Building — 5 min —
What a wall is for
Eighty centimetres of earth is not a primitive wall. It is a battery, and it is being replaced by something worse.
The standard criticism of mud-brick construction is that it is weak, short-lived and vulnerable to water. The first is a design question, the second is a maintenance question, and the third is true and solvable with a roof overhang.
What gets lost in the argument is what the thickness is doing. An eighty-centimetre earth wall has roughly a twelve-hour thermal lag: the heat that lands on its outside face at noon arrives on the inside face around midnight, by which time the air it is warming is the air you want warmed. The wall is not insulating. It is time-shifting.
A twenty-centimetre concrete block wall has a lag of about three hours. The heat of the afternoon arrives in the early evening, on top of the afternoon's own heat, and the house is at its worst exactly when it is most occupied.
This is why new villas in Kandahar run air conditioning that the houses they replaced did not need. It is not that the old buildings were cleverer. It is that they were thicker.
