Roger wrote:
The message
from "Steve Walker" contains these words:

A Petzl Ascender would do the job, eg eBay 120133093026.

I don't think an ascender would suit. They are just the modern
equivalent of the old fashioned prusik loop and, like the prusik
loop, you need to take the load off in order to move up the rope.

As I understood the OP's request, he wanted a one-way pulley -
something which would take and hold the strain. An ascender would
fulfill that perfectly, if deployed correctly, and is widely used to
protect both load-hauling and humans during cave/mountain
exploration. The conventional
technique would be to run the rope through a karabiner or pulley, and
attach
the ascender to the "pull" side, so that it provides a ratchet
effect.

I suspect you'll need to think of this as an 'upside down' location,
for that to make any sense at all. The key point is that you don't
have to relieve the load - it self-adjusts as the free end of the
rope is pulled through it. Quite hard to describe, and I can't see
a photo on google unfortunately.

If I understand you correctly that would work but what would you tie
it off to? You need a secure belay and houses typically don't have
suitable threads low down in the vicinity of the loft hatch. I
wouldn't want to trust a balustrade in such circumstances. The
roperachet works at the suspension point, not at ground level.

Heh, we're rapidly discovering the limits of textual discourse.... )

The ascender *is* located at the suspension point. Have a look at ebay
120133093026 for an example, and relate the following rig to the orientation
of that picture.

1 - Pull down the spring cam and slip a rope into the open sleeve on the
left.

2 - Clip a karabiner through the pair of holes at the top, keeping the rope
to the left of the 'bar' this creates.

3 - Clip another karabiner to the suspension point, preferably with a pulley
(http://tinyurl.com/28ac9y).

4 - Run the load rope through the suspension karabiner or pulley, with the
ascender below.

5 - Clip the first karabiner (step 2) into the second karabiner.

Hopefully you can now see in your mental picture that a ratchet effect is
created. Hauling on the free end of the rope will pull it through the
ascender easily, as the cam opens in that direction. When you stop
hauling, the load weight is held by the ascender as it won't allow the rope
to pass in the reverse direction.

One of the drawbacks to this system is that there's about 3-6" of free play,
as the metal components bunch together and stretch out under different load
states. Minimising that work-wasting free play is the subject of many pub
debates and climbing wall experiments.