Window Replacement for Renovators: How to Get the Right Fit Without Blowing the Budget

If you’re planning a full home renovation, replacing old windows isn’t optional—it’s essential. And for anyone looking at replacement windows in Perth, knowing whether to choose stock or custom sizing can save you thousands.

The truth is, not all homes are built to suit today’s standard window sizes. What seems like a small decision can quickly turn into a major cost if the windows don’t fit and walls need to be reworked. Choosing the right fit from the start avoids unnecessary construction, gives a better finish, and can improve insulation, energy use, and comfort.

In this guide, we’ll walk you through making the smart call between stock and custom sizing, spotting sizing issues early, and what really affects your window replacement cost. Whether you’re after aluminium replacement windows or tailored solutions, Ross’s Discount Home Centre offers hundreds of stock sizes and custom options by Jason Windows—backed by a 10-year warranty and six modern frame colours.

Why Standard Window Sizes Often Don’t Fit Older Homes

If you’re renovating an older home, don’t assume modern standard window sizes will slide right into your existing openings. One of the most common (and expensive) mistakes we see is homeowners ordering stock windows too early—only to find out the openings don’t match up.

Before you get to the fun part of picking frame colours or styles, it’s worth understanding how window sizing has changed over the years, and why today’s standard options don’t always work with older properties. A little knowledge upfront can save serious time, mess, and money.

What “Standard Window Sizes” Really Means

In today’s construction, standard window sizes are used to simplify building and reduce costs. These standardised dimensions suit new builds where framing and wall openings are designed to match readily available products. It speeds up installation and makes planning easier for builders.

At Ross’s, we stock a wide range of aluminium replacement windows in typical sizes for sliding, awning, double hung, and fixed configurations. This covers the majority of modern homes and extensions in Perth and the surrounding areas.

But these sizes are only “standard” in relatively new homes. Older builds—especially those pre-1980s—often don’t align with today’s sizing conventions.

Why Older Homes Don’t Match

Many Perth homes were built long before modern sizing and framing standards were introduced. Builders often worked to what fit the space, not to any formal code. As a result, older homes tend to have non-standard window openings—which means today’s stock sizes may be too small, too large, or simply not line up properly with the existing wall opening.

We also see:

• Walls that are out of square or reveal depths that vary
• Decorative trims or deep reveals in heritage windows
• Openings that have shifted over time due to settling or previous renovations
• Inconsistent sizes room to room—even on the same elevation

Trying to force a standard window into these frames often leads to frustration, costly reconstruction, and a finish that looks patched together. That’s why understanding window sizing in renovations is critical—and why custom sizing can be the smarter long-term choice.

How to Spot Non-Standard Window Openings

Before you decide between stock or custom replacement windows, you need to know exactly what you’re working with. Measuring up for window replacement in Perth isn’t just about height and width—especially in older homes.

Tools & Techniques

Start with the basics:

• Tape measure — check width and height at the top, middle, and bottom
• Spirit level — check that frames are plumb and reveals are level
• Diagonal measurement — measure from corner to corner to check for square
• Wall depth — deeper walls may require extended frames or wider reveal finishes

Always measure both inside and out. Brickwork, render, or old timber trims often hide variations that make a big difference when fitting a new window.

If you’re unsure how to take accurate measurements, check out our step-by-step guide on how to measure doors and windows before ordering.

What to Look For

Here’s what often sets off alarm bells when assessing for replacement windows:

• Inconsistent opening sizes between rooms (e.g. two lounge windows that look the same but measure differently)
• Out-of-square walls, which show up when the diagonals don’t match
• Irregular reveals, particularly in homes with builder modifications or extensions
• Past patch jobs—render lines, filler, or unusual trim work might indicate a previously forced fit

These are signs you might be dealing with non-standard window openings, and that forcing a stock size could mean costly rework.

The Real Cost of Making Stock Sizes Fit Your Reno

Stock windows can look cheaper on the surface—but if they don’t fit your existing openings, the hidden costs add up fast. Renovators often assume they’ll save by choosing off-the-shelf options, only to be hit with extra labour and finishing expenses that blow out the budget. I’ve seen it firsthand—one customer had to re-render their entire home just to cover patchwork around badly fitted stock windows. If they’d gone with custom sizing from the start, they could’ve saved thousands.

Typical Construction/Add-On Costs

When a window doesn’t fit the original opening, you’re not just dealing with a tight squeeze. Here’s what usually follows:

• Brick cutting or blockwork removal to make the opening wider or taller
• Reframing the reveal to suit a smaller unit
• Re-rendering or patching internal plaster
• Touch-up painting, both inside and out
• Trim or architrave adjustments to cover gaps or uneven finishes
• Builder labour – often $80–$110 an hour, just to make it all work

Suddenly, a $370 window might end up costing $700–$800 or more after installation and cleanup—without offering better performance or appearance.

When Those Costs Exceed Better Options

Here’s where renovators get caught out. Saving $100 on a stock window doesn’t help if it costs you $400 to modify the opening. The total project cost—not just the sticker price—matters most.

Let’s say a standard sliding window is $400, but needs to be cut into double brick, new trims, and internal patching. Add $400+ in labour and materials. You’re at $800 total.

Now compare that to a custom replacement window at $600 that fits cleanly into the existing opening—no cutting, no patching, no extra labour. Straight in, clean finish.

Stock can still be a great option—but only when it fits. If it doesn’t, custom often works out cheaper, faster, and far better looking in the end.

When Custom Replacement Windows Make Sense

Custom window sizing isn’t just for architectural homes or niche projects. In renovations—especially for older Perth homes—it is often the most practical and economical choice. Knowing when to opt for custom replacement windows can save you days of extra labour and the frustration of fixing something that should have been right from the start.

Signs Custom Is Worth It

Some jobs make the decision easy. If your windows don’t match any standard sizing—or the cost of modifying walls outweighs the savings—custom is usually the smarter path.

It’s also worth considering when:

• You want to preserve heritage features without compromise
• You’re aiming for a clean, flush finish
• You’d rather avoid delays or extra labour on-site

Even with a slightly higher upfront cost, the time and effort saved can more than make up for it—especially during full-home renovations.

Advantages of Custom Sizing

Custom doesn’t just mean “made to order”—it means you get exactly what the space calls for, with none of the compromise.

• Made to fit your exact dimensions, so there’s no need to modify walls
• The result is a neater install and cleaner finish, with less patching or filler
• Better thermal and acoustic performance because gaps are eliminated
• Available in all window types—sliding, awning, double hung, fixed, and more
• Matches the rest of your home in both style and scale

At Ross’s, we offer both stock and tailored window sizes, so you can choose the option that best suits your job—not just what happens to be on the shelf. And with Jason Windows’ quality and a 10-year warranty, custom doesn’t mean compromise.

If you’re thinking about upgrading your home with sliding doors and windows, our friendly guide, ‘How to Replace Sliding Doors and Windows,’ offers simple instructions to help you through the process.

Common Mistakes to Avoid When Buying Replacement Windows

Even experienced renovators can make mistakes when replacing windows. Some of the most common errors don’t show up until installation day—or worse, when the final finish doesn’t match the rest of the build. Here’s what to be mindful of when buying replacement windows for your home.

Ordering Before Measuring

It seems obvious, but it happens more often than you’d think.

Ordering based on assumptions—or reusing old plans—can result in windows that are slightly off. And “slightly” is all it takes to throw everything out. Misfits lead to rework, wasted materials, and extra time on site. Always measure the existing openings before locking anything in.

Buying the Cheapest Without Thinking About Total Cost

It’s easy to focus on the price tag. But replacement windows cost more than just the unit itself. Labour, trims, re-rendering, and plastering can all stack up if a “cheap” window doesn’t actually fit. The cheapest option isn’t always the most economical one.

Ignoring Energy Efficiency

Not all single-pane windows are created equal. Cheap imports or older windows might use thin, low-grade glass that lacks strength or insulation performance.

At Ross’s, our aluminium replacement windows are fitted with 5mm Grade A Toughened Safety Glass—far stronger and more thermally stable than standard float glass. It’s designed to handle Australia’s extreme heat and changing temperatures, offering both safety and comfort.

You don’t always need double glazing to get good results—but you do need the right glass.

Choosing the Wrong Frame Material

Frame choice affects not just the look, but the lifespan of your windows.

• Timber windows looks great but needs constant maintenance to prevent rot, warping, and weather damage.
• uPVC windows can degrade or yellow in Australia’s UV-heavy conditions.
• Aluminium windows, such as those offered by Ross’s, offer a strong, low-maintenance alternative that withstands harsh weather.

They also come in sleek, modern frame profiles that suit both new builds and renovated homes.

Stock vs Custom Window Options — Practical Comparison

Whether you’re renovating a 1970s brick-and-tile or a classic character home, choosing between stock and custom replacement windows often comes down to time, budget, and fit.

Here’s a straightforward comparison to help guide the decision:

Feature	Stock Windows	Custom Windows
Lead Time	Usually in stock and ready for fast dispatch	Made to order – allow production time (typically 3–6 weeks)
Price Range	~$370–$3,000+ depending on size and type	Varies by spec – often higher upfront but can reduce labour and alteration costs
Fit Accuracy	Perfect for standard openings; may need adjustment in older homes	Built to suit your exact measurements — no extra work required
Aesthetic Flexibility	Limited to existing sizes and proportions	Fully flexible – match architectural details, align with other elements
Renovation Complexity	May require reframing, patching, or custom trims to suit	Less onsite modification; often cleaner and faster overall install

Choosing the right option isn’t just about replacement windows prices — it’s about the total result. If your openings match stock, great. If they don’t, custom could actually work out cheaper once you factor in avoided labour and finish costs.

Choosing the Best Aluminium Replacement Windows for Your Reno

Once you’ve nailed down your sizes, the next step is picking the right window style and material to match your home, budget, and lifestyle. Here’s what to look for.

Material Benefits

Aluminium replacement windows continue to be the go-to choice for full-home renovations in Perth — and with good reason.

• They’re durable, won’t warp or swell, and can handle years of direct sun exposure
• Unlike timber, aluminium doesn’t need repainting, sealing, or constant maintenance
• Resistant to salt air, making them ideal for both inland and coastal homes around WA
• Slim, modern window profiles maximise natural light and suit most architectural styles

For a full breakdown of aluminium frame types, configurations, and performance features, check out our Ultimate Aluminium Doors and Windows Buying Guide.

Window Types & Functions

Whether you’re chasing airflow, light, or just matching the style of your existing home, we stock every major window type:

• Sliding windows — great for wide openings, easy operation, and space-saving
• Awning windows — perfect for ventilation, even during light rain
• Double hung windows — ideal for heritage or classic facades with great airflow control
• Fixed windows — used for uninterrupted views or feature glazing
• Raked windows — made to follow rooflines or architectural angles, often used above doors or feature spaces

Each style has its place. For example, sliding windows suit open-plan living areas, while awnings are a smart pick for bathrooms and kitchens.

Not sure which window suits each space in your home? This guide on how to choose the right window for a room breaks it down room by room.

Warranty & Build Quality

All our aluminium replacement windows are manufactured by Jason Windows — WA’s leading name in residential glazing — and backed by a 10-year manufacturer’s warranty.

Choose from six modern colours to match your exterior palette, all in durable powder-coated finishes that resist fading and flaking over time.

So whether you’re replacing every window in the house or matching new to old, you can expect quality that lasts.

Replacement Window FAQs

Conclusion

Replacing windows isn’t just about upgrading how your home looks—it’s about choosing the right fit for your space, your budget, and your renovation goals.

Measuring carefully, understanding the difference between stock and custom sizing, and factoring in the full project cost—not just the window price—can make the difference between a smooth upgrade and a costly headache.

For most Perth renovators, aluminium replacement windows offer the best long-term value. They’re durable, low-maintenance, and available in a wide range of sizes and styles to suit both modern and older homes.

If you’re after full window and frame replacement, Ross’s Discount Home Centre has you covered. We supply replacement windows Perth renovators trust, with both stock and custom options available through Jason Windows—backed by a 10-year warranty and fast turnaround.

Explore your Perth window and door replacement options with us and take the guesswork out of your next renovation.