Replacing Aluminum Windows with uPVC: What to Expect

Aluminium windows became the default for Chennai apartments built between 1995 and 2015. They are now in their second or third decade and starting to show their age. Most replacement enquiries we get for aluminium fall into two patterns. The rollers have failed and replacements are no longer available. Or the elevation is leaking during heavy monsoon. uPVC fixes both. This post covers what changes when you make the swap, what stays the same, and what to verify before signing an order.

What gets noticeably better

Heat into the room

Aluminium is a thermal bridge. The frame conducts heat from outside to inside more or less directly. On a 38°C afternoon, the inside surface of a south facing aluminium frame is hot to the touch. uPVC is not. Even with the same single pane glass, a uPVC frame keeps the room cooler because the frame itself does not conduct heat. Most customers notice this in the first week.

Quantitatively the difference is significant. We have measured 4 to 6°C lower frame surface temperature on uPVC vs aluminium under identical sun exposure. That translates to a roughly 1 to 1.5°C lower indoor air temperature in a small room with several windows of comparable area. AC running cost reduction is in the 8 to 15 percent range for a typical 2 BHK that switches all aluminium to uPVC.

Air sealing

Old aluminium sliding windows develop track wear that you cannot fix by replacing rollers alone. The sash no longer presses tight against the frame, and air leaks at the meeting stile. You feel it as a slight breeze near the window even when closed. uPVC with a fresh EPDM gasket eliminates this.

Air leakage matters more than people realise. A small continuous draft from a poorly sealing window can account for 20 to 30 percent of an air conditioner's load on the room, because the AC is fighting the fresh hot air entering through the leak. Sealing the window properly is sometimes a bigger comfort upgrade than upgrading the glass.

Monsoon water tightness

Aluminium windows installed before 2010 typically have a single weather seal and a small drainage slot. They were not designed for Chennai's wind driven monsoon rain. uPVC sliders use double EPDM compression seals and an enlarged drainage path. Water that hits the assembly drains outward instead of pooling.

If your existing aluminium window leaks during heavy rain, the uPVC replacement will solve it. We have replaced thousands of aluminium installations on south Chennai apartment blocks where the original developer cut corners on weather sealing, and the comfort improvement is immediate.

Noise

Aluminium frames ring slightly under acoustic stress, which means they transmit airborne sound through structure borne pathways. uPVC is denser and damps sound rather than transmitting it. The difference is small in absolute terms (3 to 5 dB) but noticeable in occupied rooms.

What stays the same or gets slightly worse

• Frame sightlines: uPVC frames are slightly thicker than aluminium (around 70 mm vs 50 mm), so the visible glass area is marginally smaller
• Weight: a uPVC sliding sash with double glazing is heavier than the aluminium it replaces. The track and rollers are sized for this, but the sash itself is denser
• Installation duration: aluminium replacement is typically 1 to 2 days per unit, similar to the aluminium install originally was
• Maximum panel size: very large openings (more than 4 metres in a single sliding unit) are sometimes still better in aluminium because of the lighter frame weight

What about cost

Per square foot, uPVC with single glazing is roughly comparable to a mid range aluminium window. uPVC with double glazing runs 20 to 30 percent higher than aluminium with single glazing. The decision usually comes down to whether you want to do the upgrade once for 20 years (uPVC) or accept that you will be replacing aluminium hardware every 8 to 10 years anyway.

A useful framing: a single aluminium window service call (replace rollers, replace gasket, refit a misaligned sash) costs 1500 to 3000 rupees. Over a 20 year window life you will need 2 to 4 such service visits per window, plus an eventual full replacement when parts go obsolete. That is 6000 to 15000 rupees of service cost alone over the life of the window. The uPVC alternative is closer to zero scheduled service over the same period. The maintenance side is in our annual maintenance schedule.

What to verify before ordering

The same checks we covered for wood frame replacement apply, with one addition: confirm the existing aluminium frame is fully replaced, not retained as a sub-frame. Some installers tuck the new uPVC inside the old aluminium to save labour. This produces a visually decent result but loses 20 percent of the glass area and creates a thermal bridge through the retained aluminium. A proper replacement removes the aluminium entirely and fits the uPVC into the masonry opening directly.

Apartment block bulk replacements

Many Chennai apartment associations are now coordinating bulk uPVC replacements at building scale. This is genuinely a smart approach. Bulk procurement reduces per unit cost by 10 to 15 percent. Single contractor mobilisation reduces overall mess and elevation impact on the building. Standardised specs across units means the building looks coherent rather than patchwork.

If you are part of an apartment association considering this, the typical timeline is 6 to 8 months from initial RFP to last unit installed. The first 8 weeks are scoping (member surveys, spec finalisation, vendor shortlist). Next 4 weeks are vendor selection and contracting. Then phased installation over 4 to 5 months, typically one floor or block per week. We have done several of these and can share a sample timeline and member survey template if your association is exploring it.

What does not get better

If your aluminium windows leak because of bad civil work around the opening, replacing the window with uPVC will not fix it. Water entering through a cracked plaster joint or a failed waterproof coating on the wall finds its way around any window. We will tell you this on the survey. The fix is civil, not fenestration. Replacing the window without addressing the civil issue produces a beautiful new window that still leaks.

Similarly, if your aluminium windows are noisy because the building is noisy (apartment is on a flight path, next to a transformer, etc.), uPVC will not solve it alone. The noise enters through the wall and ceiling as much as through the window. Acoustic treatment of the room as a whole is the answer for those situations.