Callum wrote:

I had a chat with a builder who's doing the same thing to a house a
couple doors down. It's slightly different as they dont have the
dormer window, it's flat fronted so theres slightly more headroom on
the top floor.

Basically they were told by the council that the minimum size beam that
could be used in their case was 8x2. These were run parallel with the
3x2s and doubled up round the chimney (to support the beams directly in
front).

If you can show calculations to the council to demonstrate that your
choice of beam is sound then you should be able to use whatever "works".
Using 8x2 however would not be a major hassle in the scheme of things
since you could simply lift the existing floor and add a 2x2 on top of
the beams to rais the height to match the new bit.

You were right in thinking the 6x2 purlin was supported by the studs so
they had to strap on another 4x2 beam to strengthen it. The actual
span of the purlin was in fact 3.6m (from party wall to party wall).

The would suggest that either the roof construction is lighter that I
assumed, or it has some extra support you have not mentioned, or, they
have gone for a solution that is not really up to spec!

According to the calcs I did, even a 12x2 is not big enough, and that
was assuming a 3m span not 3.6. Hence why I suggested a flitch beam to
get the required strength.

Unfortunately all this means I'll have a two level floor but without
taking out the ceiling below I'll have to accept this.

Unless you prove the smaller beam is ok in the back, or pad the beams in
the front.

I forgot to ask the builder about bolting beams together, is there a
standard way of doing this (i.e. what size bolts, the spacing of these,
etc)?

If you are bolting, then 12mm bolts every 600mm on alternate edges, 50mm
in from the edge. Square plate washers under the nut and bolt head. If
it is a timber to timber joint (i.e. no flitch plate) then a dog tooth
timber connector goes on the bolt between the two bits of wood.

Sometimes when you just have a double side by side joist you can simply
nail them together.

If you go for any other bolt size then the costs go up rapidly because
the dog connectors and plate washers that are commonly available are
only in 12mm usually. So you would end up having stuff made or at least
adapted.


--
Cheers,

John.

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