I live in an end terrace house and am contemplating putting insulation
(glass fibre roll?) in the loft between the roof rafters and boarding them
over as a way of increasing insulation, as well as insulating and boarding
the floor of the loft , my question is this OK to do and are their any
problems I need to be aware of by doing this ?.......i.e airflow etc?
BTW I will basically be using this area as a storage area for tools...
knick knacks etc
I have done this in a detached house, though I only boarded over a fairly
large central area and didn't go right to the extreme edges of the area,
leaving an estimated 6 foot gap around the edges.
The main thing I was concerned about was access to the wiring after the
boarding was laid. In the end I just marked the position of junction boxes
and accepted that a certain amount of butchery would be required in the
unlikely event of problems. The wiring was PVC insulated and only a year or
No problems regarding condensation, or anything else have been noted.
The boards I used were the chipboard variety, specially made for the job,
being narrow, in order to fit through most loft access traps and with their
edges profiled to lock together for strength. The problem I found in fitting
was that the ends don't lock together, being plain butt joints and when the
junction occurred centrally between the rafters I wasn't happy with the
apparent strength in this region when I stood on them. I therefore placed a
reinforcement to cover the ends when they were in this situation. Some may
be perfectly happy with the unreinforced situation but I wasn't.
Don't forget the mask for the glass fibre particles.
Sorry I misunderstood your project somewhat. My intention was only to
provide a storage area on the ceiling supports. I now understand that you
intend to proceed more along the lines of a loft conversion type task, which
I didn't do.
Sorry, can't really offer any advice about insulation behind the boarding
covering the tiles. No doubt there will be other better informed along
I haven't actually insulated the roof of my house, but in my investigations
for the garage conversion, I have seen what I would do if I DID insulate the
roof that way.
These types of insulation provide about twice the insulation of the same
thickness of fibre glass according to my council inspector. And apart from
the sawing, (which with Celotex is messy and sticks to sweat) , it's much
easier to handle. You definitely want a mask for this type of insulation too
Similar insulation is available from Kingspan, Knauf or Gyproc. Check out
Be careful about putting that type of insulation between the rafters
as you could give yourself problems later with condensation.
The normal way of insulating a loft space (as in a loft conversion) is
to put ridgid PIR insulation board between the rafters leaving a 50mm
air gap under the felt for ventilation. By the way doing this won't
increase the insulation of the house as such, as all insulation should
form one layer.
I agree with your result, but not the reasons.
I don't think it will help, but that's because the loft ventilation will
mean that the air in the loft is near to external temperature rather
than because it is separate layers. So long as you have an enclosed, or
no, space between them separate layers will work just fine.
I have previously been advised by both Kingspan, Celotex and building
control that insulating the floor and the rafters separately is not an
acceptable solution at least in terms of complying with regulations. I
agree in part about the closed space between them but this only really
applies where say the insulation layers are in relatively close
proximity. Apart from anything else if you rely on ceiling and rafter
level insulation you would would needlessly be heating your loft space
and there would only be the rafter level insulation to prevent heat
The best solution is to put all the insulation sufficient for
insulating the house at ceiling level, and then treating the loft
separately. I would suggest verifying with one of the larger
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