Roofs: Powersharing

The roofing industry is in a state of flux. Traditional construction methods are struggling to meet a range of regulatory imperatives, including those promoting high housing density (PPG3), energy conservation (Part L of the Building Regulations), the control of moisture in buildings (Part C) and renewable energy (PPS22). At the same time, there is a national need for many more homes in southern England. So, the strategic goal of the roofing industry is to find a way to produce high-quality, well insulated, environment-friendly homes that can be built at speed. Oh, and they can’t be too expensive, either.

Paul Larcey, sales and marketing director for Lafarge Roofing, gives an overview of the situation. “PPG3, especially, has had a profound effect on housebuilders, not only in promoting greater density in developments but also a greater mix of house types across a site,” he says. “This type of diverse design means that cost becomes an even bigger issue for developers and they are looking for high quality products that are easy to use, satisfy planning and regulatory requirements and are cost-effective.”

At Lafarge, these issues are tackled first at the design stage. The company’s DesignMaster and SpecMaster roof design services will do the design and specification work for architects and housebuilders, while also providing quality and longevity guarantees. Among the variables that can be decided is how long it will take to install the roof.

Innovations available include vapour-permeable underlay and dry-fix ridge solutions that are moving roof design away from traditional methods. Gone are the days of bedding ridge tiles on with mortar and cutting holes in the soffit to let the roof breathe. “Developers now have to build with whole-life costing as a priority,” says Larcey. “They want fast construction with the absolute minimum of follow-up maintenance from every roof installed.”

And, just in case housebuilders don’t have enough to contend with, there is the environmental aspect to consider. The new Part L rules are further reducing heat loss from dwellings, and PPG3 and PPS22 are calling for the “greening” of our residential environment. This means tackling the issue by passive and active means.

Lafarge's “Breathing Roof”, an energy-efficient solution for cold pitched roofs that includes its VPU and dry-fix ridge technologies, is designed to reduce heat loss through the roof. Add to this, or rather install on this, the company’s new PV 800 or PV 80 solar panel technology and the roof is a generator of energy. Larcey says: “We’ve developed the technology with a clear focus on full roof integration because we know that this produces the best results. This means the best in energy production performance from the solar panels and the elimination of any compromise in what the roof is meant to do in the first place: keep the warmth in and the weather out.”

The design work

Lafarge’s two design services mentioned above, DesignMaster and SpecMaster, have been tailored to help designers get the best out of their products while fully complying with the Building Regulations. And, through outsourcing all or part of the roof design, the architect saves a lot of time.

DesignMaster is a library of more than 5000 CAD drawings, available on CD-ROM or downloadable from Lafarge’s website. The library holds information about the company’s entire roof covering range, detailing the specification of every product at a number of common pitches. Most residential roofing design quirks are

included, along with CAD images of eaves, verge, hip, valley and ridge details. All drawings are available as dwg files for AutoCAD on PC and dxf versions for Apple Mac, and can be copied and pasted directly into working drawings.

SpecMaster goes a step further than its sister: it is a full roofing design specification service. Clients send concept drawings or simply fill out forms on Lafarge’s roofing website and the Lafarge Roofing technical team creates a full roof specification. Written in standard language to RIBA-approved NBS clauses, Lafarge’s SpecMaster specifications are guaranteed to meet all health and safety, fixing, loading, ventilation and condensation regulations. The SpecMaster designed roof is based upon the use of Lafarge Roofing products and is covered by a 15-year guarantee.

“The service is designed to save clients time and ensure that the specification is fully compliant with all regulations,” says technical manager Kevin Ley. “The architect comes to us when he knows the tile colour, style and type of roof. We ensure that the roof is designed correctly."

The products

The government’s attempt to encourage the use of sustainable energy sources has been hampered by pressure groups lobbying against “unsightly” additions to our Countryside and seashores. However, PPS22 argues that the “increased development of renewable sources of energy is vital” and that “regional and local development documents should contain policies designed to encourage, rather than restrict, the development of renewable energy sources”.

Lafarge sees its PV 80 and PV 800 solar panel systems as being that future. Both use the latest polycrystalline cell solar panels, which have an area of 100-150 cm2. These fit flush with the line of the roof tiles, making them suitable for use in areas where upstanding panel arrays are not permitted. The panels join in-series using plugs and sockets that cannot be wrongly connected, and a 40-panel array produces one-third of the energy required by an average family of four.

PV 800 is designed to be used in conjunction with five popular tile choices from the Redland range. The 40 Wp panels are dual function, meaning that they act as solar collectors and a roof covering. No special roof construction is required, other than adequate ventilation to the rear of the panels.

The PV 80 solution uses a larger 80 Wp panel that can be used on nearly all roof types – from profiled and flat tiles to slates or metal sheets. Sitting flush with the roof covering, the panels are fixed directly to the tile battens.

DuoPlain

PPG3 is shaking up the way we view housing design in many ways, and as housing sites become more densely developed the roofscape is becoming an ever more dominant factor in a development’s aesthetic. Lafarge’s new DuoPlain tile has been designed to satisfy the most conservative of planner, as it has the appearance of a small format plain tile.

However, it is not what it first appears to be. When finished, the roof looks like a traditional installation of 10½” by 6½” plain tiles, however, the tile used is actually made up of double tiles. The single-lap interlocking DuoPlain means that only one-third of the number of tiles is required to achieve the look of a conventional double-lapped plain tile roof. The product is easy and quick to fit as, effectively, two tiles are being layed at a time.

This large format tile has been tested extensively for strength and weather-tightness. With tile breakage in transport a constant issue for contractors, DuoPlain has been computer-designed for optimised strength. Intensive wind and rain tests at Lafarge’s wind tunnel facility have led to a 15-year weather-tightness guarantee.

DuoPlain is available in four colours and is launched with a full range of fittings including tile-and-a-half, left and right-hand verge tiles and a specially designed RedLine DuoPlain vent tile for for unobtrusive roof-space ventilation.

Dry-fix and vapour permeable underlay

Lafarge is addressing the need for fast, affordable and energy efficient new-build housing with two roof construction techniques – Dry-Fix to speed up construction and vapour-permeable underlays for an energy-efficient and robust roof construction.

The use of VPUs in cold pitched roofs has not been without controversy, as they have they have been connected with many condensation problems in new houses during cold spells. However, Lafarge has designed the breathing roof around the company’s Spirtech 250 VPU, Rapid Vented Ridge or Dry Vented Ridge and underlay support trays, which it will guarantee for 15 years.

Technical manager Kevin Ley explains: “To eliminate condensation risk, the whole roof construction must be considered as a system. Our solution acknowledges that it is not easy to make a ceiling air-tight but recognises that simple things can be done to seal penetrations and loft hatches in order to achieve a better sealed ceiling above living spaces. Our Breathing Roof for cold pitched roofs is a progressive but robust solution which takes into account anticipated changes in Part L.”

Now, couple this technology with Lafarge’s Rapid Range of dry-fix systems and construction times are speeded up considerably. Instead of bedding ridge and hip tiles in mortar, they are screw-fixed to a timber batten.

The system comprises ridge-to-ridge seals, METALROLL weathertight membrane, batten straps and fixings.

On-site tests have shown that installation times have been reduced by an average of 33% against traditional mortar methods, while providing guaranteed-secure ridge and hip tiles.