What damp problems do houses in Gavà Mar have?
The main problem is water and sand. Gavà lies on the western side of the Llobregat delta, on a coastal plain with often sandy soil and shallow water. Damp rises from below, and salt and pine roots add to it. How much applies to your house is shown by the plot's geotechnical report.
Damp reaches these houses by three routes: from below (capillary rise and water under the slab), from above and the sides (rain, sea wind) and from inside (condensation from weak ventilation). First you find out where it comes from, then you choose the fix. Treating the symptom without finding the source is the most expensive mistake: the plaster is stripped and redone, and a year later the stain is back.
How do you find out the soil on your plot and where the water is?
Order a geotechnical report. Boreholes or penetration tests show the soil make-up by depth, and a piezometer or a reading in the borehole shows where the water sits. One reading in the dry season says little: on a plain the water level changes from month to month and after rain, so you look at the trend or request data from neighbouring plots.
For a buyer the report is most useful before the purchase: it decides whether a basement is possible, whether drainage is needed and what the foundation for an extension costs. A coastal plain is not uniform by definition. Sand density, silt layers and water depth can differ between neighbouring plots. Those data cannot be carried over from one address to another.
Do the foundations and basement need waterproofing?
Yes, if there is a basement or part of the floor lies below ground. In a house without a basement, the walls at ground level and the slab need waterproofing. The level of protection is set by CTE DB-HS 1: it depends on how far the underside of the wall or floor sits relative to the water table and on the permeability of the ground.
The rule is as follows. Water presence is low if the underside of the floor is above the water table; medium if it is at the same depth or less than 2 metres below; high if it is 2 metres or more below. The minimum waterproofing grade for walls in the most permeable ground (Ks of 10⁻² cm/s or more) is 1 with low presence, 3 with medium and 5 with high; for low-permeability ground (Ks up to 10⁻⁵ cm/s), 1, 2 and 4. If the solution relies on drainage, the code requires a drainage well at most every 50 metres of wall and pumps, and for floors permanent automatic pumping.
In practice: if the water is above the bottom of the future basement, the basement is built as a watertight tank with control of cracks and joints, and it costs noticeably more. Sometimes the sensible choice is to drop the basement. For an existing house with damp walls you first find out whether it is capillary rise or a leak, then choose between injection, a waterproof coating or a ventilated plinth.
What should you do about pine roots near the house?
Do not cut roots blindly and do not plant pines right against the walls. On sand a pine holds on with lateral roots that usually spread to a distance comparable to the tree's height. They lift slabs, break drains and push up a pool, and a gust of wind can bring down a tree whose anchorage has been damaged.
A practical order: before the works, survey the drains with a camera, mark the roots at the foundation on the plan and ask an arborist which can be pruned. Thin lateral roots are cut cleanly; thick ones near the trunk are left alone. New pipes and slabs go in with a root barrier. If the tree blocks the design, felling goes through the administration's authorisation and is settled before the estimate, not during the works. Needles in gutters and on the roof are another item on the maintenance schedule.
What rules apply in Gavà for renovating near the coast?
Two levels need checking: the Coastal Law and municipal rules. The first covers 100 metres from the inner edge of the shore (article 23) and, on land that was urban when the law came into force, 20 metres. Within that strip an existing lawful building can be repaired and modernised if volume, height and floor area do not grow; before the works a declaración responsable is filed (fourth transitional provision).
Gavà's municipal rules (ficha urbanística, buildable area, height, type of procedure) are confirmed with the Ajuntament using the plot's address. We do not quote times or fees that we have not seen on an administration page. Gavà's shoreline is about four kilometres long, and the line of the shore on your plot is evidenced by the deslinde.
Which materials stand up to salt and sand?
Those that do not fear damp or chlorides. Fixings and hardware in A4 stainless steel, aluminium with marine coating for windows and railings, mineral or silicate exterior paint, stone with low water absorption. Timber terraces are made from heat-treated or tropical wood on a ventilated base.
A separate point is a pool where the water table is high. When it is emptied for repair, groundwater pressure can lift the shell, so the design provides relief valves or pumping and the pool is never drained without a plan. In wind, sand gets into the tracks of sliding windows, so easy-to-clean systems are chosen and their servicing goes into the schedule.
How does BCN YARD approach a house on sandy ground?
First a site visit, measurements and a read of the geotechnical report: we decide what to do about the water before discussing finishes. Then a detailed estimate. Reference prices before VAT: Premium from 1,000 €/m², Luxury from 2,000 €/m², Signature from 3,000 €/m²; on renovation of resale housing our estimates usually carry 21% VAT, on new-build housing 10%. The 21% applies because in our renovations materials usually exceed 40% of the taxable base; when they do not, renovating a private individual's home is taxed at 10% (Law 37/1992, art. 91). The exact price comes from the estimate after the visit and measurements.
We run projects in Russian and Spanish, with our own crew and vetted subcontractors, one person responsible for the project, and payment under contract in stages. We have full-cycle experience on a private house with a pool (2022–2024). We reply to an enquiry within an hour.
Frequently asked questions
Why are the walls of a house in Gavà Mar damp?
Most often damp rises from below: on the coastal plain the water is shallow, and walls without a barrier absorb it by capillary action. There is also condensation from weak ventilation and leaks through the facade. First the source is identified through readings and inspection, then the fix is chosen: injection, drainage, a ventilated plinth or a new roof.
Can you build a basement in a house in Gavà Mar?
Yes, if the geotechnical report shows the water is below the basement floor, or if the design is calculated for high water: waterproofing grade 5, drainage and pumps, or a watertight tank. In that case the basement costs noticeably more. It is decided by your plot's report, not by the house next door.
Can I prune the roots of a pine next to the house?
Thin lateral roots are cut cleanly; thick ones near the trunk are not touched without an arborist, because on sand the pine loses anchorage and can fall. Before the works the drains are surveyed with a camera and the roots at the foundation are marked. Felling needs the administration's authorisation and is raised before the estimate is signed.
How much does a house renovation in Gavà Mar cost?
Reference prices before VAT: Premium from 1,000 €/m², Luxury from 2,000 €/m², Signature from 3,000 €/m². Waterproofing, drainage, a basement and salt protection push the price up. Resale-housing renovation estimates usually carry 21% VAT. The exact figure comes from the estimate after the site visit and measurements.