5.5 metre span , on lean-to roof extension , low pitch

[clive12345]

Hello
I am going to build a single storey extension which would include a small bathroom.
I would be very grateful for some advice about the roof.
Using Trada tables I can build a flat roof using C24 220 x 75 @ 400 centres.
But I would like to pitch it , without using a box-gutter or putting too much
weight on my neighbours wall.
So it would have to be a lean-to pitched off the back of my house .
The span of the roof would be 5.5 meters, the pitch is 13 degrees.
The tiles I would use are centurion.
But the trouble is designing the roof, does anyone have any ideas on how I can do this .
I need a bathroom near the sewer so I would happily build a small supporting wall , plus wooden beam ,(as in diagram) to support a purlin.
I would prefer a cut roof without an rsj , unless it was a small one .
I have uploaded some basic plans of the extension .
Is this doable any advice would be really appreciated.
Thankyou.
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[pinenot]

I'm going to suggest a flitch beam, between the new wall end and a column built at the opposite side, this could be an internal feature, would minimise the applied weight and add central support for the span of you proposed flat roof...pinenot

 

[clive12345]

Thanks for the reply pinenot ,i have uploaded a 3d view
of the exterior ,does the flitch beam still work ?
Thanks

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[tony1851]

The easiest way to do that would be to split the span with a 152x152 steel beam. The rafters can be notched into the web, so that the beam would not show below the ceiling. With the span split in two, you could use 7x2 C16 rafters @ 400 c/s.
You would not need a column or pier at either end of the steel beam as the load will not be that much; it could sit straight into the side walls with a short padstone.
This way, your space is still open, and you can put (non-loadbearing) walls where you want.

 

[clive12345]

Thank you tony1851,that solution sounds ideal.