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EPDM roofing in Washington, DC: what the code says, and what sits under the membrane
The 2017 DC Energy Conservation Code never uses the word EPDM. What it does define is a roof recover, a roof replacement, a cool roof test for slopes of 2:12 or less, and a roof assembly that is more than the covering. This page reads that text, then turns to the layers below a rubber membrane on a District rowhouse roof, using Building America and Building Science Corporation material on vapor retarders and condensation.
- The code's cool roof section starts at slopes of 2:12 or less
- A roof recover is on the alteration exception list
- The code counts the vapor retarder as part of the roof assembly
Recover, replacement, repair: three words the code defines
An owner says roof job. The energy code says one of three things, and each triggers different language. Everything below comes from the District's published copy of the 2017 DC Energy Conservation Code, residential part first.
Roof recover
- Defined as an added covering over a prepared existing covering, with the old one left in place.
- Item 4 on the alteration exception list, so it need not meet new-construction envelope rules as long as the building's energy use does not rise.
- The commercial part of the code also lists roof recovering among its alteration exceptions.
Roof replacement
- Defined as removing the existing covering, repairing damaged substrate and installing a new covering.
- Item 5 on the same list: where there is no insulation in the cavity and the sheathing or insulation is exposed, the roof must be insulated above or below the sheathing.
- The code does not say how much, in the passage read, so the thickness is for the plan reviewer and the engineer.
A third word, repair, is defined as reconstruction or renewal of part of a roof for maintenance. The repairs section lists roof repairs as repairs and says routine maintenance and ordinary repairs exempt from permit are outside its requirements. Reroofing is the umbrella term for recovering or replacing.
The code does not draw the line between a repair and a replacement by area. A patch and a full membrane change are far apart, and the text read gives no square footage test.
Reading the cool roof section, step by step
Section R402.6 is the rule that reaches low-slope roofs. Because the code names no membrane, the test is run on the product, whatever it is made of.
- Slope. The section covers roof slopes of 2:12 or less, which the code puts at 17 percent or less, on buildings and covered parking.
- Building type. The residential part applies to detached one- and two-family homes, townhouses, and R-2, R-3 and R-4 buildings of three stories or less.
- Area. At least 75 percent of the whole roof surface, leaving out penetrations, solar equipment, rainwater harvesting and green roofing, must carry compliant products.
- Product test. A three-year-aged Solar Reflective Index of at least 64, or the criteria of the ENERGY STAR roof product specification.
- Paper. Reflectance and emittance values come from an accredited laboratory, the Cool Roof Rating Council program being the example the code gives, and carry the manufacturer's label and certification.
- Exceptions. An energy simulation showing the building uses 2 percent less than with an SRI 64 roof; parking, semi-heated and recreation roofs at an initial SRI of 29; terraces under 25 percent of the largest floor plate; and green roofs.
Now the open question. The additions list (R502.1.1.1) and the alterations list (R503.1.1) each name the envelope sections they pull in, and neither names R402.6. Whether that means a replacement escapes the cool roof test or the section applies on its own terms is not answered in the text. The Washington, DC roofing guide flags the same gap from the permit side. Put the question to DOB in writing and keep the reply.
What the code calls a roof assembly
roof covering, underlayment, roof deck, insulation, vapor retarder and interior finish
2017 DC Energy Conservation Code, definition of roof assemblyThat is the code's own list of what a roof assembly includes. A rubber membrane is the first item. The cool roof section speaks only of roof coverings, so it tests the top layer. Condensation, drying and air leakage live in the other items on the list, and the energy code does not set one rule for them in the passages read.
The Office of Planning's historic roof guideline calls single-membrane roofing a rubber roof and notes that flat roofs are rarely absolutely flat, sloping to the rear to drain. It also says a roof deck changes drainage and structure. Those are assembly facts too: the slope and the drain belong to the layers under the membrane, not to the sheet itself.
Vapor retarders and condensation below the membrane
Because the District's code text is quiet here, the neutral guidance carries the explanation. The Department of Energy's Building America Solution Center has a guide to low-slope roofs that lists EPDM among the single-ply membranes it covers, and a second guide to re-roofing and adding insulation over a flat roof on masonry walls. Both are written for residential retrofits, and the second cites the 2009 and 2012 International Residential Code, not the District's edition.
Air first
The low-slope guide says a fluttering membrane stresses itself and pumps interior air, with its moisture, into the assembly in cold and mixed climates. A lower air control layer resists the suction, and should connect to the wall at the parapet.
Rigid share
The re-roofing guide says an unvented assembly must meet the residential code table for condensation control. The share of rigid foam against fibrous fill must be enough, and rises with deeper fill and colder zones.
Inside face
The same guide reads the 2012 code to allow a Class II or Class III vapor retarder on the interior plaster or gypsum, and to prohibit a Class I polyethylene barrier because it would stop the assembly drying.
The classes are Building Science Corporation's, from a 2011 digest by Joseph Lstiburek. The digest is written for walls and floors, so use it only for the definitions, tested by the ASTM E96 method.
| Class | Permeance, in perms | In the Building America roof guide |
|---|---|---|
| Class I | 0.1 or less | Polyethylene barrier prohibited on the interior of an unvented flat roof |
| Class II | Above 0.1, up to 1.0 | Allowed on the interior plaster or gypsum |
| Class III | Above 1.0, up to 10 | Allowed on the interior plaster or gypsum |
Sources: Building Science Corporation BSD-106; Building America Solution Center re-roofing guide (September 2013). Opened October 20, 2026.
The low-slope guide says many light-colored roofs no longer get hot enough to drive moisture back down, which dark membranes did. Membrane color is therefore a condensation question as well as a cool roof question. Ask for the data sheet.
Questions to put in a written scope
- Is the work a recover or a replacement, in the code's words, and who decided?
- If the sheathing or insulation is exposed, how will the roof be insulated above or below it?
- Which layers are under the membrane: deck, insulation, any vapor retarder, interior finish?
- Where is the air control layer, and how does it meet the party wall and the parapet?
- What is on the room side of the ceiling, and is anyone proposing a polyethylene sheet there?
- Which product values, SRI or ENERGY STAR, are claimed, or which exception?
- Where does the roof drain, and does the tapered insulation or sleeper plan show it?
For the material itself, see the EPDM roofing guide, flat roof basics and roofing materials. Book a phone consultation to talk through a Washington, DC EPDM roof; the call starts with the address, the building type and what is visible from the street.
DOB pages and code editions
- In kind
- DOB lists roofing and coping replaced in kind among work needing no building permit outside historic districts, and defines in kind by likeness in proportion, appearance, texture, design, detail and dimensions. Whether a change of membrane or added insulation is in kind is not spelled out.
- Code copies
- DOB says its integrated copies omit amendments adopted after May 29, 2020, and that Title 12 of the District regulations is the official text.
- New codes
- DOB reports a rulemaking in fall 2026 with new codes planned for late 2027, so an edition question today may have another answer later.
See the District roofing hub for the permit and historic review lanes, roof replacement and services. Insurance questions are in the roofing insurance guide.
References behind this page
All opened October 20, 2026. This page reports what the sources say and does not give legal or engineering advice.
- 2017 DC Energy Conservation Code (integrated copy, DOB): definitions, R402.6, R502 to R504, commercial envelope alterations
- DC Department of Buildings: How to Get a Permit
- DC Department of Buildings: DC Construction Codes and Construction Code Development
- Building America Solution Center: Low-Slope Roofs
- Building America Solution Center: Water-Managed Roof, Re-Roofing and Adding Insulation over Flat Roof
- Building Science Corporation: BSD-106 Understanding Vapor Barriers
- Office of Planning: Roofs on Historic Buildings (guideline PDF)
Questions people ask
Does the DC energy code mention EPDM?
No. The text of the 2017 DC Energy Conservation Code that DOB publishes does not contain the word EPDM. Its only membrane wording is a list of air barrier materials that names built-up, modified bituminous and fully adhered single-ply roof membranes. It sorts roofs by slope, by the work done (recover, replacement or repair) and by the reflectance of the product, so ask the plan reviewer how a rubber membrane is treated.
Is a recover over an existing membrane exempt from the energy code?
Item 4 of the alteration exceptions lists a roof recover, provided the energy use of the building is not increased. A recover is defined as a new covering over a prepared existing one without removing it. The cool roof section is not named on that list either, so the exact reach is a question for DOB.
What does the code mean by a roof assembly?
The definition lists the roof covering, underlayment, roof deck, insulation, vapor retarder and interior finish. A membrane is one layer of that list, and the questions about condensation sit with the layers below it.
Does a flat roof in Washington need a vapor retarder?
The code pages read for this guide set no single rule for flat roofs. A Building America guide on retrofitting a flat roof says that, under the 2012 residential code it cites, an interior Class II or Class III retarder is allowed and polyethylene, a Class I vapor barrier, is prohibited. Ask DOB or your engineer which text applies to your building.
What is the condensation control ratio on a flat roof retrofit?
It is the balance between rigid insulation above the deck and any fibrous fill between the joists. The Building America guide says the rigid share must be enough to avoid condensation, grows with deeper cavity fill and with colder climate zones, and points to a table in the residential code.
What if the sheathing or insulation is exposed during reroofing?
The energy code says a roof with no insulation in the cavity, where the sheathing or insulation is exposed during reroofing, must be insulated either above or below the sheathing. That sits in the alterations section as an exception to the new construction rules.
Which edition of the DC code applies to a roof job now?
DOB says the 2017 DC Construction Codes took effect on May 29, 2020, and that it plans new codes for late 2027. Its integrated copies omit later amendments, and Title 12 of the District regulations is the official text. Confirm the edition on the day you apply.
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