My elderly parents had their roof insulated recently under some govt
grant or other; I haven't seen the result but apparently the installers
have laid a thick layer of Rockwool-type stuff at right angles to the
joists.

I recall as a teenager when I lived there myself, back in the 70s,
laying the original 3" insulation between the joists - bugger of a job
as it's an old house with lath and plaster ceilings, the spacing of the
joists is very variable, and the joists themselves are in poor shape,
very irregular in cross-section and many certainly wouldn't take a man's
weight if you were to step across them without using crawling boards.

So now, I gather from Mum (and can picture), the whole roof space is
just a homogenous sea of glassfibre; its impossible to tell where any of
the joists are, let alone the decent ones you can stand on. I'm sure
this scenario happens a lot, and probably doesn't matter too much
provided the roof space doesn't need to be accessed; but the main
problem with my parent's house is that there's a somewhat bizarre
arrangement with the chimney whereby the flue from the solid-fuel fire
it has a horizontal run of some 5 feet (IIRC) within the roof space.
This means there's a flue box up there (ie, a cast iron door in the side
of the flue) which the chimney sweep needs to access to clean the
chimney. Mum is convinced (with some justification IMO) that next time
the guy comes to clean the chimney , he's going to wind up falling
through on to the spare room bed...

Is there any obvious solution to this? Must be a reasonably common
problem. Short of lifting all the new Rockwool, all I can think of is
to just lay new, long, crawling boards between the loft hatch and the
flue box (quite a long way) and assume that there will be adequate
support along the way and at the ends...

David

On Sun, 17 May 2009 20:34:49 +0100, Lobster wrote:

My elderly parents had their roof insulated recently under some govt
grant or other; I haven't seen the result but apparently the installers
have laid a thick layer of Rockwool-type stuff at right angles to the
joists.

Warmfront I should imagine and the normal, not far removed from cowboy,
installation by the sounds of it.

Is there any obvious solution to this? Must be a reasonably common
problem. Short of lifting all the new Rockwool,

Well you only need to lift the sections between the hatch and the flue
box. How thick is the new insulation? Buy some 2 by whatever the thickness
is timber and some at least 18mm chipboard. Decide on a suitable width for
the access way say 18" and cut the 2 by whatever into those lenghts.
Locate the joists along the route and diagonal screw these bits to the top
of the joists, replace the insulation and screw the chipboard panels cut
to length as required onto the top. Screws in preference to nails so as
not to knock the lath and plaster ceiling off or crack it... I'd construct
a larger working area at the flue box.

--
Cheers
Dave.

Similar to the clowns that wanted to do my late mother's bungalow under
similar grant scheme. This was boarded and the space between the boards and
ceilings was already effectively full (OK, maybe 4 inches in a 5 inch
space). They wanted me to take up the boards. They were going to lay along
the existing joists and then I'd have to re-board. Couldn't convince the oik
that this would not in fact improve the insulation significantly. He'd been
on a course, so he knew all about it.

In article et,
"Dave Liquorice" writes:
On Sun, 17 May 2009 20:34:49 +0100, Lobster wrote:

My elderly parents had their roof insulated recently under some govt
grant or other; I haven't seen the result but apparently the installers
have laid a thick layer of Rockwool-type stuff at right angles to the
joists.

Warmfront I should imagine and the normal, not far removed from cowboy,
installation by the sounds of it.

Is there any obvious solution to this? Must be a reasonably common
problem. Short of lifting all the new Rockwool,

Well you only need to lift the sections between the hatch and the flue
box. How thick is the new insulation? Buy some 2 by whatever the thickness
is timber and some at least 18mm chipboard. Decide on a suitable width for
the access way say 18" and cut the 2 by whatever into those lenghts.
Locate the joists along the route and diagonal screw these bits to the top
of the joists, replace the insulation and screw the chipboard panels cut
to length as required onto the top. Screws in preference to nails so as
not to knock the lath and plaster ceiling off or crack it... I'd construct
a larger working area at the flue box.

The top of the insulation needs to be ventilated, so you either
need to make sure any boarding is raised a couple of inches above
the top with air flow from the sides, or lay slats (2 or 3 boards
with 1" gaps between them). If you don't do this, the underside
of the boards will become permanently wet, that being the first
cold surface which air leaking through the lath and plaster will
encounter with no ventilation, and it will eventually cause rot.

The other thing you could do is remove 12" strip of the new
insulation, and put the boards on the joists. That won't make
much difference to the effectiveness of the insulation overall.
(Same comments about ventilation apply.)

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On 19 May 2009 22:24:46 GMT, Andrew Gabriel wrote:

The top of the insulation needs to be ventilated, so you either
need to make sure any boarding is raised a couple of inches above
the top with air flow from the sides, or lay slats (2 or 3 boards
with 1" gaps between them). If you don't do this, the underside
of the boards will become permanently wet, that being the first
cold surface which air leaking through the lath and plaster will
encounter with no ventilation, and it will eventually cause rot.

Good point and one that I had completely missed. Our ceilings are foil
backed plasterboard so it wouldn't be a problem here but worth bearing in
mind with "porous" ceilings.

--
Cheers
Dave.