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Roofing/Grass seed insulation!?


My parents had a metal roof installed over their existing flat roof.  The person who installed the metal roof neglected to add the necessary component to the valley in the metal roof which allowed it to leak onto the old roof and then into the ceiling causing some damage.  The company fixed the oversight by I am concerned about the water damage to the ceiling.  Here is the bizarre twist:  the previous owner who was a well known botanist, used grass seed as insulation under the flat roof!  

I would like to remove the flat roof, remove the grass seed and install the appropriate insulation installed between ceiling joists of the flat roof and then an additional layer perpendicular to the joists.
1) is this a good idea?
2) if so, what are some Murphy's Law issues I will face?
3) will paper backed insulation provide the appropriate moisture barrier?  Or should I use poly between the ceiling and the insulation?
4) would you be interested in 500 lbs of 80 year old grass seed?


I am not too sure exactly how that grass seed was supposed to serve as a stable substrate to install a roof over!  Regardless, if you are removing all that old roofing down to the wood sheathing; it seems reasonable to me that you install your insulation directly to the top of the roof sheathing, particularly if the joist spaces under the flat roof are currently not insulated. Your visqueen vapor barrier might then be installed directly to the top surface of the roof sheathing and be covered with the insulation provided there are not too many penetrations that will make sealing the vapor barrier to them laborious.  This way you may not need to remove your ceiling below. Otherwise, the best place for the vapor barrier is between the ceiling and the joists.  If your joist spaces are not insulated, perhaps leaving the old flat roof in place and overlaying it with fiberglass batts is most prudent as the roof itself should be serving as a fairly effective vapor barrier already.  Spot check for damage and deterioration from the ceiling below to ease your concerns as it sounds like the ceiling requires some attention anyway.

I am not sure if you intended to remove the roof sheathing of the flat roof in order to insulate the joist space, so I must caution you not to, as the sheathing provides a structural diaphragm that the building most likely relies on.  Check your over framed metal roof as you will need to ensure that the attic space is properly ventilated at a ratio of 1 square inch for every 150 square inches or 1:300 with a vapor barrier.

Pit falls:
If the flat roof membrane was installed before the mid to late 80s I would recommend having a sample tested at a laboratory for asbestos so you know what you will be digging into in that enclosed space.  It will get dusty.  Debris removal might also be challenging.

Hopefully I have not misunderstood your situation and existing conditions.  No grass seed for me thank you!


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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