If you've ever wandered the timber aisle at your local building merchant and wondered why some planks look smooth and others look like they just came off a sawmill, you're not alone. The difference comes down to how the timber has been processed after cutting — and choosing the right type can save you time, money, and headaches on your project.
What Is Rough-Sawn Timber?
Rough-sawn timber (sometimes called rough-cut or undressed timber) is wood that has been cut from the log by a sawmill but has not been further processed. The surface is uneven, slightly fuzzy, and may have saw marks running along the grain. Dimensions are approximate — a piece sold as 100 × 50 mm rough-sawn will typically measure close to those figures, but with some variation.
Because it skips the extra machining steps, rough-sawn timber is generally less expensive and is available in a wider range of sizes. It also retains more of its natural moisture, so it's important to check whether it has been dried (seasoned) or is still "green" (freshly cut).
Common uses for rough-sawn timber:
- Framing and structural work (where it will be hidden inside walls)
- Retaining walls and garden landscaping
- Farm fencing and agricultural buildings
- Temporary formwork for concrete
- Rustic feature walls or cladding where a natural look is desired
What Is Dressed Timber?
Dressed timber (also called DAR — Dressed All Round — or surfaced timber) has been run through a planer or moulder after sawmill cutting. This process smooths all four faces, making the timber consistent in size, straight, and ready to use without further preparation.
Because material is removed during dressing, a dressed piece is always smaller than its nominal (rough-sawn) size. For example, a piece nominally described as 100 × 50 mm rough-sawn might finish at around 90 × 45 mm dressed — though exact finished sizes vary by supplier, so always confirm actual dimensions before ordering.
Common uses for dressed timber:
- Interior joinery: skirting boards, architraves, shelving
- Decking and handrails
- Exposed structural elements like beams and posts
- Furniture and cabinetry
- Any application where a smooth, paintable, or stainable surface is needed
Key Differences at a Glance
| Feature | Rough-Sawn | Dressed (DAR) |
|---|---|---|
| Surface finish | Rough, saw-marked | Smooth, planed |
| Dimensional accuracy | Approximate | Consistent and precise |
| Actual vs nominal size | Close to nominal | Smaller than nominal |
| Cost | Lower | Higher |
| Moisture content | Often higher (check) | Usually kiln-dried |
| Typical use | Structural, hidden, rustic | Joinery, exposed, finished |
| Paint/stain ready? | Needs sanding/prep | Generally yes |
Sizes, Grades, and the NZ Building Code
In New Zealand, structural timber used in house framing must comply with NZS 3604:2011 (Timber-framed buildings), which specifies minimum grades and sizes for different applications. BRANZ provides excellent guidance on how these standards apply in practice.
Timber grading in NZ is typically done to NZS 3631 or AS/NZS 1748, and you'll see grades like MSG8, MSG10, or VSG (visually stress-graded) on structural timber. Always check that structural timber carries the correct grade stamp for your application — this matters whether it's rough-sawn or dressed.
For non-structural work like shelving or joinery, grading is less critical, but look for timber that is straight, free of large knots, and at an appropriate moisture content for interior use (generally below 18%).
Which Should You Choose?
The right choice depends on your project:
- Choose rough-sawn when the timber will be hidden (inside wall framing, under decking), when you need a rustic aesthetic, or when budget is tight and surface finish doesn't matter.
- Choose dressed timber when the timber will be visible, when you need precise dimensions for joinery or fitting, or when you want a surface that's ready to paint or stain without major prep work.
For decking specifically, many NZ homeowners use dressed or H3.2-treated timber for above-ground outdoor use, while posts in the ground require H5-treated timber. Treatment levels are set by MBIE Building Performance and are non-negotiable for durability and compliance.
Where to Buy Timber in NZ
You'll find both rough-sawn and dressed timber at major NZ suppliers including PlaceMakers, Mitre 10, and Bunnings. Specialist timber merchants and sawmills often stock a wider range of species and sizes, and can be a great option for larger or unusual orders.
As a guide, dressed timber typically costs noticeably more per lineal metre than equivalent rough-sawn, reflecting the extra processing — but you save time on preparation.
Tips for Handling and Storing Timber
- Store timber flat and off the ground, supported at regular intervals to prevent bowing.
- Keep it dry — cover with a tarp but allow airflow to prevent mould.
- Acclimatise interior timber indoors for several days before installation to let it adjust to the room's humidity.
- Check for warp, bow, or twist before buying — sight down the length of each piece.
When to Call a Professional
While selecting and cutting timber is generally DIY-friendly, some work requires a licensed tradesperson. Any structural framing that forms part of a building's primary structure may require a Licensed Building Practitioner (LBP) to carry out or supervise the work under the NZ Building Act. Check the requirements at Licensed Building Practitioners.
If your project involves structural changes, a building consent may be required — always check with your local council first. For complex carpentry, decking, or framing projects, it's worth getting a qualified carpenter involved. You can find experienced local tradespeople on tradedirectory.co.nz.