Callum wrote:

Can anyone help me with the following problem. I'm currently
renovating a 3 storey terraced house, and have moved onto the top floor
(see diagram below). The top floor is in the roof, but isn't an attic
conversion as there is an original dormer window to the front. The
problem I have is I want to create more space by knocking down a wall
(see * in the diagram below - it's only a lathe and plaster wall, non
load bearing) and taking the room into the eaves. This should be easy,

You may well be right, but don't assume that just because it is a stud
wall it is not load bearing.

but where they used 6x2 joists (see 1) in the room, they used 3x2
joists (see 2) in the eaves. On top and across of the smaller joists
runs a 6x2 joist, which I guess is to stop them sagging with the weight
of the ceiling below. This joist is supported by the outer wall and
the last 6x2 joist. I guess this joist will have to come out
eventually as it's 3 inches higher than the floor in the room (3 inch
joist below + 6 inch joist = 9 inches vs 6 inch joist in the room)

Oh, I think I have played this game before... ;-)

How can I re-inforce these smaller joists so they can take the weight
of people moving around (although they are in the eaves, there is
enough head room for a bed, desk, etc). I'd also like to be able to
keep the whole floor at the same level.

The way it is normally done is to ignore the smaller joists and insert
ones of the required size interspaced between them so that the new ones
run parallel to the old ones.

That does mean that you will need to cut the old tie beam however. The
way to do this is one section at a time. before you cut a section you
strap what will be the cut ends to something solid so that it can not
move. After you have at least two of the new beams in place, you can
then place a noggin between them, which you fix to the old joist to
replace the function of the tie beam for that joist.

Here is one I did ealier:

http://www.internode.co.uk/loft/floor.htm

First and second photos on this page show what it sounds like you are
describing. The tie beam was only a 4x2 in my case, but the same
principle applies. The last photo shows the floor with the tie beam gone
and its function replaced by noggins.

Two things spring to mind. Firstly doing this will probably need
building regulations approval (and hence submission of a building notice
etc). The BCO may want to see calculations to show the new floor will
meet the required deflection limits etc.

Secondly, it is usual to insert new beams with a spacer under their ends
so that they keep clear of the existing ceiling. This saves and chance
of damaging the ceiling when they deflect. In your case however you may
not want to do this since it would take the floor level up a bit from
the rest of the joists. You may be able to get away slightly less deep
(but perhaps wider) joists - although you are not starting with much.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/