There's often a misconception on why cavity walls came about. They were widely introduced after WW1, not specifically to improve thermal insulation (coal was relatively cheap) but to prevent rain-penetration.
Prior to WW1, the vast majority of smaller houses were built with 9" solid walls. If carefully-laid and all joints buttered up, a 9" wall was perfectly capable of keeping rain out except in positions of high exposure.
After the War, there weren't the numbers of skilled bricklayers around to ensure quality brickwork and, at the same time, the government embarked on a large house-building programme.
As both skill and time had reduced, the cavity wall was more widely introduced as a quicker alternative to ensure dry walls. In the old days, it was usual to incorporate vents at the bottom of the wall to help dry out any rain which had penetrated the outer skin (the top of the cavity was usually open anyway so an air flow was acceptable).
Nowadays, because thermal insulation is equally important, residual cavities are not ventilated. It seems to be accepted that some rain will penetrate, so it is guided away by cavity trays and weepholes.
Prior to WW1, the vast majority of smaller houses were built with 9" solid walls. If carefully-laid and all joints buttered up, a 9" wall was perfectly capable of keeping rain out except in positions of high exposure.
After the War, there weren't the numbers of skilled bricklayers around to ensure quality brickwork and, at the same time, the government embarked on a large house-building programme.
As both skill and time had reduced, the cavity wall was more widely introduced as a quicker alternative to ensure dry walls. In the old days, it was usual to incorporate vents at the bottom of the wall to help dry out any rain which had penetrated the outer skin (the top of the cavity was usually open anyway so an air flow was acceptable).
Nowadays, because thermal insulation is equally important, residual cavities are not ventilated. It seems to be accepted that some rain will penetrate, so it is guided away by cavity trays and weepholes.
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