Finnfoam Oy always recommends insulating basement walls from the outside using either Finnfoam's standard insulation boards or the CW-300 insulation boards designed specifically for this purpose. This recommendation is also in line with building regulations. Outside insulation saves space and results in a hefty load-bearing wall that balances interior temperature. Once the basement has been insulated from the outside using Finnfoam thermal insulation boards, the structure and the waterproofing layer are also protected from protruding rocks.
Finnfoam CW-300/100 mm basement wall insulation board/barrier board
Finnfoam has developed a new structural solution for insulating socle and basement walls. Using the new solution, thermal insulation and tanking of basement walls can be done in a single installation step. The structure has been certified for use by the VTT Technical Research Centre of Finland. This solution generates significant savings in labour costs and improves the socle's moisture elimination properties. When the joints of the boards are sealed using butyl putty (such as the Sika Lastomer 710), the resulting structure is completely sealed so that rain water flows outside the structure along the Finnfoam boards to the sub-surface drain channels. Interior humidity flows out through the grooves (10 × 15 mm) of the Finnfoam board set against the socle. Due to temperature differences, the pressure of the water vapour in the grooves is much higher near the surface of the ground than down near the footing. This allows the water vapour to flow downwards due to the difference in vapour pressure, condense into water at the bottom and flow to the sub-surface drain channels.
The structure optimises the socle's moisture control properties following the laws of physics (VTT). No water or dirt can enter the structure from the outside, allowing the ventilation channels to remain operational for decades. The ventilation grooves set against the foundation are sealed from the top, preventing humidity from outside air from entering the ventilation channels.
The basement wall insulation material (CW-300) also has small grooves (2 × 2 mm) on the outside surface, allowing water to flow unobstructed into the sub-surface drain channels. A filter fabric is installed on the outside surface of the Finnfoam insulation board to protect the grooves and allow them to function in demanding conditions. The drain channels on the outside surface of the Finnfoam insulation board are protected by the filter fabric, allowing exterior filling using base soil in renovation applications. This saves costs as loads of earth and topsoil do not have to be transported back and forth. The part of Finnfoam boards exposed above the ground are plastered using an alkali-protected fibreglass mesh as specified in the instructions provided by the plaster manufacturer. The coating may also be made of stone slabs following the manufacturer's instructions. The above-ground part of the insulation must always be glued tightly to the socle using tile or renovation plaster. The above-ground joint can be secured using mechanical mounting hardware, such as the Viki mounting hardware produced by SK Tuote.
Finnfoam can also be used as a basement wall concrete pouring mould
Finnfoam boards may also be used to build exterior concrete-pouring moulds for basement walls. Water does not penetrate Finnfoam, but it may seep in at the joints between the boards, often requiring a barrier sheet to be installed on the outside.
A ventilation gap must be left between the Finnfoam board and the vapour proof barrier sheet. This allows the minimal amount of water vapour that may come through the Finnfoam board to flow out. A small ventilation gap, however, is not sufficient to ventilate large amounts of humidity, requiring the thermal insulation to be highly vapour-proof – but fortunately this is exactly what Finnfoam is.
Inside insulation with reduced risk - no ventilation gaps between the wall and the insulation!
Humidity in the ground always tries to penetrate the walls of a house. The outside walls of heated basement rooms must therefore be waterproofed using materials such as bituminous felt sheeting. As waterproofing is required on the outside and a separate vapour barrier is needed on the inside, a slow-drying insulation structure is often left between the layers and may easily cause mould, if organic mildew-prone materials are used in the structure.
Using mildew-proof Finnfoam thermal insulation boards that require no separate vapour barrier on the inside reduces the usual risks involved with interior insulation. In applications like this, it is very important to install the Finnfoam boards snugly against the wall using tile plaster or renovation plaster. No gaps must be left between the insulation and the wall, and no studwork must be used as the studs often create spaces for mould pockets. An unbroken structure of concrete and Finnfoam withstands moisture and is leakproof. The inside surface of Finnfoam insulation boards feels warm, and the inside wall material follows the relative humidity of the air inside the building.