To clean windows streak-free, wash the frames first, then apply a weak solution of washing-up liquid in warm water and pull it off the glass with a squeegee in overlapping strokes. Wipe the blade between passes and buff the edges with dry microfibre. Work on a cloudy day.
Windows streak when something is left behind on the glass as the water dries. That something is almost always detergent, hard-water minerals, or lint from the cloth you finished with. The dirt comes off easily. Getting the cleaning solution off again is the part people get wrong.
Four causes, in the order they catch people out:
If you live in a hard-water part of the country, the last of the rinse water matters more than the detergent you started with. Southern and eastern England run hard. Scotland, Wales and the north west are softer.
Streaks are lines left by water drying unevenly. Smears are a film spread across the whole pane, and they usually mean grease rather than water. The fix is different for each, which is why the same cleaning routine can clear one and leave the other.
For streaks, change your drying method. Get a squeegee, work top to bottom, and wipe the blade after every stroke.
For smears, change your solution. Cut the amount of detergent, rinse with clean water, and finish with a dry lint-free cloth rather than the damp one you washed with.
The squeegee blade is the part worth spending on and the part worth replacing. Professional cleaners change theirs every few weeks. A blade with a nick in it will leave the same line on every window in the house, and no amount of buffing hides it.
The overlap is what makes the difference. Each stroke should cover about two centimetres of the strip you just cleared, so there is no dry line between passes. Keep the blade at a shallow angle to the glass and let it flex rather than pressing it flat.
Start at the top and work down, and do the inside pane with horizontal strokes when you do the outside with vertical ones. If a streak shows up later, the direction tells you which side of the glass to go back to.
The last two centimetres at the edges are where a squeegee cannot reach cleanly. That is what the dry microfibre is for. Run it around the perimeter in one pass and do not go back over the middle of the pane.
Inside panes need less water and more care about what is underneath them. Lay a towel along the sill, use half the solution you would outside, and keep the cloth damp rather than wet. Inside glass carries grease and dust rather than traffic film, so it smears more readily than it streaks.
Upper-floor windows are the real problem, and the answer depends on what you have. A tilt and turn window swings fully inward on a side hinge, so you can reach the outside face standing in the room. A reversible window rotates within its own frame and does the same thing without swinging into the room.
If you are cleaning first-floor windows from a ladder twice a year, that is worth knowing before you next replace them. It is one of the few maintenance jobs where the window type decides whether the task is safe.
Vinegar works on glass. A one-to-one mix of white vinegar and water cuts through everyday dirt, and the mild acidity helps with the calcium deposits that hard water leaves behind. Use it on the pane, and cover any stone or marble sill first, because vinegar will etch the surface.
Newspaper does dry glass without leaving lint, and it was the standard trick for a reason. Modern newsprint ink comes off on your hands and sometimes onto a painted frame. A dry microfibre cloth does the same job and goes in the wash afterwards.
One thing vinegar is not for: the frame. Our own maintenance guidance for alu-clad frames is pH neutral soap and lukewarm water, so an acidic solution is the wrong choice against the powder-coated surface. Keep the vinegar on the glass.
Skip anything abrasive or solvent-based. On uPVC, that means no sandpaper and no solvents, because both dull and damage the surface, and the marks do not come back out. For heavier soiling on uPVC, a dedicated plastic cleaner does the job without attacking the frame.
Four more to keep away from the window:
If a pressure washer has already pushed water past a seal, the repair is the joint rather than the glass. Our guide to resealing windows covers that one.
Frames come first in the routine and they need a different product from the glass. What that product is depends on the material.
For uPVC, wipe dirt and deposits away with a damp cloth and ordinary cleaning agents. uPVC frames need no painting and no oiling, so cleaning is the whole routine. The full version is in cleaning and maintaining uPVC windows.
For alu-clad, wash the frame and sash a couple of times a year with pH neutral soap and lukewarm water. The aluminium face needs no painting, so this is all it asks for.
For timber, the paint or stain is what protects the wood, so cleaning is also an inspection. Look for flaking where the frame meets the glass while you have a cloth in your hand. Looking after timber window frames sets out the routine.
While you are there, lubricate the hardware and hinges once a year. Clean the dirt off first, because grit in a hinge works as an abrasive, and wipe any spilled oil off the frame before it stains.
Twice a year suits most homes, once in spring and once in autumn. Clean more often if you are near a busy road, where traffic film builds up fast, or on the coast, where salt spray sits on the glass and the frame.
The frames run on their own schedule. A couple of washes a year is the guidance for alu-clad, and uPVC goes as long as it looks clean. The hardware wants lubricating once a year regardless of how the glass looks.
Good luck with it. If the streaks survive a second pass with a clean blade, the problem is your water rather than your technique.
