Graphical Construction Glossary >> Roofs and roofing. >> Roof Features >> parapet gutter

Parapet gutter
A gutter at the intersection of a parapet wall and the bottom of a roof slope.

box gutter and rainwater header
Sketch of a parapet wall and roof foot.

  • P-gutters are a type box gutter. The term seems to be interchangeable.
  • They drain rainwater from the bottom edge(s) of a sloping roof surface.
  • They generally appear to be flat, that is the top edges are parallel to the parapet wall and the roof surface.
  • The bottom surface must have a fall, generally between 1:40 to 1:200 slope.
  • The design of an efficient P-gutter is not a trivial matter. Unlike an external fascia gutter the consequences of a box gutter not doing it's job can be disastrous!
  • For this reason the roof framing should be designed at the start to accommodate efficient gutters.
  • In the sketch above I have drawn metal nail plate trusses that have a specific step to allow for the gutter.
  • The actual material for the gutter is usually out of "Zincalume" type sheet steel, but galvanised sheet and stainless steel is also common.
  • The gutter boards are to provide support for the actual pressed metal. A new trend is to not use boards, but to use thicker metal, say 2.0mm instead of 0.8mm.
  • This has the decided advantage of increasing the depth of the parapet gutter.
box gutter
Known as a triangle gutter this is not recommended. It is too easy to get blocked up and has limited capacity.

parapet gutter
This is an acceptable alternative to the triangle gutter but while this may be easier to frame it does not have the capacity that is possible with the first example.

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