The St. George Building Department publishes the design criteria every house in the city is built to. Seismic Design Category D. Ground snow load 21 psf, roof snow 20 psf. Wind 105 mph. Frost line depth 12 inches. Moderate to heavy termite. It is one sheet, it is public, and most homeowners never see it.
Category D is the line that matters for a water heater. It is what turns strapping from something some plumbers do into something the code requires, and it is why a heater sitting loose on a garage floor here is not just untidy. This page covers the strapping rule itself, why the category is D in this part of Utah, and the four other things an inspector looks at on a water heater install: garage elevation, vehicle protection, the pan and drain, and the relief valve discharge pipe.
What the city publishes about your address
These are the numbers the Building Department publishes as the design criteria for St. George. They are not our numbers and they are not a manufacturer's numbers. They are the city's.
| Criterion | Published value |
|---|---|
| Seismic Design Category | D |
| Ground snow load | 21 psf |
| Roof snow load | 20 psf |
| Wind speed | 105 mph |
| Frost line depth | 12 inches |
| Termite | Moderate to heavy |
The rule, and why Utah wrote its own
Utah does not use the model code here. Under Utah Code 15A-3-205, the state deletes IRC P2801.8 and replaces it with its own version, and Utah's version has no seismic design category trigger at all. Anchoring or strapping a water heater against horizontal displacement is required statewide, in St. George and in Logan alike. The requirement is two points of restraint, one within the upper third of the appliance's vertical dimension and one within the lower third. Our own practice is to keep the lower strap clear of the controls, which is not something the adopted code specifies.
That 4 inch dimension is not arbitrary. It keeps the strap off the gas control valve and the thermostat, which are the parts you do not want a steel band bearing on when the tank moves.
Here is what makes a strap decorative rather than structural, and all four are easy to spot. A strap anchored into drywall only, with no stud or masonry behind the screw. Perforated plumber's tape used as a strap, which stretches. One strap at mid height instead of two in the upper and lower thirds. And a strap with slack in it, which lets the tank build momentum before the strap does anything at all.
A strapped heater is not about the tank. It is about what is attached to the tank. A heater that walks a few inches breaks the gas connector, the cold inlet, and the hot outlet at the same moment. That is a gas leak and an uncontrolled water leak in the same room, and the water is coming out of a vessel that holds tens of gallons.
Why the category is D here
The Hurricane fault zone runs through this area. The USGS and Utah Geological Survey Quaternary fault database records it as 87 kilometers end to end, 102 kilometers of cumulative trace, in six sections. The Anderson Junction section, 42 kilometers spanning the Utah and Arizona line, is the one nearest St. George and Hurricane. It is a normal fault, down to the west, with a minor right lateral component near Hurricane. Late Quaternary alluvial deposits along it show up to tens of feet of displacement, and displacement increases toward the north.
Utah Geological Survey Special Study 127, the hazard mapping for the St. George and Hurricane area, states the fault is capable of earthquakes as large as magnitude 6.5 to 7, and that active faults in the area are capable of magnitude 7. The recurrence interval in the fault database is listed as no data. Most recent surface faulting on the Anderson Junction section is placed at roughly 5,000 to 10,000 years ago.
You do not have to go back that far for a local example. On September 2, 1992, a magnitude 5.8 earthquake struck St. George. Special Study 127 records that it caused liquefaction and property damage, and that it triggered the Springdale landslide. Special Study 127 maps liquefaction across the area at 1:24,000 scale. It does not map ground shaking, because there was not enough data to do it.
None of that is a prediction. It is the reason the city's own criteria sheet says D, and D is the reason your heater gets two straps.
If the heater is in the garage
Two additional things apply in a garage, and both come up on almost every garage install we look at.
First, elevation. IRC P2801.7 requires the ignition source on a gas appliance in a garage to sit 18 inches above the floor. Gasoline vapor is heavier than air. It pools at floor level and it travels. The 18 inches exists so that a spilled gallon in the parking bay does not find a burner. The adopted edition carries an exception: elevation is not required for appliances listed as flammable vapor ignition-resistant, which most current production units are. Check the rating plate rather than assuming either way.
Second, impact. If the heater sits anywhere a vehicle can reach it, it needs a physical barrier in front of it. A bollard set in concrete, or a steel guard anchored to the slab. This is the item most often missing on an older garage install, and it is cheap to add.
While we are in the garage: the vent has rules too. Three inch minimum diameter, a quarter inch per foot of rise on horizontal runs, Type B double wall or an approved single wall. Aluminum vent and flexible dryer duct are prohibited. If a previous installer used dryer duct on a water heater flue, that is not a code technicality, that is combustion products in the garage.
If the heater is in the attic
Slab on grade construction dominates here. No basement, usually no crawlspace. So water heaters go in the garage, in an interior closet, or in the attic, and attic installs are common.
The code requires a pan under a water heater with a drain to an approved location wherever a leak would cause damage. In an attic over finished ceilings, that is every install, without argument. The pan and the drain line are the difference between a tank failure that drips onto a driveway and one that comes down through a bedroom ceiling.
Two things go wrong with attic pans. The drain line gets terminated somewhere nobody will ever see, which defeats the purpose of a visible warning, or it is never connected at all and the pan is just a tray waiting to overflow. A pan drain should end where a person walking past the house will notice water running out of it.
An attic install also puts the tank at the top of the house, which is the worst place for the weight and the worst place for a leak. If your heater is up there, the pan, the drain, the platform, and the straps are all doing more work than they would in a garage.
The relief valve and its discharge pipe
The temperature and pressure relief valve is the one part of a water heater that exists purely to prevent a catastrophic failure. It sits in the top 6 inches of the tank, because that is where the hottest water is.
The discharge pipe off that valve has its own rules, and they are all about making sure the valve can dump freely and that a person can see when it does. Full size of the valve outlet, never reduced. Rigid material, copper, CPVC or galvanized steel, not an unlisted plastic and not a flexible hose. It drains by gravity, with no traps and no sag. No valve anywhere in the line, ever. No threaded end, so nobody can cap it. And it terminates where the discharge is visible.
The last two rules exist because people cap them. A relief valve that is dripping is telling you something, usually about pressure rather than temperature. Capping it, plugging it, or valving it off removes the only protection between a runaway thermostat and a pressure vessel. If yours is dripping, that has an explanation and a fix, and it is never a cap.
Permits, and why they help you
A water heater installation requires a permit in Utah, including a like for like replacement of an existing unit. Homeowners are frequently surprised by that, and some installers quietly skip it.
The permit is worth having for a reason that has nothing to do with rules. The inspection is a second set of eyes on exactly the items on this page: the straps and their placement, the elevation in a garage, the pan and drain, the vent, and the relief valve discharge. If you paid someone to install a water heater and there was no permit and no inspection, the only person who ever checked that work is the person you paid.
Look up your own ground
Washington County publishes its geologic hazard mapping as free public GIS layers, and they cover faults, surface fault rupture hazard, fault special study zones, liquefaction, rockfall, collapsible soil, expansive rock and soil, gypsiferous rock and soil, wind blown sand, piping and erosion, landslides, and flooding. The Utah Geological Survey runs a statewide hazards portal as well. Both are free, both cover your parcel, and neither requires you to talk to anyone.
It is worth ten minutes. The mapping behind those layers is Special Study 127, which covers 366 square miles across Hurricane, Ivins, La Verkin, Leeds, Santa Clara, St. George, Toquerville and Washington, from nine geologic quadrangle maps.
What we’d do at your house
We look at where the heater is before we look at the heater, because the garage, the closet and the attic each carry different requirements.
Straps go into structure, two of them, upper third and lower third, with the lower one clear of the controls.
If the tank sits where a car can reach it, we set a barrier in front of it and show you what it is anchored to.
On an attic install we want a pan, a real drain line, and a termination you can actually see from outside.
We pull the permit and we let the inspector look at it, because a second set of eyes on our own work costs us nothing.
If we find a capped or valved relief discharge on your existing heater, we will tell you that day, before we quote anything else.
Sources
What this page says comes from the documents below, read in full. It describes them. It is not legal advice. Confirm with your association, your city, or an attorney before you act.
- St. George Building Department, published design criteria (Seismic Design Category D, 21 psf ground snow, 20 psf roof snow, 105 mph wind, 12 inch frost line, moderate to heavy termite) 01-plumbing-corpus.md §1.4; briefs.txt brief 15
- IRC P2801.8, water heater anchorage in Seismic Design Category D (two straps, upper and lower third, lower strap 4 inches above the controls, third strap over 52 gallons) 01-plumbing-corpus.md §1.4, citing Emergency Water Heater SLC on Utah water code requirements
- IRC P2801.3, ignition source elevation 18 inches above the garage floor 01-plumbing-corpus.md §1.4
- Water heater venting requirements (3 inch minimum, quarter inch per foot rise, Type B double wall, aluminum and flex duct prohibited) and Utah permit requirement including like for like replacement 01-plumbing-corpus.md §1.4
- T&P relief valve and discharge piping requirements (top 6 inches of tank, full size, rigid material, gravity drain, no trap, no valve, no threaded end, visible termination) 01-plumbing-corpus.md §1.4
- USGS and Utah Geological Survey Quaternary Fault Database, Hurricane fault zone (structure 998) 05-environment-water-geology-corpus.md §2.7
- Utah Geological Survey Special Study 127, Knudsen and Lund, Geologic-Hazard and Adverse-Construction-Condition Maps for the St. George and Hurricane Area (M 6.5 to 7 capability, 1992 M 5.8 earthquake, liquefaction mapping, 366 square miles, 14 hazard maps) 05-environment-water-geology-corpus.md §2.1, §2.7
- Washington County Hazards MapServer (24 public GIS layers) and the Utah Geologic Hazards Portal 05-environment-water-geology-corpus.md §2.9
- Slab on grade dominance and the resulting attic and garage water heater locations 01-plumbing-corpus.md §8.2; 05-environment-water-geology-corpus.md §5.1