What U-value do bi-fold doors need in the UK?

Under Part L, replacement doors must achieve a U-value of 1.4 W/m²K or better. For new builds the notional specification is 1.2 W/m²K. Most quality aluminium bi-folds with argon-filled double glazing achieve 1.3-1.5 W/m²K. Triple glazed comfortably meets the standard.

How many panels should a bi-fold door have?

Each panel should be 600-900mm wide. For 3m openings, 3-4 panels work well. For 4-5m, 5-6 panels. Odd numbers allow a traffic door. Maximum recommended panel width is about 1000mm to avoid excessive weight and track wear.

Do bi-fold doors need Building Regulations approval?

Yes. Bi-fold doors require compliance for thermal performance (Part L), structural opening (Part A), and accessibility (Part M). Installation must be by a FENSA-registered installer or you need a building control certificate.

Which frame material is best for bi-fold doors?

Aluminium is most popular due to slim sightlines, strength and low maintenance. uPVC is cheapest but has thicker frames. Timber offers traditional appearance but needs maintenance. Composite combines both at premium cost.

How heavy are bi-fold doors?

A typical aluminium bi-fold panel weighs 30-45 kg/m². A 3m x 2.1m 3-panel set weighs approximately 200-270 kg total. Triple glazing adds about 30% more weight. Track and rollers must be rated for the total weight.

TradeCalculator

Bi-Fold Door Calculator

Calculate bi-fold door panel configurations, costs and U-values for aluminium, uPVC, timber and composite frames with UK Part L compliance.

Frame Material

Aluminium gives slimmest sightlines

Number of Panels

Odd numbers allow traffic door

Glazing Type

Triple gives better U-value

Opening Width

Structural opening width

Opening Height

Standard 2100mm

How We Calculate This

This calculator estimates bi-fold door costs based on opening size, frame material, panel count and glazing.

The formula

Total = (Area × Base Rate × Glazing Multiplier) + Installation

Base rates vary by frame material
Triple glazing adds ~30% to supply cost
Panel width = Opening width ÷ Number of panels
Weight = Area × kg/m² × Glazing factor

Frequently Asked Questions

Related Calculators

Window U-Value Calculator

Calculate window U-value from glass, frame and spacer thermal performance.

Double Glazing Unit Calculator

Calculate DGU thickness, weight per m² and thermal performance by gas fill.

Window Condensation Risk Calculator

Calculate window condensation risk from internal temperature, RH and dew point.

Sealant and Mastic Calculator

Calculate sealant cartridges from joint volume per window frame.

Window Security Spec Calculator

Determine PAS 24 window security requirements by floor and access level.

Last updated: March 2026

All calculations are estimates. Verify with your supplier.