Technical library

Improper Use of Storefront Window Systems Leading to Costly Repairs: A Case Study

Article by Jason Popovich

Background on this topic from Inspec

This case study reveals how the misuse of aluminum storefront window systems caused significant water infiltration in a Minneapolis church. Learn how improper design decisions and overlooked drainage details led to long-term damage and why proper system selection is critical to building enclosure performance.

The wrong system in the wrong opening

A storefront window system is a shallow, front-loaded aluminum framing system developed for ground-level work: entrances, lobbies, vestibules and retail frontage in one- and two-story openings. Its frame depth, anchorage, glazing method and drainage path are all sized for that duty. When a storefront window system failure is investigated, the cause is often not a defective part or a careless installer. It is that the system was asked to do the job of a curtain wall, a window wall, or a punched window several floors above grade.

The distinction matters because a misapplied system can be installed exactly as the manufacturer intended and still leak. Nothing on site looks wrong. The problem was decided long before the first frame was set.

How a storefront ends up outside its rated application

A substitution during value engineering trades a deeper, higher-rated system for storefront on the strength of a similar-looking elevation drawing.
A detail drawn for the ground-floor lobby is repeated up the facade without recalculating wind load at the upper floors.
A performance specification delegates the design to the fabricator but omits the design pressure, the water penetration test pressure, or the deflection limit that would have ruled storefront out.
The specification says "aluminum framed glazing" and leaves the class of product to whoever is bidding.
In a renovation, a new or enlarged opening is filled with the same product already used at grade, in a wall assembly that drains very differently.
Frames are set before the sill flashing, end dams and air barrier terminations have been detailed, so the perimeter is resolved with sealant after the fact.

Where the failure shows up

Design pressure and deflection

Wind pressure rises with height and exposure, and corners and parapets see the worst of it. A shallow storefront mullion spanning a full floor deflects further than a deeper section under the same load. Gaskets unseat, glazing pockets open, and joints that were watertight in a shop test move under load in service.

Water penetration resistance

Storefront is commonly rated at a water test pressure suited to grade-level exposure. Wind-driven rain at the fourth floor of an exposed elevation does not respect that rating. Center-set, interior-glazed configurations put the primary seal where it is hardest to inspect and hardest to renew.

Drainage with nowhere to go

Storefront collects incidental water in the glazing pocket and weeps it out at the sill. That works when the sill sits at a slab edge or a curb. It fails when the sill sits over a stud wall, a shelf angle or a soffit, because the water the system was designed to discharge is discharged into the wall assembly instead. This is the same interface problem discussed in our article on window receptors.

Thermal behavior mistaken for a leak

Sections with limited or no thermal break, installed in a heated, occupied space in a cold climate, produce condensation and frost at the frame. The staining on the sill and the wet finish below look exactly like water infiltration, and the first several repair attempts are aimed at the wrong mechanism.

Movement and anchorage

Stacked storefront installed floor to floor without a head deflection allowance or a horizontal expansion joint transfers live-load deflection from the structure into the glass and the frame, which shows up as bowed sections, broken seals and cracked lites.

Why the correction costs more than the upgrade would have

Choosing a deeper, higher-rated system at bid time is a unit-price difference on a schedule. Correcting a misapplied system after occupancy is a construction project inside a working building: access equipment or swing stage, temporary weather protection, interior finishes opened up, wet insulation and sheathing replaced, corroded framing addressed, tenant coordination and phasing by elevation, and often a period of repeated sealant maintenance before anyone concludes that sealant is not the answer. The collateral scope frequently exceeds the glazing scope.

Retrofit or replace

Before either is priced, an investigation has to separate what installation can fix from what the product cannot do. That means locating the actual entry points rather than the appearance points, and confirming performance on representative units through air and water infiltration testing in the field. If units fail well below their own rating, workmanship and interface detailing are in play. If units perform at their rating and still leak in service, the rating is the problem, and remedial sealing will not close the gap.

From there the realistic options are a retrofit that adds a drainage path and a serviceable perimeter, replacement with a system rated for the exposure, or replacement of only the elevations where the exposure exceeds the product.

Catching the substitution before it is built

Misapplication is preventable at three points: the specification, which should state design pressure, water penetration test pressure and deflection limits rather than a product name; the submittal review, where product data and test reports are compared against those requirements; and the mock-up, tested before production glazing begins. Building envelope commissioning and exterior walls and window consulting both exist to keep a proposed substitution from reaching the wall.

If it is already installed and leaking

Inspec investigates and tests glazing systems, identifies whether the cause is application, detailing or installation, and prepares repair or replacement documents for an owner to bid. We do not perform the work, so the recommendation is not tied to a repair scope we would sell. Owners dealing with active infiltration can start with a forensic building enclosure investigation or contact one of our offices.

Read the full article (PDF)

Common questions

What is a storefront window system actually designed for?

Aluminum storefront framing is intended for ground-floor, low-rise openings such as entrances, vestibules and retail frontage. It is usually center-glazed, shallow, frequently not thermally broken, and tested to a water-penetration pressure that reflects that sheltered exposure. Within those limits it performs well. Problems begin when the same system is carried up a building or used as a substitute for curtain wall.

How can I tell whether my storefront system was misapplied?

Compare the design wind pressure at the actual opening location with the water-penetration test pressure listed for the installed system. If the system was substituted during bidding or construction, check the submittal record for a tested performance class. Field indicators include recurring leaks during wind-driven rain, sill corrosion, blocked weeps and sealant that has been renewed repeatedly without success.

Will resealing the perimeter joints stop the leaks?

Sometimes, but only if the sealant joint is genuinely the source. Storefront framing is a drained assembly, so it expects to admit some water and shed it through weeps and the sill. If drainage is blocked or the system is past its rated pressure, resealing hides the symptom briefly and the leakage returns. Investigation should precede any repair scope.

When should storefront systems be tested during construction?

Test a mock-up or the first installed opening before the wall assembly is closed and interior finishes begin. At that point a failed detail can be corrected for the cost of labour and a few materials. Testing after occupancy means access equipment, interior protection, tenant disruption and remediation of whatever the water has already reached.

What is the practical difference between storefront and curtain wall on a multi-story facade?

Curtain wall uses deeper sections, structural anchors at each floor and a drained, pressure-equalized glazing pocket designed for wind-driven rain at height. Storefront uses shallower sections and a simpler drainage path suited to grade-level openings. The two can look similar in elevation, which is exactly why substitutions pass unnoticed until the upper floors begin leaking.

Can a misapplied storefront be upgraded in place instead of replaced?

Sometimes. If the frames are structurally adequate for the actual wind load and the perimeter can be reworked to give collected water a route back out, a retrofit that adds sill flashing, end dams and a serviceable perimeter may be viable. If the sections deflect beyond their limit under design pressure, replacement is usually the only durable answer.

Could the water at our storefront sills be condensation rather than a leak?

It can be, particularly with sections that have little or no thermal break in a heated space during cold weather. Condensation typically appears during cold snaps regardless of rain, forms evenly along frames and glass edges, and stops when interior humidity drops. Rain-driven leaks track weather. Distinguishing the two determines whether repairs address glazing or interior conditions.

What documents should we gather before an investigation begins?

The glazing specification section, approved shop drawings, manufacturer product data with the system's performance rating, any laboratory or field test reports, and the sill, jamb and head details showing how the frame meets the wall. Together these establish what the system was rated to do and what the drawings assumed it would do.