TPO Roofing in Washington, DC: Start With the Roof You Have
In the District, TPO over TPO and TPO over something else are different questions. DOB's permit page, which matches a commercial site's copy of the building code, exempts roof covering only when it is replaced in kind, and the Office of Planning's roof guideline lists a single-ply sheet as the substitute for tar and gravel. Read your roof first.
Signs
Three roof surfaces and what a switch to TPO means for each
A diagnosis needs a person on the roof; these are only signs.
-
A black sheet with taped or glued laps
- What you see
- A black rubber-like sheet with lap lines and tape or adhesive along them.
- What it can mean
- An EPDM roof, the thermoset single-ply in the model code's table. TPO is a thermoplastic with welded laps, another material family. Whether DOB treats that as like material is its call.
- Who to call
- The Department of Buildings, and the Historic Preservation Office first if the block is a historic district.
-
Gravel or a mineral surface over layered felt
- What you see
- Gravel or a granular cap sheet, layers showing at the edges.
- What it can mean
- A built-up roof. The guideline's table of substitute materials pairs built-up (felt, tar and gravel) with single-ply (rubber) and asks owners to consult the Historic Preservation Division before a substitute. It does not name TPO, so ask how a thermoplastic sheet is read.
- Who to call
- The Historic Preservation Office for a historic block, the Department of Buildings elsewhere.
-
A light gray or white sheet
- What you see
- A light sheet. Colour is all a window or a stairwell hatch can read.
- What it can mean
- TPO, PVC or a white EPDM, since sheet membranes come in black, white and many colours. If it is TPO already, TPO for TPO in the same look is the closest case to like for like.
- Who to call
- The Department of Buildings, plus the condominium board or manager if you share the roof.
Who answers
Which office answers which TPO change?
| The change | What the pages say | Ask |
|---|---|---|
| TPO over TPO, same colour and detail | Closest to the in-kind wording, in our reading. In a historic district, DOB's special permit asks you to confirm with the Office of Planning first. | DOB; Historic Preservation Office if historic |
| TPO over EPDM or another membrane | Fits the like-material wording poorly, in our reading. DOB's permit page lists roofing in kind as exempt, while its Homeowner's Center lists roof replacement among projects it handles and says some nonstructural work needs permits. | DOB, in writing |
| TPO over built-up | A substitute on the guideline's table. | Historic Preservation Office |
| New coping on the parapet | Roofing and coping share one line on the Office of Planning's list of in-kind or compatible work. | Historic Preservation Office |
The edge
What does a new sheet have to do where the roof meets a parapet?
The guideline describes parapet caps, called copings, in stone, pre-cast concrete, metal or tile. A TPO sheet turns up that wall and ends under flashing and a cap, so a coping change can ride along with the roof question. Ask the written scope which pieces are replaced.
The guideline also says insulation rarely changes appearance but can make roof materials deteriorate if installed badly.
Colour is readable, the material is not
The model building code's single-ply table lists EPDM, TPO and PVC under separate ASTM standards (D4637, D6878 and D4434). The data sheet, or a core sample, tells you which sheet you own.
Reflectance
Does DC's own energy code put a reflectance number on a flat roof?
The 2017 DC Energy Conservation Code carries cool-roof text in two places. DOB's page says its copy omits later amendments and points to Title 12 DCMR for official wording.
Residential text (R402.6)
- Covers
- One- and two-family homes, townhouses, and apartment buildings of three stories or less.
- The number
- For slopes of 2 in 12 or less, 75 percent of the roof surface with a three-year-aged SRI of at least 64, or products meeting ENERGY STAR roof criteria.
- Exceptions
- Include green roofs.
Commercial text (5.5.3.1.1)
- Covers
- Roofs in Climate Zone 4, the zone the commercial provisions name.
- The number
- Aged solar reflectance 0.55 with aged emittance 0.75, or an initial SRI of 82 on roofs of 2 in 12 or less.
- Exceptions
- Ballasted, vegetated or mostly shaded roofs.
Whether a re-roof must meet either number is a separate question. The residential alteration clause lists the sections an alteration must meet and R402.6 is not among them, and the code treats roof repair and roof recovering separately from replacement. That is a reading of the text, so DOB's plan reviewer decides.
The Cool Roof Rating Council sets no definition of cool, and a listed product is not automatically cool under a code's. The membrane name gives no SRI value; the tested number does.
FAQ
TPO questions from DC flat-roof owners
Is going from black EPDM to white TPO a like-for-like swap in DC?
In kind means like material replicating the existing feature in appearance and texture, among other things. A new material family and colour fits that poorly, but DOB decides. Ask in writing before ordering.
Does TPO count as the rubber roof in the Office of Planning guideline?
The guideline calls a modern single sheet a rubber roof and lists single-ply (rubber) as a substitute for built-up. It does not name TPO, so ask the Historic Preservation Office how it reads a thermoplastic sheet.
Do I need a permit to replace a flat roof in DC?
DOB's own pages read differently: one lists roofing in kind as exempt outside historic districts, another lists roof replacement among Homeowner's Center projects. Ask DOB which applies.
Does the residential cool-roof text cover a rowhouse?
Its definition of a residential building includes townhouses and apartment buildings of three stories or less, for slopes of 2 in 12 or less. Whether a re-roof triggers it is for DOB.
What is SRI?
The DC Green Construction Code defines it as a value that typically runs from 0 for standard black to 100 for standard white.
Should the written scope name the membrane standard?
Yes. Colour does not identify the sheet, so the ASTM standard on the data sheet gives both offices something to compare.
Next
Where else can you read about DC flat roofs?
The Washington, DC roofing page covers the permit offices and review bodies, and the DC flat roof page sets TPO beside EPDM and PVC. Our flat roof guide explains how sheets are joined. Across the river the rules differ, in Arlington and Alexandria.
- DC Department of Buildings: Get a Permit
- DOB: Historic Property Special Permit
- DOB: Homeowner's Center
- DOB: DC Construction Codes
- 2017 DC Energy Conservation Code
- Office of Planning: Roofs on Historic Buildings
- Office of Planning: Work Qualifying for HPO Review
- DC building code section 105.2 (commercial reproduction of the code)
Talk through the next step
Talk through your roof with King's Roofing
Share the address, what you are seeing on the roof and the decision you need to make. We will tell you what to expect before anything is scheduled.
9220 Topaz St, Fairfax, VA 22031
Mon to Fri 7 AM to 8:30 PM, Sat 7 AM to 8 PM, closed Sunday