Finnfoam Oy primarily recommends insulating basement walls on the outside either using Finnfoam’s standard insulation panels or the CW-300 insulation panels, which are specifically designed for use on basement walls. This complies with the recommendations of the National Building Code of Finland. External insulation will save space and allows you to use a solid load-bearing wall to even the temperature of indoor air. By insulating the basement externally using Finnfoam thermal insulation products, you also protect the possible waterproofing layer from sharp rocks.
Finnfoam's basement wall insulation product CW-300/100 mm provides insulation and a damp barrier with a single installation!
Finnfoam has developed a structural solution for insulating footings and basement walls, which can be used to provide both thermal insulation and tanking for basement walls with a single installation. The structure is tested by VTT. This structural solution provides significant savings in labor costs and improves the moisture performance of the footing. If the joints between the panels are sealed with an elastic adhesive mass or butyl paste (for example: ARDEX CA 20 P, Casco Aquaseal, Sikaflex AT Connection or Sika Lastomer 710 butyl paste), the structure will be completely sealed such that rainwater will gutter down the Finnfoam material toward the subsurface drains. Moisture originating on the inside is able to escape through the grooves (10 x 15 mm) in the Finnfoam facing the footing. Within the grooves, the partial pressure of water vapor is significantly higher closer to the ground surface than down near the footing due to the temperature differences. Thus, the differences in the partial pressure of the water vapor will force it to travel downward, condensing at the bottom and dribbling down to the subsurface drains.
This structure makes it possible to optimize the moisture performance of the footing in accordance with the laws of physics. Water, or soil carried by water, cannot enter the structure from the outside and thus the performance of the ventilation channels will remain unchanged over decades. The ventilation grooves placed against the foundation within the structure are closed from above, thus preventing moisture from the outside air entering the channels.
The basement wall insulation (CW-300) also has small fluting (2 x 2 mm) on the exterior surface of the insulation, which allows water to easily pour down into the subsurface drains. The exterior surface of the Finnfoam can be covered with a filter cloth that will protect the flutes and maintain their functionality even under demanding conditions. The subdrainage on the exterior surface of Finnfoam, which is protected by a filter cloth, enables external backfilling with foundation soil as well at renovation sites. This provides cost savings as it reduces the need to transport soil to and from the site. The above-ground section of the Finnfoam panel is plastered according to the manufacturer's instructions using an alkali resistant fiberglass mesh. Coating can also be provided with rock panels, according to the manufacturer's instruction.
The above-ground section of insulation must always be bonded solidly with adhesive mortar to the footing (slab or renovation mortar, for example). The above-ground section may additionally be secured with mechanical anchors.
Finnfoam also functions as a casting mold for a basement wall
The sturdy Finnfoam can also be used as an external casting mold for a basement wall. Water cannot permeate Finnfoam but may escape through the joints, so in this case it may be necessary to install a damp barrier on the outside.
A ventilating slot is left between the Finnfoam and the vapor-proof damp barrier (make sure to install the damp barrier facing the right way, i.e. with the studs toward Finnfoam), which will allow the tiny amount of water vapor coming through the Finnfoam material to escape. A small ventilating slot cannot be used to vent large amounts of moisture, which is why the thermal insulation must be highly vapor-proof like Finnfoam.
Low risk internal insulation – no cavities between the wall and insulation!
Moisture in the ground will attempt to permeate inside through the walls as well, which is why the exterior surface of the basement wall typically requires waterproofing by using bituminous felt, for example. Waterproofing on the outside with a separate vapor barrier on the inside will create a slow-drying special structure, which can easily lead to mold damage if the structure uses organic or other materials that are susceptible to mold.
The impermeable and mold-proof (tested by VTT) Finnfoam thermal insulation can be used to provide interior insulation with very low risks, as a separate vapor barrier is not needed on the inside. In this case it is important to bond the Finnfoam thermal insulation solidly against the wall throughout using slab or renovation mortar, for example. Do not leave cavities between the insulation and the wall or use studwork, which could provide suitable conditions for mold colonies. A solid structure consisting of concrete and Finnfoam withstands moisture and is impermeable. The interior surface of Finnfoam is warm and the internal cladding will correspond to the relative humidity of indoor air.