I saw a program a while ago (forget what it was) where they recommended
that you overlay new insulation across the rafters over the insulation
which is already there (mineral roll type), in order to bring the depth up
to the recommended level (ours is 6 inches deep).

However, I haven't seen this mentioned anywhere else and it would make
access to the roof from inside using the rafters pretty difficult should
this be required.

Is this something I should be doing, or not?

richgk wrote:
I saw a program a while ago (forget what it was) where they recommended
that you overlay new insulation across the rafters over the insulation
which is already there (mineral roll type), in order to bring the depth up
to the recommended level (ours is 6 inches deep).

However, I haven't seen this mentioned anywhere else and it would make
access to the roof from inside using the rafters pretty difficult should
this be required.

Is this something I should be doing, or not?

It certanly reduces heatloss to next to bugger all, but as you point
out, it makes it hard to use the loft space.


It doesnt kill draughts in the loft insualation either. Rockwool is not
so good without a draught stopper.


Consider transverse joists across original,. rockwool filled and plated
with flooring chip.

If you pay attention to the edges of thus where the loft soffit vents
are bound to be, and seal teh slab against draughts, its about as good
as it gets,

In article , The Natural Philosopher wrote:
richgk wrote:
I saw a program a while ago (forget what it was) where they recommended
that you overlay new insulation across the rafters over the insulation
which is already there (mineral roll type), in order to bring the depth up
to the recommended level (ours is 6 inches deep).

However, I haven't seen this mentioned anywhere else and it would make
access to the roof from inside using the rafters pretty difficult should
this be required.

Is this something I should be doing, or not?

It certanly reduces heatloss to next to bugger all, but as you point
out, it makes it hard to use the loft space.

It doesnt kill draughts in the loft insualation either. Rockwool is not
so good without a draught stopper.

Consider transverse joists across original,. rockwool filled and plated
with flooring chip.

http://www.space-insulation.com/board.html is another option that might
be easier than transverse joists. They do a version with the chipboard
included too:
http://www.knaufinsulation.co.uk/pre...loft_deck.aspx

Possibly not the cheapest option though...

On this subject:
I recently did the energy assessors course and was suprised to find
how little effect extra loft insulation has. Playing with the software
it seems that the first 100mm of insulation will reduce your heating
bill by 12%, an extra 100mm will reduce your heating bill by only an
additional 2%. Cheap as rockwool is, you won't get any return on your
investment over 200mm.

The above figures vary depending on construction type but the
proportions are about the same.

On Tue, 14 Oct 2008 15:05:15 -0700 (PDT), Rednadnerb
wrote:

On this subject:
I recently did the energy assessors course and was suprised to find
how little effect extra loft insulation has. Playing with the software
it seems that the first 100mm of insulation will reduce your heating
bill by 12%,

Surely that depends on the other heat losses, via walls, draughts,
fenestration and so on?

--
Frank Erskine

On 14 Oct, 23:17, Frank Erskine wrote:
On Tue, 14 Oct 2008 15:05:15 -0700 (PDT), Rednadnerb

wrote:
On this subject:
I recently did the energy assessors course and was suprised to find
how little effect extra loft insulation has. Playing with the software
it seems that the first 100mm of insulation will reduce your heating
bill by 12%,

Surely that depends on the other heat losses, via walls, draughts,
fenestration and so on?

--
Frank Erskine

Yes, your right it does but the principle that the first 100mm of
insulation does 90% of the work is the point I wanted to make.

Frank Erskine wrote:
On Tue, 14 Oct 2008 15:05:15 -0700 (PDT), Rednadnerb
wrote:

On this subject:
I recently did the energy assessors course and was suprised to find
how little effect extra loft insulation has. Playing with the software
it seems that the first 100mm of insulation will reduce your heating
bill by 12%,

Surely that depends on the other heat losses, via walls, draughts,
fenestration and so on?

Indeed.

In my house the domainant heat loss is two inglenook chimneys, and the
ventilation the BCO insisted on..

In message , The Natural
Philosopher writes
Frank Erskine wrote:
On Tue, 14 Oct 2008 15:05:15 -0700 (PDT), Rednadnerb
wrote:

On this subject:
I recently did the energy assessors course and was suprised to find
how little effect extra loft insulation has. Playing with the software
it seems that the first 100mm of insulation will reduce your heating
bill by 12%,
Surely that depends on the other heat losses, via walls, draughts,
fenestration and so on?

Indeed.

In my house the domainant heat loss is two inglenook chimneys, and the
ventilation the BCO insisted on..

They didn't mention it with ours. Not so grand perhaps but still
substantial fire openings and flues.

I am still ruminating on the log burner. With a bit of effort I can put
a duct under the floor which allows me to go for a stove over 4.9kW.
Convincing myself that something with a 10 year payback is worth doing
is less easy. Hetas engineer and plumber availability is another issue.
I'm inclined to wait for the current rush to die down as people realise
that a sustainable fuel is not necessarily convenient or cheap.

regards

--
Tim Lamb