Why do finishes fail in an indoor pool?
Because of moisture and chlorine. Water at 28–30 °C evaporates all the time, the air fills with vapour, and vapour condenses on cold surfaces. Evaporation leads to corrosion, mould and flaking plaster. An outdoor pool avoids this because the vapour escapes; in a closed hall it has nowhere to go.
An outdoor pool releases moisture to the atmosphere and causes no trouble. In an enclosed volume the vapour stays inside and humidity climbs to 80–90 % without dehumidification. Condensate settles on glass, in corners, on steel parts and behind cladding. Chlorine and chloramines released with the vapour speed up corrosion: ordinary steel rusts, unprotected aluminium blooms with deposits, galvanising does not last.
In a seaside villa in Castelldefels, salt in the air adds load from outside as well. So finishes, ironmongery and ventilation are chosen to withstand both vapour and salt.
A typical mistake: a pool with flawless tile and expensive glazing but no dehumidifier. Within two or three seasons the grout turns black and stains appear on the ceiling.
Do you need a dehumidifier?
Yes, always. An indoor pool cannot be held within range by opening windows or by an ordinary air-conditioner. A private pool gets a dedicated heat-pump dehumidifier that returns the energy of evaporation to the air and the water.
The principle is simple: humid air passes over a cold evaporator, vapour condenses and drains away, the air is heated at the condenser and returns to the hall. The unit keeps humidity at around 50–65 % and the air 1–2 °C above the water. If the air is colder than the water, evaporation increases; if it is much warmer, people feel stuffy.
Capacity is chosen by water surface, temperature, bathing activity and whether there is a cover. A private pool of a few dozen square metres evaporates several litres an hour, and more when in use. A pool cover, closed overnight, cuts the dehumidifier load sharply.
The unit goes in a plant room next to the hall, with a drain and ducts with flexible connections. It must be a corrosion-protected version.
What ventilation is required and how does the air move?
Ventilation with fresh-air make-up and supply along the external walls. The dehumidifier circulates air inside the hall, while a minimum intake from outside is needed to remove chloramines and keep the air healthy.
Supply runs along the glass and cold walls to sweep away condensation; extraction sits above the water surface or at the far end of the hall. Ducts are stainless steel, plastic or coated aluminium. Grilles and fixings are AISI 316 stainless. Sections are sized for low speeds so there is no draught or noise.
The plant room, where chemicals, pumps and dosing units are kept, gets separate extraction: chlorine vapours must not enter the general system. Air-change and heat requirements are set by the engineer's design under RITE; an air-to-air heat-recovery option reduces losses.
Where part of the wall is glass, the inside surface temperature of the glass must stay above the dew point. Otherwise condensation will return with any dehumidifier.
Structure: insulation, glass and vapour barrier
The envelope of an indoor pool must be warmer and tighter than a normal house: a vapour barrier on the hall side, continuous insulation without thermal bridges and glazing with warm-edge spacers. A thermal bridge becomes the point where water collects every morning.
The vapour barrier sits on the warm, humid side, that is, the inside, and is sealed at corners and pipe penetrations. Wall insulation is moisture-resistant and cannot absorb condensate. Glazing is double or triple with low-emissivity coatings, thermally broken frames and an inclined top row so drops run off. Windows facing the sea and the sun add heat, so solar shading is designed in.
The pool shell is calculated as a structure acting with the ground and the water; waterproofing, drainage under the slab and the weight of the water are checked. One cubic metre weighs a tonne: a pool of 8 × 4 × 1.5 m holds about 48 t, so in villas the shell sits on the ground, not on a floor slab.
The sequence of works is covered in our article on the stages of building a pool.
How much energy does an indoor pool use?
Más que una piscina exterior del mismo tamaño, porque se calientan tanto el agua como el aire de la sala. Las cifras exactas se calculan en el proyecto; a ojo, para una piscina de 8 × 4 m con deshumidificador son unos 10–20 mil kWh al año, y la dispersión depende de la cubierta, la temperatura del agua y el aislamiento.
Las partidas principales son el calentamiento del agua, la electricidad del deshumidificador y las bombas, y el calentamiento del aire. Se reducen con una cubierta nocturna, una bomba de calor, la recuperación de calor del deshumidificador y paneles solares en cubierta. En una casa particular con paneles, como en nuestro proyecto de casa con piscina de 2022–2024, parte de la carga la cubre la generación propia.
La temperatura del agua también influye: cada grado de más eleva el consumo de forma notable. 27–28 °C es más cómodo para nadar con intensidad, 30 °C para una familia con niños.
La química y la filtración cuestan poco frente a la energía, pero no se puede recortar en ellas: un control deficiente del pH acelera la corrosión.
How BCN YARD works on these projects
An indoor pool ties together structure, climate, electrics and finishes. We run it with one team: our own crew, trusted subcontractors and one person responsible for the site. We have full-cycle experience: a private house with a pool and solar panels, 2022–2024.
We start with a visit and measurements, then calculate a staged estimate and handle permits. We work in Russian and Spanish, with payment by contract and in stages. We usually answer an enquiry within an hour.
Frequently asked questions
Can you skip the dehumidifier by opening windows?
No. Open windows let heat out and do not guarantee humidity control, especially on damp coastal days. Without a dehumidifier humidity rises to 80–90 % and the finishes start to fail. Windows can help in summer, but the dehumidifier is the core of the system.
What tile and glass should you choose for an indoor pool?
Tile should be porcelain stoneware or glass mosaic with epoxy grout: neither absorbs moisture or chlorine. Glazing is double or triple with warm-edge spacers and low-emissivity coatings so the inside surface stays above the dew point. Frames are thermally broken and corrosion-protected.
Do you need a permit for an indoor pool in a villa?
Yes. An indoor pool counts as construction or an extension, not just landscaping, and needs a design and a licence. The plot's built area, setbacks and height all count. The general procedure is in our article on pool permits; also check the planning parameters of the plot.