TPO vs EPDM roofing: what neutral documents say about each, side by side
Short answer: no document opened for this guide ranks one membrane above the other. They differ in polymer class, in how the seams are made, in what the sheet standard says about reinforcement, and in the colors the sources name. Both depend on the layers under the sheet, the edges and the installer. The table below puts the differences in one place and names where each line comes from. To talk through your own roof, book a phone consultation.
- Two sheet standards: ASTM D6878 for TPO, ASTM D4637 for EPDM
- Seams: hot-air welded for TPO, tape first for EPDM in the federal specs
- Neither sheet standard covers fire, field seams or wind uplift
TPO and EPDM side by side
Every cell names its source. The "federal guide specifications" are two government sections, one for TPO roofing and one for EPDM roofing, written for federal projects. They are models for a scope, not rules for a private building. Where a source says nothing, the cell says so.
| Topic | TPO | EPDM |
|---|---|---|
| Polymer class | Thermoplastic (federal laboratory guide). | Thermoset (same guide). |
| Sheet standard in Virginia's code table | ASTM D6878. | ASTM D4637. |
| Reinforcement named in the standard | The sheet "shall contain reinforcing fabrics or scrims." | The sheet may be non-reinforced, fabric or scrim reinforced, or fabric-backed. |
| Seams in the federal specification | Field laps are hot-air welded to the weld width the manufacturer requires; every seam and the continuous weld are checked. | Seam tape is the primary method; adhesive seaming in the field of the roof needs government approval; tape is at least 3 inches wide. |
| Sheet thickness in the federal specification | 80 mil nominal for fully adhered work, with a top ply of at least 0.030 inch over the scrim. | 80 mil fleece-backed, or 90 mil on projects in hail-prone areas; 60 mil non-reinforced is the guide's stated option for adhered or ballasted work. |
| Colors named | The specification's reflectance index of 94 is listed for white only. | The manufacturers' trade body names black, gray and white. |
| Attachment in the federal specification | Fully adhered; fasteners only at perimeters and penetrations. | Fully adhered, ballasted, or adhered plus fastened; the text cites a rule against fastening in the field of the roof. |
| Walking surface | Textured TPO pads, at least 0.150 inch thick. | Rubber walkboards or precast concrete pavers. |
| Service life and price | Not set by the standard or either specification. | Not set by the standard or either specification. |
Sources: PNNL Building America Solution Center; ASTM D6878 and D4637 public scope pages; Virginia Construction Code 2021 Table 1507.12.2 (UpCodes copy); UFGS 07 54 23 and 07 53 23; EPDM Roofing Association, a manufacturers' body. All opened October 26, 2026.
Both federal texts require the whole roof covering assembly to be Class A under a named fire test and listed with its deck, both require wind uplift to be validated by testing, and both bar installation below 40 degrees Fahrenheit or within 5 degrees of the dew point unless the manufacturer says otherwise. The sheet is not what separates those requirements.
Color, reflectance and the heat question
The Cool Roof Rating Council describes "coolness" with two properties, solar reflectance and thermal emittance, each on a scale from 0 to 1, and combines them into a solar reflectance index calculated under ASTM E1980. The federal texts define the index with two anchors.
Both materials appear in white in the sources, so color is a choice within a material as much as between them. A Lawrence Berkeley National Laboratory page puts a clean white roof reflecting 80 percent of sunlight at about 55 degrees Fahrenheit cooler than a gray roof reflecting 20 percent, on the standard summer afternoon in ASTM E1980. Both that page and the rating council say the winter heating penalty is small beside the summer saving.
The guide specifications note that where insulation exceeds R-24 the reflective surface has little if any influence on a building's energy performance, and that poor cool-roof design in colder climate zones has produced condensation under the membrane and, in some cases, replacement. They also warn that reflected light can overheat masonry walls, rooftop piping and equipment. Ask whoever designs the assembly whether color and insulation were chosen together.
For the wider energy picture see our energy-efficient roofing guide.
What the sheet standards cover and leave out
A quote that cites a standard is naming a sheet. Here is what the standards themselves say about their reach, and who writes the other documents a roof depends on.
ASTM D6878, the TPO line
Covers flexible sheet made from thermoplastic polyolefin as the principal polymer, for single-ply membranes exposed to the weather. It requires reinforcing fabrics or scrims.
ASTM D4637, the EPDM line
Covers flexible EPDM sheet for the same use. It allows non-reinforced, reinforced and fabric-backed sheet, so the standard alone does not say which one a roof has.
What both exclude
Each scope calls minimum quality its purpose and puts fire resistance, field seaming strength, material compatibility and uplift resistance beyond its limits. Those must come from the assembly and its listings.
Three kinds of standard
The National Roofing Contractors Association separates testing standards, rating standards and design standards. A sheet standard is a testing standard; it is not a design for your roof.
Standards for the edges
The Virginia code sends metal edge systems on low-slope single-ply roofs to ANSI/SPRI ES-1 test methods, and NRCA describes ES-1 and GT-1 as wind-resistance tests for edge metal. The SPRI page lists the other ANSI/SPRI documents by name.
Seams, foot traffic and edges
The federal texts spend much of their length on joins and edges. Neither sheet standard covers field seaming strength, so the scope should say who checks the seams and how.
TPO seams
The installer hot-air welds each lap to the width the manufacturer requires, checks all seams and the continuous weld, and seals cut edges.
EPDM seams
The sheet relaxes at least 30 minutes, laps at least 3 inches, is primed and taped, then checked for a full lap seal. Tape is 6 inches wide along lines of mechanical attachment.
Foot traffic
Both texts treat monthly foot traffic as a design condition: textured TPO pads at least 0.150 inch thick on one side, rubber walkboards or concrete pavers on the other. The EPDM text also bars walking or wheeling directly on applied sheet.
Edges and flashing
The code requires metal edge systems on low-slope single-ply roofs, other than gutters and counterflashing, to be tested to ANSI/SPRI ES-1, and puts flashing at walls, gutters, slope changes and openings. Both federal texts require temporary protection against moisture while permanent flashing is installed as the work progresses.
Facts that decide it for one building
Gather these answers before choosing between the two.
- Wind rating of the whole assembly
- The federal texts require uplift validated by testing, and the federal laboratory guide recommends fully adhered membranes in high-wind zones with an air control layer below.
- Fire listing
- The assembly, deck included, carries the Class A classification, not the sheet alone.
- Insulation and condensation
- The EPDM text warns that condensation under mechanically fastened systems can cause ice build-up, mold on the facers and early replacement, and both texts say insulation level changes what a reflective surface can do.
- Hail exposure
- The EPDM text raises sheet thickness for hail-prone projects; ask the designer what exposure was assumed for your site.
- Who walks on it
- A monthly service visit to rooftop equipment calls for a walking surface in both texts.
- Weather window
- Work stops below 40 degrees Fahrenheit or near the dew point unless the manufacturer says otherwise, so the schedule matters.
- Neighbors
- The laboratory page says glare from a bright low-rise roof may disturb occupants of taller buildings next door, a stated reason to consider a non-white sheet.
Questions to put in the written scope
These questions work for TPO, EPDM or any other low-slope covering. Ask for the answers in the written scope.
- Which sheet standard, which thickness, and is the sheet reinforced, backed or neither?
- How are the seams made, who checks them, and what is recorded?
- How is the sheet attached, and which wind listing does the quote rely on?
- What lies below: deck, air control layer, insulation layers, cover board, and why those?
- Which edge metal, and was it tested to ANSI/SPRI ES-1?
- How are walls, curbs, drains and pipes flashed, and what protects the roof during work?
- Where will people walk, and what walking surface is included?
- Which manufacturer's instructions apply, supplied in writing, and what record of completion will you receive?
Roofers of Arlington installs, repairs and replaces roofs, flat and metal systems included, in Arlington and nearby. To check answers against a real building, book a phone consultation.
How Arlington paperwork meets the choice
The Arlington hub guide holds the permit table and the building-type test, so this section only sketches where a membrane choice meets them. The county says apartment buildings of three or more dwelling units are commercial under the Building Code, and the county's commercial permit pages print no re-roofing row. A Certificate of Appropriateness in a local historic district excepts routine repairs and replacements using the same materials; whether a new sheet counts is a question for the county. The county pages and the 31 nomination texts searched on this site contain no hits for EPDM, single-ply or membrane, which is silence, not approval. Ask the Permit Arlington Center at 703-228-3800 about your address.
- Flat-roof apartments in Clarendon and Lyon Park: the building type where this choice arises.
- Condo and co-op roof replacement: the association documents that decide.
- TPO overview and EPDM overview: the layers under each sheet and the code lines.
- Flat roofs, commercial roofing and materials: the wider service pages.
- Roof lifespan and roof inspection: what ages a roof and what to note.
How the record was checked
All opened October 26, 2026, except the Arlington County pages, which were read as archived copies in the hub research.
- ASTM D6878/D6878M-21, TPO sheet, public scope page, ASTM International.
- ASTM D4637/D4637M-15, EPDM sheet, public scope page, ASTM International.
- NRCA Codes and Standards and Roofing Guidelines, National Roofing Contractors Association.
- Cool Roof and Wall FAQs, Cool Roof Rating Council.
- Cool Roofs, Lawrence Berkeley National Laboratory Heat Island Group.
- Low-Slope Roofs, Building America Solution Center, Pacific Northwest National Laboratory.
- UFGS 07 54 23, TPO roofing and UFGS 07 53 23, EPDM roofing, Whole Building Design Guide.
- Virginia Construction Code 2021, Chapter 15, UpCodes copy.
- What is EPDM, EPDM Roofing Association, a manufacturers' body.
- ANSI/SPRI standards, SPRI.
Questions people ask
Is TPO or EPDM better for a flat roof?
None of the neutral documents opened for this guide ranks one above the other. The sheet standards set minimum sheet quality only, and the federal specifications describe both as acceptable roofing. What separates a good result from a poor one in those documents is the assembly, the seams, the edges and the instructions followed, so compare written scopes rather than sheet names.
What is the difference between a thermoplastic and a thermoset membrane?
A federal laboratory guide groups TPO, PVC and KEE as thermoplastic membranes and EPDM as a thermoset membrane. The practical consequence shown in the federal specifications is in the seams: the TPO text calls for hot-air welded laps, while the EPDM text makes seam tape the primary method.
Do the ASTM standards say how long a sheet lasts?
No. The public scope of ASTM D6878 and of ASTM D4637 each say the property limits are meant to ensure minimum quality for the intended use, and each lists fire resistance, field seaming strength, material compatibility and uplift resistance as outside the standard. Neither scope gives a service life.
Can both TPO and EPDM be white?
Yes, according to the sources read. The trade body for EPDM manufacturers names black, gray and white sheets, and the federal TPO text lists a white-sheet reflectance index. A white sheet in either material does not by itself decide how much a building saves, because insulation and climate matter too.
Does Virginia require one membrane over the other?
The 2021 Virginia Construction Code, in a third-party copy, lists single-ply sheets in one table, pairing EPDM with ASTM D4637 and TPO with ASTM D6878, and says nothing in that table to prefer one. Chapter 15 requires coverings to be installed to the manufacturer's approved instructions. Ask your building official about your address.
Does a cool roof always cut energy use?
Not by itself. The federal guide specifications carry a designer note that where insulation exceeds R-24 the reflective surface has little if any influence on a building's energy performance, and that poor cool-roof design in colder climate zones has led to condensation under the membrane. The laboratory and rating-body pages describe savings as depending on several factors.
How do I read a quote that says "meets ASTM"?
As a statement about the sheet only. The standards exclude fire, field seams, compatibility with other materials and wind uplift, so a scope still needs the assembly, the attachment, the edge metal and the listings written out. The questions list in this guide is meant to be handed to any roofer.
Which membrane should a condo or co-op board look at?
The documents opened here do not choose for a board. In Virginia law the roof of a condominium is a common element unless the instruments say otherwise, so the board and the association documents decide who approves and who pays. The Arlington condo and co-op guide on this site walks through those documents.
Talk through your roof with Roofers of Arlington
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.