The short answer
Pitch decides what a roof can be covered with. Butterfield's 1867 restoration put a steeper roof over St Michael's nave and chancel, and each tile or slate has a lowest safe slope, under which wind can push rain back beneath it. Knowing your roof's pitch comes before choosing a new covering.
When William Butterfield restored St Michael's church in 1867, he placed a steeper roof over the nave and chancel. Whatever the reasons, steeper roofs shed water and snow faster, and they open up choices that a shallow roof does not allow. The same logic applies to a house in Aldbourne.
Q1.1What pitch does each covering need?
Every tile and slate has a minimum pitch, and the manufacturer's data sheet gives it. Below that pitch, rain driven by wind can be pushed up the slope and under the covering, and the roof leaks even though nothing is broken. Natural slate, for instance, has a minimum of about 20 degrees under BS 5534, depending on slate size and headlap. Some interlocking concrete tiles go lower, while concrete plain tiles need more.
Q1.2Why does pitch matter at the repair stage?
When a covering needs replacing, the pitch of the existing roof limits what can go on it. A shallow extension roof cannot always take the same tile as the main house, and a rebuilt dormer or porch may need a different material. We measure the pitch at the survey and say what the roof can take. Our guide to minimum tile pitch explains the figures.
Q1.3Can the pitch of a roof be changed?
Raising or lowering a pitch is a structural change, and may need planning permission and building control approval. We explain the consent route before any work is priced. See our pitched roofing page for how new pitched roofs are built.
For most Aldbourne homes the pitch is not going to change; the question is only whether the covering suits it, and the answer is on the manufacturer's data sheet.
Pitch is measured in degrees from the horizontal, and a quick check with a digital level on the rafters or the roof surface gives it to within a degree or so. Older cottages often have steeper pitches than the modern minimums require, which is why slate and plain tile suit them so well, while a low lean-to or porch roof beside the same cottage may only suit a flat covering or an interlocking tile with a low minimum.