Expert: Bruce E. Johnson - 9/16/2009

Question
QUESTION: I am installing a (flat) roof over my deck that will only have a 3" fall in 15' and want to make sure I put on the best roof that will insure me against future leaks.  I reside in the midwest ( Kansas City) where we have to deal with rain and snow.  I have been told about membrane, torch down (California Roof) and the latest is a PVC membrane made by IB Roof Systems that is 80 Mil but am concerned that it is not glued down.  They weld the seams with heat but the rubber is laid over 1/2" Fanfold Insulation Board.  Won't that material lift off the roof deck in a heavy wind?  What product do you think is best for my situation?

ANSWER: Hi Jerry, honestly?  I have not done an IB roof system so I can't really comment on its viability in your climate.  However with any flat or low slope roof system that I have done whether it be built up asphalt, hot tar, or composite the insulation layer is attached to the substrate somehow either by hot mopping, screwing or nailed with tabs..so I am assuming that the IB system uses some method to attach the insulation to the deck.  As far as what type of roofing works good on this type of roof I like the Firestone fiberglass reinforced products...SBS  or APP..They have proved to give many years of service when installed properly.  We have been using the SBS system successfully on top of  a polyisonanurate insulation board with integrated nail base.  The polyiso board is nice because you can get it in 2-3-4 inch thicknesses for various R-factors.  Living in Florida, the above system is approved for 120 mile winds when the nail base sheet is screwed in a a certain pattern using specific screws.  I hope this information helps feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com

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QUESTION: I know they will attach the insulation board to the substrate but they say the roofing material itself comes in 3' and 6' wide rolls and it is only attached to the substrate at the seams.  Theat means you could have up to 6' of unattached roof material between the seams and that is what concerns me.

Answer
Hi again Jerry, if this system is accepted by local building departments then it must be sufficiently attached to meet uplift requirements.  The roofing contractor should be able to quell you fears and explain how this roofing material works and how well it performs. I hope this information helps feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com