Using strong, leakproof Finnfoam insulation boards improves the functionality and structural fault tolerance in a slab-on-ground foundation structure. A structure's ability to tolerate structural flaws that may arise is one of the most important factors in terms of structural functionality and longevity. When thermal insulation is installed under the slab, the structure tolerates flooding, for example, much better. Today, as base floor insulation thicknesses increase constantly, it is very important to increase the strength of the insulation material accordingly. If this is neglected, the risk of compacting the insulation material increases, leading to expensive repairs where skirting boards must be lowered and torn waterproofing repaired in wet rooms. Further information about this is available below.
Keep the slab dry!
The relative humidity of the ground beneath the base floor insulation is always 95 to 100%. For this reason it is very important that the thermal insulation material is vapour-proof and does not become waterlogged. Waterlogged insulation no longer insulates as intended and allows the concrete floor to remain wet, which may lead to problems with indoor air quality.
In single-family homes, thermal insulation may also be used to prevent overheating of the base as the building's span length is relatively short. When floor heating is used, the risk of overheating is always bigger. As the span length of the building increases, more and more insulation will be needed. Since Finnfoam is impenetrable by vapour, it gives the concrete slab time to dry, resulting in less humidity remaining on the concrete slab and improving the elimination of humidity in the structure.
During a hot, humid summer, the water vapour flows from inside the structure down towards the ground. No additional vapour barrier sheets must be used anywhere between the slab-on-ground structure as they will interfere with the structure's ability to eliminate humidity. In order for the water vapour flows to be minimised, the thermal insulation material must be impermeable to water vapour – which is exactly what Finnfoam insulation materials are good at (source: VTT Technical Research Centre of Finland and Tampere University of Technology).
No slab compaction
As the thickness of the thermal insulation layer grows, the compression strength of the material must also increase accordingly. If this is neglected, compression of the insulation material will increase in the order of millimetres. This is especially important today as base insulation thicknesses increase constantly as the trend towards zero-energy houses continues. A rule of thumb for the thermal insulation of floors in residential buildings is: with a thermal insulation layer of 100 mm, the short-term compression strength required is 100 kPa, 200 mm = 200 kPa, 300 mm = 300 kPa, etc.
As Finnfoam boards achieve their maximum strength (short-term compression strength) at a compaction of only 2%, they are only compacted very slightly. Thanks to this, their long-term compression strength is also very good. Finnfoam boards can also be used to build unbroken thermal insulation structures around fireplaces and beneath load-bearing interior walls. In addition, Finnfoam floor insulation withstands construction-time point loads very well without crumbling.
The long-term compaction rate of Finnfoam insulation boards (F-300, 32 kg/m³) is less than 10% of the compaction of EPS material (EPS 120 20 kg/m³ or EPS 100 18 kg/m³) commonly used as floor insulation material.
Cost-efficient board size
Finnfoam insulation boards are designed to withstand the loads generated during concrete pouring when a split socle is built. Finnfoam insulation boards can be used as socle insulation material and can be used simultaneously as a concrete mould to improve productivity. The smooth-surfaced Finnfoam can be removed intact after concrete pouring as it will not stick to the concrete. If the insulation boards are intended to be attached to the concrete, the surface of the boards must be roughened or grooved slightly. Finnfoam insulation boards may also be installed on top of the socle later using remodelling mortar. Finnfoam insulation boards can also be coated using single-layer plastering following the instructions of plaster manufacturers (e.g. Fresco).
At 2500 × 600, or 1.5 m², Finnfoam's standard board size is relatively large. It is, however, ideal for many purposes and light enough to be handled by a single person, which means cost-efficient installation work.
Ventilated slab-on-ground foundations
Finnfoam insulation boards may also be used to build a ventilated slab-on-ground foundation, where small ventilation channels are left between two layers of insulation. Even minimal ventilation will be sufficient to remove the water vapour that seeps in from the ground through the bottom layer of Finnfoam boards. The ventilation does not interfere with the structure's thermal insulation properties. The ventilation channels must, however, be installed so that the channels remain unbroken.
A sufficient amount of ventilation is usually achieved through natural convection. When this method is used, the ventilation decreases naturally during the summer when it is not required. The same ventilation channels also eliminate most of the radon rising from the ground.
Finnfoam's ventilated slab-on-ground floor structure also works with large buildings where ground temperature increases towards the centre of the building. The slab's surface material may be shielded against water vapour and the structure also reduces the risk of radon.