How to compare double glazing quotes line by line

Why quotes that look similar are rarely the same job

A homeowner comparing two or three quotes can find them hard to line up. One is a single page with a total. Another runs to four pages and lists every window. A third mentions argon, Low-E and a brand name but says nothing about what happens to the old frames. The totals can be far apart, and it is tempting to decide on the number alone.

The problem is that a double glazing quote bundles several decisions that each carry their own cost. Which openings are included. Whether the existing frames stay and take new sealed units, or come out entirely. Which frame system and glass make-up are used. What happens to the plaster, architraves and cladding around each opening once the work is done. Who takes the old material away. When those decisions differ between quotes, the totals are not comparable, even when the headline wording sounds identical.

The fix is not more quotes. It is one written description of your house that every quoter prices against, followed by a line-by-line check of what each quote includes and leaves out. Keep the schedule with your quotes and update it when a supplier clarifies an item. That gives you a consistent basis for checking the totals.

Build an opening schedule before anyone quotes

An opening schedule is a numbered list of every window and glazed door you want included. Give each one a short ID that you write on a sticky note in the room, such as K1 for the kitchen window or L2 for the second living room opening. Then record, for each opening:

• the room, and which side of the house it faces
• an approximate width and height, taken inside from reveal to reveal
• how it opens today, for example fixed, sliding, awning or hinged
• whether it is ground level or upstairs, and how easy it is to reach from outside
• anything you already know you want changed, such as obscure glass in a bathroom or a different opening style

Your measurements do not need to be exact. The quoter will measure properly, and the final sizes on the order should come from their measure, not yours. The point of the schedule is that everyone is talking about the same fourteen openings, not twelve in one quote and fifteen in another because someone counted a sidelight as part of a door.

Hand the same schedule to each business and ask them to quote using your IDs. Most will do it, because it makes their job easier too. When the quotes come back, you can put them side by side in a simple table with one row per opening and one column per quote. Gaps show up immediately: a missing laundry window, a door priced as glass only, a bedroom window priced at a size that does not match anything in the house.

If you only want part of the house done now, say so in the schedule and list the rest as future openings. A quoter who knows which windows come later can advise on keeping the product consistent, which matters if you plan to finish the house in stages. We cover that in the guide to replacing windows in stages without a mismatch.

Match the product, not the adjectives

Words like premium, high performance, energy efficient and commercial grade do not describe a product. What you need on each quote is the frame material and system, the glass make-up and the hardware. The frame system is usually a named range from a manufacturer or fabricator. The glass make-up is written as layers from outside to inside, such as a pane, a cavity with its gas fill, and a second pane, with any coatings or laminates noted.

Once you have those details, two things become possible. First, you can see whether the quotes are for comparable products or whether one has quietly substituted a lighter frame or a simpler glass unit. Second, you can ask each supplier for the rated whole-window performance of that configuration. The Window Energy Rating Scheme publishes ratings that account for the frame and glass together, and the government's Your Home glazing guide suggests checking that declared values follow Australian Fenestration Rating Council procedures. Our guide to reading window energy ratings explains how to match a rating to the exact product on your quote.

Hardware deserves its own line. Handles, locks, winders and sliding rollers vary widely, and a quote that lists glass in detail but says nothing about how each window opens leaves room for surprises at handover. If a quote changes the opening style of a window from what you have now, that should be written down too, because it affects screens, furniture and how you ventilate the room. The guide to choosing opening styles covers those trade-offs.

Safety glass is another line to look for. Certain locations, such as doors, low panes and glass near bathtubs or stairs, commonly need a safety glass product. Rather than trying to work out the rules yourself, ask each quoter to identify which openings they have priced with safety glass and why. If one quote marks five openings and another marks none, that is a question worth asking before you sign.

Retrofit, reglaze or replacement changes the whole quote

Three quite different kinds of work are sold under the double glazing label. A retrofit keeps your existing frames and fits new double glazed units into them, sometimes with modified sashes or adaptors. A reglaze replaces the glass in a frame that already takes a sealed unit. A full replacement removes the old frame entirely and installs a new window.

Each carries different risks and different follow-on work. Replacement involves the most disturbance to plaster, architraves and external cladding, so making good becomes a larger part of the price. Retrofit leaves more of the house untouched but depends heavily on the condition of the existing frames, and not every frame is suitable. When one quote is for retrofit and another is for replacement, you are comparing different outcomes, not just different prices.

Ask each quoter to state the method opening by opening. It is common for a sensible quote to mix methods, for example retrofitting sound aluminium windows while replacing a rotted timber door frame. What you want to avoid is a quote that assumes retrofit everywhere without anyone having checked whether the frames can take it. The retrofit service page describes what we look at when deciding whether a frame can stay.

Removal, disposal and making good

This is where many totals quietly diverge. Removing a window leaves work on both sides of the wall. Inside, architraves may need to come off and go back on, plaster returns can be damaged, and fresh sealant and paint are usually needed. Outside, flashings, weather seals and the cladding or render around the frame need attention. Then the old frames and glass have to go somewhere.

A quote should say, for each of these, whether it is included, excluded or left to you. Watch for vague phrases such as standard finish or minor making good. Ask what those words mean on your house. Does the price include painting the new architraves, or only fixing them in place? Does it include patching render, or only sealing the gap? If the old windows are timber with painted surfaces, ask how the removal will be handled and who is responsible if paint or trim is damaged.

On older houses, the materials around a window are not always what they seem. Some eaves linings, cladding sheets and window packers in houses of a certain age can contain asbestos. You should not try to test or disturb suspect material yourself. Ask each quoter how they identify and deal with it if it turns up, and whether any removal would be done by a licensed removalist. The Victorian Government's asbestos guidance for home renovators is the place to start if you are unsure.

The budget double glazing guide lists the lines most often left off low quotes. Rather than repeat that list here, the practical point is to ask every quoter to answer the same finishing questions in writing, so a missing line is obvious rather than discovered on installation day.

Provisional sums, allowances and conditions nobody can see yet

Some things genuinely cannot be known until a window is out. A sill might be softer than it looked. A frame might be fixed with more packing than expected. An opening might be further out of square than the measure suggested. A fair quote handles this openly, usually with a provisional sum or a described allowance, plus a statement of how any extra work will be priced and approved.

The trouble starts when provisional lines are used to make a total look lower. If one quote carries several large allowances and another carries none, the second may simply have priced more risk into the fixed figure. Neither approach is wrong, but you cannot compare them until you know how much of each quote is fixed and how much could move.

For each allowance, ask three questions. What exactly does it cover? How will the final amount be worked out? Will you be told and asked to approve before extra work starts? Write the answers next to the line. If a quoter cannot explain an allowance, that tells you something about how the job will be managed if a problem turns up halfway through.

Timing is part of the scope too. Ask when final measurement happens, how long manufacture takes after that, and what happens to the price if the measured sizes differ from the quoted ones. For bigger projects, your contract and deposit arrangements may be covered by consumer or building law, and it is worth reading the paperwork carefully or getting advice if anything is unclear.

Hypothetical example: two quotes for the same nine openings

Picture a single storey brick veneer house with nine openings: four bedroom windows, a kitchen window, a bathroom window, two living room windows and a sliding door to the backyard. The owner hands both quoters the same schedule with IDs B1 to B4, K1, BA1, L1, L2 and SD1.

Quote A lists all nine openings, each marked as full replacement in a named aluminium range, with the same glass make-up throughout except the bathroom, where obscure glass is specified, and the sliding door, where safety glass is noted. It includes removal and disposal, internal architraves refitted and painted, and external sealing. It carries one provisional sum for sill repairs, described in a sentence.

Quote B is noticeably lower. On closer reading it lists eight openings, because the sliding door is marked as a separate quote to follow. It describes the glass only as double glazed Low-E, names no frame range, excludes painting and says disposal is available at extra cost. It has no provisional sums.

Before comparing totals, the owner asks Quote B for the door price, the frame range and glass make-up, and prices for disposal and painting. Once those come back, the two quotes describe the same job, and the owner can compare them fairly. The lower headline number may still win, or it may not. Either way the decision is based on the same scope.

The same method works in reverse. If the higher quote includes things you do not need, such as painting you plan to do yourself, ask for those lines to be removed rather than assuming the business is expensive.

Questions to send back to every quoter

Once you have filled in your comparison table, send each business the same short list of follow-up questions. Keep them specific to your house. Useful ones include: which openings are retrofit and which are replacement, what frame range and glass make-up each opening uses, which openings have safety glass and why, what is included in making good inside and out, whether removal and disposal are included, what each provisional line covers, and when final measurement happens.

Ask for the answers in writing, ideally as a revised quote. A business that updates its quote to answer clear questions is showing you how it will communicate during the job. When the revised quotes arrive, update your table and compare again. At that point the differences you see are real differences in product, method or price, and you can weigh them properly.