purlin support

[Arthur]

Hi all. One of the purlins in my loft is supported at a point about 2/5th's from one side by a short piece of 6" x 3". This short piece sits on a beam 4" wide x 8" deep - running front to back -

4m in length and and the ends of this sit on the front wall and the top of a wall that separates the front bedroom and back bedroom.(its a pre - 1930's mid-terrace)

The beam is 2m and 2.87m from the party walls.on each side.

So, in theory this beam could be used to carry the loft joists to span the

2m and 2.87m gaps. My question, given the large section of this beam could the fact that it is only supported at the ends be ignored to carry the loft new loft floor?

I will be getting a structural engineer's opinion anyway. I'm just hoping I won't have to go 'over' it as that will mean losing a lot of height for the conversion.

Thanks.

Arthur

[Roger Mills]

What section is the purlin? Does the *other* purlin appear to have any intermediate support?

Are you sure that this short piece of 6x3 *is* supporting the purlin, and isn't actually supporting the beam which is 'hanging' from the purlin?

[Arthur]

The purlin is actually a 'double purlin' each of which is about 10" x 3". There is no sort of jointing between the 6 x 3 and the beam below and purlin above. And there is certainly nothing supporting the 8 x 4 beam..just a lath plaster celing and mine and wife's noggin each night.

Arthur

[Roger Mills]

By 'double purlin' do you means two full legnths of 10x3 side by side, or two shorter pieces which join above the 6x3 and make up the full length between them?

I assume it's supported both ends? Remind me how long it is.

Sounds to me like a job for structural engineer - I can't work out what's going on from your description.

[Arthur 51]

Thanks, Roger. By 'double purlin' I mean two 10" x 3"s extending the full width of the house. The 'beam' is about 4.1m (13' 6")

A

[Arthur 51]

Actually, the 'beam' in question sits above the lath and plaster wall separating the 2 front bedrooms. So it may be getting some support from below along its length albeit minimal.

Arthur

[Roger Mills]

A lath and plaster wall may well have a substantial frame - which would give more support than you may think.

Nevertheless, I can't honestly believe that the purlin is being supported by this beam. If a purlin needs support in the middle (which yours very probably doesn't), that support needs to be provided by something solid going down to ground level - not by something which is going to flex under load.

When's your structural engineer coming?

[Arthur 51]

Not booked him yet. I'm a bit antsy about it as I don't know how to specify exactly what I want from him. If I say the wrong thing he will be billing me for $$$$ $$$$$

Arthur

[Roger Mills]

Well, decide what you want to achieve in practical terms. You mentioned something a a new loft floor.

Tell him what you want to do, and what contraints you have - height-wise - and ask for his advice on how to achieve it from a structural point of view. He will have to analyse the existing structure to work out what additional load (if any) it would support, and then come up with a structural design - possibly involving steel beams if they are needed. Simple really!

[Arthur 51]

Good stuff. Thanks, Roger.

Arthur