A lot of condensation in attic

22-12-2021 01:49PM #1

My house and my neighbours were built identically. I am a DIYer, I just can’t help myself. My neighbour is the opposite. He needed some help with some unrelated DIY work, so I went into his attic and the inside of the roof was dripping wet, as it looks ok from the outside I am guessing that this is condensation. I checked mine and can confirm that I have no issue with this.

The differences between our houses are:

1) His attic insulation is very poor. I added a lot of rock wool to mine.

2) I put rock wool under the upstairs floor to try to keep a bit more heat down stairs and to deaden the noise.

3) When he puts his heating on downstairs remains quite cold and upstairs gets too hot, as the heat goes straight up. Upstairs in my house never gets as hot.

4) His attic hatch door provides a poor seal and is not insulated. I have fixed these issues.

5) Steam from the upstairs shower is not vented out from his bathroom as well as mine.

So, which of the above would you think is causing the issue? Do you agree that this is condensation? It is everywhere.

I am guessing that it is a combination of all.

Thanks

10-10-20 · 22-12-2021 02:09PM

6) Soffit vents?

If he has almost zero cross-flow ventilation then it's an endless trap of condensing & evaporating.

22-12-2021 02:14PM

Was also going to say vents. We had zero attic condensation, I stored empty boxes in the attic and over time the pile grew taller. One day I went up and there were drips all over the inside of the roof. I moved the boxes around so they weren't as tall, no more condensation. One (final straw) box had obviously stopped an air flow that had previously been doing its job.

22-12-2021 02:57PM

https://www.boards.ie/discussion/comment/118361175#Comment_118361175

As above, my home and my neighbor’s home were built identically (we live in the same estate). We both have the same soffit vents and I do not have this issue. We would both have good cross flow ventilation. Therefore I do not think it is a soffit vent issue.

mickdw · 22-12-2021 03:06PM

Cold roof surface, hot attic.

Ventilation and insulation is the cure and if his shower steam is not getting out properly, it's magnifying the issue.

Insulate on ceiling, keep soffit vents active and address shower issue.

22-12-2021 06:51PM

https://www.boards.ie/discussion/comment/118361491#Comment_118361491

Thank you. That is what I was thinking. My suggestion is start by insulating the attic properly. It is quite hot up there.

the vents are good.

mickdw · 22-12-2021 08:25PM

https://www.boards.ie/discussion/comment/118362489#Comment_118362489

You have the answer from your own home.

Insulating under 1st floor won't make a difference to condensation in the roof as long as the attic is sufficiently insulated on ceiling.

22-12-2021 09:17PM

https://www.boards.ie/discussion/comment/118362959#Comment_118362959

I was wondering if the steam from the upstairs shower would make much of a difference. Or the poorly sealing attic door. Maybe these make a negligible contribution to the condensation. Thoughts?

22-12-2021 09:30PM

Maybe the cause is steam leaking or venting into the attic? In one instance, a relative got a bathroom retiled plus some other work,the chap vented the extractor straight up into the attic, immediately within a week condensation was dripping from the underside of the felt in the attic, been a while since that happened, but got it sorted and fixed at the time and it resolved the problem immediately.

Id be surprised if its simply heat escaping from the rest of the house that is causing that condensation,but maybe if the ventilation is poor or blocked it is, Id be thinking look at the shower extraction, fix that for sure. All potential problems seem to have been pointed to.

tnegun · 22-12-2021 09:33PM

If the attic door is poorly sealed warm moist air is escaping into the attic through it, more so if the show steamer isn't being properly vented adding to the condensation in the attic. A long shot but also check that his boiler isn't pitching and dumping hot/boiling water into the cold water tank generating lots of steam in the attic.

10-10-20 · 22-12-2021 09:48PM

Not knowing any RH values or biological loading here, we can only guess, but warm air does not automatically mean humid air.

Semi-worst-case scenario: at 20 degrees C and 70% RH, 1kg of air (0.77m^3) will carry 0.010 kg (~10ml) of moisture.

The DP (saturation) in that situation will be 14.4 degrees C and a equivalent RH at 5 degrees C would carry 0.004kg (~4ml) of moisture, indicating that at least 6ml becomes condensate per kilo of air.

"Fun-time" chart for reference: 😁

But back to my point about the soffit vents, are they maintained free of insulation and is the aspect of both houses similar? Are any downlighters fitted within the upper floors?

Also how does the living-space ventilation differ and could yours be more effective, while he's trapping damp air? A higher general RH would permeate more moisture into the attic.

C. Eastwood · 22-12-2021 10:55PM

https://www.boards.ie/discussion/2058223928/a-lot-of-condensation-in-attic

Hi 2011. It’s important to have through ventilation in the attic to reduce the risk of surface condensation.

The more insulation fitted on the ceiling in the attic, will lower the temperature in the attic, which will increase the risk of condensation, and will therefore require more attic void through ventilation

In most instances the condensation in the attic is caused by moisture created in the house escaping in to the attic.
Firstly, it is important to reduce the amount of condensation within the house.
it is also important to prevent as much condensation created in the house from escaping in to the attic space. In doing this you will also reduce the amount of draughts from the vented attic space from getting in to the house.
There are 5 main areas in most houses where air is exchanged between the house and the attic void, especially in older houses. (A) holes in the ceiling of the hot press where the pipes from the plumbing and heating pass through at this point. (B) Attic access doors that are poorly fitted and are not fitted with draught excluders. (C) Where the electric wires from the attic void pass down through the ceiling to the Fuse Board (consumer electrical distribution board) and (D) through the holes in the ceiling where the electric wires pass down through the ceiling to the electric light fitting in every room. (E) Downlights that are not air sealed above the ceiling, and /or not properly sealed below the ceiling.
To reduce heat loss and draughts and reduce the amount of condensation getting from the house to the attic these holes should be completely blocked and made air tight. Downlighting should be replaced with sealed units.
Health & Safety. Only persons competent in walking in the attic, should go in to the attic to carry out the sealing of these holes. No person except a competent electrician should open any electrical fittings. Expanded foam should only be used by competent persons and strictly in accordance with the manufacturers safety instructions.
All of these holes could be sealed with silicone mastic —-( would be my choice of sealant.) For large gaps it can be built up over a few days.
The attic access door should be fitted with a rubber draught excluder with some fittings to compress the rubber. Also put 100 minimum Insulation on the upper side of the access door ( could be glued on with silicone mastic).
To reduce the amount of condensation in the house:-
Don’t dry clothes on radiators,
Fit mechanical extractor in the shower/ bathroom and kitchen. Must be exhausted to the external air. Must never be exhausting in the the attic void.
When cooking/ creating steam - turn on the extractor and open window. Close the kitchen door to prevent moist air escaping in to the other parts of the house.
After a shower/ bath - switch on the extractor, or before you leave - open the window and then close the bathroom door behind and allow the moist air created to escape.
Rooms in the attic would have other gaps and air leaks which are not mentioned above.

23-12-2021 08:34AM

In response to 10-10-20

"Not knowing any RH values or biological loading here, we can only guess, but warm air does not automatically mean humid air."

Good point about hot air not necesserialy being humid. My guess is that the high RH must be due to the shower.

Can you explain "biological loading"?

"But back to my point about the soffit vents, are they maintained free of insulation and is the aspect of both houses similar?"

Soffit vents are identical and good on both houses and the aspects are the same.

"Are any downlighters fitted within the upper floors?"

Only in my house, so this is nto the issue. I have not seen those phychrometric charts in a long time, thanks 😀

In response to C. Eastwood:

Point 1: Agree

Point 2: Makes sense. I forgot to add earlier I suspect that the room vents are poor. I recall fixing all of mine as they were very restricted. This would make it harder for humid air to escape. They alos have black mould in a few places. I installed an extract fan in the upstaris bathroom, and they did not.

Points 3 & 4: Makes sense

Point 5: there are no downlighters in thsi house.

Point 6: Agree, I am a qualified electrican so I understand this very well.

Points 7 to 14: Agree, points well made.

Although this is not my area, I told my friend that I believed that if this was not resolved it could lead to serious issues. He needs to take some action now. I think this starts with the low hanging fruit, fix room vents and change behaviours (open window wide after showers etc.). I take it you would both agree?

Many thanks to both of you for providing such detailed response. Clearly you are both experts in this area.

10-10-20 · 23-12-2021 11:28AM

"Can you explain "biological loading"?"

I'm using that as a term to describe the moisture generated by you and yours (or presumably him and his in this case) during daily activities - washing, showering, cooking, perspiring, etc.

Merry Christmas to all. 😊

Emma2019 · 23-12-2021 12:02PM

This thread is really interesting. Am taking notes for when I get my attic insulated!

C. Eastwood · 24-12-2021 12:13AM

https://www.boards.ie/discussion/comment/118364653#Comment_118364653

2011 Thank you for your kind comments. Kind Regards and Merry Christmas. C.Eastwood.

A lot of condensation in attic

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