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Flat roof questions.

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Joined: Mar 20 2012

I have a custom built 1959 home in Scarsdale, NY which has a flat roof.  Nothing has been touched in the house since it was built and as a new owner I am worried about the roof.  I see a few small leaks but nothing major. 

What I see from the inside is laminated beams with 6'-5" spacing with Tongue and Grove cedar on top of this.  From the roof I see white gravel on top of some black surface.  It looks very flat with ramp ups where skylights exist.  The perimeter has 3' overhangs and little copper u-shaped spouts where the water runs off.  I am unsure if there is any insulation between the Tongue and grove and the black water proof layer.  I have not done a core test.  

If there is no insulation between is this a problem?  What I mean is why would this house have been built without it?  This is NY so hot summers and cold winters.  The house has forced hot air and AC, with lots of windows.  If there is no insulation what is the best solution?  

Being that the waterproof layer on the roof is probably 52 years old does this need replacing?  I see no rot or warping of the tongue and groove boards.  Some of them have gaps between board and in some places I see gravel in this space.  This is strange and don't know how this could be the case.  


If a complete new waterproof layer is needed for the house, what would you recommend?  I am planning to build a second floor to one section so the roof will be visible so I think I would like to keep the white gravel look.  

And finally does anyone have a recommendation for a flat roof specialist in the NYC area?

Thanks.  It is a new purchase and this roof thing has me worried,  Robert

Joined: Apr 20 2006

Robert in New York

Congrats on your new house.  The gravel stuck between your roof boards shows that your roof has been replaced.....likely several times.  Hot and cold and wet weather is hard on a tar roof.  Your roof must have insulation between the tar paper and wood.  Look for a little change in roof height where your overhangs start.  The insulation usually stops at the overhangs.

Here is an article from the Eichler Network giving you a good look at the insulation and wiring underneath...

Here is one important concern that I did not mention in the article; Water condenses on a cold surface.  The underside of your tar roof is very cold during much of the year.  Moisture from inside the home migrates to the cold surface and condenses as the air cools.  The moisure ends up in the insulation.   The foam boards are not waterproof.  It is rare in New York to find this kind of roof.  Usually, there is an air space with outside air (cold air) under your roof.  Cold air is very dry.  It takes much longer for the insulation to gradually dry during dry weather.  Damp insulation does a poor job of insulating, compounding the condensation problem.

When you have your roof replaced, you must find a local contractor that understands the potential moisture problems.  Steps can be taken to stagger multiple layers of foam boards and/or install vapor barriers to protect the insulation from the moist air underneath.  Foam boards loose 25% of their value just because they have edges on the 4x8 boards.  I am not sure if there is a foam contractor near your city.  In your case, a foam roof on the outside of the building envelope would keep the wood and insulation at room temperature and eliminate the problem.  When you eliminate the potential for condensation and moisture getting into your wood, you eliminate the potential for dry rot. 
Randy from Dura-Foam Roofing and Solar Center

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