The four questions only a section can answer
Plans answer how much. Sections answer whether. Four questions that decide if a brief is buildable - and why we cut the section before we draw a single plan.
7 min read
Why we start with the cut
Almost every project that arrives at this studio arrives as a plan. Sometimes it is a sketch on the back of an estate agent’s particulars, sometimes it is a full set drawn by somebody else. It is nearly always a plan, and it nearly always looks achievable, because a plan is very good at hiding the four things that decide whether a building can be built.
A plan answers how much: how many bedrooms, how many square metres, how the furniture fits. A section answers whether. Daylight, sound, structure and water are all vertical problems, and a drawing taken horizontally through a building cannot show you a single one of them.
If your project has a drawing already, is it a plan? And has anybody yet drawn the same building cut from roof to foundation?
One: how far does daylight actually reach?
A window lights the part of the room it can see. That sounds obvious until you draw it, at which point the useful number appears: with an ordinary 3.1 m storey and a head height of 2.4 m, useful daylight reaches roughly 2.5 times the head height into the room before it becomes light you would still switch a lamp on in.
At House Verlat this was the whole project. The plot is 8.4 m wide with party walls on both sides, so the only way to light the middle of the house was a courtyard, and the only question worth asking was how wide it had to be. Drawn in section, with the reflectance of the facing wall in the drawing, it came out at 4.2 m. Every other decision in that house was made afterwards.
Sizing the courtyard with what is left over
The usual method is to plan the rooms you want, discover a leftover gap in the middle, and call that gap the courtyard. It is normally about 2.5 m wide, which lights its own walls and nothing else. You then own a house with a small damp yard in it and a back room that needs a lamp at noon.
Fix the daylight dimension first, in section, and let the rooms take what is left. You will lose a bedroom about a third of the time. You will know that in week two, for a fixed fee, rather than in month nine.
Two: where does the sound go?
Sound between floors and between neighbours travels through structure, and structure is the thing a plan draws as two thin parallel lines with no thickness worth noticing.
Two Sisters is a pair of houses for two sisters who wanted to live next door to each other and not hear it. In plan that project is a boring rectangle divided down the middle. In section it is a 365 mm wall with an unbridged 50 mm cavity, joists hung off each leaf separately and never carried through, and both stairs pushed against it because a stair is the room least bothered by a neighbour. The finished separation measured 58 dB - well past what the regulations ask for, which was the point of drawing it that way.
Three: what is actually holding it up?
Long spans, big openings and clear rooms all have a depth, and depth lives in the section. This is where the plan lies most cheerfully: a 6 m opening costs nothing to draw in plan and about 400 mm of ceiling height to build.
Our structural engineer sits in the studio rather than being posted a finished design to check, which means the beam depth arrives in week two instead of week fourteen, while the section can still change to accommodate it.
Heads up If a structural engineer has not seen your project before planning permission is applied for, the drawings you have been given are a hypothesis. It is usually still a good hypothesis. It is not a building.
Four: where is the water?
Groundwater is the constraint that appears last and costs most, because it is invisible on every drawing except one.
At Waterline Depot the archive needed a floor at -3.40 and the water table sits at -2.10. That single relationship - two horizontal lines on one sheet, 1.3 m apart - determined the structure, the sequence of the pour, the drainage strategy, two pumped sumps and roughly a fifth of the construction cost. It is the drawing that got the building consented, and it now hangs in the reading room.
How to cut a section on your own site
- Draw the ground first, as it really falls, from a levels survey and not from memory. Everything else is measured from it.
- Put the finished floor levels on, all of them, with real numbers.
- Draw the openings at their true heads and sills, not as gaps in a wall.
- Add the things you cannot see: water table, drain invert, tree roots, the neighbour’s foundation.
- Only now draw the rooms. If they do not fit, you have learned the useful thing.
What we send back
Our first stage is one section at 1:100 and a page of notes, for a fixed fee, in two weeks. It is deliberately the cheapest thing we do, because it is the stage most likely to conclude that the project should change shape - or occasionally that you do not need an architect at all.
Before you write to us
- The address, or a pin on a map
- What you want to build, in two sentences
- The budget you actually have
- The one constraint you believe is fixed
That fourth item is the one clients most often leave out and the one that most often turns out to be the project.
Send us the site and the constraint
Two weeks later you get a section and a page of notes. Whether you go on with us afterwards is entirely open, and the drawing is yours either way.