How to assess windows for replacement

In this Onsite with Andersen video, we’re demonstrating the steps that will help you properly assess your replacement project — where good installation begins!

The takeaway: An in-person assessment that includes examining the interior and exterior allows you to see the details. A good understanding of which will facilitate more precise measurement, better window selection, more accurate bidding, and better installation plans.

Keep reading for lessons learned from the video and best practices that will set you up for successfully assessing your replacement projects.

Assessment best practices

When you go to assess a replacement project, a level and a tape measure are essential, of course. We recommend using the longest level possible as that will help you assess plum, level, and square most accurately — the short mason’s level used here was just for demonstration purposes.

Beyond these basic tools, your eyes and experience can guide you — here's how:

Observe: Noticing certain details can clue you into the state of the current windows and even help you anticipate what you might find inside the walls. For example, in this home, the headers were visibly sagging, and some windows were clearly out of square. If you notice a roof is directing water at a window, that might be a clue there could be rot.
Verify: Using a level and measuring precisely can help verify what you’ve observed and help you make necessary adjustments. For example, in this home, undersizing the measurement of a particular window helped account for a rough opening that had changed shape over time. Your level will help you more correctly judge how much to decrease sizing.
Measure: Taking three measurements and using the smallest will help you make the best sizing decisions and account for the possibility that windows are out of square. This approach should be taken with the horizontal and vertical plane on the interior and exterior. It can also be used when measuring details like brickwork. Additionally, measuring from the right point is essential. For example, in this home, horizontal measurements were taken jamb-to-jamb on the interior and brick-to-brick on the exterior.

Remember that even in historic homes, like this one, authenticity can be maintained while bringing a home up to modern standards. For example, here, the decision to replace four individually set double-hung windows with joined 400 Series Double-Hung Windows will give the homeowners 12 to 15" of extra glass for a brighter space overall. At the same time, the style of the replacement windows and replication of original trim work will help preserve the home's traditional look.

TIP: If you’re replacing a bank of windows, it’s essential to remove the interior header casing and mull covers before deciding on the appropriate replacement products and installation plan. It could be necessary to replace the header if it’s not properly sized and/or supported by existing mull material. If the header needs alteration, it will significantly expand the project scope and complexity and could likely require the help of a design professional. It’s important to know that our products are not designed to take any vertical load. A laser level or a stretched string can be helpful in determining the magnitude of deflection.

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Interior finish assessment

Without a doubt, your customers will have strong opinions about how their interiors should look, so taking their aesthetic preferences into account will be key as you work through decisions related to window sizing and installation.

The home featured in this video has beautifully crafted traditional interior trim. Unfortunately, it had been damaged, so the plan was to remove, replicate, and replace it. In a scenario where there's trim like this in good condition, a homeowner might wish to preserve it. An insert replacement window allows interior trim to remain in place.

In addition to the trim, you’ll also want to take note of the following as you’re assessing interior conditions:

Are any windows installed into tile or adjacent to a tile backsplash? Assuming this is a feature the homeowner will want to keep, it will be important to maintain the same frame depths, frame sizes, and extension jambs so the new trim aligns with customer expectations.
Are there custom or expensive window treatments that the homeowner wants to keep using? If so, make sure the new windows and trim are planned in a way that will accommodate their continued use.

Replacement windows and their installation

The conditions you observe and your customer’s priorities can help you select the best windows and installation method.

Here are the three types of replacement windows:

Insert windows fit into an existing frame that’s in good condition (not out of square, rotted, etc.).
Full-frame windows with installation flange include both window and frame and a flange that’s secured on the exterior side. The type of installation used with these windows is most similar to a new construction scenario.
Full-frame flangeless windows include both window and frame but no installation flange. They are installed through the jambs and are sealed on the interior and exterior.

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Siding and facade material assessment

An exterior assessment begins with understanding what’s moveable versus what’s immovable. For example, brick or stone facades generally are considered immovable.

The home featured here is made of brick. Unless there’s a desire to change the facade, this exterior material will ultimately determine the size of the new windows. With masonry homes (brick, stucco, and concrete), installation flanges are typically not an option, and windows are set back in the opening. In addition, exterior trim is needed to cover any gaps left for shimming, foam, or backer rod.

Once you understand the requirements dictated by the siding or facade, you should also ask yourself:

Are you willing to alter, modify, or remove the siding? If not, then you should consider it immovable and let that guide your decisions about product and installation.
Could the exterior trim be reused? Take note of any fading or damage and find out if the customer wants to change the color.
What issues might be uncovered if the trim is removed? How might those issues affect labor and materials estimates?

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Water management assessment

Besides understanding the requirements determined by the siding material, you'll also want to pay attention to water management.

Is there already a water management system in place? Look for the following:

Drip cap: Is there a drip cap currently in place?
Undersill: What size is it?
Roof: Does it direct water toward the windows? Is there anything in place to protect windows, like gutters?
Flashing and WRB: Can you tell if the windows were properly flashed and connected to the WRB? Often, you won’t be able to tell without a more invasive approach.

Investing time in an assessment will help you make the best decisions for a particular project. And bigger picture, those good decisions will lead to good outcomes that can grow your reputation and your business!

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More about this project

split image of measuring a window and an install job

split image of measuring a window and an install job

How to assess windows for replacement

In this Onsite with Andersen video, we’re walking you through the steps that will help you properly assess your replacement project — where good installation begins!

Watch the video

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Assessment best practices

When you go to assess a replacement project, a level and a tape measure are essential, of course. We recommend using the longest level possible as that will help you assess plum, level, and square most accurately — the short mason’s level used here was just for demonstration purposes.

Beyond these basic tools, your eyes and experience can guide you — here's how:

Observe: Noticing certain details can clue you into the state of the current windows and even help you anticipate what you might find inside the walls. For example, in this home, the headers were visibly sagging, and some windows were clearly out of square. If you notice a roof is directing water at a window, that might be a clue there could be rot.
Verify: Using a level and measuring precisely can help verify what you’ve observed and help you make necessary adjustments. For example, in this home, undersizing the measurement of a particular window helped account for a rough opening that had changed shape over time. Your level will help you more correctly judge how much to decrease sizing.
Measure: Taking three measurements and using the smallest will help you make the best sizing decisions and account for the possibility that windows are out of square. This approach should be taken with the horizontal and vertical plane on the interior and exterior. It can also be used when measuring details like brickwork. Additionally, measuring from the right point is essential. For example, in this home, horizontal measurements were taken jamb-to-jamb on the interior and brick-to-brick on the exterior.

Remember that even in historic homes, like this one, authenticity can be maintained while bringing a home up to modern standards. For example, here, the decision to replace four individually set double-hung windows with joined 400 Series Double-Hung Windows will give the homeowners 12 to 15" of extra glass for a brighter space overall. At the same time, the style of the replacement windows and replication of original trim work will help preserve the home's traditional look.

TIP: If you’re replacing a bank of windows, it’s essential to remove the interior header casing and mull covers before deciding on the appropriate replacement products and installation plan. It could be necessary to replace the header if it’s not properly sized and/or supported by existing mull material. If the header needs alteration, it will significantly expand the project scope and complexity and could likely require the help of a design professional. It’s important to know that our products are not designed to take any vertical load. A laser level or a stretched string can be helpful in determining the magnitude of deflection.