Douglas Raw Joist / Rafter – Decking and Framing, Sections 60x40mm and 60x80mm

This raw solid douglas rafter / joist is a rectangular-section piece intended for decking joists, floor supports, light interior framing — excluding roof covering structures. Available in two sections — 60x40mm for light structures and 60x80mm for more demanding spans — and in two lengths: 200cm and 240cm. The piece is delivered sawn and untreated.

Raw solid douglas retains its natural sawn appearance — slightly rough texture, characteristic golden-orange hue. Its natural resistance to fungi and insects (class 3) allows it to be used outdoors without mandatory treatment, provided it is not in direct contact with the ground or standing water. The term "rafter" refers to use in roofing or an inclined structure, "joist" refers to horizontal use as a support for decking boards or flooring — the piece itself is identical, only the use changes. Indoor and outdoor use.

Main characteristics

Key points

• ✓ 2 sections — 60x40mm (light structures) and 60x80mm (more demanding spans)
• ✓ 2 lengths — 200cm and 240cm, can be cut on site
• ✓ Raw solid douglas — class 3 — natural resistance, outdoor use away from ground contact
• ✓ Dual use joist / rafter — decking, flooring, light framing excluding roof covering
• ✓ Untreated — to be protected according to final exposure
• ✓ Sold individually — order the exact quantity needed

Uses and applications

As a decking joist: the primary use for these sections. The 60x40mm section is suitable for centres of 40cm maximum under 21mm boards (compliant with DTU 51.4). The 60x80mm section is suited to longer spans between supports (up to 60cm) or thicker boards. For a roof covering structure (roofing, tiles), larger sections are required according to DTU 31.1 — consult a carpenter for sizing.

As a decking joist: horizontal support to which decking boards are fixed. The 60x40mm section is suitable for centres of 40cm maximum under 21mm boards (DTU 51.4), the 60x80mm section for bearing spans up to 60cm. These sections are suited to decking joists and light framing — not designed for roof structures (DTU 31.1 required). Allow a 5 to 8mm gap between joists to ensure ventilation beneath the decking.

As interior framing: partition studs, counter-wall battens, interior cladding support or low-level flooring.

Installation advice

Store pieces flat on a ventilated support, off the ground and sheltered from rain before installation — untreated douglas absorbs moisture quickly. For decking, use A4 stainless steel screws or fixing clips. For timber framing, prefer bolts or galvanised nails in accordance with best practice. Outdoors, apply a fungicide-insecticide treatment before installation if the species is not naturally resistant.

Maintenance and protection

Outdoors, apply a wood saturator or exterior wood oil before installation to slow greying and limit shrinkage cracks. Renew every 2–3 years. Douglas greys naturally without treatment but retains its mechanical properties. Avoid direct contact with the ground.

WoodUp tip

For a douglas 60x40mm decking joist, maintain a maximum centre spacing of 40cm under a 21mm board (DTU 51.4). These sections are suitable for joists and light framing. For a roof structure, sections of at least 75mm are required according to DTU 31.1 — these pieces are not designed for that use. For further guidance on sizing, consult the carpentry guide.

Please note before purchasing: Raw untreated douglas may feature knots and colour variations — natural characteristics of the species, with no impact on structural resistance.

Frequently asked questions

Complementary products

Planed douglas rafter — same species, 4-sided finish

Raw fir rafter — interior alternative

Planed douglas post — same species, square section

Oils and saturators for outdoor douglas timber