CPVC SDR 11 vs SDR 13.5: Class 1 or Class 2, and Where Each Goes

Quick answer: SDR 11 is Class 1 CPVC pipe and SDR 13.5 is Class 2, under IS 15778. Same outside diameter, but SDR 11 has the thicker wall, so it is rated higher: 28.1 kg/cm² at 23°C and 7.0 kg/cm² at 82°C, against 22.5 and 5.6 kg/cm² for SDR 13.5. On 3 November 2026 the price gap at our counter was 6 to 20 percent a length depending on size, for example ₹435 against ₹409 for a 3/4 inch Ashirvad pipe. Use SDR 11 on hot lines, risers and anything a pump feeds, SDR 13.5 on cold gravity branches.

The question usually arrives in one of three forms: "SDR 11 vs SDR 13.5", "CPVC Class 1 vs Class 2" or "what does SDR 11 mean". They are the same question. This page answers it with the manufacturers' own numbers and our current prices, then says where each pipe belongs in a house.

What SDR 11 means

SDR stands for standard dimension ratio: the pipe's outside diameter divided by its wall thickness. A 1 inch CPVC pipe is 28.6 mm across the outside. At SDR 11 the wall is about 28.6 divided by 11, which is 2.6 mm. At SDR 13.5 it is about 28.6 divided by 13.5, which is 2.1 mm. A bigger SDR number means a thinner wall.

The Indian standard for CPVC hot and cold water pipe, IS 15778, turns those ratios into pressure classes. The BIS product manual for IS 15778 lists:

Pressure class	SDR	Sizes
Class 1	SDR 11	15 to 50 mm (1/2 to 2 inch)
Class 2	SDR 13.5	15 to 50 mm (1/2 to 2 inch)
Class 3	SDR 17	65 to 150 mm

So "Class 1" on a bill and "SDR 11" on a pipe are the same thing. Above 2 inch, the brands we sell move to Schedule 40 and Schedule 80 pipe instead, which our CPVC size chart covers.

Wall thickness by size

The outside diameter is fixed for each size, so the two classes fit the same fittings. Only the wall, and therefore the bore, changes. Two manufacturers publish the walls in slightly different ways, so both are shown.

Size	Outside diameter	SDR 11 wall, minimum (Astral)	SDR 11 wall (Ashirvad)	SDR 13.5 wall, minimum (Astral)	SDR 13.5 wall (Ashirvad)
1/2 inch	15.9 mm	1.73 mm	1.95 ±0.25 mm	1.40 mm	1.65 ±0.25 mm
3/4 inch	22.2 mm	2.03 mm	2.25 ±0.25 mm	1.65 mm	1.95 ±0.25 mm
1 inch	28.6 mm	2.59 mm	2.85 ±0.25 mm	2.12 mm	2.35 ±0.25 mm
1 1/4 inch	34.9 mm	3.18 mm	3.45 ±0.25 mm	2.59 mm	2.85 ±0.25 mm
1 1/2 inch	41.3 mm	3.76 mm	4.05 ±0.25 mm	3.06 mm	3.35 ±0.25 mm
2 inch	54.0 mm	4.90 mm	5.20 ±0.30 mm	4.00 mm	4.30 ±0.30 mm

Astral's CPVC PRO catalogue prints the minimum wall with a plus tolerance. Ashirvad's CPVC technical manual prints a middle figure with a plus-or-minus tolerance. Read across a row and the two describe almost the same band. Astral also notes that at 1/2 inch the minimum wall is not set by the ratio, which is why 15.9 divided by 1.73 comes to about 9 rather than 11. The smallest pipe gets extra wall for handling.

Pressure ratings at 23°C and 82°C

Because every size in a class has the same ratio, every size in that class has the same pressure rating. That is the point of the SDR system.

Class	Astral, 23°C	Astral, 82°C	Ashirvad, 27°C	Ashirvad, 82°C
SDR 11 (Class 1)	28.1 kg/cm² (400 psi)	7.0 kg/cm² (100 psi)	28.14 kg/cm²	6.93 kg/cm²
SDR 13.5 (Class 2)	22.5 kg/cm² (320 psi)	5.6 kg/cm² (80 psi)	22.23 kg/cm²	5.61 kg/cm²

The figure that matters in a house is the hot one. At 82°C a CPVC pipe keeps only a quarter of its 23°C rating. Astral's catalogue gives the derating factors: 1.00 at 23 to 25°C, 0.65 at 49°C, 0.50 at 60°C, 0.25 at 82°C and 0.20 at 93°C. Multiply the 23°C rating by the factor for your water temperature. At 60°C, SDR 11 works out to 14.05 kg/cm² and SDR 13.5 to 11.25 kg/cm².

Ashirvad's manual sets the limits for its warranty at 93°C for short term use and 82°C for continuous use. Neither class is meant to run hotter.

For scale: every 10 metres of height between the overhead tank and a tap adds roughly 1 kg/cm². A house fed by gravity from its own terrace tank sits far below either rating, even on the hot side. The margin gets thin where a pump is involved, because a pump's pressure is added on top and its start-up surge more so. Ashirvad's manual says the first two fittings after a pump should be metal and the line after them Schedule 80.

Fittings are the same for both

This is the part that makes the decision easy. Astral states that its CPVC fittings are produced as per SDR 11. Ashirvad's manual lists SDR 11 fittings against both its Class 1 and Class 2 pipe. A 3/4 inch elbow is the same elbow whichever pipe goes into it.

So the price difference between the two classes is only in the pipe, and the pipe is the smaller part of a bathroom bill. You can tell them apart on site by the stripe. Ashirvad's manual and Astral's catalogue both describe SDR 11 as tan with a red stripe and SDR 13.5 as tan with a brown stripe.

Price difference per length, all three brands

Our prices on 3 November 2026, before GST, per pipe. Ashirvad and Astral are 5 metre lengths. Each price links to the product page.

Size	Ashirvad SDR 11	Ashirvad SDR 13.5	Astral SDR 11	Astral SDR 13.5	Supreme SDR 11	Supreme SDR 13.5
1/2 inch	₹325	₹285	₹252	₹220	₹279	₹246
3/4 inch	₹435	₹409	₹337	₹317	₹400	₹370
1 inch	₹673	₹598	₹522	₹463	₹622	₹534
1 1/4 inch	₹1,152	₹984	₹893	₹763	₹1,026	₹866
1 1/2 inch	₹1,581	₹1,361	₹1,226	₹1,055	₹1,407	₹1,188
2 inch	₹2,744	₹2,309	₹2,129	₹1,791	₹2,340	₹1,951

List prices for every row are on each product page and on the brand price lists for Ashirvad, Astral and Supreme.

Read the gap, not the totals. At 3/4 inch, the size most of a house is plumbed in, the step up to SDR 11 is ₹26 a length in Ashirvad, ₹20 in Astral and ₹30 in Supreme. That is 6 to 8 percent. At 2 inch it is ₹435, ₹338 and ₹389, which is 19 to 20 percent. If a house takes ten lengths of 3/4 inch, plumbing all of it in SDR 11 costs ₹200 to ₹300 more before GST. On a building's 1 1/2 and 2 inch risers, the same decision is worth real money and deserves the line by line thinking below. For the same pipes priced by the metre, see CPVC pipe price per metre.

Where each class belongs in a house

This is the advice we give at the counter. It is not a substitute for a plumbing consultant's drawing on a large building.

• SDR 11: every hot water line, from geyser or solar heater to the mixer. Any line on the outlet of a pressure pump. Vertical risers that feed more than one floor. Anything buried in a slab or a floor where replacing it would mean breaking tile.
• SDR 13.5: cold water branches fed by gravity from the overhead tank, inside the bathroom and kitchen, in a house or a low-rise building.

On a single house, at 1/2 and 3/4 inch, our advice is to run SDR 11 throughout. The saving from SDR 13.5 is a few hundred rupees, and one class on site means nobody puts a brown stripe on a hot line by mistake. On larger diameters and multi-storey work, splitting by line is worth doing.

Whatever you choose, pressure test before the wall is closed. Ashirvad's warranty excludes joints not pressure tested before plastering, and our guide to pressure testing CPVC before tiling walks through it. If the hot line is from a solar heater, read which pipe to use for a solar water heater as well.

What about SDR 9?

Two of our brands also make a heavier SDR 9 CTS pipe in 3/4 and 1 inch: Astral SDR 9, 3/4 inch, ₹436 (list ₹969) and Supreme SDR 9, 3/4 inch, ₹486 (list ₹1,080). It is not one of the two IS 15778 classes discussed here, and few house jobs need it. Ask us if a consultant has specified it.

Buying CPVC pipe from us

We stock both classes in all three brands, 1/2 inch to 2 inch, at the Viveknagar counter. Send your list through the quote page or WhatsApp 99801 00987, and say which lines are hot, which are pumped and which are gravity. We will price each line in the class it needs. GST on CPVC pipe is 18 percent, under HSN 3917; the details are in our CPVC pipe GST and HSN code post.

Questions we get asked

What does SDR 11 mean in CPVC pipe?

The outside diameter is 11 times the wall thickness. Under IS 15778 it is called Class 1, the thicker of the two classes for 1/2 to 2 inch pipe.

Is SDR 13.5 good for hot water?

It is rated for it: 5.6 kg/cm² at 82°C. We still put SDR 11 on hot lines, because that is where the margin is thinnest and the price difference at house sizes is small.

Which is better, CPVC Class 1 or Class 2?

Class 1 (SDR 11) is stronger. Class 2 (SDR 13.5) is cheaper and enough for cold gravity lines. Neither is better everywhere.

Can SDR 11 and SDR 13.5 pipe be joined?

Yes. They have the same outside diameter and use the same SDR 11 fittings and the same CPVC cement.

Prices are our counter prices before GST, checked on 3 November 2026. Classes are from the BIS product manual for IS 15778. Wall thicknesses, pressure ratings, derating factors, stripe colours and fitting standards are from Astral's CPVC PRO catalogue and Ashirvad's CPVC technical manual, linked above.