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Raw douglas rafter
Rough-sawn untreated solid Douglas fir rafter and joist, sections 60x40mm and 60x80mm, lengths 200cm and 240cm, sold individually. Class 3 natural durability: suitable for timber decking or exterior framing not in contact with the ground without mandatory prior treatment — to be protected according to exposure once installation is complete. Decking, framing, flooring — excluding roof structures; cut to length according to layout and screw or nail to joists.
Joist / Rough-Sawn Douglas Fir Rafter - Decking and Framing, Sections 60x40mm and 60x80mm
This rough-sawn solid Douglas fir rafter / joist is a rectangular-section piece intended for decking joists, floor supports, light interior framing — excluding roof structure. 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 rough from sawing and untreated.
Rough-sawn solid Douglas fir retains its natural sawn appearance — slightly rough texture, characteristic golden-orange colour. 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" to horizontal use as a support for decking or flooring boards — the piece itself is identical, only the use changes. For interior and exterior use.
Main characteristics
| Characteristic | Value |
|---|---|
| Species | Solid Douglas fir |
| Finish | Rough-sawn - untreated |
| Available sections | 60x40mm and 60x80mm |
| Available lengths | 200cm and 240cm |
| Use class | Class 3 - natural durability, exterior above ground |
| Treatment | Untreated - to be protected according to use |
| Use | Decking, framing, flooring - excluding roof structure |
| Sawing | Sold individually |
Key points
- ✓ 2 sections - 60x40mm (light structures) and 60x80mm (more demanding spans)
- ✓ 2 lengths - 200cm and 240cm, on-site cutting possible
- ✓ Rough-sawn solid Douglas fir - class 3 - natural durability, exterior above ground
- ✓ Dual use joist / rafter - decking, flooring, light framing excluding roofing
- ✓ Untreated - to be protected according to final exposure
- ✓ Sold individually - order the exact quantity required
Uses and applications
As decking joist: the primary use for these sections. The 60x40mm section is suitable for spacings of 40cm maximum under a 21mm board (compliant with DTU 51.4). The 60x80mm section is suited to longer spans between supports (up to 60cm) or thicker boards. For a roof structure (roofing, tiles), larger sections are required in accordance with DTU 31.1 — consult a carpenter for sizing.
As decking joist: horizontal support to which decking boards are fixed. The 60x40mm section is suitable for spacings of 40cm maximum under a 21mm board (DTU 51.4), the 60x80mm section for bearing spans up to 60cm. These sections are suited to decking joists and light framing — not sized for roof structure (DTU 31.1 required). Allow a gap of 5 to 8mm between joists to allow ventilation under the deck.
For interior framing: partition studs, counter-wall batten, interior cladding support or ground floor.
Installation advice
Store pieces flat on a ventilated support, off the ground and sheltered from rain before installation — untreated Douglas fir absorbs moisture quickly. For decking, use A4 stainless steel screws or fixing clips. For 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 durable.
Maintenance and protection
Outdoors, apply a saturator or exterior wood oil before installation to slow greying and limit shrinkage cracks. Renew every 2–3 years. Douglas fir greys naturally without treatment but retains its mechanical properties. Avoid direct contact with the ground.
WoodUp tip
For a Douglas fir 60x40mm decking joist, maintain a maximum 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 in accordance with DTU 31.1 — these pieces are not sized for that use. For further guidance on sizing, consult the structural guide.
Before buying: Untreated rough-sawn Douglas fir may show knots and colour variations — natural characteristics of the species, with no impact on structural strength.
Frequently asked questions
Which section to choose between 60x40mm and 60x80mm?
The 60x40mm section is suitable for light structures: decking joists at spacing ≤ 40cm, light roofing rafters at span ≤ 1.5m, framing battens. The 60x80mm section is suited to longer spans, heavier loads (heavy tiles, snow) or wider spacings. If in doubt about sizing, consult a carpenter or timber engineering consultant.
What is the difference between a rafter and a joist?
It is the same piece of timber — the difference lies solely in the use. As a rafter, the piece is laid at an inclined bearing under a roof covering. As a joist, it is laid flat, horizontally, as a support for decking or flooring boards. The cross-section and length are identical in both cases.
Does this Douglas fir joist need to be treated before use?
Untreated Douglas fir is naturally resistant to fungi and insects (natural class 3) — it can be used outdoors in sheltered conditions without treatment. For direct exposure to the weather or contact with a damp substrate, apply a saturator or exterior wood oil before installation and renew every 2–3 years.
Can these pieces be cut to the desired length?
Yes. Solid Douglas fir cuts cleanly with a circular saw or mitre saw. Order the length immediately above your requirement (200 or 240cm) and cut on site. Deburr the cut edges and apply a protective coat to the cut ends if used outdoors.
Which joist section for a deck with 21mm boards?
For 21mm thick boards laid on joists, the 60x40mm section with a spacing of 40cm maximum is the standard configuration. For 27mm boards or dense timbers (IPE, thick Douglas fir), the spacing can increase to 50cm. The 60x80mm section is recommended if the spacing exceeds 50cm or if you are laying thick cladding boards.
Complementary products
Planed Douglas fir rafter - same species, 4-sided finish
Rough-sawn fir rafter - interior alternative
- Species/material
- Douglas
- Use class
- Class 3 - Above ground contact outdoors
- Delivery label
- Framework
CHEVDOUBRU60402000
955 Products
3420610005320
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Dispatched within 6-8 weeks
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Satisfied or refunded
Satisfied or refunded if returned within 14 calendar days (Sundays and public holidays included) following delivery.
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