Construction drawings in London

Stairs, headroom and the geometry that gets checked

Stairs are where a design is most easily caught out. For a private stair, Approved Document K sets limits on rise, going and pitch. The rise and going ranges, the maximum pitch and the formula that links them are in the table.

Headroom is the other constraint. Approved Document K expects clear height over the stair, and in a loft it is the stairwell, not the room, that often decides where the stair can land. We draw the stair in section against the roof before the layout is frozen.

A stair that fails these numbers will be marked up by building control, and moving it on site costs far more than moving it on paper.

We also draw handrail and balustrade heights and the landings at top and bottom, because the examiner checks the whole stair, not only the flights.

Escape routes, fire detection and ventilation

Fire safety shows up in the drawings in practical ways. Where a loft or first-floor room is a bedroom, an escape window must have a minimum clear opening and a limited sill height. The measurements are in the table. All dwellings need mains-operated smoke alarms to a stated grade and category.

Ventilation is drawn in as extract rates for kitchens, utilities, bathrooms and WCs, and as background ventilation to habitable rooms. We note the fan capacities so the electrician and builder install what the examiner expects.

Our building regulations drawings page explains how these requirements are submitted for approval.

Insulation and U-values on new elements

New walls, roofs, floors, windows and doors in an existing home must meet limiting U-values, which cap how much heat each element loses. The table lists each limit from Approved Document L, and the specification on our sheets names a build-up that meets them.

Meeting the number is a design choice with consequences. A thicker roof build-up changes the ridge height, which may matter for planning. A better window changes the cost. We resolve those trade-offs before the set is issued, so the price your builder gives is the price you pay.

Where a project needs an energy assessment, our SAP calculations service coordinates it.

Materials, workmanship and who carries the duties

The materials and workmanship Approved Document sets the standard for products and site work, and our specification refers to it. It means a builder cannot substitute an unsuitable product without it showing up as a departure from the drawings.

Under the Part 2A rules, a domestic client's duties pass to the contractor or principal contractor. Our handover notes summarise this, so you know what your builder takes on. For larger or riskier jobs, our Principal Designer service covers the design-side duties.

How we produce the set

The set grows from the approved model. We add the structure, the services and the details, and derive the plan layouts, cross-sections and elevations from the same model, so they agree. Our structural calculations feed the beam and foundation sheets directly.

Every sheet is checked by a second technologist before issue, and a senior review signs off the set. A first issue normally follows the survey within about a week. If the council or building control wants amendments, we revise them without charge.