Sawn Timber Firrings

Sawn Timber Firrings are used to create a fall on a flat roof system. Typically these would be nailed onto a ceiling or roof joist to create a sloped roof. Despite its name, a flat roof (according to building regulations) should have a slight slope to reduce "ponding" or pooling of water on the roof. 

Flat Roof Firrings are typically cut to order, according to the specifications required for the job at hand. Our Flat Roof Firrings are cut to specification and can be made in a variety of heights and lengths. Typically these would fall under standard sizes of 50mm, 100mm and 150mm depending on the size of the roof. We can offer sizes outside of these measurements, both larger and smaller based on your requirements.

Most DIY'ers and general building work usually would be using firring that runs to 0mm. A "to 0mm" flat roof firring would run from a specified height at one end down to 0mm at the other. 

Building Regulations with regards to flat roofing systems:

The building regulations encourage a minimum fall of 1:40. The minimum finished fall required according to BS6229 is 1:80. Each roofing material has a minimum recommendation, which should be specified by either the architect or the roofing product manufacturer.

Remember - Timber is often measured as a nominal size. Timber that has been regularised (Such as the timber for firrings) finishes around 5mm less than advertised sizing (i.e 50mm becomes 45mm). Building regulations will specify falls based on units, NOT on timber sizing.

For a 50mm to 0mm firing: Building regulations recommend a run of no longer than 1800mm. (1:40 Fall)

For a 50mm to 0mm firing: The maximum run permissible according to BS6229 is 3600mm. (1:80 Fall)

A quick way to measure the correct size firring is to use the following formula:

• Length of run divided by fall.
• For a 3600mm roof, building regulations recommended fall of 1:40 - Take 3600mm divided by 40 = 90mm Fall Required
• For a 3600mm roof, BS6229 minimum recommended fall of 1:80 - Take 3600mm divided by 80 = 45mm Fall Required

90mm fall over 3600mm would be in line with building regulations 1:40 fall. Note: not all firrings need to fall to 0mm. A 100mm to 10mm timber firring would be suitable for use as a 90mm drop. Some roofers may specify a thicker end firring (i.e 100mm to 10mm) rather than a "to 0mm" firring. 

Where reference to building regulations or to BS6229 is made, this is based on reference material freely available and may not be the most up to date revision. For the latest regulations and guidelines, you should always check with the relevant government department or professional body.