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    Roofing materials


    Building a new roof requires a high level of skill and expertise and should be left to a professional builder. However, there is no reason why minor repairs should not be attempted, therefore knowledge of roof construction and the components will be useful.

    Basically there are five main components in roofing:

    • Timber framework
    • Felt underlay
    • Timber battens
    • Roof covering
    • Flashing

    Timber structures

    Most houses have a pitched roof structure with a timber framework. The four main types of roof structure are Gabled, Hipped, Mono-pitched and Mansard.

    A gabled roof has two pitched planes that slope around triangular extensions of the end walls. The triangular extension is the gable.

    A simple hipped roof will have four sloping planes. The hip is the joint between two adjacent slopes. Some roofs are extremely complex with numerous hips. 

    A mono-pitched roof has only one slope and is commonly found on extensions.

    A mansard roof comprises of two planes sloping at different angles on each side of the building. Mansard roofs create a spacious living area in the roof space.


    Straps and plates

    Metal straps and plates are used in timber roof construction to securely hold rafters, joists and struts together. The straightforward way in which straps and plates are fixed to the timber eliminates the need to cut complicated joints, thus speeding up the construction.

    Restraint strap

    Straps come in various designs and are used to secure roof timbers to walls. The L-shaped restraint strap fixes to the end of a rafter and is then attached to a gable wall.

    Timber connector

    A timber connector is a rectangular metal plate perforated with small fixing holes for screws. These are used where roof timbers join together.

    Truss clip

    Truss clips are used to connect the ends of roof joists to the wall plate which is the timber beam that runs across the top of the wall.


    Heavy-duty truss clip

    A heavy-duty truss clip is more robust than an ordinary truss clip and has a deeper recess to accommodate wider joists.

    Roofing felt

    Roofing felt is laid beneath the tiles to create a waterproof barrier. It can be laid directly over the rafters in horizontal strips with the edges of each strip overlapping. Alternatively, timber sheathing can be fixed to the rafters and then the roof felt laid over the ply.

    Timber sheathing is usually sheets of plywood. It is laid across the rafters, staggering the joints as you move up towards the ridge. To fix the sheathing in position nail the sheets of plywood to the rafters using a fixing every 150mm (6in). To improve ventilation in the roof space gaps are sometimes left between the sheathing, as you get closer to the ridge. Sheathing is generally used when the roof has only a slight pitch, but in some areas the Building Regulations make it a requirement. If you are making a repair to the roof felt always match the new material to the existing felt.


    Breathable felt

    Breathable felt allows moisture within the roof space to escape while preventing external moisture from entering.

    Bitumen-based roof felt

    A very durable roofing felt with excellent waterproof properties commonly used for covering flat roofs.


    Plastic felt

    Plastic felt, as its name suggests, is not a genuine felt material but it is widely used as an alternative to bitumen-reinforced felt. It is also not a breathable material.

    Timber battens

    Roof tiles need a fixing point and this is provided by fixing timber battens horizontally across the pitch of the roof. They are fixed in position by nailing them to the rafters. Timber battens must be evenly spaced. The space between the battens (also known as the gauge) will be determined by several factors:

    • The size and type of the tile
    • The pitch of the roof
    • Prevailing weather conditions
    • The fixings (see below)

    Fixings

    The type of nails or screws used in roof construction may differ with local building regulations. But generally, anti-corrosive fixings are used: stainless steel, copper or galvanised. The galvanised clout nail is probably the most widely used fixing in roof construction.

    Roof coverings

    The roof of your property will almost certainly be covered with roof tiles of one sort or another. The only situation where this will not be the case is if you have a thatched roof. As thatching is a highly skilled craft taking years to learn, it is highly advisable to engage the services of a professional thatcher.

    Roof tiles are available in a variety of styles and materials, and the type of tile you use will depend on the pitch of the proof and the prevailing weather conditions. When fixing tiles it may be sufficient to hook the protruding nibs over the timber battens, but if the property is located in an area of strong winds you may want to consider nailing some or even all the tiles in place. The most common types of roof tiles are described below.


    Clay tiles

    These tiles have an attractive, traditional look, but cost more than the similarly styled concrete tiles. There are three main types of clay tile; the Plain tile, the Pan tile (which is an interlocking single-lap tile) and the Roman tile, another interlocking tile with a decorative ridge running down the middle.

    Concrete tiles

    These tiles are very similar style to the clay variety, but are cheaper and designed to interlock more easily. Although the tiles are not as attractive as their clay counterparts, they are quicker to fix to the roof.

    Slate tiles

    Lighter than clay tiles, slate tiles are strong and durable thus providing a longer life span than most roof coverings. However, they can be quite expensive. Slate is a natural and dense material that is split into thin sheets and cut into small units used on pitched roofs. There is also an option of having synthetic slate tiles, which are stronger, look similar but are less expensive.

    Each slate tile is fixed by nail to the roof. A shallow roof pitch and high winds will make slates susceptible to vibration, which can loosen the tiles and even cause breakage.


    Wooden shingles

    These are usually made from Western Red Cedar because of its durability. Wood shingles are machine cut which gives them a smooth texture; the more rustic, rough-hewn wooden tiles are called shakes and are cut by hand. Although almost unheard of in urban areas wooden shingles and shakes are still used as roof coverings on older properties in rural areas.

    Asphalt shingles

    Asphalt shingles are lightweight, available in different colours and relatively inexpensive. They are manufactured in sheets made of several shingles making them quick and easy to install. Asphalt shingles require very little maintenance and will last up to twenty years depending on the prevailing weather conditions. Some asphalt shingles are reinforced with fibreglass for greater strength and improved fire resistance.

    Other types of roofing tile

    The main area of the roof will be covered with either Plain, Pan or Roman tiles. However, specialist tiles are made in different designs to finish different parts of the roof where the roof changes direction. These are ridge tiles, hip or bonnet tiles, cloaked verge tiles and valley tiles.

    Ridge tiles

    These are used along the ridge of the roof and are usually fixed in place with mortar.

    Hip or bonnet tiles

    Hip tiles (also know as bonnet tiles) are fixed where two roof plains come together to form a joint. Depending on the design of the roof ridge, tiles can be used for this purpose, but a hip iron would have to be used at the eaves to support them.

    Cloaked verge tiles

    A verge is the joint between the roof and a gabled wall. A cloaked verge tile is designed to lap over the edge of a gable to produce a neat finish.

    Valley tiles

    Valley tiles are also used where two roof planes are joined, this time replacing the need for flashing (see below).

    Flashing

    Flashing is the waterproof material used in roof valleys, around chimneys and at other joints where different parts of the roof come together. Once again there are a number of different types of materials used for flashing.

    Lead flashing

    The most traditional flashing material, which has stood the test of time because it is durable and waterproof as well as being very malleable, allowing it to be moulded into the required position.

    Self-adhesive flashing repair

    This tape is used for repairing damaged flashing. Primer may be required before application for it to work effectively.

    Flashing strip primer

    Used for priming porous surfaces such as, concrete cement and lightweight concrete blocks prior to apply self-adhesive flashing strip.

    Glass-reinforced polyester (GRP)

    Often used as flashing for valleys and abutments, GRP is being used more widely as an alternative to lead flashing.


    Ventilation materials

    Poor roof ventilation will cause problems with damp and so serious consideration should be given to ventilating the roof space. Different types of roof vents are available.

    Tile or slate vents

    Basically this is a tile with a vent incorporated in its design. Generally used in situations where a solid wall separates the roof space. Fitting tile or slate vents at the bottom and top of each side of the roof will ventilate the roof space either side of the wall.


    Ridge vent

    This system provides ventilation channels though the ridge tiles on top of a roof. If a room has been built within the roof space ridge vents should be used in conjunction with tile or slate vents positioned near the eaves. This will draw air through any narrow spaces between the roof and the construction within the roof space.

    Soffit vent

    The soffit is the underside of the eaves. If you have insulated the slope of your roof there will a 50mm (2in) gap between the insulation material and the roof covering which will still need to be ventilated. This can be achieved by fitting soffit vents along the eaves and tile or slate vents towards the ridge of the roof.

    Butyl rubber roofing material

    Excellent material for covering sheds and flat roofs, the reinforced butyl rubber will not contract over time. It is also frost and rot proof. Self-adhesive products are available


    Cold adhesive

    Will bond roofing felt and butyl rubber roofing materials to most surfaces.

    Liquid bitumen compound

    Waterproof liquid bitumen used in roof repairs. Can be purchased form most builders' merchants.


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