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PVC roofing in Bethesda, MD: grease, oil and the roof around an exhaust
Grease is the one rooftop stain that sets PVC apart in neutral papers. A federal guide spec and a trade association both speak to it, and the Maryland Mechanical Code sets what a kitchen exhaust may do to the roof beside it. This page starts with the Bethesda housing stock to show which buildings the question can reach, then reads those papers, and ends with the lines a written scope should carry.
- 12,512 Bethesda homes sit in buildings of 5 or more units
- 2 of 3 federal single-ply guide specs name kitchen exhaust
- 40 in. minimum grease outlet height above the roof
Which Bethesda buildings the question reaches
A grease-resistance question only matters on a low-slope roof, and in Bethesda the Census Bureau’s housing tables show where large buildings sit. The 2024 five-year American Community Survey counts 30,095 housing units in the Bethesda area, vacant ones included, and sorts them by units in the structure.
Another table sorts occupied homes by when the building was built. Taking only buildings of five or more units gives a different cut from tenure alone.
| Building built | Owner homes | Renter homes | All | Share |
|---|---|---|---|---|
| 2020 or later | 0 | 393 | 393 | 3.6% |
| 2000 to 2019 | 817 | 2,881 | 3,698 | 33.5% |
| 1980 to 1999 | 654 | 1,320 | 1,974 | 17.9% |
| 1960 to 1979 | 1,652 | 2,381 | 4,033 | 36.5% |
| 1940 to 1959 | 199 | 626 | 825 | 7.5% |
| 1939 or earlier | 7 | 113 | 120 | 1.1% |
Census Bureau ACS 2024 five-year estimates, tables B25024 and B25127, Bethesda, MD; 11,043 occupied homes in buildings of 5 or more units; shares are ours and rounded. The tables count homes, not roofs, offices or shops.
Two bands stand out: 4,033 homes in buildings from 1960 to 1979 and 3,698 from 2000 to 2019. Together with the rest, 4,091 homes (37.0%) are in large buildings built in 2000 or later and 4,978 (45.1%) in ones built before 1980. A build year says nothing about what is on the roof today, so it is a reason to ask about the roof’s history, not an answer.
Apartment and condominium buildings
Ask whether a restaurant, shared kitchen or commissary sits below or beside the roof, and who owns that tenant’s equipment on it.
Mixed-use and office buildings
The housing tables leave out business space. Ask the owner whether any tenant vents cooking exhaust through the roof, and where the discharge points.
Houses and townhouses
A PVC membrane would sit on a low-slope part of such a house at most. Ask whether any outdoor cooking vent or similar equipment discharges onto it.
Nothing here says any Bethesda building has a kitchen exhaust or a PVC roof. The Bethesda roofing guide covers the license check and the county permit lanes that come before any of these questions.
What neutral papers say about PVC and grease
The federal guide specification
Unified Facilities Guide Specification 07 54 19, Polyvinyl-Chloride Roofing, dated August 2023, is written by the Army Corps of Engineers, Navy and Air Force for their roof contracts. A designer note says the section can also be used with a separate membrane for roof areas needing more protection, and names the case: next to kitchen or food service exhaust discharge ducts.
“Supplemental grease, chemical and oil-resistant PVC roofing membranes are available.”
Designer note, UFGS 07 54 19 (August 2023)SPRI, the single-ply trade association, published a primer in January 2019 that puts TPO and PVC together as chemical resistant and then says of PVC:
“excellent resistance to rooftop chemicals, including acids, oils, and greases”
SPRI, Single-Ply Roofing 101, January 9, 2019- Vinyl Roofing Division
- The PVC industry division of the Coated Fabrics and Film Association lists thermal cycles, wind loads, structural movement, ponding water, alkaline conditions and plant roots on its durability page. That page carries no grease or oil statement. It is a trade source, and its comparisons with other materials are not used here.
- Maryland Building Code
- Table 1507.12.2 lists PVC and PVC/KEE under ASTM D4434. The single-ply text has no grease or chemical wording, so a grease claim on a quote is the maker’s, not the code’s.
The PVC guide is not alone in addressing the subject. Reading the three federal single-ply guides side by side:
| Guide spec (August) | Kitchen exhaust wording |
|---|---|
| 07 54 19 PVC (2023) | Names the case; a supplemental grease, chemical and oil-resistant PVC exists; consult the maker |
| 07 53 23 EPDM (2025) | Excludes roofing next to the discharge ducts and states that grease and oil attack EPDM |
| 07 54 23 TPO (2025) | No kitchen exhaust or grease wording in the text read |
UFGS texts downloaded from the Whole Building Design Guide October 24, 2026; the TPO line is silence in the text, not a finding about TPO.
What is PVC-specific, then, is a named supplemental product and a federal note that sends the buyer to the maker. What is missing is any number: no exposure test, no discharge rate, no distance from the duct.
What the Maryland code puts on the roof
The roofing chapter is silent on grease, but the Maryland Mechanical Code 2021 is not silent on what a commercial kitchen exhaust does at the roof. The county’s master list shows the 2021 International Mechanical Code effective December 10, 2024. UpCodes publishes the Maryland text, and county amendments were not read.
- Section 506.3.13.1, the outletA grease duct outlet serving a Type I hood that ends above the roof has its discharge opening at least 40 inches above the roof surface.
- Section 506.3.13.3, the distanceOutlets sit at least 10 feet horizontally from the same or adjacent buildings and property lines, with a 5 foot exception where the air discharges away from them.
- Section 506.5.3, the fanExhaust fans are positioned so the discharge does not impinge on the roof. A vertical discharge fan has a drain outlet at the lowest point of its housing, leading to an approved grease reservoir.
- Section 506.5.4, the hingeUpblast fans on Type I hoods are hinged, on a flexible weatherproof cable, with a restraint, and the ductwork extends at least 18 inches above the roof surface.
These sections are written for the mechanical contractor. For a roof scope they show where the grease leaves the system: the drain outlet and reservoir under the fan, and the outlet and the 40 inches above the surface. Whether either is on a given building is for the owner and the county to say.
What else the guide keeps off the membrane
Contact the guide warns against
- Reinforced PVC in direct contact with asphalt, coal tar pitches or petroleum-based products.
- Asphalt or coal-tar products as a temporary seal at a cutoff.
- PVC adhered directly to polystyrene, perlite or standard wood fiber insulation, unless the maker verifies it.
- Fire-retardant-treated wood against the membrane, unless the maker and the owner’s representative approve.
What the guide asks for instead
- Walk tread where the roof bears foot traffic once a month or more.
- Walkways laid on a loose pad of membrane, with no stone ballast over or under them.
- Prefabricated equipment curbs at least 10 inches above the finished membrane, with a 4 inch flange.
- Accessories supplied or approved by the membrane maker.
The walk tread line matters for an exhaust fan that is hinged for cleaning. A SPRI-posted article by an industry supplier makes the same point from the other side: trades people carry tools and drag cords that can puncture a membrane. It is opinion from a supplier, but it explains why a service path is drawn on the plan.
The guide does not say whether kitchen grease counts as a petroleum-based product, and it does not name animal or vegetable fats. That is why the maker’s written statement, not the word PVC, carries the weight.
Lines for a PVC scope near an exhaust
- Whether any exhaust discharges onto or beside the roof, answered by the owner in writing.
- The exact membrane product, and whether a grease, chemical and oil-resistant sheet is specified within a stated distance of each discharge.
- The maker’s written statement for that product near grease, since the code and the guide give no rating.
- The fan housing drain outlet and grease reservoir, and who services them.
- The curb height above the finished membrane and the flashing the maker approves.
- A walk tread route from the roof hatch to each fan, drawn on the plan.
- What lies under the new sheet: insulation type, any old asphalt or tar, and the separation the maker states.
- Which edge, flashing and recover limits from the Maryland building code apply, and any written reply from the county or association.
Book a phone consultation to talk through a Bethesda PVC roof. For the material in general see the PVC roofing guide, roofing materials, flat roofs, commercial roofing, roof replacement and services. The Bethesda guide has the permit path.
Papers opened for the PVC question
Each document below was opened October 24, 2026. UpCodes publishes the Maryland code text; county amendments were not read.
- UFGS 07 54 19 Polyvinyl-Chloride Roofing (August 2023), with UFGS 07 53 23 EPDM and UFGS 07 54 23 TPO (August 2025)
- SPRI, Single-Ply Roofing 101 (January 9, 2019) and SPRI, Hammers and Rollers and Drills, Oh My (March 6, 2023)
- Vinyl Roofing Division, Coated Fabrics and Film Association: durability, a trade source
- Maryland Mechanical Code 2021, Chapter 5 Exhaust Systems and Maryland Building Code 2021, Chapter 15, third-party publication
- Montgomery County DPS: Master List of Building Codes and Standards
- Census Bureau ACS 2024 five-year, tables B25024 and B25127, Bethesda, via Census Reporter
Questions people ask
Does PVC resist grease and oil?
SPRI, a single-ply trade association, says PVC offers excellent resistance to rooftop chemicals, including acids, oils and greases. A federal guide spec says supplemental grease, chemical and oil-resistant PVC membranes are available and tells the reader to consult the maker. Neither gives a test method or a rating, so ask for the maker’s written statement about the exact membrane.
Is the standard PVC sheet the same product as a grease-resistant one?
The federal guide spec treats them as two products. Its note says the text also applies to a supplemental, chemical and grease-resistant PVC membrane for areas such as next to kitchen or food service exhaust discharge ducts. The sheet named in a quote should be named by product, not just by the word PVC.
Does the Maryland code say anything about grease reaching a roof?
The Maryland Mechanical Code, chapter 5, says exhaust fans must be positioned so the discharge does not impinge on the roof. It also requires a vertical discharge fan to have a drain outlet at the lowest point of its housing, leading to an approved grease reservoir. These are mechanical rules for kitchen hood systems, not roofing rules.
How high must a restaurant exhaust outlet stand above a Maryland roof?
For grease ducts serving Type I hoods that end above the roof, the code text requires the discharge opening to be at least 40 inches above the roof surface. Upblast fans on those systems must have ductwork that extends at least 18 inches above the roof surface. A mechanical contractor and the county confirm the figures for a given system.
Is a TPO roof treated the same as PVC beside a kitchen exhaust?
The federal guide specs differ in what they say. The PVC and EPDM guides both address kitchen exhaust, and the EPDM guide states that grease and oil attack EPDM. The TPO guide text read for this page has no kitchen exhaust wording. Silence in a guide is not a rating, so the question goes to the maker.
Can PVC be laid against old asphalt or tar?
The federal guide says not to use reinforced PVC membrane in direct physical contact with asphalt, coal tar pitches or petroleum-based products, and not to use asphalt or coal-tar products for sealing a cutoff. It does not list kitchen grease in that sentence. Where an old roof sits below, the maker states what separation the new membrane needs.
Which Bethesda buildings does this apply to?
The Census table counts homes, not roofs and not businesses, so it cannot say which roofs sit near an exhaust. It does show 12,512 of 30,095 Bethesda homes in buildings of five or more units. For those, ask whether a restaurant, shared kitchen or other cooking equipment is below or beside the roof.
Who signs the scope for an association-owned roof?
Whoever owns the roof under the governing documents, and the county pages say they do not cover association rules. Ask the board or manager before a bid is accepted. To talk through a Bethesda PVC roof, book a phone consultation and have the building type, the roof access and any rooftop kitchen exhaust ready to describe.
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