COLA construction
What COLA structure types work best for schools?
The three main COLA structure types for schools are steel-framed metal roof (Colorbond), steel-framed fabric membrane (PVC or PTFE), and shade sail (HDPE mesh). Each suits different use cases: metal and fabric membrane provide full weatherproofing for year-round timetabled use, while shade sails provide UV protection and suit spaces where wet-weather use isn't required. The right choice depends on how the school intends to programme the space.
Steel Colorbond COLAs come in gable, curved barrel vault, skillion, and cantilever roof profiles. Gable is the most common and cost-efficient layout. Metal roofs are fully waterproof with a 50-year-plus steel frame design life. Skylights typically cover 5 to 10% of roof area, with electrical lighting used alongside. Insulation and acoustic treatment suit applications where summer heat management and rain acoustics are priorities. Fabric membrane COLAs use PVC or PTFE material stretched over a steel frame. PVC provides 100% UV protection, full waterproofing, and 9 to 13% natural light transmission, which means electrical lighting is usually unnecessary during school hours. Fabric structures can be built in curves and non-rectangular shapes as standard, and the membrane absorbs more rain sound than metal. HDPE shade cloth (often called shade sail or shade mesh) starts at 84% UV protection and blocks 60 to 70% of rain, making it a permeable cover. HDPE suits applications where UV protection is the main requirement and the structure can be replaced over its working life. Schools that need a reliable, timetabled space should specify metal or fabric membrane; shade cloth fits different use cases. The choice between metal and fabric typically comes down to acoustic needs, natural light priorities, and budget.
Steel vs fabric COLA: what's the difference?
Steel (Colorbond) and fabric membrane (PVC) COLAs both provide full weatherproofing on a steel frame, and they differ in natural light, rain acoustics, installation speed, shape flexibility, and long-term lifecycle costs. Steel roofs use metal cladding with skylights for natural light; fabric roofs transmit natural light through the membrane and absorb more rain sound. For an equivalent outcome including bird-proofing, lighting, and acoustic treatment, the two are comparable in price.
A steel Colorbond COLA uses hot-dip galvanised columns and beams with metal sheet cladding. Skylights covering 5 to 10% of the roof area supplement natural light, with electrical lighting used alongside during the day. Metal roofing transmits rain sound, which is worth factoring into acoustic planning when the space hosts assemblies or teaching during wet weather. Steel structures suit rectangular and square layouts where straight lines match the site, and angled or curved steel involves additional fabrication. Installation happens sheet by sheet. A PVC fabric membrane COLA stretches architectural-grade PVC over the same steel frame. The membrane transmits 9 to 13% of natural light, so the space feels open and naturally lit even on overcast days, with no electrical lighting required during school hours. PVC absorbs substantially more rain sound than metal, so teaching and assemblies continue uninterrupted during downpours. Membrane installation takes roughly three days regardless of structure size, because the crew scales up as structure size grows. Curved and non-rectangular shapes are standard with fabric. The steel frame underneath a PVC COLA has a 50-year design life; the membrane lasts 30-plus years, and replacement runs about 20 to 30% of the original build cost because the frame stays. Greenline builds both steel and fabric structures, and the decision between them usually comes down to whether the school prioritises natural light and quieter rain acoustics (fabric) or the permanence and familiarity of a traditional metal roof (steel).
Prefab vs custom COLA: what's the difference?
A prefab COLA is a pre-engineered kit structure (typically a standard gable steel shed in set sizes), while a custom COLA is designed from scratch around the school's specific site, timetable, and programming needs. Prefab is faster to quote and often cheaper per square metre. Prefab fits simple applications like lunch area or walkway coverage. For spaces that will carry varied programming, a purpose-designed structure typically delivers a better-fitting outcome because the design follows from how the school will use the area.
The prefab approach works from a product catalogue: the school picks a span width, a length, and a roof profile, then the supplier delivers a standard kit. This suits simple shade-only applications where the main goal is basic weather coverage over a lunch area or walkway. For a multi-use sports court or assembly space, a purpose-designed structure can account for sport-specific clearance heights, court orientation relative to sun path, acoustic treatment for assemblies, and run-back safety zones around court edges. A purpose-designed COLA starts with the use case and works backward to the structure. That process defines the span, height, orientation, roof material, acoustic provisions, lighting, and integrations (retractable hoops, AV, access for community hirers) before a single steel member is specified. Greenline's Consult. Design. Construct. methodology follows this sequence: consultation on how the space will be used, engineering and design built around that brief, then construction with a locked-in budget. One example is Blackburn High School, where Greenline changed the court orientation during consultation to achieve a better build within budget. The trade-off is timeline and upfront effort: custom projects require more planning, a Development Application, and engineering sign-off, and the resulting space is built to serve the school's specific use case.
How long does a school COLA installation take?
A school COLA project typically takes several weeks to a few months from design through to completion, depending on structure size, council approval timelines, and site complexity. On-site construction is the shortest phase when off-site fabrication is used, because steel components arrive ready to assemble rather than being built from raw materials on the school campus.
The overall timeline breaks into distinct phases: consultation and brief definition, design and engineering, council approval or Development Application (DA), off-site fabrication, and on-site construction. The DA phase is often the least predictable, because council processing times vary by jurisdiction and project scope. A Complying Development Certificate (CDC) fast-track approval can take 5 to 15 business days with correct documentation, while a full DA typically takes 6 to 12 weeks. For context, Blackburn High School's 38-metre by 61-metre multi-court COLA started construction in August 2018 and was completed in early 2019, covering two full basketball courts, four volleyball courts, tiered seating, and integrated sports equipment. PVC membrane installation specifically takes roughly three days on site regardless of structure size, because the crew scales up as the structure grows. Schools can shorten overall timelines by defining their brief clearly before engaging a builder, scheduling construction during holiday periods, and using an integrated design-and-construct provider that avoids the handoff delays between separate architects, engineers, and builders.
