Why You Only Need One Size Spring Bronze

Spring bronze is one of the oldest and most long lasting weatherstripping you can find for windows and doors. It’s immensely versatile working on both casement and double-hung windows as well as any door. It’s immensely versatile, seals against those annoying drafts, and never seems to wear out (I’ve seen installations over 100 years old still going strong!)

It also one of the easiest metal weatherstrips to install, making it a favorite of DIYers, but when you go shopping for spring bronze you’ll often see a bunch of different sizes. Everything from 3/4” wide to 1 3/4” wide is common and this variety may leave you thinking “what size do I need?”

Great question! As the owner of a window restoration company in Florida we install miles of this stuff every year and we only use one size (I’ll tell you which in a second) for all our windows and doors. The truth is for 90% of projects you only need one size and everything else is just noise and waste.

What Size Spring Bronze Do You Need?

So what is that magical one size that fits all? Drumroll please. The answer is…1 1/4” spring bronze. But why is that the magical size? Let me explain.

Spring bronze seals wood windows and doors by compression against the side of the sash in the case of windows and the door slab in the case of doors when it is closed. How much of the bronze has to press against the side of the door or windows to seal? In many cases just 1/4” of bronze pressed tight is all it takes to adequately seal against drafts.

I know this because there is another weatherstripping piece called 27b lock strip (a sexy name I know!) and it accomplishes that same seal with only 1/4” of metal pressing in. If old 27b can do it why can’t it’s big brother do the same?

Size Doesn’t Matter

The vast majority of historic wood windows and doors are 1 3/8” to 1 3/4” thick which makes them perfect candidates for 1 1/4” bronze. That extra 1/8” of wiggle room on the thinner windows prevents binding if your install isn’t perfect. And the extra 1/2” gap on the thicker windows and doors doesn’t pose a problem either. Simply install your bronze toward the exterior side.

There are of course some larger commercial windows that can be as thick as 2 1/4” in my experience, but even those can be effectively sealed with 1 1/4” spring bronze. Occasionally, you’ll encounter very old single-hung windows that are as thin as 1 1/8” or even 1”. In those case you will need to spring (pun very much intended!) for the smaller stuff, but other than that there is no need.

This should save you considerably if you are installing spring bronze because the wider varieties cost more than the more narrow ones. Additionally, you don’t have to have a bunch of leftover pieces in a variety of sizes sitting in your garage just waiting to bring it to the recycler to try to recoup some of your investment.

The Most Efficient Way to Use Spring Bronze

Over the 15 years I’ve been restoring windows the cost of bronze has gone up ridiculously (as have many metals). Spring bronze is typically sold in rolls of 100 feet which, for some folks, can be a lot more than you need. You’re stuck paying for a bunch of bronze you don’t need.

To combat that we started selling spring bronze cut to size for our customers. Now you can get that sweet spot 1 1/4” spring bronze and only pay for what you need in increments of 10 feet. My hope is that it will save a lot of people money on their weatherstripping and encourage folks to seal up those old windows with a lower cost barrier to entry.

Saving historic windows and sealing them with spring bronze is a big win for not only your energy bills but also the environment. If you’re looking for some advice on how to install spring bronze and other ways to seal up your windows check out our other tutorials on the topic.

• How To: Install Spring Bronze
• How To: Weatherstrip Windows
• Spring Bronze vs V-bronze
• How To: Cure Drafty Windows