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Roofing/Insulation under the EPDM Roofing


If you are replacing an EPDM roof with a new EPDM roof do you also replace 1/2" insulation immediately under the existing EPDM roofing.
I was informed by 1 of the contractors that for flat roofing
normally there is 1/2" wet insulation between the existing EPDM roofing and existing tapered insulation that is over the roof deck.He also advised that you need to replace that 1/2" insulation with the new EPDM roof.
Based upon this senario if the tapered insulation goes from 2" minimum to 6" . The top 1/2" insulation is a seperate insulation board making the actual tapered insulation from 1 1/2" to 51/2".
Is my thinking is correct?. Please advise


There are numerous scenarios and configurations possible with EPDM roof systems and not knowing the composition and attachment of the entire assembly, I can only respond in general terms.

Your thinking is correct that on top of the tapered insulation there could be an "overlay" or "cover" board which serves to separate the insulation from the roof membrane.  Generally, insulation boards are not stable over time and are subject to shrinkage and other conditions which change the board over time.  It is advantageous to the overall long term performance of the roof membrane to divorce the membrane from the insulation with a more stable board of silconized gypsum or wood fiber or other.

If your roof has been leaking, it is important to remove all wet and water damaged insulation and replace it with new. Depending on the insulation attachment and composition, removal of the 1/2" overlay board can be detrimental to the assembly, at which point attaching a new overlay board over the existing membrane is most advantageous.


Bruce Ryan II, RRO
Professional Roof Consultants, Inc.


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Bruce A. Ryan II, RRO


I offer solid knowlege of all types of Commercial and Residential Roofing, Waterproofing, and, Building Envelope systems. Experience ranges across low slope and steep slope roof systems. I am also well versed in matters regarding condensation and ventilation. I enjoy donating some of my time and knowledge to the betterment of others.


Bruce Ryan has 20 years of roofing, waterproofing, and building envelope consulting experience with PRC, with 5 years of commercial roofing experience prior to joining the firm. He became Vice President of the company in 1998. Bruce Ryan plays a key role in the development of practical, long-term roofing and waterproofing solutions, along with implementation of on-site forensic studies. Bruce also has a high level of experience with regard to the impacts of roofing materials and construction for demanding clients with heavily occupied structures.

Oregon Construction Contractors Board Construction Specifiers Institute National Roofing Contractors Association The Institute of Roofing, Waterproofing, & Building Envelope Professionals Oregon Board of Investigators Installation Masters

University of Maryland BS Business & Administration Registered Roof Observer - RCI Private Investigator Certified EIFS inspector - Northwest Wall and Ceiling Bureau Certified InstallationMaster™ - The Installation Masters™ Training and Certification Program (developed by American Architectural Manufacturers Association)

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