The free diy home improvement guide with answers to your questions on a wide range of do it yourself projects.


DIY Double Glazing

person standing at a windowWe are all familiar with the double glazing salesman who comes knocking at the door and while we hate to give in to their sales talk, the thought of doing the job yourself might seem just a little bit daunting.

Chances are you will pay over the odds for your windows, despite their very “generous” two for one offers, so it is worth investing a little time to investigate whether you could do this job yourself.

There are two types of double glazing – the sealed unit, which needs to be fitted into the window opening. Or the secondary glazing unit which can be fitted over the existing window.

Obviously the second type is the easier of the two, but if you have reasonable DIY skills and a “can do” attitude then consider the first option too.

Secondary Glazing

  • The usual way of fitting secondary glazing is by fitting it to either the window frame itself or to a timber framework within the window frame.
  • The ideal width between the original glass and the new glass should be around 20mm, making the first option more efficient.
  • You don't have to use glass as clear plastic sheeting or even plastic film will also work well.

Take care when placing a rigid material such as plastic or glass in front of a window opening and not attached to the window casement, as it will prevent the window from opening.

Demountable Glazing – These are set within the window casement and fixed to the existing window with clear tape or magnetic catches. These allow you to remove the secondary sheet of glass or plastic should you need to use the window. Or even to remove it in the summer.

Open able Glazing – These secondary glazing units are often fitted into sliding tracks and attached to the window frame. In some cases, the window may be hinged to allow opening. The sheet of glass is edged in draught strips to keep the heat in once closed. These units are often sold in kit form and are easy to install.

Double Glazing

  • Measure your opening carefully (although many windows are now fairly standard when it comes to size) and either order your units from a double glazing saleroom or try a DIY store.
  • Remove your old window as carefully as possible, taking care not to ruin the surrounding brick work. Measure the opening once again to ensure you have the correct sized windows. Some gaps are inevitable however.
  • Check the integrity of any damp courses or insulation before continuing.
  • The frame will arrive separate to the sill and will need to be installed separately. The sill is likely to need cutting to size on site.
  • Attach the sill to the outside using mastic sealant, apply a bead of silicone to the top of the sill along the back edge and rest the frame on top of that. Do not seal the gap between the sill and the frame; it is required for drainage.
  • Square up the frame using spacers and drill through the frame and into the wall. Countersink the hole and fix with screws and plugs. Ensure the screw is not positioned so it might interfere with the opening of the window.
  • Offer up the glass unit and push back into the rebate, add 2mm glass packers to square it up. Add the glazing beads, doing the top then the bottom then the sides.
  • Run a bead of silicone between the masonry and the frame, repeat on the inside.

This advice is very simple and does not replace doing your own research, but it does show that it is a job which most people can tackle and you will save a lot of money by giving it a go.