Almost every billboard failure story begins underground. A foundation has to resist overturning, sliding and uplift from wind on a large flat face, and it has to do so in the ground that is actually on your site, which may be clay, sand, fill, weathered rock or a high water table.
We carry out the civil works for the structures we build, and this page explains how a billboard foundation is designed and constructed.
Typical specifications
- Footing typespad, drilled shaft or pile, chosen from loads and ground
- Reinforcementfixed to the engineered detail before concrete
- Anchor boltsset in a rigid template and checked before and after the pour
- Concretepoured, compacted and cured before steel erection
- Investigationinspection, test pits or boreholes as the structure requires
- Servicesunderground services located before excavation
- Rooftop and wallexisting structure assessed and loads spread by steel base frames
What the foundation must resist
A billboard acts like a sail. Wind pushes the face and the force reaches the base as a large overturning moment, plus shear at ground level. For a single column, the foundation is usually a concrete pad or a drilled shaft, sized so the soil and the weight of concrete resist that moment. Gantries and lattice structures divide the load between several footings.
The foundation is therefore sized from the structure's loads and the ground's capacity, not from a standard drawing.
Uplift is easy to overlook. A tall structure in strong wind can try to lift one side of its base while pressing the other side into the ground, so the footing has to resist both. This is why foundation size and weight are set by calculation and why anchor bolts must be long enough to engage the reinforcement and concrete properly.
Site investigation
Ground conditions are checked before design. This can range from inspecting an existing excavation to arranging test pits or boreholes on larger structures. We also check for underground services, drainage paths, retaining walls, nearby buildings and slope, since any of these can move the structure or change the footing depth.
Where the soil is poor, options include a deeper or wider base, piles, or ground improvement, each with a different programme that is confirmed on your quotation.
Existing structures are often investigated differently. If a billboard is being relocated or upgraded, we can inspect the existing foundation where it is accessible, look for cracking, settlement or loose anchor bolts, and recommend whether it can be reused. A foundation that was suitable for one face may not be suitable for a heavier one.
Excavation, reinforcement and concrete
The hole is excavated to the designed size, with shoring where the sides are unstable. Blinding concrete gives a clean base, reinforcement is fixed to the engineered detail, and the anchor bolt cage is set in a rigid template at the correct level, projection and position. Concrete is poured, compacted and cured before steel is lifted.
The anchor bolts are the most unforgiving part of the job, which is why their position is checked before the pour and again after.
Drainage matters around the base. Water pooling against the steel will speed corrosion, so the top of the concrete is finished to shed water away from the base plate, and grouting under the plate is done to prevent trapped moisture. In some soils, such as expansive clays, the ground moves with moisture, and the design has to allow for it.
Rooftop and wall-mounted sites
On buildings the foundation is the roof or wall itself. We assess whether the existing structure can take the load, and where it cannot, loads are spread onto columns or walls with steel base frames. See rooftop billboards and wall-mounted billboards. A building owner's consent and an engineer's input are essential.
Curing time and weather affect foundations. Concrete placed in cold or very hot conditions needs protection, and heavy rain can wash out an excavation or delay the pour. We plan the work so that the structure is only erected on a foundation that has reached the strength the design needs.
Approvals and landowner consent
Excavation on private land needs the owner's consent, and work near roads can involve a roads authority such as SANRAL or a provincial department. We assist with supporting documents and approval rests with the authority. Read the approvals guide and see billboard structural design.
Piles and difficult ground
Where soft or variable ground makes a pad footing impractical, drilled piles carry the load to firmer material below. This approach is also used where the footprint is limited, such as next to a boundary wall or a roadside servitude. Rock may need breaking or drilling, and a high water table may need pumping or casing.
These conditions affect programme and cost, which are confirmed on your quotation after we have seen the site and any ground information available.
At a glance
Billboard foundations and civil works from Billboards Africa are designed for the ground and the wind loads on your site. We excavate, reinforce and pour concrete pads, drilled shafts or piles, and set anchor bolts in rigid templates so the steel column or lattice legs can be lifted into place and bolted without force.
Good billboard foundations resist overturning, sliding and uplift on a large flat face, whether the site is clay in Gauteng, sandy coastal ground near Durban or weathered rock in Limpopo. We check underground services, drainage and nearby buildings before digging, and we assess the structure first on rooftop and wall-mounted installations. Landowner consent and any roads authority input are needed before work starts, and we assist with the supporting documents. Send your site details through the quote form to request a quotation for billboard foundations and civil works in South Africa and Africa. Ground information you already hold, such as a geotechnical report, helps us quote more precisely. Foundations are quoted with the structure, or on their own where another supplier provides the steel and you need the base prepared.
Common questions
How deep is a billboard foundation?
It depends on the structure, loads and soil. The depth and size come from the design for your site, not a standard figure.
Do you do the civil work yourselves?
Yes, for the structures we build. Specialist drilling or geotechnical work may be arranged with partners where needed.
What if the ground is rocky or wet?
Rock, water or soft soil change the design and method. We assess these at survey and confirm the approach on your quotation.
Can I mount a billboard on my roof?
Possibly. The building must be assessed by an engineer, and the owner and authorities must consent.
Is the foundation included in your quotation?
We quote foundations with the structure unless you ask for the steel only. Scope is confirmed on your quotation.
