SDR-35 PVC Pipe

SDR-35 PVC is the standard pipe for buried gravity sewer lines and storm drainage. It’s for sewer and storm drainage purposes only, available in two joining methods — gasketed or solvent weld — and it extends from the end of the building drain and conveys the discharge to a sewer or other point of disposal. Non-pressure. Gravity-fed. That’s the job.

The name tells you what it is. SDR stands for Standard Dimension Ratio — the outside diameter equals 35 times the wall thickness. The higher that number, the thinner the wall relative to the pipe size. That thin wall is why SDR-35 is light and easy to handle, and also why it has no business carrying pressurized water.

Here’s the part that bites people: SDR-35 is not interchangeable with Schedule 40. Different outside diameters, different jobs, different fittings. Get that wrong and you’re buying transition adapters or redoing the connection. More on that below.

What SDR-35 Is Built to Do

The standard that governs it is ASTM D3034. All pipe and fittings meet the requirements of ASTM D3034 for 4-inch through 15-inch SDR 35/26, and F679 for 18-inch through 36-inch sewer pipe. So the smaller sizes most contractors handle fall under D3034; the big municipal diameters jump to F679.

The pipe is green for a reason. The pipe is colored green for in-ground identification as sewer pipe. Dig it up years from now and there’s no guessing what it is.

Corrosion is where PVC earns its keep underground. Ring-Tite PVC sewer pipe is unaffected by the fluids found in ordinary domestic sewage. It is immune to sewer gases and the sulfuric acid generated by the completion of the hydrogen sulfide cycle. It is also immune to corrosive soils — both alkaline or acidic. That matters in Montana’s variable valley soils, where a buried line sits in whatever the glacial deposits left behind.

It also holds its shape under load. The pipe joints must be able to withstand a minimum hydrostatic pressure of 50 psi without leakage. The minimum ring stiffness is 46 psi for DR35 pipe and 90 psi for DR 28. And it flexes rather than cracks — the design of the pipe allows for a long-term deflection of 7.5%, without failure or damage.

SDR-35 vs. Schedule 40 — Don’t Mix Them Up

This is the single most important thing to get right.

Schedule 40 PVC is pressure-rated DWV pipe. PVC is the most widely used DWV pipe material in new construction — lightweight, resistant to corrosion and chemical attack, joined using a two-step solvent welding process with primer and cement. PVC DWV pipe is manufactured in Schedule 40 wall thickness and conforms to ASTM D2665 for DWV applications and ASTM D1785 for pressure-rated applications. That’s the pipe inside the building walls and where pressure or higher heat is in play.

SDR-35 is the opposite end of the job. For underground sewer piping outside of buildings, code often requires PVC pipe classified by Standard Dimension Ratio rather than schedule. SDR 35 pipe, conforming to ASTM D3034, is the most common for municipal sewer mains and storm drainage. SDR 26 is required for underground piping within buildings in many jurisdictions. The distinction between Schedule 40 DWV pipe and SDR-rated sewer pipe is an important one that affects material selection on every project.

On a typical building sewer lateral, the split looks like this: building sewer laterals are typically 4-inch or 6-inch PVC, with SDR 35 (ASTM D3034) being the standard material for the underground portion outside the building footprint. Schedule 40 PVC DWV pipe may be used for the transition section near the building, depending on local code requirements.

If you’re stepping up wall thickness for heavier loads or lateral runs, that’s where SDR-26 and SDR-28 come in — heavier-wall options. Main line sewers will be PVC DR35 sewer pipe; sewer laterals will be PVC DR28 sewer pipe.

Sizes, Types, and Joining Methods

SDR-35 covers a wide size range. SDR35, PC 46 psi: 4 – 60 inches. The common nominal sizes carried run 4-inch, 6-inch, 8-inch, 10-inch, and up. Western Building Center stocks 4-inch SDR-35 sewer and drain fittings — couplings, 45- and 90-degree elbows, wyes, slip caps, and sanitary tees — to match the underground portion of a residential lateral.

Lengths are long for a reason. The standard laying lengths are 14 and/or 20 feet. This means more ground can be covered during installation while eliminating the cost of unnecessary joints.

Spec	Value
Governing standard (4”–15”)	ASTM D3034
Governing standard (18”–36”)	ASTM F679
Size range	4” to 60”
Laying lengths	14 ft and 20 ft
Minimum ring stiffness (SDR-35)	46 psi
Long-term deflection allowance	7.5%
Joint pressure (gasketed)	50 psi without leakage
Color	Green (in-ground sewer ID)
Max operating temperature	140°F

Two ways to join it, and you pick based on the application.

Gasketed is the push-together method. The Ring-Tite joint can be assembled quickly. Seated in a deep groove, the flexible elastomeric gasket provides a tight seal that protects the line from shock, vibration, earth movement, and compensates for expansion and contraction of pipe lengths. That movement tolerance is exactly what you want in freeze-prone ground where frost heave shifts a rigid line. There’s no field mixing or application of cement — it’s a simple push together joint that remains tight under normal operating conditions. The gaskets themselves meet ASTM F477, and joints meet or exceed ASTM D3212 for joint tightness, including a 22 in. Hg vacuum and a 25 feet of head pressure test.

Solvent weld chemically fuses the joint. The piping system is joined using a two-step solvent cement joining process with primer conforming to ASTM F656 and solvent cement conforming to ASTM D2564. Prime first, then cement — two steps, not one.

There’s also a perforated option. The fittings are compatible with solvent weld sewer pipe in both solid wall and perforated styles. Perforated pipe is what you reach for on footing and foundation drains, where the goal is collecting water, not just moving sewage.

Installation Basics

Bedding makes or breaks a buried line. The trench should run at least 18 inches wide with a minimum 6 inches of clearance on each side of the pipe, bedded in compacted crushed stone or coarse sand. In freeze-prone Montana soils that bedding matters more, not less — it keeps the line stable through seasonal heave.

Cut square. The spigot has to seat uniformly in the gasket, so mark your insertion depth before you cut. For gasketed joints, clean the bell, spigot, and gasket of any debris, lubricate only the spigot with manufacturer-approved lubricant, and insert the pipe to the stop mark — never past it. The pipe field-cuts easily; you can cut it with a power saw or an ordinary handsaw, and it can be beveled without expensive machinery. A 14-foot length of 8-inch SDR-35 weighs approximately 55 pounds.

Keep a consistent downward slope so gravity does the work the pipe was designed for. Protect the system from ultraviolet light exposure from the sun or other source. Stack it covered — UV degrades PVC sitting in the yard all summer.

One hard rule on testing: never use compressed air. PVC piping systems are suitable for oil-free air handling to 25 psi, not for distribution of compressed air or gas.

Frequently Asked Questions

Can SDR-35 fittings be used with Schedule 40 pipe? No — not directly. The two have different outside diameters, so the fittings don’t match. The pipe connects into I.P.S., cast/ductile iron pipe and fittings with adapters and/or transition gaskets. The correct transition adapter is what joins the two systems.

Why is SDR-35 pipe green? The pipe is colored green for in-ground identification as sewer pipe. Anyone who digs it up later knows immediately what they’ve found.

Is SDR-35 rated for pressurized water? No. It’s a non-pressure, gravity-flow pipe. PVC D3034 sewer main pipe is for sewer and storm drainage purposes only and extends from the end of the building drain and conveys the discharge to a sewer or other point of disposal. Pressurized systems call for Schedule 40.

What’s the difference between gasketed and solvent-weld joints? Gasketed joints push together with an elastomeric ring and tolerate ground movement and thermal cycling — they compensate for expansion and contraction of pipe lengths. Solvent-weld joints chemically bond the PVC using a two-step solvent cement joining process with primer conforming to ASTM F656 and solvent cement conforming to ASTM D2564.

How much deflection can SDR-35 handle without failing? The design of the pipe allows for a long-term deflection of 7.5%, without failure or damage. Proper bedding keeps it well within that range.

What sizes does SDR-35 come in? SDR35 runs 4 to 60 inches. Common nominal sizes are 4-inch, 6-inch, 8-inch, and 10-inch, sold in 14- and 20-foot laying lengths.