Type 20 and Type 21 are the most commonly used flat layouts in the terrace blocks. Type 20 slightly predominates. They are found in the blocks which face north and south, with flats running from front to back. There are 54 in Andrewes House, 59 in Defoe House, 36 in Speed House and 48 in Thomas More House.
The garden flats at the bottom of a block and the maisonettes at the top have their own designs but Type 20s and 21s make up the flats in the floors in between. They are designed to slot together round the stair and lift section of each stairwell of the block. The Type 20 loses space at the rear behind the stairwell to its companion Type 21, which thereby gains a second bedroom. In return the Type 21 sacrifices space at the front to the Type 20. The extra frontage gives a Type 20 flat room for a study next to the living space, facing over the lake or garden. So Type 20 provides 1 bedroom, a living room, and a study (3 rooms).
