On Sep 22, 1:50*am, neil wrote:
Hi Guys

A mate of mine wants help [1] insulating his loft in his old house and
I'm after any ideas and guidance on options, a quick archive check has
only some old suggestions, so I'm after newer info or a better solution
than mine below.

The house is 100 years old, the attic room was servants quarters(!) and
bit that needs doing is vast at 5.6m square, with a walk under purlin at
1.9m, the flat bit of the ceiling is probably over 3m high forming an
area 1.2m wide but with no access above. The roof is 8" x 6" rosemary
tiles with failing tiering mortar so damn windy. The eaves areas are to
be conventionally insulated with space roll between the joists and the
'walls' probably with EPS slab, the rafters are only 4" deep and with
tiering mortar encroaching on that gap above and Lath and Plaster nibs
below, so no easy access to insulate above L+P and below the tiles (but
see below) so an internal solution is needed.

The lath and plaster ceiling is in fairly poor condition and really
needs pulling down and replacing with PIR between rafters and insulated
plasterboard below, BUT he doesn't have enough money for that, so 'plan
A' (TM) is to stud the ceiling and use EPS and normal plasterboard, or
plan B is to use insulated plasterboard screwed straight onto the
existing ceiling (hopefully ?).

Any of this a goer?

Yes. There's not a lot of point pulling the ceiling down.

I haven't checked the rafter pitch yet but I think 16" is likely, but it
looks a bit variable... The plan is only to board the roof area between
the purlins but try and shove some rigid insulation up to there from the
eaves area, and to purlin level it is just that bit wider and taller by
a gnats (I think) and this keeps the cost and complexity down.

I envisage 8'x4' sheets running along the existing flat ceiling and then
cut sheets following the angle, with just a batten just to fiddle the
old curve transition if fixing boards direct is possible.

Given the lack of funds, what is likely to be the best 'bang for buck'?
I hope directly fixed PIR insulated plasterboard, rather than EPS and
plasterboard, as this might get better insulation values for the same
outlay?

If I have to batten the roof for EPS, is just along the roof sufficient,
so four timber lengths with end framing? If I can fix insulated
plasterboard straight to the existing ceiling I assume a screw every
rafter at say 4 across a board would do?

As you might tell I'm a bit out of my comfort zone and realise I need
guidance, I know if I use EPS I should put a vapour layer between it and
the PB and if I use 'good' insulated board it will have foiled PIR but
how to arrange a seal between ceiling and sloping boards for instance,
would SBR or somesuch on the PB side be enough if the seam was sealed?

The vapour barrier doesn't have totally water tight. You just need to
stop /most/ of the vapour getting through and condensing.

Getting a draught tight seal is /extremely/ worthwhile though. You
would be amazed how warm 16 degrees feels when there are /no/
draughts. Make sure you go round all the edges with expanding foam
(if sealing around EPS) or caulk (if sealing around PB).


Good luck.