Let’s look at the roofline with Swish

// the building envelope

Dave Osborne takes a look at the roofline – the part of a building where the roof structure meets the 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.

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. 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 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 a softwood fascia board is unlikely to survive more than a decade, especially if it doesn’t receive regular maintenance.

Cellular PVC – the material of today
Cellular PVC is probably the most efficient material for use at the roofline because it costs roughly the same as timber to install and requires no maintenance. Most importantly, especially from any landlord’s point of view, when it is installed correctly it will probably last the lifetime of the dwelling.
As far as roof void ventilation is concerned, the preferred method these days is to use a continuous venting unit that sits on top of the fascia board and supports the roofing felt and the lower row of tiles. This method does away with slots or ugly vent discs set into the soffit board.
On a very practical note, Cellular PVC roofline systems are also good at providing both visual and physical support for the other essential components in rainwater management – guttering and downpipe systems with all the attendant bracketry and fixings.

Co-ordinating finishes
Cellular PVC is an extruded, foamed material with an integral smooth and durable skin. A wide range of colours and foil finishes are available, providing a considerable degree of flexibility in co-ordinating with popular window and door styles as well as coloured rainwater management systems.
Cellular PVC Roofline products from my own Company, Swish Building Products, also represent an environmentally responsible use of plastics. Not only do they not contain CFCs, lead or cadmium, which are considered harmful to the environment, but the Company itself has also taken huge strides over the last decade in reducing its CO2 footprint and use of water in manufacturing. Cellular PVC also has a very long-life span and when replaced, can be fully recycled.

Complementary Rainwater Systems
Swish also manufactures a complementary range of guttering, fall pipes and attendant bracketry – all designed to efficiently collect and dispose of rainwater run-off from building roofs. Swish standard rainwater systems all contain a high proportion of recycled materials and the Company is the only UK plastics manufacturer to be awarded BES 6001 Responsible Sourcing Certification for both their roofline and rainwater products.

Dave Osborne is Technical Manager for PVC roofline and rainwater systems specialists, Swish Building Products.

For more information on Swish Cellular PVC roof line products, contact: Swish Building Products: 01827 317 200


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