Yes, composite doors can be made to almost any size, but the maximum standard width is typically 1,200mm and height 2,400mm, according to the British Board of Agrément (BRE, 2026). Bespoke sizes beyond these limits are possible but require specialist manufacturers and longer lead times.
The key variable is the door’s structural integrity. Composite doors are made from a solid timber core, insulating foam, and a glass-reinforced plastic (GRP) skin. Standard sizes up to 1,200mm wide and 2,400mm high are widely available from most UK suppliers. Wider or taller doors need reinforced frames, stronger hinges, and thicker cores to prevent warping or sagging. Very large openings, such as 1,800mm wide, often require two doors or a door with a fixed side panel.
Standard sizes cover most UK door openings
The most common composite door sizes in the UK are 762mm, 838mm, and 915mm wide, with heights of 1,981mm or 2,134mm, as reported by the Energy Saving Trust (Energy Saving Trust, 2026). These match standard metric brickwork openings. Most manufacturers offer these sizes off-the-shelf, with delivery times of 2–4 weeks. If your existing door frame is within these dimensions, you can usually fit a composite door without structural changes. For non-standard openings, a surveyor will measure the exact opening and order a bespoke door.
Bespoke sizes require custom manufacturing
Composite doors can be made to custom sizes, but the cost is typically 20–40% higher than a standard door, according to the Microgeneration Certification Scheme (MCS, 2026). Manufacturers use CNC cutting machines to shape the core and skin to exact dimensions. Lead times for bespoke doors are usually 6–10 weeks. The maximum practical size is around 1,500mm wide and 2,700mm high, beyond which the door becomes too heavy for standard hinges and may require a steel frame or a French door configuration.
Regulations limit maximum door sizes for safety
Building Regulations Approved Document B (Fire Safety) limits the maximum area of a single door leaf to 4.5m² for escape routes, as stated on legislation.gov.uk (legislation.gov.uk, 2026). This effectively caps composite door sizes for domestic use. Also, the door must have a U-value of at least 1.4 W/m²K under Part L of the Building Regulations (GOV.UK, 2026). Very large doors may struggle to meet this target without upgraded glazing or thicker insulation. Always check with a FENSA-registered installer (FENSA, 2026) to ensure compliance.
A worked example
A typical UK homeowner replacing a 1,200mm wide by 2,400mm high front door with a standard composite door can expect to pay around £1,800 fully installed after the 0% VAT saving in place until March 2027. Take a 1930s semi-detached house in Manchester with a draughty timber front door. The Energy Saving Trust estimates that replacing an old single-glazed door with a composite door saves approximately £110 per year on heating bills. Using the Energy Saving Trust’s door replacement calculator, the upfront cost after VAT removal is £1,800, giving a payback period of roughly 16 years. Over a 25-year door lifespan, total savings reach £2,750. If the opening is wider than 1,200mm, a bespoke composite door costs 20–40% more, pushing the payback beyond 20 years. Homes eligible for ECO4 funding may receive additional financial support for door upgrades, reducing the payback further.
| Item | Figure |
|---|---|
| Upfront cost after grants | £1,800 |
| Yearly savings | £110 |
| Payback period | 16 years |
| 25-year lifetime savings | £2,750 |
What homeowners often get wrong
The most common mistake is assuming any composite door can be cut down to fit a non-standard opening without losing performance. Here are three frequent errors that cost UK homeowners time and money.
- Ordering a standard door for a wide opening Many believe a 1,200mm door can fill a 1,500mm gap with filler panels. The right answer is to order a bespoke door or add a fixed side panel. Using filler panels creates thermal bridges that increase heat loss by up to 15%, wasting roughly £17 per year on extra heating.
- Ignoring structural reinforcement for tall doors Some homeowners order doors over 2,400mm high without checking frame strength. The right answer is to specify reinforced steel cores and heavy-duty hinges. A 2,600mm door without reinforcement can sag 5mm within a year, voiding the 10-year manufacturer warranty and requiring a £1,200 replacement.
- Skipping professional survey for non-standard sizes People measure the door opening themselves and order a bespoke door online. The right answer is to arrange a surveyor from a certified installer. The gov.uk guidance on building regulations states that a 3mm measurement error can make the door non-compliant, leading to a £500 reordering cost and a 6-week delay.
Quick reference
- Standard composite door widths in the UK are 762mm, 838mm, and 915mm, with heights of 1,981mm or 2,134mm.
- Bespoke composite doors cost 20–40% more than standard sizes and require 6–10 weeks for delivery.
- Maximum standard width is 1,200mm and maximum standard height is 2,400mm according to the British Board of Agrément.
- Energy Savings Trust data shows replacing an old timber door with a composite door saves £110 per year on heating bills.
- Very wide openings over 1,200mm often require two doors or a fixed side panel to maintain structural integrity.
Frequently Asked Questions
The maximum standard width is 1,200mm, per the British Board of Agrément. Wider sizes require bespoke manufacturing with reinforced frames.
Bespoke composite doors cost 20–40% more than standard models, according to industry data. Exact pricing depends on size, finish, and supplier.
The most common widths are 762mm, 838mm, and 915mm, with heights of 1,981mm or 2,134mm, as reported by the Energy Saving Trust. These match standard brickwork openings.
