5 Mistakes That Get Timber Window Specs Rejected by Heritage Officers
5 Mistakes That Get Timber Window Specs Rejected by Heritage Officers
If your timber window spec gets rejected in a conservation area, you don’t just lose time—you lose trust, budget, and your edge as an architect.
At AtoZ Design and Glass, we’ve helped dozens of projects sail through planning in strict boroughs like Kensington & Chelsea, Hampstead, and Richmond. Here’s what we’ve learned—and what to avoid.
❌ Mistake #1: Using the Wrong Timber (Softwood That Fails Over Time)
Many suppliers use budget softwood without proper primer or lamination. Heritage officers know this leads to warping, flaking, and early replacement.
✅ What to do instead: Specify Meranti hardwood with full weatherproof treatment. We supply heritage profiles in Meranti, primed and ready to last 40+ years.
❌ Mistake #2: Incorrect Sash Dimensions or Moulding Profiles
One of the top reasons for rejections: wrong sightlines or bead detailing. If it looks “new” instead of matching the original, expect a no.
✅ What to do instead: We match exact original profiles using CNC templates or site surveys—even for curved, Georgian, or Victorian styles.
❌ Mistake #3: Glass Thickness or Reflection Too Modern
Double-glazing with visible spacers or high-reflective coatings will get flagged. It ruins the character of period buildings.
✅ What to do instead: We use heritage glazing units (12-14mm) with warm-edge spacers and low-reflection coatings that look single-glazed but perform like modern glass.
❌ Mistake #4: PVC or Aluminium Disguised as “Wood-Effect”
It might look convincing at first—but heritage officers spot it instantly. And your planning approval goes out the window.
✅ What to do instead: Stick to real wood, joinery-crafted and site-measured. We never substitute material just to win price.
❌ Mistake #5: Submitting a Generic Manufacturer’s Drawing
A generic CAD detail from a supplier won’t satisfy planning in sensitive boroughs. They need context, scale, material evidence.
✅ What to do instead: Use our Heritage Spec Pack, which includes joinery sections, glazing specs, timber data sheets, and past approvals.
🎯 Want to Avoid Rejection?
We’ve already helped over 40 architects get their specs approved in London conservation zones.
Or book a free 15-minute call with our technical advisor:
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