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How a Roof is Built

Posted by dave on July 2, 2011 at 7:09 AM

How a Roof is Built

 

Once the walls and interior structure of a building is complete, the roof will be built above.

The first step is to order the roof trusses. These give the roof its shape, and also provide a base for the covering. Most trusses are made to order to your specific size and load-bearing requirements, though for some common buildings such as garages they can be bought pre-fabricated.

Trusses come in several designs, which have different properties. The truss design you choose will be affected by the shape and size of your building, the weight of your roof and the shape you want your roof to be. Architects can design a suitable design (or designs) for your house.

Many use special software which can plan and design a visual representation of the trusses, and how they fit on a house. This is especially useful when designing for a large house which may have a complex roof. Using computer aided design (CAD) allows the carpenter to use computer aided manufacture (CAM), which allows high levels of precision. Thus, all rafters will be the same shape and same dimensions so there will be no nasty surprises once the roof has been built! If the trusses are not equal, the roof may move, or have structural weak points, which could cause collapse. In such cases, costly repairs would be required.

When the truss is delivered, it will normally be provided ready-built, so that all you need to do is lower it into place on the supporting walls. The trusses should be placed at regular intervals on the supporting walls.

Once the trusses are in position and secured, you can start to sheath the trusses. This is typically done with a solid material such as plywood. All the rafters must be covered. The plywood must have its boundaries above a rafter for adequate support, and a surface upon which to secure the panels. The boards should also be staggered, which is normally done by cutting a panel in half, and using these half panels to start each alternate course.

 

For safety, during this period of the construction, it is wise to temporarily nail in a 'toe board' on the lowest panel, offering grip while securing the levels above. The toe board should ideally be a 2 x 4 piece of wood (or similar dimensions).

Once the trusses have been completely covered, you will need to remove any excess overhang. This is best done by a circular saw. Before cutting, it is advisable to mark out the line along which you want to cut, in order to make the cutting as accurate as possible, and to avoid excess wastage.

On top of the boards, place roofing felt. This is waterproof, and so acts as a waterproof barrier between the tiles and the rafters. It is important that the felt is applied in dry conditions, to avoid moisture being trapped, causing damage later. The layers must also be overlapped, to allow water to run off the layers. Ensure the felt is applied smoothly, removing all air bubbles as again they can cause problems.

Once the waterproofing material has been laid, pieces of wood called battens must be laid on top. It is these battens that tiles are laid and secured upon. The battens are usually made from timber measuring 25mm x 55mm, and are applied horizontally, i.e. across the roof trusses. Most tiles now have 'nibs', which allow the tiles to be hung on the battens. As the tiles are of a uniform size, the layout of the tiles along the batten will be regular. Previously, tiles were nailed into position, and had a small hole to enable this. They were not actually nailed into the batten; instead the nail played a similar role to the nib, in that it allowed the tile to hang from the batten.

Where roofs are fully boarded, rather than laid with battens, it is possible to nail the tiles directly into the boards beneath the tiles.

Tiles can be laid in various different ways. Tiling a roof is always done from top to bottom, however the actual there are different ways of going about this.

 

Horizontal Banding is when the tiles are secured horizontally along the specified course, with every row being fully secured before moving to the row above. This can cause issues when the tiler reaches about 10 courses up the roof, as he will have to stand on the battens above the tiles he just fixed, or on the tiles he just laid; neither of which is ideal.

Diagonal banding is when tiles are laid diagonally. This is a little more difficult, as each tile must be secured before moving up a course, else the tiler risks covering a nail hole with a tile from the course above. It is important to remember which tiles are secured so that they are not covered. Diagonal banding is better used on roofs with hips or valleys, as they can be laid parallel to one another. It is also little safer for the tiler, as he can stand on the batten to the side of the diagonal course.

Vertical banding is where tiles are laid in a vertical band; this is best for steep gabled roofs as it allows the tiler to stand on the battens to the side of the vertical course.

The banding method should be selected depending on the type of roof, taking health and safety into consideration. For example, horizontal banding is dangerous on a steep roof as it offers fewer methods of stability while fixing tiles. By the same token, vertical banding could be needlessly complex for a shallow roof, when diagonal or horizontal banding may be a more efficient and effective way of tiling the roof.

Regardless of the type of tile; its camber, clay, concrete, or whether it is hand or machine made, it is important to ensure tiles are mixed. Ideally, if you have 3 pallets of tiles, the tiles should be mixed to ensure the colours are mixed, so that particular areas or bands on the roof do not have obvious colour differences. This is less important if you know all the tiles are from the same production run, however it is a good habit to get into as it prevents patchiness. While tiles may all look the same, they each have subtle differences in their width, length, hanging length, thickness, camber, colour and texture.

Call the experts on 01253692110 or 07837980512 to discuss your requirements thank you D.pearce.........

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