How to specify a brick in NBS
What a complete brick specification clause needs, and the information to gather before you write it.
A brick clause has one job: to describe the product precisely enough that someone else could source it.
Most fall short in the same few places.
Under Uniclass, clay facing bricks sit at Pr_20_93_52. What follows is the information a complete clause carries, where each piece comes from, and the fields that are most often left blank — usually because nobody could find them at the time of writing.
What a complete clause carries.
Roughly two thirds of a brick clause is manufacturer data that should come straight off a datasheet. The rest is project-specific: where the brick is going, what it is bedded in, and what happens if it cannot be supplied.
The distinction matters. Manufacturer data can be verified and substituted against. Project decisions cannot be inferred by anyone downstream, so if they are missing they will be guessed.
If a field is unknown, write "to be confirmed" rather than leaving it blank. A gap reads as an oversight; a marker reads as a decision still open.
| Comes from | Fields |
|---|---|
| Manufacturer | Product name and reference, dimensions, compressive strength, water absorption, freeze/thaw category, soluble salt category, configuration, density, fire class |
| Standards | BS EN 771-1, and PD 6697 where durability designations are being justified |
| You | Location on the building, mortar, bond, joint profile, sample panel requirement, substitution policy |
Fields that go missing.
These are the ones that most often arrive blank, and each has a real consequence further down the line.
Appearance
The face description — colour and texture in words rather than a product name. Without it, a substitution can match every number and look wrong.
Compressive strength category
Distinct from the declared value. The category is what a structural engineer checks against.
Configuration
Solid, perforated, frogged or cellular. Affects fixings, cutting and how the brick performs in detail.
Density tolerance
Needed for loading calculations, and routinely omitted because it is buried in the DoP rather than the brochure.
Thermal conductivity
Required for U-value calculations. If the specification does not carry it, someone will use a generic figure instead.
Mortar
The brick is half the elevation. A clause that names the brick and not the mortar has specified half a wall.
What it looks like written down.
A short clause covering the essentials. Real specifications run longer, but anything shorter than this is leaving decisions to somebody else.
Facing brickwork (Pr_20_93_52)
Clay facing bricks to BS EN 771-1.
Appearance: light red, wirecut.
Dimensions: 215 × 102.5 × 65mm.
Freeze/thaw resistance: category F2.
Active soluble salt content: category S2.
Compressive strength: not less than 50 N/mm².
Configuration: perforated.
Mortar: designation (iii), natural sand, colour to match approved panel.
Bond: stretcher. Joint: 10mm, bucket-handle profile.
Sample panel: 1m² minimum, to be approved before the order is placed.
Substitutions: only with written approval, assessed against appearance and all declared performance categories.
Where the numbers live.
Declaration of Performance
The DoP is the authoritative source for every declared category. Brochures summarise; the DoP is what the manufacturer stands behind.
Ask the supplier
If a figure is not published, it usually exists. A supplier who cannot produce it is worth knowing about before the brick is on the drawing.
Every product we put in front of you carries a technical datasheet, and brick products come with an NBS-format clause set generated from the same data — so the specification and the sample you approved describe the same brick.