Where a quiet house is really decided
Sound insulation in a house is decided in the design and the structure: the mass of walls and floors, floating floors, windows and where the noisy plant goes. Finishes at the end only improve slightly on what was built in earlier. If quiet comes up when choosing paint colours, most of the options are already gone.
First be clear which noise you are fighting: from the street, between rooms, footsteps from upstairs, or machinery. Our article on the acoustic brief covers that. This one is about something else: which construction decision deals with which problem, and when it has to be made.
Airborne noise: mass and layers
Voices, the TV, music next door: that is airborne noise. It is stopped either by mass or by a mass-spring-mass system: two linings separated by air and mineral wool. A plasterboard partition with the right infill and a double layer of board can perform as well as a heavy brick wall, but only if it is built with no gaps and no rigid bridges.
Sound bridges hide in the details: back-to-back sockets in the same wall between bedrooms, a ventilation duct without an attenuator serving two rooms, a door with no seal. The main bedroom and the children's room, or the guest room and the study, are better separated by wardrobes or a bathroom than by a single wall. It costs nothing on the plan, and no amount of insulation can replace it later.
Impact noise: footsteps, chairs and the stair
Footsteps upstairs, a dropped toy, a chair dragged across the floor: that is impact noise, and it travels through the structure. The main defence is a floating floor: the screed sits on a resilient layer and touches the walls nowhere, with an isolation strip around the edge. Bridge the screed to a wall or a pipe in just one spot and the effect drops noticeably.
The floating floor is decided before the screed and, in practice, before the frame, because the resilient layer and screed add thickness. Those centimetres have to be allowed for in floor heights, thresholds, doors and the stair. A staircase rigidly tied to the slab also transmits impacts; isolating its fixings is resolved in the design.
Windows and facade: the weak spot is the fitting, not the glass
For a house near a road, a railway line or under the flight path out of El Prat airport, as parts of Castelldefels are, windows play the lead role. A good acoustic unit uses laminated glass and panes of different thickness. But even the best glazing loses out if the roller-shutter box is uninsulated and the gap between frame and wall is sealed with nothing but foam.
Check three things: which glazing is specified, how the shutter box is built, and how the installation joint is finished. Trickle vents in the wall or frame also let sound through, so their type is chosen together with the ventilation system. In a well-ventilated house the street-side windows can stay shut, and you do not trade fresh air for quiet.
Services: the most underrated source of noise
The heat pump's outdoor unit below a bedroom window, the pool pump behind the living room wall, an ordinary plastic soil stack running through the study: these get noticed only after moving in. The fix is simple if made in time: a plant room away from bedrooms, anti-vibration mounts under equipment, acoustic soil pipes, and attenuators in the ventilation and air conditioning.
Air speed in ducts makes noise too: ducts that are too small, squeezed into a shallow dropped ceiling, whistle. Duct sizes are fixed before ceiling heights are agreed.
When and how to raise it with the team
Sound insulation requirements for new homes are set by the Código Técnico de la Edificación in its noise protection document (DB HR). That is the minimum. If you want it quieter than that, say so at the first meeting and describe real situations: 'not hearing the kids while we watch a film', 'sleeping with the windows shut next to the road'.
We build houses in Barcelona and along the coast with one person in charge of the site, in Spanish or Russian. Send us the plot or the project; we reply within an hour and show you which acoustic decisions need to be fixed before the frame goes up.