A Beginner's Guide to Roofing
Whether traditional slate, thatch or contemporary metal, the roof of a house is always one of the most important elements in terms of both cost and appearance.
"Spend the money on the roof” is a favourite piece of advice from architects which is well worth taking. The roof of a house is often a wasted opportunity – seen only as a functional covering to keep out the elements. With a little imagination, though, it can be far more: a design statement, full of character, which can totally transform a dull dwelling into something special. Today the roof of a newly built house can be covered in turf, copper or glass as well as more traditional slates or tiles, with fantastic eye-catching shapes, roof lanterns and possibly solar panels.
A good roof design does not need to be expensive or radical to succeed, but should be well thought out and in keeping with both the building and its setting. As with windows, the style of the roof should be appropriate to the type of house being built.
If your site is part of an existing street then you will often be expected to keep your ridge height, eaves line, roof pitch and possibly even the roof covering consistent with the rest of the road. Where the plot is in a Conservation Area, close to listed buildings or somewhere with a strong architectural tradition, the planners will have very clear ideas on what you can and cannot build, sometimes going so far as to insist on a certain tile, which can literally put the cost through the roof.
Emphasis is often placed on selecting the type and colour of roof covering which will satisfy the planners, with less regard for the design, structure and construction. The overall effect of the roofscape should be considered by taking into account the shape, colour, chimneys, rainwater goods and overhangs, and seeing how they work together.
The pitch of a roof is particularly important, and if this is too shallow or too steep certain roof coverings will be unsuitable. Complicated roof shapes can be attractive but, on a relatively small area, they can appear overly fussy, prove expensive and create maintenance problems.
Height restrictions are a common problem which can be overcome by building the upper storey of the house projecting into the roof space, producing sloping ceilings in the upper rooms. This can add character, but also creates a degree of ‘dead space’ towards the outer edges of a room where head height may be limited.
Most traditional homes have pitched roofs, and flat roofs are rarely chosen for new houses, except for ultra modern designs. Flat roofing systems have come a long way since the 60s and 70s, however, when bitumen and asphalt leaked and needed to be frequently replaced. Modern single-ply roofing membranes are highly insulated and built to last. When planted, a flat roof will help to keep the internal temperature stable, with turf roofs particularly suited to underground houses and eco homes.
The more complex the house plan the more difficult it will prove to roof. If your roof structure and wall layout cannot easily be made to work together then an engineer may need to be employed to come up with a solution at additional cost.
For pitched roofs there are two basic methods of construction. Cut roofs are traditionally measured, cut and assembled on site using rafters and joists.
This is a relatively expensive and time consuming process, but the finished structure may be easily altered or converted into living space at a later date. The cheaper form of construction, using factory produced trussed rafters, is now largely shunned by selfbuilders, who want to maximise the overall liveable space of their new home. The trussed roof is delivered to site complete and simply erected as a series of frames, which cannot easily be altered.
Factory-produced attic trusses maintain the speed of erection achieved with a pre-manufactured roof truss, and allow the roof space to be utilised by leaving the main loft area open. Laminated timber beams and I-profile rafters are stronger, lighter, cheaper and more environmentally friendly than solid timber, and may be used for large spans and if you want to create a dramatic feature a green oak structure with additional cruck beams is truly impressive.
It’s important to choose the roof covering prior to felting and battening, as the spacing of the battens is set by the gauge of slate or tile, and varies considerably. Building regulations require that whatever roof covering you choose there should be a layer of roofing felt or ‘sarking’ underneath. Not only is this inexpensive and easy to fit, but it provides a temporary waterproof cover for work going on below.
Building regulations also insist that the roof space is adequately ventilated. This is because warm, moist air rising inside the house is likely to condense on the cooler timbers, eventually causing them to rot and their steel connectors to rust. With pitched roofs this can be provided by narrow vents at the eaves, with appropriately designed vent tiles at the ridge or high up the slopes.
Increasingly, ‘warm’ roofs are being specified, incorporating a specialised roofing felt which allows water vapour to pass through it. As a result, insulation can be positioned above the rafters, with the felt then fixed on top. This increases head height within a loft area – making it more practical as living space.
Slates are perfect for both traditional and contemporary homes, and are a mid-priced option, with Welsh slate being one of the more expensive choices compared to imported slates from countries such as Spain, China and Brazil. Handmade clay tiles are beautiful but are more costly than machine-made versions. It’s also possible to buy replica slates or clay tiles, which are cheaper and can be very convincing.
Concrete tiles are around 20 per cent cheaper than clay but won’t weather or improve with age. Make sure you wet any sample roof covering to see how they’ll look in the rain, as the colour can change dramatically. Interlocking concrete tiles are available in a variety of profiles and colours, and have a system of grooves and ridges which prevent water getting past the tile. They are quick to lay on simple roofs, but lose this cost advantage when more cutting is involved.
If you’re building in a stone belt, such as the Cotswolds, you may be required by the planners to use local materials. Alternatively, there are a number of reconstituted stone tiles available which are less expensive and may be acceptable to the planners.
Metal roofing, such as zinc and copper, is a more contemporary option and comes in flexible sheet form, making it ideal for curves or for flat roofs – which are currently enjoying a comeback.
Nowadays thatching is mainly used for restoring and replacing existing thatched buildings, as few are built from scratch. The house is usually designed around the roof, which is expensive and requires regular upkeep. The National Society of Master Thatchers holds a directory of members (www.nsmtltd.co.uk).
Never buy from a catalogue without first seeing samples, and try to view the chosen product in place on a roof before you make your final decision. A single slate or tile can look very different from an entire roof, viewed from the ground. Bear in mind who will actually be undertaking the roofing and the amount of skill and experience they will need.
CHANGING AN EXISTING ROOF
Changing your roof can be both expensive and disruptive, and it can also have a huge impact on the overall look of a house. Some roofs will last for more than 100 years, others will deteriorate after 40 or less, depending on the roof structure and covering, the location of the house and the workmanship.
At some point every roof will require repairing or replacing, and stains on ceilings after rainfall are a sure sign that water is leaking into the roof space. Always repair any damage as soon as possible to protect internal decoration and the fabric of the house from water damage. Many houses built in the 1950s, 60s and 70s were roofed in ugly, poor quality concrete tiles. Changing these can totally transform a house, and homeowners are increasingly choosing this option for the visual appeal alone – regardless of whether the roof actually needs to be replaced. Others go one step further and totally change the shape and pitch of their roof, which can involve major structural work.
Planning permission isn’t usually required for re-roofing your house, subject to certain conditions, which can be found on the planning portal website (www.planningportal.gov.uk).
If you’re repairing or replacing less than 25 per cent of a roof you won’t need to submit a building regulations application, although you will need approval for any structural alternations or if the new roof covering will be significantly different from the old. For larger repairs or replacement roofs the thermal insulation will usually have to be improved to meet current regulations.