In article . com,
wrote:
Is there a recommended way of working out the size of a joist (e.g.
50x150) required to span a 3m distance? It needs to be robust as it
will be supporting a washing machine pretty much on its center point.

The old rule of thumb for floor joists was to halve the span (in feet)
and add 1 to get the required joist depth in inches - i.e. for 10' you
need 6"x2" [at 16" centres] - or 50x150 at 400c/s in new money. This
assumes a superimposed load of 1.5kN/m2 or 30lb/ft2, so one of these
joists is good for 30x10x16/12 400lbs. Do the sums using a well known
program g and you'll find that the calculated maximum span is about
3.1m. If all the load is at the centre of the joist the load it can take
about 1.4kN or about 320lbs. Your washing machine probably weighs less
than this and the floor deck will spread the load over several joists.

One of the walls that the joist will attach to is a conventional brick
wall. To attach to this wall I was planning on cutting a grove with an
angle grinder and then using joist hangers.

Given the curve of the blade, stitch drilling with a suitable drill bit
might be better

At the other end, the wall is soft breeze block - so soft that I can
easily push a screwdriver blade into it. I'm assuming on this side that
I'll need to support it from ground level rather than attaching to the
breeze blocks - The new floor is only going to be about 2ft above an
existing concrete garage floor, so this would be relatively straight
forward as a solution.

Soft as in aerated concrete - like an Aero choc bar but grey? Assuming
that the blocks are 100mm thick or more they are perfectly capable of
holding your joists.

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Is there a recommended way of working out the size of a joist (e.g.
50x150) required to span a 3m distance? It needs to be robust as it
will be supporting a washing machine pretty much on its center point.

One of the walls that the joist will attach to is a conventional brick
wall. To attach to this wall I was planning on cutting a grove with an
angle grinder and then using joist hangers.

At the other end, the wall is soft breeze block - so soft that I can
easily push a screwdriver blade into it. I'm assuming on this side that
I'll need to support it from ground level rather than attaching to the
breeze blocks - The new floor is only going to be about 2ft above an
existing concrete garage floor, so this would be relatively straight
forward as a solution.

Don

On 10 Oct 2005 05:15:01 -0700, wrote:

Is there a recommended way of working out the size of a joist (e.g.
50x150) required to span a 3m distance? It needs to be robust as it
will be supporting a washing machine pretty much on its center point.

One of the walls that the joist will attach to is a conventional brick
wall. To attach to this wall I was planning on cutting a grove with an
angle grinder and then using joist hangers.

At the other end, the wall is soft breeze block - so soft that I can
easily push a screwdriver blade into it. I'm assuming on this side that
I'll need to support it from ground level rather than attaching to the
breeze blocks - The new floor is only going to be about 2ft above an
existing concrete garage floor, so this would be relatively straight
forward as a solution.

Don

The building regs have a load of tables, which tell you the sizes. I
don't have my copy handy, else I'd look for you. The type of wood
effects the size.

If you can support from ground level all the way accross, you can make
dwarf walls to hold the joits, which can now be much smaller.

Rick

wrote in message
ups.com...
Is there a recommended way of working out the size of a joist (e.g.
50x150) required to span a 3m distance? It needs to be robust as it
will be supporting a washing machine pretty much on its center point.

SNIP

At the other end, the wall is soft breeze block - so soft that I can
easily push a screwdriver blade into it. I'm assuming on this side that
I'll need to support it from ground level rather than attaching to the
breeze blocks - The new floor is only going to be about 2ft above an
existing concrete garage floor, so this would be relatively straight
forward as a solution.

Don

I've used joist hangers in lightweight block cut with an angle grinder for
a 4m span and it worked fine.

Alistair