Granab ventilated subfloors
Avoid moisture, mould and stale indoor air with a Granab system and underfloor ventilation. A large number of single-family dwellings and other buildings are subjected to moisture damage each year in the basement, or elevated moisture content in basement slabs. To make sure buildings are fresh, it is important that moisture from concrete floors in basements or bottom slabs is removed through ventilation and not built into the floor construction.
Besides performing checks and taking possible measures involving new drainage and filling materials around the foundations, the wooden joists or plastic floor covering installed or placed directly on the basement floor must be removed, and the concrete floor is then dried. Granab systems with galvanised steel floor girders are made entirely from inorganic materials and adjusted up from the concrete floor to the desired height. The air in the space between the subfloor and surface flooring is then continuously ventilated, leaving a dry, pleasant environment.
If there is uncertainty and risk concerning humidity content or emissions from the bottom slab or subfloor construction, air gaps under the finished floor should be ventilated using mechanical ventilation in combination with fitting a moisture barrier under the floor girders. In its standard configuration, the height of the Granab system is adjustable from 30–420 mm and provides an open airflow under the girders. The space under the floor constitutes a separate “room unit” (sealed box), which is ventilated independently or in special cases combined with other ventilation.
System 3000N with moisture barrier above the girders.
System 7000N with moisture barrier above the girders.
Granab ventilated subfloor principle
Separate mechanical ventilation in the “room unit” under the floor using an exhaust fan that draws air out via perforated air ducts of, for example, standard spiral ducting. Inlet air to the ducts is obtained via a filter-equipped air terminal device that takes inlet air from the respective room units. Additional inlet air can be obtained with, for example, an additional outdoor air valve.
Ventilation system planning
Granab can provide ventilation planning that also includes function, operation and maintenance instructions. Installation of ventilation is conducted by a local HVAC installer or building contractor.
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Installation of Granab ventilated subfloors
01. The old flooring is removed.
02. The original floor is cleaned of all organic material. In the case of timber floors, exposed joists require a sheet material layer of OSB or plywood. Where there are floor boards and they are in good condition the Granab system can be fitted directly on top.
03. The Granab subfloor system with underfloor ventilation and insulation is installed.
04. The new floor is laid. Done!