"Sliding window storm" is a phrase that points at three different products, and they are tested against three different things. A hurricane-rated slider in a high-velocity hurricane zone, a storm panel fitted over an existing slider, and an ordinary aluminium slider that simply has to survive a bad night of wind-driven rain are not variations of one product. They are three separate questions with three separate sets of paperwork. Sorting out which one you are actually buying matters more than any single performance number, because the wrong answer fails in a way that looks like a manufacturing defect but is really a specification error made months earlier.
This article separates the three, then spends most of its length on the one you can actually specify from a factory drawing: what a sliding window has to do in a storm, where it fails first, and what belongs in the enquiry. If you are sourcing a china top sliding storm windows factory for a coastal or cyclone-exposed project, the last three sections are the ones worth pasting into your RFQ.
The fastest way to waste money on a storm-exposed project is to answer the wrong one of these. A buyer in Miami asking for a storm slider means something legally defined. A facilities manager in Manchester asking for a storm window means a retrofit panel. An architect in Shenzhen asking how a slider performs in a typhoon means neither — they mean wind load and water management, and no certificate for the first two answers the third.
| If they mean | What it protects against | Who mandates it | What proves it | What it does not do |
|---|---|---|---|---|
| 1. Impact-rated (hurricane) sliding window | Wind-borne debris penetration, then pressure loss of the building envelope | Local building code in defined wind-borne debris regions | A product approval covering that exact configuration, issued by the authority having jurisdiction | Does not improve thermal performance, and does not tell you the design pressure you need |
| 2. Storm window / secondary glazing over a slider | Heat loss, draughts and noise through an existing window that stays in place | Nobody, usually — it is a discretionary retrofit | Air-gap width, inner seal continuity, and how it is retained | Standard secondary glazing is not automatically tested for impact or forced entry |
| 3. How the slider itself behaves in a storm | Wind-driven rain, wind pressure, and repeated gust cycling over decades | The building code through design pressure, plus the fenestration standard | Laboratory test reports to a named standard, at a named pressure, on a named size | Does not mean the window resists debris impact |
An impact-rated slider is not a stronger slider. It is a system in which three layers have to work together, and the failure of any one of them makes the other two irrelevant.
Laminated impact glazing is built as a sandwich: an outer ply takes the strike and may crack, a PVB or SGP interlayer retains the fragments, and an inner ply supports the laminate so the barrier survives. The performance goal is explicitly no penetration — not an unmarked pane. A compliant window can look badly damaged after a strike and still have done its job, because the building stayed pressurised. "Unbreakable glass" is the wrong expectation to write into a specification, and setting it will cause you to reject a product that passed.
This is where a slider differs most from a casement. A casement sash is held by hinges and a multi-point lock that pulls it into compression seals on all four sides. A sliding sash is held by rollers at the bottom, a head guide at the top, and an interlock where the sashes meet. Under the suction phase of a gust, the load path is completely different. The interlock, the roller assembly and the track geometry carry it — which is why the roller load rating in a storm specification is a structural number, not a comfort feature. It is also why "can the sash be lifted out from outside" is treated as both a hurricane question and a security question in the same detail.
This is the single most expensive misunderstanding in storm procurement. Approvals are issued against a specific combination of panel dimensions, glazing make-up, frame configuration, hardware, anchoring and installation detail. A manufacturer may hold several approvals and still have none that cover the size you want. Before you accept a product family name, check five things in the approval document:
In North American usage a storm window is a secondary sash fitted to an existing window to create an insulating air gap; in UK and Australian usage the near-equivalent is secondary glazing, normally fitted on the room side. Either way the original window stays in place, which is the whole point — it is the reason this route stays available on heritage facades, in conservation areas, and in tenanted buildings where the primary window cannot be altered.
Decide first which problem you are solving, because the two answers conflict. Sound attenuation between two panes improves as the gap widens, and useful acoustic performance wants a wide cavity — far wider than any sealed insulating glass unit can offer. Thermal performance goes the other way: beyond a moderate gap the air in the cavity begins to convect and carries heat across, so a very wide gap is no better thermally than a moderate one. You cannot have both optima at once. Two panes of different thickness also perform better together acoustically than two identical ones, because they resonate at different frequencies.
Fitting a secondary panel to a sliding window is harder than fitting one to a casement for a reason that has nothing to do with the panel. A slider needs clear horizontal travel in front of it. An interior panel must clear the full slide path of the sash, plus the handle; an exterior panel must not block drainage openings or trap water against the frame. And somebody has to clean two glass surfaces that now cannot both be reached from inside. On wide openings the honest answer is often that a new sealed unit in a new frame is simpler than a retrofit that fights the slider's own geometry.
This is the section that applies to every slider on a storm-exposed elevation, certified or not. A sliding window does not fail in a storm the way a casement fails. It fails in three specific places, and all three are consequences of the sliding principle rather than of poor manufacturing.
| Failure point | Why it is structural to a slider | What the specification must name |
|---|---|---|
| The sill track | A sliding sill collects water by design. Horizontal rails form shallow channels that catch wind-driven rain and drain it outward through weep slots. Water in the outer track is normal; water past the inner sill is not. | Track height, weep provision and whether they are covered, sill pan with back dam and end dams, and a written instruction that weep holes must never be sealed. |
| Sash retention | Rollers, head guide and interlock carry the suction phase. Worn rollers let the sash sit unevenly and open a gap at the top; a sash that rattles or needs force to lock is already out of adjustment. | Roller load rating against actual sash weight, adjustability after installation, anti-lift detail, interlock engagement depth. |
| The sliding seal interface | Sliding sashes seal with pile or fin weatherstripping because the surfaces move against each other. Pile seals cannot deliver the compression seal a casement gets from locking down onto gaskets. This is inherent, not a defect. | Pile versus fin seal, whether fin seal is specified for dust and salt exposure, and the air infiltration figure with the test standard that produced it. |
Clear and test the weep path before the rainy season. Vacuum the track, flush it with water, and confirm it discharges to the exterior immediately. Do not seal weep holes to stop a draught — sealing them traps water in the frame and changes where it eventually escapes, which is usually inward. Also re-check lock engagement: a latch that no longer pulls the sash firmly against its seals leaves a gap for driving rain, and on a slider the fix is usually a roller adjustment rather than a new lock.
Under the North American fenestration standard AAMA/WDMA/CSA 101/I.S.2/A440, the three performance tests are separate sequences and they are not interchangeable. Understanding the relationship between them stops you from comparing the wrong figures:
First, design pressure is calculated from the building — location, height, exposure, building configuration — using the relevant load standard and the local code. It is not selected from a catalogue. A supplier who offers you a DP without asking for your site data is not helping. Second, a figure obtained under one standard is not the same figure under another: EN/ISO and North American test methods use different boundary conditions, and a value converted between psf, Pa and kPa is a converted number, not a test result. Always submit the number in the unit your authority's form asks for, from a test performed to the standard it recognises.
The table below lists the drainage and load provisions that matter on a storm-exposed elevation, using published ALPES figures. Treat it as a map of what to ask about, not as a certificate.
| Series | Frame width | Water and drainage provisions | Load and retention |
|---|---|---|---|
| TS130 side press window | 130 mm; track height 53/31 mm | Four-sided continuous sealing strip plus sealant between the upper rail and the frame; side-pressure rubber strip seal | 200 kg pulleys; eight-point locking; ROTO side-pressure hardware |
| SL112/167 | 112 mm single/two track; 167 mm three track | 45 mm high-ｄｒｏｐ bottom track for instant drainage; optional 85 mm water barrier; sash sink design with mechanical sealing | Driving capacity up to 220 kg; frame-enclosing-sash interlocked structure |
| SL126/182 (96 mm sash) | 126 mm two track; 182 mm three track; high track 43 mm, low track 8 mm | Patented eave-style waterproof design; bottom track water-blocking edge; continuous four-side sealing plus sealant between top track and frame | Locally reinforced to 3.0 mm in critical zones; single sash up to 2.5 m by 3.0 m |
| SL126/182 (75 mm sash) | 126 mm two track; 182 mm three track; high track 43 mm, low track 8 mm | Butyl rubber waterproof gasket at frame-sash joints; interchangeable drip-eave inserts; continuous four-sided sealing | Multi-point locking in precision-cast reinforced casings; locally reinforced to 3 mm; 27A insulating glass with inert gas filling |
| SL155 | 155 mm, four track | Passive check valve drainage to prevent backflow; four-sealing design; recessed sash for a tighter seal | Single-panel double-rail self-balancing pulley, 20 wheels, 400 kg; single sash max 2800 mm by 2600 mm |
Frame depth is a property of the series, not a function of track count. The four-track SL155 is 155 mm deep, which is shallower than the three-track SL126/182 at 182 mm. Do not let anyone on site assume that more tracks means a deeper frame to build into — the wall opening is set by the series you choose.
ALPES does not publish whole-window U-values for the sliding series. What is published for the casement and tilt-and-turn ranges are system K-values — 1.6 for the C120, 1.7 for the C116 and 1.3 for the AW90 — and those are system figures, not the whole-window value your energy model wants. If thermal performance is a compliance item, ask for the whole-window figure calculated for your exact size and glass configuration, in the unit and to the standard your authority recognises.
We can evidence the material and construction baseline: 6060-T66 alloy at 1.8 mm to 2.5 mm profile thickness with local reinforcement to 3.0 mm in critical zones, PA66GF25 multi-chamber thermal breaks, 240-hour salt spray corrosion testing and 5,000 N shear resistance on the AW90, CMECH hardware cycle-tested to 30,000 operations, and the roller load ratings listed above. We can supply test specimens, section drawings and material declarations.
We cannot supply a Notice of Acceptance for a high-velocity hurricane zone, and we do not claim one. Product approvals in those jurisdictions are issued to the applicant for a tested configuration by the authority having jurisdiction, and they do not transfer across a product family name or across national borders. If your project sits in an approved-product jurisdiction, the testing has to be commissioned for your configuration under your local programme, and the applicant of record will be you or your local representative. What we can do is build to the specification those tests require and supply the specimens and documentation the laboratory will ask for.
The same discipline applies to frame material choices driven by sightlines. If your elevation is calling for a steel casement window for the narrowest possible sections, treat corrosion protection and thermal bridging as separate line items in the specification — a storm rating does not resolve either, and in a salt-laden coastal atmosphere both get worse, not better, as sections get thinner.
Sliders are excellent for wide openings where nothing may project, and poor in a specific set of circumstances. Being explicit about those circumstances is cheaper than discovering them after handover.
| Situation | Why a slider struggles | Consider instead |
|---|---|---|
| Very high design pressure on a large panel | Load path runs through rollers, head guide and interlock rather than through hinges and perimeter compression | Fixed glazing for the non-ventilating part, with a smaller operable unit beside it |
| Air-tightness is a compliance target | Pile and fin seals cannot reach the compression seal a closing sash achieves | Outward-opening casement, or a side-press slider where the geometry allows |
| Nobody will maintain the tracks | A blocked weep path turns a managed water system into an overflow | Fixed units, or a drainage strategy with a sill pan that does not depend on occupant maintenance |
| Fine dust or salt-laden air | Particles migrate through standard pile; seals and tracks both degrade | Fin seal specification plus a defined maintenance interval, or a compression-sealing opening type |
| The opening is also the emergency escape | Net clear opening has to satisfy the escape rule after the sash is fully slid, not just the glass area | Check the escape dimension against your local code before finalising sash count |
| Very large single panels | Weight drives roller class, glass make-up, handling and installation equipment together | Split the opening, or use a lift-and-slide configuration with a confirmed roller rating |
The panel-size question deserves one more sentence, because it is the one that catches projects late. Whatever governs the largest tilt and turn window on a project governs a large slider even more tightly: as the panel grows, hardware capacity and glass weight become the controlling variables, and the window stops being a glazing decision and becomes a structural and logistics decision.
Send these ten lines to every supplier you are comparing. The third column is what a vague answer usually means.
| Ask | A good answer looks like | Red flag |
|---|---|---|
| What design pressure is this unit rated to, positive and negative? | A figure tied to a stated test size, with the report reference | A single number with no size, no direction and no report |
| Which standard was it tested to? | The full standard designation and edition, matching your authority's requirement | "Tested to international standards" |
| What is the water penetration test pressure? | The derived fraction of DP, with the test method named | Water resistance quoted without any pressure at all |
| How does the sill drain, and can it be blocked? | Track heights in mm, weep locations, whether covered, and cleaning access | "Fully sealed system" |
| What is the roller rating, and what does this sash actually weigh? | A rated capacity above the calculated sash weight, with margin stated | Heavy-duty rollers with no number |
| Can the sash be lifted or forced out from outside? | A named anti-lift or interlock detail shown on a section | The question not understood |
| Pile or fin seal, and why? | A recommendation that references dust, salt and your exposure | "Standard weatherstripping" |
| What is the anchoring schedule? | Fastener type, spacing, substrate and edge distance in writing | "Installer to determine on site" |
| Which parts are replaceable in ten years? | A named spare parts list with roller and seal part numbers | No answer, or "contact us when the time comes" |
| Who is the applicant of record for the local approval? | A clear statement of who commissions and holds the approval | A supplier implying their existing certificate covers your project |
No. An impact-rated slider is a complete window tested to resist debris impact and pressure cycling, and it is usually mandated by code in defined wind-borne debris regions. A storm window is a secondary panel added to an existing window to improve thermal and acoustic performance. Standard secondary glazing is not automatically tested for impact or forced-entry resistance.
Not by adding a standard panel. Impact performance is a property of the tested assembly — glass make-up, frame, hardware, anchoring and installation together — not of an extra pane. An added pane may improve comfort and noise, and it may keep rain off the primary sash, but it does not convert an untested window into an approved impact assembly. There is also a practical problem specific to sliders: the panel must clear the sash's full travel without blocking the drainage path.
Not necessarily. A sliding sill is designed to collect wind-driven rain and discharge it to the outside through weep slots, so water in the outer track can be normal. Water past the inner sill, staining below the opening, or a track that still holds water hours after the rain stops are the signs of a real problem — usually a blocked weep path or failed perimeter sealant rather than a glass or sash defect.
Do not. Sealing the drainage path traps water inside the frame and it will find another way out, usually inward, where it damages finishes and the wall below. If the draught is real, the fix is to address the seal that is letting air through — weatherstripping condition, roller adjustment and lock engagement — not to block the drain. Covered weep slots with flap valves exist precisely to reduce wind ingress while keeping gravity drainage working.
Not always a useful one, and never a substitute for the calculation. Design pressure is derived from your site — wind speed, height, exposure and building geometry — through the load standard your code adopts. Specifying a much higher figure than the site requires adds cost and weight without adding compliance value, and a figure chosen from a catalogue rather than calculated may still be wrong for the corner of the building where the load is actually highest.
No, and we do not claim one. Approvals of that kind are issued by the authority having jurisdiction to an applicant for a specific tested configuration, and they do not transfer by product family or across borders. What we can do is manufacture to the specification those tests require, provide the material and construction evidence an applicant needs, and supply test specimens. For projects outside approved-product jurisdictions, the practical route is usually third-party testing to the standard your authority recognises, commissioned for your configuration.
If you are specifying sliding windows for a storm-exposed elevation and want the section drawings, drainage details and roller ratings for a specific opening size, send the dimensions and your target design pressure through the ALPES contact page and ask for the weather-resistance package.
