We live in an old house (1840)and the roof of this house has its lower part
pitched and the upper part has a more conventional flat ceiling, rather
like this (in x-section)
Where the upper part (above the ceiling) is sealed. My problem is that the
room is very cold so today I sawed a hole in the ceiling to see how much
insulation was there. I was surprised to see that a previous owner has
laid fibreglass wool perpendicular to the joists and not in between them.
I can't think why this would have been done. Does anyone else know why? My
plan is to re-lay this insulation in between the joists and to poke
additional insulation wool down each of the channels (formed by the
joists) in the the pitched part of the roof. Can anyone think of a better
Hmm, that'll help the temperature won't it? :)
to see how much
Not normally a good idea to lay it perpendicular since you can't see
the weight-bearing joists to stand on; also any wiring should be
attached to said joists (and hence visible). However, I would think
laying a given thickness of fibreglass perpendicular, rather than
parallel to the joists would actually improve the insulating
properties since there will be a layer of insulating air trapped
between fibreglass and ceiling. Maybe that was why it was laid that
way; the installer reasoning that since in his wisdom he didn't bother
installing an access hatch, nobody was likely to be going up there for
a wander round.
Count yourself fortunate there's any insulation up there at all! In
the last place I bought, the roof void above half the house was
totally inaccessible from below (no hatch) and there was a brick wall
separating it from the attic over the rest of the house. However, I
could just squeeze my digital camera through a small brick hole in the
eaves and shot off some flash photos - revealing that the whole
area had no insulation at all (despite having a brand new, freshly
skimmed and painted plasterboard ceiling.
Suggest you have a google for the thread "Loft Insulation - Best Type
and Tips for Installation" in which a roof of similar construction to
yours was discussed in this ng a few weeks ago.
 Very Useful Tip for exploring dark otherwise inaccessible places
where you can't get you eye and/or light to the hole...!
On Fri, 31 Oct 2003 21:53:15 +0000, a particular chimpanzee named
I can't think of a worse solution.
You get less value from insulation between the joists than covering
them, as heat is lost through the joists leaving up to 12% of your
ceiling uninsulated. As other posters have said, the insulation has
traditionally been laid between the joists to allow access, but as
your roof void is sealed, then this is not a consideration.
You need to leave a gap between the insulation and the underside of
the felt to allow for ventilation and for the felt to drape. Use a
rigid insulation board such as Celotex or Kingspan to a depth of 50mm
less than your rafters.
"You know, I'd rather see this on TV,
I did mine when the slates were off the roof. My firebglass runs both ways,
first in the joists, and then over the top of the whole lot, there is about
450mm in all up there now.
For the sloping sides you have a problem, anything you poke down, will in time
slide to the bottom. I would call round a few cavity wall type people and see
if their cavity wall stuff is suitable - I have no idea if it is or not. You
also see adds for people that spraf insulation onto the unserside of old
roofes, maybe thay can help ? Squirting something in that sets sounds like the
way to go to me .......
Nooooo!!!. If there is one thing I'd never do to insulate a roof, it is to
have the underside of the roof sprayed with foam insulation. In all honesty
it is probably the worst solution, restricting airflow over the timbers
(causing damp/rot) and potentialy making future roof maintenance more
difficult. Furthermore, I know of a couple of surveyors who will knock down
the value of properties with this form of insultation simply because there
is no way of assessing the state of the roof timbers.
If you want to insulate the underside of the roof, use a sheet material such
as Celotex or Kingspan.
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