"DjB" wrote in message
...
snip
A couple of things I'm not clear about - when installing the hangers into
a
brick wall, do they have to be bolted? Or is it sufficient to cut a small
chase into the wall, slot the hanger in place and apply some mortar? The
other ends of the joists have to be fitted to hangers that are fitted to
the
joist running across the fireplace, I presume I need to find some sort of
hooked hanger that will hook over the joist. I had a look in a timber
yard
over the weekend and they had some that had long ends which can be bent
over
but they didn't look that strong. Are there stronger ones available or is
there a better way of doing this?
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The joist hanger provides support for the end of the beam against downwards
movement.
This is either done by hooking over a beam or wall, where the hook carries
the weight, or by directly fixing to a wall if the wall is already built.
Where you are directly fixing to the wall the fixings carry the weight, not
the hook (as there is no hook!).
So you have to think about how strong a fixing you need to carry the weight
of e.g. a 2" * 6" beam and the floor above (plus furniture etc.).
The ones I have used have large holes in them to take wall bolts - these can
carry a large weight.
If you are using these there is no need to chase into the wall; they are
designed to fix directly to the wall like a very large shelf bracket.
Page 141 of the Collins DIY manual has a picture of a face fixing joist
hanger but the usual sheds and B&PM don't seem to carry them - I had to go
to a specialist supplier on an industrial estate.

If you are taking up the floor you can then hook over the wooden joist by
your fireplace.
In this case IIRC you just have to secure the hanger to the wood with nails.
The nails don't take the weight, just make sure the hanger doesn't shift or
twist.
This way you can be sure that the load is being taken by the hook at the
top.
When I first saw these I thought they were too flimsy to take the load, but
apparently they work.

I guess you could cut a notch in the mortar above a brick and insert the
hook bit at the top of a hanger to take the weight of the joist.
However I am not sure if you are supposed to fix down through the top flange
into the underlying brick/block work.
The pictures on P182 of the Collins manual clearly show holes in the top
flange and presumably they are there for a reason :-)
However this may just be for nailing if you are fixing to wood.

P188 of the Collins manual has a good write up on replacing a joist.
Might be worth going into a bookshop and reviewing these bits.

HTH
Dave R

P.S. with face fixing hangers you shouldn't have to take up the floor - you
prop the beam up, offer up the hangers from underneath the beam, bolt them
to the walls and Robert is your parent's brother.
However this method does not guarantee a tight fit up against the floor,
hence my comments about an extra spacer (packing) between the joist and the
bottom of the joist hanger to take up any slack. A piece of thin ply can be
used.