PVC roofing in Fairfax, VA: when the storms arrive and how the sheet is held down

The storm clock: Fairfax County by hour

NOAA logs every Storm Events report with a start time. The county rows, filed under the label FAIRFAX, total 792 for 2016 through 2026: 396 thunderstorm wind, 40 hail and the rest flood, tornado and funnel entries. The Fairfax hub page counts them by month. This page counts them by hour, a cut that bears on how a roof is staged and left at the end of a work day.

NOAA Storm Events yearly detail files, 2016 through the September 2026 release, county label FAIRFAX, counted by script on October 24, 2026. Reports, not inspections or claims. Every row carries the time zone label EST-5, and the NOAA format sheet says its 24-hour times are usually local standard time, so a summer reading can sit an hour off the wall clock.

The strong end follows the same pattern. 383 wind rows are at 50 knots or more, about 58 mph. 45 are at 60 knots or more, about 69 mph, and 39 of those 45 begin between noon and 6 p.m. The highest value is 78 knots, about 90 mph, logged in three rows. Only 16 of the 396 carry a measured gust; the other 380 are estimated gusts, a split the NOAA format sheet defines.

The county also prints design numbers: an ultimate wind speed of 115 mph for Risk Category II and residential work and a ground snow load of 25 psf. Those are inputs to a calculation, so this page does not set them against the gust reports above. The county adds that 25 psf holds only if the design team uses the 2021 code snow figures with ASCE 7-16, and it says the state is correcting that code. Ask the plans reviewer which figures govern your parcel.

Hail by month and stone size

Hail rows are fewer and tied to the warm season. April has 4, May 19, June 10, July 2 and August 5. None of the 40 begins from September through March in these files. The rows fall on 22 distinct dates, and 11 of them are from one afternoon, May 2, 2016.

The 11 rows at 1.50 inches or more all begin between 2:15 p.m. and 5:35 p.m. Wind rows add a second fact. In 379 of the 396 narratives the text mentions a tree, branch or limb. The narratives say what fell or moved, not what any roof was made of.

That is the sheet standard for PVC. Hail and wind are questions about the whole assembly: the same scope lists wind uplift resistance among factors beyond the standard.

The ASTM page read is an archived copy of the 2021 edition, so confirm the current edition at ASTM before relying on any clause.

Three ways a PVC sheet is held down

Unified Facilities Guide Specification 07 54 19, PVC Roofing, is a federal document. It is not a Fairfax rule, but it spells out each attachment method in public text.

Two more points from the same text. It says adhered and fastened PVC systems must use reinforced membrane, always, outside prefabricated detail flashings. For regular extreme wind with airborne debris it names a 0.096 inch sheet instead of the 0.08 inch minimum. The Fairfax rows do not say how often debris strikes a roof, so that note is a question to put to the designer, not a finding.

What the Virginia code asks for wind

These clauses come from the 2021 Virginia Construction Code and Residential Code, read in third-party UpCodes copies because the code publisher blocks scripts. Check the official text before relying on a clause.

Section 1504.1

Roof decks and coverings are designed for wind loads under Chapter 16 and the rest of Section 1504.

Section 1504.4

A covering that is mechanically attached or adhered to the deck must resist the component and cladding wind pressures. Allowable stress design is permitted for the covering.

Section 1504.4.1

Fully adhered or mechanically attached single-ply systems are tested to FM 4474, UL 580 or UL 1897. The text lists three methods and does not choose among them, and it treats adhered and attached the same.

Table 1507.12.2

PVC, or a PVC and KEE blend, is paired with ASTM D4434. KEE alone is paired with D6754. The residential code lists D4434, D6754 or D6878 for thermoplastic coverings.

Sections 1504.5 and 1507.12.3

Ballasted low-slope single-ply roofs follow ANSI/SPRI RP-4 and stone ballast follows ASTM D448 or D7655. The federal PVC text says no stone or gravel on any PVC roof, so the two sources differ and a quote that includes ballast should say which governs.

Section 1504.7

Low-slope coverings that flex in wind must not lose significant breaking strength, for reinforced membranes, after 2,000 hours of accelerated weathering tests.

Residential R905.1 and R905.13.3

Coverings go on per the manufacturer instructions and resist the component and cladding loads of the residential tables.

A roof day set against the afternoon window

The federal specification also orders the work of a day, and its steps can be laid against the hours in the table above. It governs federal work, so a private job follows its own contract and the manufacturer instructions. Ask to see them.

• Laps and seamsOverlaps run at least 3 inches at sides for adhered sheets, 5.5 to 7 inches for fastened sheets and 4 inches at ends. Laps lie so water flows over them, not against them.
• On the day of the weldThe entire length of every hot-air-welded seam is probed on the day of installation. Defects are rewelded, fishmouths are cut out and covered with membrane welded on all sides, and the repairs are probe tested.
• Before the afternoon rows beginIf work stops before the whole roof is weatherproof, the membrane is sealed to the deck at the cutoff. Asphalt and coal-tar products are not used for that seal.
• At the edgesFlashing seams are sealed 3 inches beyond the fasteners that hold the sheet to the nailers, and the top of the flashing is fastened at no more than 12 inches on centers.
• Next morningThe cutoff is opened by pulling the membrane free or cutting it to expose the insulation, and the fill-in insulation sheets are removed.

Checks before a PVC order is signed

• Does the quote name the attachment method, adhered, plated or a combination, with the perimeter and corner pattern stated apart from the field?
• Does the scope name the wind test, FM 4474, UL 580 or UL 1897, for the assembly, and say who supplies the pressure calculation?
• Does the product data sheet cite ASTM D4434, or D6754 for a KEE sheet, and say the sheet is reinforced?
• If ballast is proposed, which source governs, given that the federal PVC text bars stone?
• What is the written cutoff plan if a storm builds at 3 p.m. on a day when the roof is open?
• Which office reviews the permit for the parcel, the City of Fairfax or Fairfax County, as the Fairfax hub page compares?

PVC is one of several low-slope membranes, and the general PVC page and the materials overview compare it with the others. Roofers of Arlington installs, repairs and replaces roofs, including flat roof systems. See also commercial roofing, roof replacement and services. To talk through a Fairfax PVC roof, book a phone consultation.