This article opens an interventions strand dedicated to analyze possible "solutions" to the problem of rising damp. Now we deal with the under-floor cavity analyzing all the details that have never been explained to you.

Under-floor cavity: what it is

The under-floor cavity is an air chamber under the buildings that improves environment conditions inside the houses. Its specific function is to separate habitable insole from the ground below, thus avoiding contact between the first one and humidity present in the latter.

History of under-floor cavity

The system at the base of the under-floor cavity dates back to ancient times: since man became sedentary, building real homes, he had to deal with humidity, which made home cold and unhealthy. Since in Roman times, amphorae (or more plausibly their fragments) were used to obtain empty spaces below buildings, still found during archaeological excavations. In more recent times, ventilated cavities were often built, creating a floor slightly raised off the grounds, provided with small openings that served as outside air intakes (called wolves’ mouths). Alternatively, under-floor cavity was built with cobblestone or very coarse gravel, on which the base of the building was placed. Today the most common under-floor cavity method is based on the use of so-called "igloo" (dome-shaped plastic structures), above which the slab is then cast. These structures are supported by small pillars in the empty spaces between them. Above under-floor cavity you may place an integrated thermal insulation. Recently, EPS domes have also been developed acting simultaneously as support and isolation.

How to install under-floor cavity

Under-floor cavity construction is an invasive work usually performed during property construction. The construction of under-floor cavities in pre-existing building is a long, delicate and not always possible operation. In the case of new construction, it is sufficient to realize ventilated air chambers under the floor and then to continue the works. In the case of pre-existing construction, a thorough investigation of the structure and the ground below is required and, if this intervention is possible, it will be necessary:

  • To demolish the flooring
  • To dig into the ground to create an air chamber
  • To create ventilation holes in the perimeter walls
  • To replace the insole and the flooring

Pros of the under-floor cavity

  1. The under-floor cavity guarantees good thermal insulation of the building
  2. if properly ventilated it eliminates rising damp from the floors
  3. it eliminates any fumes from the ground below

Cons of the under-floor cavity

  1. an under-floor cavity cannot prevent rising humidity in load-bearing walls or those in direct contact with the ground
  2. if not carried out during construction it has very high costs
  3. if not properly ventilated it causes water stagnation, accentuating rising damp

Costs of under-floor cavity

The construction of under-floor cavity (during building construction) costs € 100/150 per square meter. The construction of under-floor cavity (under pre-existing building, if technically feasible) costs around € 1000/1200 per square meter.