How to Calculate Window and Door Quantities for a New Build

Calculating window and door quantities for a new build involves systematically reading your architectural drawings, identifying every opening, and compiling a detailed schedule that lists each unit's type, size, and specification. Getting this right early saves money, avoids delays, and helps your quantity surveyor (QS) produce an accurate cost plan. Here's how to approach it methodically.

Start With Your Architectural Drawings

Your primary source of information is the architectural drawing set, which typically includes:

• Floor plans – show the position and width of every door and window opening
• Elevations – show the height of openings and how they look from outside
• Sections – confirm head heights, sill heights, and reveal depths
• Window and door schedule – a table (often drawn by the architect) listing every unit with a reference code

If your architect has already produced a window and door schedule, your job is to verify it against the plans rather than start from scratch. Discrepancies between the schedule and the drawings are common and can be costly if not caught early.

Understand the Referencing System

Architects typically label each opening with a reference tag (e.g., W1, W2, D1, D2) on the floor plan and elevation, then describe each tag in the schedule. When counting quantities:

1. Go through each floor plan systematically — room by room, or elevation by elevation.
2. Mark off each tag as you count it to avoid double-counting or missing openings.
3. Tally how many times each reference appears (e.g., W3 may appear six times, meaning six identical windows).

A simple tally sheet or spreadsheet works well for this. Many QS professionals use cost-planning software, but a well-organised spreadsheet is perfectly adequate for a homeowner checking their own build.

Build Your Window and Door Schedule

A good schedule captures everything a supplier needs to quote and manufacture. Use a table like this as a guide:

DGU = double-glazed unit. Under the NZ Building Code, new residential buildings must meet minimum thermal performance requirements (clause H1), which in most NZ climate zones now effectively requires double glazing. Always confirm the current H1 requirements with your designer or council, as these have been updated in recent years.

Measure Openings Correctly

When dimensions aren't clearly stated on drawings, you'll need to scale them — but only do this as a cross-check, not as your primary source. Scaling introduces error. The nominal size (the rough opening size in the framing) and the unit size (the actual joinery frame) differ, so clarify with your architect or joinery supplier which dimension is being quoted.

• Rough opening (RO): the framed hole in the wall structure
• Unit size: the manufactured joinery frame that fits into the RO
• Daylight opening: the clear glass area — relevant for natural light calculations

For NZ timber-framed construction to NZS 3604, lintels above openings must be sized to suit the span and load — your builder or engineer handles this, but it's worth knowing that large openings may require engineering input.

Account for All Opening Types

Don't overlook less obvious openings:

• Garage doors – often large and expensive; confirm whether roller, sectional, or tilt
• Skylights and roof windows – shown on roof plans and sections
• Bi-fold and stacker doors – count the number of panels, not just the opening
• Internal doors – often forgotten in early cost plans
• Access hatches – to roof space or under-floor areas

Check Against the Healthy Homes and Consent Requirements

For rental properties, Tenancy Services Healthy Homes standards require adequate ventilation and draught stopping — window type and quantity can affect compliance. For all new builds, your local council will check that window and door placements meet the Building Code (including natural light under clause G7 and ventilation under G4). Confirm consent requirements with your council before finalising your schedule.

Cross-Check Your Quantities

Once you have your schedule, cross-check it by:

1. Counting all tags on each elevation and confirming they match your schedule totals
2. Checking the schedule against the joinery supplier's quote — any discrepancy is a red flag
3. Having your QS or builder review the schedule before ordering

A missed window or incorrectly sized door can cause significant delays and cost overruns, particularly given current lead times for joinery manufacturing in New Zealand.

When to Call a Professional

While a homeowner can compile a preliminary window and door schedule as a useful exercise, for contract documentation and cost planning you should engage a licensed quantity surveyor or your architect. A QS will produce a formal elemental cost plan that prices your joinery schedule against current market rates and flags any specification gaps. For complex or large builds, errors in the schedule can translate directly into budget blowouts. You can find qualified quantity surveyors and other building professionals on tradedirectory.co.nz.

Also note: any structural changes to opening sizes during construction may require a building consent amendment — always check with your council before altering approved plans.

Sources & Further Reading

• MBIE Building Performance – NZ Building Code
• BRANZ – Building Research
• Standards NZ – NZS 3604 Timber-framed Buildings
• Tenancy Services – Healthy Homes Standards
• Licensed Building Practitioners