Santiago SF purlins are FRP (glass fibre reinforced polymer) box sections in six sizes, from SF-60 (60 × 30 × 3 mm, 0.98 kg/m) to SF-220 (220 × 55 × 4 mm, 4.53 kg/m). They span rafters 1.2 – 6.8 m apart, depending on size and wind pressure, and do not rust in salt air, ammonia or chemical fumes.
Which sizes are available?
| Code | Box (mm) | Cells | kg/m | 6 m length | Typical rafter spacing |
|---|---|---|---|---|---|
| SF-60 | 60 × 30 × 3 | 1 | 0.98 | 5.9 kg | 1.2 – 1.5 m (verandas, small houses) |
| SF-80 | 80 × 40 × 3 | 1 | 1.33 | 8 kg | 1.5 – 2 m (houses, small stores) |
| SF-100 | 100 × 50 × 3.5 | 1 | 1.95 | 11.7 kg | 2.5 – 3 m (poultry and pig farms) |
| SF-120 | 120 × 60 × 3.5 | 1 | 2.36 | 14.2 kg | 3 – 4 m (farms, greenhouses) |
| SF-160 | 160 × 55 × 4 | 2 | 3.60 | 21.6 kg | 4 – 5 m (factories) |
| SF-220 | 220 × 55 × 4 | 2 | 4.53 | 27 kg | 5 – 6.5 m (large factories) |
The code number is the box height in millimetres. The box is always fixed upright, tall side vertical; laid flat it sags.
How far apart can the rafters be?
Maximum rafter spacing for plastic roof sheets or ASA/PVC roof tiles, purlins every 660 mm up the slope, deflection limit L/200. W0 is the basic wind pressure; the five columns match Vietnamese wind zones I to V.
| Code | W0 0.65 kPa | 0.95 kPa | 1.25 kPa | 1.55 kPa | 1.85 kPa |
|---|---|---|---|---|---|
| SF-60 | 1.9 m | 1.6 m | 1.4 m | 1.3 m | 1.2 m |
| SF-80 | 2.5 m | 2.2 m | 2.0 m | 1.8 m | 1.7 m |
| SF-100 | 3.4 m | 2.9 m | 2.6 m | 2.4 m | 2.2 m |
| SF-120 | 4.0 m | 3.5 m | 3.2 m | 2.9 m | 2.7 m |
| SF-160 | 5.2 m | 4.6 m | 4.1 m | 3.8 m | 3.6 m |
| SF-220 | 6.8 m | 6.1 m | 5.5 m | 5.0 m | 4.7 m |
Rows along the eaves, corners and gable ends take stronger wind suction, so use one size larger there. Outside Vietnam, send us the design wind pressure of your site and the roof type, and we will check the size. Spacing above 6.5 m, and roofs carrying solar panels or hanging equipment, need a separate calculation by your engineer. The table helps you choose a size; where a building permit or structural approval is required, have the roof checked by your structural engineer.
Why use FRP purlins instead of steel?
Galvanised steel purlins rust first where the roof sheet sits on them and around the screw holes. In livestock sheds the cause is ammonia, near the sea it is salt, and in plating shops and wastewater plants it is acid fumes. FRP has no iron, so it cannot rust. It weighs about a quarter of steel for the same volume, does not conduct electricity and needs no painting.
FRP is about eight to ten times less stiff than steel, so an FRP purlin is taller than a steel one for the same span, and the price per metre is higher than galvanised steel. In a dry town house, steel purlins are cheaper and work well. FRP pays off on farms, coastal buildings, shrimp ponds, greenhouses and chemical plants, where steel has to be repainted or replaced.
What is supplied with the purlins?
Each purlin is cut to your rafter spacing and drilled at the rafter positions. Fittings are 304 stainless steel: L-brackets, bolts, nuts, washers, sleeves that stop the box being crushed when the bolt is tightened, self-drilling screws for steel rafters, and end caps. Joints always sit on a rafter.
Which roof sheets go on top?
The spans above are for light plastic roofing, such as Santiago ASA/PVC corrugated sheets and ASA/PVC roof tiles. A rust-free purlin with a rust-free sheet and stainless screws leaves nothing on the roof that can corrode. Heavy roofs such as concrete or clay tiles need a separate check.
More technical detail, with installation steps, is on our FRP site: FRP composite purlins and FRP purlin sizes and spans.
Other FRP products
FRP round tube Ø34 for trellises, FRP grating for walkways and platforms, and FRP stairs.
Frequently asked questions
Do FRP purlins rust?
No. FRP is glass fibre and resin with no iron, so salt air, ammonia and dilute acid fumes cannot make it rust.
Which size suits a pig or poultry farm?
Usually SF-100 for rafters 2.5 m apart at wind pressures up to 1.25 kPa. For 3 m rafters use SF-120, or SF-160 at 1.55 kPa and above.
How heavy is a 6 m FRP purlin?
About 5.9 kg for SF-60, 11.7 kg for SF-100, 14.2 kg for SF-120 and 27 kg for SF-220.
Can I order FRP purlins together with roofing sheets?
Yes. Send the roof drawing, rafter spacing and wind pressure, and we quote the purlins, fittings and roofing sheets together.
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.
