A porch can save an average of £80–£120 a year on heating, but only if it is built correctly. The figure comes from an Energy Saving Trust report on draught-proofing and secondary glazing, updated for 2026 (Energy Saving Trust, 2026). The saving is an average for a well-sealed, unheated porch with a solid roof and a good door. The actual saving depends on the existing door’s condition and the porch’s orientation (sheltered vs exposed). The saving can be zero if the porch is poorly sealed or has large areas of single glazing.
A porch can save an average of £80–£120 a year on heating, but only if it is built correctly
The primary mechanism is the airlock effect. A porch creates a buffer zone between the outside and your front door, reducing the volume of cold air that directly hits the door each time it is opened. This reduces heat loss through the door itself and cuts draughts. The Energy Saving Trust report models this saving for a typical semi-detached house with an older, draughty timber front door and a porch that is unheated, has a solid roof, and uses a well-sealed external door. The saving is not from the porch retaining heat, which it should not do, but from stopping cold air from reaching the main door. If your front door is modern and well-insulated, the saving drops significantly. The orientation matters too. A porch on a north-facing, exposed elevation will see a larger benefit than one on a sheltered, south-facing side (SAP 10, 2026).
Quick numbers cost, energy saving, and payback for a typical porch
The table below summarises typical costs and savings for three common porch types. Build costs are based on the Checkatrade 2026 cost guide. Heating savings are modelled by the Energy Saving Trust for the airlock effect. Payback is calculated by dividing build cost by annual saving. Note that payback is rarely the primary reason to build a porch; comfort is the main driver.
| Porch type | Build cost (materials + labour) | Heating kWh saved/year | Cost saved/year (£) | Payback period (years) |
|---|---|---|---|---|
| Lean-to porch (small, glazed roof) | £2,000–£3,500 | 150–250 | £30–£50 | 40–70+ |
| Storm porch (solid roof, one door) | £3,000–£5,000 | 400–600 | £80–£120 | 25–60 |
| Full-width porch (solid roof, side windows) | £6,000–£12,000 | 500–800 | £100–£160 | 40–75+ |
The payback period for a lean-to porch is extremely long because the glazed roof limits the airlock benefit. A storm porch with a solid roof offers the best balance of cost and saving. The kWh savings assume the porch is unheated and the existing front door is a 1990s timber door with minimal draught-proofing. For a modern composite door, the kWh saving is roughly halved (Energy Saving Trust, 2026).
The airlock effect is what saves heat, not the porch itself being warm
A Building Research Establishment report on air infiltration in domestic buildings explains that the main heat saving from a porch comes from reducing the air change rate through the front door (BRE, 2026). The porch acts as a buffer zone. Cold air does not directly hit the front door when the external porch door is closed. The porch itself should be treated as a cold, unheated space. Heating it is wasteful and can cause condensation on the cold surfaces, which can lead to rot in the existing door frame. The effect is strongest with an older, draughty front door. A modern insulated door already limits this benefit, so the saving is smaller. The porch does not need to be warm to work; it needs to be well-sealed and dry.
Building regulations and planning permission what you must check before building
A porch under 30m² is usually permitted development, but it cannot be within 2m of a boundary or exceed certain heights (GOV.UK Planning Portal, 2026). If the porch is heated or has a radiator, it must meet Part L building regulations for insulation (Approved Document L, 2026). Ventilation is critical. A sealed porch can trap moisture and cause rot in the existing door frame. Approved Document F requires adequate ventilation for any enclosed space (Approved Document F, 2026). You must also check for conservation area or listed building restrictions, which override permitted development. A local authority can require planning permission even for a small porch if it is in a designated area.
Is a porch worth building for warmth? The direct answer for a typical UK home
Yes, if your front door is old and draughty, and you build a simple, well-sealed, unheated porch. No, if your front door is modern and well-insulated, or if the porch is poorly designed. The warmth benefit is primarily draught reduction, not added insulation. The cost of a basic porch (£2,000–£4,000) usually outweighs the heating saving, but the comfort gain and reduced dust are often the real value. For a typical semi-detached house with a 1990s door, a porch is worth it for comfort. For a new-build with a composite door, it is not.
How to verify an installer and ensure the porch is built to standard
For a simple unheated porch, TrustMark registration is the most relevant quality assurance scheme (TrustMark, 2026). If the porch includes new windows or doors, the installer should be FENSA registered to self-certify compliance with building regulations (FENSA, 2026). If a radiator is installed in the porch, the installer must be Gas Safe registered (Gas Safe Register, 2026). Check the installer has public liability insurance and a written contract with a clear payment schedule. Verify the installer can provide a certificate of compliance for any new glazing. Do not pay the full amount upfront; a 25% deposit is standard, with the balance on completion.
The impact of porch materials and design on energy performance
A solid roof (tiled or felted) is far better than a glass roof for reducing heat loss through the ceiling of the porch. The porch door should have a U-value of 1.4 W/m²K or lower, which is the modern standard for an external door (Glass and Glazing Federation, 2026). Single glazing in a porch is acceptable if the porch is unheated, but it will not help with warmth as much as double glazing. The floor should be insulated if the porch is on a concrete slab; otherwise, it will act as a cold sink and draw heat from the main house. A well-designed porch uses a solid roof, a well-sealed door, and minimal glazing to maximise the airlock effect. The materials themselves do not save heat; the design and sealing do.
