Airtightness should ideally be taken into account from the start, and is best if carefully planned in (list of requirements) and described. Coordination is essential to achieve a good level of airtightness, a general contractor will give a better guarantee of a good result. But relatively cheap measures can still lead to a major improvement in airtightness.
Plaster on the inside of brickwork ensures a high degree of airtightness. When insulating roofs and a wooden framework (external wall, ceiling ...) you need to apply a separate airtight membrane. This vapour proof layer also prevents the internal moisture from cooking or the bathroom ending up in the insulation and reducing the insulation value.
In addition special attention needs to be paid to the trims and joints. Window frames alone can be responsible for more than 1/3rd of all air leaks, and so certainly merit special attention.
λ-value:
The thermal conductivity or the heat transmission coefficient of a material, expressed in W/m-K (the m here stands for metre). The lower it is, the less conductivity and so the better the insulation value.
R-value:
Thermal resistance of a layer of material (thickness/λ) (m²K/W). The inverse of the U-value and so the higher it is the better.
U-value:
Thermal conductivity coefficient of a construction element (W/m²K). Measure of the energy lost from one m² of a given material given a temperature difference of 1 K between the two sides of a construction element. The lower it is the better.
Ψ-value:
Linear thermal transmittance coefficient. Also a measure for heat transmission, but this time seen in metre lengths joins between 2 construction elements, and so possibly to be applied as a correction to the U-values of specific construction elements in the outer shell of the building. Applies to thermal bridges (cold bridges). A number of threshold values have been defined in the energy performance regulations in Flanders. The ψ-value for connections between masonry and joinery must be 0.1 W/mK or less.
In a window frame in a classic cavity-wall construction the SWS Inside Tape provides a damp-proof and airtight barrier. This pink tape has a high moisture transmission resistance (µ-value, Sd-value > 50 m). SWS Inside Tape can be plastered over later with no problems.
In a mono-block wall construction (without coating), both tapes are used, so the white SWS Outside Tape is applied on the outside. The combination of the two tapes ensures correct damp protection in the joints. The SWS Outside Tape allows breathing, so that any damp in the joints can be dissipated outwards. This tape therefore has a low µ-value and Sd-value.
The SWS Inside Tape is best applied before inserting the joinery, using the self-adhesive strip, on the side of the frame and before inserting the window fixing clamps. These then need to be placed with care on top of the tape (avoid perforations). In the corners an 'ear' needs to be created (an extra length of material that is folded in).
Using the other side of the adhesive strip, the tape can potentially be positioned after the joinery is in place, this time on the inside of the frame
A cold bridge / thermal bridge is a place in a construction element where the thermal insulation (potentially) is discontinuous or where the insulation elements do not connect to each other. A lot of heat is lost here, but the warm interior air also cools down through contact with a cold surface. This can create a risk of condensation, resulting in unpleasant odours and growth of mould. Take particular care with joints above windows and doors and around doorsteps and balconies.
Flexifoam is airtight. This can be seen from a number of test reports on airtightness. The level of the foam's airtightness does depend on the thickness and width of the joint and the care with which it is applied (moisten!). Flexifoam makes a significant contribution in a number of different ways to making window frames airtight.
The water vapour diffusion resistance or moisture resistance is stated as the so-called µ-value, a dimensionless number which shows the ratio between the moisture resistance of the material compared to the moisture resistance of a layer of air of the same thickness. Materials without any pores have an infinite moisture transmission resistance. (E.g. air has a µ-value of 1, insulation materials have between 30-80 and bitumen from 10,000 to 100,000).
Each insulation material has an insulation value: its lambda-value (λ). The lower this value, the better heat insulation the material provides. To achieve the same insulating power (R-value), an insulation material with a higher λ-value needs a thicker layer than insulation with a lower λ-value.
Both solutions are possible in principle. Both types of foam are good insulation products and will prevent loss of heat. Flexifoam has the major advantage that it can follow movement in the joints much better. This means that the chances of the foam breaking loose from the frame or the wall are much lower. This ensures insulation and airtightness over the long term. Flexifoam also has very strong sound insulation properties.
Flexifoam ensures EPB-compliant thermal bridges. The PU foam also needs to be applied such that the insulation layer is not interrupted (wall insulation – foam – thermal break window frame). In this way you can avoid a thermal bridge and potential condensation forming on the inside of the joint. Flexifoam has a λ-value of 0.0345 W/mK.
Both tapes come with a adhesive strip which ensures initial adhesion to the window frame. But a full-surface adhesive layer is necessary in order to ensure a professional application. For the SWS Inside Standard, Soudafoil 330D can be used, but we recommend to use Soudafoil 360 H for both SWs Inside Standard as SWS Outside Standard tapes. Soudafoil 360H is a bit stronger and will also adhere to slightly moist surfaces.
You get condensation whenever damp air comes into contact with a cold surface. Just think of the windows in a kitchen when the extractor fan is not switched on, or the mirror in the bathroom after a shower. The best-known example is the condensation on a glass of cold water. Moisture that is not extracted remains in building materials and then causes mould to grow. Condensation can only be avoided by having good continuous insulation and possibly also good ventilation (you do not find any condensation on a thermos flask containing a cold drink).
Particularly when applying the SWS Inside Tape you must ensure that the printed text can be read 'normally'. The tape is in fact provided with a special coating on one side to provide perfect adhesion for plastering.