An alum sliding window replacement is the act of taking an existing aluminium sliding window out of the wall and fitting a new unit in its place — not swapping a roller or a lock, but replacing the whole sash-and-frame assembly. If you are weighing a component fix instead, that is a different job. This article is about the replacement decision itself: when a swap beats a repair, how to measure the opening the way installers do, and what an aluminium slider from a system maker such as ALPES actually changes versus the window you are pulling out.
Two related pieces we wrote elsewhere: a condo-specific renovation walkthrough, and a component-level guide to sliding-window latch and lock replacement. This page is about the whole-unit swap, so we keep the focus there.
A sliding window fails in predictable ways, and most of them are cheap to fix. The trick is matching the symptom to the right fix before you order a whole new unit. The table below is a field-tested decision aid, not a warranty.
| Symptom | Usually means | Smallest fix that works | When a full replacement is the smarter call |
|---|---|---|---|
| Hard to slide, sticking | Dirty track or worn rollers | Clean track, ｒｅｐｌａｃｅ rollers | Frame bent or out of square |
| Draft at the sill, leaks when closed | Worn brush weatherseal or slipped sash | ｒｅｐｌａｃｅ weatherseal, reseat sash | Frame warped or has gaps |
| Fog or moisture between glass panes | Failed insulated-glass seal | Glass-only or sash swap, if frame is sound | Frame rotted, or window past service life |
| Soft or corroded frame at the sill | Long-term water ingress | None, this is structural | Always, after cutting out the rot |
| Opening racked out of square | Wall movement | Rebuild and square the opening | Any window will bind until the opening is true |
An honesty point about seals. Sliding windows seal by contact: brush pile and fin seals ride against the frame rather than being clamped shut the way a casement compresses a gasket. That is the trade you accept for a sash that never projects into a walkway. It is not a defect; it is the mechanism.
A side-press sliding window closes that gap by adding a lateral locking action that compresses the seal instead of only contacting it. But the basic slider you are replacing was always a contact-seal product, and a 20-year-old one will show it. Do not let a salesman tell you a plain slider ever sealed like a casement — ask instead what the new unit does differently.
Once you decide to ｒｅｐｌａｃｅ, the next fork is how much of the wall you open up. The two methods are genuinely different jobs.
| Method | What happens | Choose it when |
|---|---|---|
| ｉｎｓｅｒｔ / pocket / retrofit | New unit nests inside the existing frame line; trim and cladding stay put | Existing frame is sound and square; goal is a clean, low-disruption upgrade |
| Full-frame | Old frame removed down to the rough opening; opening inspected and re-flashed | Frame rotted, out of square, or you are changing the size |
The house decides. A cheaper ｉｎｓｅｒｔ fitted over a deteriorated frame becomes the expensive job later, once the hidden rot you sealed over has spread. Ask the installer, before the old unit comes out, which method your opening actually allows.
The single biggest reason a replacement does not fit is measuring once and ordering to that number. A wall opening is almost never perfectly square, so installers measure three points in each direction and order to the smallest.
Do not measure the sash. The sash rides inside the frame, so a 36-inch sash lives in a frame at least a quarter inch wider. Measure the frame opening, then deduct the clearance the manufacturer specifies — commonly about a quarter to half an inch all round for shimming and sealing. The opening is a fact, not a catalogue number; write down all three readings per direction and never average them.
A replacement inherits some things from the window it replaces and discards others. Knowing which is which stops you from over-ordering or under-specifying.
If your existing aluminium slider sits in a shallow pocket detail, confirm the new frame’s wall width actually fits the cavity before ordering. A 130 mm frame wall will not ｄｒｏｐ into a 90 mm pocket without rebuilding the reveal, and that turns a like-for-like swap into a full-frame job.
ALPES lists one sliding window: the TS130 Side Press Window. It matters to understand what it is, because it is not a plain slider — and that distinction is exactly the upgrade a replacement buyer is in a position to make.
| Property | TS130 specification |
|---|---|
| Profile | 6060-T66 aluminium, 1.8–2.0 mm wall |
| Frame wall width | 130 mm |
| Glass sash thickness | 55 mm |
| Sash width | 75 mm |
| Frame width | 26 mm |
| Track height | 53 / 31 mm |
| Operation | One fixed + one movable, or middle fixed + two movable |
| Hardware | German ROTO side-pressure system, 200 kg load-bearing pulleys, eight-point locking |
| Sealing | Four-sided continuous seal strip with upper-rail frame sealant; the side-pressure action compresses the seal |
Two honest points that the brochure will not lead with:
Replacement is also the moment some owners consider changing how the window opens — converting a horizontal sliding window to a tilt-turn or casement for tighter sealing or in-board cleaning. That is a larger renovation decision: it changes the opening, the hardware and often the structural opening. Those families (AW90, C120, C116) carry published K-values and full-perimeter compression sealing, but they are not “the same window in a different colour.” Treat a change of operation as a separate project and measure for it specifically.
Many replacements are premature. Before you order, check the cheap failures that masquerade as “the window is dead”:
On coastal sites, salt settles on the frame and works into the track and hardware. Rinse it off before it builds up, keep the drainage paths clear, and confirm the powder-coat grade and the maintenance the maker expects to keep any coverage valid. A maintenance routine matched to exposure beats a premature replacement.
A sliding window replacement quote is only as good as the data behind it. Record the following for every opening before you ask for pricing.
| What to record | Why it matters | What happens if you leave it blank |
|---|---|---|
| Opening width, 3 readings + smallest | Sets the order size | Unit will not fit |
| Opening height, 3 readings + smallest | Sets the order size | Unit will not fit |
| Diagonals | Detects a racked opening | Binds after installation |
| Jamb / frame depth, both sides | Confirms unit fits wall thickness | Reveals over, or clears, exterior cladding |
| Wall type | Fixing and flashing method | Wrong anchors, later leaks |
| Current operation | Like-for-like vs change | Wrong product family quoted |
| Glass requirement | Orientation, acoustic, safety | Wrong insulated glass unit |
| Finish colour | Match to existing | Repaint or visible mismatch |
| Sill condition and water staining | Hides rot | Failure within a season |
| Access for delivery and install | Logistics and equipment | Delay or extra access cost |
Can I keep my existing frame and just put in a new slider?
Yes, as an ｉｎｓｅｒｔ or pocket replacement — but only if the existing frame is sound and square. If it is rotted or racked, the ｉｎｓｅｒｔ just seals the problem in.
Do I measure the glass or the frame?
Measure the frame opening with the three-point method and use the smallest reading in each direction. The sash always sits inside the frame and is not your order size.
My slider is hard to push — do I need a new window?
Probably not. Hard sliding is usually dirty track or worn rollers, both cheap fixes done from indoors. ｒｅｐｌａｃｅ the window only when the frame itself is bent or out of square.
Why is there a draft even when the window is closed?
A plain slider seals by contact, so worn brush seals let air through; a side-press unit compresses its seal instead. First ｒｅｐｌａｃｅ the weatherseal; only move to a new frame if the frame has gaps.
Does ALPES publish a K-value for the sliding window?
Not as a single brochure number. Ask for the thermal value against your chosen glass build; it is a system value, not a fixed figure, and it differs from the published casement and tilt-turn values.
Can I change a slider to a casement on replacement?
Yes, but treat it as a separate renovation: it changes the opening, hardware and often the structural reveal. Measure for the new operation specifically rather than assuming the old opening fits.
