I have a loft that I want to insulate better, but also use as storage
space - so I don't want to lay deep insulation roll loosely on top.

It is currently fully boarded, with a bit of old fibreglass between the
joists. These are about 4-5 inches deep, holding lath and plaster ceilings
below. I have several LV lights in the ceilings below, which poke up
into the void I want to insulate.

The boards are currently up for other reasons, and here are the options
I have considered before putting them back down:

(1) Do nothing (but the fibreglass looks rather badly layed and isn't
filling the space well)

(2) Replace the old fibreglass with new insulation and put the boards
back. I guess Celotex blocks is the way to go? They could be about 4
inches deep. Can these rest on the lath and plaster ceilings or do
they need their own support? Or is the fibreglass just as good?
Would obviously cut around the LV lights.

(3) Make the joists deeper by adding 2x2s or 3x2s on top to get more
insulation, then reboard. This is probably too hard, and I'm hoping
4 inches of insulation is enough.

(4) Add a new layer of in insulation on top of the existing boards, and
lay new board on laths on top of this for my storage space.

A builder mentioned a new insulation product that was very thin but
effective, but not sure what he was referring to.

Any thoughts?

On 18 Jun 2004 15:42:44 +0100, John Richer wrote:

(3) Make the joists deeper by adding 2x2s or 3x2s on top to get more
insulation, then reboard. This is probably too hard, and I'm
hoping 4 inches of insulation is enough.

100mm is pretty thin by modern standards I think they recomend 200mm
these days but that would be open on the exposed sides the boarding
will have some insulating effect as well.

It's more faff to lay extra timbers but on the whole probably better.

You want to lay them across the existing timbers not along. Fill to
the top of the existing ceiling joist with glass fibre or WHY. Lay the
new timbers then fill to the top of them. This means that the only
direct through timber path from the ceiling to flooring is the small
areas where the timbers cross rather than the full area of each joist.
Laying the new joists cross ways also helps to spread the load across
the whole ceiling as well. Ceilings are not normally designed to take
much weight...

If you use celotex or similar you need to arrange ventilation between
it and the ceiling to avoid possible damp problems. Glass fibre is
breathable.

--
Cheers
Dave. pam is missing e-mail

On 18 Jun 2004 15:42:44 +0100, a particular chimpanzee named John
Richer randomly hit the keyboard and produced:

I have a loft that I want to insulate better, but also use as storage
space - so I don't want to lay deep insulation roll loosely on top.

The best insulation is currently Celotex (Kingspan is equivalent).
It's almost twice as effective as mineral wool. 100mm of mineral wool
isn't particularly effective, and you should be looking for at least
200mm thick, or 100mm Celotex between the joists.

When you start getting to these thicknesses of insulation, the heat
loss through the joists starts to become significant and you get
better 'value for money' out of your insulation if you can cover your
joists.
--
Hugo Nebula
"The fact that no-one wants a piece of this
shows just how far you've strayed from the pack"

Dave Liquorice wrote

If you use celotex or similar you need to arrange ventilation between
it and the ceiling to avoid possible damp problems. Glass fibre is
breathable.

Dave, in "normal" conditions of up to say 75% RH and a comfortable temperature,
vapour will always condense first on the cold side of the insulation, not on the
warm side. That's why "cold" roofs need to be ventilated. If there is a vapour
barrier it has to be on the warm side. Abnormal conditions would be something
like a steam bath in an igloo!

Peter

"Dave" == Dave Liquorice writes:

On 18 Jun 2004 15:42:44 +0100, John Richer wrote:
(3) Make the joists deeper by adding 2x2s or 3x2s on top to get
more insulation, then reboard. This is probably too hard, and
I'm hoping 4 inches of insulation is enough.

100mm is pretty thin by modern standards I think they recomend
200mm these days but that would be open on the exposed sides the
boarding will have some insulating effect as well.

It's more faff to lay extra timbers but on the whole probably
better.

You want to lay them across the existing timbers not along. Fill
to the top of the existing ceiling joist with glass fibre or
WHY. Lay the new timbers then fill to the top of them. This means
that the only direct through timber path from the ceiling to
flooring is the small areas where the timbers cross rather than
the full area of each joist. Laying the new joists cross ways
also helps to spread the load across the whole ceiling as
well. Ceilings are not normally designed to take much weight...

....but I think I am OK for load bearing in this case: it's a 3-storey
Victorian house and the joists in the ceiling of the 2nd floor look
closely spaced and large. The boards are also original Victorian in the
main so I think it was designed to be a storage space.

So your interesting idea of cross laying new timbers and insulation is
intriguing - also means it wouldn't be too hard to access the ceiling
for maintenance. But maybe 100mm celotex is enough.

If you use celotex or similar you need to arrange ventilation
between it and the ceiling to avoid possible damp problems. Glass
fibre is breathable.

Thanks for raising this - but is it really an issue in this location - a
ceiling void? I'll look at the celotex literature... If I really need a
50mm air gap there then I am only going to squeeze in 50mm of
insulation...

"Hugo" == Hugo Nebula writes:

On 18 Jun 2004 15:42:44 +0100, a particular chimpanzee named John
Richer randomly hit the keyboard and
produced:

I have a loft that I want to insulate better, but also use as
storage space - so I don't want to lay deep insulation roll
loosely on top.

The best insulation is currently Celotex (Kingspan is equivalent).
It's almost twice as effective as mineral wool. 100mm of mineral
wool isn't particularly effective, and you should be looking for
at least 200mm thick, or 100mm Celotex between the joists.

Thanks - the relative performance was just what I was looking for.

When you start getting to these thicknesses of insulation, the
heat loss through the joists starts to become significant and you
get better 'value for money' out of your insulation if you can
cover your joists.

So this suggests that if I do get to 50mm celotex, then I have done
enough. The attic rooms have sloping ceilings with loose fill
insulation poured between slates and lath-and-plaster sloping walls (a
previous owner's contribution to the house) so they will dominate the
heat flow.

On 18 Jun 2004 15:42:44 +0100, John Richer wrote:


I have a loft that I want to insulate better, but also use as storage
space - so I don't want to lay deep insulation roll loosely on top.

It is currently fully boarded, with a bit of old fibreglass between the
joists. These are about 4-5 inches deep, holding lath and plaster ceilings
below. I have several LV lights in the ceilings below, which poke up
into the void I want to insulate.

The boards are currently up for other reasons, and here are the options
I have considered before putting them back down:

(1) Do nothing (but the fibreglass looks rather badly layed and isn't
filling the space well)

(2) Replace the old fibreglass with new insulation and put the boards
back. I guess Celotex blocks is the way to go? They could be about 4
inches deep. Can these rest on the lath and plaster ceilings or do
they need their own support? Or is the fibreglass just as good?
Would obviously cut around the LV lights.

(3) Make the joists deeper by adding 2x2s or 3x2s on top to get more
insulation, then reboard. This is probably too hard, and I'm hoping
4 inches of insulation is enough.

(4) Add a new layer of in insulation on top of the existing boards, and
lay new board on laths on top of this for my storage space.

A builder mentioned a new insulation product that was very thin but
effective, but not sure what he was referring to.

Any thoughts?

Whatever you do, DO NOT use the shredded/treated newspaper loose fill
that is blown in. The ruddy stuff gets everywhere. I wouldn't
recommend it to my worst enemy. Earlier this year I removed all of it
and put the standard roll-type down. This was not expensive at all (I
got mine from B&Q).

MM

On 18 Jun 2004 20:49:59 +0100, John Richer wrote:

So your interesting idea of cross laying new timbers and insulation
is intriguing ...

Two benefits. Less heat loss through the timbers as mentioned by
someone else with 200mm it starts to get significant. Spreads the
load.

Thanks for raising this - but is it really an issue in this location
- a ceiling void?

Your lath and plaster ceiling has no DPM so the warm damp air will be
getting into a cooler area. Mr Taylor is correct that any condensation
will be on the cold side of the insulation but unless you are covering
the whole ceiling area there is going to be somewhere with less
insulation or where the warm air gets into the roof void proper.

I personally think that fitting rigid insulation in the confines of
loft will be a PITA...

--
Cheers
Dave. pam is missing e-mail

On 18 Jun 2004 20:52:59 +0100, a particular chimpanzee named John
Richer randomly hit the keyboard and produced:

Thanks - the relative performance was just what I was looking for.

The conductivity ('k-value' or 'lambda-value') is the relative
performance. AFAIR, the k-value for mineral wool is 0.037W/m^2K,
whereas for Celotex it's 0.023W/m^2K

So this suggests that if I do get to 50mm celotex, then I have done
enough. The attic rooms have sloping ceilings with loose fill
insulation poured between slates and lath-and-plaster sloping walls (a
previous owner's contribution to the house) so they will dominate the
heat flow.

I think I suggested at least 100mm thick Celotex. Although something
is better than nothing.

Your previous owner's contribution appears to be to create a high risk
of condensation in your roof by blocking the ventilation path between
the insulation and the roof felt.
--
Hugo Nebula
"The fact that no-one wants a piece of this
shows just how far you've strayed from the pack"

Hugo Nebula wrote:

On 18 Jun 2004 20:52:59 +0100, a particular chimpanzee named John
Richer randomly hit the keyboard and produced:


Thanks - the relative performance was just what I was looking for.


The conductivity ('k-value' or 'lambda-value') is the relative
performance. AFAIR, the k-value for mineral wool is 0.037W/m^2K,
whereas for Celotex it's 0.023W/m^2K


So this suggests that if I do get to 50mm celotex, then I have done
enough. The attic rooms have sloping ceilings with loose fill
insulation poured between slates and lath-and-plaster sloping walls (a
previous owner's contribution to the house) so they will dominate the
heat flow.


I think I suggested at least 100mm thick Celotex. Although something
is better than nothing.

Your previous owner's contribution appears to be to create a high risk
of condensation in your roof by blocking the ventilation path between
the insulation and the roof felt.

Agreed. You should try and put the celotex down the sloping bits, with
an air gap above.

Probaly means ripping out all the ceilings tho.

Mike Mitchell wrote in message . ..
Whatever you do, DO NOT use the shredded/treated newspaper loose fill
that is blown in. The ruddy stuff gets everywhere. I wouldn't
recommend it to my worst enemy. Earlier this year I removed all of it
and put the standard roll-type down. This was not expensive at all (I
got mine from B&Q).

Heard a brilliant tale about this stuff from a joiner the other day.
Another customer had put the stuff down all over the roof space, then
some months later needed to get up there again for something. He
removed the access panel in the landing ceiling, and was promptly
deluged with the tons of the stuff - apparently the loft had been very
well ventilated and the prevailing wind had blown the whole lot down
one end of the loft, where the hatch was. SWMBO was delighted, I'm
told.

David

Your previous owner's contribution appears to be to create a high
risk of condensation in your roof by blocking the ventilation path
between the insulation and the roof felt.

Yes, I have had concerns about this, but the surveyor did not flag this
up [1]; and there is no felt, just original welsh slate laid on battens,
so perhaps there is enough air movement to keep things dry?

[1] I know, one shouldn't expect 750 pounds worth of surveyor's report
to tell you anything useful.

The Natural Philosopher wrote in message ...

Agreed. You should try and put the celotex down the sloping bits, with
an air gap above.

Probaly means ripping out all the ceilings tho.

As my house has this same configuration, and comes with the original
vintage 1913 insulation down the slopey bits (ie none) I've been
wondering about doing this myself. However, not sure I have the
stomach to pull down all that lath and plaster etc.

If I was to stuff Celotex slabs down the sloping 'slots' from above,
how worthwhile would that be, given that the slabs would certainly not
be a perfect fit between the rafters? Would the small airgaps I'd
inevitably leave cause so much heat loss as to render the Celotex not
cost effective?

In comparison, how effective would it be to attach that thermal-lined
plasterboard(?) over the top of my existing ceilings?

Thanks
David

Lobster wrote:
The Natural Philosopher wrote in message ...


Agreed. You should try and put the celotex down the sloping bits, with
an air gap above.

Probaly means ripping out all the ceilings tho.


As my house has this same configuration, and comes with the original
vintage 1913 insulation down the slopey bits (ie none) I've been
wondering about doing this myself. However, not sure I have the
stomach to pull down all that lath and plaster etc.

If I was to stuff Celotex slabs down the sloping 'slots' from above,
how worthwhile would that be, given that the slabs would certainly not
be a perfect fit between the rafters? Would the small airgaps I'd
inevitably leave cause so much heat loss as to render the Celotex not
cost effective?


Probably. To be honest.

In comparison, how effective would it be to attach that thermal-lined
plasterboard(?) over the top of my existing ceilings?

If you have the room, FAR more effective IMHO.


Thanks
David

Hugo Nebula wrote:
On 18 Jun 2004 20:52:59 +0100, a particular chimpanzee named John
Richer randomly hit the keyboard and produced:

Thanks - the relative performance was just what I was looking for.

The conductivity ('k-value' or 'lambda-value') is the relative
performance. AFAIR, the k-value for mineral wool is 0.037W/m^2K,
whereas for Celotex it's 0.023W/m^2K

So this suggests that if I do get to 50mm celotex, then I have done
enough. The attic rooms have sloping ceilings with loose fill
insulation poured between slates and lath-and-plaster sloping walls
(a previous owner's contribution to the house) so they will dominate
the heat flow.

I think I suggested at least 100mm thick Celotex. Although something
is better than nothing.


Which particular celotex product? Looking on their website I can't see
any "loft insulation"....

The Natural Philosopher wrote:
Lobster wrote:
The Natural Philosopher wrote in message
...


Agreed. You should try and put the celotex down the sloping bits,
with
an air gap above.

Probaly means ripping out all the ceilings tho.


As my house has this same configuration, and comes with the original
vintage 1913 insulation down the slopey bits (ie none) I've been
wondering about doing this myself. However, not sure I have the
stomach to pull down all that lath and plaster etc.

If I was to stuff Celotex slabs down the sloping 'slots' from above,
how worthwhile would that be, given that the slabs would certainly
not
be a perfect fit between the rafters? Would the small airgaps I'd
inevitably leave cause so much heat loss as to render the Celotex not
cost effective?


Probably. To be honest.

In comparison, how effective would it be to attach that thermal-lined
plasterboard(?) over the top of my existing ceilings?

If you have the room, FAR more effective IMHO.


What would be the best way of attaching it?