How to replace glass in a window

If you’re dealing with a broken or cracked window pane, knowing your way around window glass replacement can save time and money. 

In the case of single glazing, it’s possible to just replace the glass of your windows and not the entire frame, which you may want to do if your frames are relatively new or don’t otherwise warrant replacement. 

Here’s how to replace your window glazing.

You can usually replace just the broken or damaged pane for single-glazed windows in timber frames. The process is fairly simple when dealing with a like-for-like swap in the case of a cracked or broken pane.

You can also sometimes upgrade to double- or triple-glazed panes if the existing frame can handle the dimensions of the new unit, although this will vary on a case-by-case basis and require advanced woodworking skills, or professional help. 

If your window is double– or triple-glazed, you’ll generally have to replace the entire unit (the entire assembly of glass, frame and sealant). uPVC windows also aren’t suitable for DIY replacement panes.

Essential equipment for replacing window glass

Before replacing your window, you need to have the right tools for the job. 

Here’s what you should consider obtaining before changing a window:

• Safety gloves: Broken glass can be extremely sharp and cause deep cuts if handled without gloves. Choose thick, cut-resistant gloves that offer both flexibility and protection
• Safety goggles: Shards of glass or other particles can easily fly into your eyes, so safety goggles are a non-negotiable item
• Tape measure: Taking precise measurements is crucial to ensure the new glass fits perfectly within your window frame
• Putty knife: This is a versatile tool that you’ll use to remove old putty, scrape away debris and smooth new putty into place
• Glass cutter: If you need to cut glass yourself, get a glass cutter that has a comfortable grip and a tungsten carbide cutting wheel
• Linseed oil putty: This type of putty is ideal for setting new glass into a window frame. It’s easier to work with than some other types and offers good adhesion
• Glass pane: Your new piece of glass should match the thickness and type of the old glass (eg tempered or insulated). It’s worth purchasing more than you need in case of mistakes
• Metal glazier’s points: These small metal pieces are invaluable for securing the glass pane to the frame
• Paintbrush: This is used to clean the window frame and apply linseed oil to the new putty, aiding in adhesion and providing a neat finish
• Caulking gun: To fill gaps or seal the window, you’ll need a caulking gun and appropriate window caulk
• Window cleaner: A good window-cleaning product will remove any streaks or smears and leave your newly installed glass clear and sparkling

Step 1: Remove the broken or old glass

The following four steps are for single-glazed windows. The first step is to remove the existing glass from the frame.

1. Secure the area: Lay down a tarp or a thick dust sheet underneath the work area. This will accelerate clean-up later and protect your floors from shards of glass
2. Wear protective gear: It’s crucial to wear safety goggles to protect your eyes from splinters and heavy-duty gloves to protect your hands
3. Remove large shards: Carefully pick out the larger pieces of broken glass one by one, gripping them at the end farthest away from the break. Place these immediately in a dedicated disposal box
4. Remove small shards: If you encounter shards that won’t budge, use your putty knife to gently pry them loose. For extra-stubborn pieces, gently tap the end of the putty knife with a hammer

Step 2: Clear out the old putty and glazing

Window putty is a flexible adhesive that forms an airtight seal around windows. You’ll need to remove any old putty from around the frame. 

1. Scrape out old putty: Use the putty knife to scrape away old putty. Hold the knife at a 45-degree angle and apply even pressure as you go along the frame
2. Remove stubborn putty: If the old putty doesn’t come off easily, you can use a heat gun to soften it. Hold the heat gun about 15-20cm away from the surface and move it along the putty in a slow, even motion. This makes it easier to remove the old material without damaging the wood

Step 3: Measure and prepare the window frame

It’s now time to prepare the new glass to fit into the frame. 

1. Measure the frame: Use your tape measure to ascertain the height, width and depth of the window aperture
2. Record the measurements: Jot down these dimensions; you’ll need them to ensure the new pane is cut to size. Most glass shops will cut a pane based on your given dimensions. It’s typically recommended to downsize the pane to 3mm smaller than the window aperture on each side to allow for fitting
3. Clean the frame: Use a wire brush to remove any loose debris from the frame. After brushing, use a damp cloth to wipe down the surface
4. Repair the frame: Use sandpaper to smoothen any rough areas. If the frame has holes or cracks, use wood filler to repair them

Step 4: Apply new putty and install the new glass pane

Finally, you can lay the new pane in the frame and seal it with putty and caulk sealant. 

1. Prepare the new putty: Knead the linseed oil putty in your hands until it’s soft and malleable
2. Apply the putty: With your hands, shape the putty into long rolls and then press these onto the ledge of the window frame. Use your putty knife to make it a uniform 3mm layer
3. Install the glass: Lift the new glass pane carefully and set it into the window frame against the bed of putty you’ve just laid. Press lightly to adhere the glass to the putty
4. Secure the glass: Use glazier’s points to secure the glass into the frame. Place these at 10-15cm intervals along the sides of the pane. Use your putty knife or a dedicated point driver to push these into the wood
5. Seal the edges: Roll more putty into thin ropes and press these into the frame over the glass, thereby covering the glazier’s points. This also helps fill any remaining gaps between the glass and the wood
6. Smooth out the putty: Use your putty knife to smooth it out. You can also apply a layer of linseed oil over the putty to help it set and provide a clean finish

Replacing double- or triple-glazed window units is a slightly different process to swapping out single-glazed panes. It is generally accepted that replacing double- or triple-glazed windows is best left to a professional, ideally one with FENSA accreditation. 

Again, always wear gloves and protective eyewear, and take the appropriate steps to secure the area around the window.

Start by measuring the dimensions of the existing pane to ensure you order the correct size for the replacement. You can usually find these measurements by removing the window trim or beading that holds the glass unit in place. 

Once you have the replacement unit, you’re ready to begin the installation process.

1. Carefully remove the window trim or beading: Retain any screws or fasteners and use a utility knife to remove caulk or sealant around the existing glass unit
2. Remove the pane: Gently pry out the old double-glazed window with a chisel or a similar tool. It might be heavy, so you may benefit from having an extra pair of hands to help lift it
3. Clean the window frame thoroughly: Remove any old caulk or adhesive. Dry fit the new double-glazed unit to ensure it fits snugly into the frame before taking out again
4. Prepare the frame: Apply a bead of silicone caulk or a glazing compound around the frame’s edges, then place the new unit into the frame
5. Secure into place: Reattach the window trim or beading. If you’re using sealant, apply it around the edges for extra weatherproofing. Finally, wipe away any excess caulk or sealant and clean the glass
6. Test the window: Allow the sealant to dry according to the manufacturer’s instructions. Once it’s dry, test the window to make sure it opens and closes smoothly

While swapping out window panes to repair or upgrade windows is possible to do yourself without prior experience, it can be a trickier job than you might expect. Professional installation ensures a neat, airtight finish. 

Let’s take a closer look at the pros and cons of replacing glass yourself or hiring a professional. 

Pros of DIY glass window repair

• Cost-effective: One of the most compelling reasons to do the job yourself is to save money. Professional labour costs can add up quickly, especially if the job becomes more complex than initially thought. Depending on the hourly rate and the time taken, you could save up to £500
• Provides an immediate solution: DIY glass window replacement means there’s no need to wait for a professional to fit you into their schedule, which could be vital if you’ve got a gaping hole in your window and it’s winter. If the glass breaks at an inconvenient time, you can replace it immediately
• Gives you personalised choices: When you handle the job yourself, you get to pick every material, including the type of glass and the quality of the putty, ensuring that everything meets your specific standards

Cons of DIY glass window repair

• Higher risk of injury: Window glass repair is inherently risky. Even with safety gear, such as gloves and goggles, accidents can happen. A slip of the hand can lead to deep cuts that need medical attention
• Greater potential for mistakes: Unless you’re experienced, there’s always a risk of making errors, such as mismeasuring or improperly installing the pane. These mistakes can be costly in terms of time and material waste. They can also compromise the insulation and security of your home
• Time-consuming: A task that a professional can complete in a couple of hours might take you an entire weekend or longer
• Lack of warranty: When you perform a DIY job, there’s no warranty on the labour. If something goes wrong, the onus is on you to fix it, which can lead to additional time and expense

How much does replacing glass windows cost, both in terms of materials if you’re carrying out the replacement yourself and labour for professional installation? 

Cost of glass

• Standard glass panes: The costs of replacement glass for windows can vary depending on the size and quality of the glass, but for a typical window, you can expect to pay £20 to £40 for a single-glazed pane
• Tempered glass: This is stronger and safer than regular glass but can cost you between £50 and £100 per pane, depending on size and thickness
• Double- or triple-glazed glass: Double- or triple-glazed window replacement glass starts at around £100 and extends up to £300 or more, depending on specifications

Cost of equipment and materials

• Linseed oil putty: Expect to pay between £2-£10 depending on the quantity and brand
• Metal glazier’s points: These usually come in packs and can cost around £5 per pack
• Safety gear: Quality gloves and goggles can cost you in the region of £30 to £40
• Additional tools: Items such as a putty knife, glass cutter and measuring tape might already be in your toolbox. If not, plan to spend at least £20 to £50 for these basic tools

Labour costs for professional installation

While DIY replacement saves labour costs, hiring a professional can offer peace of mind and a guaranteed quality finish. 

Depending on the job’s complexity, you can expect to pay a tradesperson anywhere from £100 to £500 for their labour, which may or may not include the cost of materials. 

Simple single-glazing jobs come in at the lower end of the spectrum. In some cases, a very simple job, such as replacing a small single-glazed pane, will cost £50 or so and will be about an hour’s work. 

Additional costs

Here are some additional costs to keep in mind:

• Window frame repair: If your window frame also needs some attention, this will add to your overall cost. Repairs could cost between £50 and £200, depending on the extent of the damage
• Consultation fees: Some companies charge a consultation fee, especially if they provide custom solutions, such as upgrading double-glazed units to triple-glazed ones. These fees can range from £30 to £100
• Warranty or insurance: Some professional services offer optional warranties or insurance coverage, which might add £20 to £50 to your bill

Given the complexity and the risks involved in replacing glass, hiring a professional for window glass replacement might be the best route for most people. 

Professional installation ensures a good-quality, airtight fit that provides security, insulation and longevity. 

If you’re replacing double-glazing, consider upgrading to triple-glazed units. These offer superb energy insulation and aren’t vastly more expensive than double-glazed units.