Building a simple deck step without a stringboard is very achievable for a competent DIYer. Instead of cutting angled stringers, you construct a solid box frame — essentially a rectangular timber frame that sits on the ground and supports your tread — which is sturdy, straightforward to build, and suits most single-step situations.
What Is a Box-Frame Step?
A box-frame step (sometimes called a platform step) uses a rectangular perimeter frame made from treated timber, with internal noggins for support, topped with decking boards as the tread. There are no angled cuts or stringboards involved. It's the go-to method for a single step down from a deck to a path or lawn.
NZ Building Code and Consent Considerations
Before you pick up a saw, check whether your step needs a building consent. Under Schedule 1 of the Building Act 2004, many small deck structures are exempt — but the rules depend on height, size, and your specific council. As a general guide, a single freestanding step that is low to the ground is unlikely to need consent, but always confirm with your local council before starting.
For decks and steps, the NZ Building Code clause B1 (Structure) and B2 (Durability) are the key references. Timber used in ground-contact or exposed situations must meet the correct hazard class (H3.2 or H4) as set out in NZS 3602. Check with your timber supplier — PlaceMakers and Mitre 10 staff can advise on the right treated pine for your application. For general guidance on the Building Code, visit MBIE Building Performance.
Materials You'll Need
- Treated timber for the frame — typically 140 × 45 mm or 190 × 45 mm H3.2 treated pine (height depends on your step rise)
- Decking boards for the tread — 90 × 19 mm or 140 × 19 mm H3.2 treated pine or hardwood decking
- Galvanised or stainless steel framing nails or screws — never use plain steel fixings outdoors
- Post anchors or packing if the frame needs to be raised off the ground
- Concrete pavers or compacted gravel as a base
- Saw, drill/driver, square, tape measure, and a level
Step-by-Step: Building the Box Frame
1. Determine Your Rise and Run
A comfortable step rise is between 150 mm and 190 mm, and the going (run) should be at least 250 mm — ideally 300 mm or more for comfort. Measure the height from the deck surface to the ground to work out how deep your frame needs to be. If the drop is more than about 190 mm, you may need two stacked box frames.
2. Prepare the Base
Never sit timber directly on bare soil. Lay a bed of compacted gravel or set concrete pavers level on the ground where the step will sit. This keeps the frame off the ground, improves drainage, and extends the life of your timber.
3. Cut and Assemble the Frame
Cut your treated timber to form a rectangle — two long side pieces and two shorter end pieces. The width should match your deck (typically 900 mm minimum for a comfortable step). Nail or screw the corners together using galvanised joist hanger nails or 75–90 mm structural screws. Add one or two internal noggins across the middle for rigidity, especially if the tread span is over 600 mm.
| Frame component | Typical size | Timber grade |
|---|---|---|
| Side rails | 140 × 45 mm or 190 × 45 mm | H3.2 treated pine |
| End pieces | Same as side rails | H3.2 treated pine |
| Noggins | 90 × 45 mm or 140 × 45 mm | H3.2 treated pine |
| Tread boards | 90 × 19 mm or 140 × 19 mm | H3.2 treated pine |
4. Fix the Frame in Position
Place the completed frame on your prepared base and check it is level in both directions. If the step will sit directly against the deck, you can toe-screw or use a joist hanger bracket to connect it to the deck's rim joist for extra stability. If it's freestanding, ensure it cannot shift by using galvanised post anchors or by packing it securely.
5. Lay the Tread Boards
Fix your decking boards across the top of the frame, leaving a 3–5 mm gap between boards for drainage. Use two stainless steel or hot-dipped galvanised screws per board per joist. Pre-drill near the ends to prevent splitting. Ensure the boards overhang the front of the frame by about 25 mm for a neat, finished look and to help shed water.
6. Finishing Touches
Sand any rough edges and apply a decking oil or stain to match your existing deck. Resene and Dulux both offer suitable exterior timber coatings. Check that the step feels solid, doesn't rock, and that there are no protruding fixings or splinters.
Safety Notes
- If the deck is more than 1 metre above the ground, handrails and balustrades are required under the NZ Building Code — check with your council.
- Wear appropriate PPE when cutting treated timber: a dust mask (P2 rated), safety glasses, and gloves. Treated timber preservatives can be hazardous. See WorkSafe NZ for guidance.
- Dispose of treated timber offcuts responsibly — do not burn them.
When to Call a Professional
If your step is part of a larger deck project, if the deck is elevated, or if you're unsure about consent requirements or structural connections, it's worth getting a qualified deck builder to assess or complete the work. Licensed Building Practitioners (LBPs) are required for certain restricted building work — check LBP to find a registered professional. You can also find experienced local deck builders on tradedirectory.co.nz.
Licensed Building Practitioner (LBP)
