How to install frameless windows into an insulation system.

Find out more about how we approach this building scenario.

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 these windows when installing our insulation systems so we’ve put together the following guide to doing so.

Step 1

Whether on masonry or timber frame, cut the wood fibre boards on the front face of the wall flush with the window opening and install the Ampacoll SillSkin layer along the sill and at least 50mm up each side of the opening and 50mm down the front of the wood fibre boards, as drawn.

Step 2

Install the reveal boards to the head and sides of the reveal but instead of finishing the reveal board flush with the front of the window, extend it further back to around 20mm from the inner face of the window frame. This allows enough of a smooth rendered surface to be exposed so that the window can seal against the surface.

Once glued in place, fit a 6mm stop bead to the surface of the reveal boards to create a neat edge to finish the render base coat against. The surfaces of the SillSkin should be covered with Ampacoll Fenax tape to enable the render to bond adequately.

Step 3

The render base coat can be applied and taken into the reveals, right up to the stop bead. This should be trowelled smooth within the reveals so that a weather-tight seal can be created.

Before applying the finish coat, apply masking tape to the reveal where the window will sit and seal against the rendered surface. This will create a neat edge for the finish coat and prevent it interfering with the sealing down the sides of the window frame, leaving the bare base coat render as per the model above.

Step 4

The window and sill can be installed once the render is cured. The perimeter of the window frame is typically sealed with 60mm wide Ampacoll Komprimax joint sealing tape. The ends of the sills must have a vertical upstanding to support them and enable them to be sealed against the surface of the render. This should be done using polyurethane sealant and regularly checked to ensure that they do not leak.

Great care and attention must be paid to the junction between the ends of the sills and the rendered surface to ensure that no water can leak down the sides.

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 frameless windows with an insulation system and would like to discuss your project with us, please call on 01392 861763.