Wednesday 19 January 2022

Installation of windows

Improper installation of windows – underestimated source of heat loss

Thermographic image of a flat-building before the reconstruction – heat losses due to bad joints sealing





Thermographic image of a flat-building after the insulation and replacement of windows using three-part window sealing system




Reducing heat losses and energy consumption is a purpose of each customer when purchasing new window. In its selection, an important role plays technical parameters of the window (heat transfer coefficient) and an overall appearance. The installation of the window and a detail of the connection to walling tend to be much less important.

Non-professional installation can reduce good technical parameters of high-quality window and it happens quite regularly that thermal and acoustic insulation features of the window aren’t the same at the assembly as features of the window facing. By purchasing of the window, the customer actually gets quality window facing seal. The customer wants to get back the investment in insulation glass with rare gases and five or six chamber profiles by saving the cost of heating or cooling.

The quality of window is significantly influenced by the solution in contact with the walling. The detail of the window embedding in the opening must transmit the load of the window into outer walling by anchors, balance motions of various construction materials and compensate asperities of the construction opening. Heat escapes through the improperly made connection joint of the window, return of the investment is prolonged and user window features are worsened (condensation, mold making, blowing under window board).
Connection joint of the window to the outer walling should achieve:

  • at least the same heat transfer coefficient as the window
  • at least the same air soundproofing as the window
  • zero permeability on the interior side of the window
  • elimination of water vapour condensation, which prevents mold
  • weather resistance
  • dilatation ability to various construction materials

Classic window installation using polyurethane foam as thermal and acoustic insulation and additional coating applying no longer meets the current requirements for the connecting joint. The excess foam must be cut off after hardening. Consequently, the structure of the foam is opened and it starts sucking humidity. When humidity is saturated up to 5% of the foam volume, thermal insulating capability of the foam decreases by 50%. This results in a shift of isotherm 13 °C (temperature of mold creation) to the interior. In winter season and when ventilation is inadequate, this causes mold creation. Another problem is that the polyurethane foam after application to connection joint isn’t protected from UV radiation and it leads to its rapid degradation. Hidden problem arises by prolonged exposure of the frame dilatation, when polyurethane foam isn’t able to compensate frame motions and it tears from the bedding. Thus damaged foam no longer meets the basic technical requirements of connecting joints. The three-part system of window strips can meet these requirements in a long term. Particular components of this system perform different functions. The outer permeable seal protects from weather exposures and it also ventilates connecting joint to prevent condensation of water vapour and mold creation. The central sealing serves as thermal and acoustic insulation. Internal paro-impermeable sealing separates the inner climate from the outside one and it also protects the central sealing from humidity from the interior. This system provides the required parameters of the connecting joint according to the motto ‘tighter inside than outside’. The customer has an option of choosing the window from various suppliers who are able to mount it according to new requirements to the connecting joint. The question of the customer about the assembly should be one of the fundamental to be asked. Nonuse of complex materials at assembly (three-part system of window strips) could cause many problems in the future. After all, the window isn’t bought for one season…

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