The Sustainability Case: Waste Reduction in Large-Format SLA vs. Foam/CNC for Site Models
Architectural site models are powerful tools for effective communication. They help planning officers, investors, and communities tangibly visualize projects. But creating them comes with a cost—both financial and environmental.
Traditionally, site models have been carved from foam boards or dense model-making sheets using CNC routers. More recently, additive methods like large-format SLA (stereolithography) 3D printing have become a viable alternative. Both approaches deliver the scale and presence architects need, but they differ dramatically in how they use (and waste) materials.
This article explores the sustainability case for each method, focusing on waste reduction, energy use, transport, and reusability. The aim isn’t to declare one approach “better,” but to help practices choose the method—or combination—that aligns with their sustainability goals.
Why Waste Matters in Architectural Model-Making
Before diving into processes, it’s worth asking why waste deserves attention in the first place.
Volume of material: Site models, especially urban masterplans and campus layouts, cover wide areas. They require substantial baseboards, terrain, and massing. That means a lot of input material before you even start adding detail.
Short lifespans: Many models are created for competitions, exhibitions, or planning submissions. After their purpose is served, they’re often dismantled or discarded.
Hidden costs: Waste doesn’t just sit in a bin. It carries embodied carbon from extraction, processing, and transport. Foam offcuts and dust also present recycling challenges, while resin and solvent waste needs careful handling.
For design studios aiming to cut their environmental footprint, waste is no longer just a workshop problem—it’s a reputational and strategic concern.
Foam and CNC: Subtractive Speed with Heavy Offcuts
CNC routing with foam or model board has been a mainstay for decades. It’s fast, relatively low-cost, and allows big volumes to be shaped quickly. However, its subtractive nature means that waste is built into the process.
How CNC Works in Model-Making
A block of foam or dense polyurethane board is fixed onto the CNC bed. A router bit cuts away material layer by layer until the desired contours and building forms are revealed. The process is guided by CAD/CAM software.
Where Waste Arises
Offcuts and dust: For every piece shaped, there are chips, dust, and unused sections of board. These offcuts are rarely recyclable, especially once adhesives or paints are applied.
Over-sized stock: To ensure coverage, makers often start with larger blocks than needed, leading to excess trimming.
Revisions and re-runs: Planning models often change mid-process. If a design update arrives after milling, an entire sheet may become redundant.
Packaging and transport: Foam panels are bulky and fragile. They need protective wrapping, increasing material use for delivery.
The Environmental Impact
CNC workshops require dust extraction systems running throughout the process. These consume additional energy and rely on filters that need replacement. While foam itself is lightweight, its production is energy-intensive, and its disposal is problematic due to contamination and low recyclability.
In short, CNC’s efficiency at shaping comes at the cost of significant physical waste.
Large-Format SLA: Additive Precision with Smart Material Use
Large-format SLA 3D printing flips the equation. Instead of carving away from a block, it builds up models layer by layer using liquid photopolymer resin cured by lasers or UV light.
How SLA Works
A build platform lowers into a vat of resin. A laser selectively cures areas layer by layer until the model is complete. With modern machines capable of printing volumes of 750 × 750 × 550 mm, entire site sections can be produced in one piece.
Where SLA Saves Waste
Material efficiency: Only the model’s geometry is printed. Hollowing and lightweight lattice infill reduce resin use without sacrificing strength.
Support optimization: Clever orientation and custom supports cut down on excess material.
Part consolidation: SLA can combine multiple details into one print, avoiding the need for separate milling and gluing stages.
Reusable components: Printed tiles, façades, or street blocks can be re-painted and repurposed across projects.
Post-Processing Waste
SLA isn’t perfectly clean. Supports must be clipped, and models are rinsed in solvents like IPA. Gloves, paper towels, and used resin add up. But compared with bags of foam offcuts and bins of dust, the scale of waste is far smaller and easier to manage.
Comparing Energy and Operational Impacts
Energy Demand
CNC: Energy spikes while cutting. Dust extraction and ventilation systems run continuously. Large jobs may require several machine hours, but once cutting stops, so does consumption.
SLA: Printers consume energy steadily throughout long builds, often overnight. Post-curing also uses UV ovens. However, batch printing multiple parts on one platform can improve efficiency.
Emissions and Health
CNC workshops create fine dust particles that require protective equipment and extraction to safeguard staff health.
SLA workshops avoid airborne particulates but involve handling liquid resins, which require gloves and proper disposal.
Both methods carry environmental and health considerations, but SLA eliminates the problem of airborne foam dust—an often-overlooked hazard.
Five Ways SLA Minimizes Waste in Practice
The sustainability advantage of SLA becomes clearer when you look at specific design strategies:
Hollowing and Shelling
Solid building masses can be reduced to thin-walled shells (1.5–3 mm) with internal ribs. This slashes resin use while maintaining surface quality.Lattice Infill
Instead of solid cores, models can feature gyroid or honeycomb infill. They retain stiffness but require far less material.Smart Orientation
Tilting a building or terrain tile reduces support density, especially on detailed façades. This not only saves resin but also reduces sanding and finishing.Parametric Level of Detail
Near-field areas can carry high detail, while peripheral blocks use simplified geometry. Material is focused where it matters most for storytelling.Reusable Modules
Context buildings, streets, or terrain tiles can be re-skinned, painted, or swapped. Unlike foam offcuts, these parts don’t have to be discarded after one use.
Where Foam/CNC Still Has a Role
It’s not all or nothing. Foam and CNC still have valid applications in sustainable workflows.
Large terrain forms: For low-detail landforms, a thin foam core milled quickly may be more efficient than printing vast, simple slopes.
Speed on simple shapes: CNC can remove bulk quickly when deadlines are extremely tight.
Hybrid builds: Many studios now combine methods—milling the terrain in foam, then adding SLA-printed buildings for detail. This balances speed, cost, and material efficiency.
The key is using CNC where it’s inherently low-waste and SLA where precision and reusability matter most.
Transport and Logistics: Hidden Waste Factors
Sustainability isn’t just about the workshop. How models move also affects their footprint.
Foam/CNC models: Bulky, fragile panels require careful packing. Couriers often add layers of plastic wrap and foam sheets.
SLA models: Resin prints, especially when hollowed, are lighter and can be designed to break down into modules. This reduces packaging needs and allows for easier transport by hand luggage or compact cases.
If you’re presenting internationally, these logistics can be the difference between a dozen protective crates and a single carry-on case.
Practical Steps for Architects to Reduce Waste
Whether you use SLA, CNC, or both, your design choices can directly influence sustainability outcomes.
Share clean geometry: Provide watertight CAD exports so the model shop can hollow or split parts efficiently.
Declare sustainability goals: Add waste reduction or reusability to your project brief. This gives vendors permission to optimize.
Prioritize local production: A nearby SLA workshop cuts courier miles and packaging waste.
Specify smart finishes: Request primer-ready surfaces and modular painting rather than heavy coatings.
Design for reuse: Incorporate magnets, dowels, or interchangeable tiles so elements can live on after one project.
The Bigger Picture: From Models to Practice Sustainability
Choosing SLA over CNC doesn’t make a practice sustainable overnight. But it’s part of a larger story: reducing hidden waste in everyday workflows. Clients and planning authorities increasingly ask about environmental impacts, and physical models are a visible symbol of your approach.
By demonstrating that your presentation materials are considered, efficient, and designed with circular use in mind, you reinforce your commitment to sustainability beyond the building design itself.
Conclusion: A Balanced, Low-Waste Future
If we measure strictly by waste, large-format SLA holds a clear advantage over foam/CNC. Additive manufacturing builds only what’s needed, and smart preparation can significantly reduce resin consumption. Foam/CNC, while quick and familiar, is inherently waste-heavy due to its subtractive nature.
That doesn’t mean CNC is obsolete. For terrain and speed, it still has a role. But the sustainability case increasingly points toward hybrid approaches: milling where it’s efficient, printing where precision and reusability matter, and combining both to minimize scrap.
Ultimately, reducing waste in site models isn’t about tools alone. It’s about mindset—designing with material efficiency in mind, choosing local production, and planning for reuse. For practices serious about sustainability, the message is clear: rethink not only the buildings you design but also the way you present them.