Condensation in Attic Dripping down from the Felt onto the Insulation

The plumber who refitted our bathroom ducted from the fan over the new shower cubicle to the soffit and vented it.
 
This problem could be caused by foggy ( water saturated ) air from outside entering the attic . The weather conditions over the last few nights could cause this internal condensation to form. Outside 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 same effect happens in unheated garages. Objects like cans of paint will reach low temperatures during prolonged cold spells. If the outside temperature rises and the relative humidity of this outside air is very high condensation will form on the cold objects in the garage. When this happens it will often be possible to see the level of paint in the can by observing the height of the condensation on the outside of the can.
 
I checked my attic this morning. It is normally bone dry. At present there is slight dampness in some of the rafters at the upper edge where they contact the roof felt, and in isolated patches there is slight dampness on the felt itself. This is only on the north facing side of the roof as it is slightly colder than the south facing side. I reckon that the more ventilation the attic has, the more this effect will occur in certain weather conditions.
 
bstop, I have worked on humidity measuring equipment, I need to clarify your statement.
If you heat up cold air it becomes dryer, and is able to absorb more moisture. (the measurement is called (RH or relative humidity) the air must obtain the moisture from somewhere, if not it should dry your attic if it is heated up. The air in the house takes up moisture because of the fact we are living in it, breathing, cooking, washing, etc. If air leakes from the house in to the attic it bring with it moisture and condenses in the cold parts and possibly cause dripping. The attic should be sealed from the house to prevent air entering, convected heat from the house should heat the attic without moisture.
All holes including the attic hatch should be sealed.
 
i am talking about warmer air (say 5 degrees C) entering from outdoors into a colder attic ( say 0 degrees C) and being cooled in the attic and causing the described condensation. This can occur due to a rapid increase in outdoor temperature and often this warmer air is moisture laden Atlantic air due to a warm front. A well ventilated attic will behave in a similar fashion to the outdoor environment and will suffer condensation on cold surfaces.
Did you ever notice an outdoor oil tank in these weather conditions. Condensation will form on the tank up to the level of the oil in the tank. This is because the oil remains cold long after the outside air has warmed. Similarly the attic surfaces will be slower to heat up than the outside air and will attract condensation.
 
I had the same problem with condensation on attic felt during the very cold weather last year - only realised there was a problem when we saw small damp patches on the plasterboard in the attic conversion... got into a big panic about it afraid the rafters would be damaged or the insulation would get wet etc. Discovered when I was up there that the shower extractor fan was vented directly into the attic space ... Couldn't wait until summer to get tile vents fitted and proper venting of shower - never did either in the end because the condensation disappeared as soon as the cold spell ended.
I do wonder if it would be worth getting that foam insulation sprayed in between the rafters. They're advertising it at the moment, claiming to prevent pipes ever bursting - would it prevent the condensation ??? Or does the felt need to "breath" ?
 
Hi Jeananne and all,
Sorry I am reopening this thread after 2 years .
I have the same problem in my attic. I have recently fitted a ladder in to my attic and put 100 sq ft of attic flooring. 4 weeks ago when I saw the amount of condensation on the felt I was shocked. I have called in a plumber immediately and fixed all three vents which were left opened (celtic tiger builder work) in the attic and also put a dehumidifier for 3 days which extracted nearly 8 litres of water.
It looked dry for the next one week but condensation came back again on the felt. It looks bad.

Did you ever fix this condensation problem in your attic? If Yes, can you please share your solution?

Thank you very much.


 
is there adequate air circulating in the attic space? have you inadvertently blocked the ventilation at the eaves with insulation?
 
lowCO2design said:
is there adequate air circulating in the attic space? have you inadvertently blocked the ventilation at the eaves with insulation?
Click to expand...

Hi, thanks for your reply.
I think there is adequate air circulating in the attic because I feel it very cold when I go up.
I have no idea if the ventilation at the eaves is blocked. I put 100 sq ft of attic flooring in the centre of the attic, that's all.
How do I check if I have blocked ventilation at the eaves?

Thanks again.
 
If you're up there today, with the strong winds, you should feel the flow of air through the attic.
 
that's your problem so
http://www.environ.ie/en/Publications/DevelopmentandHousing/BuildingStandards/FileDownLoad,1647,en.pdf
start reading on p 26
 
Thank you Roker,Leo and lowCO2design for your replies.

I couldn't feel the wind in the attic, when I came home last night there were no winds.

I see a little bit of light from the edges of the roof. So I think some ventilation is provided in the attic but I don't feel wind coming in to the attic.

Thanks for the document, it gives lot of information. I should look at "effective seal to the attic access hatch"... because we fixed this a few months ago. From outside it looks fine...
 
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