Matching brick on a 1930s semi extension
Interwar houses used imperial bricks around 68 to 73 mm high, so a standard modern facing will not course with the old wall. What to measure, what to specify and what the council needs to approve the samples.
If you are matching brick on a 1930s semi extension, start with the size of the original brick rather than its colour. Interwar houses were built with imperial bricks, usually around 68 mm to 73 mm high, while a standard modern UK brick is 65 mm high in the 215 x 102.5 x 65 mm format. Get the height wrong and your new brickwork will not course with the old at window heads, string courses or the eaves, and no amount of colour matching will hide it.
Colour comes second. It still matters, because a council that imposes a materials condition is reserving judgement on exactly that point.
Why the council conditions materials instead of approving them
On a householder application, the drawings usually say something like "brick to match existing". That is not a specification, and officers know it. So the permission arrives with a condition requiring samples or details of the external materials to be submitted to and approved in writing by the local planning authority before the relevant work begins.
Two things follow. Most drafting requires approval before the relevant work begins, so starting the brickwork first is a breach, and the discharge application is a separate submission with its own fee. Check the current schedule on the national fee pages, because planning fees have been indexed annually since April 2025.
Where the work is permitted development rather than a full application, the control is tighter in one respect and looser in another. Condition A.3(a) of Schedule 2 Part 1 Class A of the Town and Country Planning (General Permitted Development) (England) Order 2015 requires the materials used in any exterior work to be of a similar appearance to those used on the exterior of the existing house. Nobody approves that in advance. If a neighbour complains and the council agrees that the brick is not of similar appearance, the extension loses its permitted development status, which is a far worse outcome than a refused sample panel. The same condition is why householders in Article 4 areas get caught out replacing windows, a point we cover in replacing windows under an Article 4 direction.
Identifying what the original brick actually is
Look at four things before you ring a supplier.
- Brick height, measured over four courses. Count up four courses on an undisturbed elevation, measure the total and divide by four. Four courses of modern 65 mm brick with 10 mm joints is 300 mm. Four courses of a 73 mm imperial brick comes out closer to 332 mm. That difference of 32 mm over a metre of wall is what makes a badly specified extension look wrong.
- Face texture. Interwar London stocks, Fletton commons, Accrington reds, sand faced facings and rustic wirecuts all weather differently. A sandfaced brick that has lost its surface to 90 years of rain cannot be matched by a new sandfaced brick straight from the pallet.
- Mortar. Pointing colour and joint profile change the apparent colour of a wall more than the brick does. A grey cement joint reads cold next to the warm yellow sand mortar typical of the 1930s.
- Where the brick came from. Many 1930s estates used a local brickworks. If the works still operates, or if a current manufacturer makes a close equivalent, that is your shortest route.
Take the sample from a hidden area, such as below a window inside the extension footprint or from a section of wall being demolished. Do not cut a brick out of the front elevation.
Reclaimed, handmade and machine made options
Reclaimed brick is the obvious answer and often the wrong one. The supply is inconsistent, you pay for sorting, and reclaimed bricks of unknown frost resistance can fail in an exposed position or below damp proof course level. Where a reclaim is used, specify the source, the sorting standard and the proportion of acceptable face damage, and order around 10 per cent extra.
Handmade and stock bricks give the softest match on a weathered elevation because the variation within the pallet mimics the variation within the old wall. They cost more per thousand and the coursing needs care.
Machine made facings in an imperial format are made by several UK manufacturers precisely for extension work. They are the sensible default on a rear extension that is partly visible from the street. Ask for an imperial height rather than accepting a metric brick with a thicker mortar joint, because a 15 mm joint looks like what it is.
A quick comparison of the trade offs:
| Option | Coursing match | Weathered appearance | Supply risk |
|---|---|---|---|
| Reclaimed imperial | Exact | Very close | High, inconsistent batches |
| Handmade imperial | Exact if specified | Close | Lead times of several weeks |
| Machine made imperial facing | Exact if specified | Fair, improves over a few years | Low |
| Standard metric facing | Needs a thicker joint | Fair | Low |
Tonal variation across one elevation
Old brickwork is never one colour. A south facing elevation bleaches, a north facing one holds algae, and the brick under a leaking gutter is permanently darker. Officers who refuse a sample usually do so because the panel is uniform where the existing wall is varied.
Blend from at least three packs rather than working pack by pack, and load the scaffold so that the bricklayer draws from all three. On a long elevation, ask for a slightly darker blend at the base. And accept that a new wall will look new for a while. Lime bloom and surface dust settle within two or three years, which is the usual answer to a neighbour who says the extension stands out.
Offering a sample panel
A sample panel is one square metre of the proposed brick, laid in the proposed bond with the proposed mortar and joint profile, built on site next to the existing wall and left for the officer to look at. It answers the condition far more convincingly than a photograph.
Build it early, before the brickwork is ordered in full. Keep it up until the work is finished so that the bricklayer has a reference. Photograph it in overcast light, in the same frame as the existing wall, and include a scale rule.
Where a site visit is impractical, submit three photographs of the panel, a manufacturer's data sheet with the format and dimensions, and the mortar specification stating sand source, binder and joint profile.
When a deliberate contrast is the better answer
Sometimes matching is the weaker design argument. A single storey rear extension that is fully glazed on the garden elevation with a contrasting brick plinth can read more honestly than a half hearted match, and conservation officers often prefer a clearly modern addition to a pastiche. The same logic applies to a rear dormer, where setting the dormer back matters more than its cladding, as we explain in setting a rear dormer back from the eaves.
Two conditions have to be met before contrast works. The extension must be subordinate to the host dwelling in scale and position, which usually means at the rear and behind the original rear wall line, a measurement we set out in measuring extension depth from the original rear wall. And the contrast has to be deliberate and detailed, with a clean junction, a recessed joint or a glazed link rather than a ragged toothing.
If the house is listed or in a conservation area, run the argument through a Heritage Statement and expect the officer to want traditional materials on anything visible from the street. For a straightforward suburban semi, the design reasoning belongs in a Design and Access Statement.
What to submit to discharge the condition
A discharge submission that gets approved first time usually contains:
- The manufacturer's name, product name and format, with the brick dimensions stated in millimetres
- Photographs of the sample panel against the existing wall, with a scale
- Mortar specification: binder, sand, mix ratio and joint profile, with a named joint type such as flush or bucket handle
- The bond, and where snapped headers or slips are used, a detail showing how
- Roof tile, rainwater goods, window and door specifications if the condition covers them
Allow eight weeks from submission. Councils are not obliged to determine a discharge application faster than that, and bricklayers booked for a date in six weeks are the single most common reason extensions start in breach of condition.
Enter your postcode on PlanScope to see which supporting documents your extension is likely to need.
This is general guidance rather than legal advice. Check the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.
Frequently asked questions
Do I need planning permission to use a different brick on an extension?
If the extension is permitted development under Class A, the materials must be of a similar appearance to the existing house, so a markedly different brick can take the work outside permitted development. If you have planning permission, the materials are controlled by condition instead and a contrasting brick can be approved on design grounds. A Lawful Development Certificate is the only formal way to confirm that works are lawful.
How do I measure the original brick size without damaging the wall?
Measure four courses on an undisturbed elevation and divide by four to get the brick height plus one joint. Four courses of modern 65 mm brick with 10 mm joints comes to 300 mm, while a 73 mm imperial brick gives about 332 mm. For the brick length and depth, measure an exposed header and stretcher at a reveal or an opening.
Is reclaimed brick always the best match?
No. Reclaimed brick matches weathering and coursing well, but batches vary, frost resistance is often unknown and sorting costs add up. It is a poor choice below damp proof course level or in exposed positions. Many UK manufacturers make imperial format facings designed for extension work, which course correctly and arrive in a consistent batch.
Can the council refuse my sample panel?
Yes. A discharge of conditions application can be refused, and the usual reasons are a uniform panel against a varied existing wall, a metric brick with an oversized joint, or a mortar that reads too grey. You can revise and resubmit. Building the brickwork before approval is a breach of condition, which the authority can enforce against.
What mortar should I use next to 1930s brickwork?
Match the existing pointing colour and profile, which on interwar houses is usually a warm sand coloured mortar with a flush or slightly weathered joint. A local sand often gets closer than a pigmented cement mix. On softer handmade or reclaimed brick, a lime based mortar is gentler than a strong cement mix and allows the wall to dry out.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.