CHK Arquitectura Notes on small house design, plans under 120 m²
Project CHKARQUITECTURA.COM Sheet 00
Section Index Date 2026-08

Small house design notes, 60 to 120 square metres

CHK Arquitectura designs houses between 60 m² and 120 m². Four sheets follow in the order a project settles the decisions: the plan and its circulation percentage, the staircase that consumes 3.4 m² on each level, the wall thickness that decides both the reveal depth and the usable floor area, and the courtyard that lights the middle of a narrow plot. Every dimension below is a working figure from a drawing, checked against the building code named beside it.

Line drawing of a small two storey house showing the ground floor plan, the stair and a walled courtyard
Sheet 00: study house, 96 m² over two levels, courtyard to the centre of the plot

Series: four sheets

01
Plan

How is a small house plan under 120 square metres organised?

Circulation is the first number CHK Arquitectura measures on a small plan. A two storey house of 96 m² that spends 15.4 m² on entrance hall, corridor, landing and stair footprint has given away 16 percent of its floor area, which is one double bedroom of 9.9 m² plus a shower room of 3.2 m² plus a cupboard.

Sheet 01 sets circulation targets of 8 to 12 percent for a two storey house with one stair, tabulates three room adjacencies that each save 0.8 m² to 3.0 m², gives workable minimum dimensions for six rooms, and shows how 450 mm external walls take 23.5 percent of an 8.0 m by 6.5 m footprint.

Read sheet 01
02
Stairs

What compact staircase dimensions still feel safe?

A staircase occupies floor area on two levels at once. A straight flight of 16 risers at 181 mm, 900 mm wide with a going of 250 mm, covers 3.4 m² on the lower floor and cuts a void of 3.4 m² through the floor above, so one stair costs 6.8 m² of a 96 m² house.

Sheet 02 compares six riser and going pairs between 170 by 290 mm and 200 by 220 mm with the pitch of each in degrees, tabulates the footprint of straight, quarter turn, half turn, spiral and alternating tread flights, and sets out where UK Approved Document K and the Spanish CTE DB SUA disagree.

Read sheet 02
03
Reveals

How deep should a window reveal be in a 450 mm wall?

A wall 450 mm thick leaves an internal reveal of 350 mm once a 70 mm frame sits 30 mm behind the outer face. A square reveal of 350 mm removes about 13 percent of the daylight reaching a point 4 m into the room, and a splay of 45 degrees returns that figure to 97 percent.

Sheet 03 tabulates reveal depth against daylight, gives window seat heights of 420 mm to 450 mm and depths of 450 mm to 700 mm, compares five wall build ups between 0.18 W/m²K and 1.7 W/m²K with their decrement delays, and specifies sill falls of 10 to 15 degrees.

Read sheet 03
04
Courtyard

How big does an internal courtyard need to be on a narrow plot?

On a plot 6.5 m wide and 22 m deep built to both side boundaries, the middle of the house sits 8 m from the nearest window. An internal courtyard of 3.4 m by 3.0 m, 10.2 m², lights two rooms, ventilates the centre of the plan and turns the darkest part of the section into the brightest.

Sheet 04 tabulates courtyard width to wall height ratios between 0.7 to 1.0 and 2.0 to 1.0 against hours of direct sun at 40 degrees north, sets surface falls at 1.5 to 2 percent, specifies two 100 mm outlets against a runoff of 0.21 litres per second, and gives soil depths of 400 mm to 1000 mm.

Read sheet 04
How to read these notes

Building components are dimensioned in millimetres, rooms and plots in metres and square metres, angles in degrees, thermal performance in W/m²K. Sun angles are calculated for latitude 40 degrees north, where the noon sun stands 73.4 degrees above the horizon in June and 26.6 degrees in December.

Codes are named wherever a figure depends on one, because a riser of 200 mm passes UK Approved Document K and fails the Spanish CTE DB SUA ceiling of 185 mm. Background on the practice and the writing conventions sits on the about page.