Short answer: ground and geometry first, wall second
A retaining wall maintains a difference in level and must resist lateral earth pressures. Before choosing concrete, blocks or another solution, therefore, show the top and toe of the slope, heights, boundaries, street, buildings and nearby services on a topographic section. A photograph or rough measurement does not define the geometry that will govern the calculation. The practical decision is to commission a survey with sections along the proposed alignment first, then allow the designer to determine a wall type compatible with the soil, available space and permissible movements.
The geotechnical study is not a decorative formality
The Technical Building Code’s DB-SE-C includes the geotechnical study and retaining structures within structural safety related to the ground. Studying the wall requires information on soil layers, strength and deformability, groundwater and the parameters relevant to short- and long-term conditions. If a study already exists for the house, the designer must check that its investigations and conclusions apply to the wall’s alignment and depth; this should not be assumed. The competent professional specifies the testing needed for the ground and the works.
Map nearby loads, neighbours and services
Record what will be above and below the wall: a house, pool, vehicles, fill, fences or circulation areas. Also mark pipes, utility connections, trees, nearby buildings and any sign of a buried service. Wall analysis considers permissible movements and the effect of nearby buildings and services, as well as stability during excavation and temporary stages. If a solution proposes anchors, their feasibility must be checked without entering neighbouring property or interfering with services. These conditions can change both the solution and the construction sequence.
Drainage belongs in the quote
Water can add pressure behind the wall and alter ground behaviour. DB-SE-C notes the benefit of long-term drainage behind the wall compared with designing without controlling water pressures. Ask the proposal to identify the drainage layer, filters, pipework, outlets, backfill and maintenance access, as well as the authorised destination for the water. If the wall adjoins a basement or habitable space, coordinate waterproofing and junctions too. Weep holes alone are not a universal answer: the system must suit the design and retain an effective discharge route.
Compare quotes against the same technical scope
Give every contractor the same topographic survey, geotechnical study and design or scope document. Separate design and calculations, excavation, temporary shoring or support, foundation, structure, drainage, backfilling and compaction, finishes, waste management, monitoring and reinstatement. Clarify which quantities are final or provisional, how changes will be valued and which permits, charges or third-party works are excluded. Comparing only the total can place bids for different geometries and risks side by side; comparing items on a common basis exposes exclusions before appointment.
What to prepare before making contact
Gather the location and plot reference, a topographic plan with sections, the available geotechnical study, photographs from both sides and an estimate of length and level difference. Add plant access, nearby buildings and services, signs of water or cracking, the intended use above and below the wall, and any planning or permit information you hold. State whether the plot will remain occupied during the work. Send the same pack to the professionals and identify missing documents so they can explain what must be visited or studied before producing a comparable quote.
Your plot deserves a well-prepared proposal.
If you own the plot, present it confidentially to explore contacts with builders and developers. You can also look for a company to build on your land.
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A Constructores.com guide. Informational content; every project requires professional assessment.