A Building Regulations specification is the written half of a building control application. The drawings show where everything is. The specification says what everything is: how each element of the building is constructed, layer by layer, what it is made of, what standards it is built to, and what performance it achieves.
Building control reads the two together. A section through a wall on a drawing shows a cavity wall; it does not say what fills the cavity, what the inner leaf is made of, or what U-value the whole thing achieves. The specification does. When it is missing or generic, the plan checker has to ask, and every question is a week.
What it covers
A specification for a domestic project in England is organised the way a building control officer reads a pack: by element, then by topic.
Part A, the construction build-ups
Each element of the building described from the outside in: foundations, external walls, internal walls, floors, roofs, and on a conversion the separating walls and floors between dwellings. Each build-up names the materials and their thicknesses, the products and their alternatives, and the standard it is built to. Where an element has a thermal target, the build-up states the U-value it achieves and the target it has to beat, and the calculation that produced the figure is printed so that it can be checked.
Part B, the general notes by topic
Everything a drawing sheet has no room for: structure, means of escape and fire, sound, ventilation, condensation, drainage, hot water safety, electrical work, the conservation of fuel and power, and the newer Parts that apply to new dwellings such as overheating, security, electric vehicle charging and broadband. Each topic is one note, written once, so that nothing in the document repeats and nothing contradicts.
The cover, and the responsibility statement
The practice's own name, the named designer, the project, the site address, the local authority, the application type and the revision. And a statement of what the document is: the designer's specification of the work, to be read with the drawing pack and the engineer's design, not an approval of anything.
A specification states facts, not hopes. "To achieve a maximum U-value of 0.18 W/m²K" is the target. "Actual U-value achieved 0.17 W/m²K" is the fact, and it is only a fact if a calculation to the relevant standard produced it. A figure with no working behind it is an assertion, and a plan checker is entitled to ask for the working.
What it is not
It is not a certificate of compliance. No document issued by a designer certifies that a building complies; compliance is determined by the building control body, on inspection of the work as built. It is not a substitute for the drawings, the structural engineer's design, or the calculations that go with them. And it is not a template to be reused unread: a specification that carries clauses for a septic tank on a house on mains drainage, or a wind turbine on a rear extension, tells building control that nobody read it before it was issued.
Who writes it
The designer, or someone under the designer's direction, and the designer's name goes on it. Practices build their own libraries of clauses over years, and most of the work on any one job is choosing which apply, checking the figures against the current Approved Documents, and removing what does not. That is the work a maintained library does for you, and it is the whole point of one: the clauses are written once, from the source, checked, and kept current, and the job is reduced to the choices that are genuinely the project's.
What changes, and when
The Approved Documents change. The 2026 editions of Approved Documents L and F were published on 24 March 2026 and come into force on 24 March 2027. A specification issued in 2026 is written to the editions in force at the date of issue, and should say so, with the transitional provisions stated so that the reader knows which standards the application is made under.