May 2024

Pitched Roofing
LOW-PITCHED ROOFS:
ALL YOU NEED TO KNOW...
Roof pitches not only contribute to a building’s aesthetic appeal but also play a crucial role
in its functionality and durability. With this in mind, Ardit Strica, Technical Manager at
Onduline Building Products, provides a comprehensive overview of low-pitched roofs, their
challenges, and the transformative benefits of sub-roof systems.
Understanding roof pitches
The definition of a pitched roof, according to
British Standard BS 5534, is a roof with a
pitch greater than 10° and less than 75°.
For low-pitched roofs, anything under 20° is
generally considered as low pitch, while anything
below 10° is deemed a flat roof.
Several factors influence the selection of a roof
pitch, including material availability and cost,
aesthetics, construction ease or difficulty,
weather conditions, and local building
permissions. The client’s preferences and the
architect’s designs also play a pivotal role in
determining the roof pitch, as it significantly
impacts the external appearance of a building,
making it a crucial aesthetic consideration.
The pitch of a roof is not only an aesthetic choice
but also a practical one. Different loads, such as
snow, wind, dead load, and live load, exert forces
on a roof structure, making it essential to tailor
the pitch to suit the local weather conditions. The
choice of roofing material further influences the
final pitch, with concrete, clay, and slate being
common options. However, low-pitched roofs
present unique challenges, particularly in terms
of effective water drainage.
The challenge of low-pitched roofs
Low-pitched roofs, which are often applied to
extensions, come with their set of advantages
and challenges. While they may be considered
more aesthetically pleasing than flat roofs, slow
water runoff and limited tiling options are key
drawbacks.
In contrast to steep pitched roofs, where water
runoff is rapid due to gravity, low-pitched roofs
struggle to shed water efficiently. This can lead to
water pooling on the roof, causing leaks and
potential damage to the property. Additionally, the
limited availability of suitable tiles for low-pitched
Images show Onduline’s ISOLINE
LOW LINE roofing system.