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A homeowner in Westchester County, New York, described a proposed over-roof to replace a poorly installed, aging EPDM membrane and address ponding and insulation gaps. The plan outlines a target near R-60 while retaining the house’s low-profile appearance, but the source is a homeowner’s question, not a completed project or an approved design.
A homeowner in Westchester County, New York, has proposed replacing a failing flat-roof assembly with a sloped, insulated over-roof aimed at correcting ponding and bringing the roof close to R-60 insulation. The account describes a design under consideration—not completed work or a verified construction plan—and leaves key structural, drainage and moisture questions open.
The existing roof has an EPDM membrane the homeowner describes as poorly installed, repeatedly patched and near the end of its service life. The house, a contemporary post-and-beam home from the early 1970s, has a tongue-and-groove 2-by-6 roof deck supported by large glulam beams. The homeowner reports little existing insulation and several areas where water ponds, partly because sections of the rear drip edge sit higher than the roof surface.
The proposed work would strip the roof layers and cover the deck with taped 7/16-inch ZIP sheathing to create an air barrier. Above that, the homeowner proposes mineral-wool board, a sloped structure framed with 2-by-8s at 24 inches on center, mineral-wool batts between the framing, four inches of polyiso insulation and a new EPDM membrane. The stated aim is a roof slope of 0.5 inch per 12 inches toward the back of the house, with parapets concealing the slope from view.
The homeowner estimates the insulation layers would total just under R-60, counting the proposed materials. That is a target, not a measured result; the source does not provide an independently reviewed assembly calculation, product specifications or construction outcome. The plan would also remove existing skylights and cover them over. The original overhangs would remain roughly their current thickness, preserving the building’s horizontal profile.
Drainage and Insulation in One Roof
The proposal addresses two problems in the same part of the building: standing water on a nearly flat membrane and a roof assembly the homeowner says has almost no insulation. A new slope could direct runoff toward the rear gutters, while added insulation and air sealing are intended to improve comfort and reduce heat loss. Whether the design achieves those goals depends on details that are not established in the source.
The house’s architectural character also shapes the decision. Its exposed beams, broad glass openings and slim roof overhangs are central to the design, so simply adding visible roof thickness may conflict with the owner’s goal of retaining its appearance. An over-roof can shift much of the new assembly above the existing deck, but the parapets, edges, gutters and transitions still need to be designed to manage water and fit the building.
Because the proposal adds framing and multiple material layers above an existing structure, it is not only a roofing-material choice. Structural capacity, attachment, drainage and moisture control affect whether the assembly is suitable. The source provides no engineering review or permit determination, so readers should not treat the described stack-up as a construction specification.
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A 1970s Post-and-Beam House
The home is described as a custom contemporary house built in the early 1970s, in climate zone 4A. Large sliding glass doors occupy much of the exterior walls, and the owner says their air tightness and insulation are poor. The longer-term renovation goal is to improve energy performance while retaining the home’s architectural language, including reducing some glazing and replacing some moving glass.
The roof is supported by glulam beams spaced about 6 feet 6 inches apart, with posts at the exterior walls and around midspan. The tongue-and-groove deck remains exposed in some rooms, while a previous owner drywalled other areas. The homeowner believes the existing roof layers include an original torch-down roof, fiberboard and the later EPDM membrane, but describes that layer history as an assumption rather than a confirmed inspection finding.
The proposed assembly would sit over the living space and be enclosed by short parapets on three sides. The owner says tapered foam was also considered, but the supplied account ends while explaining why that approach may be less attractive. It does not include the remainder of that reasoning or a final choice of roof system.
“I would like to do an “over-roof” that would (i) fix the drainage and ponding issues with a 0.5/12″ slope to the back of the house and (ii) create space for significant insulation with the goal of getting to the R-60 range.”
— The homeowner, in the GreenBuildingAdvisor question
Design Details Still Unverified
The source is a homeowner’s request for feedback, and it does not report a professional assessment, permit approval, construction schedule or completed roof. It is also unclear whether the existing beam-and-post structure can support the added framing, insulation, sheathing and membrane, or what connections and load calculations would be required.
The homeowner’s estimate of just under R-60 is based on proposed material values, including an estimated R-23 from four inches of polyiso. The source does not identify the exact products, confirm installed performance or present a full assembly analysis. It also does not establish that the proposed insulation distribution will control condensation in this specific roof, despite the owner’s reference to guidance for climate zone 4A.
Other unresolved details include how the sloped roof would connect to the existing overhangs and parapets, how water would pass into the rear gutters, and how the assembly would handle the tapered cavity beneath the new framing. The supplied account cuts off during the homeowner’s discussion of tapered foam, so the comparison with that alternative is incomplete. No source material confirms the condition of concealed roof layers or the final drainage route.
Professional Review Before Construction
The homeowner’s next step is not stated. Before construction, the proposed assembly would need review by qualified roofing and building professionals familiar with low-slope roofs, along with a structural assessment of the existing beams, posts, connections and foundations. Local permit and code requirements also need to be checked rather than assumed.
A project review would need to resolve the roof’s drainage geometry, membrane and edge details, parapet and gutter transitions, air-barrier continuity and moisture strategy. It should also confirm product-specific insulation values and the assembly’s expected performance. Until those checks and any required approvals are documented, the R-60 figure and drainage improvement remain design targets, not confirmed outcomes.
Key Questions
Has the over-roof been built?
The source does not say that construction has begun or been completed. It presents a homeowner’s proposal and questions about the design.
What problems is the proposed roof intended to address?
The homeowner wants to replace an aging, poorly installed EPDM membrane, reduce ponding by adding slope toward the rear, and add insulation and air sealing.
Is the proposed roof confirmed to reach R-60?
No. Just under R-60 is the homeowner’s estimate based on proposed materials. The source does not provide an independent calculation or measured result.
What should be checked before building an over-roof?
Qualified professionals should assess structural capacity, drainage, attachment, moisture control and code or permit requirements. The source does not report that these checks have been completed.
Source: greenbuildingadvisor.com
