I went up into the loft yesterday to search out the Christmas Decs,
and discovered that the roofing felt on the underside of the roofing
tiles has condensation on it - to the extent that there is a line of
drips along the loft floor boards where the condensation has dripped.

The loft is well insulated with about 8" of rockwool, except where the
loft boards are, where there is about 4" underneath the boards. The
soffits were replaced last year with ventilated soffits and I can see
light at the edges of the roof when in the loft with the lights off,
and the air bricks in the gable walls are clear - free from
blockage/obstruction.

What do I need to do to stop the condensation? The only source of warm
air I can think of is from the loft hatch which has draught excluder
around it as it can't be insulated due to the loft ladder.

Do I need to improve the air flow? If so, how? or are there other
things that I need to do?

Ta

Steve

Steve Bilton wrote:
I went up into the loft yesterday to search out the Christmas Decs,
and discovered that the roofing felt on the underside of the roofing
tiles has condensation on it - to the extent that there is a line of
drips along the loft floor boards where the condensation has dripped.

The loft is well insulated with about 8" of rockwool, except where the
loft boards are, where there is about 4" underneath the boards. The
soffits were replaced last year with ventilated soffits and I can see
light at the edges of the roof when in the loft with the lights off,
and the air bricks in the gable walls are clear - free from
blockage/obstruction.

What do I need to do to stop the condensation? The only source of warm
air I can think of is from the loft hatch which has draught excluder
around it as it can't be insulated due to the loft ladder.

Do I need to improve the air flow? If so, how? or are there other
things that I need to do?

Ta

Steve

Live with it I reckon. We currently have a small puddle under the velux
window but it only happens in very cold weather

"Steve Bilton" wrote in message
...
I went up into the loft yesterday to search out the Christmas Decs,
and discovered that the roofing felt on the underside of the roofing
tiles has condensation on it - to the extent that there is a line of
drips along the loft floor boards where the condensation has dripped.

The loft is well insulated with about 8" of rockwool, except where the
loft boards are, where there is about 4" underneath the boards. The
soffits were replaced last year with ventilated soffits and I can see
light at the edges of the roof when in the loft with the lights off,
and the air bricks in the gable walls are clear - free from
blockage/obstruction.

What do I need to do to stop the condensation? The only source of warm
air I can think of is from the loft hatch which has draught excluder
around it as it can't be insulated due to the loft ladder.

Do I need to improve the air flow? If so, how? or are there other
things that I need to do?

Ta

Steve


More ventilation required.

I have been to a number of properties,one just occupied for three months
where the wardrobes are mouldy/ back of leather suite mouldy. Client put a
dehumidifier in and got 6 pints of water from the bedroom in one day. To
solve problem open the windows and put the heating on !
The country has gone made with insulation insulation insulation and this is
the result ! Not to mention plastic windows and no open fireplaces.

Steve Bilton wrote:
I went up into the loft yesterday to search out the Christmas Decs,
and discovered that the roofing felt on the underside of the roofing
tiles has condensation on it - to the extent that there is a line of
drips along the loft floor boards where the condensation has dripped.

The loft is well insulated with about 8" of rockwool, except where the
loft boards are, where there is about 4" underneath the boards. The
soffits were replaced last year with ventilated soffits and I can see
light at the edges of the roof when in the loft with the lights off,
and the air bricks in the gable walls are clear - free from
blockage/obstruction.

What do I need to do to stop the condensation? The only source of warm
air I can think of is from the loft hatch which has draught excluder
around it as it can't be insulated due to the loft ladder.

Do I need to improve the air flow? If so, how? or are there other
things that I need to do?

Ta

Steve

Steve,

It's interstitial condensation and more ventilation is required (possibly a
couple of tile vents on either side of the roof [in the middle] to create a
cross-flow of ventilation).

Cash

On Dec 14, 10:44*am, Steve Bilton wrote:
I went up into the loft yesterday to search out the Christmas Decs,
and discovered that the roofing felt on the underside of the roofing
tiles has condensation on it - to the extent that there is a line of
drips along the loft floor boards where the condensation has dripped.

The loft is well insulated with about 8" of rockwool, except where the
loft boards are, where there is about 4" underneath the boards. The
soffits were replaced last year with ventilated soffits and I can see
light at the edges of the roof when in the loft with the lights off,
and the air bricks in the gable walls are clear - free from
blockage/obstruction.

What do I need to do to stop the condensation? The only source of warm
air I can think of is from the loft hatch which has draught excluder
around it as it can't be insulated due to the loft ladder.

Do I need to improve the air flow? If so, how? or are there other
things that I need to do?

Ta

Steve

warm moist air infiltrating will cause condensation, or lack of
venting.

Cash wrote:
Steve Bilton wrote:
I went up into the loft yesterday to search out the Christmas Decs,
and discovered that the roofing felt on the underside of the roofing
tiles has condensation on it - to the extent that there is a line of
drips along the loft floor boards where the condensation has dripped.

The loft is well insulated with about 8" of rockwool, except where the
loft boards are, where there is about 4" underneath the boards. The
soffits were replaced last year with ventilated soffits and I can see
light at the edges of the roof when in the loft with the lights off,
and the air bricks in the gable walls are clear - free from
blockage/obstruction.

What do I need to do to stop the condensation? The only source of warm
air I can think of is from the loft hatch which has draught excluder
around it as it can't be insulated due to the loft ladder.

Do I need to improve the air flow? If so, how? or are there other
things that I need to do?

Ta

Steve

Steve,

It's interstitial condensation and more ventilation is required (possibly a
couple of tile vents on either side of the roof [in the middle] to create a
cross-flow of ventilation).

Cash



So a cross flow of freezing air at 90% relative humidity will dry it out?

On 14 Dec, 16:44, Steve Bilton wrote:
I went up into the loft yesterday to search out the Christmas Decs,
and discovered that the roofing felt on the underside of the roofing
tiles has condensation on it - to the extent that there is a line of
drips along the loft floor boards where the condensation has dripped.

The loft is well insulated with about 8" of rockwool, except where the
loft boards are, where there is about 4" underneath the boards. The
soffits were replaced last year with ventilated soffits and I can see
light at the edges of the roof when in the loft with the lights off,
and the air bricks in the gable walls are clear - free from
blockage/obstruction.

What do I need to do to stop the condensation? The only source of warm
air I can think of is from the loft hatch which has draught excluder
around it as it can't be insulated due to the loft ladder.

Do I need to improve the air flow? If so, how? or are there other
things that I need to do?


Weirdest thing ... same thing happened to me ! However I'm a little
puzzled because a couple of years ago I put about 20 3" vents in the
eaves to counter the damp after we had new insulation fitted. This has
worked for the past two years.

My query is because the damp is localised to one part of the roof (of
course the one where the decs were stored !). We live in an "L" shaped
bungalow, so there are 4 roof sides. It's just the one which was damp.
It's the one above the bathroom, if that's significant.

For a short term fix, I intend to put a small fan up in the affected
corner, and try and circulate some air out of the loft. Can anyone
suggest why this is happening ?

stuart noble wrote:
Cash wrote:
Steve Bilton wrote:
I went up into the loft yesterday to search out the Christmas Decs,
and discovered that the roofing felt on the underside of the roofing
tiles has condensation on it - to the extent that there is a line of
drips along the loft floor boards where the condensation has dripped.

The loft is well insulated with about 8" of rockwool, except where the
loft boards are, where there is about 4" underneath the boards. The
soffits were replaced last year with ventilated soffits and I can see
light at the edges of the roof when in the loft with the lights off,
and the air bricks in the gable walls are clear - free from
blockage/obstruction.

What do I need to do to stop the condensation? The only source of warm
air I can think of is from the loft hatch which has draught excluder
around it as it can't be insulated due to the loft ladder.

Do I need to improve the air flow? If so, how? or are there other
things that I need to do?

Ta

Steve

Steve,

It's interstitial condensation and more ventilation is required
(possibly a couple of tile vents on either side of the roof [in the
middle] to create a cross-flow of ventilation).

Cash


So a cross flow of freezing air at 90% relative humidity will dry it out?

yes, if the temperature inside is enough to lift that temp even sightly.

But in this case vapour barrier under the insulation is probably at
least as advisable.

Jethro wrote:
On 14 Dec, 16:44, Steve Bilton wrote:
I went up into the loft yesterday to search out the Christmas Decs,
and discovered that the roofing felt on the underside of the roofing
tiles has condensation on it - to the extent that there is a line of
drips along the loft floor boards where the condensation has dripped.

The loft is well insulated with about 8" of rockwool, except where the
loft boards are, where there is about 4" underneath the boards. The
soffits were replaced last year with ventilated soffits and I can see
light at the edges of the roof when in the loft with the lights off,
and the air bricks in the gable walls are clear - free from
blockage/obstruction.

What do I need to do to stop the condensation? The only source of warm
air I can think of is from the loft hatch which has draught excluder
around it as it can't be insulated due to the loft ladder.

Do I need to improve the air flow? If so, how? or are there other
things that I need to do?


Weirdest thing ... same thing happened to me ! However I'm a little
puzzled because a couple of years ago I put about 20 3" vents in the
eaves to counter the damp after we had new insulation fitted. This has
worked for the past two years.

My query is because the damp is localised to one part of the roof (of
course the one where the decs were stored !). We live in an "L" shaped
bungalow, so there are 4 roof sides. It's just the one which was damp.
It's the one above the bathroom, if that's significant.

For a short term fix, I intend to put a small fan up in the affected
corner, and try and circulate some air out of the loft. Can anyone
suggest why this is happening ?

no vapour barrier between bathroom and loft.

"Jethro" wrote in message
...
Can anyone suggest why this is happening ?

Moisture vapour from your nice warm rooms below is getting up into the
roofspace, where the cold air cannot hold as much vapour, it reaches dew
point and the vapour condenses on the cold surfaces.

Ventilation in the roofspace is one way to remove the vapour but in cold
weather the effect is limited. A vapour barrier on the ceiling (even a coat
of oil paint under the emulsion) would certainly help, also ventilating away
the moisture from the rooms below with fans or by opening windows and
trickle vents, and considering ways you can reduce the amount of vapour you
create, such as drying clothes indoors, cooking, bathing and showering etc.

"The Natural Philosopher" wrote in message
...
stuart noble wrote:
So a cross flow of freezing air at 90% relative humidity will dry it out?

yes, if the temperature inside is enough to lift that temp even sightly.

But in this case vapour barrier under the insulation is probably at least
as advisable.

I don't have any felt or underlay under the tiles on my roof and it blows a
gale up there. I never see any condensation at all, even in the coldest
weather.

Peter Taylor wrote:

"The Natural Philosopher" wrote in message
...
stuart noble wrote:
So a cross flow of freezing air at 90% relative humidity will dry it
out?

yes, if the temperature inside is enough to lift that temp even sightly.

But in this case vapour barrier under the insulation is probably at
least as advisable.

I don't have any felt or underlay under the tiles on my roof and it
blows a gale up there. I never see any condensation at all, even in the
coldest weather.

condenation is the result of warm vapour ingress exceeding the ability
of ventilation to remove it.

You can solve it by increasing ventilation or reducing vapour ingress.

or both.

Generally the less ventilation you have, the better the roof will stay
warm in icy blast conditions.

stuart noble wrote:
Cash wrote:
Steve Bilton wrote:
I went up into the loft yesterday to search out the Christmas Decs,
and discovered that the roofing felt on the underside of the roofing
tiles has condensation on it - to the extent that there is a line of
drips along the loft floor boards where the condensation has
dripped. The loft is well insulated with about 8" of rockwool, except
where
the loft boards are, where there is about 4" underneath the boards.
The soffits were replaced last year with ventilated soffits and I
can see light at the edges of the roof when in the loft with the
lights off, and the air bricks in the gable walls are clear - free
from blockage/obstruction.

What do I need to do to stop the condensation? The only source of
warm air I can think of is from the loft hatch which has draught
excluder around it as it can't be insulated due to the loft ladder.

Do I need to improve the air flow? If so, how? or are there other
things that I need to do?

Ta

Steve

Steve,

It's interstitial condensation and more ventilation is required
(possibly a couple of tile vents on either side of the roof [in the
middle] to create a cross-flow of ventilation).

Cash



So a cross flow of freezing air at 90% relative humidity will dry it
out?

Yep - and in fact specified in many contracts where heavy loft insulation
has been done and where interstitial condensation is present and a
breathable (Tyvek) sarking felt has not been used under the roof covering.

As a matter of interest - leaving loft insulation short of the fascia/soffit
space causes a barely sufficient cross flow of air to prevent condensation
(especially of there is a 'heat leak' into the attic) - even when soffit
vents are fitted on occasions.

Cash

So a cross flow of freezing air at 90% relative humidity will dry it
out?

Yep - and in fact specified in many contracts where heavy loft insulation
has been done and where interstitial condensation is present and a
breathable (Tyvek) sarking felt has not been used under the roof covering.


I'll take your word for it.

On Dec 15, 5:23*pm, stuart noble wrote:
So a cross flow of freezing air at 90% relative humidity will dry it
out?

Yep - and in fact specified in many contracts where heavy loft insulation
has been done and where interstitial condensation is present and a
breathable (Tyvek) sarking felt has not been used under the roof covering.

I'll take your word for it.

1) Ventilate, ventilate, ventilate the attic. One code calls for 0.3%
of the area (that's 3 sq feet venting per 1000 sq. feet area.) and
must allow 'cross-ventilation'.
2) The moisture is coming from somewhere. For example warmed heated
house air infiltrating into attic/loft! Seal up as much as possible.
3) Make sure bathroom and kitchen fans are used and/or window open
slightly when cooking. Ventilate house from time to time (open unused
chimney etc.).
4) Proper ventilation healthier for house and inhabitants.
5) At an extreme install an air-heat exchanger and run it either
continuously or frequently.

stuart noble wrote:

So a cross flow of freezing air at 90% relative humidity will dry it
out?

Yep - and in fact specified in many contracts where heavy loft
insulation has been done and where interstitial condensation is
present and a breathable (Tyvek) sarking felt has not been used under
the roof covering.


I'll take your word for it.


he's right. I have more hole in my soffiits and ridge than there are in
Gordon Browns economic policy. Totally wrecked the insulation
effectiveness till I boarded over it.

But that's what they said was the regulations.

Dry as a bone too!

The Natural Philosopher wrote:
stuart noble wrote:

So a cross flow of freezing air at 90% relative humidity will dry it
out?

Yep - and in fact specified in many contracts where heavy loft
insulation has been done and where interstitial condensation is
present and a breathable (Tyvek) sarking felt has not been used under
the roof covering.


I'll take your word for it.


he's right. I have more hole in my soffiits and ridge than there are in
Gordon Browns economic policy. Totally wrecked the insulation
effectiveness till I boarded over it.

But that's what they said was the regulations.

Dry as a bone too!

My point is that freezing air with 100% relative humidity, such as we
have now, can't, by definition, dry anything. I wouldn't go looking for
a solution to a problem that may exist only on odd days in the year.

"stuart noble" wrote in message
...
The Natural Philosopher wrote:
stuart noble wrote:

So a cross flow of freezing air at 90% relative humidity will dry it
out?

Yep - and in fact specified in many contracts where heavy loft
insulation has been done and where interstitial condensation is present
and a breathable (Tyvek) sarking felt has not been used under the roof
covering.


I'll take your word for it.


he's right. I have more hole in my soffiits and ridge than there are in
Gordon Browns economic policy. Totally wrecked the insulation
effectiveness till I boarded over it.

But that's what they said was the regulations.

Dry as a bone too!

My point is that freezing air with 100% relative humidity, such as we have
now, can't, by definition, dry anything. I wouldn't go looking for a
solution to a problem that may exist only on odd days in the year.

Well, your first point was actually referring to 90% humidity which will dry
slowly. You have now switched to the safer 100% which, of course, won't dry
anything.

Ventilation is always the key as it will stay dryer in the lead up to days
like we have now and will dry quicker afterwards so the incidence and
persistence of such conditions in the loft will be much improved. If there
are freezing, wet conditions with no wind for an extended period AND you
introduce warm damp air into the loft, you will have a problem whatever,
granted, but, over a year, a well ventilated loft will have fewer problems.


--
Bob Mannix
(anti-spam is as easy as 1-2-3 - not)

On 16 Dec, 08:52, "Bob Mannix" wrote:
"stuart noble" wrote in message

...



The Natural Philosopher wrote:
stuart noble wrote:

So a cross flow of freezing air at 90% relative humidity will dry it
out?

Yep - and in fact specified in many contracts where heavy loft
insulation has been done and where interstitial condensation is present
and a breathable (Tyvek) sarking felt has not been used under the roof
covering.

I'll take your word for it.

he's right. I have more hole in *my soffiits and ridge than there are in
Gordon Browns economic policy. Totally wrecked the insulation
effectiveness till I boarded over it.

But that's what they said was the regulations.

Dry as a bone too!

My point is that freezing air with 100% relative humidity, such as we have
now, can't, by definition, dry anything. I wouldn't go looking for a
solution to a problem that may exist only on odd days in the year.

Well, your first point was actually referring to 90% humidity which will dry
slowly. You have now switched to the safer 100% which, of course, won't dry
anything.

Ventilation is always the key as it will stay dryer in the lead up to days
like we have now and will dry quicker afterwards so the incidence and
persistence of such conditions in the loft will be much improved. If there
are freezing, wet conditions with no wind for an extended period AND you
introduce warm damp air into the loft, you will have a problem whatever,
granted, but, over a year, a well ventilated loft will have fewer problems.

--
Bob Mannix
(anti-spam is as easy as 1-2-3 - not)

It suddently occured to me that there is a toilet vent going into the
roof space from the upstairs toilet which comes on automatically with
the light, and children being children it tends to get left on. If I
turn this off and cap the vent pipe while it is turned off this will
reduce the amount of warm air getting into the loft, as when it is off
the fan is a clear straight route into the roof...

A job for tonight.

Thanks all for the help - and as always the additional "discussion"

Cheers

Steve

Steve Bilton wrote:

It suddently occured to me that there is a toilet vent going into the
roof space from the upstairs toilet which comes on automatically with
the light, and children being children it tends to get left on.

I think you've found the source of your damp! Are you going to admit who
bodged it? ;-)

Tim

Bob Mannix wrote:
"stuart noble" wrote in message
...
The Natural Philosopher wrote:
stuart noble wrote:
So a cross flow of freezing air at 90% relative humidity will dry it
out?
Yep - and in fact specified in many contracts where heavy loft
insulation has been done and where interstitial condensation is present
and a breathable (Tyvek) sarking felt has not been used under the roof
covering.

I'll take your word for it.

he's right. I have more hole in my soffiits and ridge than there are in
Gordon Browns economic policy. Totally wrecked the insulation
effectiveness till I boarded over it.

But that's what they said was the regulations.

Dry as a bone too!
My point is that freezing air with 100% relative humidity, such as we have
now, can't, by definition, dry anything. I wouldn't go looking for a
solution to a problem that may exist only on odd days in the year.

Well, your first point was actually referring to 90% humidity which will dry
slowly. You have now switched to the safer 100% which, of course, won't dry
anything.

Ventilation is always the key as it will stay dryer in the lead up to days
like we have now and will dry quicker afterwards so the incidence and
persistence of such conditions in the loft will be much improved. If there
are freezing, wet conditions with no wind for an extended period AND you
introduce warm damp air into the loft, you will have a problem whatever,
granted, but, over a year, a well ventilated loft will have fewer problems.


Can't argue with that, but most lofts have "sufficient" ventilation by
design i.e. a flow of air under the roof tiles

stuart noble wrote:
The Natural Philosopher wrote:
stuart noble wrote:

So a cross flow of freezing air at 90% relative humidity will dry it
out?

Yep - and in fact specified in many contracts where heavy loft
insulation has been done and where interstitial condensation is
present and a breathable (Tyvek) sarking felt has not been used
under the roof covering.


I'll take your word for it.


he's right. I have more hole in my soffiits and ridge than there are
in Gordon Browns economic policy. Totally wrecked the insulation
effectiveness till I boarded over it.

But that's what they said was the regulations.

Dry as a bone too!

My point is that freezing air with 100% relative humidity, such as we
have now, can't, by definition, dry anything. I wouldn't go looking for
a solution to a problem that may exist only on odd days in the year.

If there is enough heat to carry in condesnable moisture, that air wont
be freezing when its in the loft. And neither therefore will it be at
100% humidity.

And in any case, that air will be whisked out of the roof as a stream of
steam, before it can settle on the beams.

And even if it does, the first dryer day, it will evaporate again.

If you seal the roof, that doesn't happen. Water vapour builds up

On 16 Dec, 10:07, "Tim Downie"
wrote:
Steve Bilton wrote:
It suddently occured to me that there is a toilet vent going into the
roof space from the upstairs toilet which comes on automatically with
the light, and children being children it tends to get left on.

I think you've found the source of your damp! *Are you going to admit who
bodged it? ;-)

Tim

All I'll say is - it was like that when we bought the house... it
helps keep the unpleasant smells at bay... but for no longer!

Steve

"Steve Bilton" wrote in message
...
I went up into the loft yesterday to search out the Christmas Decs,
and discovered that the roofing felt on the underside of the roofing
tiles has condensation on it - to the extent that there is a line of
drips along the loft floor boards where the condensation has dripped.

The loft is well insulated with about 8" of rockwool, except where the
loft boards are, where there is about 4" underneath the boards. The
soffits were replaced last year with ventilated soffits and I can see
light at the edges of the roof when in the loft with the lights off,
and the air bricks in the gable walls are clear - free from
blockage/obstruction.

What do I need to do to stop the condensation? The only source of warm
air I can think of is from the loft hatch which has draught excluder
around it as it can't be insulated due to the loft ladder.

Do I need to improve the air flow? If so, how? or are there other
things that I need to do?

Ta

Steve

A few replies say more ventilation, but the weather recently has been very
cold with little or no wind. It seems to me that the amount of ventiliation
would be irrelevent unless there is at least a breeze?

Or have I missed something?

Graham

Graham Jones wrote:
"Steve Bilton" wrote in message
...
I went up into the loft yesterday to search out the Christmas Decs,
and discovered that the roofing felt on the underside of the roofing
tiles has condensation on it - to the extent that there is a line of
drips along the loft floor boards where the condensation has dripped.

The loft is well insulated with about 8" of rockwool, except where the
loft boards are, where there is about 4" underneath the boards. The
soffits were replaced last year with ventilated soffits and I can see
light at the edges of the roof when in the loft with the lights off,
and the air bricks in the gable walls are clear - free from
blockage/obstruction.

What do I need to do to stop the condensation? The only source of warm
air I can think of is from the loft hatch which has draught excluder
around it as it can't be insulated due to the loft ladder.

Do I need to improve the air flow? If so, how? or are there other
things that I need to do?

Ta

Steve

A few replies say more ventilation, but the weather recently has been
very cold with little or no wind. It seems to me that the amount of
ventiliation would be irrelevent unless there is at least a breeze?

Or have I missed something?

Graham
Google diffusion.

"Graham Jones" wrote in message
...
"Steve Bilton" wrote in message
...
I went up into the loft yesterday to search out the Christmas Decs,
and discovered that the roofing felt on the underside of the roofing
tiles has condensation on it - to the extent that there is a line of
drips along the loft floor boards where the condensation has dripped.

The loft is well insulated with about 8" of rockwool, except where the
loft boards are, where there is about 4" underneath the boards. The
soffits were replaced last year with ventilated soffits and I can see
light at the edges of the roof when in the loft with the lights off,
and the air bricks in the gable walls are clear - free from
blockage/obstruction.

What do I need to do to stop the condensation? The only source of warm
air I can think of is from the loft hatch which has draught excluder
around it as it can't be insulated due to the loft ladder.

Do I need to improve the air flow? If so, how? or are there other
things that I need to do?

Ta

Steve

A few replies say more ventilation, but the weather recently has been very
cold with little or no wind. It seems to me that the amount of
ventiliation would be irrelevent unless there is at least a breeze?

Or have I missed something?


Yes, the rest of the year! Ventilation stops damp building up and speeds its
disappearance, to the extent you may never see it.


--
Bob Mannix
(anti-spam is as easy as 1-2-3 - not)