old school roof

[ydkdy73]

ok this is a first for me so bear with me pleas. I have been in the construction buss for about two years now and gaining some valueable experience. Yesturday i went with one of the guys i work with to check out this job and what we found was real strange we are looking at putting a new roof on this house and the home owner has just replaced about 1/4 of the interior cealing. which is 2x6 toung and grove it is also exposed inside of the home. i hope from what im describing you can picture this. well we get on the roof and discover that there is some sort of cork board panels most likley installation under the shingles so here is my problem. what is the best way to go about this to put a new roof on this house. my initle thought was to put wood slats in and cover with 3/8 plywood then put new shingles on from there. IF ANYONE HAS RUN INTO THIS OR HAS A BETTER SUGGESTION FOR ME PLEAS DO TELL.

THANKS Chris

[lw@buyerbewareinc.com]

Late reply to cork board over T&G ceiling question

I'll venture a guess since no one else jumped in on this question. Sorry the answer is probably too late to help you, but may help someone else with a similar problem.

What you found is a rigid insulaton board installed over the 2 inch by six inch tongue and groove car decking used for the interior ceiling and roof sheathing. If one quarter of it needed to be replaced, that indicates the wood may have deteriorated due to trapped moisture in the roof assembly.

Check for a vapor barrier under the cork board. If there is no plastic vapor barrier or tar paper under the insulation, moisture vapor inside the house will move through the tongue and groove ceiling and insulation to the underside of the shingles. If the shingles are composition shingles or wood shingles installed over a roofing felt (tar paper), the moisture vapor will condense on the underside and soak the insulation board and car decking from the top.

If some of the car decking rotted due to moisture, the whole roof needs to be stripped down to the top of the car decking so a vapor barrier can be installed on the warm side of the insulation. This will give the owner a chance to increase the amount of insulation in the roof by switching to rigid foam.

I used six mil plastic for a vapor barrier over tongue and groove car decking I installed on a floating home back in the 1970's. The plastic sheet vapor barrier was covered with two inches of rigid foam insulation and the composition shingles were fastened directly to the foam with three inch long square head nails. The nails had to be long enough to reach through the foam and anchor into the tongue and groove wood without showing from inside the house.

In a case where the home is not floating and extra weight is not an issue, put one-half inch plywood or Oriented Strand Board over the foam insulation so the roof shingles can be installed with standard roofing staples or nails following the manufacturers requirements for felt under the shingles.

The lack of an attic space for roof venting requires careful attention to the location of the vapor barrier. A classic example of this was a municipal indoor swimming pool structure built new in my neighborhood. The first time the weather turned cold after the pool opened to the public, it started raining out of the tongue and groove ceiling above the pool.

Everybody in the city government, the architects and contractors were so convinced the tile roof was leaking they tore it off and replaced it during the next summer. The only problem was they didn't realize the problem was the vapor barrier in the roof assembly was on top of the insulation, not under it, close to the heated space inside the building. The second time around they installed a standing seam steel roof. When the weather turned cold the rain returned inside the pool building.

Needless to say, the next summer the second roof was torn off, and thanks be, someone on the next roofing contractors crew realized the problem. When reassembled properly with a vapor barrier underneath the insulation and a composition shingle roof over it, condensed moisture stopped raining back into the pool building during cold weather.