My loft has a minimal amount of insulation that was probably put in
about 20 years ago. The house was built in 1984 and the loft is pitched,
unheated and ventilated.

Not sure of the correct terminology, but I refer to joists as the
horizontal wooden beams in the loft that the ceiling is fixed to and
what you actually walk around on. Rafters are the sloping wooden beams
that the sarking and tiles are fixed to.

(1)
I want to add more insulation. Current regulations say 270 mm for glass
wool, 250 mm for rock wool, or 220 mm for cellulose. Are there any other
rollable insulation systems that have a higher level of insulation thus
needing less height?

(2) If I need to add height to my joists, (it's a small house and need
to use the loft for storage) can I lay wood strips (of the same
dimensions as the existing joists) on top of the the existing joists?
How do you fix them in place, glue and the occasional nail or screw?

(3) I have electrical cables in the roof, although these are for
ordinary electrical lighting. Is it OK to have these covered by the
insulation? The cables are already covered with insulation by the
previous insulator/owner.

(4) Although it is an unheated and ventilated loft, will I get any
benefit from adding insulation between the rafters? I want to use some
thing that is enclosed in an aluminized bag so that it will (hopefully)
reflect some heat away during the summer.

Thanks.

Rob Horton wrote:
My loft has a minimal amount of insulation that was probably put in
about 20 years ago. The house was built in 1984 and the loft is pitched,
unheated and ventilated.

Not sure of the correct terminology, but I refer to joists as the
horizontal wooden beams in the loft that the ceiling is fixed to and
what you actually walk around on. Rafters are the sloping wooden beams
that the sarking and tiles are fixed to.

(1)
I want to add more insulation. Current regulations say 270 mm for glass
wool, 250 mm for rock wool, or 220 mm for cellulose. Are there any other
rollable insulation systems that have a higher level of insulation thus
needing less height?

Not rollable. Celotex between the joists would be the alternative, but
more work, and a lot more money.

(2) If I need to add height to my joists, (it's a small house and need
to use the loft for storage) can I lay wood strips (of the same
dimensions as the existing joists) on top of the the existing joists?
How do you fix them in place, glue and the occasional nail or screw?

(3) I have electrical cables in the roof, although these are for
ordinary electrical lighting. Is it OK to have these covered by the
insulation? The cables are already covered with insulation by the
previous insulator/owner.

(4) Although it is an unheated and ventilated loft, will I get any
benefit from adding insulation between the rafters? I want to use some
thing that is enclosed in an aluminized bag so that it will (hopefully)
reflect some heat away during the summer.

Rockwool slabs between rafters works well if you use the loft enough to
make it worthwhile.
Nobody seems to have much faith in the aluminium/bubblewrap sandwich
stuff you see in the sheds

Thanks.

On Thu, 15 Mar 2007 10:36:04 +0000 someone who may be Rob Horton
wrote this:-

(2) If I need to add height to my joists, (it's a small house and need
to use the loft for storage) can I lay wood strips (of the same
dimensions as the existing joists) on top of the the existing joists?

You can do. A better strategy is to top up the existing level to the
top of the joists and then lay rolls of insulation material at
ninety degrees to the joists around the edge of the loft, leaving a
central core that does not have this extra insulation or adding
boards above just the central core if this does get extra
insulation.

Lightweight items can be stored on top of the insulation and heavier
items stored in the central core.

Remember not to insulate under water tanks.

(3) I have electrical cables in the roof, although these are for
ordinary electrical lighting. Is it OK to have these covered by the
insulation?

Probably. Make sure there are only lighting cables though as the
cables of other circuits don't have as much capacity in reserve.



--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

Rob Horton wrote:

Not sure of the correct terminology, but I refer to joists as the
horizontal wooden beams in the loft that the ceiling is fixed to and
what you actually walk around on. Rafters are the sloping wooden beams
that the sarking and tiles are fixed to.

Yup, that would be my understanding also.

(1)
I want to add more insulation. Current regulations say 270 mm for glass
wool, 250 mm for rock wool, or 220 mm for cellulose. Are there any other
rollable insulation systems that have a higher level of insulation thus
needing less height?

Not that I am aware of. You would normally need to go to the rigid foam
board systems like celotex etc to get more insulation in less space.

(2) If I need to add height to my joists, (it's a small house and need
to use the loft for storage) can I lay wood strips (of the same
dimensions as the existing joists) on top of the the existing joists?
How do you fix them in place, glue and the occasional nail or screw?

If you don't need to store stuff in the space, then insulation just laid
counter to the exiting (i.e. across the joists rather than between)
will actually work better. No need for extra joist depth.

If you do want to floor it, then you can extend the joist height (screws
would be my favoured fixing since there is less chance of damaging a
ceiling with hammering). Alternatively you can use a roll insulation
between the joists, and a foam board over them, with the floor directly
fixed through it. If you only do a section like this is is not as
expensive, and it is quite easy to do.


FFFFFFFFFFFFFFFFFFFFFF --- floor boards
IIIIIIIIIIIIIIIIIIIIII --- say 50mm of foil covered PIR foam
##;;;;;;;;##;;;;;;;;## --- Existing joists with rock/iso wool between
##;;;;;;;;##;;;;;;;;##

(3) I have electrical cables in the roof, although these are for
ordinary electrical lighting. Is it OK to have these covered by the
insulation? The cables are already covered with insulation by the
previous insulator/owner.

Lighting cables usually have sufficient spare capacity that the
derrating effect of the insulation is not a problem (assuming your
lighting circuits are protected with a 5/6A Fuse/MCB). Take care that
other circuit cables are not buried though.

(4) Although it is an unheated and ventilated loft, will I get any
benefit from adding insulation between the rafters? I want to use some
thing that is enclosed in an aluminized bag so that it will (hopefully)
reflect some heat away during the summer.

Depends on whether you want have a "warm loft" - it may make for more
stable environmental conditions for things stored up there.


--
Cheers,

John.

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