DIY: secondary glazing

Acrylic secondary glazing

For some windows, replacing them with double glazing is not a possibility. In this case acrylic secondary glazing may offer the solution. Acrylic sheets can protect an existing window and offer sound and thermal insulation. Acrylic sheets are easy to order and even easier to work with, making them ideal as secondary glazing for windows with complex forms like round of arch shaped. You can easily make permanent or temporary secondary glazing using an acrylic sheet. In this article we provide you with handy tips and tricks to get the job done.

Extruded or cast acrylic secondary glazing?

An acrylic secondary window is an affordable solution if you want the advantages of double glazing, without actually replacing the whole window. This is often the case with old stained-glass windows, windows with an unusual shape or large window areas. Acrylic, also known by trade names Plexiglas® or Perspex®, is available in a wide range of thicknesses, colours and prices. There are two types of acrylic, namely extruded ‘cheap’ acrylic and cast acrylic. Extruded acrylic is cheaper than cast acrylic because of its production process. During this process, more acrylic sheets result from the same amount of raw material. However, the rolling process increases the internal tensions of the acrylic sheets, leaving them more prone to breaking that cast acrylic. Cast acrylic is poured into a mould during production, creating a sheet with almost no internal tensions. Therefore, we recommend choosing a cast acrylic sheet when you are planning on making your own secondary glazing.

For secondary glazing the most common choice is clear acrylic. Other shades or finishes, like frost or tinted acrylic, are useful for creating a sunblock or a privacy screen. Acrylic can easily be ordered in our online shop, we cut the sheets to size free of charge and have your order ready for shipment within 48 hours. We recommend using a sheet that is at least 4 millimetres thick. Keep in mind that acrylic can expand due to temperature fluctuation. If you are planning on placing the secondary glazing inside the window frame, order a sheet that is 5 mm less wide and 5 mm less high. With the right instalment method, the sheet will stay securely in its spot and have the necessary room to expand.

Highlighted products for this DIY-project

Cutting acrylic to size for secondary glazing cuts sheets to size in square or rectangle shapes, for different window shapes you can cut the acrylic sheet to size yourself. With a quality jigsaw and the proper preparations, sawing acrylic sheets can be achieved by anybody. Keep the protective film on both sides of the sheet and use masking tape and a pencil to draw out the cutting line. Use a fine cut sawing blade, preferably a blade that is suited for non-ferrous metals. Support the sheet as close as possible to the cutting line during the sawing process, if possible at a distance of less than 2 cm. Straight lines can be cut by following a straight bar that is attached to the sheet with clamps, this bar will help guide the jigsaw in a solid line. Start up the saw before applying it to the sheet, work at medium-high speed of ca. 75% and let the saw glide through the material. You will only need to apply a light amount of pressure.

Installing secondary glazing

There are two ways you can install secondary glazing to a window: on the inside of the window frame or against the window frame. Placement against the window frame makes (dis)mounting the window easier, making it ideal for temporary and seasonal purposes. Instalment on the inside of the window frame requires glazing beads with foam tape to deal with the expansion due to temperature fluctuation.

Placing the secondary glazing against the window frame requires a screw connection. Therefore, you must drill holes in the acrylic sheet, using a regular metal drill. Start by drawing the placement of the holes on a piece of masking tape. The holes cannot be placed too close to the edge of the sheet, it is important to keep a distance of at least 2.5 times the sheet thickness. Use a drill that is 1 mm bigger than the diameter of the screws, this will prevent the sheet from tearing near the screws when it expands in warm weather. For the same reason, it is also important not to turn the screws too tightly. For better insulation you can seal off the secondary glazing by placing foamtape on the window frame underneath the sheet.