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TPO roofing in Silver Spring, MD: what the weather record and the insulation underneath mean for a membrane
A TPO sheet is only the top layer of a low-slope roof. Under it sit insulation boards, sometimes a cover board, and a deck, and Building Science Corporation says the sheet goes through thermal stress that has to reach the deck through those layers. This page counts the NOAA storm and winter rows around Silver Spring, reads Montgomery County's design sheet and the Maryland code text for thermoplastic roofs, and adds what two neutral building-science sources say about insulation, condensation and membrane movement.
- 51 NOAA rows carry the Takoma Park place label
- 30 psf ground snow load on the county design sheet
- Code section R905.13 covers thermoplastic single-ply
Insulation, cover board and the membrane
Building Science Corporation's Joseph Lstiburek wrote in 2012 that a roof membrane goes through thermal stress, and that the key is moving that stress to the deck. He says that when the stress is not transferred properly through insulation between sheet and deck, it concentrates at the roof edges and can suck in a parapet. His article describes a cover board as a hygric buffer that reduces membrane blistering and as the layer that carries membrane stress down to the deck. It also says the assembly needs an allowance for membrane movement at the perimeter. This is an expert's published view, not a code rule.
His 2009 article adds a cold-weather point: fluttering stresses a membrane and pumps airborne moisture from the interior into the roof assembly. He writes that this has typically been a cold climate phenomenon but the problems are migrating south as membranes become white rather than black, and that air barriers make fluttering go away.
The Building America Solution Center, run for the U.S. Department of Energy, publishes a guide for adding insulation over a flat roof. Read as a checklist of layers from the deck up, it says:
- Seal the deck with an air control layer, then add polyisocyanurate rigid foam over it.
- With several layers of board, offset the seams in two directions, lay a continuous sealant bead at the perimeter between layers and tape the seams.
- Add a cover board over the foam. The guide describes the cover board as typically fiberglass-faced gypsum board and says to ensure the cover board is compatible with the roof assembly.
- Install the cover board and the roofing membrane with flashing as the water control layer.
- Slope low-slope roofs to drains or scuppers at a minimum slope the guide gives as a quarter inch per foot.
Foil-faced polyisocyanurate
The guide says a protective cover board should go over it before the membrane.
Glass-fiber-faced polyisocyanurate
The guide says this board can be installed without a cover board.
"The amount of exterior (rigid) insulation needed to avoid condensation problems increases" in colder climate zones.
Building America Solution Center, flat-roof insulation guideThat guide covers a residential retrofit with cavity insulation under the deck, and its condensation tables are from the 2009 and 2012 residential code. They are not a design for any Silver Spring building. They do show why a re-roof that adds board thickness is also a moisture question, and why the question belongs in writing.
Counting the NOAA rows near Silver Spring
NOAA's Storm Events database lists each report under a place label chosen by the forecast office. No Montgomery County row uses "Silver Spring" as its label, so the count below uses the nearest label with rows, Takoma Park, and the county total for comparison. Files read cover January 2016 through June 2026.
| Event type | County rows | Takoma Park label |
|---|---|---|
| Thunderstorm Wind | 469 | 21 |
| Flood | 160 | 10 |
| Flash Flood | 136 | 16 |
| Hail | 55 | 4 |
| Lightning | 9 | 0 |
| Tornado | 7 | 0 |
Source: NOAA Storm Events details files, Montgomery County, Maryland, counted by this site on October 20, 2026. Winter events are filed by forecast zone and are counted separately below.
The four hail rows under the Takoma Park label are all from April 21, 2017, with stone sizes of 1.00, 1.25, 1.25 and 1.75 inches. The 70 in the wind field is an estimated gust, and NOAA records it for July 26, 2021, when the narrative says numerous trees and wires came down in and near Silver Spring and Takoma Park. For a low-slope membrane, hail and falling limbs are impact questions. That is a different issue from the insulation and movement questions the rest of this page covers, and none of the NOAA rows says what any roof was made of.
Winter rows. Winter events sit in the forecast zone named Central and Southeast Montgomery, which has 141 rows in these files. They include 48 Winter Weather, 9 Winter Storm, 2 Blizzard, 1 Ice Storm, 12 Frost/Freeze and 6 Cold/Wind Chill rows. For the January 2016 blizzard, NOAA's narrative says reports of 19 to 39 inches came from southeastern Montgomery County. The files contain no sentence about freeze and thaw cycling, so this page makes no claim about it.
County design sheet: snow, wind and frost
Montgomery County's Department of Permitting Services posts a sheet titled Climatic and Geographic Design Criteria. It is one line for the whole county, not a table by community, so it applies to Silver Spring only because Silver Spring is inside the county.
- Ground snow load
- 30 psf. A ground value is the starting point for a designer, who adjusts it for the roof. The sheet does not say what any given roof must carry.
- Wind speed
- 115 mph, with topographic effects marked No and no special wind region.
- Weathering
- Listed as Severe, alongside a frost line depth of 30 inches.
- Ice barrier underlayment
- Required: Yes. This is a steep-slope item and the sheet does not tie it to membranes.
- Air freezing index
- 300, as printed.
The sheet names no roofing material. It is written for residential construction, so for a commercial or multifamily low-slope roof ask the county which criteria its reviewer uses.
What the Maryland code copy says
The text read is the UpCodes copy of Chapter 9 of the Maryland residential code, 2021 edition. It is a third-party copy, so confirm the edition and any county amendments with the Department of Permitting Services.
- Thermoplastic coverings section R905.13 sets a design slope of at least 1/4 in 12, lists ASTM D4434, D6754 and D6878, and says to install per the chapter and the manufacturer. TPO is not named.
- Insulation section R906.1 says above-deck insulation must be covered with an approved roof covering and meet NFPA 276 or UL 1256. Table R906.2 lists polyisocyanurate to ASTM C1289 Type I or II among several board types.
- Loads section R905.1 says coverings resist the component and cladding loads in the code's wind tables, adjusted for height and exposure.
- Reroofing section R908.3 removes existing layers to the deck, while R908.3.1 allows a recover when the covering maker's approved instructions are followed. Section R908.3.1.1 bars a recover on a water-soaked or deteriorated roof, tile, or a roof with two or more applications. An exception waives the minimum slope for roofs with positive drainage.
The county's Home Improvements list puts "Roof (covering only)" among work that most likely will not need a permit, and says it excludes municipality and association rules. The code copy is silent on cover boards and on condensation checks, so those stay with the manufacturer and your engineer. The Silver Spring hub covers who decides in each building type, and the TPO roofing guide covers the membrane in general.
Questions to settle in the contract
Roofers of Arlington installs, repairs and replaces roofs, including flat systems. To talk through a Silver Spring TPO roof, book a phone consultation. On a call we would ask for the address, the building type, who owns the roof and what is visible. See also flat roofing, commercial roofing, roof replacement, materials and services.
- The insulation type, facer, thickness and number of layers, with seams offset.
- Whether a cover board is used, its type, and the written word of the membrane maker that the pairing is acceptable.
- How the membrane is attached and what allowance exists at parapets and edges.
- Who checked condensation for the assembly, and the result on paper.
- Slope to drains and whether any tapered board is added.
- Which load figures the designer used, since the county sheet is a starting point.
- Which offices were asked: county permitting, the Historic Preservation Office, Takoma Park, your association.
- Owner
- Household, council of unit owners or landlord signs the contract.
- Assembly
- Ask for the layers under the sheet in writing, not only the membrane.
- Office
- Ask the county, your association and your engineer. Nothing here is legal or engineering advice.
Documents opened for this page
All opened October 20, 2026.
- NOAA NCEI: Storm Events database bulk files
- Montgomery County DPS: Climatic and Geographic Design Criteria
- Montgomery County DPS: Home Improvements
- Building America Solution Center: Water-Managed Roof, Re-Roofing and Adding Insulation over Flat Roof
- Building Science Corporation: BSI-050, Parapets and BSI-019, Uplifting Moments
- UpCodes: Maryland Residential Code 2021, Chapter 9 (third-party copy)
Back to the Silver Spring roofing hub or all service areas.
Questions people ask
Is there a NOAA storm record labeled Silver Spring?
Not as a place label. In the Storm Events files for Montgomery County from January 2016 through June 2026, no row begins at "Silver Spring". The nearest label with rows is Takoma Park, with 51, and 18 county rows have an event or episode narrative that mentions Silver Spring by name. Treat the county rows as the record for the area.
What does the county design sheet say about snow for a Silver Spring roof?
Montgomery County's Climatic and Geographic Design Criteria sheet lists a ground snow load of 30 psf. It is a county-wide sheet with no separate Silver Spring line, and ground snow load is not the same as the design load on a given roof. Ask the county or your engineer how it applies to your building.
Why does insulation matter to a TPO roof?
The membrane is fastened or adhered to whatever is under it. The Building America Solution Center describes the layers of a low-slope roof as insulation board, cover board and membrane, and Building Science Corporation says membrane stress has to reach the deck through the insulation. The layers under the sheet are part of the decision.
Does a TPO membrane need a cover board?
The Building America Solution Center says foil-faced polyisocyanurate needs a protective cover board under the membrane, while glass-fiber-faced board can go without one. That is one guide's statement about one assembly. The membrane maker's instructions and your engineer settle your roof.
Does colder weather raise the condensation risk in a flat roof?
The Building America Solution Center says that in colder climate zones the amount of exterior rigid insulation needed to avoid condensation problems increases. The page it comes from is about a residential flat roof retrofit. For your building, ask whoever designs the assembly to show the condensation check in writing.
What does the Maryland code copy say about thermoplastic roofing?
In the UpCodes copy of the Maryland 2021 residential code, section R905.13 sets a design slope of at least 1/4 in 12 and lists ASTM D4434, D6754 and D6878 for thermoplastic coverings. It says installation follows the manufacturer's instructions. It does not name TPO. Confirm the edition in force with the county.
Can a second roof be laid over an existing low-slope roof in Maryland?
The code copy permits a recover under conditions, including following the covering maker's approved instructions, and bars it where the existing roof is water soaked, has deteriorated, or has two or more applications. Whether your roof qualifies is a question for the county and an engineer.
Who approves a membrane replacement on a Silver Spring condominium?
Maryland law gives the council of unit owners power to regulate repair and replacement of common elements, and the declaration decides what counts as one. The county permit list says nothing about association rules, so ask your association for its process before asking any roofer for a scope.
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.