Secondary Glazing vs Replacement Windows

Cost and disruption

Secondary glazing is fitted from inside, needs no scaffolding, does not disturb external render, brick or stone, and generates almost no mess because the units arrive made to template. Replacement means removing the existing window, making good inside and out, and often external access. On a period property with deep reveals and decorative plaster, the making good alone can outweigh the price difference between the two products.

• No scaffolding or external access
• Original window and reveal untouched
• Little to no making good
• Room usually back in use the same day

Noise

Secondary glazing wins clearly, because a cavity of 100mm or more decouples the panes in a way a sealed 20mm unit cannot. If the reason you are spending money is traffic, trains, aircraft or nightlife, this is not a close comparison, and it is why acoustic consultants specify secondary glazing on noise sensitive projects.

Heat loss

Modern replacement windows with warm edge spacers and argon fill are excellent thermally, and on a straightforward modern house they are hard to beat. Secondary glazing with Low E glass closes much of that gap and also removes the draught, which is often the real source of discomfort. On a period property where the alternative is doing nothing, the improvement is transformative.

When replacement is genuinely the better buy

If the existing windows are rotten, beyond economic repair, of no historic interest and not protected, replacing them is the sensible answer and secondary glazing would only be dressing up a failing frame. If sight lines matter enormously to you and the building is not protected, replacement gives a cleaner look. We will say so rather than sell a second window in front of a window that needs to go.