Minimum Pitch for PVC Roofing: 20 to 45% Slope

Mr Quyen - Santiago. Posted 14/11/2026

The minimum pitch for a Santiago ASA/PVC roof, tile sheet or corrugated, is a 20% slope: 20 cm of rise for every metre of horizontal run, which is about 11.3° or 2.4 in 12. The confirmed range is 20 – 45%, about 11 – 24°. Santiago does not recommend its sheets on slopes under 20%, because rain drains off too slowly.

A steep grey tile roof, Vietnam

A steep grey tile roof, Vietnam

What is the minimum pitch for PVC roofing?

A 20% slope. Every joint in a sheet roof (side laps, screw holes, the ridge) relies on water running past it quickly. At 20% and above, rain leaves the roof before it can build up at a lap. Under 20%, water slows down, sits in the valleys longer and can be blown sideways under a lap or up towards a screw cap. Santiago's installation rules give a slope of 20 – 45% for both the tile sheet and the 5, 6 and 11-wave sheets.

How do percent, degrees and x-in-12 convert?

Builders measure slope three ways. Percent is rise ÷ run × 100. Degrees is the angle whose tangent is rise ÷ run. "x in 12" is the rise over a run of 12, used in the USA and some other markets, and equals percent × 12 ÷ 100.

Slope %	Degrees	x in 12	For Santiago sheets
10%	5.7°	1.2 in 12	Too flat, not recommended
15%	8.5°	1.8 in 12	Too flat, not recommended
16.7%	9.5°	2 in 12	Too flat, not recommended
20%	11.3°	2.4 in 12	Minimum
25%	14.0°	3 in 12	Within range
30%	16.7°	3.6 in 12	Within range
33.3%	18.4°	4 in 12	Within range
40%	21.8°	4.8 in 12	Within range
41.7%	22.6°	5 in 12	Within range
45%	24.2°	5.4 in 12	Top of the confirmed range
50%	26.6°	6 in 12	Above the confirmed range: ask Santiago first

The figures above are plain geometry. If your drawings give a pitch in a unit not listed, convert it to percent and compare it with 20 – 45%.

Red tile roof with several slopes, Vietnam

Red tile roof with several slopes, Vietnam

How much rise does a lean-to roof need?

A lean-to has one slope, from a high wall plate down to a low beam. Take a lean-to that projects 3.0 m from the house wall.

Slope	Rise over 3.0 m run	Length along the slope	Tile sheet length in 219 mm steps
20%	0.60 m	3.06 m	14 steps = 3.066 m
30%	0.90 m	3.13 m	15 steps = 3.285 m
40%	1.20 m	3.23 m	15 steps = 3.285 m

The length along the slope is √(run² + rise²). Add the eave overhang your installer plans before rounding up to whole 219 mm steps. At 20% the wall end of this lean-to has to be 60 cm higher than the outer end; if the wall is not tall enough for that, the roof will be too flat for these sheets.

How does pitch work on gable and hip roofs?

On a gable roof each face is a simple slope. An 8 m wide house has a 4 m run on each side; at 30% the ridge sits 1.2 m above the wall plates and each face is about 4.18 m long along the slope. The top purlin goes 15 – 18 cm below the ridge so the ridge cap can be screwed down.

On a hip roof the 20 – 45% rule applies to every face, including the triangular hip ends. The hip lines themselves run at a lower angle than the faces, but they are covered by diagonal hip ridge pieces, and the rain runs off the faces, not along the hip. Where hips meet a ridge, a three-way piece closes the junction; on a pyramid roof a four-way piece closes the top.

Orange tile roof slope, Vietnam

Orange tile roof slope, Vietnam

What happens if a PVC roof is below 20%?

Rain drains slowly and stays in the valleys and at the laps for longer.
Wind can push water sideways under the one-wave side lap.
Leaves and dust settle instead of washing off.
The roof is outside Santiago's installation rules, and the 10-year warranty applies to roofs installed as Santiago recommends.

If the building only allows a very low slope, change the frame so the slope reaches 20%, or choose another roof type for that building. Do not lay the sheets flatter and hope for the best.

Which other rules go with the slope?

Rule	Tile sheet	Corrugated sheets
Slope	20 – 45%	20 – 45%
Purlin spacing	440 or 660 mm, one under each tile step foot	Less than 700 mm
Top purlin	15 – 18 cm below the ridge	15 – 18 cm below the ridge
Side lap	One wave	One wave
Screws	70 mm, through the top of the wave over a purlin, 4 – 5 sets per m²	Same
Holes	Pre-drilled 6 mm	Pre-drilled 6 mm

Each sheet is cut to the length of its roof face, so one sheet runs from ridge to eave and the face needs no joints along its length.

Gable edge of a red tile roof, Vietnam

Gable edge of a red tile roof, Vietnam

What does a correctly pitched tile-sheet roof look like on site?

Mr Quyen shows a green ASA/PVC sheet in the Santiago factory, then climbs onto a grey tile-profile roof that installers are still screwing down. Near the end he and a colleague walk along a finished grey tile roof next to the gutter.

Santiago uPVC tile roofs on site (Santiago video on YouTube).

Santiago – a leading exporter of ASA/PVC roofing from Vietnam

Santiago roofing is produced and loaded into containers at our factory in Vietnam. It has been exported to India since 2023, Thailand since 2024 and the USA since 2025. Every export shipment comes with a commercial invoice, packing list, bill of lading and a certificate of origin (C/O) issued by Vietnam's Ministry of Industry and Trade, which importers use to claim the duty preference of their trade agreement.

Item	Details
HS code	3925.90.00 (ASA/PVC roofing sheets)
Certificate of origin	Form D (ASEAN), Form AI (India), Form AK / VK (Korea), Form AJ / VJ (Japan), Form VC (Chile), CPTPP proof of origin
Shipped from	Vietnam, by container

Certificate of origin Form AI (ASEAN–India) for Santiago ASA/PVC roofing sheets, HS 39259000, certified on 24 September 2026. Buyer details are hidden.

Certificate of origin Form AI (ASEAN–India) for Santiago ASA/PVC roofing sheets, HS 39259000, certified on 24 September 2026. Buyer details are hidden.