By Chris 19 June 2024

What are the Different Methods of Installation for a Sash Window?

What are the Different Methods of Installation for a Sash Window?

Understanding the Differences Between ‘In the Box’ and Full Frame Window Replacements

When it comes to replacing windows, there are different methods of installation that you can choose from. 

Two common methods are “in the box” window replacement and full frame window replacement. And the choice between them depends on various factors including budget, the condition of existing frames, and desired finishes. 

In this expert article, we will explore the differences between these two methods and help you understand which one may be the best choice for your home. Let’s start by understanding the fundamentals of In the Box and Full frame window replacements and discuss their pros and cons. 

What exactly is “In the Box” Window Replacement?

“In the box” refers to the process of replacing only the glass panes of your windows while keeping the existing frames intact. This method is also known as insert window replacement. 

It is indeed a popular choice when the existing window frames are still in good condition and only the glass needs to be replaced.

The process of in the box window replacement involves removing the old glass panes and installing new ones in their place. This can be done without disturbing the existing frames, trim, or siding. 

It is a relatively quick and cost-effective method compared to full frame window replacement.

One of the advantages of in the box window replacement is that it allows you to maintain the original look and style of your windows. If you have historic or architecturally significant windows, this method can help preserve their character while improving energy efficiency and functionality!


  • Cost-effective
  • Quick installation 
  • Less Disruption 
  • Preserves the Original Look & Aesthetics 


  • Does not Address Existing Frame Issues 
  • Slightly Reduces the Glass area, affecting Natural Light 

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What is Full Frame Window Replacement?

Full frame window replacement involves replacing both the glass and the entire window frame. This method is recommended when the existing frames are damaged, deteriorated, or not energy efficient. It is also a good option if you want to change the size, shape, or style of your windows.

The process of full frame window replacement is more involved and time-consuming compared to in the box window replacement. It requires removing the entire window, including the frame, trim, and siding. This allows for a complete inspection of the window opening and ensures maximum glass space and energy efficiency.

This replacement option offers several benefits. It allows for a perfect fit between the new window and the frame, minimising air leakage and improving insulation. 

It also provides an opportunity to address any underlying issues such as rot, moisture damage, or structural problems. Additionally, full frame replacement gives you the flexibility to choose new window styles and features that can enhance the aesthetics and functionality of your home.


  • Addresses Structural Issues
  • Updates Aesthetics
  • Improves Insulation 
  • Enhances Energy Efficiency


  • Higher Cost
  • Takes longer to install compared to ‘In the box’ Replacements

Choosing the Right Method for Your Home

The choice between in the box and full frame window replacement depends on multiple factors. If your existing frames are in good condition and you want to maintain the original look of your windows, in the box replacement may be the best option for you. It is also a more cost-effective choice for smaller projects or when the frames are still structurally sound.

On the other hand, if your existing frames are damaged, deteriorated, or not energy efficient, full frame window replacement is recommended. It allows for a complete upgrade of your windows, addressing any underlying issues and providing maximum energy efficiency and functionality.

Our friendly team here at Fenster Glazing would be more than happy to assess your specific needs and determine the best method for your home. We can provide expert advice, recommend suitable products and ensure professional installation for long-lasting results. 

Fenster Glazing: Your Window Replacement Experts

To learn more about our window replacement options and to get a free personalised quote by using our online quoting tool. Input your preferred styles and your home’s dimensions, and we will provide you with a detailed quote. 

Alternatively, you can contact our friendly team using our online contact form or by giving us a call. 

We are here to discuss your requirements and help you transform your home with our top-notch window replacement solutions. Get started now!

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Based on 67 reviews
Heather Scott
Heather Scott
This is the second set of windows we’ve had fitted by Fenster. They are brilliant at every stage and I would highly recommend them. The staff are friendly and professional, they got the job done quickly and well, we’re very pleased with both sets of windows they fitted and would definitely use them again.
Dan Alger
Dan Alger
I contacted Fenster last week to see if they could help me. My French doors were failing to lock meaning we couldn’t leave the house. They sent Ben out the next morning who replaced the mechanism and also adjusted the door, closing up an annoying gap that’s been there for years. I wouldn’t hesitate to recommend Fenster to friends and family, a really helpful and efficient company.
Alison Budd
Alison Budd
We couldn't be more delighted with the professional service we received from Fenster Glazing. Nick turned up on time for the initial visit/quote which was fair and reasonable. After accepting the quote a survey was was carried out. The installers arrived on time and were polite and friendly. They covered everything up and left everything clean and tidy. After installation Perry called to check we were happy with the service. The quality of the french doors and windows installed were outstanding. We have no problem recommending this company. We would rate Service, installation and aftercare as 5 star.
I live in Milton Keynes, I contacted Fenster Glazing for an uPVC replacement door. From the beginning to the end, they conducted professional communication, from sales to the technicians coming to replace the door everything was perfect. I had a draught issue with my door and it is resolved now. I want to mention that I am also happy with the quality of the material of the door. I am hoping to have the same quality of service in the future if anything comes up—special thanks to Perry for dealing with everything. Ben
CMH Yoga
CMH Yoga
Highly recommended. I wanted a very specific style of doors to fit into our 1930s front porch. Fenster designed them, advised on colour & finish and they have produced exactly what I was looking for. The fitters were very polite and made sure everything was to my standards, and no mess left.
Chris Pike
Chris Pike
Great company. Very friendly, helpful. The work was completed to a very high standard, at a very reasonable cost, and I would highly recommend them.
Martin Cassin
Martin Cassin
Used Fenster glazing to replace two large panes of glass in our conservatory. Everything so Easy from obtaining a quote from Fenster to agreeing installation date and completing installation, polite, professional installation staff, very happy with service from start to finish

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