Rafter Lengths

Rafter Lengths

Have you ever wanted to know how to work out the rafter length for your roof?

Here are two ways you can do this by applying a little bit of maths depending on what facts you already know.

Method 1  –  You know both the rise and run

The simplest way is to use Pythagoras’ Theorem which we have already written about here. Mathematically the rafter length, c, is found using the following equation:

1409736816Pythagorad1.jpg
1409736999Rafter length.jpg

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

For example. Rise = 1.8m, Run = 2.4m

Rafter length  =  √ [ (2.4)2 + (1.8)2 ]  =  3.0m

The eagle-eyed will have spoted this is another example of a 3-4-5 triangle.

Method 2  –  You know the roof pitch, θ, and the rise or the run.

Using a bit of trigonometry you can find the rafter length using the following equations.

Rafter length            =         Run ÷ cos θ       =         Rise ÷ sin θ

For example. Run = 2.4m, roof pitch = 45°

Rafter length  =  2.4 ÷ cos(45°)  =  3.39m to 2 d.p.

Any modern mobile phone will be able to perform these calculations.

There is a useful table below for your convenience.

Just multiply the rise or run by the appropriate rafter length factor corresponding to your roof pitch.

For example, if your roof pitch is 30ﹾ and your run is 2.4m then reading from the table the rafter length factor is 1.15. Multiply this factor by your run which gives your rafter length. If you want to add on a rafter foot (overhang) add this to your rafter length.

(   2.4     x     1.15  )     +     0.45     =     3.21 metre

                Run                Factor              Overhang           Rafter length

Roof Pitch
10 15 20 25 30 35 40 45 50 55 60
Rafter factor for rise (to 2 d.p.) 5.76 3.86 2.92 2.37 2.00 1.74 1.56 1.41 1.31 1.22 1.15
Rafter factor for run (to 2 d.p.) 1.02 1.04 1.06 1.10 1.15 1.22 1.31 1.41 1.56 1.74 2.00

Door Sizes Chart

Door size conversion chart

Please see below our helpful door size conversion chart.  If you still work in feet and inches, the chart will help you work out the metric equivalent size of our doors.

HEIGHT & WIDTH

Metric (mm)

Imperial (inches)

Imperial (feet & inches)

1981 x 457 78″ x 18″ 6′6″ x 1′6″
1981 x 533 78″ x 21″ 6′6″ x 1′9″
1981 x 610 78″ x 24″ 6′6″ x 2′0″
1981 x 686 78″ x 27″ 6′6″ x 2′3″
1981 x 711 78″ x 28″ 6′6″ x 2′4″
1981 x 762 78″ x 30″ 6′6″ x 2′6″
1981 x 838 78″ x 33″ 6′6″ x 2′9″
1981 x 915 78″ x 36″ 6′6″ x 3′0″
1981 x 1067 78″ x 42″ 6′6″ x 3′6″
1981 x 1168 78″ x 46″ 6′6″ x 3′10″
1981 x 1220 78″ x 48″ 6′6″ x 4′0″
1981 x 1372 78″ x 54″ 6′6″ x 4′6″
1981 x 1524 78″ x 60″ 6′6″ x 5′0″
2032 x 813 80″ x 32″ 6′8″ x 2′8″
2134 x 915 84″ x 36″ 7′0″ x 3′0″
2040 x 526 80 1⁄4″ x 20 11⁄16″ 6′8 1⁄4″ x 1′8 11⁄16″
2040 x 626 80 1⁄4″ x 24 5⁄8″ 6′8 1⁄4″ x 2′0 5⁄8″
2040 x 726 80 1⁄4″ x 28 5⁄8″ 6′8 1⁄4″ x 2′4 5⁄8″
2040 x 826 80 1⁄4″ x 32 1⁄2″ 6′8 1⁄4″ x 2′8 1⁄2″
2040 x 926 80 1⁄4″ x 36 7⁄16″ 6′8 1⁄4″ x 3′0 7⁄16″

Composite garden decking – Carpenter Built

Composite garden decking

Nice little project for a builder and his client in Burley-In-Wharfedale, Leeds, West Yorkshire.

Constructed using treated timber posts in the ground in concrete with timber joists forming the raised foundation.

Composite Witchdeck decking boards and trims. Uses a clip system to allow for movement.

I think that you’ll agree that this looks nice and with little maintenance other than a clean it has to be the future.

Call me to discuss

07544 030486

 

Have A Project or Need Guidance ? I Can Help.

Need a Hand ?

As Qualified Joiners we have the knowledge, expertise, experience and commercial tools to do a professional Bespoke Joinery service

Contact Robert 07544 030486 for Assistance and Guidance

Or if you prefer, email me at robert@coulsy.co.uk

Fully Qualified City and Guilds Advanced Craft Carpenter & Joiner since 1988 

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Handmade onsite Louvre Doors

Joiner Handmade onsite Louvre Doors.

When a client needs and urgent set of Timber vented Louvre doors making fo a bin store.

Had to grab the best redwood from the local merchant which wasn’t the best, but such a rush job.

However they turned out fine and when painted black looked like they were from the factory.