help advise

good luck

Paint the bath and kitchen surfaces with a vapor barrier paint and when you get around to replacing the roof, cover all of the roof sheathing with WR Grace Ice & Water Shield.

jejvtr -- Yes, there are two exits from the attic apartment: The main door from the apartment into the center hall/stair, and another door on the other side of the apartment onto a flat roof that runs the entire width of the house.

Something I just learned from my contractor: The issue is not so much providing ways for the occupants to get OUT of the apartment in case of fire, but providing ways for firefighters with all their gear to get IN to the apartment.

And yes, the old roof is coming off very soon. My insurance company is making sure of that. I couldn't get a regular homeowner's policy. I had to get a renovation policy at three times the cost until I address that and other issues.

mightyanvil -- Good suggestion. I will discuss with my roofer.

I have some pictures on flickr if anyone is interested:

http://www.flickr.com/photos/kthnry/

Especially check out the pictures of the back of the house before the initial repairs. Yes, that really is the same house.