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Double pitched roof

Pitched roof: types & common defects

Pitched roofs are the most common types of roof found on buildings. They are most often used because they are effective at shedding water whereas the other type of roofs, such as a flat roof, aren’t. A pitched roof is most likely to be found on the main buildings on most domestic properties.

Types of pitched roofs

Anyone who knows about roof construction will tell you that the highest quality roofs tend to be from 1900-1914. Shortages of material and rationing of wood in the 1945-54 period meant that there was typically poor roof construction. Then the modern truss roofs started to become more common up to 1970 and is now the only type of roof construction typically used in the UK.

Here are the different types of pitched roofs:

  • Lean to or mono-pitch roof:This is the simplest form of roof normally used for small extensions. It should only span a short distance.
  • Couple roof: This is a simple roof which includes the rafters and the ridge beam. But it is rarely used nowadays as there is no lateral support. This can lead to roof spread and other defects. A collar roof is more often used, bringing us to our third type of pitched roof.
  • Collar roof: This is a simple roof with a collar to prevent roof spread. However, despite being more popular that the pitched couple roof, the collar roof is rarely used for roofs as it has a max recommended span of 4.5m.
  • Perlin roof: collared or coupled roof where there are purlins.
  • King post truss roof: This has additional supports in terms of the king post and the struts as seen below and is often used where a larger span is needed.pitched roof king post truss
  • Mansard roof with king/queen post: This is a pitched roof with an additional pitch and is often used when space is needed within the roof.
  • Modern Truss roofs: These pitched roofs have webs as bracing and tend to be prefabricated in a factory. They are easy and efficient to install as no specialist carpenters are needed when installed.These have become the norm in modern roof construction

Defects in a pitched roof

Defects in pitched roofs normally caused by 3 main factors; poor design, damp penetration and failure of the roof covering which we sometimes see in out house surveys in London.

Poor Designs found in pitched roofs

  • Inadequately sized members: Typically before 1890, nineteenth-century roofs often contained narrow rafters. Earlier roofs tend have extremely broad shallow timbers made worse by heavier roof coverings. It is therefore essential to check that the roof structure can take the additional load if a new type of covering is replacing it.

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