Preparing Your Rebate: Measuring for Replacement Units

Nearly every remake we produce traces back to the same few measuring mistakes. Ten careful minutes with a tape avoids all of them.

Measure the aperture, not the old glass

The visible glass is smaller than the rebate that holds it. Remove a bead if you can and measure the full tight opening — width and height, in three places each. Use the smallest figure of the three: frames are rarely square.

Apply the right deduction

The unit must sit with clearance for expansion and drainage. Standard practice is to deduct 10mm from each tight dimension (5mm clearance all round). uPVC and timber frames follow this rule; aluminium systems sometimes specify their own — check the gasket detail first.

The three forgotten measurements

• Unit thickness: read the spacer stamp or measure the old unit edge-on — 24mm and 28mm dominate but 20mm exists in older frames
• Spacer offset in stepped units: conservatory roof panels and some doors use stepped edges; note step size and direction
• Which pane carries what: obscure, toughened stamp, low-E coating — record the orientation before the old unit goes in the skip

When in doubt

The full measuring guide covers bead-in and bead-out frames with diagrams, and the weight calculator tells you whether the new unit is a one-person or two-person lift. Send us the tight sizes and we will confirm the deductions before anything goes into production.