A well-fitted uPVC window shouldn’t let water in during Pune’s monsoon. If it does, the problem is almost never the profile itself.

Every June we get the same call, sometimes from a client whose windows are barely a year old. Water pooling on the sill, a damp patch spreading below the frame, sometimes a faint whistling sound when the wind picks up before a storm. Nine times out of ten it’s not a bad window. It’s a drainage channel that got blocked, a gasket that was never seated properly, or a sealant joint that was rushed during installation. The profile itself is rarely the actual fault.

So here’s what’s actually going on inside a uPVC window during heavy rain, and where things tend to go wrong.

Where the Water Is Supposed to Go

A uPVC frame isn’t a solid barrier that simply blocks water. It’s designed to let a small amount in through the outer seal and then drain it back out deliberately, through small weep holes cut into the bottom of the outer frame. Water gets in, runs down an internal channel, and exits through those holes rather than pooling anywhere inside the frame cavity.

This is by design, not a flaw, and it’s the same principle used in most quality window systems worldwide. The problem shows up when those weep holes get blocked, by dust, by a stray bit of construction debris left behind after painting, or occasionally by someone sealing them shut entirely thinking they’re a manufacturing defect. Block the exit and the water that’s supposed to drain out just sits there instead, eventually finding its way inside.

A Flat Near Bibwewadi That Took Us a While to Diagnose

We got called out to a flat near Bibwewadi two monsoons ago where water was showing up on the inside sill during heavy rain, despite the windows being installed less than a year earlier. Took us almost an hour on site to find it, the weep holes had been painted over during the building’s exterior repainting work, a thin coat of paint had sealed them shut without anyone realising. Cleared them out with a thin probe, water started draining properly again within the next storm. No hardware fault, no bad installation, just blocked drainage from an unrelated job done months later.

The Gaskets Are Doing More Work Than People Realise

Around the glass and along the sash, rubber gaskets create the actual seal that keeps wind driven rain from pushing through the gap between sash and frame. These compress when the window closes, and over years of opening and closing, plus exposure to heat and UV, they can lose a bit of their elasticity.

A gasket that’s degraded doesn’t always look obviously worn. Sometimes it’s just slightly less springy than it used to be, which is enough to let a fine mist of wind driven rain through during a genuinely bad storm even though the window still closes and locks fine. Replacing gaskets isn’t a major job or a major cost, but it’s one of those maintenance items that gets forgotten because nothing looks visibly broken until the rain actually tests it.

Where Installation Quality Changes Everything

This is probably the single biggest factor in how a uPVC window handles monsoon conditions, and it has almost nothing to do with the window itself. The gap between the window frame and the surrounding wall needs proper sealant, usually a weatherproof silicone bead, applied cleanly all the way around. Rush that step, or skip sealant on one edge because it’s awkward to reach, and that becomes the entry point water finds first, regardless of how good the profile or the glazing is.

We’ve walked into more than one job where a previous fabricator had used ordinary sealant instead of a proper weatherproof grade, and it had already started cracking and pulling away from the frame within two monsoon seasons. It looked fine from a distance. Up close, there were hairline gaps all along one edge where water had clearly been finding its way through for a while.

Some Flats Just Get Hit Harder Than Others

Exposure matters more than most people think when judging whether a window is performing badly. A window on the top floor, especially one facing open ground with nothing blocking wind, deals with genuinely different conditions than a similar window three floors down with a building or a row of trees breaking the wind before it arrives. We’ve had two flats in the same building, same window spec, same installer, where one performed perfectly through a monsoon and the other showed a small amount of misting on the sill purely because of which direction it faced and how exposed that particular corner was.

This isn’t really something you can design around entirely, but it does explain why two seemingly identical windows in the same building can have different experiences. On genuinely exposed corners facing the prevailing monsoon wind direction, which in Pune tends to come from the southwest, it’s worth asking your fabricator for a slightly heavier gasket spec or double checking the sealant work more carefully on install day, since that window is doing more work than a sheltered one right next to it.

What Actually Needs Checking Before Monsoon Hits

Weep holes deserve a quick visual check every year, ideally right before the rains start, just to confirm nothing’s blocking them from outside. Gasket condition is worth a look too, run a finger along the seal and check it still has some give to it rather than feeling stiff or brittle. And if you notice a sealant joint around the frame edge that’s visibly cracked or pulling away, that’s worth fixing before the first heavy storm rather than after water’s already found its way in.

None of this requires a technician most years. It’s a five minute check that catches the vast majority of monsoon leak issues before they actually become a problem inside the flat.

Quick Answers

Do uPVC windows leak in heavy rain?

A properly installed one shouldn’t, no. Most leaks trace back to blocked weep holes, degraded gaskets, or poor sealant work rather than the window itself failing.

What are weep holes and why are mine sealed shut?

Small drainage holes at the base of the frame. If yours are sealed, it’s almost always accidental, often from exterior painting work done after installation.

How often should gaskets be checked?

Once a year is enough for most homes, ideally just before monsoon.

Is it normal for a little water to enter the frame during rain?

Yes, that’s actually how the drainage system is designed to work. It’s meant to enter, drain, and exit through the weep holes, not stay sealed out entirely.

If your windows are letting water through this monsoon, send us a photo of the sill and we’ll tell you honestly whether it’s a five minute fix or something that needs a site visit.