Doctor Drivel wrote:
"Dave Page" wrote in message
...
Lobster wrote:

I was intending to replace the existing insulation - it's only about an
inch thick, dead old (over 10 years), and patchily installed. Plus
insulation seems to come (from Wickes at least, who are selling rolls ad
near-half-price until this weekend) in 170mm and 100mm depths.

The joists are 14" / 355mm apart, so there are plenty of them (this is
particularly annoying since insulation roll seems to come in 400mm
widths). The thought of laying new joists crosswise is interesting, not
least because it would save me a few screws.

As it was, I'm not planning on putting too much weight up there, and was
considering only raising every other joist to save on timber. On the other
hand, the loft hatch is only 750mm wide, so if I want the boards to be
supported by three joists, I'll need to space the joists at roughly 350mm
anyway

That sounds pretty useful. Wickes have some 40 x 100mm pre-cut 2.4m
lengths, I'll ask someone at the store whether it's suitable for my
purposes if it works out cheaper than a timber merchant.

Dave


Lets review the options.

1. Lay new joists on old at 90 degrees
This will leave you with a very weak floor, as well as being a pain to
insulate.

2. Lay new joists at 90 degrees on joist hangers into the walls
This is illegal in a lot of properties under the Party Wall Act, and
might get you into a bundle of trouble.

3. Add new 4x2 joists to the top of the old ones, inline, attaching
with glue and screws.
This is legal, and will bring a dramatic increase in strength to your
floor/ceiling structure, enabling you to stack goods to the roof
without worry of collapse, distortion, etc.
When joining timbers, (since it isnt easy to get a full length one in
there) the structure will be stronger if you glue joint them rather
than just butt them, but eiher will help.
Laying insulation is easy.

4. Add new wood on every other joist
This will cause damage to the ceiling, as the differing loads will try
to mildly corrugate the non-flexible plaster ceiling. Expect cracking
and damage.

Any 2x4 will do, as long as its straight. Spruce aka whitewood is
cheapest.


NT