The short version
- Pick a scale your printer can handle: usually 1:100–1:200 for a building, 1:500 for a site.
- Make a 3D view that shows only what should be printed.
- File › Export › CAD Formats › STL: Binary, millimetres.
- Open it in your slicer, check that it's manifold, scale it by 1 ÷ your scale, and print.
Most failed prints come from the same few things: walls too thin at the chosen scale, geometry that isn't closed, and the wrong units. The steps below deal with each of them.
1. Choose the scale first
Decide the scale before you touch the model. It decides which details survive, how thick every wall becomes, and whether the model fits on your printer's bed. Printed size is simply the real size divided by the scale:
| Real size | 1:50 | 1:100 | 1:200 | 1:500 |
|---|---|---|---|---|
| 100 mm partition | 2 mm | 1 mm | 0.5 mm | 0.2 mm |
| 200 mm wall | 4 mm | 2 mm | 1 mm | 0.4 mm |
| 3 m storey | 60 mm | 30 mm | 15 mm | 6 mm |
| 50 m facade | 1,000 mm | 500 mm | 250 mm | 100 mm |
- Thinnest printable wall: on an FDM printer with a 0.4 mm nozzle, walls of about 0.8–1 mm print reliably, and anything under about 0.4 mm usually disappears. Resin printers manage finer detail, down to roughly 0.5 mm.
- Will it fit? Multiply your bed size by the scale. A 256 mm bed holds 25.6 m of building at 1:100, 51.2 m at 1:200 and 128 m at 1:500.
- Typical choices: 1:100 or 1:200 for a single building, 1:500 or 1:1000 for a site or masterplan.
2. Make a print view
Revit's STL export uses the visibility and graphics settings of the current 3D view, so set up a view just for printing.
- Duplicate the default {3D} view and name it, for example, 3D print.
- Set Detail Level to Coarse. Fine detail such as door handles and window frames is too small to print anyway.
- In Visibility/Graphics, turn off what you don't want printed: furniture, casework, plumbing fixtures, lighting, MEP, entourage, planting and annotations. Loose small objects are the most common cause of messy prints.
- Set the view's phase to the design you want to show, for example new construction only.
- Use a section box to keep only the part you want. Where it cuts through elements, check the result in your slicer (step 4), because cut faces aren't always closed.
3. Export the STL
Revit 2024 and later have STL export built in. With your print view open, go to File › Export › CAD Formats › STL and set:
- Format: Binary. Binary files are smaller and better for 3D printing than ASCII.
- Resolution: Medium for most models. Fine gives smoother curves but more triangles and more memory, and Coarse helps when Revit struggles with a large model.
- Units: Millimetres. STL files carry no units, and every slicer assumes millimetres.
On older Revit versions, use Autodesk's free STL Exporter add-in, or export FBX and convert it to STL in Blender. If a big model makes Revit stop responding, export it in pieces: one view and section box per wing or per level.
4. Check that it's watertight
Slicers need closed volumes, also called watertight or manifold meshes. Open edges cause missing walls, holes and strange infill. Revit can't check this itself, but these free tools can:
- PrusaSlicer: import the STL. The object info panel shows whether the mesh is manifold and how many errors were repaired automatically.
- Bambu Studio: it warns when a model has non-manifold edges. On Windows, right-click the object and choose Fix model.
- Blender: enable the 3D-Print Toolbox and run Checks › Solid. It counts non-manifold edges and can also check wall thickness.
Automatic repair closes small holes, but it can't know what a wall should look like. If the counts run into the hundreds, fix the cause in Revit (step 5) rather than relying on repair.
5. Fix the usual problems
| What you see | Why | What to do |
|---|---|---|
| Walls, mullions or railings missing after slicing | Thinner than the nozzle can print at this scale | Use a larger scale, give the walls a thicker "print" type in Revit, or switch the slicer's wall generator to Arachne (PrusaSlicer, Bambu Studio), which copes better with thin walls |
| Holes or missing faces | Geometry that isn't closed: surfaces imported from CAD or SketchUp, old toposurfaces | Hide those elements, replace toposurfaces with a toposolid (Revit 2024+), or repair in the slicer or Blender |
| Small loose bits on the bed | Furniture, fixtures, balusters and other small objects | Hide those categories in the print view |
| Glazing missing or broken | Glass and curtain panels are only a few centimetres thick, a fraction of a millimetre at scale | Hide curtain panels and keep the openings, or give the panels a thicker type for printing |
| Wrong size in the slicer | Exported in feet or inches, or not scaled | Export in millimetres, then scale by 1 ÷ scale (1:200 → 0.5%) |
| Too big for the bed | Printed size is larger than the build volume | Choose a smaller scale, or cut the model into parts with the slicer's Cut tool and glue them after printing |
| Thin walls around empty rooms that warp or break | At small scales, rooms become cavities surrounded by very thin walls | Fill the rooms with solid in-place families (Generic Model) in a print-only view, or print at a larger scale |
Site models: toposolids (Revit 2024 and later) export as closed solids. Give the toposolid enough thickness that the base is at least 2–3 mm thick at your scale.
6. Slice and print
- Scale: if you exported at full size in millimetres, scale uniformly by 1 ÷ your scale: 1:100 → 1%, 1:200 → 0.5%, 1:500 → 0.2%.
- Orientation: flat on its base. The ground floor slab gives a good first layer.
- Layer height: 0.12–0.16 mm for detail, 0.2 mm for quick test prints.
- Walls and infill: 2–3 walls and 10–15% infill are plenty for an architectural model.
- Supports: only where needed, for canopies, balconies and overhangs. Tree supports are easier to remove.
- Material: matte white or light grey PLA reads like a classic card model and shows the form best.
Questions
FDM or resin?
FDM is cheaper, prints larger models and needs little cleanup. Resin prints much finer detail, such as thin mullions and railings, but has smaller build plates and needs washing and curing. For massing and student models, FDM is usually the better start.
Why do my windows disappear?
Mullions and frames are usually thinner than the nozzle can print at model scale. Use a larger scale, give them a thicker type in your print view, or accept openings without frames, which often reads better anyway.
Can I print in colour?
STL files don't carry colour reliably. A simple workaround is to export separate STLs, one per material or category with its own print view, then import them together in the slicer as parts of one object and give each part its own filament.
How long does it take?
Setting up the view and exporting takes minutes. Fixing a model by hand can take hours, especially thin walls and open geometry. The print itself often takes several hours to a day, depending on size and layer height.
The shortcut
Everything above is what PrintBIM does inside Revit in one step. It is a Revit add-in that turns your model into a watertight, correctly scaled STL:
- picks the largest scale that fits your printer with Best fit;
- leaves out furniture, fixtures and annotations automatically;
- fills enclosed interiors and closes gaps too small to print;
- thickens free-standing thin parts such as canopies, parapets and railings;
- splits models that don't fit your bed into closed parts;
- reads every saved STL back and checks it: every edge closed.
Your Revit model is never changed. The free plan includes 1 export a week (with a small printbim.com mark), so you can try it on your own project.