Hi

I'm planning to insulate my loft with insulating board for occasional use as
an office.

Need some help on use of foil; backed insulation products. Looking at
Celotex website they recommend a 2" gap between old fashioned non permeable
roofing felt and the Celotex fixed in between rafters, to allow ventilation.
In my case with only 3" rafters means that I can only use the 25 mm
insulation board. Does anyone have experience of using a smaller gap say 1"
to allow thicker insulation between rafters and does this lead to
condensation problems.

Second I understand the foil on Celotex acts as both an impermeable membrane
avoiding condensation, and a thermal barrier by reducing radiation loss.
Does this radiation loss reduction work when for example 2 celotex boards
are mounted on top of each other or is an air gap required for the foil to
work effectively.This to my mind also would give extra conductive insulation
if the air gap is sealed.

Does anyone have experience on using multi layer foil insulation, it seems
to give only a small thickness but expensive, but main thing does it work.
the manufacturers seem to claim better insulation performance than board
products but only give very overall figures in combination with celotex
boards and not for foil used alone.

Regards Dave

Please note only respond by newsgroup as email not working.

On 14/03/16 23:51, Dave wrote:
Hi

I'm planning to insulate my loft with insulating board for occasional use as
an office.

Need some help on use of foil; backed insulation products. Looking at
Celotex website they recommend a 2" gap between old fashioned non permeable
roofing felt and the Celotex fixed in between rafters, to allow ventilation.
In my case with only 3" rafters means that I can only use the 25 mm
insulation board. Does anyone have experience of using a smaller gap say 1"
to allow thicker insulation between rafters and does this lead to
condensation problems.

Second I understand the foil on Celotex acts as both an impermeable membrane
avoiding condensation, and a thermal barrier by reducing radiation loss.

That is really almost irrelevant.

Yui can line with foil backed pboard if you really care.


Does this radiation loss reduction work when for example 2 celotex boards
are mounted on top of each other or is an air gap required for the foil to
work effectively.This to my mind also would give extra conductive insulation
if the air gap is sealed.


Forget the radaiation. Its am almost irrelevant issue.

Does anyone have experience on using multi layer foil insulation, it seems
to give only a small thickness but expensive, but main thing does it work.
the manufacturers seem to claim better insulation performance than board
products but only give very overall figures in combination with celotex
boards and not for foil used alone.


If you put celotex between and then celotex over it will be fabulous.

However even an inch is WAY better than nothing. and the key is toi
totally get rid of draughts from e.g. eave and ridge vents and let that
lot circulate above the 'tex.

so use decorators caulk, extending foam and the foil tape to really
eliminate all the draughts and the result will be well good enough for
occasional use even with an inch.

Id p'board over fill and sand and then use lining paper and cheap
emulsion for a basic 'room' finish



Regards Dave

Please note only respond by newsgroup as email not working.




--
"It is an established fact to 97% confidence limits that left wing
conspirators see right wing conspiracies everywhere"

On Monday, 14 March 2016 23:51:28 UTC, Dave wrote:
Hi

I'm planning to insulate my loft with insulating board for occasional use as
an office.

Need some help on use of foil; backed insulation products. Looking at
Celotex website they recommend a 2" gap between old fashioned non permeable
roofing felt and the Celotex fixed in between rafters, to allow ventilation.
In my case with only 3" rafters means that I can only use the 25 mm
insulation board. Does anyone have experience of using a smaller gap say 1"
to allow thicker insulation between rafters and does this lead to
condensation problems.

Second I understand the foil on Celotex acts as both an impermeable membrane
avoiding condensation, and a thermal barrier by reducing radiation loss.
Does this radiation loss reduction work when for example 2 celotex boards
are mounted on top of each other or is an air gap required for the foil to
work effectively.This to my mind also would give extra conductive insulation
if the air gap is sealed.

Does anyone have experience on using multi layer foil insulation, it seems
to give only a small thickness but expensive, but main thing does it work.
the manufacturers seem to claim better insulation performance than board
products but only give very overall figures in combination with celotex
boards and not for foil used alone.

Regards Dave

Please note only respond by newsgroup as email not working.

Foil does not insulate. Multifoils have poor insulation, the manufacturers game the specs. You need foil on the warm side to avoid interstitial condensation.


NT

On 14/03/16 23:51, Dave wrote:
Hi

I'm planning to insulate my loft with insulating board for occasional use as
an office.

Need some help on use of foil; backed insulation products. Looking at
Celotex website they recommend a 2" gap between old fashioned non permeable
roofing felt and the Celotex fixed in between rafters, to allow ventilation.
In my case with only 3" rafters means that I can only use the 25 mm
insulation board. Does anyone have experience of using a smaller gap say 1"
to allow thicker insulation between rafters and does this lead to
condensation problems.

2" is the minimum *unless* you have breathable membrane, then it can be
reduced to 1". Straight from my building inspector's mouth.

If you want more, you'll have to go under the rafters.

Second I understand the foil on Celotex acts as both an impermeable membrane
avoiding condensation, and a thermal barrier by reducing radiation loss.
Does this radiation loss reduction work when for example 2 celotex boards
are mounted on top of each other or is an air gap required for the foil to
work effectively.

In that case it makes no difference. Just layer them.

This to my mind also would give extra conductive insulation
if the air gap is sealed.

The celotex is a better insulator than air (it cannot convect for one).
Don't leave air gaps between sheets.

Does anyone have experience on using multi layer foil insulation, it seems
to give only a small thickness but expensive, but main thing does it work.
the manufacturers seem to claim better insulation performance than board
products but only give very overall figures in combination with celotex
boards and not for foil used alone.

Con...


Regards Dave

Please note only respond by newsgroup as email not working.

On Mon, 14 Mar 2016 23:51:24 +0000, Dave wrote:

Hi

I'm planning to insulate my loft with insulating board for occasional
use as an office.

Need some help on use of foil; backed insulation products. Looking at
Celotex website they recommend a 2" gap between old fashioned non
permeable roofing felt and the Celotex fixed in between rafters, to
allow ventilation.
In my case with only 3" rafters means that I can only use the 25 mm
insulation board. Does anyone have experience of using a smaller gap say
1" to allow thicker insulation between rafters and does this lead to
condensation problems.

Second I understand the foil on Celotex acts as both an impermeable
membrane avoiding condensation, and a thermal barrier by reducing
radiation loss. Does this radiation loss reduction work when for example
2 celotex boards are mounted on top of each other or is an air gap
required for the foil to work effectively.This to my mind also would
give extra conductive insulation if the air gap is sealed.

Does anyone have experience on using multi layer foil insulation, it
seems to give only a small thickness but expensive, but main thing does
it work. the manufacturers seem to claim better insulation performance
than board products but only give very overall figures in combination
with celotex boards and not for foil used alone.

Regards Dave

Please note only respond by newsgroup as email not working.

Slightly OT - the head office is in Hadleigh, not that far from us, so you
would think that you could nip over for some seconds.

Looks like they don't have a factory seconds shop, though :-(

Cheers

Dave R

--
Windows 8.1 on PCSpecialist box

On Mon, 14 Mar 2016 23:51:24 +0000, Dave wrote:

Hi

I'm planning to insulate my loft with insulating board for occasional
use as an office.

Need some help on use of foil; backed insulation products. Looking at
Celotex website they recommend a 2" gap between old fashioned non
permeable roofing felt and the Celotex fixed in between rafters, to
allow ventilation.
In my case with only 3" rafters means that I can only use the 25 mm
insulation board. Does anyone have experience of using a smaller gap say
1" to allow thicker insulation between rafters and does this lead to
condensation problems.

Second I understand the foil on Celotex acts as both an impermeable
membrane avoiding condensation, and a thermal barrier by reducing
radiation loss. Does this radiation loss reduction work when for example
2 celotex boards are mounted on top of each other or is an air gap
required for the foil to work effectively.This to my mind also would
give extra conductive insulation if the air gap is sealed.

Does anyone have experience on using multi layer foil insulation, it
seems to give only a small thickness but expensive, but main thing does
it work. the manufacturers seem to claim better insulation performance
than board products but only give very overall figures in combination
with celotex boards and not for foil used alone.

Reading stuff about insulating the rafters, there seems to be an
implication that there will be ventilation at the ridge as well as the
eaves.

If I insulate, there will be a ventilation gap beneath the tiles and
membrane from eaves to ridge and back to eaves, but no ridge vents (unless
I pay someone to go up on the roof).

How necessary are ridge vents?

I can see that warm moist air (for example from a sunny day in winter)
would rise up through the 50mm gap between the insulation and the roofing
but potentially have nowhere to go, unless there is an air flow across the
roof down to the opposite eaves.

A requirement for ridge vents seems to change this from a simple (possibly
in slow stages) DIY project to one requiring the services of a roofer.

Cheers


Dave R


--
Windows 8.1 on PCSpecialist box

On 15/03/16 13:13, David wrote:
On Mon, 14 Mar 2016 23:51:24 +0000, Dave wrote:

Hi

I'm planning to insulate my loft with insulating board for occasional
use as an office.

Need some help on use of foil; backed insulation products. Looking at
Celotex website they recommend a 2" gap between old fashioned non
permeable roofing felt and the Celotex fixed in between rafters, to
allow ventilation.
In my case with only 3" rafters means that I can only use the 25 mm
insulation board. Does anyone have experience of using a smaller gap say
1" to allow thicker insulation between rafters and does this lead to
condensation problems.

Second I understand the foil on Celotex acts as both an impermeable
membrane avoiding condensation, and a thermal barrier by reducing
radiation loss. Does this radiation loss reduction work when for example
2 celotex boards are mounted on top of each other or is an air gap
required for the foil to work effectively.This to my mind also would
give extra conductive insulation if the air gap is sealed.

Does anyone have experience on using multi layer foil insulation, it
seems to give only a small thickness but expensive, but main thing does
it work. the manufacturers seem to claim better insulation performance
than board products but only give very overall figures in combination
with celotex boards and not for foil used alone.

Reading stuff about insulating the rafters, there seems to be an
implication that there will be ventilation at the ridge as well as the
eaves.

If I insulate, there will be a ventilation gap beneath the tiles and
membrane from eaves to ridge and back to eaves, but no ridge vents (unless
I pay someone to go up on the roof).

How necessary are ridge vents?


Necessary unless you have breathable membrane. Otherwise the air cannot
circulate and is trapped (with breathable membrane it is sufficient that
moisture diffuses through the membrane and out between tile joints.

I can see that warm moist air (for example from a sunny day in winter)
would rise up through the 50mm gap between the insulation and the roofing
but potentially have nowhere to go, unless there is an air flow across the
roof down to the opposite eaves.

A requirement for ridge vents seems to change this from a simple (possibly
in slow stages) DIY project to one requiring the services of a roofer.

'fraid so.

I faced that dilemma too. Solved as the roof was more knackered than I
thought, so I got it re tiled, adding breathable membrane at the same
time and additional ventilation on the flat roof section.

On 15/03/16 13:13, David wrote:
On Mon, 14 Mar 2016 23:51:24 +0000, Dave wrote:

Hi

I'm planning to insulate my loft with insulating board for occasional
use as an office.

Need some help on use of foil; backed insulation products. Looking at
Celotex website they recommend a 2" gap between old fashioned non
permeable roofing felt and the Celotex fixed in between rafters, to
allow ventilation.
In my case with only 3" rafters means that I can only use the 25 mm
insulation board. Does anyone have experience of using a smaller gap say
1" to allow thicker insulation between rafters and does this lead to
condensation problems.

Second I understand the foil on Celotex acts as both an impermeable
membrane avoiding condensation, and a thermal barrier by reducing
radiation loss. Does this radiation loss reduction work when for example
2 celotex boards are mounted on top of each other or is an air gap
required for the foil to work effectively.This to my mind also would
give extra conductive insulation if the air gap is sealed.

Does anyone have experience on using multi layer foil insulation, it
seems to give only a small thickness but expensive, but main thing does
it work. the manufacturers seem to claim better insulation performance
than board products but only give very overall figures in combination
with celotex boards and not for foil used alone.

Reading stuff about insulating the rafters, there seems to be an
implication that there will be ventilation at the ridge as well as the
eaves.

If I insulate, there will be a ventilation gap beneath the tiles and
membrane from eaves to ridge and back to eaves, but no ridge vents (unless
I pay someone to go up on the roof).

How necessary are ridge vents?

Not really necessary at all


I can see that warm moist air (for example from a sunny day in winter)
would rise up through the 50mm gap between the insulation and the roofing
but potentially have nowhere to go, unless there is an air flow across the
roof down to the opposite eaves.

A requirement for ridge vents seems to change this from a simple (possibly
in slow stages) DIY project to one requiring the services of a roofer.

Cheers


Dave R




--
"I am inclined to tell the truth and dislike people who lie consistently.
This makes me unfit for the company of people of a Left persuasion, and
all women"

On 15/03/16 13:33, Tim Watts wrote:
Necessary unless you have breathable membrane. Otherwise the air cannot
circulate and is trapped (with breathable membrane it is sufficient that
moisture diffuses through the membrane and out between tile joints.

The point being that with celotex in, there wont BE any warm moist air.
Any rain will run down towards the eaves vents.




--
New Socialism consists essentially in being seen to have your heart in
the right place whilst your head is in the clouds and your hand is in
someone else's pocket.

On Tuesday, 15 March 2016 14:45:04 UTC+1, The Natural Philosopher wrote:
On 15/03/16 13:13, David wrote:
If I insulate, there will be a ventilation gap beneath the tiles and
membrane from eaves to ridge and back to eaves, but no ridge vents
(unless I pay someone to go up on the roof).

How necessary are ridge vents?

Not really necessary at all

Well, not unless you want to prevent condensation on the timber rafters.
(Or, to put it slightly less elliptically, "Actually quite necessary").

--
Martin

On 15/03/16 13:47, The Natural Philosopher wrote:
On 15/03/16 13:33, Tim Watts wrote:
Necessary unless you have breathable membrane. Otherwise the air cannot
circulate and is trapped (with breathable membrane it is sufficient that
moisture diffuses through the membrane and out between tile joints.

The point being that with celotex in, there wont BE any warm moist air.
Any rain will run down towards the eaves vents.



And the cold moist air?

Your advice seems to be at odds with my discussions with the BCO.

On 15/03/16 13:52, Martin Bonner wrote:
On Tuesday, 15 March 2016 14:45:04 UTC+1, The Natural Philosopher wrote:
On 15/03/16 13:13, David wrote:
If I insulate, there will be a ventilation gap beneath the tiles and
membrane from eaves to ridge and back to eaves, but no ridge vents
(unless I pay someone to go up on the roof).

How necessary are ridge vents?

Not really necessary at all

Well, not unless you want to prevent condensation on the timber rafters.
(Or, to put it slightly less elliptically, "Actually quite necessary").

Where does the water come from then?

(Or, to put it slightly less elliptically, "Actually quite unnecessary").

--
You can get much farther with a kind word and a gun than you can with a
kind word alone.

Al Capone

On 15/03/16 14:55, Tim Watts wrote:
On 15/03/16 13:47, The Natural Philosopher wrote:
On 15/03/16 13:33, Tim Watts wrote:
Necessary unless you have breathable membrane. Otherwise the air cannot
circulate and is trapped (with breathable membrane it is sufficient that
moisture diffuses through the membrane and out between tile joints.

The point being that with celotex in, there wont BE any warm moist air.
Any rain will run down towards the eaves vents.



And the cold moist air?


Cold air isn't moist enough to condense of rafters that are no colder
than it is.

What about 'condensation requires warm moist are to come into contact
with *colder* surfaces' do you fail to get?

If the insulation is done properly, the rof beyond and the air beyond
are all at the same temperature, and you already have an air gap from
eave to eave (or if you don't, don't take the insulation right up to the
ridge top - leave a cross roof space.

the space beyond the insulation is simply 'outside' and will no more rot
than an open barn with a roof will.






Your advice seems to be at odds with my discussions with the BCO.


BCOs don't have degrees in engineering by and large.

Worthy souls though they are.


--
You can get much farther with a kind word and a gun than you can with a
kind word alone.

Al Capone

On 15/03/16 15:04, The Natural Philosopher wrote:
On 15/03/16 13:52, Martin Bonner wrote:
On Tuesday, 15 March 2016 14:45:04 UTC+1, The Natural Philosopher wrote:
On 15/03/16 13:13, David wrote:
If I insulate, there will be a ventilation gap beneath the tiles and
membrane from eaves to ridge and back to eaves, but no ridge vents
(unless I pay someone to go up on the roof).

How necessary are ridge vents?

Not really necessary at all

Well, not unless you want to prevent condensation on the timber rafters.
(Or, to put it slightly less elliptically, "Actually quite necessary").

Where does the water come from then?

(Or, to put it slightly less elliptically, "Actually quite unnecessary").


Damp air.

My shed had no humans living in it. Nor does it have a source of water
vapour other than the air.

However, if I leave it all winter, during the worst months it will have
condensation running down the windows, mould growing on odd bits of ply
and tools will go rusty.

That was last year - before I starting running a dehumidifier in it.

Warm air gets in, cold makes it condense, without adequate ventilation
the water remains liquid and makes things damp.

I believe the same thing is likely to happen in a roof unless you have
an adequate air path.

The BCO advised me to ensure I had a through air path under my flat roof
decking as I was sealing the inside up with celotex. He even advised
mushroom vents either side of teh chimney as that was blocking the
natural air path from the north soffit vents to the south soffit vents
(being continuous airpath inside).

On 15/03/16 15:09, The Natural Philosopher wrote:
On 15/03/16 14:55, Tim Watts wrote:
On 15/03/16 13:47, The Natural Philosopher wrote:
On 15/03/16 13:33, Tim Watts wrote:
Necessary unless you have breathable membrane. Otherwise the air cannot
circulate and is trapped (with breathable membrane it is sufficient
that
moisture diffuses through the membrane and out between tile joints.

The point being that with celotex in, there wont BE any warm moist air.
Any rain will run down towards the eaves vents.



And the cold moist air?


Cold air isn't moist enough to condense of rafters that are no colder
than it is.

What about 'condensation requires warm moist are to come into contact
with *colder* surfaces' do you fail to get?

See my other post shed.


Your advice seems to be at odds with my discussions with the BCO.


BCOs don't have degrees in engineering by and large.

Worthy souls though they are.



Now let me see. Listen to the BCO with his knowledge of the regs and
years of experience in this field - or someone on the internet?

On 15/03/16 15:21, Tim Watts wrote:
On 15/03/16 15:04, The Natural Philosopher wrote:
On 15/03/16 13:52, Martin Bonner wrote:
On Tuesday, 15 March 2016 14:45:04 UTC+1, The Natural Philosopher
wrote:
On 15/03/16 13:13, David wrote:
If I insulate, there will be a ventilation gap beneath the tiles and
membrane from eaves to ridge and back to eaves, but no ridge vents
(unless I pay someone to go up on the roof).

How necessary are ridge vents?

Not really necessary at all

Well, not unless you want to prevent condensation on the timber rafters.
(Or, to put it slightly less elliptically, "Actually quite necessary").

Where does the water come from then?

(Or, to put it slightly less elliptically, "Actually quite unnecessary").


Damp air.

My shed had no humans living in it. Nor does it have a source of water
vapour other than the air.

However, if I leave it all winter, during the worst months it will have
condensation running down the windows, mould growing on odd bits of ply
and tools will go rusty.

well it cant be ventilated then


My garage is the same, but has none of that



That was last year - before I starting running a dehumidifier in it.

Warm air gets in, cold makes it condense, without adequate ventilation
the water remains liquid and makes things damp.

I believe the same thing is likely to happen in a roof unless you have
an adequate air path.

The BCO advised me to ensure I had a through air path under my flat roof
decking as I was sealing the inside up with celotex. He even advised
mushroom vents either side of teh chimney as that was blocking the
natural air path from the north soffit vents to the south soffit vents
(being continuous airpath inside).




--
You can get much farther with a kind word and a gun than you can with a
kind word alone.

Al Capone

On 15/03/16 15:23, Tim Watts wrote:
On 15/03/16 15:09, The Natural Philosopher wrote:
On 15/03/16 14:55, Tim Watts wrote:
On 15/03/16 13:47, The Natural Philosopher wrote:
On 15/03/16 13:33, Tim Watts wrote:
Necessary unless you have breathable membrane. Otherwise the air
cannot
circulate and is trapped (with breathable membrane it is sufficient
that
moisture diffuses through the membrane and out between tile joints.

The point being that with celotex in, there wont BE any warm moist air.
Any rain will run down towards the eaves vents.



And the cold moist air?


Cold air isn't moist enough to condense of rafters that are no colder
than it is.

What about 'condensation requires warm moist are to come into contact
with *colder* surfaces' do you fail to get?

See my other post shed.

It is obviously badly ventilated.

Or more likely is not even waterproof.




Your advice seems to be at odds with my discussions with the BCO.


BCOs don't have degrees in engineering by and large.

Worthy souls though they are.



Now let me see. Listen to the BCO with his knowledge of the regs and
years of experience in this field - or someone on the internet?


--
You can get much farther with a kind word and a gun than you can with a
kind word alone.

Al Capone

On 15/03/2016 13:13, David wrote:

Reading stuff about insulating the rafters, there seems to be an
implication that there will be ventilation at the ridge as well as the
eaves.

If I insulate, there will be a ventilation gap beneath the tiles and
membrane from eaves to ridge and back to eaves, but no ridge vents (unless
I pay someone to go up on the roof).

Ideally you would need ridge and soffit vents.

How necessary are ridge vents?

You will need *some* ventilation at the ridge. This could be swapping in
some vent tiles toward the top between each pair of rafters, or a
continuous vent bedded in under the ridge itself.

If you can't manage that, then you could cut away a 6" strip of the
underfelt at the top of the roof just before the ridge to allow some air
to pass through the tiles - but it may not be adequate.

I can see that warm moist air (for example from a sunny day in winter)
would rise up through the 50mm gap between the insulation and the roofing
but potentially have nowhere to go, unless there is an air flow across the
roof down to the opposite eaves.

A requirement for ridge vents seems to change this from a simple (possibly
in slow stages) DIY project to one requiring the services of a roofer.

You might just be able to install a vent tile from the inside...


--
Cheers,

John.

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

On 15/03/16 15:35, The Natural Philosopher wrote:
See my other post shed.

Reversing your lines to answer:


Or more likely is not even waterproof.

It's *very* waterproof thank you. It has tyvek under the cladding and a
felt roof in excellent order plus moderate roof overhang. The door fits
well.

It is obviously badly ventilated.

Thank you!

That is the whole point I have been making. And the same will happen to
the OP's roof if he doesn't have an air path right through (ie ridge or
top tile vents in his case).

By the way - I just noticed that my BCO does hold a BSc(Hons). Not sure
what in, but likely a relevant subject as he has it in his email sig.
I'll ask him next time.

In article ,
The Natural Philosopher writes:
On 15/03/16 14:55, Tim Watts wrote:
On 15/03/16 13:47, The Natural Philosopher wrote:
On 15/03/16 13:33, Tim Watts wrote:
Necessary unless you have breathable membrane. Otherwise the air cannot
circulate and is trapped (with breathable membrane it is sufficient that
moisture diffuses through the membrane and out between tile joints.

The point being that with celotex in, there wont BE any warm moist air.
Any rain will run down towards the eaves vents.



And the cold moist air?


Cold air isn't moist enough to condense of rafters that are no colder
than it is.

Trouble is, a well insulated roof is often colder than the outside
air (actually, always colder with a clear night sky), and does get
condensation on it, both inside and outside. The stuff inside needs
to be able to get out later.

What about 'condensation requires warm moist are to come into contact
with *colder* surfaces' do you fail to get?

That's the way it works.

If the insulation is done properly, the rof beyond and the air beyond
are all at the same temperature,

Unfortunately, that's not true. A roof has a much higher emissivity
than the air, and so radiates its heat away into space much faster.
That's why dew forms on (and under) roofs which are well insulated
from the house heat, particularly in winter when the the air is 100%
humidity much of the time, so any temperature difference generates
condensation.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

Two questions or thoughts on this topic which I started.

I have a bungalow and wiuld not be too worried about roof climbing and don't
need extra long ladders. Would it not be at least a help if I put
ventilation in the two gable ends at oppodite sides of the ridge as I will
be leaving a couple of feet or so between the ridge board and the insulation
board which of course leaves a good coupling space between the eaves. To my
mind ventilation only happens with air flow and opposite side of a roof will
have different air pressure during any breeze or wind which should drive
some air through even without ridge ventilation. I know that warm moist air
will rise due to convection and can condense depending on dew point, but I
think any breezy day would clear stagnant air. How often do we get a totally
calm set of days in the UK?? I sometimes think building regs are a bit over
the top and are dreamed up for job creation.

Notwithstanding because my rof timbers are at risk, does anyone know of a
semi-round ridge tile replacement with ventilation built in. I'm sure I've
seen rooves with the odd ventilator on the ridge and not a continuous strip.


Dave


"John Rumm" wrote in message
o.uk...
On 15/03/2016 13:13, David wrote:

Reading stuff about insulating the rafters, there seems to be an
implication that there will be ventilation at the ridge as well as the
eaves.

If I insulate, there will be a ventilation gap beneath the tiles and
membrane from eaves to ridge and back to eaves, but no ridge vents
(unless
I pay someone to go up on the roof).

Ideally you would need ridge and soffit vents.

How necessary are ridge vents?

You will need *some* ventilation at the ridge. This could be swapping in
some vent tiles toward the top between each pair of rafters, or a
continuous vent bedded in under the ridge itself.

If you can't manage that, then you could cut away a 6" strip of the
underfelt at the top of the roof just before the ridge to allow some air
to pass through the tiles - but it may not be adequate.

I can see that warm moist air (for example from a sunny day in winter)
would rise up through the 50mm gap between the insulation and the roofing
but potentially have nowhere to go, unless there is an air flow across
the
roof down to the opposite eaves.

A requirement for ridge vents seems to change this from a simple
(possibly
in slow stages) DIY project to one requiring the services of a roofer.

You might just be able to install a vent tile from the inside...


--
Cheers,

John.

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On 22/03/16 14:17, Dave wrote:
Two questions or thoughts on this topic which I started.

I have a bungalow and wiuld not be too worried about roof climbing and don't
need extra long ladders. Would it not be at least a help if I put
ventilation in the two gable ends at oppodite sides of the ridge as I will
be leaving a couple of feet or so between the ridge board and the insulation
board which of course leaves a good coupling space between the eaves. To my
mind ventilation only happens with air flow and opposite side of a roof will
have different air pressure during any breeze or wind which should drive
some air through even without ridge ventilation. I know that warm moist air
will rise due to convection and can condense depending on dew point, but I
think any breezy day would clear stagnant air. How often do we get a totally
calm set of days in the UK?? I sometimes think building regs are a bit over
the top and are dreamed up for job creation.

Notwithstanding because my rof timbers are at risk, does anyone know of a
semi-round ridge tile replacement with ventilation built in. I'm sure I've
seen rooves with the odd ventilator on the ridge and not a continuous strip.

YOu are perfdectly correct. What causes ROT is water that persists for
long enough to get spores established. That's not a soaking from a
shower or a week of winter condensation (dew). Its months of damp that
can't escape.

Almost ANY vent will do.


--
"What do you think about Gay Marriage?"
"I don't."
"Don't what?"
"Think about Gay Marriage."

On 22/03/2016 14:17, Dave wrote:
Two questions or thoughts on this topic which I started.

I have a bungalow and wiuld not be too worried about roof climbing and don't
need extra long ladders. Would it not be at least a help if I put
ventilation in the two gable ends at oppodite sides of the ridge as I will
be leaving a couple of feet or so between the ridge board and the insulation
board which of course leaves a good coupling space between the eaves. To my
mind ventilation only happens with air flow and opposite side of a roof will
have different air pressure during any breeze or wind which should drive
some air through even without ridge ventilation. I know that warm moist air
will rise due to convection and can condense depending on dew point, but I
think any breezy day would clear stagnant air. How often do we get a totally
calm set of days in the UK?? I sometimes think building regs are a bit over
the top and are dreamed up for job creation.

Yup if you have coupled all the rafter gaps to a big space at the top,
then you can just ventilate the big space and do pretty much the same job.

Notwithstanding because my rof timbers are at risk, does anyone know of a
semi-round ridge tile replacement with ventilation built in. I'm sure I've
seen rooves with the odd ventilator on the ridge and not a continuous strip.

When I did my loft, we just took off the exiting ridge tiles and then
bedded them back on with some cavity wall weep vents installed under
them at a downwards slant... investigation with a smoke match showed
they worked nicely.

These kind of things:

http://www.builderdepot.co.uk/cavity...erracotta.html



--
Cheers,

John.

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

On 15/03/2016 15:34, The Natural Philosopher wrote:
On 15/03/16 15:21, Tim Watts wrote:
On 15/03/16 15:04, The Natural Philosopher wrote:
On 15/03/16 13:52, Martin Bonner wrote:
On Tuesday, 15 March 2016 14:45:04 UTC+1, The Natural Philosopher
wrote:
On 15/03/16 13:13, David wrote:
If I insulate, there will be a ventilation gap beneath the tiles and
membrane from eaves to ridge and back to eaves, but no ridge vents
(unless I pay someone to go up on the roof).

How necessary are ridge vents?

Not really necessary at all

Well, not unless you want to prevent condensation on the timber
rafters.
(Or, to put it slightly less elliptically, "Actually quite necessary").

Where does the water come from then?

(Or, to put it slightly less elliptically, "Actually quite
unnecessary").


Damp air.

My shed had no humans living in it. Nor does it have a source of water
vapour other than the air.

However, if I leave it all winter, during the worst months it will have
condensation running down the windows, mould growing on odd bits of ply
and tools will go rusty.

well it cant be ventilated then

My lawn had loads of wet dew on it the other day... that's quite well
ventilated!




--
Cheers,

John.

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

On 15/03/2016 15:21, Tim Watts wrote:
On 15/03/16 15:04, The Natural Philosopher wrote:
On 15/03/16 13:52, Martin Bonner wrote:
On Tuesday, 15 March 2016 14:45:04 UTC+1, The Natural Philosopher
wrote:
On 15/03/16 13:13, David wrote:
If I insulate, there will be a ventilation gap beneath the tiles and
membrane from eaves to ridge and back to eaves, but no ridge vents
(unless I pay someone to go up on the roof).

How necessary are ridge vents?

Not really necessary at all

Well, not unless you want to prevent condensation on the timber rafters.
(Or, to put it slightly less elliptically, "Actually quite necessary").

Where does the water come from then?

(Or, to put it slightly less elliptically, "Actually quite unnecessary").


Damp air.

My shed had no humans living in it. Nor does it have a source of water
vapour other than the air.

However, if I leave it all winter, during the worst months it will have
condensation running down the windows, mould growing on odd bits of ply
and tools will go rusty.

That was last year - before I starting running a dehumidifier in it.

Warm air gets in, cold makes it condense, without adequate ventilation
the water remains liquid and makes things damp.

I believe the same thing is likely to happen in a roof unless you have
an adequate air path.

Yup... tis why you need ventilation for a traditional cold deck flat
roof. Even if you have an adequate vapour barrier to block the escape of
warm moist air into the roof void, you will still get some condensation
in the void space.

Modern warm deck construction (i.e. with the insulation "outside" the
roof timbers) does away with the problem generally.

BS 5250 "Control of condensation in buildings" is worth a read for
chapter and verse...



--
Cheers,

John.

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

On 22/03/16 18:45, John Rumm wrote:
On 15/03/2016 15:34, The Natural Philosopher wrote:
On 15/03/16 15:21, Tim Watts wrote:
On 15/03/16 15:04, The Natural Philosopher wrote:
On 15/03/16 13:52, Martin Bonner wrote:
On Tuesday, 15 March 2016 14:45:04 UTC+1, The Natural Philosopher
wrote:
On 15/03/16 13:13, David wrote:
If I insulate, there will be a ventilation gap beneath the tiles and
membrane from eaves to ridge and back to eaves, but no ridge vents
(unless I pay someone to go up on the roof).

How necessary are ridge vents?

Not really necessary at all

Well, not unless you want to prevent condensation on the timber
rafters.
(Or, to put it slightly less elliptically, "Actually quite
necessary").

Where does the water come from then?

(Or, to put it slightly less elliptically, "Actually quite
unnecessary").


Damp air.

My shed had no humans living in it. Nor does it have a source of water
vapour other than the air.

However, if I leave it all winter, during the worst months it will have
condensation running down the windows, mould growing on odd bits of ply
and tools will go rusty.

well it cant be ventilated then

My lawn had loads of wet dew on it the other day... that's quite well
ventilated!




But does it still?


--
Outside of a dog, a book is a man's best friend. Inside of a dog it's
too dark to read.

Groucho Marx

On 22/03/16 18:38, John Rumm wrote:
On 22/03/2016 14:17, Dave wrote:
Two questions or thoughts on this topic which I started.

I have a bungalow and wiuld not be too worried about roof climbing and
don't
need extra long ladders. Would it not be at least a help if I put
ventilation in the two gable ends at oppodite sides of the ridge as I
will
be leaving a couple of feet or so between the ridge board and the
insulation
board which of course leaves a good coupling space between the eaves.
To my
mind ventilation only happens with air flow and opposite side of a
roof will
have different air pressure during any breeze or wind which should drive
some air through even without ridge ventilation. I know that warm
moist air
will rise due to convection and can condense depending on dew point,
but I
think any breezy day would clear stagnant air. How often do we get a
totally
calm set of days in the UK?? I sometimes think building regs are a bit
over
the top and are dreamed up for job creation.

Yup if you have coupled all the rafter gaps to a big space at the top,
then you can just ventilate the big space and do pretty much the same job.

Notwithstanding because my rof timbers are at risk, does anyone know of a
semi-round ridge tile replacement with ventilation built in. I'm sure
I've
seen rooves with the odd ventilator on the ridge and not a continuous
strip.

When I did my loft, we just took off the exiting ridge tiles and then
bedded them back on with some cavity wall weep vents installed under
them at a downwards slant... investigation with a smoke match showed
they worked nicely.

These kind of things:

http://www.builderdepot.co.uk/cavity...erracotta.html





Clever - and much more subtle than tile vents.