64 EXTERNAL ENVELOPE
walls – and where detailing needs careful consideration to ensure the long-term integrity of the building envelope. The roofline is a tricky area where two
expanses of quite different materials meet – the roof tiles and the brick wall. Each does its job well but neither is completely satisfactory in covering this crucial junction. Our island nation is subject to some of the
most searching of weather conditions with areas of Wales, Scotland and the Pennines enduring up to 180 inches of rainfall per year, making them some of the wettest areas in Europe. In particularly exposed areas, high rainfall intensity in combination with strong winds will test the integrity of any structure to the very limit. Consequently, the roof-to-wall union
has to be defended rigorously against water and wind ingress whilst at the same time, allowing proper ventilation of the roof void to take place. But, you may ask; “Why ventilate the roof
void at all – why not seal it all up and be done?” A perfectly valid question but the answer is rot.
Protecting against the scourge of rot
Every day, building occupants generate huge amounts of hot air which is laden with water vapour. Baths, kettles, saucepans, boilers, washing machines and even breathing sets off
clouds of the stuff. And, as we all know, hot air rises. In addition to this, moisture occurs naturally in the air outside and a lot of this damp air finds its way into the roof void. Now, consider that the average attic is a
cold uninviting place that encourages moisture to condense on its vulnerable timber surfaces and you have the perfect micro-world in which mould and rot can take
Cellular PVC boarding is the most efficient material for use at the roofline.
hold if the air-born moisture is not kept moving. Roofline systems, the broad, industry term
to describe fascias, soffits, bargeboards and all the associated ventilation components, are rather good at the double trick of protecting the eaves while fully venting them. Timber was for many years, the preferred material for roofline components but in such
Let’s look at the roofline with Swish D
ave Osborne takes a look at the roofline – the part of a building where the roof structure meets the
Swish Roofline systems - fascias, soffits, bargeboards and ventilation components. All rather good at protecting and ventilating the eaves and roof-space.
The preferred method of roof ventilation is a continuous venting unit that sits on top of the fascia board.
WWW.ARCHITECTSDATAFILE.CO.UK
ADF OCTOBER 2017
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