Sash Windows: Restoration vs. Replacement – Which Should You Choose?

If you own a period property, you’ve likely stood beneath a draughty sash window and asked yourself the same question: Do I restore my sash window what I have, or bite the bullet and replace the whole thing?

It’s a decision that carries significant financial and logistical weight. After two decades in this trade, I can tell you that the answer is rarely as clear-cut as the salesperson wants it to be. But if we strip away the marketing fluff and look purely at cost, hassle, and what actually happens to the timber once we open it up, one option wins by a landslide for the vast majority of homeowners.

Here is the reality check you need.

The Cost Gap: It’s Not Even Close

Let’s cut straight to the figures, because this is where most people's eyes start to water.

At the end of the day, if you are putting a window into a typical UK period home, you are looking at roughly £1,200 per window for a high-quality full restoration, including the labour to take the sashes out, strip them, repair the timber, re-glaze, and re-install.

Now, look at the replacement route. For a standard-sized timber sash window, like-for-like, you are staring down the barrel of approximately £5,000 each. That’s not for a gold-plated frame—that’s for a decent, standard, made-to-measure double-glazed replacement.

That is a £3,800 difference per window. For a typical terrace with six sash windows, we are talking about a saving of nearly £23,000. Ask yourself: could you use that money better elsewhere on your property?

The Reality of Timber Frames (From 20 Years on the Job)

Here’s the honest truth that most replacement companies won't tell you: the original timber is almost always in remarkably good structural condition.

I’ve been restoring sash windows since 2005, and in the vast majority of cases, the frames are perfectly sound. What looks "rotten" to the untrained eye is usually just surface decay, failing putty, and paint that has cracked and trapped moisture against the outside layer.

When we get in there, we can chop out the few rotten sections, splice in precision-matched, kiln-dried timber, and carry out any other necessary repairs to the wood. By the time we’ve stripped, primed, and painted the sashes, you genuinely cannot tell the difference—we are effectively giving you a brand-new window sash window, but one that still holds the original character, the beautiful wafty glass, and the historical integrity of your home.

The Planning Permission Minefield

One of the biggest hidden headaches of replacement is one that sales reps conveniently forget to mention until the contract is signed: Council approval.

If your home sits in a conservation area (and millions of UK period homes do), replacing your timber sash windows with new ones is not a given right. You are almost certainly looking at a full Planning Application, and often an Article 4 direction which removes your permitted development rights. That means drawings, applications, neighbour consultations, and an 8-to-12-week wait—with no guarantee of a yes.

Here’s the beautiful secret about restoration: it is legally classed as 'repair and maintenance'. You do not need council approval. You don't need to fill out a single form. You aren't asking for permission—you are simply preserving what is already there.

"But Won't It Still Look Old and Draughty?"

This is the question we hear most often, and it is the one that surprises clients the most.

When we explain the scope of a full restoration, clients are genuinely shocked at how much work you can actually do to make a 100-year-old window look brand new. We aren't just slapping paint over cracks.

A proper restoration involves:

• Removing the sashes and stripping back decades of paint.

• Cutting out rotten timber and splicing in new wood where needed.

• Replacing all the putty and glazing sprigs.

• Installing new parting beads and staff beads for a tight, rattle-free fit.

• Draught-proofing the tracks with spring bronze or brush seals.

When we are finished, the window sits flush, opens smoothly, and looks indistinguishable from a new factory-built unit. And crucially, because the original hardwood oak or pitch pine is denser than modern softwoods, it actually holds screws and fixings better than a brand-new off-the-shelf replacement ever could.

The Caveats: When Restoration Fails

Now for the honesty. Restoration isn’t always the right call. There are two hard deal-breakers you need to check before you pick up the phone:

1. The Timber Percentage – Take a screwdriver and gently poke the bottom rail and the lower corners of the sash. If the wood is so rotten that your tool goes through it like butter in more than 30% of the frame, the cost of splicing becomes prohibitive. You are no longer restoring; you are rebuilding from scraps. (Though, again, in my 20 years of doing this, that is the exception, not the rule.)

2. Your Thermal Expectations – Here is the uncomfortable truth: the £1,200 restoration usually preserves your single-glazed glass (U-value of roughly 5.0). The £5,000 replacement usually includes slimline, argon-filled double glazing (U-value of roughly 1.4).

If your primary goal is to slash your energy bills and eliminate that cold draught entirely, a basic restoration won't get you all the way there. However, there is a golden middle ground: ask your restorer to fit retrofitted slimline double glazing into your existing sashes. This adds roughly £300–£500 per window to the restoration cost, bringing your total to ~£1,700. That is still 66% cheaper than the £5,000 replacement, and it gets you 80% of the thermal performance.

The Final Verdict

For 90% of pre-1930s UK homeowners, the choice is crystal clear: choose restoration.

Unless your timber is practically dust, or you are building a Passive House from scratch, you simply cannot justify the astronomical cost, the planning delays, and the loss of character that comes with a full replacement. The wood is better than you think, the work is more comprehensive than you imagine, and the savings are too big to ignore.

Restoration gives you a window that looks brand new, functions perfectly, retains your home's value, and leaves thousands of pounds in your bank account. Don't waste your money on replacing the window—and definitely don't waste your time getting council approval you don't even need.

Keep the character. Keep the cash. Restore what you already have.