JH Site

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Some basic terms:

Pitched roof:
A tradiitional type of "pointy" roof.

Pitch:
The pitch of a roof is the amount it slopes.

Flat roof:
Almost but not completly flat. Even a "flat" roof has to have a slight pitch so rainwater can run off.

Ridge:
The highest part of a pitched roof.

Eaves:
The bottom of the sloping part of the roof where it meets the walls.

The Roof Covering.

The roof covering is usually slate, clay tile or concrete tile.

• Slates will be either natural or artificial. Natural slate has a very long life and, if good slates are properly installed the roof can have a life of 60-80 years before first major maintenance.
• Artificial slates can be recognised by their very smooth, regular appearance. They generally have a 20-30 year guarantee on the material.
• Concrete tiles are available in a wide variety of colours and styles. They are generally much heavier than slates and therefore should not be used to re-cover a roof designed for slates without professional advice. Some types of concrete tile have a sanded finish, some of these can shed the sand finish when first installed, this can block gutters.
• Some form of flexible, waterproof sheeting is often used immediately below the slates or tiles. The traditional form of this is known as sarking felt. There may also be some insulation in this layer.

The Roof Structure.

There are two basic ways of supporting the roof covering. Older houses will have cut timber roof where the individual members are cut and joined on site. Because construction of this type of roof requires skilled labour and is vulnerable to weather conditions until the roof is weather-tight, many modern houses have trussed rafter roofs. These are made up of a series of factory made frames which only have to be fixed into place on site.

Rafters:
These are the sloping timber members which support the roof covering. They may be part of the trussed rafters or be separate members in a cut timber roof. They are typically 50mm wide and 200mm deep but this will vary depending on the slope of the roof, the spacing of the purlins and the weight of the roof covering. They are usually about 600mm (2 feet) apart.

Purlins:
These are horizontal members which span between two supports, often walls, and support the rafters. They will usually only be encountered in a cut timber roof. In a house they will usually be timber. A small roof may not have any, larger roofs will have one or two on each slope.

Braces:
These are additional members that may be present supporting the purlin(s). They may be vertical or sloping. Because they are intended to support the purlin they will be positioned so the bottom end is on a strong part of the structure, this will often be above a wall.

Ties:
These are members which link the two sides of a double pitch roof or link a single pitch roof to another part of the structure. They stop the roof spreading. They are usually horizontal and fairly small.

Never remove any part of the structure from a roof without taking proper professional advice.

You may be tempted to try to make more space for storage, or even do a basic loft conversion.
Don't!
If the roof structure is changed, it may collapse. Even if it does not, it can start to spread, the ridge drops and the eaves move outwards. This can affect the walls and be very expensive to put right.