Damp attic since insulation

E

eamonn123456

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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.
 
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...
 
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?
 
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...
 
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..
 
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/Publications/DevelopmentandHousing/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]
 
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!
 
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.
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!
Click to expand...

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.
 
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.
 
Last edited:
eamonn123456 said:
Thanks again ONQ.
<big snip>
Click to expand...
#

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.
 
"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.
 
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?
 
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. :)

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.
Click to expand...

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:
  1. Vapour check.
  2. Ventilate.
  3. 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.; -
  1. laying visqueen or plastic in the attic over downlighters or sources of heat like transformers.
  2. failing to route services separately at high level above the insulation to avoid damage
  3. 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.
 
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?
Click to expand...

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.
 
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.
 
eamonn123456 said:
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.
Click to expand...

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.
 
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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