Moisture Control when Adding Insulation Above Existing Roof Deck

[RoofDetail](//muut.com/u/brownstoner/s1/:brownstoner:UkXa:roofdetail.png.jpg)
Hi All,
My partner and I are looking to add insulation to an existing, uninsulated, low-slope brownstone roof at the same time as we replace the roof membrane and skylights. I would have assumed that adding rigid insulation above the existing roof deck would be commonplace in NYC by now, but I haven’t found a roofer with experience with this type of roof retrofit. The attached detail is adopted from a presentation by Joseph Lstiburek of Building Science Corp., and to the best of my knowledge, it is the best option for me. Has anyone else completed a similar roof retrofit with rigid insulation installed above deck (aka warm roof)? How did your roof assembly compare with the attached detail? What are some of the potential points of failure? Can someone recommend a roofing contractor with experience/expertise in insulating existing roofs in this manner? Thanks.

mheimbinder

in General Discussion 3 years and 4 months ago

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MDR | 3 years and 4 months ago

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It seems like a reasonable detail and its definably more effective for the insulation to run continuously over the deck. The extra thickness will require the curbs for skylights and hatch, etc. to be rebuilt and extended. That’s not too hard but where your roof connects to the next house there might not be much of a wall there so detailing the edge may be tricky and different than what’s shown in your drawing. It might work better to do one layer of foam instead of three. I got a quote to do something similar for my house and the contractor did not have a problem installing the foam necessarily but it got pricy because I wanted to get rid of all the old layers of asphalt and that led to potential asbestos and deck repair costs.

jimhillra | 3 years and 4 months ago

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We’ve done insulated/warm roofs before and they will become much more common as the newer energy codes require uninterrupted insulation to cover thermal bridging provided by beams and joists. Correctly done, with the right materials, they should definitely not be squishy. I would assume Cate’s example used the wrong insulation. Products made for this application have a hard surface for walking, or if using more standard insulation, a wear layer, like Densdeck, should be installed on top of the insulation.

kassie319 | 3 years and 4 months ago

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I’ve worked with Jose Santamaria (formerly of United Roofing and Riconda) for many years. He is definitely familiar with this type of system. Call him at 201 960 0866, tell him Brendan sent you. To Cate’s comment- I’m not a roofer (I build roof gardens) but I have seen this type of installation and recently reviewed a set of drawings for new membrane/ insulation on a wood decked/ flat roof in Manhattan that had details by Sika and Siplast similar to those in the OP’s example.

Lurker | 3 years and 4 months ago

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We had a quote from Royal Renovators that specced Duro-Guard Densdeck which I think had a layer of insulation? We didn’t use them due to $$ and then also saw some posters here had issues. I did find they were polished with proposal, knowledge etc.

cate | 3 years and 4 months ago

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No experience with this. I do know someone who added insulation above the roof layer. Later roofers said it was not the proper way to handle. It created a squishy roof. It was later removed and redone.

mheimbinder | 3 years and 4 months ago

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Any responses would be appreciated. Thanks.