Warm Roof Assembly, Steep Slope

Typical Church, built in 1962. 12/12 slope on Sanctuary and Main Roof Area. 2 layer t-off.

Sanctuary has Cathedral ceilings w/ T&G 2 x 6. What it also has is two layers of 1/2" fiberboard as an attempt at insulation. Unvented roof assembly.

What it does not have, is an underlayment, near as I can tell (one small test area).

2 questions: #1) What would you expect the condition of the FB to be in after tearing off 2 layers? #2) Would you put an underlayment on it? I s'pose Code might answer that question.

My thought is w/ an underlayment we might be wasting time and money and cause a problem. The fact that we can dry the job in as we go appeals to me even more tho. I have not done enough of these to have a handle on it w/ practical experience.

Thanks

---If you move the insulation there will be a dust storm through the T&G decking. And it will continue for months as the dust in the cracks works through. We have rolled visqueen to protect the interior on such situations. The only problem is that the visqueen is removed when we are done but the dust continues. We once vacuumed an entire roofdeck to prevent this. ---If you have to replace the insulation then I would use 15 lb under the new insulation to protect the insulation from the building's moisture. We have done some houses like this and we hand nailed the comp with 2 1/2 inch nails. ---There is no venting because there is no trapped air. ---There is probably no money for 2 to 4 inches of ISO then screwed down 1/2 inch plywood over that. That will make heating the building cost much less. Last year we did a 4 inch ISO on a house replacing a 1 inch crumbling mess. The homeowner raves about how warm the house is now in the winter. Those T & G ceilings make a building terrible to heat. ---I don't think it matters regarding underlayment on top of the insulation. The shingle application would require it IMHO for the warranty to be honored, however. What they did in the 60's is not the standard for today. Lanny

I roofed one like that 4 or 5 years ago...wierdest shapped roof I have ever roofed...it was nick-named the boat church for a good reason.

The shingles were put on with 2' nails through the fiberboard into the 2.5 " wood deck. We just pulled them off and put a new layer back on. There was just a few rotten places where it had leaked, and we didn't have any problems with it and havn't had any since. We did put ice and watershield on the entire thing.

You know some roof decks don't need to be vented. If the deck has mass to it, it can absorb the heat without getting really hot. I think it's called the heat-sink concept.

If you have ever seen a loadmaster deck, they use that concept.

26' ft. on the run guppy. O/S they say it is hot i the sanctuary in the summer and comfortable in the winter. Not sure of the budget, we may have to talk more here.

I don't think they want the whole ventilation package. But they will still spend plenty tiptoeing around it!

I would think the fibreboard will be very crumbly, and will fall apart as the old shingles are removed.You may get a lot of dust and debris inside, been there, done that It would be safer to dry in as you go, as it will be slow. How long is the rafter? I am quoting one now, no fb, 2 layers-32 ft. rafter,

Sounds like it is almost venting itself. Two layers of the old celotex sheeting was pretty standard back then. Later we used a couple layers of the Fesco board and still later a couple layers of Urethane. That started to get tricky as we were still just using longer nails and the urethane wasn't as dense and solid as the fesco or the Celotex board. That is why we started to screw down OSB or plywood over the layers of insulation for a niling surface and then we started to vent the system.

What do they want, and what are they willing to spend?