Learning Center · Roofing
The Building Code for Roofs in Texas: What the IRC Requires, and What We Install
Texas cities build to the International Residential Code, and Chapter 9 of that code sets the minimum for a shingle roof. This guide starts with what we install on every roof, next to that minimum, then walks through the code itself, topic by topic, with the section numbers so you can read it yourself.
Updated October 19, 2026
Read This First
The short version
- Inside city limits, Texas law makes the International Residential Code the home building code. Each city picks its edition by ordinance.
- Around Round Rock, cities use the 2018, 2021 or 2024 edition, and the roof rules that matter most read the same in all three.
- The code is a minimum: at least 4 nails per shingle, drip edge at every eave and rake, a cricket behind any chimney wider than 30 inches.
- Our install standard goes past it on purpose: 6 nails per shingle, a full tear-off on every roof, and a cricket from 24 inches.
- The shingle maker’s installation instructions are part of the code, so a roof that ignores them does not meet code either.
To have your roof checked against the code and the shingle maker’s instructions, use Get Help or call or text 512-575-5052.
Short version: 3 min. Full page: 12 min. Want the detail? Each section below opens with a tap, or switch to Full at the top to open them all.
Our Standard
What we install on every roof, next to the code minimum
Our install standard sets most parts of the roof at the strictest line we found, and none below the code.
One standard for every roof
Our install standard sets most parts of the roof at the strictest line we found across the shingle makers, the 2021 and 2024 code and the industry bodies, and where David has ruled stricter, his ruling. Where a line is not the strictest, it still meets the code; the full list is our installation standard. The installed product’s own instructions still apply in full, and where they are stricter than our line, they win on that job.
Tear-off and the deck
Every roof replacement we do is a full tear-off to the deck, with no layover. The code allows a new roof over one existing layer in some cases; we do not use that allowance. Each extra old layer is photographed before it comes off, and a bonded membrane that cannot come off without ruining the deck is shown to you and handled as the code allows.
Nails: 6, not 4
The code minimum is 4 nails per strip shingle, 12 gauge with a 3/8 inch head, driven at least 3/4 inch into the deck or through it. We set 6 nails per shingle, at least 1-1/4 inch long, no staples. At completion no nail head is visible or raised, except the few the maker requires, such as the last ridge cap, which are covered with roofing cement.
Drip edge and underlayment
Drip edge goes on every eave and every rake, as the code requires, with every joint lapped at least 2 inches and the higher piece over the lower one, nailed every 8 to 10 inches where the code allows 12. Underlayment end laps are 6 inches, where the code asks 4 (see deck and underlayment). Any face from 2:12 to under 4:12 gets two layers or a self-adhered membrane, and no face under 2:12 ever gets shingles.
Above the Minimum
Where our standard goes past the code
Valleys, chimneys, walls and vents are where our standard is most above the code.
Valleys
The code allows open metal valleys of 26 gauge galvanized steel, 24 inches wide. We lay self-adhered leak barrier in every valley first, and where the valley is open metal, the metal is 24 gauge and at least 24 inches wide. Flashing and penetrations explains why valleys leak.
Chimneys and crickets
The code requires a cricket, a small peaked diverter, on the uphill side of a chimney or penetration more than 30 inches wide. We put one behind any chimney 24 inches wide or wider, and it is priced on your estimate before the contract.
Walls and pipes
Self-adhered leak barrier goes under every wall and step flashing, 5 inches up the wall. Kick-out flashing goes wherever an eave meets a sidewall, which the code requires, and a missing one gets installed. Every vent, cap and pipe flashing in our scope is metal, with no plastic left exposed.
Attic ventilation
The code sets how much vent opening an attic needs, and our vent plan meets the code that applies to your house; it is shown on your estimate, and our attic ventilation guide explains the balance. Shingle makers and industry bulletins also warn against mixing two kinds of exhaust over one attic, such as a ridge vent with box vents.
Texas Law
How the building code becomes law in Texas
State law adopts the IRC for homes inside city limits, and each city moves to a newer edition by ordinance.
The state sets the floor
Texas Local Government Code Section 214.212 adopts the International Residential Code as the residential building code for cities, as it stood on May 1, 2012. It applies to the construction, alteration, remodeling, enlargement and repair of homes in a city, which includes a roof.
Each city picks its edition
A city may adopt a newer edition and its own amendments, which can add, change or remove requirements. A local amendment needs a public hearing first and must be adopted by ordinance. That is why two cities a few miles apart can be on different editions.
Outside city limits
A county applies these standards only if it opts in, and then only to new homes and large additions (Sections 233.151 to 233.153). In a city’s extraterritorial jurisdiction, a city code adopted for it controls. On our reading, a reroof outside city limits generally is not covered by a residential building code, though other county rules may still apply. We install to the same standard there anyway.
Editions
Which edition your city uses
Round Rock, Austin and Hutto are on the 2024 edition; Georgetown, Pflugerville, Cedar Park and Leander on 2021.
2024 edition
Round Rock, Austin and Hutto list the 2024 International Residential Code as adopted. Austin’s local amendments took effect July 10, 2025, and include a wildfire code and a fire-retardant rule for wood shingles and shakes; see the Austin wildfire code.
2021 edition
Georgetown (effective November 1, 2023), Pflugerville (Ordinance 1544-22-03-22, March 22, 2022), Cedar Park (effective June 1, 2022) and Leander list the 2021 edition. We read Georgetown’s page through a summary only, so confirm it with the city.
Taylor
Taylor adopted the 2018 edition on October 14, 2021, and its page says it is adopting the 2024 edition, with the ordinance not yet signed when we read it. We read these editions on October 19, 2026, on each city’s own page or its published code, Georgetown aside as noted; a city can change editions at any council meeting, so confirm with yours. Fees and permits by city are in roof permits and codes.
Section R905
The code’s rules for a shingle roof
Slope, deck, underlayment, nails and the shingle’s wind rating, all in Section R905 of the code.
Instructions are part of the code
Section R905.1 says a roof covering is applied by the code and by the manufacturer’s installation instructions. A roof that skips the maker’s steps does not meet code, even if every numbered rule is met.
Slope and deck
Shingles go only on a slope of 2:12 or steeper, and from 2:12 up to 4:12 the underlayment must be doubled (R905.2.2). The deck must be solid sheathing; the 2024 edition names wood structural panels or solid lumber (R905.2.1).
Underlayment and nails
On 4:12 and steeper, one layer of underlayment lapped 2 inches, or a self-adhered membrane, which the 2018 and 2021 editions allow as an exception and the 2024 edition lists in its table. Nails: galvanized, stainless, aluminum or copper, 12 gauge with a 3/8 inch head, 3/4 inch into the deck, and at least 4 per strip shingle (R905.2.5, R905.2.6).
Wind rating
Shingles must carry a wind class on the package (R905.2.4.1). At the design wind speed in Austin’s adopted table, 105 mph, the code minimum is Class D under ASTM D7158 or Class A under ASTM D3161. Check the class printed on the bundle against your city’s table.
Leak Points
Flashing, drip edge and crickets
Drip edge at every eave and rake, step flashing at least 4 by 4 inches, and a cricket behind wide chimneys.
Drip edge
Required at the eaves and rakes of a shingle roof, lapped 2 inches, reaching 2 inches onto the deck and 1/4 inch below it, nailed no more than 12 inches apart. Underlayment goes over the drip edge at the eaves and under it at the rakes (R905.2.8.5). More in roof edges and drainage.
Valleys
An open metal valley is at least 24 inches wide, in a listed metal such as 26 gauge galvanized steel. A closed valley is lined with one ply of roll roofing or a self-adhered membrane at least 36 inches wide (R905.2.8.2).
Walls, chimneys and kick-outs
Sidewall flashing, continuous or step, is at least 4 inches high and 4 inches wide, with its vertical leg under the siding (R905.2.8.3). Flashing is required where a roof meets a wall, including a kick-out where an eave meets a sidewall, and a cricket goes behind any chimney or penetration more than 30 inches wide, skylights excepted (R903.2.1, R903.2.2).
Climate Table
Is an ice barrier required in Texas?
Only where the city’s own climate table says ice has formed at the eaves, and Austin’s says No.
Where the code requires it
The code requires an ice barrier at the eaves only in areas with a history of ice forming there, as marked in the city’s own climate table, Table R301.2. Where it applies, it runs from the roof edge to at least 24 inches inside the wall line (R905.1.2).
Around Round Rock
Austin’s adopted table marks the ice barrier No, and Taylor’s draft 2024 table does too. We did not find Round Rock’s own table. Leak barrier in valleys and at walls and pipes is a separate matter; our standard puts it there on every roof.
Section R908
What the code says about a new roof on an old house
A replacement goes down to the deck, a recover is limited, and damaged flashing must be replaced.
Replacement or recover
A roof replacement removes the old layers down to the deck (R908.3). The code allows a recover, a new roof over the old one, in some cases, but not over a water-soaked or deteriorated roof, not over slate, clay or cement tile, and not where there are already two or more layers.
Flashing on a reroof
Existing flashing, edging, outlets and vents are replaced where rusted, damaged or deteriorated (R908.5), and flashing is rebuilt to the maker’s instructions (R908.6). Under R908.3, the 2024 edition also lets sound self-adhered underlayment stay in place under the new roof.
Is the new roof held to today’s code?
Section R908.1 says reroofing materials and methods meet Chapter 9, and the code’s rule for repairs and alterations holds new work to new-construction standards without upgrading the rest of the house. On our reading, a tear-off’s new underlayment and drip edge must meet the edition your city enforces. A documented roof inspection shows what your roof has today.
Section R806
How much attic ventilation the code requires
One square foot of vent opening per 150 square feet of attic, or per 300 with a high and low balance.
The ratio
A vented attic needs open vent area, after screens and louvers, of 1/150 of the attic floor. It may drop to 1/300 only when 40 to 50 percent of that area sits high, within 3 feet of the ridge, and the rest low, in the bottom third of the attic (R806.2). Williamson, Travis, Bell and Hays counties are Climate Zone 2A, so the vapor retarder condition for colder zones does not apply.
A worked example
A 1,500 square foot attic needs 10 square feet of vent opening at 1/150, which is 1,440 square inches, or 5 square feet (720 square inches) at 1/300 with the high and low balance. Insulation may not block the eave vents, and a 1 inch air space is kept between insulation and the deck at the vent (R806.3).
Primary Source
Where to read the code yourself
The International Code Council lets anyone read the code online, read only, without paying.
Read the code online
The International Code Council publishes the code and lets anyone read it online, read only, without paying. Chapter 9 is the roof chapter, and attic ventilation is in Chapter 8, Section R806. Read the edition your city has adopted. The section numbers in this guide work in all three recent editions, with two changes in 2024: the recover rules moved from R908.3.1 to R908.4, and the repairs rule from R102.7.1 to R102.6.1.
Common Questions
Questions homeowners ask
Does Texas have a statewide building code for roofs?
For homes inside city limits, yes: Texas Local Government Code 214.212 adopts the International Residential Code, and each city may adopt a newer edition and its own amendments by ordinance after a public hearing. Outside city limits, counties apply standards only to new homes and large additions, and only if they opt in.
How many nails per shingle does the building code require?
At least 4 per strip shingle, or more if the shingle maker requires it, 12 gauge with a 3/8 inch head and at least 3/4 inch into the deck (IRC R905.2.5 and R905.2.6). Our install standard uses 6 per shingle on every roof.
Is drip edge required by code in Texas?
In a city on the 2018, 2021 or 2024 International Residential Code, yes, unless a local amendment removed it: Section R905.2.8.5 requires drip edge at the eaves and rakes of a shingle roof, lapped 2 inches and nailed no more than 12 inches apart.
Can a new roof go over the old one in Texas?
The code allows one recover in some cases, but not over a water-soaked or deteriorated roof, not over slate or tile, and not where there are already two layers (IRC R908). Every roof we install is a full tear-off to the deck instead.
How much attic ventilation does the code require?
Open vent area, after screens and louvers, of 1/150 of the attic floor, or 1/300 when 40 to 50 percent of it sits within 3 feet of the ridge and the rest low in the attic (IRC R806.2). A 1,500 square foot attic needs 1,440 square inches at 1/150.
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