Construction drawings that make every builder price the same job

What is the difference between construction drawings and planning drawings?

Construction drawings are the set a builder prices and builds from: 1:50 plans, sections and elevations, 1:5 to 1:20 details, a structural layout and the schedules. Planning drawings answer whether you may build; construction drawings answer how. Given only the former, every builder prices a different building.

Source: MHCLG District Planning Application Statistics (PS1 and PS2), decisions made in the twelve quarters 2023 Q2 to 2026 Q1, retrieved 1 September 2026. Open Government Licence v3.0.

What is actually in a construction drawing package?

A construction drawing package is the document a builder prices from and builds from. If something is not in it, someone on site decides it instead, and you pay for that decision twice: once when it is made and again when it turns out to conflict with something else.

The schedules are the part homeowners are most often missing and the part builders most want. A window schedule that says which of eleven openings is fire-egress, which is obscure-glazed and which is restricted to 100 mm opening removes eleven separate phone calls.

How do construction drawings differ from planning drawings?

They answer different questions and are read by different people. A planning officer is deciding whether the proposal is acceptable in its context. A bricklayer is deciding where to put a brick. Those need different documents, and a drawing that tries to be both is usually bad at each.

Both stages are covered in our Complete package, and the planning drawings are produced first because the construction set is drawn against whatever permission was actually granted, including any conditions attached to it.

Why do builders price the same job so differently?

Usually because they are not pricing the same job. Given planning drawings only, each builder has to invent the missing 60 per cent, and they invent it according to their own risk appetite. One assumes a 150 mm insulated slab, another assumes 100 mm. One prices a steel goalpost, another prices a padstone and a lintel. The spread you are looking at is not competition, it is uncertainty.

There is a measurable version of this in the planning data. Across London, 7.4% of applications in the twelve quarters to March 2026 were withdrawn before any decision was made — that is the applicant pulling out, not the council refusing. Withdrawal is what an underspecified scheme looks like from the outside.

Source: MHCLG District Planning Application Statistics (PS1 and PS2), decisions made in the twelve quarters 2023 Q2 to 2026 Q1, retrieved 1 September 2026. Open Government Licence v3.0.

What does a construction drawing package cost in London?

A fixed fee, quoted before we start, that does not move because a junction took three attempts.

Add to that the statutory application fee, which is set nationally and paid to the council rather than to us: £548 for a householder planning application and £274 for a Lawful Development Certificate.

Do you need full plans, or will a building notice do?

For a house extension or a loft conversion you may usually choose either route, and the choice decides how much gets settled on paper before anyone starts. A full plans application is assessed against the regulations before work begins; a building notice has no plan check at all, so every detail is judged on site by the inspector who happens to visit. The second route is not cheaper. It moves the same decisions to the most expensive moment to make them.

Two features of the current regime are worth knowing before you choose. The relevant authority must tell you the outcome of a full plans application within five weeks, or a longer period agreed with you in writing. And if it says nothing at all, silence is neither an approval nor a refusal — the application simply remains undetermined. That is the opposite of the planning system, where non-determination gives you a right of appeal. Waiting out a building control authority gains you nothing.

The choice is also not always yours. A building notice cannot be used where the work is subject to the Regulatory Reform (Fire Safety) Order 2005, where a building fronts onto a private street, where paragraph H4 of Schedule 1 applies, or for certain electrical work in England — a new circuit, a replacement consumer unit, or an addition to an existing circuit in a special location such as a bathroom. A flat conversion or a mixed-use building will often fall into the first of those.

Source: Building Regulations 2010 (SI 2010/2214) regulations 12 and 14A, as amended by the Building Regulations etc. (Amendment) (England) Regulations 2023 (SI 2023/911), in force 1 October 2023. Retrieved 2 September 2026. Open Government Licence v3.0.

What does building control actually look at?

Not the same things your case officer looked at. Planning judged how the building sits in the street; building control judges whether it stands up, keeps heat in, gets people out in a fire, and does not poison anyone slowly. Those are answered by build-ups and dimensions, not by elevations. A set that satisfied a planning officer will usually not satisfy a plans checker, which is why the second set exists.

In practice a checker reads four things closely. The structural drawings and the engineer’s calculations, together, since a beam size means nothing without the load case behind it. The thermal build-ups for every new element, wall, roof and floor, each with its calculated U-value. The fire strategy — escape route, door ratings, alarm grade — which for a loft conversion is usually the item that fails first. And the drainage layout, including where a new soil connection meets the existing run and at what fall.

Each of those is a drawing or a schedule, and each is one an average builder will otherwise decide on site. That is the honest argument for a construction set: not that it satisfies a regulation, but that it moves four decisions from the week they are most expensive to the week they are cheapest.

When do you also need a structural engineer?

Whenever load moves. Removing a wall, cutting a new opening, taking the roof off a storey, or putting a dormer where a rafter used to run — each of those changes the path a load takes to the ground, and a checker will want the calculation, not an opinion. We draw the arrangement and specify the member; the engineer sizes it and signs the numbers. The two documents are read together, and neither passes alone.

What does not need an engineer is a like-for-like refit, a non-structural partition, or a window replaced in an existing opening at the same width. If your builder says a beam is “obviously fine”, that is exactly the sentence a plans checker will ask him to put in writing, and he will not.

Construction drawing questions