How Do I Calculate the Number of Fixings Needed for a New Deck?

Calculating the number of fixings for a new deck is a core quantity surveying task — and getting it right saves you money, wasted trips to the hardware store, and delays on site. The good news is that with a methodical approach and your deck plans in hand, most homeowners can produce a reasonably accurate fixings schedule before they buy a single screw.

Understand What 'Fixings' Covers

For a typical NZ timber deck, fixings fall into several categories:

• Decking screws or hidden clips — fastening the deck boards to the joists
• Joist hanger nails or screws — securing joist hangers to the bearer/ledger
• Structural bolts and coach screws — connecting posts, bearers, and ledger boards
• Post base hardware — fixing posts to concrete pads or piles
• Framing nails or screws — general framing connections
• Balustrade fixings — if your deck is elevated and requires a handrail

Each category needs its own take-off (quantity calculation), so work through them one at a time.

Step 1 — Draw Up or Obtain Your Deck Plan

Before you count a single fixing, you need an accurate plan showing:

• Overall deck dimensions (length × width)
• Joist spacing (typically 400 mm or 600 mm centres for residential decks under NZS 3604)
• Bearer and post layout
• Ledger board attachment points (if the deck attaches to the house)

If your deck requires a building consent — generally when it is more than 1.5 m above ground or over a certain area — your council will require stamped plans anyway. Always confirm consent requirements with your local council before starting; MBIE Building Performance has useful guidance on Schedule 1 exemptions.

Step 2 — Calculate Decking Screws or Hidden Clips

This is usually the largest single fixing quantity.

Decking screws

1. Count the number of deck boards — divide the deck width by the board width plus the gap (e.g. 90 mm board + 5 mm gap = 95 mm; a 4,000 mm wide deck needs roughly 42 boards).
2. Count the number of joists each board crosses — this equals the number of fixings per board run.
3. Multiply: boards × joists × fixings per crossing (typically 2 screws per board per joist).

Example: 42 boards × 10 joists × 2 screws = 840 screws. Add a 10–15% wastage allowance for snapped screws, mis-drives, and offcuts.

Hidden clips

Manufacturers specify clips per lineal metre of board edge — check the product datasheet for the exact rate, as it varies by brand.

Step 3 — Joist Hanger Nails or Screws

Count the total number of joist hangers on your plan (one per joist end, both sides where applicable). Each hanger manufacturer specifies the number and size of nails or screws required — this information is on the product packaging or technical datasheet. As a rough guide, a standard joist hanger uses around 6–10 nails. Multiply hangers × nails per hanger, then add 10% wastage.

Step 4 — Structural Bolts and Coach Screws

Use your framing plan to count each bearer-to-post, ledger-to-house, and post-to-bearer connection. Standard practice under NZS 3604 typically requires:

Always follow the fixing schedule in your consent documents or the hardware manufacturer's load tables — do not substitute a smaller fixing to save money.

Step 5 — Post Base Hardware

Count the number of posts, then confirm the post base product's fixing requirements (number and diameter of anchor bolts into concrete). This information is always on the manufacturer's technical sheet.

Step 6 — Balustrade Fixings

If your deck is above the ground at a height that triggers the NZ Building Code barrier requirements, a compliant balustrade is required. Check with your local council or refer to MBIE Building Performance guidance for the applicable threshold. Count the number of balustrade posts and rails, then refer to the balustrade system supplier's installation guide for fixing quantities — these vary significantly between systems.

Step 7 — Compile Your Fixings Schedule

A simple table works well:

Fixings are generally sold in boxes — round up to the nearest box size to avoid short orders.

Material Quality and Corrosion

In NZ's coastal and high-humidity environments, corrosion resistance is critical. BRANZ recommends stainless steel or hot-dip galvanised fixings for exterior decks, especially within a few kilometres of the coast. Check that your fixings are compatible with any treated timber (H3.2 or H4 treated timber can corrode certain metals faster).

When to Call a Professional

If your deck is complex — elevated, on a slope, attached to the house, or requires an engineer's input — it's worth engaging a Licensed Building Practitioner (LBP) for the structural work. You can find qualified local deck builders and quantity surveyors on tradedirectory.co.nz. A quantity surveyor can also produce a full materials schedule and help you avoid costly over- or under-ordering.

Note: if your deck involves any electrical work (outdoor lighting, power points), this is restricted work under the Electricity Act and must be carried out by a registered electrician — see EWRB for details.

Sources & Further Reading

• MBIE Building Performance — Decks and consent requirements
• BRANZ — Weathertightness and fixings guidance
• Standards NZ — NZS 3604 Timber-framed buildings
• Licensed Building Practitioners — Find an LBP
• Bunnings NZ — Decking fixings and hardware
• Mitre 10 NZ — Decking materials and fixings