In the same way that a gore-tex jacket protects a walker or a cyclist, a breathable membrane protects your building from wind, rain and condensation.
With the improvement of quality and the tightening of building regulations, modern properties are becoming ever more airtight. This is great for reducing cold drafts and your heating bills. However, a negative impact is that the steam created by cooking, showers and the very air you breathe, has no-where to escape but upwards into your roof.
When this water-laden air comes into contact with a barrier (i.e. your roof tiles), the water molecules trapped within the air condense back into the water – which will then start dripping downwards.
Condensation becomes especially heavy if the barrier is colder than the water vapour. (This is the same principle that creates that lovely condensation on a glass of cold beer on a warm summers day!)
When moisture-laden air escapes into a roof constructed without a breather membrane, the water will condensate on the inside of the roof tiles. This water will then drip down into the eaves or onto the ceiling below. This issue is escalated during colder months and is especially an issue for new build properties where the wet trades (plaster, cement, etc) are drying out.
If this condensation continues to be left unchecked, your house is likely to suffer from the effects of mildew and rot. Apart from being visually unattractive, this may require the expensive repair or replacement of your roof timbers.
What is a breather membrane and how does it help?
A breather membrane is a thin sheet of fabric that sits above your insulation and rafters but underneath your roof slates. The construction of the fabric allows any condensation to rise up into the roof void but prevents the condensing water from dripping back down into your roof. Instead, it channels the water down into your gutter, preventing many problems.
Purists may point towards that old fashioned roofs made no use of membranes. However, this takes no account that natural ventilation is much reduced in newer properties. In addition, a breathable membrane also blocks airborne dust, pollen and insects from entering the attic – a room now considered as a vital storage area by many of us.
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