Structural Surveys

August 25, 2021

We already know that installing a solar array on your roof is a great way to reduce your electricity bill, reduce your reliance on the grid and slash your carbon footprint; solar is a mature technology and is being used by daily millions of homes and businesses across the globe.
However, because solar panels are designed to be exposed to the elements for as long as 30 years, it’s important to consider – in detail – the chosen location for the system.
 
Assuming your roof will last the test of time we must be satisfied that the structure will cope with the additional weight of the solar panels, mounting system, cabling/cable trays and optimisers. We must also satisfy ourselves that the building can cope with this additional weight in the event of high winds, heavy snow and snow drifts if the roof has a low pitch.

How Much Does a Solar Array Weigh?

Broadly, and subject to the specific design, solar systems weigh approximately 13kg per m2. This, however, can change dramatically if the roof chosen is flat and a non-penetrative ‘ballast’ system is specified. (use ballast picture)
 
In addition to the weight of the equipment, the weight of humans/our cleaning robot must be factored as well as this can add significant – albeit temporary – additional weight.

Static Load Vs. Dynamic Load

When assessing whether or not a building can take the weight of a solar array, a structural engineer will consider two loads – static and dynamic.
 
Static load refers to weight of the solar equipment resting on the roof. It’s fair to say that most buildings in the UK that have been designed for prolonged human occupation can safely cope with the additional dynamic loads.
 
Dynamic load refers to the effects of mother nature on the building; wind, snow and ice all have the ability to increase the load on the roof dramatically. Owing to the fact the panels will almost certainly sit proud of the roof, heavy winds could rip the solar panels from, or push them into, the building. Snowfall on panels will obviously add significant additional weight, and for buildings that have multiple pitches, there may be occasions where snow falls on day one, doesn’t fall from the roof, so is added to on day 3, 4 and 5.
 
All of this needs to be factored in.

How Is a Building Assessed?

As part of our thorough development process, we will contract an independent structural engineer to assess the building. 

 
He or she will visit site and measure all of the steelwork pertinent to the assessment before modelling it in their software package. At the same time we will provide copies of the proposed system layout, as well as specification sheets for the chosen equipment. 
 
Invariably the structural engineer will come back will one of three conclusions –

1. Pass – subject to adherence of the proposed design
2. Pass – subject to some minor tweaks of the proposed design
3. Fail
 
If the structural engineer fails the structure for the addition of solar panels, this may not necessarily mean the end of the project. Subject to why the structure has failed, it may be possible to undertaken modest strengthening works in order to permit the work. 

If, however, the business case for the installation was already thin, and the strengthening works are wide in scope with a high price, it may render the project uneconomical
 
To discuss assessing your building(s) for solar panels, please contact BeBa today.