# Damp attic since insulation



## eamonn123456 (16 Dec 2009)

I live in a 20 year old house with standard tiled apex roof.  Since we got 300mm blown rockwool insulation in a year ago, I have noticed the attic feels damp in cold weather.

We felt that the eaves, while not blocked, may be less clear than before, thus impeding ventilation.  We inserted 4 vents front and back in the soffit to help with this (wooden soffit & fascia).

Seemed to help but today was up there and stuff has got damp and mouldy, bit of mould in one or 2 trusses, and some slight drips off the felt esp on the north side, where the felt feels damp.

I have sealed around the hatch, also holes in hot press ceiling for pipes are now sealed.

1.  Is this normal?  assume not, as can't even store stuff there now.

2.  Is this bad for my roof?  assume so

3.  Is this going to impact on the effectiveness of the insulation? assume so

4.  Would more vents help? Maybe in the apex

5.  Maybe I should clear out the eaves a bit?

6.  What is the source of the moisture anyway - damp in the Irish air?  Or water penetration?

Who should I get to investigate - a roofer?  general builder?

Hoping for some help please.


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## elchanco (18 Dec 2009)

hi eamonn,

I’ve been battling condensation in my attic for the last two xmas! You will have to add more cross ventilation in the attic. I still haven’t solved my problem...


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## eamonn123456 (18 Dec 2009)

Thanks Elchanco.

Just went up there today and cleared out the eaves a bit to ensure the rockwool is not all the way up to the felt, have 2 or 3 inches clearances throughout now whereas before there was some level of blockage.  

Also doubled the number of soffit vents to 20 instead of 10 (2 inch round vents).

Lots of droplets formed last night due to the cold conditions.

If it doesn't clear, am going to put vents in the gable ends at the apex.

Not sure if I can get vent *tiles*, maybe only exist for flat slates?

Also, my chippy / roofer is not sure about ridge vents or how they work, as he says that ridge tiles are bedded straight into mortar.  Might have to replace the whole ridge?

Any more ideas / comments?


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## sydthebeat (18 Dec 2009)

if its a gable roof... have you the possibility of drilling 2-3 4" vents on each gable to allow cross ventilation??

older roofs have a tar like felt that is non breathable... thats fine when theres little condensation, but when good insulation is introduced condensation becomes more prevelant. cross ventilation is the key...


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## elchanco (18 Dec 2009)

You can get vent tiles to fit any type of slate/tile. I have two vent tiles on the northside of the roof but this hasn’t helped.

Next step will be putting two more, one on each side. higher up on the roof..

Make sure u seal any gaps/cracks in the ceiling where warm air can escape..


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## onq (18 Dec 2009)

Hi eamonn123456,

Thank you for this excellent post showing the perils of extra insulation and ventilation in a damp, cold climate.
Damp problems appear to have begun with the "blown rockwool" insulation according to your first post.
I have never worked with blown rockwool - normally it comes in rolls and is laid down by hand.
Blown insulation of any kind runs the risk of blocking vents at the eaves and low level.

Prior to that heat escaping from below kept the attic warm.
After insulating the attic got cold and moisture condensed.
You chose to vent as opposed to install a vapour check.

Not the weather to be trying to dry out a cold attic by venting.
Not a great time of year be opening even more vents when that failed

The reason I say this is because I was on site yesterday and I witnessed an unusual level of condensation - droplets on everything.
Looking straight at a metal stairs I was seeing constantly dripping water with no apparent source - as if it was coming directly from the air.
I was taking some evidence photos a short while later and realised why, as a huge hailstone went down the back of my collar - precipitation!
Almost 100% relative humidity on a very cold day meant I was seeing exactly what I thought I was seeing - water condensing directly from the air..

the relative humidity was very high
the ambient temperature was very low - 2 or 3 degrees
thus water was condensing on any cold surface exposed to this damp freezing air.
The metal stairs was just the most obvious and real-time evidence of it.
Under better conditions we seldom see water on everything else, just metal or glass.
When its drier and warmer water won't condense on anything but the metal, but with everything so cold, dew forms everywhere.

Now apply this to your attic - with the weather as cold and damp as it is.
It looks like you're adding cold damp air from outside to the cold damp air already inside.
As your attic and the materials in it are cold, and the wind is cold and damp, very little moisture is evaporating.

Short term you need to close a few vents and heat the attic.
A dehumidifier for a couple of days will help the attic and materials in it dry out.
Longer term you should consider installing a vapour check to the underside of the ceiling.
Finally if you're using the attic to store materials you should consider insulating between the rafters.

Given the result of your insulating efforts to date you should request a competent installer to carry out this work.
A minimum 50mm air gap must be preserved above the insulation between the rafters.
For 150mm rafters install 100mm insulation flush to the underside.
You can add more insulation below this again if required.

You'll need an air gap equivalent to 25mm continuous at the eaves and 5mm at the ridge.
Look at diagram 6 sketch D in Part F here: http://www.environ.ie/en/Publicatio...ng/BuildingStandards/FileDownLoad,1647,en.pdf

Yes the principle of preventing moisture transfer using vapour checks is on Page 10.
Ih particular read the paragraph on sealing around penetrations.
Revert back and let us know how you get on.

HTH

ONQ.

[broken link removed]


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## eamonn123456 (18 Dec 2009)

Thanks for the comprehensive reply, ONQ.  Some interesting ideas there.

Funny enough, I stuck a dehumidifer and a heater up there this evening!  Just as a short term fix.  

I don't want to be contradictory, but I am not sure about some of your comments.  Having said that I am completely open to correction.

I honestly don't feel that putting in extra venting was a wrong move long term, although short term I suppose it could be.  Unfortunately, I don't have an easy way of opening and closing those vents, 2 stories up.

I agree the prob is due to a colder attic space - which was the whole idea of insulation in the first place.

I think putting in vapour control layer (ie new ceilings?) is an expensive option, especially if you reckon that the source of the moisture is the external atmosphere anyway.

I think insulating the rafters is a high risk solution, given that this might hide the problem and lead to unseen rot of rafters.

I wonder would removing the tiles and putting in breathable felt be the answer?  I know that's radical and expensive, but I need a solution.

Maybe I should just remove the insulation!


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## eamonn123456 (18 Dec 2009)

PS thanks Syd and Elchanco too!


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## onq (18 Dec 2009)

eamonn123456 said:


> Thanks for the comprehensive reply, ONQ.  Some interesting ideas there.
> Funny enough, I stuck a dehumidifer and a heater up there this evening!  Just as a short term fix.
> I don't want to be contradictory, but I am not sure about some of your comments.  Having said that I am completely open to correction.
> I honestly don't feel that putting in extra venting was a wrong move long term, although short term I suppose it could be.  Unfortunately, I don't have an easy way of opening and closing those vents, 2 stories up.
> ...



Oops, I've confused you and I apologise - that was too complex a post.
Only in the current instance may the external air be adding to the problem.
This is because of the very cold and damp weather we're having at the moment.
This comment will not apply when the weather gets a bit warmer and drier.

I think you may need to vapour check the ceiling, because:

The original problem was first seen a while ago and re-occurred in cold weather and was probably caused by water vapour condensing in the attic - the source was more than likely from inside the house - human activity.
The recent problem, where the place was starting to get saturated shows that the problem was becoming more critical, possibly due to inadequate ventilation relative to a high water vapour content in the air in the attic - in drier, warmer weather conditions, adding more ventilation should have cleared this up.
The current problem, where adding more vents didn't sort out the incidence of damp is probably due to the damp cold weather outside.
So, to summarize, I think you need to install a sealed vapour check and adequate but not excessive ventilation.
The link I posted shows a few methods of attic insulation/ventilation - check the vented area you've put in.
More ventilation than normally recommended, drawing more wintry air into the attic won't improve matters.
You need to get the balance between vapour checking, insulation and ventilation right.

Actually I'm surprised at the severity of the problem.
I wouldn't have thought that blown fill insulation was so good that it would freeze the attic.
Die-hard aficionados please feel free to correct me.

Re the vapour check:

This can be integral in the form of foil-backed plasterboard, which can be hard to seal perfectly.
Or you could put up lapped and sealed visqueen layer, then fix on a layer of plasterboard.
Finally you could also consider a painted vapour check:
http://www.wondertex.co.uk/crossproductpages/wondertex-drywall-topcoat.asp
I haven't used one and I have no connection to the company.

BTW, you have checked all around for sources of water ingress, haven't you?

torn roofing felt
loose lead flashing
broken slates/tiles
weeping pipe joints
flat roof coverings
blocked gutters/downpipes
blocked overflows, etc.
Because any leak in the space would make a nonsense of the vapour check.

Insulating between the rafters is labour intensive, because the insulation must fit tightly between them.
It is better than blown or quilted insulation because it is precise and won't accidentally block the vents.
Some people like to treat the rafters with preservative, but this shouldn't be necessary once its vented.
The benefit if this last approach is that the entire attic is usable as a store room and won't get damp.
Assuming the roof structure allows you to use it as a space, that is.

FWIW

ONQ.


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## eamonn123456 (18 Dec 2009)

Thanks again ONQ.

To respond (your original comments in *bold)*:

*This is because of the very cold and damp weather we're having at the moment.
This comment will not apply when the weather gets a bit warmer and drier.
*
OK, but this type of weather occured last year (approx 10 consecutive weeks of very cold weather in the winter if I recall correctly), and the air in the west of Ireland is usually very humid, so these conditions will recur annually.

*The original problem was first seen a while ago*

Yes about a year ago in similar weather.  And when the wind blew, it cleared it.

*The current problem, where adding more vents didn't sort out the incidence of damp is probably due to the damp cold weather outside.*
I haven't been clear enough:  the extra vents went in today, so not much chance yet to clear it, and the weather is very cold, damp and still.


_*The link I posted shows a few methods of attic insulation/ventilation - check the vent area you've put in.
More ventilation than normally recommended, drawing more wintry air into the attic will solve nothing.*

_A total of 20 x 2" diameter vents is nowhere near the equivalent area of a 10mm continuous strip.  

*You need to get the balance between vapour checking, insulation and ventilation right.
*
Insulation = 300mm as recommended.

_*Actually I'm surprised at the severity of the problem.
I wouldn't have thought that blown fill insulation wasso good it would freeze the attic- although die heard aficionados please feel free to correct me.*
_
One side of the roof faces almost exactly north so it does get very very cold, hence the condensation on that side.

*You could simply add a layer of plasterboard to the existing ceiling - either foil-backed of putting up a lapped and sealed visqueen layer first - stapled and sealed.
*
Expensive option to reslab and skim 4 bedrooms, 2 bathrooms and a landing...

_*You could also consider a painted vapour check:*
_ 
Sounds a better option, thanks.

_*PS, you have checked all around for sources of water ingress, haven't you?

* _No sign of anything, although I have not been up on the roof itself.

Thanks again, lots more stuff to consider.


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## onq (19 Dec 2009)

eamonn123456 said:


> Thanks again ONQ.
> <big snip>


#

You#re welcome and here's another link to one of those applied vapour checks.

[broken link removed]

The trick is to reduce the amount of water vapour getting through the insulation to such a degree that the ventilation provided can talk avay any condensate.

BTW, you say

"A total of 20 x 2" diameter vents is nowhere near the equivalent area of a 10mm continuous strip."

That's apples and oranges. To compare them you need to give a rate per linear metre for the incidence of the 2" dia. vents. 

I make that 2024 sqmm per vent - which equates to 202.4mm of continuous 10mm vent - you'd need one every 8".

ALso not a lot admittedly when you consider a standard room vent area is 6500sqmm.

ONQ.


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## eamonn123456 (19 Dec 2009)

*"A total of 20 x 2" diameter vents is nowhere near the equivalent area of a 10mm continuous strip."

That's apples and oranges. To compare them you need to give a rate per linear metre for the incidence of the 2" dia. vents. 

I make that 2024 sqmm per vent - which equates to 202.4mm of continuous 10mm vent - you'd need one every 8".

*Off the top of my head, I dunno the rate per linear metre etc, but my house is wider than 80", so I still reckon I am not going overboard on the vents......



As regards that Gyproc sealer - would it work on a painted ceiling do you reckon or would it only work on bare Gyproc?  I'm thinking only on bare Gyproc.


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## elchanco (19 Dec 2009)

Thanks lads for the interesting discussion on ventilating the attic.

Is it possible to over ventilate the attic?

I put two vents in the north facing roof which showed no improvement. I think I should have put one on each side?


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## eamonn123456 (19 Dec 2009)

Couple of interesting links 



www.*sandtoft*.com/roof ventilation 
Note the warning about balancing ridge vent with soffit vent........


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## onq (19 Dec 2009)

eamonn123456 said:


> *"A total of 20 x 2" diameter vents is nowhere near the equivalent area of a 10mm continuous strip."
> 
> That's apples and oranges. To compare them you need to give a rate per linear metre for the incidence of the 2" dia. vents.
> 
> ...



A standard house is around 8M wide - yours is over 24M.

That isn't a house its a mansion - unless its a bungalow ,of course... 
But of course, bigger house ---> bigger problems.
So no it definitely isn't over ventilated and it points to the real source of the problem assuming its all occupied and heated.

I should've asked you to describe the house first.
Still, the same problem arises 8M or 24M.
Its just a bigger problem than I thought.

As for the sealer, no never used it - I was trying to find you an economical solution.

To recap again:

You've attempted to perform house "improvements" without seeking professional advice.
On this forum you've got some good general advice, but it was remote .
In other words it was from people who hadn't inspected the house.

You have been also referred to Part F.
This explains the basic principles.
To make these clear:

Vapour check.
Ventilate.
Insulate.
This is the correct order when upgrading.

BTW the weather in Dublin today is perfect - cold but dry, light breeze.
Great drying out according to my resident in-house [sic] expert in such matters.
If its similar in the West and the problem still isn't going away, its caused by insulating without any vapour checking and inadequate ventilating.

Bungalows have no intermediate floors with openable windows and/or permavents to help dissipate the water vapour in the air.
Downlighters are difficult because they accelerate warm air laden with water vapour flowing past them into the attic.
You really need both ventilating AND vapour checking in place to deal with the problem on a house like yours.
It seems to me that only ventilating OR only vapour checking won't be able to deal with the problem.

I think it would be useful for you to get the house professionally assessed.
For example, when you blew in your 300mm insulation did you also; -


insulate all the pipes in the attic
insulate the sides of your water tank(s)
install an insulated cover on the tank(s)
make sure there was no insulation under the tank(s)
Unforced errors by amateur installers [and some so-called "professionals"] can actually cause increased hazard in your home when insulating, e.g.; -

laying visqueen or plastic in the attic over downlighters or sources of heat like transformers.
failing to route services separately at high level above the insulation to avoid damage
covering downlighters or sources of heat like transformers with insulation.
That's just a short-list of three issues off the top of my head - there are many more.

There are other threads on this forum dealing with such issues in some depth, but thsi remote-viewing stuff could leave you exposed to risk somewhere else.

ONQ.


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## onq (19 Dec 2009)

elchanco said:


> Thanks lads for the interesting discussion on ventilating the attic.
> 
> Is it possible to over ventilate the attic?
> 
> I put two vents in the north facing roof which showed no improvement. I think I should have put one on each side?



Cross ventilating anything - rooms or attics - is the only way to go to promote adequate airflow.
Let's hope our evangelical Green minister is well-advised by the people pushing us to MVHR systems.
Otherwise, improperly designed vent systems will short circuit within rooms leading to dead pockets of air.

It is possible to over ventilate any unconverted attic or other interstitial space, but Part F is mostly silent on this.
This can occur with normal well-ventilated walls on elevations that face the prevailing wind or on sites with unusual micro-climates

Also if you have recessed downlighters in the attic I have heard persuasive anecdotal evidence that you can develop draughts at every downlight fitting. Not sure how since the light would tend to create an updraught, but a strong pressure differential and dross flow will push past anything.

I have also heard some anecdotal evidence from people who claim to know that unfixed cavity wall insulation [in board form, obviously] can lift off the outer face of the inner leaf in the cavity and reduce the insulation properties of such a wall when there is windy weather.

FWIW

ONQ.


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## eamonn123456 (19 Dec 2009)

Hi ONQ, 

a couple of things I should clarify / respond on:

My house is not 80' (feet) wide, just my attempt at humour saying that it is more than 80" (inches) wide. 
A rough calculation suggested that my 12 x 2" vents on each side would be adequate for that width (just making the point that I am NOT over ventilating according to what you said).

I don't have any downlighters.

I didn't do home improvements without professional advice - I used a well known professional company to carry out the insulation work.  They did indeed insulate the pipes, around the tanks (not under) and put a lid on them.  

However, they did not give any advice regarding ventilation or vapour control, which one may say with hindsight was negligent, but to be honest I would imagine that almost all of the installers of insulation who are doing thousands of installations each year in Ireland would not address this either.

Finally, of course I understand that internet advice is unpaid advice, and is sometimes worth every penny, so I would never rely on it alone.  

But of course it is often helpful, as in this case, for which I am grateful.


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## onq (19 Dec 2009)

eamonn123456 said:


> Hi ONQ,
> 
> a couple of things I should clarify / respond on:
> 
> ...



Well, my last post could be read as a belated disclaimer but there ya go - better late than never.

By professional advice I didn't mean you used a cowboy to do the work.

I mean you hadn't consulted an architect in relation to foreseeable risks and compliance issues that arise when installing insulation.

The advice is given "pro bono publico", for the public good, commonly shortened to "pro bono" work.

If its given by a professional, it should be to a professional standard regardless of whether or not its free 

As for the insulation installers, "doing a professional job" in that context may mean prompt attendances, performing as you noted above.

They are specialist insulation contractors.

This doesn't mean they are giving professional advice that a compliant upgrading installation requires.

They are not building professionals per se, such as a consultant structural engineer, mechanical and electrical engineer or architect.

Anyway you know enough now to ask the right questions of them if you want to get them back to sort thsi out for you.

Personally I think you need an architect versed in this kind of situation to advise you as there may be other facts no coming ot light in thsi online forum.

ONQ.


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## davebrien (20 Dec 2009)

Hi,

I installed 150 mm fibre insulation about 3 weeks ago I checked after reading this and it damp also - I installed the insulation right up to the felt all around so from reading through information should I have left 10MM between the fibre and the felt all around?

Thanks,

D


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## eamonn123456 (21 Dec 2009)

50mm as far as I know


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## onq (21 Dec 2009)

davebrien said:


> Hi,
> 
> I installed 150 mm fibre insulation about 3 weeks ago I checked after reading this and it damp also - I installed the insulation right up to the felt all around so from reading through information should I have left 10MM between the fibre and the felt all around?
> 
> ...



D and ,

This is not the case.
I realise this is a detailed technical discussion in relation to principles, but a few rules can be distilled.
Here is the link to Part F again http://www.environ.ie/en/Publicatio...ng/BuildingStandards/FileDownLoad,1647,en.pdf

10mm is not a good practice airgap within the roofspace - you couldn't maintain a 10mm air gap with quilted insulation, it will creep, sag and bunch up.
A 300-400mm passage from eaves gap to attic of only 10mm depth would restrict airflow - its a long tunnel as opposed to a 10mm gap at the eaves through a 19mm board .

10mm is the eaves air gap required for a roof without dormer conversion or restrictions in flow.
Good practice and Part F compliance requires installing a 50mm eaves air gap to serve such a roofspace.
Condensation can also occur on the roofing felt above any insulation - the 50mm gap encourages good venting.

In fact any roof type, anywhere within the roof requires the 50mm gap - look at the dormer roof requirements in Part F.
The eaves gap is now 25mm but the clear air gap within the roofspace requires to be 50mm - this is the dimension to work to.

Its also important that you don't block airflow above insulation that extends across the wall plate.
You may have have either frozen the wall plate out of it or else enclosed it completely
 Hard to say and in fact this is the hardest detail to get right with quilted insulation.
The aim is to insulate over it but leave a 50mm gap above the insulation.

You can form the 50mm gap by fixing "solid" insulation [not quilt] appropriately.
Snugly cut it to fit between the rafters and mechanically fix it if required.
Slide the cut sections down the rafter gap but it must be a snug fit.

If using quilt, you need to fix a thin board between the rafters to leave 50mm above it.
Don't install from a 200mm roll and then compress it by 100mm to leave 50mm.
This halves the trapped air and doubles the glass fibre - doesn't work well.
That why I advice HD "solid" insulation between the rafters.

Fixing with a board stops the quilted insulation bunching up and restricting the gap.

As I've noted before, insulating anfd venting detailing like this benefits from the advice of a professional.
Professionals deal with such matters on every building and are able to offer competent advice.
More importantly, they have gained experience of several different methods of compliance.
thus most situations can be competently addressed avoiding condensation build up.

D and , one final word in relation to "wet" insulation:

Depending on your insulation type, you may need to wholy remove and renew your installations.
Some insulation types absorb water and holds it, while other types can be dried by venting.
In severe instances the insulation will actually get wet and become very hard to dry.
Working remotely and not being familiar with the type I cannot say more on this.

Wet insulation can be even worse than no insulation, BTW.
It will conduct heat and evaporation is a cooling process.
Plus the water in it will move around and land elsewhere.
It can badly effect gypsum based materials and timber.
That is why wet insulation usually should be removed.

Remember.

1. Vapour check - restrict the passage of water vapour into the attic - attic hatches, downlights, ceilings without visqueen above or foil-backed plasterboard all allow passage.
2. Ventilate - ensure its equivalent to 10mm continuous eaves vent for an unconverted attic and 25mm eaves and 5mm ridge for converted/restricted attic space.
3. Insulate - after you've vapour checked and ensured adequate ventilation, insulate - review services, and insulate pipes and tanks [but not under tanks].

BTW , I cannot see how you can properly insulate water tanks using blown fill insulation.
You need to take the insulation from "floor" level in the attic, up the sides of the tank, leaving none below it.
You can do this by fixing quilted insulation or HD insulation boards around the tank, but blown fill will just slump away.
Its also a good idea to check all sides of the tanks, not just the ones you can see by looking from the attic access hatch.
And be very careful in an insulated attic - its very difficult so see where to place your feet properly and its easy hurt yourself.
Personally I never investigate attics alone if I can avoid it - always attend with someone to hold hte ladder and stay within earshot.

I hope this gives a little clarity.

FWIW

ONQ.

[broken link removed]


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## eamonn123456 (23 Dec 2009)

Hi ONQ, to answer your query on insulating the tanks: they are fitted with insulated 'jackets'. Seems to be doing the job in terms of keeping them ice free, I checked them this morning to make sure.

I appreciate all the input you have given, and I don't want to shoot the messenger, by no means, but I am *wondering* (taking an optimistic outlook) that maybe:

1. there is some moisture in my attic which entered either a) after I insulated but before I sealed around the hatch / pipe holes in the hotpress etc or b) in the recent very cold and damp weather where there was very high relative humidity in the air. Continuing in the same optimistic vein, the moisture is not *necessarily* currently entering through the ceiling ( I also have a small attic over my extension which is insulated in like fashion, but has no vents per se, and is not damp);

2. the main attic has never been properly vented out due to having no vents (up to a year ago) or inadequate vents (up to when I doubled them a week ago);

3. it only manifests itself in calm conditions and with temperatures in and around 0C;

4. it is not causing any serious damage to timbers as long as it doesn't stay damp for too long;

5. it should clear up when we get a bit of 'normal' (breezier) weather, any lingering moisture (if any) in the insulation should get flushed out when the roof gets hot in the summer;

6. now that there are double vents, a new balance should be established between any damp that might build up in still and damp conditions and the extra ventilation that should hopefully keep it clear.

7. if it needs a bit more help I can try ridge vents / tile vents / gable vents.

And they all lived happily ever after.

Or am i completely codding myself? 

Or maybe, with so many variables at play, the only way to find out is to wait and see?


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## onq (24 Dec 2009)

Not at all Eamon.

Questioning advice is important.

I gave you a top down set of options.

Bottom up testing of each is useful in practice.

Your questioning and alert mindset will serve you well.



ONQ.


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## eamonn123456 (19 Jan 2010)

Update:  had a roofer out today who got up there and had a look (outside).  

Straightaway he reckoned some of the ridge tiles are not pointed properly, hence the source of the moisture onto the felt and eventually into the attic space. No cracked tiles.  

He's going to take off about 5 or 6 ridge tiles and replace them, properly bedded in with waterproofing and properly pointed.  

Sounds plausible.  Let's hope its has the desired effect.  Will post when it settles down.


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## eamonn123456 (10 Feb 2010)

Update:

*Condensation seems to be gone since the work on the ridge was done.*

Seems that the simplest explanation was the correct one - that water was penetrating from above.  

I suppose what threw me was that it was manifesting as condensation, not as a single 'leak' per se.

I now think it was getting in at the ridge, seeping down along the felt, hitting a batten, travelling left and right along the batten across the roof, and also seeping down along several rafters.  It was soaking in (maybe via nail holes) along the sides of the rafters.

Once it was getting into the air in the attic, it was ready to condense out across the entire north facing felt when temps dropped, esp as I have a good depth of insulation now keeping the attic nice and cold.

At least that is my current theory!

Will be keeping an eye on it for any recurrence.

Thanks for all the inputs and hope this thread is of some use to anyone else with this problem.


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## ANIKIN (10 Feb 2010)

Eamon, I'm new to this forum and was glad to come across your posts. I noticed water droplets on the underside of the felt in my attic today; I guessed it was either condensation or a problem with the ridge tiles. Can you confirm what the tiler charged you for refixing the ridge tiles? Thanks.


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## eamonn123456 (10 Feb 2010)

They charged me about 220 I think it was.  They took off about 6 ridge tiles, cleared off old mortar, stripped off some tiles as well to investigate, and put it all back together, but watertight.

Anyway, in your case it may not be the ridge tiles, but hopefully it will be something simple, good luck with it.


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## onq (11 Feb 2010)

HI eamonn123456

You got a good price for the work and I'm glad the source of moisture appears to have been cleared up.

However...

You'd be surprised how these things can recur, partly because there may be more than one cause at work.

ONQ.

[broken link removed]


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## roker (11 Feb 2010)

I have managed to dry my attic by clearing the insulation away from the vents, it was previously dripping, but I am getting an alarm amount of loud cracking noises which is keeping me awake at night, I assume this is the timber shrinking, is this normal?


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## eamonn123456 (11 Feb 2010)

ONQ, I didn't always fully agree with some of your analysis (just most of it!), but I really have to say you were spot on about checking first for ingress of water, I should have got someone up on the roof (again) much sooner.  Thanks again!


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## onq (11 Feb 2010)

<chuckle>

Oh ye of little faith!

My analisis is based on case examples I have come across and the use of Occam's razor to miminise confusion.

Keep an eye on things still and check your insulation for dampness, if not wetness.

HTH

ONQ.

[broken link removed]


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## eamonn123456 (24 Feb 2010)

Hate to say it - but this problem is not sorted out yet.

Am seeing dampness along the top edge of some of the rafters, still on the north side of the roof.

Seems to seep down from above the felt, possibly via nail holes.

The only good thing is that the felt itself is dry now, even on the cold nights, so there must be less water vapour within the attic.  

This dampness recurred just before the end of the dry cold spell, so I can't blame the rain.

I wonder if it is residual damp between the tiles and the felt.

If all else fails I think I am going to have to refelt the roof.

Dammit!


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## onq (25 Feb 2010)

If the felt has "gone" at the ridge as you confirmed earlier, it could have gone elsewhere.
If it is I'd be asking the boys who repaired the roof how come they didn't spot it.

We once had a leak at our chimney, thought it was a loose flashing, discovered it was the felt, then spotted an old tear in the felt elsewhere and renewed that plus renewed all the felt edge along the gutter as a precaution because it was "threadbare".

FWIW

ONQ.

[broken link removed]


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## eamonn123456 (25 Feb 2010)

Thanks for responding ONQ.  

Not sure where you got the idea that the felt was gone at the ridge - maybe I wasn't clear - it was the pointing.  

The felt in general looks fine from the underside at least.


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## onq (25 Feb 2010)

HI again eamonn123456

When you wrote

"I now think it was getting in at the ridge, seeping down along the felt"

I assumed that meant the felt was leaking.

The scenario you describe cannot or should not normally occur if the felt is in good condition and properly installed.

The felt should have been carried over the ridge preventing ingress here.

Ridge tiles are usually bedded in mortar resting on the slopign tiles or slates.

The felt on the slopes "sags" allowing valleys to form between roof rafters down which any penetrating rain can run in rivulets down to the gutter.

FWIW

ONQ.

[broken link removed]

All advice on AAM is remote from the situation and cannot be relied upon as a defence or support - in and of itself - should legal action be taken.
Competent persons should be asked to advise in Real Life with rights to inspect and issue reports on the matters at hand.
My best advice is that you should retain a competent building professional to advise you on these matters.


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## eamonn123456 (25 Feb 2010)

Thanks ONQ.  I hear what you are saying.  It shouldn't seep in along the rafters, any moisture should tend to run down the middle of the valley in the felt.  Wonder why it does though....

I just don't see any leaks in the felt, nor is it threadbare.  I am pretty much at a loss now as to what is going on.  I think I have 2 options:

a.  strip off the tiles, at least on the north side, re-felt (with breathable felt), put tiles back on;

or

b.  wait til warmer weather, which shouldn't be TOO far away, and see if the roof dries out.  If not, proceed with plan (a).  
If it does dry out, keep an eye on it come autumn / winter, and see if it recurs.  If it does, then proceed with plan (a).  If it doesn't, then keep any eye on it.

Might be better to go straight to plan (a).


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## eamonn123456 (9 Apr 2011)

Update!  Problem recurred.

Roofer said the chimney cap was not fitted right - the infill part around the pots was only filled level to the precast cap and over time had weathered, allowing rain to pool and later on seep down the stack, eventually percolating thru the stack and presumably evaporating into the air in the attic.  That's the latest theory anyway!

So, he redid the infill, putting an extra layer of waterproofed mortar over the chimney cap, sloping it off to allow rain to run off.

Got the (cold type zeolite) dehumidifier on up there, got the RH down, checking with an electronic hygrometer.

Let it sit and hoped for the best.

Looks like it has dried out and no sign of seeping even after 3 days bad enough rain.  RH is low at the moment due to hot weather, but can still get high on damp days.  No sign of condensation last time we had frost.  Fingers xed.  Next winter will tell I think.

Thanks again ONQ for your insights!


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## bstop (10 Apr 2011)

This problem can be caused by warmer outside air  entering a colder attic. If the outside air is say 5 deg.C high RH and the attic surfaces are say 0 deg.C then condensation will occur on the attic surfaces. Air ventilation will not always have a drying effect. If the outside temperature rises quickly it will be warmer than the temperature of the roof felt. if this air is near 100% relative humidity it will condense when it hits the roof felt.   The weather conditions which cause this effect occur frequently in Ireland. A dry cold period is often followed by a rapid increase in outside temperature and usually this warmer air comes in from the Atlantic and is very high RH. The attic surfaces will not increase in temperature as quickly as this outside air and so become wet.


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## Arabella (26 Apr 2011)

We did our attic last year. The rafters were 4" deep and the guy put in 4" thick rockwool. Then a film of polythene all over before fixing plasterboard. Will the rockwool get damp from interstitial condensation? We have two velux windows and a gable window.


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## bmcintyre (3 May 2011)

Arabella said:


> We did our attic last year. The rafters were 4" deep and the guy put in 4" thick rockwool. Then a film of polythene all over before fixing plasterboard. Will the rockwool get damp from interstitial condensation? We have two velux windows and a gable window.


 It depends on whether there is felt or a breateable membrane under the tiles? If it's felt, then you may have a problem. If you have a non-breathable membrane such as felt, you need to have a 50mm ventialtion gap between insulation and felt to prevent condensation issues. 

If there is a breathable membrane, you're ok.


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## roker (4 May 2011)

bstop: that statement puzzles me, how can the attic be colder than the outside air?


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## bstop (4 May 2011)

If there is a rapid rise in outside air temperature due to changing weather conditions, the temperature of the attic structures will be colder than the outside air for a considerable warm up time period. These rapid rises and falls in outside temperature are regular in Ireland and often quite dramatic. Last Christmas the outside temperature changed from -15 to +10 Degrees over a period of hours into Stephens Day.


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## bmcintyre (5 May 2011)

bstop said:


> If there is a rapid rise in outside air temperature do to changing weather conditions, the temperature of the attic structures will be colder than the outside air for a considerable warm up time period. These rapid rises and falls in outside temperature are regular in Ireland and often quite dramatic. Last Christmas the outside temperature changed from -15 to +10 Degrees over a period of hours into Stephens Day.


 That's a pretty rare occurrence though, all the same.


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## bstop (5 May 2011)

Rapid temperature changes are a common occurrence in Ireland's changeable climate. The change at Christmas 2010 is an extreme example.


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## bmcintyre (6 May 2011)

bstop said:


> Rapid temperature changes are a common occurrence in Ireland's changeable climate. The change at Christmas 2010 is an extreme example.


 Rapid changes are relatively common but the temperature differential involved is rare.

The most common occurrence of condensation in an attic after installation of insulation, by far, is the ventilation being blocked off by the insulation or that it was an older house with a weak airflow into the attic but one just about strong enough to ventilate before the extra insulation was put in.


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## roker (6 May 2011)

That is exactly what happened to my house, the insulation was blocking the vents, plus the shower extractor was not ducted to the outside, but I recall the severe low temperature was for a couple of weeks and my attic was dripping. I will add that there must be no entry for the warm air from the house to the attic, this carries moisture.


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## bstop (6 May 2011)

bmcintyre said:


> Rapid changes are relatively common but the temperature differential involved is rare.
> 
> What does this statement mean?
> 
> ...


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## roker (9 May 2011)

With warm air on the outside, surely the condensation will be on the outside not the inside. Its the warm air that carries the moisture


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## bmcintyre (10 May 2011)

bstop said:


> bmcintyre said:
> 
> 
> > Rapid changes are relatively common but the temperature differential involved is rare.
> ...


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## bstop (10 May 2011)

roker said:


> With warm air on the outside, surely the condensation will be on the outside not the inside. Its the warm air that carries the moisture




The warm outside air enters the attic if it is well ventilated and wets the inside as I have previously explained.


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## bstop (10 May 2011)

bmcintyre said:


> bstop said:
> 
> 
> > That statement meant that temperature changes of 25 degrees are very rare in Ireland.
> ...


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## roker (10 May 2011)

bstop:
I disagree. If you heat up cold air it will go dryer and can absorb more moisture, so it will be dryer inside, it’s measured as Relative Humidity.
When I was living abroad in a hot country, I had my air condition on inside the house and the windows used to condense on the ouside.


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## bmcintyre (10 May 2011)

bstop said:


> bmcintyre said:
> 
> 
> > I have stated that the scenario I have outlined is a cause of attic condensation. I have not stated that it is as big a cause as anything else as you are suggesting.
> ...


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