2.2 Protection of Pipes: Contact, Notching, Shield Plates, and Freezing

Protection against contact and corrosion

IPC 305.1 keeps dissimilar and aggressive materials apart:

Metallic piping, except for cast iron, ductile iron and galvanized steel, shall not be placed in direct contact with steel framing members, concrete or cinder walls and floors or other masonry. Metallic piping shall not be placed in direct contact with corrosive soil.

Where sheathing is used to prevent contact, the model IPC requires the sheathing to be plastic and not less than 0.008 inch (8 mil) thick. Where the sheathing protects pipe penetrating concrete or masonry, it must be installed so the pipe can move within the sleeve.

Colorado field note (not exam-scored): Board Rule 1.2(E)(1)(h) replaces 305.1 outright. The Colorado version drops the word "metallic," so the rule reaches all piping except cast iron, ductile iron and galvanized steel, and it raises the sheathing thickness to not less than 0.025 inch. Answer 8 mil on the exam; install 25 mil in Colorado.

IPC 305.2 requires piping to be installed so as to prevent strains and stresses exceeding the structural strength of the pipe, with provisions made for expansion, contraction and structural settlement.

Foundation walls, and the two-pipe-size sleeve

IPC 305.3: any pipe passing through a foundation wall must be provided with a relieving arch, or a pipe sleeve built into the foundation wall. The sleeve must be two pipe sizes greater than the pipe passing through it.

"Two pipe sizes" means two nominal steps, not two inches. A 4-inch building drain through a foundation wall needs a 6-inch sleeve (4 to 5 to 6). A 3-inch pipe needs a 5-inch sleeve (3 to 4 to 5). The point of the sleeve and the arch is the same: keep the wall's settlement load off the pipe.

Freezing

IPC 305.4 is short and heavily tested:

Water, soil and waste pipes shall not be installed outside of a building, in attics or crawl spaces, concealed in outside walls, or in any other place subjected to freezing temperatures unless adequate provision is made to protect such pipes from freezing by insulation or heat or both. Exterior water supply system piping shall be installed not less than 6 inches below the frost line and not less than 12 inches below grade.

Two numbers, and both must be satisfied: 6 inches below the frost line and 12 inches below grade. In a Front Range jurisdiction with a 30-inch frost line, the controlling depth is 36 inches, because 6 below the frost line exceeds the 12-inch floor. In a warm jurisdiction with no measurable frost line, the 12-inch minimum still applies.

IPC 305.4.1 Sewer depth is a bracketed section in the model code — the numbers are left blank for the adopting jurisdiction. Do not memorize a number for it.

Colorado field note: the Colorado Plumbing Code contains no statewide table of water service bury depths by elevation. Frost depth is a local determination, set by the city, town or county building department. Do not assume a mountain-county figure applies on the Front Range or vice versa; call the jurisdiction. Colorado also deletes IPC 903.2 Frost closure entirely, so the model code's cold-climate vent-terminal enlargement does not apply in Colorado even though it is scored on the exam (see Chapter 11 of this guide).

IPC 305.5 requires joints at the roof and around vent pipes to be made watertight with lead, copper, galvanized steel, aluminum, plastic or other approved flashing, and exterior wall openings to be made watertight.

Shield plates — the 1-1/4 inch rule

IPC 305.6 is one of the most frequently missed numbers on the exam because the IRC and the electrical trade both use 1-1/2 inches for a similar rule. The IPC does not.

In concealed locations where piping, other than cast iron or galvanized steel, is installed through holes or notches in studs, joists, rafters or similar members less than 1-1/4 inches from the nearest edge of the member, the pipe shall be protected by steel shield plates of not less than 0.0575 inch (No. 16 gage). Such plates shall cover the area of the pipe where the member is notched or bored, and shall extend not less than 2 inches above sole plates and below top plates.

Read the four qualifiers carefully, because each one is a distractor on a multiple-choice item:

1. Concealed locations only.
2. Not cast iron and not galvanized steel — those are tough enough on their own.
3. The trigger distance is less than 1-1/4 inches to the nearest edge (front or back face of the stud).
4. The plate thickness is 0.0575 inch, which is No. 16 gage steel.

IPC 305.7 adds that plumbing components along alleyways, driveways, parking garages or other locations exposed to damage must be recessed into the wall or otherwise protected in an approved manner.

What the IPC says about cutting and notching

Here is a distinction that trips up experienced plumbers: the IPC does not publish notching and boring limits. IPC 307.2 says only that "a framing member shall not be cut, notched or bored in excess of limitations specified in the International Building Code." For one- and two-family dwellings the parallel limits live in IRC R502.8 (joists) and R602.6 (studs). On a Colorado exam item, the correct answer to "what does the IPC allow" is that the IBC (or the IRC for dwellings) governs.

The rest of IPC 307 gives the plumber four hard rules that are in the IPC:

307.4 is absolute. There is no "small hole" allowance for an engineered truss. A plumber who bores a 2-inch hole through a truss web to run a vent has created a structural defect that only a design professional can approve after the fact.

Applying the bearing-plane rule

A footing's outside bottom edge is 48 inches below grade. A sewer trench runs parallel to the wall, 30 inches from the footing edge, at a depth of 6 feet.

• The bearing plane rises at 45 degrees, so at 30 inches out from the footing edge, the plane is at 48 + 30 = 78 inches (6 feet 6 inches) deep.
• The trench bottom at 6 feet (72 inches) is above the plane at that offset — it cuts into the bearing zone.
• Fix: move the trench farther from the wall, or underpin. At 6 feet deep the trench must be at least 72 - 48 = 24 inches clear of the footing edge... and because the trench must stay entirely below the plane, the safe rule of thumb is that the horizontal offset must be at least as great as the vertical distance the trench bottom sits below the footing edge.

Putting it together on a rough-in

A 2-inch PVC lavatory arm passes through a 2x4 stud wall. The bored hole leaves 1 inch of wood between the hole and the face of the stud.

• Is the pipe cast iron or galvanized steel? No — it is PVC, so 305.6 applies.
• Is the location concealed? Yes, it will be drywalled.
• Is the edge distance less than 1-1/4 inches? Yes, 1 inch.
• Required: a No. 16 gage steel shield plate covering the bored area, extending at least 2 inches above the sole plate and below the top plate where applicable.