Building shapes: rectangle, L, T, U compared

The building-shape selector on every generator on this site offers four choices: rectangle, L-shape, T-shape, and U-shape. Most users keep it on rectangle, and that is the right default — rectangular envelopes are space-efficient, structurally simple, and match how the majority of apartment buildings are actually built. The non-rectangular options exist for the cases where the site, the planning constraint, or the design intent forces a different envelope. Knowing when each makes sense saves time.

Rectangle: the default that earns its place

A rectangular floor plate is the most efficient ratio of perimeter to floor area. Less perimeter means less external wall, less window glazing, less heat loss, lower construction cost per m², and easier internal partitioning. Rectangular plans also fit cleanly between party walls in apartment buildings — the units stack in a grid, the elevations align, and the structural columns can be regularly placed.

About 80% of apartment buildings use rectangular floor plates per unit. About 90% of single-family houses do. The non-rectangular options below address the remaining 10–20% of cases where rectangles don't fit the site or the programme.

L-shape: the corner site

An L-shaped plan has two rectangular arms meeting at a right angle, leaving a cut-out at one corner. L-shapes appear in three common situations: corner sites where the building wraps a corner; existing buildings being renovated where part of the original floor plate has been removed; and houses with attached garages, where the garage is one arm of the L and the living spaces are the other.

L-shapes give one extra exterior wall, which means more natural light from another orientation. They also give a sheltered courtyard at the inside corner — useful for outdoor space in a house. The trade is more perimeter wall (typically 15–20% more for the same floor area than a rectangle) and more complex internal circulation: the corridor has to turn at the L's corner, which the generator handles but which feels slightly less efficient than a straight corridor.

T-shape: the row-house cross-arm

A T-shape has a long main arm and a shorter arm attached at the centre, creating two rectangular cut-outs at the back. T-shapes appear in row-house developments where each unit has a forward main mass and a back projection containing the kitchen and a small yard, and in larger houses where the master suite or the kitchen-dining wing is differentiated from the main block.

The T provides three orientations of natural light (the main arm has two long sides facing front and back, the cross-arm has its own light) and creates two distinct exterior zones (front and back yard). It also has the highest perimeter-to-area ratio of the four shapes, so it costs more per m² to build than a rectangle.

U-shape: the courtyard layout

A U-shape has three rectangular arms enclosing a courtyard on three sides, with the courtyard opening on one side. U-shapes appear in larger houses, in some apartment buildings around a central courtyard, and in offices where the U creates a sheltered private outdoor space.

The U gives the most exterior wall area for natural light (every room can have a window) and the largest sheltered outdoor space. It is also the most expensive shape per m² (highest perimeter-to-area ratio), and the courtyard claims floor area that doesn't count as habitable indoor space. Generally a feature of plans above 150 m² where the inefficiency cost is acceptable.

What the generator does at non-rectangular envelopes

When you select L, T, or U on an apartment generator, the template engine fits the same templates inside the chosen envelope and the post-processing handles the corners. This is an approximation rather than a precise fit — the templates are designed for rectangular envelopes first, and the non-rectangular envelopes use the rectangular templates with extra walls added to match the chosen shape.

For the house and office generators, the grid-based room placer is more flexible: it places rooms by adjacency scoring inside any envelope, so non-rectangular envelopes work better in those generators than in apartments. Even so, a real architect's plan will outperform any generator on heavily irregular sites — sites with diagonal walls, curves, or significant slopes need hand-design.

Rule of thumb

Use rectangle for almost all cases. Use L when you have a corner site or an attached garage. Use T for a back-projection wing. Use U for a courtyard house above 150 m². If your real site is more complex than these four shapes can model, the generator is the wrong tool — sketch the envelope by hand or commission a real plan.