How to install frameless windows into an insulation system

When installing windows, particularly windows with no visible fixed frame such as Velfac windows, it's really important to get the detailing correct. Few manufacturers seem to offer details for awkward junctions such as sill corners which can lead to poor or leaking installations.

We regularly get asked how to detail windows when installing our insulation systems so we’ve put together some key points to bare in mind when doing so.

  • Windows without any fixed frame to finish the render system against, require more planning than a standard casement window. We usually recommend lining the head and sides of the reveal with our 20mm wood fibre reveal boards and covering the area from the front of the reveal to the inner face of the window. These boards need to be glued in place with UdiSPECIAL adhesive if in timber frame or UdiFOUNDATION COAT if in masonry.
  • For the sill we recommend using one of the UdiALU window sill options. The simple reason for this is that very few manufacturers consider what happens at the end of the sill, where it meets the reveals and how that junction is made water tight.
  • The UdiALU sills have great end caps that allow neat and weathertight finishing of the render system along with an effective method of preventing water from penetrating sideways into the walls, as you can see here. The sills come in all RAL colours so will match the colour chosen for the exterior of the windows.
  • The reveals must be rendered with UdiFOUNDATION COAT render before the windows are installed. Follow the standard procedure as per our online videos with the exception of using the UdiREINFORCEMENT window edging strip. This bead can be swapped for a 6mm stop bead and placed in line with the inner edge of the reveal to give a neat edge to finish the render against. The finish should be smooth and without pits to allow effective sealing between the window frame and the render.
  • The UdiPERL finish coat should not be used where any of the sealant materials will be used. This can be achieved by simply applying masking tape to the area that will be covered by the window and removing it prior to installing the window. The surface it creates is difficult to seal against and can, under driving rain and strong winds, allow rain to penetrate around the frame.

    Do bare in mind that these suggestions should be used in addition to the manufacturers recommended details and that every situation is slightly different so not all points made may apply.

    If you’re trying to install Velfac’s frameless windows with an insulation system and would like to discuss your project with us, please call on 01392 861763.

    Chris Brookman
    Chris Brookman

    Author