SF-120 is an FRP box purlin 120 mm tall and 60 mm wide with a 3.5 mm wall, weighing 2.36 kg per metre. It spans 3.2 m at 1.25 kPa basic wind pressure, so it is the usual size for farms with 3 m rafters and for greenhouses with rafters 3.5 – 4 m apart in low-wind areas.
| Item | SF-120 |
|---|---|
| Section | Box 120 × 60 mm, 3.5 mm wall, single cell |
| Weight | 2.36 kg/m (a 6 m length is about 14.2 kg) |
| Material | Pultruded FRP, no metal |
| Fittings | 304 stainless L-brackets, bolts, sleeves, screws and end caps |
How far can SF-120 span?
| Basic wind pressure W0 | 0.65 kPa | 0.95 kPa | 1.25 kPa | 1.55 kPa | 1.85 kPa |
|---|---|---|---|---|---|
| Maximum rafter spacing | 4.0 m | 3.5 m | 3.2 m | 2.9 m | 2.7 m |
For plastic roof sheets or ASA/PVC roof tiles, purlin rows 660 mm apart, deflection limit L/200.
When do I choose SF-120 over SF-100?
- Farms with 3 m rafters at 0.95 – 1.25 kPa.
- Eave, corner and gable rows of a roof that uses SF-100 in the field.
- Greenhouses with rafters 3.5 – 4 m apart at 0.65 kPa.
- Factories with 6 m frames that add a middle rafter, giving 3 m spacing.
Why a tall box with a thin wall?
FRP bends about eight to ten times more than steel under the same load, so FRP purlins are sized by deflection. Height adds stiffness much faster than wall thickness does, which is why SF-120 is 120 mm tall with a 3.5 mm wall instead of a lower, thicker box.
Greenhouses and net houses
Misting keeps greenhouse air wet, and fertiliser and spray residue settle on the frame, so steel purlins rust quickly. SF-120 does not. If tomato or cucumber wires will hang from the purlins, send us the number of rows and the crop, because the span table covers only the roof, workers and wind.
Frequently asked questions
What size is SF-120?
A single-cell FRP box 120 × 60 mm with a 3.5 mm wall, 2.36 kg per metre.
Which size for a greenhouse with 4 m rafters?
SF-120 at 0.65 kPa basic wind pressure; at 0.95 – 1.25 kPa use SF-160.
Does SF-120 need anti-rust paint?
No. It contains no metal, so it needs no anti-rust paint.
All six sizes with the full span table: FRP Composite Purlin – SF Series.
Contact: Santiago Import Export Co., Ltd, Vietnam. WhatsApp +84 935 391 495 (Mr. Quyen), hotline +84 965 437 316 (Mrs. Ly), email salessantiagoroofing@gmail.com.
Updated October 2026.
