Condensation in Rooves

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Inspected my roof on a cold damp winters morning only to find a lot of condestation running down the inside plastic membrane (i know this is not breathable) onto the roof edge which is causing the plaster not to dry.
Has anyone tried easy vents or the felt lap vents available on ebay and with videos on youtube?
Are these effective?
The loft is fully insulated and the property is currently empty being refurbed, no heating so i know there is a lot of water vapour in the house as the plaster et al dries.
Thanks all
 
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They stopped manufacturing that plastic membrane for that reason, vents may help.
It seems that roof vents are going to be required (but might not work) according to a local roofer i had look at the roof.
What is your experience with how effective these vents are? Is the positioning of the vents critical. Are top level vents more effective than low level (there are no soffit ventilations), im expecting i would require both? Its a small 3 sided hip roof perhaps 25-30 degrees with a gable at one end.
Thanks in advance.
 
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as the house is unoccupied and is drying out, leave the loft hatch open. This will encourage airflow through the loft. As long as the eaves have not been blocked with insulation (pull back if so) the extra airflow will help take the water vapour away. On a sunny day the loft will warm up.
 
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Found couple of interesting link which seems like the same problem.

http://www.diynot.com/forums/viewtopic.php?t=166127

http://www.buildingconservation.com/articles/roof/roof-ventilation.html

Any further comments?

Seems like ventilation is key, a reroof may not even fix the problem, but that film is a real problem, perhaps i should just cut the film from the heavily condensed areas. Will the bare tiles still condense in this case? As stated previously they are tightly fitting cement tiles which from the outside appear in good nick.
 
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I have removed all the insulation from the edges of the roof. It was pressed into the corners. There is some daylight showing through now.
I also added some roof vents at some expense :( A gamble who knows if it will work or not or i have chucked money away.
Will let you know later after a few weeks to see if there are problems.
Cheers,
 
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Thought id post back with a quick update.
There have been a few very cold nights well below dew point and there is still some condensation but it appears improved considerably. One side where the vents were installed at low level, the condensation appears to have gone altogether, but there is still some condensation on another side of the roof where there were no vents fitted.
I guess this says that the vents are working effectively in the localised area. They appear to work by clearing the condenstation in a local area and up to the vent in the ridge. I think with vents along the other side it may be sorted. Hope this is helpful to someone further down the line. I have chucked a fan in the roof pointing at the remaining condensing area lets see what that does.
 
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