Your windows look fine - but are the gaskets (EPDM seals) actually working? There's a ridiculously easy test used by professional window fitters across Europe that requires zero tools: the A4 Paper Test (or Glue Test).
You need only a single sheet of A4 paper and less than 30 seconds per point. If the paper comes out easily, your gaskets need adjusting or replacing - and we explain exactly what to do.
A detailed guide in 4 easy steps, with no tools - just one A4 sheet of paper.
1. Open the window sash. 2. Place an A4 sheet crosswise so half is inside and half is outside, resting on the gasket. 3. Close the sash and lock the handle normally. 4. Pull the paper slowly with your fingers (without tearing). If it slides out easily, there's a problem.
Don't check just one spot! The gaskets may seal perfectly on top but leave a gap at the bottom. Run the test at at least 8 points per sash: top, bottom, left, right - and especially at all 4 corners (where failure is most common).
Interpretation is dead simple: the answer depends on how easily you pull (or whether the paper tears).
If it takes real effort to extract the paper, or if it tears as you pull, the gaskets are gripping excellently. Airtightness at this point is 100%. Move on to the next spot.
If you pull the paper with two fingers without resistance, or - worst case - it drops on its own without touching it, then the gasket isn't contacting the frame. This means: (1) cold air infiltration in winter, (2) heat and dust in summer, (3) higher heating/cooling bills, (4) potential water ingress in heavy rain.
Before rushing to replace gaskets, there's a free and very likely solution: adjusting the compression pressure the closing mechanism exerts on the gasket.
Each locking point (mushroom cam) on the sash has an eccentric cam that rotates with an Allen key. By turning it a fraction, you pull the sash tighter against the gasket. The operation is beautifully simple: "summer" (light compression) → "winter" (firm compression). Some manufacturers (e.g. Roto, GU) mark the cams with dots or arrows.
Don't max out all cams to "winter" if it's not necessary - excessive pressure wears gaskets faster. The correct setting is the one that provides just enough compression for the A4 test to pass (paper tears). If the test still fails after adjustment, the gaskets need replacing.
EPDM gaskets (ethylene-propylene-diene monomer) don't last forever. Greek solar radiation, frost, salt-laden moisture (in coastal areas) and dust age them within 8-15 years.
Hard (they don't spring back when pressed), peeling, cracked or flat (they've lost their hollow cross-section) - in any of these cases, adjustment alone won't suffice. A "dead" gasket will never seal properly again, no matter how tight you set the cams.
Replacement is done at your home, without removing the sash from the wall. The technician removes the old gasket, pushes the new one into the channel (snap-in) and tests again with the A4 method. Cost: €15-30 per sash (full perimeter). An entire home of 5-6 windows is completed in a single morning.
Every autumn, before the heating kicks in, run a 2-minute A4 test on every window. A sheet of A4 paper costs €0.01 - a forgotten loose seal can cost hundreds of euros in heating bills or moisture damage. Prevention > cure, always.
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