Window replacement removes the old unit, sets a new frame and sash into the opening, then restores insulation, airtightness, and weather protection around it. The window specification matters, but accurate measurement, a square frame, continuous perimeter sealing, and a final operation test are what keep rain and draughts out.
When this work is needed
Replacement is worth considering when condensation, draughts, leaks, noise, or damaged hardware persist, or when balcony alterations require a different window. First locate the cause. Failed external sealant or a crack in the surrounding wall may need a focused repair rather than a complete new unit.
Decide before ordering
Set the installation conditions as carefully as the product specification.
Opening width and height at several points, both diagonals, wall depth, and final order size
Treatment of railings, outdoor equipment, drainage falls, and existing leak marks
External-grade sealant, primer, expanding foam, packers, and structural fixings
Lifting route, falling-object control, and the weather limits for high-level work
Check in the quote
These questions reveal whether the price covers a finished weatherproof installation rather than the window alone.
Are the window model, glass build-up, hardware, and insect screen identified?
Does the price include removal, disposal, and repair of the opening?
Are frame fixings, foam insulation, and internal and external sealing listed separately?
Are lifting equipment, common-area protection, and high-level safety measures included?
Who is responsible for operation, draught, and water-spray tests and for correcting failed sealant?
What to check on site
Once the frame is fixed, errors in the opening and perimeter gap become difficult to correct. Check the geometry before fixing, then carry the same standard through sealing and final testing.
01Prepare the opening
After the old frame and sealant are removed, measure the opening at several heights and widths and compare the diagonals. Repair broken corners and investigate damp areas before the new frame is brought into position.
02Install and fix the frame
Support the frame on packers, then use a laser or level to set it plumb, level, and square. Fix it to sound structure without pulling the frame inward, and recheck the diagonals as each fixing is tightened.
03Insulate and seal the frame
Fill the perimeter gap in controlled passes so expanding foam does not distort the frame. Keep the external weather seal and internal airtight layer continuous at corners and along the sill, without blocking drainage paths.
04Assemble sash and glass
Fit the glass and sashes, then adjust roller height and overlap. A sash should stay where it is left, run without wobble, and meet the frame with an even gap on every side.
05Install hardware and accessories
Install handles, locks, insect screens, and weather strips, and operate each part. A lock should engage without force, and the screen should remain securely within its track.
06Final test and finish
Open, close, and lock every sash several times, then check for air movement around the perimeter. Once the external seal has cured, spray-test the sill and corners and close the internal finish only after the opening remains dry.
Where problems usually start
Distorted frame and sticking sashToo much expanding foam or uneven fixing pressure can bow the frame until the sash catches or no longer closes evenly.
Leak around the frameA missed external joint, unsuitable sealant, or a poorly prepared surface can let rain track behind the window frame.
Draughts and condensationMisalignment, incomplete insulation, or weather strips that do not meet evenly can admit cold air and create cold internal surfaces.
If a sash catches or the lock will not align, check frame level, plumb, and diagonals before forcing an adjustment at the hardware.
Leaks and draughts may come from the product, the perimeter seal, incomplete foam, or cracks in the adjacent wall. Isolate each path before deciding the repair scope.
Timing and records
Allow roughly 8 to 16 hours for two window installers per opening. Size, quantity, access, lifting, opening repairs, and weather can change this, so separate removal, installation, sealing, and testing in the programme.
Keep the order specification and site measurements, frame geometry before and after fixing, foam filling, external sealant, glass markings, hardware, and the operation, draught, and spray-test results. Recheck sealant shrinkage or separation within the first month.
If you have the survey sheet, opening photos, or a window quote, I can help check the order size and the fixing, airtightness, and water-test scope.
