Condensation in attic

pissed · 22-12-2009 8:55pm #1

Just been up in the attic and noticed condesation on the underside of the tile felt. Also slight damp marks on the roof trusses. The likes of the christmas tree box felt damp too but not wet. The floor of the attic is insulated with rock wool but its over 20 years old.

Would it be advisable to put more rockwool up along the trusses or would this make the problem worse.

What would be the main factors causing this?

nb1967 · 22-12-2009 9:37pm

I've noticed a similar problem this afternoon. I have an earlier thread about it in this forum where I've included a couple of images of what I've seen in the attic - is this the kind of thing you're seeing also ?

pissed · 22-12-2009 10:04pm

Hi had a look at your pics mine is more noticable where the thrusses meet the felt under the tiles. Its not on all the thrusses. The felt feels wet when I rub my hand along it. I have not heard any drops but then again I dont imagine I would seeing as its rockwool.

Maybe something to do with the current cold spell we are having. Just thought I would post here for a second opinion.

Ludo · 22-12-2009 10:46pm

I noticed this last week on my house. Identical to the pics in the earlier thread. This has never happened before and I have very recently had the attic insulated. I called back the guys who did it and they said it happens from time to time particularly when there is a low pitch roof like ours. Their solution was to insulate the attic door. The attic was previously as warm as the rest of the house but after the insulation is it very noticibly colder. They say this can cause problems if there is still "damp" air getting up through the attic door. I'll keep you posted how it gets on.

sullzz · 22-12-2009 11:32pm

is the felt wet all over the roof or is it just around where your storage tank is , if its just where your storage tank is , and if you have a headder tank check that when your heating is on that it is not pitching i.e. steam/hot water coming out of vent pipe , or also check that if using your immersion the stat is not faulty causing water to overheat and allow excesive heat out expansion pipe in attic .
more than likely not either of these but just something to check.

nb1967 · 22-12-2009 11:41pm

sullzz wrote: »

is the felt wet all over the roof or is it just around where your storage tank is , if its just where your storage tank is , and if you have a headder tank check that when your heating is on that it is not pitching i.e. steam/hot water coming out of vent pipe , or also check that if using your immersion the stat is not faulty causing water to overheat and allow excesive heat out expansion pipe in attic .
more than likely not either of these but just something to check.

In my case the immersion is not on at all (gas fired central heating only) and I didn't see anything that looked like hot air or steam in the attic. As in Ludo's post the attic is noticeably colder thant the house below - a good thing I suppose

My attic entry hatch is not that well insulated though so maybe that is an area I'll have a look at and I'll ask the maintenance guy tomorrow morning about it also

pissed · 23-12-2009 12:41am

My attic door is not insulated, neither is under my water tank. Will have to check when the heating is on if there is steam coming from the header. I think the wet is all over but not certain. Again I will have to check tomorrow.

Again going back to my earlier post, is there any advantage - disadvantage of using the rockwool between the thrusses going up the roof?

RKQ · 23-12-2009 12:14pm

pissed wrote: »

is there any advantage - disadvantage of using the rockwool between the thrusses going up the roof?

No advantage but could be a big disadvantage.
Your problem is condensation caused by a lack of air ventilation.
It is not a problem on a normal windy day but the last week has been very frosty (damp air) and still. The lack of wind is causeing damp wet air to condensate in your attic. Any warm air from your house is also condensating in your very cold attic, approx -6 last night!

Bitumen felt does not breathe. So if you put rockwool up against it you will cause a worse problem. Lack of ventilation can cause dry rot. There are plenty of threads explaining roof ventilation. There are a number of ridge vents, slate vents, eave vents & wall vents on the market.

pissed · 23-12-2009 1:34pm

Thanks for the reply, maybe add another layer of rockwool to the floor of the attic? Would this help on heat loss entering the attic from the house? The existing rockwool as I said is over 20 yrs old and patchy in places.

I should be getting some building work done in the new year so might ask if they can stick a few vent tiles in the roof while they are at it and see if that will help

RKQ · 23-12-2009 2:37pm

Hi Pissed, its hard to be specific without seeing your attic.
In general 300mm of Rockwool would be considered minimum. This should be laid in 2 layers, one between the joists and the second perpendicular to the joist.

So if your existing Rockwool was 150mm thick, over the whole area of your attic then you could lay a layer of 150mm or 200mm at 90 degress to the joists.

A storage platform may be required for Chrismas Decorations etc as the joist won't be visible once the second layer is installed. Preventing warm moist air entering your attic from your home is also very important.

Check also to ensure the existing insulation is not blocking the eaves ventilation. What is the cross ventilation like on a windy day? You should feel air movement / draught in your attic on a windy day.
Vent slates can be installed if required. A new wall vent drilled in the gable wall can be a cheaper DIY alternative.

elchanco · 23-12-2009 9:23pm

i have the same problem... its fairly common around this time of the year (xmas decorations coming down + cold weather)! Proper cross ventilation should help...

I installed two vent tiles but this didn’t help... there’s a lot of posts on boards relating to this problem..

pissed · 24-12-2009 11:53am

Thanks for the replies, my main concern was that the roof thrusses would be damaged with the water, will wait till the new year and get extra insulation and maybe a few roof vents.

happy christmas

mosii · 16-01-2021 7:18pm

Hi ,any solution to this problem?

listermint · 17-01-2021 10:01am

Yes make sure your attic has airflow

grassylawn · 17-01-2021 11:48am

My boiler is in my bathroom. I discovered a big hole around the pipes going up to the attic. I taped it up with duct tape and that reflective tape for pipe insulation.

I also suspect there is insulation shoved into the soffirlts or against the corner. Very awkward to access but have one of those claws people use to pick up litter to see if I can pull anyrhing out.

Only observed the condensation in my case on the north side of the roof (which is always shaded) and only during the recent icy time. There is mould on the rafters now though. I need to clean that off.

I put a dessicant dehumidifier up there while the condensation was observable. It filled up fast. A condenser dehumidifier would probably not work because they don't work well in the cold.

mosii · 17-01-2021 12:06pm

listermint wrote: »

Yes make sure your attic has airflow

Thank You, what is the most effective way of doing this,?

grassylawn · 18-01-2021 10:22am

Make sure your kitchen and bathroom extractor fans aren't venting into the attic. If you can't see where they vent to, the vents could be under insulation or otherwise obscured. (Some kitchen fans don't vent out of the room at all though.)

mosii wrote: »

Thank You, what is the most effective way of doing this,?

The first thing to do is to check insulation isn't blocking ventilation. It shouldn't be tight against the bottom of the roof at the sides.

Outkast_IRE · 18-01-2021 10:30am

A small amount of condensation would of been noticed by alot of people in ireland over the past month.

There were weeks where the wind wasnt strong , and this reduces the cross flow ventilation in the attic to clear the condensation easliy. You would find you rarely have noticeable condensation after a windy spell its most prevalent after cold frosty spell with very little wind.

Once you are sure your vents arent blocked and your extractor fans are connected up correctly there is very little to be concerned with.

mosii · 18-01-2021 4:56pm

Outkast_IRE wrote: »

A small amount of condensation would of been noticed by alot of people in ireland over the past month.

There were weeks where the wind wasnt strong , and this reduces the cross flow ventilation in the attic to clear the condensation easliy. You would find you rarely have noticeable condensation after a windy spell its most prevalent after cold frosty spell with very little wind.

Once you are sure your vents arent blocked and your extractor fans are connected up correctly there is very little to be concerned with.

Thank you, would it be necessary to put a roof vent in the roof tiles. ?I have light around the attic ,from the vents, but as you say ,there was no cross wind in the last few weeks. Also will the roof timbers dry out fully, and would there be any point in treating them in the summer?
Thanks for time and effort.

Outkast_IRE · 18-01-2021 9:52pm

mosii wrote: »

Thank you, would it be necessary to put a roof vent in the roof tiles. ?I have light around the attic ,from the vents, but as you say ,there was no cross wind in the last few weeks. Also will the roof timbers dry out fully, and would there be any point in treating them in the summer?
Thanks for time and effort.

Roof vents can help , but I would be more inclined to take a good look at the roof timbers in a few weeks time and see are they good and solid or do they seem to be rotting or weakening .

mosii · 19-01-2021 11:24pm

Thanks for reply, can i just ask ,is there a single job that you done that you could say, that that made a big reduction to the condensation in the attic space, thanks.

listermint · 20-01-2021 9:54am

mosii wrote: »

Thanks for reply, can i just ask ,is there a single job that you done that you could say, that that made a big reduction to the condensation in the attic space, thanks.

Airflow. Again airflow.

Check your ventilation in the soffits. If it's blocked up then no air gets in and everything else is a problem.

Outkast_IRE · 20-01-2021 9:58am

mosii wrote: »

Thanks for reply, can i just ask ,is there a single job that you done that you could say, that that made a big reduction to the condensation in the attic space, thanks.

If you really feel you need to reduce condensation, then improve airflow firstly , if you feel you need an additional roof vent then do that on both sides, you may be in a sheltered spot. Where i live we are off a large natural harbour so its like living next to the sea with quite noticeable wind alot of the time , which obviously aids airflow in the attic space.

Ash.J.Williams · 20-01-2021 10:00am

pissed wrote: »

Hi had a look at your pics mine is more noticable where the thrusses meet the felt under the tiles. Its not on all the thrusses. The felt feels wet when I rub my hand along it. I have not heard any drops but then again I dont imagine I would seeing as its rockwool.

Maybe something to do with the current cold spell we are having. Just thought I would post here for a second opinion.

Same here , never noticed it before

mosii · 20-01-2021 10:40am

Outkast_IRE wrote: »

If you really feel you need to reduce condensation, then improve airflow firstly , if you feel you need an additional roof vent then do that on both sides, you may be in a sheltered spot. Where i live we are off a large natural harbour so its like living next to the sea with quite noticeable wind alot of the time , which obviously aids airflow in the attic space.

Thanks.Its not that i feel the need to put up vents,i m trying to find the most effective way of reducing condensation in the attic,in periods of cold calm weather.I am beginning to think there is no silver bullet ,improve air flow seems to reduce the condensation,but if its cold and calm and very little air flow,then condensation will take place.

listermint · 20-01-2021 10:42am

mosii wrote: »

Thanks.Its not that i feel the need to put up vents,i m trying to find the most effective way of reducing condensation in the attic,in periods of cold calm weather.I am beginning to think there is no silver bullet ,improve air flow seems to reduce the condensation,but if its cold and calm and very little air flow,then condensation will take place.

Yes and it will go away the following day. It's not a problem if your airflow is generally good. It is a problem if your soffits are blocked with insulation and or the soffits contain no vent holes.

mosii · 20-01-2021 10:46am

listermint wrote: »

Yes and it will go away the following day. It's not a problem if your airflow is generally good. It is a problem if your soffits are blocked with insulation and or the soffits contain no vent holes.

Thanks for reply,i have cleared the soffit vents,and still get condensation.It does go away quickly ,but the timbers do get wet,and i am concerned about the long term effects,Tks

listermint · 20-01-2021 10:47am

mosii wrote: »

Thanks for reply,i have cleared the soffit vents,and still get condensation.It does go away quickly ,but the timbers do get wet,and i am concerned about the long term effects,Tks

Timbers are fine getting wet as long as they have capacity to dry afterwards.

If your seeing condensation on ten days out of the entire year your attic is fine. Don't be concerned.

mosii · 20-01-2021 10:52am

listermint wrote: »

Timbers are fine getting wet as long as they have capacity to dry afterwards.

If your seeing condensation on ten days out of the entire year your attic is fine. Don't be concerned.

Thanks for time and effort.That does ease my concerns to be fair,as its only about a week every Winter .

GreeBo · 20-01-2021 10:54am

mosii wrote: »

Thanks for time and effort.That does ease my concerns to be fair,as its only about a week every Winter .

Are they at all soft or black?

mosii · 20-01-2021 11:02am

GreeBo wrote: »

Are they at all soft or black?

No,but some are discoloured

Condensation in attic

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