145x100 Rafters ???

[jigabyte]

Thanks for that but that means nothing to me sorry. If I am going out by 3.6 meters and the outer wall it going to standard french door height and it starts 16.5 bricks up from the door level how can I work the pitch. This is another issue because on the drawings he wanted me to have 3 coarse of brick on the projected wall but that would give me a 12.5 degree pitch so I am now putting the rafters staight on to the catnic (wall plate). So I can hope to get 15 or more degrees for the velux windows.

 

[noseall]

Pitch is actually worked out using soh-cah-toa.

In this case you will use toa, i.e. tangent = opposite over adjacent.

Divide the rise by the going then press inv. tan on a scientific calculator and the figure will be the pitch in degrees.

So lets say the going was 3.6m and the rise say 1m. 1 divided by 3.6= 0.277777778. inverse/tangent= 15.52411 degrees.

Using Pythagoras will merely work out the lengths of a right angle triangle particularly the hypotenuse.

 

[Shytalkz]

Your rafter span isn't 4.2m up the slope then, between plate and existing wall.

 

[jigabyte]

With the overhang it will be.

 

[cmother1]

Jigabyte - Sounds as if the old boy has simply made a mistake & meant to say 50mm instead of 100. As an old boy myself I can sympathise with him! I'd have thought 8x2's would be fine for your job, but building inspectors are a funny breed...

Your mate has done well to get away with 6x2's (as we used to call them) for his roof. 12 years ago the BC inspector for my extension said the maximum span for this size of timber was 3.2m.

NB: You'll probably be asked to double up the timbers down the side of the rooflight so budget/buy enough timber to cover this.

 

[jigabyte]

Thank you very much for you reply. I have ordered 7x2 and the building inspecter says this is fine. My span out going is 3.6 meters and 7x2 aparantly supports 4 meters.

I need to double up for the velux's which I can understand.

O the joys of having an extension;

Thanks again,

jiggy!