Choosing the Right Wood for Window Restoration
The Secret to Long-Lasting Windows: Picking the Right Wood
If your historic windows could talk, they’d probably say, "They don’t make 'em like they used to!" And they’d be right. One of the biggest reasons historic windows have lasted for decades—or even centuries—is the old-growth wood they were made from. Unlike today’s fast-grown lumber, old-growth wood is incredibly dense, naturally rot-resistant, and full of tight, stable grain that makes it perfect for window construction.
What is Old-Growth Wood?
Old-growth wood comes from trees that grew naturally for hundreds of years in undisturbed forests. Because they took their time growing, the grain is tighter and more uniform, making the wood significantly stronger and more durable than the fast-growth lumber used in most modern construction. Old-growth wood is naturally resistant to moisture, insects, and decay, which is why so many original windows remain intact even after more than a century of exposure to the elements.
Why Can’t We Just Use Old-Growth Wood Today?
Simply put, they don’t make forests like they used to. Most old-growth forests have been heavily harvested, and modern timber is grown quickly for commercial use. This means today’s wood isn’t as dense or durable as the wood used in historic windows. If your old-growth window sash is beyond repair, finding a suitable replacement material is key to maintaining the longevity and integrity of your restoration project.
Modern Alternatives: Accoya & Red Grandis
While old-growth wood isn’t as readily available, there are modern, sustainable alternatives that offer similar durability and performance.
✔ Accoya: Accoya is a modified wood that undergoes a process called acetylation, which alters the wood’s cellular structure to make it more dimensionally stable, rot-resistant, and long-lasting. Accoya doesn’t absorb moisture like untreated wood, meaning it won’t swell, shrink, or warp when exposed to humidity or rain. It also carries a 50-year warranty! It used to be that this wood was manufactured in the Netherlands, but it is now also manufactured in the USA. This makes it an excellent choice for historic sash replacement.
✔ Red Grandis: Red Grandis is a sustainably grown hardwood with properties similar to mahogany. It is highly durable, stable, and has a fine grain that makes it easy to work with. Red Grandis is a popular choice for replicating historic profiles in window restoration, as it allows for intricate detailing while maintaining durability.
How to Choose the Right Wood for Your Window Restoration
When replacing damaged window sashes, matching the original profile and material is crucial to maintaining the historic character of your home. Here’s what to consider when choosing your replacement material:
1. Authenticity
If possible, salvage old-growth wood from another historic window to maintain authenticity.
If old-growth isn’t available, choose a high-quality alternative like Accoya or Red Grandis that mimics the original material’s durability and aesthetic.
2. Stability & Longevity
Accoya is dimensionally stable, meaning it won’t expand or contract with changing temperatures. This is especially important for windows exposed to extreme seasonal shifts.
Red Grandis is excellent for historic reproduction work due to its smooth grain and workability.
3. Sustainability
Both Accoya and Red Grandis come from sustainably managed forests, making them eco-friendly alternatives to cutting down remaining old-growth trees.
4. Cost & Maintenance
Accoya and Red Grandis are more expensive than standard pine or fir, but their longevity and resistance to decay make them more cost-effective in the long run.
Regular maintenance, such as repainting and sealing, will extend the life of any restored sash, regardless of the wood type.
Restoring vs. Rebuilding a Sash: When to Replace
Not all window sashes need to be replaced—sometimes, they just need a little TLC. Here are some indicators that a sash should be restored rather than replaced:
✅ Minimal rot – Small sections of damage can be repaired with epoxy or wood consolidants.
✅ Sash is still structurally sound – If the joints are intact and the wood is not brittle, restoration is usually the best option.
✅ Original glass is present – Keeping historic glass is preferable for maintaining the window’s character. Historic style glass can be sourced, but will add to restoration costs.
However, if the sash is severely rotted, warped, or missing significant portions, a full historic replication may be necessary. In this case, rebuilding the sash with Accoya or Red Grandis will ensure it lasts for another century or more.
The Importance of Skilled Craftsmanship
Whether restoring or rebuilding a sash, skilled craftsmanship is essential. Custom milling and joinery ensure that the new sash fits seamlessly with the original window frame. If using Accoya or Red Grandis, an experienced restoration professional can shape and finish the sash to match the original design perfectly.
Final Thoughts: Choosing the Best Wood for Longevity
Historic windows are an investment in your home’s character and history. Choosing the right materials—whether preserving old-growth wood or incorporating Accoya and Red Grandis—ensures that your windows will last for generations to come.
If your window sashes need rebuilding, don’t settle for subpar modern materials that won’t stand the test of time. Work with a restoration expert who understands the nuances of historic craftsmanship and quality wood selection.
