DIY double glazing

DIY double glazing is possible if you’re a confident DIYer: you can buy made-to-measure windows supply-only and fit them yourself. However, you still have to meet Building Regulations, which means applying to building control before you start and paying for an inspection, and you lose the installer’s guarantee on the fitting. For most houses, the saving is smaller than it looks.

What DIY double glazing involves

There are three quite different jobs that people call DIY double glazing:

• Fitting replacement windows yourself, bought supply-only from a manufacturer or merchant.
• Replacing a misted sealed unit in an existing frame, which is the easiest of the three.
• Fitting secondary glazing inside existing windows, popular in rented flats and older houses.

Each has its own skills and risks, covered below.

The rules still apply to DIY double glazing

Replacing a window is building work, so it must meet the same double glazing regulations as a professional job: the energy standard of 1.4 W/m²K, safety glass in doors and low panes, fire-escape openings in upstairs bedrooms, and ventilation at least as good as before.

A registered installer certifies all of that. When you do it yourself, you have to apply to your council’s building control, or a registered building control approver, before you start. They inspect the work and issue a completion certificate, and you pay their fee. Without that certificate, you’ll have a problem when you sell; see FENSA and CERTASS.

The rules on planning permission for windows apply too, so check before changing the look of a listed house or one in a conservation area.

Fitting a replacement window step by step

This is an outline, not a substitute for the manufacturer’s fitting instructions.

1. Measure the opening accurately. Measure the brick-to-brick width and height at several points, and order the frame slightly smaller to allow for packing and sealing. An error here means a window that doesn’t fit, and made-to-measure windows can’t be returned.
2. Check the lintel and sill. The window doesn’t hold up the wall. If the lintel above is cracked or missing, that’s a structural job first.
3. Remove the old window. Take out the sashes and glass first, then cut through the frame and lever it out. Wear gloves and eye protection; old glass breaks unpredictably.
4. Fit the new frame. Set it on packers so it is level, square and plumb, and fix it to the wall at the intervals the manufacturer gives. A frame that’s out of square won’t open and close properly.
5. Glaze and adjust. Fit the sealed units on glazing packers so the weight sits on the frame, then fit the beads and adjust the hinges.
6. Seal and finish. Fill the gap with expanding foam, then seal inside and out. Fit the cill and trims, and make good the reveals.

Tools and materials for DIY double glazing

Beyond the windows themselves, budget for the things an installer brings with them:

• a multi-tool or reciprocating saw to cut out the old frame, and a pry bar;
• a long spirit level and a tape measure you trust;
• frame fixings, glazing packers and frame packers in several thicknesses;
• low-expansion foam for windows, and a neutral-cure silicone with a decent gun;
• cills, trims and plaster or filler for the reveals;
• dust sheets, gloves, eye protection, and a way to get rid of the old frames and glass.

If you don’t already own most of these, the cost adds up quickly, which is part of why a fitted job is better value than it first looks.

The risks

• Measuring mistakes are expensive, because the windows are made to order.
• Bay windows often carry the weight of the roof or wall above. Taking one out without propping it is dangerous; leave bay windows to a professional.
• Heights. Upstairs windows need a safe working platform, which usually means a tower or scaffolding.
• The guarantee. The manufacturer guarantees the window, but nobody guarantees your fitting. If it leaks, that’s your problem.
• Glass weight. Large double and triple glazed units are heavy, and two people are the minimum to lift them safely.

Is DIY double glazing cheaper?

Supply-only windows cost much less than a fitted job, so on paper the saving is large. However, fitting is only part of an installer’s price. Once you add building control fees, tools and hire, waste disposal, a tower for upstairs windows, and your own time, the gap narrows. Meanwhile, a registered installer handles certification and gives a guarantee on the whole job.

For comparison, a typical three-bedroom semi in uPVC windows costs £5,000 fitted, including VAT, and a single sash window costs about £900. Get a fitted quote before deciding: our quote checker shows whether it’s reasonable.

The easier DIY jobs

Replacing a misted sealed unit

If the frame is sound, swapping a misted unit is the most realistic DIY glazing job. Measure the glass, order a unit to the same specification, then remove the beads, swap the unit and refit them. Toughened glass is required in doors and low panes. A glazier typically charges £90 per unit fitted, so the saving is modest; see misted double glazing.

Fitting secondary glazing

Secondary glazing kits fix inside the existing reveal and need no change to the window itself. It’s well within most DIYers’ skills, reversible, and usually acceptable in listed buildings. A professionally made and fitted panel typically costs £280; see secondary glazing.

Maintenance

Oiling hinges, clearing drainage holes and resealing round the frame are all straightforward DIY jobs that extend the life of your windows; see window maintenance.

When to call an installer

Use a registered installer if you’re replacing more than a couple of windows, any window above the ground floor, a bay, or a door that needs a level threshold. In addition, use one if you’re selling soon and want the paperwork simple. The Planning Portal explains the building control route if you decide to go ahead yourself. Otherwise, get quotes from local FENSA and CERTASS installers and compare them with the cost of doing it yourself.