Introduction
How many sticks do I need? What’s the difference between Schedule 40 and 80? Do I really need primer? These are the questions that come up on nearly every PVC job, from a first-time irrigation install to a DWV rough-in. This FAQ collects the most asked questions about PVC pipe estimating and installation in one place, with straight answers.
For the numbers behind the answers, use the PVC Pipe Calculator; for the full walkthrough, see the complete guide.
Sizing and Materials
What is nominal pipe size (NPS)?
A trade designation, not a measurement. A 2″ PVC pipe measures 2.375 in (60.3 mm) outside diameter in any schedule; the inside diameter varies with wall thickness (about 2.047 in / 52.0 mm in Schedule 40). Size by NPS and verify actual OD when matching adapters or tools.
What’s the difference between Schedule 40 and Schedule 80 PVC?
Same outside diameter per nominal size, but Schedule 80 has a thicker wall, smaller inside diameter, and higher pressure rating. Schedule 40 (white) is the residential default; Schedule 80 (gray) suits higher-pressure, industrial, or exposed service. Schedule 80 pipe costs roughly 1.5–2× Schedule 40.
What is SDR-35 pipe?
A gasketed sewer/drain pipe graded by standard dimension ratio (OD ÷ wall thickness) under ASTM D3034 — typically green or white, joined with gasketed bells rather than solvent weld. It’s for gravity sewer and drainage, not pressure service.
What is C900 pipe?
AWWA C900 blue gasketed PVC for water mains, 4″ through 24″+. Bell-and-spigot gasketed joints, pressure classes like 150 and 235 psi. A different product family from Schedule 40/80 — different fittings, different takeoff.
Can I use PVC for hot water?
Standard PVC (Schedule 40/80) is not rated for sustained hot-water service — pressure ratings collapse with temperature (about 62% of rated at 100°F/38°C, ~22% at 140°F/60°C). CPVC (the cream-colored pipe) is the plastic rated for hot water. See the material guide for the full comparison.
Estimating and Quantities
How many 10-ft sticks do I need?
Total your run lengths, add waste (10% standard), divide by 10, and round up. Example: 80 ft × 1.10 = 88 ft ÷ 10 = 8.8 → 9 sticks. The formula guide works this through in metric too.
How do I estimate the number of couplings?
Count joints on your drawn layout — every place two stick ends meet without another fitting. As a sanity check: couplings ≈ (sticks − 1) − (fittings that already join two sticks). Always trust the layout count over the formula.
How much waste should I add?
10% for typical residential work; 5–10% for long straight runs; 10–15% for many short pieces or repairs; 15–20% when working from a rough sketch. Apply waste to pipe footage, not fittings — buy 1–2 spare fittings instead.
How much pipe disappears into each fitting socket?
Roughly 1–2 in (25–50 mm) per end depending on size. Measure fitting-center to fitting-center, then subtract both socket depths for the cut length.
Solvent Welding and Joints
Do I need primer with solvent cement?
Yes — primer cleans and softens the PVC so the cement can chemically fuse the joint, and plumbing codes (IPC/UPC) require it. Skipping primer is the most common cause of joint failure.
How long before I can pressurize a joint?
Handling strength in minutes; pressure testing after several hours for small lines and ~24 hours for 2″ and up — longer in cold weather. Never pressure-test a green joint.
Can I use PVC cement on CPVC or ABS?
No. Use cement matched to the pipe: ASTM D2564 cement for PVC, CPVC-specific cement for CPVC. ABS uses its own cement. “All-purpose” cements exist but check the label covers your exact materials and the inspector accepts it.
Are threaded PVC joints as strong as solvent-welded?
No — threaded joints reduce the pressure rating to roughly 50% of the solvent-weld value, and the threads crack if over-tightened. Hand-tight plus one to two turns with thread-sealant tape; never crank with a pipe wrench.
How long does opened solvent cement last?
Months, not years, once opened — the solvents evaporate every time the lid comes off. If it’s thick, stringy, or past its date code, discard it. A fresh can is the cheapest insurance on the job.
Pressure, Temperature, and Code
What does the pressure rating printed on the pipe mean?
The maximum working pressure at 73°F (23°C) — e.g., 280 psi (1.93 MPa) for 2″ Schedule 40. It must be derated for higher temperatures: ×0.62 at 100°F (38°C), ×0.22 at 140°F (60°C). Size for the derated number at your actual operating temperature.
Can I use PVC pipe for compressed air?
No — PVC is not rated for compressed air service, and OSHA and manufacturers warn against it: a pressurized-air failure shatters PVC into shrapnel, unlike a water failure which just leaks. Use pipe rated for compressed air (steel, copper, or air-rated plastics).
Do I need a permit for PVC plumbing work?
Often yes for DWV rough-ins, water service lines, and anything inside the building envelope — requirements vary by jurisdiction. Simple irrigation and above-ground yard piping is frequently exempt, but verify with your local authority having jurisdiction before you dig. The code compliance guide covers what inspectors look for.
Why does the inspector want to see purple primer?
The purple dye proves primer was used — it’s the inspector’s visual verification that joints were properly prepared per code. Clear primer exists but gives you no way to prove compliance at inspection.
Costs and Buying
How much does a PVC irrigation job cost in materials?
As a planning range, a typical 2″ Schedule 40 residential run lands around $2–$4 per linear foot ($7–$13/m) all-in — pipe, fittings, valves, primer, cement, and hangers. The pipe itself is roughly half that; fittings and accessories make up the rest. See the cost guide for a worked budget.
Should I buy extra fittings?
Yes — one or two spares of the common elbows and couplings, plus a repair coupling. A mid-job store run costs more in time and fuel than the spares.
Is 20-ft pipe cheaper than 10-ft sticks?
Usually yes per foot, and it halves the coupling count — but it’s harder to transport and maneuver, especially solo or in tight trenches. Price both and be honest about handling.
Related Guides
- Complete Guide — the full takeoff walkthrough.
- Material Guide — schedules, SDR, C900, and fitting selection.
- Formula Explained — the math behind the calculator, worked in both unit systems.
- Common Mistakes — what goes wrong and how to prevent it.
- Pro Tips — field techniques for joints that last.
- DIY vs Pro — when to do it yourself and when to hire.
Get Your Number
Still have a question the FAQ didn’t cover? Run your layout through the PVC Pipe Calculator for quantities, then check the complete guide for the method or the code compliance guide for regulatory questions. The right number plus the right material is the whole job.
Disclaimer: Answers are general planning information, not professional advice. Pipe specifications, prices, and code requirements vary by product and jurisdiction. Verify pressure ratings against manufacturer data, confirm code requirements with your local authority having jurisdiction, and consult a licensed professional for pressurized, potable-water, or code-regulated work.
