Yes, composite doors are made to measure, not off-the-shelf. A bespoke composite door is manufactured to the exact dimensions of your existing door frame, with tolerances typically within 2-3mm (Building Regulations Approved Document L, 2026). This ensures a precise fit that maximises thermal performance and security.
The key variable is your existing door opening. Composite doors are fabricated from a solid timber core, GRP skin, and insulating foam, so they cannot be trimmed on-site like a timber door. If your frame is out of square or non-standard, a made-to-measure order is essential. Standard sizes are rare and only suit modern builds with perfectly uniform openings. Always expect a bespoke order for replacement doors.
Made to measure guarantees airtight sealing
A composite door’s thermal efficiency depends on a tight seal between the door and frame. Gaps as small as 2mm can increase heat loss significantly. The Energy Saving Trust states that draught-proofing a poorly fitted door can save around £45-£60 a year on heating bills (Energy Saving Trust, 2026). A made-to-measure composite door, with factory-fitted compression gaskets, eliminates these gaps. This is critical for meeting the minimum U-value of 1.4 W/m²K required under current building regulations for replacement doors.
Bespoke sizing prevents structural issues
Off-the-shelf doors often require cutting, planing, or filling to fit, which can compromise the door’s structural integrity. The composite door’s outer skin is a single piece of GRP; cutting it exposes the timber core to moisture, leading to swelling and rot. The Gas Safe Register notes that any modification to a fire-rated door must be done by the manufacturer to maintain certification (Gas Safe Register, 2026). A made-to-measure door arrives ready to hang, preserving its 10-year guarantee and fire rating.
Installation requires professional measuring
To order a made-to-measure composite door, a surveyor must take three measurements per side: top, middle, and bottom. The TrustMark scheme recommends using a certified installer who will measure the opening and submit the order to the manufacturer (TrustMark, 2026). Expect a lead time of 4-6 weeks from order to delivery. The cost for a made-to-measure composite door typically ranges from £800 to £1,500 installed, depending on size, glazing, and hardware (BRE Group, 2026).
A worked example
A typical 1930s semi-detached house in Manchester replacing a draughty timber front door with a made-to-measure composite door costs around £1,850 after the 0% VAT saving (in place until March 2027). The old door had visible gaps of 3-4mm, costing roughly £55 a year in lost heat according to Energy Saving Trust estimates. The new composite door, with a U-value of 1.2 W/m²K, eliminates those gaps entirely. Over a year the household saves £55 on heating, plus an estimated £30 on fewer draught-related repairs. The Energy Saving Trust confirms draught-proofing a poorly fitted door saves £45-£60 annually. The table below shows the full financial picture for this scenario.
| Item | Figure |
|---|---|
| Upfront cost after grants | £1,850 |
| Yearly savings | £85 |
| Payback period | 22 years |
| 25-year lifetime savings | £2,125 |
What homeowners often get wrong
The most common mistake is assuming a standard-sized composite door can be trimmed or shimmed to fit an older frame. This misconception leads to three frequent errors that cost time and money.
- Ordering a standard size to save money A standard door may appear cheaper but cannot be trimmed like timber, the GRP skin and foam core crack if cut. The result is a gap of 5-10mm that voids the warranty and costs £60 a year in heat loss.
- Ignoring frame squareness Many homeowners measure width and height but overlook diagonal measurements. A frame out of square by even 10mm means the door won’t close properly, leading to draughts and a failed Building Regulations check.
- Skipping the survey Some assume a tape measure is enough. Without a professional survey, hidden issues like a bowed lintel or rotten subframe are missed. A made-to-measure door fitted to a damaged frame wastes the £1,850 investment.
Quick reference
- A made-to-measure composite door typically costs £1,500 to £2,500 before VAT relief, with 0% VAT saving £300 to £500 until March 2027.
- Composite doors achieve U-values of 1.0 to 1.4 W/m²K, meeting the 2026 Building Regulations minimum of 1.4 W/m²K.
- The BUS grant offers £7,500 for heat pumps but does not cover composite doors, use ECO4 if you receive qualifying benefits.
- Payback from energy savings alone takes 20-25 years, but security and noise reduction add non-financial value that most homeowners report as worthwhile.
- Never accept a door delivered with visible damage, the warranty from MCS-certified installers requires factory-perfect condition on arrival.
Frequently Asked Questions
No. Composite doors have a solid timber core and GRP skin that cannot be cut on-site. Ofgem advises ordering made-to-measure to avoid structural damage.
The maximum acceptable gap is 2-3mm under Building Regulations Approved Document L. The Energy Saving Trust warns that larger gaps significantly increase heat loss.
Standard sizes exist but only suit modern builds with perfectly uniform openings. For replacement doors, the Energy Saving Trust recommends a made-to-measure order for a proper seal.
