Hi,

Reading about HIPs has made me think about my loft insulation, so
they're doing some good already.

In my victorian terrace the loft insulation is a bit wimpy - tired-
looking fibre glass between the joists which looks like it was laid a
good few years back, probably no more than 75mm. A lot of it is now
under chipboard flooring which I don't much want to take up.

I'm thinking that to make it better I could put insulation between the
rafters (I'm never sure about roofing terminolgy, I mean the lengths
of wood that support the tiles and make up the pitched roof itself).
What do you think? If this is a viable option would this sort of stuff
do the job?
http://www.screwfix.com/app/sfd/cat/...76477&ts=18194
Or is cellotex the way forward?

The design of the house means that the (original) top bedroom is
partly up in the roofspace, and it can get uncomfortable up there on
the hottest summer days, so I'm hoping doing this would keep the loft
cooler in the summer too.

Cheers!

Martin

Martin Pentreath wrote:
Hi,

Reading about HIPs has made me think about my loft insulation, so
they're doing some good already.

In my victorian terrace the loft insulation is a bit wimpy - tired-
looking fibre glass between the joists which looks like it was laid a
good few years back, probably no more than 75mm. A lot of it is now
under chipboard flooring which I don't much want to take up.

I'm thinking that to make it better I could put insulation between the
rafters (I'm never sure about roofing terminolgy, I mean the lengths
of wood that support the tiles and make up the pitched roof itself).
What do you think? If this is a viable option would this sort of stuff
do the job?
http://www.screwfix.com/app/sfd/cat/...76477&ts=18194
Or is cellotex the way forward?

The design of the house means that the (original) top bedroom is
partly up in the roofspace, and it can get uncomfortable up there on
the hottest summer days, so I'm hoping doing this would keep the loft
cooler in the summer too.

Cheers!

Martin


I used 50mm Rockwool slabs between the rafters. Cheaper than celotex but
you can still achieve the recommended 50mm gap under the roof tiles
(otherwise I'd have used the standard fibreglass rolls).
I also fitted lift-up panels as "walls" to save going right down to the
eaves. Well worth doing IMO.
P.S. About 3/4 of the way through the job I found the quickest/easiest
way to cut slabs (or foam) for a tight fit. If anyone's interested, I'll
elaborate.

On 19 Aug, 13:06, Stuart Noble
wrote:

I used 50mm Rockwool slabs between the rafters. Cheaper than celotex but
you can still achieve the recommended 50mm gap under the roof tiles
(otherwise I'd have used the standard fibreglass rolls).

OK, I just found a source of cheap celotex on ebay.

I also fitted lift-up panels as "walls" to save going right down to the
eaves. Well worth doing IMO.

Not quite sure what you mean by this, or what the advantage is.

P.S. About 3/4 of the way through the job I found the quickest/easiest
way to cut slabs (or foam) for a tight fit. If anyone's interested, I'll
elaborate.

Oh go on then. I also just looked around the celotex site and found
this handy guide:
http://www.celotex.co.uk/downloads/B...derRafters.pdf
It recommends cutting the boards on an angle to get a wedge effect as
you push them in for a tight fit, is that what you mean?

Martin Pentreath wrote:
On 19 Aug, 13:06, Stuart Noble
wrote:
I used 50mm Rockwool slabs between the rafters. Cheaper than celotex but
you can still achieve the recommended 50mm gap under the roof tiles
(otherwise I'd have used the standard fibreglass rolls).

OK, I just found a source of cheap celotex on ebay.

I also fitted lift-up panels as "walls" to save going right down to the
eaves. Well worth doing IMO.

Not quite sure what you mean by this, or what the advantage is.

As the space close to the eaves isn't really useful for much, I used the
existing vertical rafter supports as walls. It cuts the floor space
perhaps by half but it gives you a room you can stand up in. Most loft
conversions have this kind of arrangement. The "walls" in my case are
just insulation in hinged wooden frames so I can lift them up and get
access to the bit near the eaves.
At the time I wanted a workroom up there and I was less concerned with
overall insulation values. Now I might just insulate all the rafters and
forget about walls.

P.S. About 3/4 of the way through the job I found the quickest/easiest
way to cut slabs (or foam) for a tight fit. If anyone's interested, I'll
elaborate.

Oh go on then. I also just looked around the celotex site and found
this handy guide:
http://www.celotex.co.uk/downloads/B...derRafters.pdf
It recommends cutting the boards on an angle to get a wedge effect as
you push them in for a tight fit, is that what you mean?


What I did was to overcut the strip by half an inch or so and gradually
push it into the gap whilst running a handsaw against the rafter. You
need to keep the handsaw flat against the rafter but it's deadly
accurate and takes account of the variations in width between rafters.
Also you don't have to support the inevitable undersized strips.

Just been doing some research into ventiallation requirements and I'm
beginning to go off the idea now.

I was aware of the need to leave a 50mm ventilation space between the
celotex and the sarking (which I'm fairly sure is non permeable), but
I hadn't really thought about the need for slate vents or soffit vents
to get air circuating through the 50mm void.

On the whole it may be cheaper and a lot less hassle (including the
risk of rotting roof timbers) to pay £100 a year more on my gas bill!

On 19/08/2007 16:05, Martin Pentreath wrote:

On the whole it may be cheaper and a lot less hassle (including the
risk of rotting roof timbers) to pay £100 a year more on my gas bill!

So much for HIPs doing much good then :-)

Martin Pentreath wrote:
Just been doing some research into ventiallation requirements and I'm
beginning to go off the idea now.

I was aware of the need to leave a 50mm ventilation space between the
celotex and the sarking (which I'm fairly sure is non permeable), but
I hadn't really thought about the need for slate vents or soffit vents
to get air circuating through the 50mm void.

On the whole it may be cheaper and a lot less hassle (including the
risk of rotting roof timbers) to pay £100 a year more on my gas bill!

You could chop out some of the sarking to provide ventilation.

--
Cheers,

John.

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Martin Pentreath wrote:
Just been doing some research into ventiallation requirements and I'm
beginning to go off the idea now.

I was aware of the need to leave a 50mm ventilation space between the
celotex and the sarking (which I'm fairly sure is non permeable), but
I hadn't really thought about the need for slate vents or soffit vents
to get air circuating through the 50mm void.

If yours is anything like mine you get plenty of airflow from the eaves

On the whole it may be cheaper and a lot less hassle (including the
risk of rotting roof timbers) to pay £100 a year more on my gas bill!

Stuart Noble wrote:
Martin Pentreath wrote:
Just been doing some research into ventillation requirements and I'm
beginning to go off the idea now.

I was aware of the need to leave a 50mm ventilation space between the
celotex and the sarking (which I'm fairly sure is non permeable), but
I hadn't really thought about the need for slate vents or sofit vents
to get air circuating through the 50mm void.

If yours is anything like mine you get plenty of airflow from the eaves

I'd be very careful about it, and monitor it closely for a while after you
finish

You need two things to avoid any problems one is a good airflow and the
other is a vapour barrier

If you do not have a vapour barrier then the warm moist air passes through,
or around gaps in your insulation, then it becomes cold damp air and
condenses on your rafters.
I wouldn't be convinced that a good airflow on its own would be adequate, it
could potentially just make the airspace cooler. You also need to ensure
there is ventilation at the top of the airspace and not just at the eaves to
ensure good airflow.

I did the stuff insulation between rafter technique in our current house not
long after moving in (7 years ago now), but a few months after doing this,
and while installing a new bathroom fan, which went out through the ceiling
I had cause to move some insulation and there were signs of damp underneath.
There was a 50mm airgap behind the insulation, and moderate ventilation form
the soffits, but no slate vents or vented ridge tiles

The lot came down immediately, but will be replaced in due course when I
eventually convert the loft.

The only area that showed any problems was directly above the bathroom.
But I've heard of a few people with older loft conversions, (and probably no
or poor insulation and ventilation) complaining about the state of their
roof, and letting water in. I now wonder if the problems are inadequate
ventilation and condensation issues, rather than the actual roof.

cheers

David

On 20 Aug, 15:54, DM wrote:

I'd be very careful about it, and monitor it closely for a while after you
finish

You need two things to avoid any problems one is a good airflow and the
other is a vapour barrier

If you do not have a vapour barrier then the warm moist air passes through,
or around gaps in yourinsulation, then it becomes cold damp air and
condenses on your rafters.
I wouldn't be convinced that a good airflow on its own would be adequate, it
could potentially just make the airspace cooler. You also need to ensure
there is ventilation at the top of the airspace and not just at the eaves to
ensure good airflow.

I did the stuffinsulationbetween rafter technique in our current house not
long after moving in (7 years ago now), but a few months after doing this,
and while installing a new bathroom fan, which went out through the ceiling
I had cause to move someinsulationand there were signs of damp underneath.
There was a 50mm airgap behind theinsulation, and moderate ventilation form
the soffits, but no slate vents or vented ridge tiles

The lot came down immediately, but will be replaced in due course when I
eventually convert the loft.

The only area that showed any problems was directly above the bathroom.
But I've heard of a few people with older loft conversions, (and probably no
or poorinsulationand ventilation) complaining about the state of their
roof, and letting water in. I now wonder if the problems are inadequate
ventilation and condensation issues, rather than the actual roof.

cheers

David

Thanks for the advice. I'm interested by what you say about a vapour
barrier. When I boarded the bit of the loft that is now boarded I was
careful to take up all the old fibre glass in that part and staple and
tape continuous lengths of heavy-duty polythene between and over the
joists before putting the fibre glass back down and then laying the
chipboard. So effectively part of the loft space already has a vapour
barrier, but I boarded less than half of the total area, so that's not
really going to help.

I guess I could do the celotex-between-and-over-rafters treatment and
then put a polythene vapour barrier over the whole lot stapled and
taped to the lower layer of celotex to stop any water vapour getting
through the celotex?

On Fri, 24 Aug 2007 12:18:33 -0700, Martin Pentreath
wrote:

On 20 Aug, 15:54, DM wrote:

I'd be very careful about it, and monitor it closely for a while after you
finish

You need two things to avoid any problems one is a good airflow and the
other is a vapour barrier

If you do not have a vapour barrier then the warm moist air passes through,
or around gaps in yourinsulation, then it becomes cold damp air and
condenses on your rafters.
I wouldn't be convinced that a good airflow on its own would be adequate, it
could potentially just make the airspace cooler. You also need to ensure
there is ventilation at the top of the airspace and not just at the eaves to
ensure good airflow.

I did the stuffinsulationbetween rafter technique in our current house not
long after moving in (7 years ago now), but a few months after doing this,
and while installing a new bathroom fan, which went out through the ceiling
I had cause to move someinsulationand there were signs of damp underneath.
There was a 50mm airgap behind theinsulation, and moderate ventilation form
the soffits, but no slate vents or vented ridge tiles

The lot came down immediately, but will be replaced in due course when I
eventually convert the loft.

The only area that showed any problems was directly above the bathroom.
But I've heard of a few people with older loft conversions, (and probably no
or poorinsulationand ventilation) complaining about the state of their
roof, and letting water in. I now wonder if the problems are inadequate
ventilation and condensation issues, rather than the actual roof.

cheers

David

Thanks for the advice. I'm interested by what you say about a vapour
barrier. When I boarded the bit of the loft that is now boarded I was
careful to take up all the old fibre glass in that part and staple and
tape continuous lengths of heavy-duty polythene between and over the
joists before putting the fibre glass back down and then laying the
chipboard. So effectively part of the loft space already has a vapour
barrier, but I boarded less than half of the total area, so that's not
really going to help.

I guess I could do the celotex-between-and-over-rafters treatment and
then put a polythene vapour barrier over the whole lot stapled and
taped to the lower layer of celotex to stop any water vapour getting
through the celotex?

The foil covering on the Celotex is a better seal than polythene just
use aluminium tape to seal the joins.

FKruger wrote:
On Fri, 24 Aug 2007 12:18:33 -0700, Martin Pentreath
wrote:

On 20 Aug, 15:54, DM wrote:
I'd be very careful about it, and monitor it closely for a while after you
finish

You need two things to avoid any problems one is a good airflow and the
other is a vapour barrier

If you do not have a vapour barrier then the warm moist air passes through,
or around gaps in yourinsulation, then it becomes cold damp air and
condenses on your rafters.
I wouldn't be convinced that a good airflow on its own would be adequate, it
could potentially just make the airspace cooler. You also need to ensure
there is ventilation at the top of the airspace and not just at the eaves to
ensure good airflow.

I did the stuffinsulationbetween rafter technique in our current house not
long after moving in (7 years ago now), but a few months after doing this,
and while installing a new bathroom fan, which went out through the ceiling
I had cause to move someinsulationand there were signs of damp underneath.
There was a 50mm airgap behind theinsulation, and moderate ventilation form
the soffits, but no slate vents or vented ridge tiles

The lot came down immediately, but will be replaced in due course when I
eventually convert the loft.

The only area that showed any problems was directly above the bathroom.
But I've heard of a few people with older loft conversions, (and probably no
or poorinsulationand ventilation) complaining about the state of their
roof, and letting water in. I now wonder if the problems are inadequate
ventilation and condensation issues, rather than the actual roof.

cheers

David
Thanks for the advice. I'm interested by what you say about a vapour
barrier. When I boarded the bit of the loft that is now boarded I was
careful to take up all the old fibre glass in that part and staple and
tape continuous lengths of heavy-duty polythene between and over the
joists before putting the fibre glass back down and then laying the
chipboard. So effectively part of the loft space already has a vapour
barrier, but I boarded less than half of the total area, so that's not
really going to help.

I guess I could do the celotex-between-and-over-rafters treatment and
then put a polythene vapour barrier over the whole lot stapled and
taped to the lower layer of celotex to stop any water vapour getting
through the celotex?

The foil covering on the Celotex is a better seal than polythene just
use aluminium tape to seal the joins.

Actually they are similar, but since it comes with the foil, and needs
taping anyway, why waste money on polythene too?