How is a Solar PV System Fitted to a House Roof

Overview of Solar Panel Installation Process

While the process of fitting solar panels to a roof may initially appear intricate, it essentially revolves around two primary components: roof hooks and rails.

Roof Structure and Preparation

In a typical house, the roof is constructed of rafters running from the ridge down to the gutter line, usually spaced approximately 400mm or 600mm apart. These rafters resemble the ribs of the roof structure and are eventually concealed by roof tiles such as Spanish tiles, concrete tiles, or slate during construction.

Wind Loading Calculation and Hook Installation

To ensure a secure solar PV system installation, the first step involves performing a wind loading calculation. This calculation determines the necessary fixing points required in the roof, the roof hooks are then used for these fixing points. Subsequently, these hooks, typically constructed from robust steel, are fixed to the rafters by drilling two screws into the rafter through pre-drilled holes in the hook. Check out our quick video of this in action.

Roof Hook Placement

Strategically, roof hooks are evenly distributed along the roof, with the exact placement determined by factors such as the system's weight and the required load-bearing capacity. During installation, roofers carefully remove tiles from the area where a roof hook is to be positioned. Following secure installation, the tiles are restored to their original position. Occasionally, tiles may require slight modification with a grinder to ensure a snug fit on the roof, maintaining structural integrity. The roofer will grind out a small section on the back of the tile so that it can fit back over the tile and not ‘kick up’. If you watch this video here, you can see a close up of a tile that has had this done to it, fitting back over the roof hook after a small section on the underside of the tile has been removed.

Rail Installation and System Weight Distribution

The primary objective is to efficiently distribute the system's weight throughout the house's structure. Subsequently, aluminium rails, usually available in 3 to 3.5 or 6-meter lengths, are fastened to the pre-fixed roof hooks. This process creates an exceptionally sturdy and secure framework ready for the panels to be fixed to. The diagram below shows the rails for an eight panel installation, these are represented by the grey horizontal lines. The blue dots are the roof hooks that will be fixed to the rafters and the white lines represent the panels that are fitted to the rail.

A diagram of the mounting system showing fixing points (hooks - blue dots) and rail (grey lines).

Solar panels are then fixed to the rails using clips (in the above image they are the tiny black squares on the vertical white lines that represent the panels edges), securing them at four points: two on the left and two on the right. The clips come in two variants: middle clips, for panels flanked on either side, and end clips, used for the end of a panel row. Not only do these clips secure the panels, but they also allow for thermal expansion and contraction during fluctuating temperatures.

Importance of Additional Components

Apart from roof hooks and rails, smaller components play integral roles during the solar panel installation. Spacers, for instance, facilitate expansion and contraction between different rail lengths, ensuring a seamless and adaptable structure. Additionally, lead flashing is employed to weatherproof penetrations created during installation, such as those around roof hooks and bolts. This meticulous sealing process significantly contributes to preventing water infiltration through critical points in the roof structure, guaranteeing a water-tight and long-lasting solar panel mounting system.

Finishing the Installation

The panels are then connected together and connected to the inverter, which is usually located in the roof space just below them.

If you would like to know anything further about the roofing part of a solar pv installation, or any part of the install for that matter, please get in touch with SolarandBatteryCompany.com and one of our experienced and helpful team will be happy to answer any questions.