Yes, a jigsaw is one of the best tools for making notch cuts in decking boards around posts — it's manoeuvrable, easy to control, and handles both straight and curved cuts with ease. With a bit of careful measuring and the right blade, most confident DIYers can achieve a clean, tight fit that looks professional.
Why a Jigsaw Works Well for This Job
Unlike a circular saw, which can only make straight cuts and can't easily stop mid-board, a jigsaw lets you cut in multiple directions without repositioning the board. This makes it perfect for the notch cut (also called a cope cut) needed to fit a decking board snugly around a post. You can plunge-cut, change direction, and finish corners cleanly — all in one pass.
What You'll Need
- Jigsaw with a wood-cutting blade (medium tooth, 6–10 TPI works well for timber decking)
- Tape measure and pencil
- Speed square or combination square
- Scrap timber or offcut for test cuts
- Safety glasses and hearing protection
- Dust mask (especially important when cutting treated timber — see safety note below)
- Clamps to secure the board
How to Mark the Notch Accurately
Getting the measurement right before you cut is the most important step. A sloppy notch looks untidy and can let water pool around the post base.
- Measure the post position — measure from the last fixed board (or the rim joist) to the near face of the post, and from the edge of the deck to each side of the post.
- Transfer the measurements to your decking board using a pencil and square. Mark all four lines of the notch clearly.
- Double-check by holding the board in position and confirming the marks line up with the post before cutting.
- Allow a 3–5 mm gap around the post to account for timber movement and to let water drain away — a tight fit can trap moisture and accelerate rot.
Making the Cut
- Secure the board firmly with clamps on a stable work surface.
- Drill a small starter hole (10–12 mm) inside each internal corner of the notch. This gives the jigsaw blade room to turn and prevents the corners from cracking.
- Cut along your marked lines, keeping the jigsaw base plate flat on the board at all times.
- Cut the two side lines first, then the back line — this stops the offcut from pinching the blade.
- Test-fit the board. If it's slightly tight, use a rasp, chisel, or coarse sandpaper to ease the fit rather than re-cutting.
Blade and Speed Tips
| Decking Material | Recommended Blade | Speed Setting |
|---|---|---|
| Treated pine (H3.2/H4) | Wood blade, 6–8 TPI | Medium–high |
| Hardwood (kwila, vitex) | Fine wood or bi-metal blade | Medium |
| Composite decking | Fine-tooth wood blade | Medium |
For hardwoods, let the blade do the work — don't force it or you'll get a rough, splintered edge.
Treating the Cut Ends
This step is often skipped but is critical in New Zealand's variable climate. All cut ends of treated timber must be re-treated with an approved end-grain preservative to maintain the timber's hazard class rating. This is especially important for H3.2 or H4 treated pine used in ground-contact or exposed situations. Check the timber manufacturer's recommendations and use a compatible end-grain treatment product, available from Bunnings or Mitre 10.
For composite decking, check the manufacturer's instructions — some products require cut ends to be capped or sealed.
Safety Note: Working With Treated Timber
Most NZ decking timber is treated with preservatives (such as CCA or LOSP). Cutting treated timber produces fine dust that can be harmful if inhaled. Always:
- Wear a P2-rated dust mask
- Work outdoors or in a well-ventilated area
- Never burn treated timber offcuts
Refer to WorkSafe NZ for guidance on working safely with treated timber.
NZ Building Code Considerations
If your deck is new or you're making significant changes, it may require a building consent depending on its height, size, and proximity to boundaries. Decks over a certain height above ground may require consent — check with your local council or the MBIE Building Performance website to confirm the current threshold that applies to your project. Schedule 1 of the Building Act lists some exemptions, but you should always confirm with your local council before starting work. The MBIE Building Performance website has clear guidance on when consent is needed.
Structural decking work should also comply with NZS 3604 (Timber-framed buildings) where applicable.
When to Call a Professional
Cutting boards around posts is well within DIY territory for most homeowners. However, consider hiring a qualified deck builder if:
- You're unsure about the structural layout of the deck frame around the post
- The post is a structural or bracing post and you're concerned about cutting or notching near it
- You need a building consent and want the work signed off correctly
- You're working with expensive hardwood and want a guaranteed result
A licensed deck builder can also advise on the best decking layout to minimise awkward cuts in the first place. You can find qualified local deck builders on tradedirectory.co.nz.
Licensed Building Practitioner (LBP)
