Consulting on solar carport & foundation planning: Cost factor of the ground foundation for solar carports

Quick assembly and easy installation – these are the attributes often found in offers for solar carports. But that's just the tip of the iceberg. For competitive reasons, the price usually doesn't include the cost of the foundations, and for some types of solar carports, the crucial support beams for structural stability are also not factored in. This makes a direct comparison difficult.

Groundwork is the big unknown factor when it comes to solar carports. Strip foundations are a common type of foundation. They bear the entire weight of buildings and transfer it to the ground. This is extremely demanding work, sometimes requiring heavy machinery. Therefore, strip foundations must possess very specific properties. For a building to stand stably, the ground must be load-bearing.

To achieve a larger load-bearing area between the wall and the ground, the strip foundation is generally made wider than the wall itself. Strip foundations must be carefully planned and constructed. Any savings made at this stage will prove costly later and jeopardize the entire building project. Of course, this also depends on the soil composition and type. Every strip foundation requires dense and load-bearing soil. In soft subsoil, the foundation must be designed with a correspondingly large area to better distribute the load to the ground and prevent the building from sinking.

The situation is similar, yet slightly different, with solar carports. Depending on the type of support structure for the solar roof, leveling at ground level is necessary. Depending on the leveling required and the soil conditions, a strip foundation may no longer suffice, necessitating the use of a concrete slab.

What might not be so noticeable with single and double carports will become a major financial factor with large solar carport systems.

Therefore, point foundations are not only the more cost-effective choice, but also, and especially for solar carports, the simpler and more flexible construction method. However, point foundations are not possible or applicable for solar carports with beam compensation.

Point foundations are more fault-tolerant and easier to adapt. They can also be individually adjusted to the specific soil conditions at any time. Especially with curved arrangements or angled parking spaces for solar carports, the 4-column technology of the respective modular solar carport system, the point foundation or base plate application (depending on the existing ground sealing) has proven to be very flexible and versatile.

Undoubtedly, all solar carports must meet structural requirements. However, there are differences depending on vehicle and parking frequency. There is certainly a difference between single and double carports for private homes and large solar carport installations with high visitor traffic, such as those found in shopping centers, company parking lots, and similar locations.

The high volume of traffic and parking therefore necessitates solid planning in the foundation design to avoid having to initiate the first restoration work after only a few years. Often, corners are cut in the wrong place.

4-column solar carport system with 2 columns each (4+2+) Expandable per double parking space

Modular solar carport system with 4+ 2+ columns, round – Image: Xpert.Digital

Cost-effective point foundations are only possible with the 4-column technique. It is the preferred choice for secure installation compared to slab or strip foundations. Furthermore, it requires very little building material.

In addition to the simple modular expandability of the 4-column construction with only 2 additional columns (4+2+ technology/system) for each additional parking unit, this technology can also be used for sloping open parking areas. Furthermore, 4-column solar carport substructures are lighter and more individually adaptable for curved parking sections, unlike other constructions.

With base plate, support shoe or post shoe for already sealed surfaces

Modular solar carport system with base plate – Image: Xpert.Digital

Depending on the soil conditions of the already sealed areas, it is also possible to bolt the post supports to the ground. This eliminates the need for further groundwork and does not affect underground utilities.

Because the 4-post system also allows for bolting to the ground, it is ideally suited for parking facilities with open, uncovered and accessible upper deck or roof parking spaces!

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T-beam solar carport

Solar carport with T-beams – Image: Xpert.Digital

Depending on the structural requirements, a support leveling layer must be provided on the ground for the solar roof substructure of the T-beam. T-beams require a ground foundation. Depending on the soil conditions, a concrete slab may also be essential, in each case requiring heavy equipment for assembly and alignment.

Solar carport with offset T-beam

Solar carport with offset T-beam – Image: Xpert.Digital

Subsequent adjustments and corrections are very difficult, and some work already carried out has to be reversed, which impacts costs. Arranging solar carports with slight curves or angled parking spaces is not possible with this system.

Construction changes due to "unforeseen" alterations in soil properties can also increase costs retroactively, which in turn raises suspicions that a deliberately low price was set during the bidding phase to gain a competitive advantage. With point foundations, such "unforeseen" changes are not significant, as adjustments can be made flexibly.

V-beam solar carport – Image: Xpert.Digital

Depending on the structural requirements, a support leveling system must be provided on the ground for the solar roof substructure of the V-beam. V-beams require a ground foundation. Depending on the soil conditions, a concrete slab may also be essential, in each case requiring heavy equipment for assembly and alignment.

V-beam solar carport with retaining wall – Image: Xpert.Digital

A solar carport with concrete retaining walls on the sides is considered a particularly robust construction. The robustness and weather resistance of these concrete retaining walls with foundations below ground (strip foundations) come at a price. This is extremely hard work and can only be carried out with heavy equipment.

Compared to concrete buildings, damage to concrete retaining walls, material-related cracks or external forces are correspondingly higher, which can no longer prevent the ingress of moisture during the next rainy period and damages the material.

Compared to four-column construction, the risk of soiling from environmental and external influences is significantly higher with concrete retaining walls. This includes illegal spraying by third parties and other factors. Even small debris blown in by the wind cannot be carried away as easily as with four-column construction, but instead clings to the retaining walls, requiring all parking areas to be swept periodically.

Similarly, the indestructibility of the retaining walls in the event of a collision is only limited. Depending on the type of collision, the system can also become instability, and due to the heavy construction, repairs can only be carried out with heavy equipment and involve significantly higher maintenance costs than with other solar carport systems.

Impact protection posts (with point foundations) have proven to be considerably more cost-effective on the respective solar carport systems, unlike the systems with concrete retaining walls on the sides.

TV-supported solar carport with retaining wall – Image: Xpert.Digital

Another option is to reduce the size of the retaining wall and move it to the end of the parking area. This allows the driver to get in and out of the vehicle without difficulty if they park skillfully. Otherwise, the points mentioned above remain the same.

Solar carports: sensitive entry zones – Image: Xpert.Digital

Related to this:

• The parking space requirement, the solar obligation, parking space types and the solar carport strategy for open parking spaces
• Solar carports where standard no longer applies – The optimal solution for every challenge with solar roofing for open parking spaces

But there's a smarter way: combining timber construction with the four-column solar carport system, where the supports are made of steel. In the upper section, directly beneath the solar panels, the wooden substructure for the solar modules is protected from the weather, while the supporting columns remain made of steel, as with all other large solar carport systems. With this method, the wood used requires virtually no further treatment against the elements, even for decades.

Related to this:

• Architects love them: Aesthetic diversity with semi-transparent double-glazed solar modules for solar carports and terraces

This combination also saves significantly more steel, which is reflected in the price.

Another important aspect concerns aesthetics and appearance.

The combination of wood and steel with a translucent roof made of semi-transparent double-glass modules not only enhances the parking area itself, but also has a great positive impact on people and the environment.

We know this from the construction industry. There are various methods for discouraging people from entering certain areas, encouraging them to come only when absolutely necessary. On the other hand, many sectors thrive on high customer traffic, such as shopping centers. Competition is fierce. Therefore, it's particularly important in these areas to create spaces that attract people and make them feel comfortable.