Tony Bryer wrote:

On 29 Dec 2006 12:53:37 -0800 Dob wrote :
What I am interested to know is,as I haven't got access to software to
calculate necessary sizes,is it possible to span an 18 1/2 foot gap
with timber ? - if so what would the dimensions need to be,I'd prefer
to work in timber or possibly construct a flitch beam

Not easily, particularly since headroom is a factor. You would need to
take the advice of a structural engineer.

I only intend on putting one room up there with a dormer at the back
and a velux at the front.The stairs will access directly under the
apex,flush with the wall so will have 2m head room,if the present
floor height remained unchanged.

Is there a minimum requirement for headroom within the room,it
wouldn't be a problem for me as I'm 5'8",but obviously the world is
generally full of taller people than me.

The only headroom rules relate to staircases and landings, but
substandard headroom is likely to be a major turn-off for most potential
buyers. I suspect that any design is likely to involve a floor level
that is higher than the top of the existing joists.

Is the property detached? If so, I'd be inclined to think about a total
roof reconstruction to make proper rooms possible.

--
Tony Bryer SDA UK 'Software to build on' http://www.sda.co.uk


Yes the property is detached.
What I was considering was putting two beams across the narrowest span
and running joists alongside the current ones.The size of the main
supporting beams doesn't matter too much as they can be at the side of
the room to be constructed and be the base of the dwarf wall rising to
the rafters,so if I could use joist hangers on the main supporting
beams that have the cup that holds the joist lower than top of the main
beam I may be able to get enough headroom? if that makes sense