TPO Roofing in Rockville, MD: One Local Rule Decides More Than the Membrane Name
When Rockville adopted the 2021 building code it added a section of its own: a cool-roof test for low-slope roofs, stated as a minimum initial SRI of 78 on at least 75 percent of the roof. It sits in the commercial building code, so it reaches apartment and office roofs, not the house next door.
Reach of the rule
Four assumptions about Rockville flat roofs, set against the ordinance
Each answer below is taken from City of Rockville documents opened on 11 October 2026. The main text is Ordinance 06-24, page 15.
Cool-roof rules belong to hot states. In this part of Maryland nobody asks about roof reflectance.
The model energy code's reflectance table covers Climate Zones 0 through 3, and Montgomery County sits in 4A. The county's own energy-code amendments (Executive Regulation 13-24, in force since December 2024) rewrite the commercial roof-reflectance clause to read Zones 0 through 4, so the county's version does reach zone 4, and whether the City applies that amendment as well as its own section is a question for the Inspection Services Division. The City also wrote its own: Ordinance 06-24 adds section 1507.1.3, headed "Cool roof requirements", to the International Building Code as Rockville adopted it.
It applies to every flat roof in the city, a house addition included.
The section covers roof slopes "less than two units vertical in 12 units horizontal (less than 17-percent slope) for buildings and covered parking". It was added to the building code. Houses and townhouses sit in a separate article, the one- and two-family dwelling code, which follows on the same page of the ordinance. A flat porch top on a house is a question for the Inspection Services Division, not a given.
The whole roof has to be reflective.
The ordinance asks for "a minimum of 75%" of the roof surface, and it leaves out the area "used for roof penetrations, onsite renewable energy systems, or vegetated roofing systems". Rooftop units, vents, a solar array and a green roof area are not counted against you.
A white membrane passes, and a gray one does not.
The printed test is a number, "a minimum initial solar reflective index (SRI) of 78". Sheet membranes are made in black, white and a range of colours, so a colour word is not a rating. The Cool Roof Rating Council says it does not define "cool" and leaves that to the code bodies, and that a listing on its directory does not by itself make a product cool under a given code.
What does the ordinance mean by an "initial" rating?
The section says "initial" and leaves the term to the reviewer. A product's rating as new and its rating after weathering can differ, so ask the Inspection Services Division which value it wants on the submittal and where it wants to see it listed.
Does a rooftop unit or solar array count against the 75 percent?
By the wording, the area used for roof penetrations, on-site renewable energy systems and vegetated roofing is set aside before the 75 percent is measured. Show where those areas are on the roof plan so the reviewer can see the split.
Three facts settle whether the section is in play
The building's use (an apartment or commercial building, or a house), the roof slope against that 2:12 line, and the product's initial SRI as published by its rating listing. A quote that says only "TPO" gives you none of the three.
Reading it for a membrane job
Three more assumptions that show up when a TPO quote arrives
TPO is a cool roof by definition, so the section is automatically met.
The EPA describes a cool roof by its behaviour: it "absorbs and transfers less heat", and high solar reflectance is "the most important characteristic". The part of Rockville's section printed in the ordinance names no membrane at all. It tests the product in front of you.
A re-roof is exempt, because the City exempts re-roofing from permits.
The permit exemption names "group R-3 one- and two-family dwellings and townhouses" and an in-kind covering with the deck untouched. Administrative Bulletin 2024-01, effective 29 May 2024, calls the apartment-side version "limited cases for group R-3 structures". The cool-roof text carries no re-roof sentence of its own, so how the Division applies it to a replacement is a question for the Division. Our Rockville page holds the permit table.
Historic review is about shingles on old houses, not membranes on flat roofs.
The same section states that replacement of a roof in a Historic District Zone, "including any change to design or materials", must be approved by the Historic District Commission. The City lists roofing among the exterior alterations it reviews in a district, so check the address with the Historic Preservation Division.
Does a cool roof cost heat in winter?
The EPA says a cool roof may raise winter heating use in cold climates, calls this a "heating penalty", says it is typically offset by summer cooling savings, and notes that good insulation can reduce it. It writes about the effect in general, not about a Rockville building.
Does the City ask for SRI on house roofs too?
Its residential permit submittal list asks for roofing system details including solar reflectance (SRI), alongside material, slope and ice barrier. That is a checklist line for a submittal. It is not the 75 percent test, which lives in the building code section above.
Who answers the question at the City?
The Inspection Services Division reaches people at 240-314-8240 or permits@rockvillemd.gov, Monday to Friday, 8:30 a.m. to 5 p.m. The Historic Preservation Division, at 240-314-8236, answers district questions.
Which roofs on the Montgomery County side of the line follow this rule?
The section is part of Rockville's own code, so it follows the City's boundary. For a Bethesda or Silver Spring address, start with the county and see Bethesda or Silver Spring.
Where to read more
Official pages checked on 11 October 2026
- Ordinance 06-24, amending Chapter 5 of the Rockville City Code (section 1507.1.3 is on page 15)
- Administrative Bulletin 2024-01, local amendments to the 2021 I-Codes
- Residential building permit submittal requirements
- Apply for a building or trade permit
- Make alterations to a historic property
- EPA: using cool roofs to reduce heat islands
- Cool Roof Rating Council FAQs
For how a membrane roof is built and judged on any building, read our flat roof guide. For the rest of the City's rules, return to Rockville.
Talk through the next step
Bring the roof slope and the product sheet
Tell us the building type, the slope and what the membrane data sheet lists. We will help you work out what to ask the City before anything is ordered.
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