New Construction vs Replacement Windows: Myths Busted

What do I mean by “new construction” and “replacement” windows?

The way most people understand the difference between the two is that new construction windows utilize a nailing flange (fin that protrudes out from the window frame surrounding entire perimeter of the window) to install the windows and replacement windows have NO nailing flange. This over simplification of these terms often leads to buying the wrong product and poor installations. However, for the sake of mutual understanding, when I use those terms assume that is what I mean.

 Nailing Flange Around Window Frame

1st Myth: When replacing windows, always use "replacement windows" - aka no nailing flange.

It’s actually almost the exact opposite. Replacement windows should almost always HAVE a flange for installation. 

The only times I would deem it acceptable to replace a window withOUT a flange is twofold:

1. Your house was build pre 1945 and you have the old sash weight wood double hung windows. For installing new windows into these wood pockets, you can simply remove the old sash’s, ropes, pulleys and weights… then install a new “block frame” or “insert” window into the existing wood frame. These old openings have a sloped sill which allows any water that may enter into the frame, to drain out. Minimal disturbance occurs during this type of installation and would be okay to do so.

Old wood double hung windows

2. You have stucco, stone or masonry as your exterior cladding. Cutting back or removing any of these facades is challenging at best and a lot of the times isn’t possible. This would be another reason to install a window with no flange.

Brick exterior... utilizing the flange isn't possible for replacement

The reason why you WANT to utilize a flange for installation for all other applications is because it allows for a more secure install and provides much better water proofing details. More on that later.

2nd Myth: New construction windows can't be used when replacing windows

Flat out wrong. As I mentioned before, you actually will WANT to utilize the flange for install which means buying “new construction” windows. In my eyes they are just windows though. Using the flange that’s integral to a window makes for a more time consuming and intricate replacement process, but the outcome will be much better. Make sure you hire someone who knows what they’re doing. On the exterior, it will require either cutting back your siding, removing your trim or removing/reinstalling vinyl siding. On the interior it will require either cutting back the liners (trim) on all four sides or replacing the interior trim entirely.

3rd Myth: Replacement windows are better suited for when replacing windows

BY ALL MEANS, NO.

In my opinion, the term “replacement windows” is just another marketing technique used to sell more windows. If you see the picture below, it shows you that in the description of a “replacement window” product it says that the block frame style (no flange) installs neatly without disturbing siding… those are carefully chosen words used to help sell the product. (It also says for new construction… but more on that below.) 

This is actually in a description of a "replacement window" product from Lowes

Are they faster to install? Sure. Are they easier and more DIY friendly? Sure. Will you save money on labor? Sure. Will the windows function perfectly for 20 years? Probably not. Will they be water and air tight? Only for as long as the caulking lasts. After all, these “replacement windows” are just slid into the existing openings, screwed through the frame and then caulked on the outside. That big bead of caulk between the edge of the window frame and siding joint is the one and only defense against water and air intrusion. Here is what a “replacement window” looks like that has been installed into a home....

Replacement window installed into a home with cedar siding... as you can see
it was slid into the opening and just screwed through the inside frame to attach it.

It typically leaves a large gap that gets filled with caulk. This not only looks 
terrible but it is also the one and only line of defense for water intrusion.

4th Myth: Replacement windows can be used on new construction homes

If we are maintaining the thought that replacement windows are windows that are flange-LESS, then they should NOT be used on new construction houses (unless you’re a high performance builder and are aware of the extreme difficulties of detailing windows like this. Passive houses use European windows for example which are usually flange-less). The reason to not use them on a new construction house is because the flange is typically integral to the window and used as the structural component (hence why it's called a "nailing flange." Additionally, it used as the waterproofing location where it is tied in to the building wrap (or WRB) and the overall building envelope. So again, despite of what someone tells you, do not use a “replacement window” or flange-LESS window on a new construction house unless you are a highly experienced builder that is building a high performance home - which if that’s the case you probably aren’t reading this article since it’s aimed towards homeowners, DIY’ers and new builders.

New construction house utilizing the flange as the mounting point and the
main water proofing location... bottom is left unsealed for drainage.

Conclusion:

Just because you are replacing windows doesn’t mean you should be using “replacement windows” (flange-LESS). Most of the time it should be the opposite. Using the flange will be your mounting point and assist you in water proofing around the windows/openings. There are only certain circumstances where you could install windows with no flange: 

1. Old double hung window openings 
2. Exteriors where altering the siding isn’t possible (stone, masonry or stucco)
3. High performance homes where the builder has the expertise to do so
4. Passive houses 
5. Maybe a couple other scenarios but always check with an experience professional first

Other than those applications, a flange is recommended. I hope that clears up the difference between the two and when and when not to use each type of window. 

Please ask me if you have any questions or need help.