Moisture in the ceiling space

[alexking]

In a house I visited last week, the building paper under the roof was wet over a large area. There was no ientified problem with the roof (ie, it wasn’t just in one area) and no evidence of water flowing or staining joists or mould growth.

It was above the bathroom; the house is mostly unheated and being in Dunedin the outside temperature is cold. The bathroom has an extractor but I’m not sure if they’re using it. The house is a 1950s state house.

What would people think is the likely source of the moisture? Is it more likely to be condensation from internal air, or more likely to be a roof leak? I will recommend they both get the roof checked and take steps to reduce internal moisture.

Add New Note to this Reply

[Phil Squire]

Hi Alex

Sounds likely to moisture condensing on the building paper. If the temp of building paper falls below the air dew point (which may happen if the air temp falls or the roofing iron gets v cold on clear Dunedin night). this can happen if the ceiling is insulated which will mean the ceiling cavity is cooler than before.

Solutions include:

– ensure all extract vents are vented outside
– get rid of downlights (to ensure house air isn’t drawn into ceiling)
– install vents in ceiling space (or perhaps solar extractor fan – making sure you’ve got a vent for inlet air on teh opposite side of the attic
– one other solution is

Add New Note to this Reply

[nickcollins]

The old tin roof. Unlikely to be a leak
It is not unusual for moisture to condense on the underside of iron roofs. This is where the dewpoint occurs. On a cold day, warm moisture within the home condenses on underside of the cold roofing material (particularly evident when there is no vapour barrier beneath the floor, no insulation in ceiling and poor ventilation).
On a warm sunny Dunedin day, (common occurrence I am told) you may also have condensation as the roof heats up and moisture from cold damp house condenses on the underside of the roof.

You need to get moisture out of house – vapour barrier (as above) , ventilate bathroom (suspect extractor fan in bathroom may only be ducted into ceiling cavity, which is exacerbating the problem), range hood in kitchen must be ventilated to outside. Obviously insulation will make a big difference in keeping warm air contained within the house.

Add New Note to this Reply

[Richard Popenhagen]

Hi Alex

From what you have described it is not a roof leak. Roof leaks will manifest as a wet patch generally limited to a small area of around 1 to 2 square metres. Multiple roof leaks will appear as small isolated patches. A large area of moisture covering the underside of the roof is condensation, caused by the moisture content of the air in the roof space being too high.
Often this problem is caused by a number of different sources which combined overload the roof space air with moisture. You need to be a bit of a detective as sometimes the source of the problem is not obvious.
To cover it all in detail would take quite a bit of time but here is a quick snap shot of some of the things to consider:
First check the usual suspects such as range hoods and bathroom fans are not venting into the roof space but are ducted to outside the building. Sometimes there are passive vents installed in ceilings in laundries and cupboards that duct straight into the roof space.
Ceiling access hatches in bathrooms and laundries can let a lot of moisture laden air past as they usually don’t seal very well.
Downlights in ceilings are another big problem, especially in bathrooms and laundries but even in living areas, especially if they are drying clothes inside or using a un-flued gas heater (either of which they should not be doing!!!)
Then you get into the problem of moisture transfer from other areas, sub-floor spaces are a big problem, but because it is under the house, most people don’t release the link to the roof space moisture issue.
The hub is developing a moisture tool to assist home advisors work through this issue and come up with potential solutions, so watch this space.
I am also right in the middle of writing a paper on this subject to deliver a presentation on moisture problems in New Zealand homes, at the Build A Better New Zealand Conference in September, with some case studies illustrating exactly the problem you have encountered, the causes and the solutions to rectify these problems. It is looking like a great conference and I would recommend all advisors attend if they are able to.
I have come across this problem in a lot of homes, not just old ones but also homes built to the current building code. It will continue to be an ongoing issue until we are able to educate both industry and home occupiers about how we should be not only building our homes, but also how we operate them.

Cheers
Richard

Add New Note to this Reply

[Vicki Cowan]

I agree with Nick’s comments – I’d be checking the state of the underfloor with a view to installing a vapour barrier and also checking where the extract fan is ducted.
I’m assuming an uninsulated house? Or is there ceiling insulation?

I don’t think I’d recommend installing vents in the cavity space or a solar extractor fan from the cavity at this stage – it is most likely that it’s an internal moisture problem – which should be addressed first as it will be making the living conditions less healthy as well.

Add New Note to this Reply

[alexking]

Thanks for the comments.

The ceiling is insulated with batts, there are no recessed downlights (1950s home). There is extraction from the bathroom and kitchen with grills under the eaves which I assumed is external venting from the extractor fans, but I didn’t actually confirm that the external venting is working properly, I need to do that.

Add New Note to this Reply

[Author]

Posts