TPO roofs in Herndon, VA: what does the federal storm log list for the town?
Hail reports make Herndon owners wonder whether a flat membrane holds up. The National Weather Service's storm log has dates, sizes and wind speeds for the town, and one blank where roofs should be: seventy-two entries name Herndon, and not one mentions a flat or membrane roof.
Seventy-two entries, four hazards
The detail files of NOAA's Storm Events Database, 1995 through September 2026, were filtered to Fairfax County entries that carry a Herndon label or name Herndon in their text. The log is built from reports by spotters, officials and the public, so it lists what was reported, not everything that happened.
| Hazard | Entries labelled Herndon | Span | What the text describes |
|---|---|---|---|
| Hail | 11 on 10 dates | 1995 to 2024 | Sizes only, 0.75 to 1.50 inches; no damage figure |
| Thunderstorm wind | 26 on 20 dates | 1997 to 2023 | Trees and limbs; 23 give a speed of 50 to 61 knots |
| Tornado | 1 | 6 April 2017 | EF0, 1.91 miles long, 25 yards wide, trees and fences |
| Flood and flash flood | 11 | 2005 to 2023 | Roads, cars, a footbridge, Sugarland Run near apartments |
When did reporters put hail in Herndon, and how big was it?
The largest is 14 July 2023: "Up to ping pong ball size hail was reported in Herndon," logged by a weather service employee at 1.50 inches. The latest is 29 August 2024, quarter size, reported by broadcast media.
Read the other three hazards for what they say about roofs
What the entries do say
- 14 July 2023
- A wind entry adds that a large garbage dumpster was displaced.
- 8 April 2020
- "some shingles off of several houses," the only roof covering named in all seventy-two.
- 6 April 2017
- A tornado path began between two apartment complexes, and a tree landed against one apartment window.
What they never say
- Flat roofs
- No entry names a flat roof, a membrane or a roof leak.
- Floods
- The water was stream and street water, not water reaching a roof.
- What follows
- Wind prompts a look at edge metal, where wind gets under a sheet. Trees and floods are not membrane questions.
The log cannot tell you what TPO survives
No neutral document in our file ties a hail diameter to a TPO sheet, so none is printed here. Section 1504.8 of the 2021 model building code, as we read it, wants low-slope roof coverings to show impact resistance through ASTM D3746, ASTM D4272 or the FM 4470 foot-traffic test. The section never says hail. Our reading: any diameter quoted on a product sheet raises the question of which test it came from.
What should a Herndon owner ask for when a storm has passed?
SPRI, the single-ply membrane trade group, tells owners to inspect low-slope roofs twice a year and after any major storm. Here is what we would write into a scope.
- The storm date and the part of the building you saw it from, so any condition has an event attached.
- Photos of edge metal, flashings at vents and equipment, and each drain, shot before anyone cleans or repairs.
- The sheet identified by standard (TPO is ASTM D6878) rather than by a product name.
- The uplift test listing for the whole assembly (FM 4474, UL 580 or UL 1897) and the edge metal's ES-1 test.
- Whether the job is patching, coating, covering over, or stripping to the deck.
We quote no lifespan for TPO, and SPRI declines to give one for any sheet membrane. TPO is a thermoplastic with hot-air welded seams; the regional TPO guide covers the sheet itself.
Herndon storm log questions, answered from the file
Which Herndon hail entry is the largest?
14 July 2023, at 1.50 inches, described as up to ping pong ball size. The next largest is 1.25 inches on 18 June 2015.
Does the log say a Herndon roof was damaged?
No entry uses the word roof. One, from 8 April 2020, says some shingles came off several houses. None names a flat roof or a membrane.
Does eleven hail entries mean hail falls on Herndon eleven times in thirty years?
No. It means eleven entries were reported and logged. Hail that nobody reported is not in the file, and several entries sit on the same afternoon as others.
Does the log separate the Town of Herndon from Herndon addresses in Fairfax County?
It does not. Every entry sits under Fairfax County, so the file cannot answer which office handles your parcel. Our Herndon page explains that test.
Do the flood entries mean roofs leaked?
No. They describe closed roads, flooded cars and a stream spilling around apartment communities. Nothing in them involves water reaching or passing through a roof.
Why do the wind speeds in the log read as knots?
NOAA's file format sheet says wind speeds are in knots and hail sizes in inches, and that damage amounts are estimates. A reading of 56 knots is a little over 64 miles an hour.
Should I have someone look at a flat roof after a storm with no leak?
SPRI's own maintenance answer includes a check after any major storm: loose metal at the edges, flashings around penetrations and open drains. We would start by asking what you saw.
Talk through the next step
Name the building and the day of the storm
Send the address, the storm date you have in mind and anything you noticed from the ground. One short call sorts out what deserves a closer look.
9220 Topaz St, Fairfax, VA 22031
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