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Installation of Box & Sash Window from our Joinery.

Installing a box and sash window (also called a sash window, particularly traditional timber sash windows with a box frame) requires precision, especially if you’re working with heritage buildings or replacing old units. Here’s a step-by-step guide for installing a box and sash window:

Tools & Materials Needed

  • New box & sash window unit

  • Spirit level

  • Tape measure

  • Hammer & chisel

  • Drill & bits

  • Screws/fixings

  • Expanding foam / window packers

  • Sealant (silicone or frame sealant)

  • Wood filler (if needed)

  • Insulation

  • Primer/paint (if timber)

✅ Step-by-Step Installation Guide

1. Remove the Old Window (if replacing)

  • Remove internal beading/stops carefully.

  • Remove lower sash and then the upper sash.

  • Take out the weights and cords if present.

  • Remove the box frame if needed (can be left if retrofitting).

2. Prepare the Opening

  • Clean the reveal (sides of the opening).

  • Check for rot or structural issues.

  • Measure the opening and ensure the new window fits.

  • Apply DPC (damp-proof course) if required at the sill.

3. Insert the Box Frame

  • Fit the box frame into the opening.

  • Use packers/shims to level and plumb the window:

    • Check level at the sill.

    • Check plumb (vertical) on jambs.

    • Check square by measuring diagonals.

4. Fix the Frame

  • Fix through the box sides into the wall (brick or timber).

  • Use appropriate frame fixings or screws.

  • Fill around the frame with insulation or foam.

  • Do not over-tighten – maintain frame square.

5. Install the Sashes

  • Install the sash cords or chains.

  • Attach weights to the cords and feed them into the box cavity.

  • Insert the upper sash first, then the lower sash.

  • Ensure smooth operation and balance.

6. Refit Staff Beads & Parting Beads

  • Fit parting beads between upper and lower sash.

  • Fit staff beads inside to hold the lower sash in place.

  • Use brush seals or draught proofing as needed.

7. Final Finish

  • Fill any gaps with frame sealant or caulk.

  • Paint or varnish as required.

  • Clean the glass and test operation.

🔧 Tips

  • Double-check measurements before ordering the new unit.

  • If doing a heritage or listed property, consult local planning authorities before replacing.

  • Consider double-glazing or draught-proofing upgrades for thermal efficiency.