Metal roofing in Oakton, VA: what the code and the county permit pages name

The record at a glance

Four numbers frame the paperwork for a metal roof on a detached house in Oakton. Each comes from a county page or from the Virginia Residential Code text as displayed on UpCodes, a third-party site. The official code controls.

The Oakton place is part of Fairfax County, so the Oakton roofing guide covers the town-wide questions and this page stays with metal.

What the county pages say, and what they leave out

The same county page lists the 2021 Virginia Residential Code, and the state's own text calls the 2021 codes the "2021 edition of the USBC."

Metal panels and metal shingles are different sections of the code

The Residential Code does not treat panels and shingles as one product: chapter 9 gives metal roof panels section R905.10 and metal roof shingles section R905.4, and the two differ in what they require.

The class table for metal shingles lists classes A, D or F for ultimate design wind speeds up to 110, 116 and 129 mph, and F only from 142 mph. The county figure of 115 mph sits below the 116 row. That is arithmetic on two published tables, not a ruling on any product. A panel roof is not governed by that table, so ask your roofer what test or engineering basis supports the panel and attachment chosen.

For the profile families themselves, see our metal roofing guide, which carries the minimum slope numbers, and the materials overview.

Thickness: what the code table prints and what it leaves blank

Table R905.10.3(1) lists standards for metal roof coverings over structural decking. It prints a thickness for some metals and only a standard for others.

Aluminum

ASTM B209, 0.024 minimum thickness for roll-formed panels, 0.019 inch for press-formed shingles.

Zinc

0.027 inch minimum thickness, with an alloy specification in the table.

Copper

ASTM B370, 16 oz per square foot for metal-sheet systems, or 12 oz for high-yield copper and for preformed shingles.

Galvanized steel

ASTM A653, G90 zinc coated. No thickness is printed.

Steel

ASTM A924. No thickness is printed.

Stainless steel

ASTM A240, 300 series alloys. No thickness is printed.

Metal flashing

Corrosion resistant, not less than 0.019 inch, "No. 26 galvanized sheet," under R903.2.1.

A second table sets minimum corrosion resistance for coated steel: 55 percent aluminum-zinc alloy to ASTM A792 AZ 50, galvanized to ASTM A653 G-90, and prepainted steel to ASTM A755 over those coatings. The table prints no steel gauge, so a quote that says only "26 gauge" has not yet told you the standard or the coating. No neutral source opened for this page gives gauge classes for steel panels, so the page gives none. Metal-sheet systems that include supporting structural members are designed under the International Building Code instead.

Layers under the panel, from deck to flashing

1. Deck. The code allows panels on solid or spaced sheathing. The Metal Construction Association adds a limit for one family: architectural steep slope metal roofs "always require a solid substrate beneath them." Ask which family the quote prices.
2. Underlayment. The code sends panels to a table row that reads "Manufacturer's instructions" where wind design is not required and to ASTM D226 Type II or ASTM D4869 Type III or IV where it is. Ask for the product label.
3. Ice barrier. The county table answers yes to ice shield underlayment. The code list names shingles, shakes and roll roofing, and omits panels. The two do not contradict each other, and neither says how a panel roof is handled. Ask the county.
4. Panels and fasteners. Thickness and coating follow the table above. Fastener and clip choice follows the manufacturer's instructions under the attachment section.
5. Flashing. Flashing goes at wall and roof intersections, at every change in slope or direction and around roof openings, in metal at least 0.019 inch thick. A cricket or saddle goes on the ridge side of any chimney or penetration wider than 30 inches.

Over the old roof or down to the deck

Section R908.3 defines replacement as removal of existing coverings down to the deck. Section R908.3.1 lists exceptions that matter for metal:

• Complete and separate roofing systems "such as standing-seam metal roof systems," built to carry roof loads to the structure without relying on the old covering, need not have the old coverings removed.
• Metal panel, metal shingle and tile coverings may go over existing wood shake roofs where the concealed space is dealt with under R908.4.
• A new protective coating over an existing metal roof panel is allowed without tear-off.

What a written metal scope should name

Use this list against any written quote. It follows the sections above and does not assume your roof qualifies for anything.

• The panel family and the code section it falls under: panel (R905.10) or shingle (R905.4).
• The metal, its ASTM standard, and for steel the coating designation, not a gauge number alone.
• The deck type, and whether the family chosen needs a solid substrate.
• The underlayment product, its label, and which table row it answers.
• The ice shield plan, and the county answer behind it.
• Flashing metal and thickness at every wall, valley, chimney and penetration, and whether old flashings are replaced.
• The existing layers, and tear-off or recover with the section that allows it.
• Who asked Land Development Services about the permit, and what the answer was in writing.

Roofers of Arlington installs, repairs and replaces roofs, including flat and metal systems. Book a phone consultation to talk through an Oakton metal roof: your address, the house and what you can see from the ground. The services page lists the work, and the Oakton guide has the town-wide checks.