Hi,

In the long saga of fixing a mouldy bungalow - I have totally given up on
the idea of insulating it from the inside. The dormer conversion means
getting celotex between the rafters will be next to impossible - too much
criss-crossing of timbers. And the ventilation requirements with old sarking
are nearly impossible to achieve.

So, I said "sod it", let's get some quotes for a retile. Been about 40 years
since it was done, the pointing is going, gutter boards are shot and the
existing sarking is falling apart.

So "they" can slap 3" celotex in from the outside, which will be trivial,
leave a 1" air gap (BCO wants this) and cover with Tyvek (which allows the
BCO to reduce to 1" airgap).

I've not talked to the BCO yet with actual diagrams, which I want to prepare
so I can give the roofing guys detailed specifications. I wante to sound
some things out for my understanding here, so I can get it as near to
"right" as possible first time. Then I'll ask him for comments and
provisional approval, then get the quotes, aiming for work next spring[1]


With Tyvek, does one usually still have soffit vents[2]? And what about up
top? In this case "up top" would need to be vent tiles, probably, due to the
dormer roof making ridge vents a non starter[3].

I'm rather hoping Tyvek avoids the need for top or bottom vents - would that
be correct?


Cheers,

Tim

[1] I have to get quite a bit of stuff done at the same time. I will get the
roofrs to fit cedar (or equivalent wood) gutter boards so they can do that
as part of their work. I will have to clean and refit the ali gutter (doubt
they want to be bothered with wibbling around) as well as drop lots of
conduit through for possible soffit lights, power drops to shed etc before
it gets sealed tight. And do proper rectangular vent duct for extractor fans
instead of the flexy stuff I have now.

[2] I'll be replacing the soffits, roofers tear off, I will refit as it is
easy access (bungalow) and not time critical as I want to screw it on for
easy access.

[3] The dormr roof is flat - I will get them to sort out vents in both
facias and I will be able to insulate that from inside, 2" between and 2"
under.


--
Tim Watts

[Default] On Tue, 18 Oct 2011 17:26:03 +0100, a certain chimpanzee,
Tim Watts , randomly hit the keyboard and wrote:

So, I said "sod it", let's get some quotes for a retile. Been about 40 years
since it was done, the pointing is going, gutter boards are shot and the
existing sarking is falling apart.

Is this a detached bungalow? If so, then why not consider insulating
above the rafters? It would eliminate the need for ventilation.
--
Hugo Nebula
"If no-one on the internet wants a piece of this,
just how far from the pack have I strayed"?

Hugo Nebula wrote:

[Default] On Tue, 18 Oct 2011 17:26:03 +0100, a certain chimpanzee,
Tim Watts , randomly hit the keyboard and wrote:

So, I said "sod it", let's get some quotes for a retile. Been about 40
years since it was done, the pointing is going, gutter boards are shot and
the existing sarking is falling apart.

Is this a detached bungalow? If so, then why not consider insulating
above the rafters? It would eliminate the need for ventilation.

Hi Hugo,

Yes it is - and I did consider that (it would seem obvious).

The roofer I spoke to last year, number from a pin in phone book, felt it
would be difficult to do given the dormer juts out of the roof and goes
nearly to the ridgeline. I'd agre with him, but I'm not a roofer and do not
have a depth of knowledge on funky tricks that may be possible.

We also have 4 ground level bays with 3x1m flat roofs that marry into the
roof near the gutterline.

But I will certainly ask the next guy (personal recommendation from
neighbour).

Cheers

Tim

--
Tim Watts

[Default] On Tue, 18 Oct 2011 18:16:55 +0100, a certain chimpanzee,
Tim Watts , randomly hit the keyboard and wrote:

The roofer I spoke to last year, number from a pin in phone book, felt it
would be difficult to do given the dormer juts out of the roof and goes
nearly to the ridgeline. I'd agre with him, but I'm not a roofer and do not
have a depth of knowledge on funky tricks that may be possible.

We also have 4 ground level bays with 3x1m flat roofs that marry into the
roof near the gutterline.

But I will certainly ask the next guy (personal recommendation from
neighbour).

Even if you can't insulate above the rafters (and I can't think why
not), then how about counterbattening? With a breather membrane it
would allow you to use the full depth of the rafters for insulation.
--
Hugo Nebula
"If no-one on the internet wants a piece of this,
just how far from the pack have I strayed"?

On 18/10/2011 17:26, Tim Watts wrote:
Hi,

In the long saga of fixing a mouldy bungalow - I have totally given up on
the idea of insulating it from the inside. The dormer conversion means
getting celotex between the rafters will be next to impossible - too much
criss-crossing of timbers. And the ventilation requirements with old sarking
are nearly impossible to achieve.

If one looked from the other side - i.e. stripped some tiles of a
section, hack off old tile batten and sarking, slapped in full rafter
depth of PIR foam, covered with breathable sarking and then re-batten
and tile (possibly with same tiles if they are ok), would that be
doable/easier?

So, I said "sod it", let's get some quotes for a retile. Been about 40 years
since it was done, the pointing is going, gutter boards are shot and the
existing sarking is falling apart.

So "they" can slap 3" celotex in from the outside, which will be trivial,
leave a 1" air gap (BCO wants this) and cover with Tyvek (which allows the
BCO to reduce to 1" airgap).

With breather membrane there is no need for a gap at all IIRC...

I've not talked to the BCO yet with actual diagrams, which I want to prepare
so I can give the roofing guys detailed specifications. I wante to sound
some things out for my understanding here, so I can get it as near to
"right" as possible first time. Then I'll ask him for comments and

With Tyvek, does one usually still have soffit vents[2]? And what about up
top? In this case "up top" would need to be vent tiles, probably, due to the
dormer roof making ridge vents a non starter[3].

Based on info from when I did my loft (so probably not current), you
only needed the vents with non breathable sarking.

I kept my sarking and did the airgap and vent thing. I cheated a bit, in
the we pulled the ridge off, slapped in a row of weep vents (them things
with the "up turn" at one end, mortared them back on. No change in the
ridge height at all really, an only a visible difference on one side. We
then chopped away a strip of felt from the inside just below the ridge.

I'm rather hoping Tyvek avoids the need for top or bottom vents - would that
be correct?

Think so. If not you can probably get a dry ridge system now that
includes ventilation anyway.



--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

Hugo Nebula wrote:

[Default] On Tue, 18 Oct 2011 18:16:55 +0100, a certain chimpanzee,
Tim Watts , randomly hit the keyboard and wrote:

The roofer I spoke to last year, number from a pin in phone book, felt it
would be difficult to do given the dormer juts out of the roof and goes
nearly to the ridgeline. I'd agre with him, but I'm not a roofer and do
not have a depth of knowledge on funky tricks that may be possible.

We also have 4 ground level bays with 3x1m flat roofs that marry into the
roof near the gutterline.

But I will certainly ask the next guy (personal recommendation from
neighbour).

Even if you can't insulate above the rafters (and I can't think why
not),

Hi Hugo,

I think it was the effect the change of geometry of adding 3-4" to the
height of the roof that worried the bloke. But he wasn't the brighted tool
in the box which is why I went off him, so I'll raise the very same idea
with the next chap.

Normally, adding to the thickness of the roof would be agreeably no problem,
but when you have various flat bits jointed in (that ideally should be left
alone because they were re-leaded/refelted only 10 years ago) he may have
had a point. This is going to not be cheap job so I'm trying to avoid
touching the leadwork and felt if possible until their time comes naturally.
Doing the roof is pushing a point, it *could* last another 5-10 years, but I
have enough justification for that part.

Here's a picture of the relevant parts:

https://plus.google.com/u/0/photos/1...24517602?hl=en

I hope that link works - Google have done something very weird to PicasaWeb!

It shows the major outcrops from the main roof.

then how about counterbattening? With a breather membrane it
would allow you to use the full depth of the rafters for insulation.

That would also be a very inteteresting idea - 1" should not make much
difference to the roof geometry but will make a significant difference to
the insulation. I (and my BCO) would be *very* happy with 4" celotex all
over.

Cheers

Tim

--
Tim Watts

John Rumm wrote:

On 18/10/2011 17:26, Tim Watts wrote:
Hi,

In the long saga of fixing a mouldy bungalow - I have totally given up on
the idea of insulating it from the inside. The dormer conversion means
getting celotex between the rafters will be next to impossible - too much
criss-crossing of timbers. And the ventilation requirements with old
sarking are nearly impossible to achieve.

If one looked from the other side - i.e. stripped some tiles of a
section, hack off old tile batten and sarking, slapped in full rafter
depth of PIR foam, covered with breathable sarking and then re-batten
and tile (possibly with same tiles if they are ok), would that be
doable/easier?

That was exactly my conclusion. As you know, because you've seen it, I was
hoping to retrofit celotex from within. But after uncovering various parts
internally, the only easy bit to do like that would be the dormer flat roof
as it has nice regular joists, end to end and could be easily ventilated
from both facias allowing a cross draught over the top of the insulation
(the centre if the flat under the ridge is unimpeded).

So, I said "sod it", let's get some quotes for a retile. Been about 40
years since it was done, the pointing is going, gutter boards are shot
and the existing sarking is falling apart.

So "they" can slap 3" celotex in from the outside, which will be trivial,
leave a 1" air gap (BCO wants this) and cover with Tyvek (which allows
the BCO to reduce to 1" airgap).

With breather membrane there is no need for a gap at all IIRC...

He did stress he wanted 1" (it would have been 2" without Tyvek and
complicated venting arrangements).

I've not talked to the BCO yet with actual diagrams, which I want to
prepare so I can give the roofing guys detailed specifications. I wante
to sound some things out for my understanding here, so I can get it as
near to "right" as possible first time. Then I'll ask him for comments
and

With Tyvek, does one usually still have soffit vents[2]? And what about
up top? In this case "up top" would need to be vent tiles, probably, due
to the dormer roof making ridge vents a non starter[3].

Based on info from when I did my loft (so probably not current), you
only needed the vents with non breathable sarking.

It seems reasonable. As the soffits will be planked (my soffits are nearly a
foot wide) it would be slightly easier to not need venting. Otherwise I'd
leave a 1" gap between the last plank and the wall and put some mesh or a
fancy plastic comb in.

I did drill and fit lots of circular vents to the soffits for the bays
though - as they are leaded it would make sense to keep these.

I kept my sarking and did the airgap and vent thing. I cheated a bit, in
the we pulled the ridge off, slapped in a row of weep vents (them things
with the "up turn" at one end, mortared them back on. No change in the
ridge height at all really, an only a visible difference on one side. We
then chopped away a strip of felt from the inside just below the ridge.

I'm rather hoping Tyvek avoids the need for top or bottom vents - would
that be correct?

Think so. If not you can probably get a dry ridge system now that
includes ventilation anyway.



OK - guess it's time to invite favoured chap #1 over. He's popular so if I
talk to him now, I might just get him for next spring/summer at a time I can
be ready to deal with the gutter and soffits (= week off work).

On an aside, the project plods on, very slowly due to new job (inherited a
broken-assed VMWare system running 100 linux virtual servers - much
firefighting. Once I have the new system in and migrated, it will get more
relaxed there.

I am painting the kitchen ceiling and bays over the next 2 weeks while SWMBO
+ kids are in China. Then skirting tiles (probably sub that out - I like our
floor tiler), paint the walls except for where wall tiles will go and it
will be a lot nicer and might inspire me to buy some units - well, wall ones
anyway, which will clear the crap up and make me more inspired to do the
bottom units and worktops.



Cheers

Tim

--
Tim Watts

On 18/10/2011 23:47, Tim Watts wrote:
John Rumm wrote:

On 18/10/2011 17:26, Tim Watts wrote:
Hi,

In the long saga of fixing a mouldy bungalow - I have totally given up on
the idea of insulating it from the inside. The dormer conversion means
getting celotex between the rafters will be next to impossible - too much
criss-crossing of timbers. And the ventilation requirements with old
sarking are nearly impossible to achieve.

If one looked from the other side - i.e. stripped some tiles of a
section, hack off old tile batten and sarking, slapped in full rafter
depth of PIR foam, covered with breathable sarking and then re-batten
and tile (possibly with same tiles if they are ok), would that be
doable/easier?

That was exactly my conclusion. As you know, because you've seen it, I was
hoping to retrofit celotex from within. But after uncovering various parts
internally, the only easy bit to do like that would be the dormer flat roof
as it has nice regular joists, end to end and could be easily ventilated
from both facias allowing a cross draught over the top of the insulation
(the centre if the flat under the ridge is unimpeded).

Yup. Getting at it from the other side is often overlooked, and lifting
some tiles off and sticking them back later is not actually that difficult.

So, I said "sod it", let's get some quotes for a retile. Been about 40
years since it was done, the pointing is going, gutter boards are shot
and the existing sarking is falling apart.

So "they" can slap 3" celotex in from the outside, which will be trivial,
leave a 1" air gap (BCO wants this) and cover with Tyvek (which allows
the BCO to reduce to 1" airgap).

With breather membrane there is no need for a gap at all IIRC...

He did stress he wanted 1" (it would have been 2" without Tyvek and
complicated venting arrangements).

Might need to check that.

The other option would of course be to go "warm deck", with the
insulation on top of the rafters (hence no titting about cutting in) fix
battens through the insulation, and tile that. Flat roof abutments will
usually be below the tile level and are hence "easy"...

I've not talked to the BCO yet with actual diagrams, which I want to
prepare so I can give the roofing guys detailed specifications. I wante
to sound some things out for my understanding here, so I can get it as
near to "right" as possible first time. Then I'll ask him for comments
and

With Tyvek, does one usually still have soffit vents[2]? And what about
up top? In this case "up top" would need to be vent tiles, probably, due
to the dormer roof making ridge vents a non starter[3].

Based on info from when I did my loft (so probably not current), you
only needed the vents with non breathable sarking.

It seems reasonable. As the soffits will be planked (my soffits are nearly a
foot wide) it would be slightly easier to not need venting. Otherwise I'd
leave a 1" gap between the last plank and the wall and put some mesh or a
fancy plastic comb in.

I did drill and fit lots of circular vents to the soffits for the bays
though - as they are leaded it would make sense to keep these.

I was about to say the circular vents are easy to fit if needs be.
Failing that you can also get ventilated uPVC (spit) facia boards.

I kept my sarking and did the airgap and vent thing. I cheated a bit, in
the we pulled the ridge off, slapped in a row of weep vents (them things
with the "up turn" at one end, mortared them back on. No change in the
ridge height at all really, an only a visible difference on one side. We
then chopped away a strip of felt from the inside just below the ridge.

I'm rather hoping Tyvek avoids the need for top or bottom vents - would
that be correct?

Think so. If not you can probably get a dry ridge system now that
includes ventilation anyway.



OK - guess it's time to invite favoured chap #1 over. He's popular so if I
talk to him now, I might just get him for next spring/summer at a time I can
be ready to deal with the gutter and soffits (= week off work).

On an aside, the project plods on, very slowly due to new job (inherited a
broken-assed VMWare system running 100 linux virtual servers - much
firefighting. Once I have the new system in and migrated, it will get more
relaxed there.

Sounds like fun!

I am painting the kitchen ceiling and bays over the next 2 weeks while SWMBO
+ kids are in China. Then skirting tiles (probably sub that out - I like our
floor tiler), paint the walls except for where wall tiles will go and it
will be a lot nicer and might inspire me to buy some units - well, wall ones
anyway, which will clear the crap up and make me more inspired to do the
bottom units and worktops.

Ah yes inspiration - I find that nearly as hard to find as the tape
measure I put down somewhere!

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On Wed, 19 Oct 2011 03:38:37 +0100, John Rumm
wrote:



Yup. Getting at it from the other side is often overlooked, and lifting
some tiles off and sticking them back later is not actually that difficult.


Some bungalows near me, approx 20 years old, have had what I assume to
be grant-aided loft insullation installed by having the tiles removed
entirely and reinstated followed by pressure washing. Where only one
of a pair of semis was done one half has a bright clean roof and the
other a dark and dirty one.

Peter Johnson wrote:

On Wed, 19 Oct 2011 03:38:37 +0100, John Rumm
wrote:

Yup. Getting at it from the other side is often overlooked, and lifting
some tiles off and sticking them back later is not actually that
difficult.

Some bungalows near me, approx 20 years old, have had what I assume to
be grant-aided loft insullation installed by having the tiles removed
entirely and reinstated followed by pressure washing. Where only one
of a pair of semis was done one half has a bright clean roof and the
other a dark and dirty one.

So far as I know the only grants available for insulation are either for
cavity walls, or laying the fluffy stuff 10" deep on attic floors. I can't
see how stripping a roof would be part of that - unless someone scammed the
house-owner?

--
Jeremy C B Nicoll - my opinions are my own.

Email sent to my from-address will be deleted. Instead, please reply
to replacing "aaa" by "284".

Peter Johnson wrote:

On Wed, 19 Oct 2011 03:38:37 +0100, John Rumm
wrote:



Yup. Getting at it from the other side is often overlooked, and lifting
some tiles off and sticking them back later is not actually that
difficult.


Some bungalows near me, approx 20 years old, have had what I assume to
be grant-aided loft insullation installed by having the tiles removed
entirely and reinstated followed by pressure washing. Where only one
of a pair of semis was done one half has a bright clean roof and the
other a dark and dirty one.

Thanks fo rthe tip off... Might enquire about grants. I assumed grant-aided
insulation was "lob a few rolls of glass wool on the loft floor" which is
exactly was will not work here.

They weren't council houses were they?
--
Tim Watts

Tim Watts wrote:

I assumed grant-aided insulation was "lob a few rolls of glass wool on the
loft floor" which is exactly was will not work here.

I was told recently by the Energy Saving Trust:

http://www.energysavingtrust.org.uk

that even that's not grantable if someone already has some slightly more
than minimal amount of insulation... It's madness. You'd think they'd be
happy to help people top-up stuff as well as install when there's nothing
there at all.

--
Jeremy C B Nicoll - my opinions are my own.

Email sent to my from-address will be deleted. Instead, please reply
to replacing "aaa" by "284".

On Wed, 19 Oct 2011 19:01:58 +0100, Jeremy Nicoll - news posts wrote:

that even that's not grantable if someone already has some slightly more
than minimal amount of insulation... It's madness. You'd think they'd
be happy to help people top-up stuff as well as install when there's
nothing there at all.

'Tis madnness but just lobbing a few rolls out is quick, cheap and a
monkey can do it (badly). Same with cavity wall insulation, what
about all the housing stock that doesn't have cavities? Of course
doing anything with them inside is very disruptive and expensive but
why shouldn't a household that is prepared to go through that have to
pay the full costs with no financial support? Seems very unfair to
me. But then I might be biased as we are going through it ATM. Old
drylining strippped out and replaced with 50mm celotex type backed
plaster board on the inside of all external walls, solar thermal
store system with wood burner and existing oil burner as input as
well. What grant can we get? Just the £300 RHPP and VAT at 5% on
part of the solar system. It will be eligiable for RHI payments if
they every get that sorted out for domestic systems. But even at the
rumoured 18p/kWHr that isn't a great deal of money from a solar
system costing £8k plus.

--
Cheers
Dave.

On 19/10/2011 19:01, Jeremy Nicoll - news posts wrote:
Tim wrote:

I assumed grant-aided insulation was "lob a few rolls of glass wool on the
loft floor" which is exactly was will not work here.

I was told recently by the Energy Saving Trust:

http://www.energysavingtrust.org.uk

that even that's not grantable if someone already has some slightly more
than minimal amount of insulation... It's madness. You'd think they'd be
happy to help people top-up stuff as well as install when there's nothing
there at all.

I am in the process of getting estimates to have my property re-roofed.
It has thrown up some interesting informations. Pertinent to you Tyvex
needs slightly larger battens than standard, this it seems is a
requirement of their guarantee, Worth checking I think.

--
Residing on low ground in North Staffordshire

On 19/10/2011 19:01, Jeremy Nicoll - news posts wrote:
Tim wrote:

I assumed grant-aided insulation was "lob a few rolls of glass wool on the
loft floor" which is exactly was will not work here.

I was told recently by the Energy Saving Trust:

http://www.energysavingtrust.org.uk

that even that's not grantable if someone already has some slightly more
than minimal amount of insulation... It's madness. You'd think they'd be
happy to help people top-up stuff as well as install when there's nothing
there at all.

Well you could argue that if you are trying to make as much difference
overall as possible with your grants, then you will have most effect
adding some insulation to places with none, than you will adding more to
places that already have some.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

John Rumm wrote:

Well you could argue that if you are trying to make as much difference
overall as possible with your grants, then you will have most effect
adding some insulation to places with none, than you will adding more to
places that already have some.

Your argument kind of implies that there's no ROI from increasing say 4" of
insulation to 10". But if that's the case why do they now recommend a 10"
minimum?

They can't have it both ways.

--
Jeremy C B Nicoll - my opinions are my own.

Email sent to my from-address will be deleted. Instead, please reply
to replacing "aaa" by "284".

On Thu, 20 Oct 2011 12:43:10 +0100, Jeremy Nicoll - news posts wrote:

John Rumm wrote:

Well you could argue that if you are trying to make as much difference
overall as possible with your grants, then you will have most effect
adding some insulation to places with none, than you will adding more
to places that already have some.

Your argument kind of implies that there's no ROI from increasing say 4"
of insulation to 10". But if that's the case why do they now recommend
a 10" minimum?

Surely there *is* - it's just the ROI is much bigger for 10" of
insulation on a property that has none, vs. 6" on one that already has 4".

They can't have it both ways.

Perhaps what's missing are grants in proportion to the estimated benefit
- e.g. (purely from a economic standpoint) someone adding 6" to an
existing 4" should get 60% of what someone adding 10" can claim? (In the
real world there are probably other factors to consider, such as comfort
of the occupants - someone with no insulation will often be freezing and
miserable, but someone with 4" already won't be quite so bad, so the
weighting might be non-linear)

I don't think insulation grants even exist this side of the Pond - so,
question: what's to stop someone pulling up their existing insulation,
claiming they have none, then laying it back down again along with the
freebies they just got? Are they subject to random (and mandatory, i.e.
they have to let an inspector in) house inspection after installation?

cheers

Jules

In article id, Jeremy Nicoll - news posts wrote:
John Rumm wrote:

Well you could argue that if you are trying to make as much difference
overall as possible with your grants, then you will have most effect
adding some insulation to places with none, than you will adding more to
places that already have some.

Your argument kind of implies that there's no ROI from increasing say 4" of
insulation to 10". But if that's the case why do they now recommend a 10"
minimum?

They can't have it both ways.

Don't the grants cover the cost of fitting as well as the materials?
Saying "if we're going to pay for someone to go in at all, they might as well
do it to a decent standard while they are there, put we'll only pay for them
to do it on the currently worst houses" sounds reasonable.

It's tough if you struggled to pay for 4" and now don't get an upgrade when
your neighbour didn't bother and now gets 10" free, but making that fairer
without making the grants more costly to administer (and intrusive to apply
for) is tricky.

[Default] On Tue, 18 Oct 2011 22:59:49 +0100, a certain chimpanzee,
John Rumm , randomly hit the keyboard
and wrote:

On 18/10/2011 17:26, Tim Watts wrote:

With breather membrane there is no need for a gap at all IIRC...

Yes there is, unless there are counterbattens above the membrane. If
so...

I'm rather hoping Tyvek avoids the need for top or bottom vents - would that
be correct?

If there is a gap below the membrane, then correct, provided there is
a vapour barrier underneath the insulation. If no gap, then there
should be ventilation to the batten space _above_ the membrane.
--
Hugo Nebula
"If no-one on the internet wants a piece of this,
just how far from the pack have I strayed"?

Hugo Nebula wrote:

[Default] On Tue, 18 Oct 2011 22:59:49 +0100, a certain chimpanzee,
John Rumm , randomly hit the keyboard
and wrote:

On 18/10/2011 17:26, Tim Watts wrote:

With breather membrane there is no need for a gap at all IIRC...

Yes there is, unless there are counterbattens above the membrane. If
so...



I'm rather hoping Tyvek avoids the need for top or bottom vents - would
that be correct?

If there is a gap below the membrane, then correct, provided there is
a vapour barrier underneath the insulation. If no gap, then there
should be ventilation to the batten space _above_ the membrane.

It makes sense - the wind will blow through between the tiles, but I guess
it still needs a little space to flow around to remove any condensation from
the tops of the rafters.

Yes - the underside (inside) will be as near as dammit vapourtight for
*most* of the surface - that means: The celotex will be fitted tight between
the rafters and will be foamed in where there are difficult bits (criss-
crossing wood etc) - that will be in the specification I will give to the
contractor.

Further, most of the inside will be sheeted in vapour barrier plasterboard.



There are just a few difficult areas, right down near the top of the wall
that are difficult to get to and installing PB right down the last couple of
feet (up from the wall plate) might be not possible. Services in the way
compound this.



Not sure what to do about these... As I say, the celotex will be foamed in
in this region (because of the difficulty of covering, I want this section
100% airtight or draughts will negate the insulation).

So the risk is about 2' of the bottom face of a 2x4" rafter being exposed to
air inside times number of rafters. The air will be void air rather than
general room air, though one will leak to the other.

Do you think this is a big issue? Would it be sufficient to varnish the
inside face of the rafter - something that could be quickly one from the
outside while the tiles are off?

Or try to staple some DPM sheet in place - again possible from the outside.

Cheers - and thanks Hugo

Tim



--
Tim Watts