Structural Requirements for Roofs

When you build a roof, your structure needs to be robust enough to support various weights from several different sources. Consider the following:

• Building Materials: First, you have the weight of the roof itself – this includes all your tiles, the wooden battens they rest on, the protective felt, and any insulation you install.

• Environmental Factors: Next, your roof must withstand the forces of nature, such as the uplift from strong winds, the accumulated weight of snow, and the pressure of heavy rain.

• Maintenance Access: Finally, remember the people who might need to go up there. Your roof must safely support the weight of an individual carrying out repairs or routine maintenance.

Wind Load

Powerful winds can exert significant upward force, attempting to lift your entire roof from the building. To prevent this from happening, you must ensure your roof is securely fastened to the main structure below.

The standard way to achieve this is by fitting special metal straps. These straps are approximately 1.2 metres long and feature a bend (or 'cranked end') at one end. You will attach them to the 'wall plate' – this is the timber beam where your roof timbers, known as rafters, typically rest – and then securely fix them into the inner layer of the wall. You need to space these straps consistently every 2.0 metres along the wall.

Preventing Roof Spread

The sloping timbers of your pitched roof, called rafters, naturally tend to push outwards at their bases. This outward force, if unchecked, could cause the roof to spread apart.

To counteract this, horizontal timbers known as ceiling joists (which typically form the support for your ceiling) are securely fastened to the bottom ends of these rafters. They act like a strong tie, pulling the rafter bases together and effectively stopping them from spreading outwards.

However, what if you plan to remove your ceiling to create an exposed roof structure, where the rafters are visible? If you choose to do this, you absolutely must implement an alternative system to securely tie the rafters to the walls and prevent them from pushing outwards. For any exposed roofs where ceiling joists are absent, we strongly advise you to seek expert guidance from a qualified structural engineer.