In this guide
2. Constructing a new roof (eg for an extension)
A new roof will be required to:
- resist weather
- resist the spread of fire from one property to another
- be able to support loads (weights)
- provide resistance to heat loss (insulation)
- be ventilated to protect from condensation (in most cases)
- have adequate drainage
There are generally two types of roof construction used:
- pitch roof: this is where tiles or slates are used and a void is usually created underneath
- flat roof: this usually consists of felting which has a slight fall to allow rain water to drain off
To enable compliance with the requirements of the Building Regulations to be demonstrated, full details of the new roof will be needed - including materials and their dimensions and performance properties.
The materials used to cover the roof should be durable and capable of resisting the elements of the weather. With a pitched roof the type of tile or slate you wish to use will be partly governed by how steep or shallow the slope is. If the roof is close to a boundary, which is often the case, the roof should also have properties to limit the risk from fire spreading across the boundary.
Not all roofs need to be ventilated. Ventilation is not required to a warm roof system, which is where the insulation is placed above the joists or rafters. Otherwise ventilation is required and this is known as a 'cold roof system'.
When ventilating a roof the air should be able to enter at one end and travel through to the other end where it can exit.