The basis for designing in listed buildings
Deformation-accurate survey of historic buildings
Captured by 3D laser scanning, drawn up by technicians who read point clouds and know historic building craft. As a 2D drawing or a 3D model.
The building as it is. Not as it ought to be.
A deformation-accurate survey represents a building exactly as it actually is: with leaning walls, sagging floors, compressed lintels and all the irregularities a historic building has accumulated over centuries. Nothing is straightened, nothing idealised. In heritage conservation this corresponds to accuracy levels III and IV of the German recommendations for building documentation; the usual scales are 1:50 and 1:25.
Capture by 3D laser scanning is always deformation-accurate. The scanner samples entire surfaces at point spacings of a few millimetres and shows every deviation, whether you want it to or not. The actual work begins afterwards, in the drawing and modelling. An ordinary as-built drawing abstracts the point cloud into straight walls and right angles. A deformation-accurate drawing transfers the actual geometry into the drawing. Deformation-accurate is a property of the evaluation, not of the scanner.
Metrika360 delivers both from one source: the capture on site and the deformation-accurate evaluation by technicians who know point clouds and historic building craft.
Three levels, three efforts, three purposes
Level 1: the point cloud
Always deformation-accurate and available immediately. It documents the state on the survey date, allows virtual walk-throughs and serves as a reference for all further evaluation. Because the whole building has been captured, later drawings can be supplied from it without anyone travelling out again.
Level 2: the deformation-accurate 2D drawing
Floor plans, sections and elevations in which the actual geometry is drawn, with the point cloud as a template. This is the standard in heritage conservation and the basis for consent, funding applications and restoration planning.
Level 3: the deformation-accurate 3D model
The most demanding form. BIM software such as Revit or ArchiCAD is built on regular geometry: plumb walls, level floors, components from a library. A historic roof structure, however, consists of one-offs. Every rafter has its own curvature, no joint is like another. We therefore model such structures in Rhino, where every free-form element is built up individually against the point cloud. The result carries structural analysis, shop drawings and restoration.
The effort at level 3 is several times that of a regular model because there is no repetition: every component is rebuilt individually. We therefore recommend the model only where a downstream purpose demands it, and otherwise combine: roof structure as a model, the rest of the building as a 2D drawing, the point cloud as a reference over everything. Which level makes sense for which part of the building is settled before the quotation.
What goes into the drawing is decided by its purpose
How much a deformation-accurate drawing shows is agreed before the quotation, because the level of detail is the biggest driver of effort. Depending on the accuracy level and intended use, the drawings contain:
- Detailed representation of the structure
- Decorative elements on the façades
- Timber joints such as tenons and scarfs
- Historic door frames
- Stone joints and tooling marks
- Fixing holes
- Carpenters’ and masons’ marks
For restoration planning, the carpenters’ marks belong in the drawing. For a funding application the level below is often enough. The difference decides weeks of drawing work, which is why we ask about the purpose before we talk about the price.
Four groups, four reasons
Architects and designers in heritage conservation. Consent planning on a listed building does not get past the authority without a deformation-accurate basis, and funding depends on the quality of documentation.
Structural engineers. Assessing the stability of a historic structure depends on its actual geometry. Deflection, tilt and reduced sections appear only in the deformation-accurate survey; in a straightened drawing they are invisible.
Carpentry and restoration firms. Replacement components are made to the existing fabric. A rafter is cut to the measured curvature, not to an idealisation.
Church administrations, foundations and public clients. The duty to document a listed building is permanent. The point cloud records the state on a given date, also for damage cases, insurance questions and later construction phases.
Not every old building needs a deformation-accurate survey
For an ordinary conversion in unlisted fabric an ordinary as-built drawing is enough, and it is considerably more economical. Even on a listed building not every storey has to be drawn at level IV: often the combination is the right answer, for instance the roof structure deformation-accurate and the storeys below as regular drawings. If you are unsure which level your project calls for, that is the first question we settle together with your designer or the conservation authority.
Church towers, roof surfaces, inaccessible areas
Tall towers, roof surfaces and built-in rear elevations cannot be reached completely by the scanner from the ground. There we add photogrammetry by drone: overlapping images produce a point cloud that is merged with the laser scans on the same control network. The result is a complete representation of the building from foundation to spire, all of a piece and in one coordinate system.
Further reading
- 3D laser scanning – the capture the survey grows out of
- 2D as-built plans – the regular drawing as the economical alternative
- Orthophoto – the true-to-scale image for damage mapping
- Virtual tours – the walkable version of the same capture
- Drone surveying – tower and roof from the air
Frequently asked questions about deformation-accurate surveys
What does deformation-accurate mean?
The drawing shows the building as it is, not as it ought to be: leaning walls leaning, sagging floors sagging. In heritage conservation this corresponds to accuracy levels III and IV; the usual scales are 1:50 and 1:25.
Is not every laser scan survey automatically deformation-accurate?
The point cloud yes, the drawing no. It is at the drawing stage that it is decided whether the actual geometry is transferred or abstracted into straight walls and right angles. Deformation-accurate is a property of the evaluation, not of the scanner.
When do I need a deformation-accurate survey, and when not?
It is needed on listed buildings, in assessing the stability of historic structures and in restoration. For an ordinary conversion in unlisted fabric an ordinary as-built drawing is enough and is considerably more economical.
What does it cost compared with an ordinary survey?
The capture costs roughly the same, the evaluation considerably more, because nothing comes from libraries or repetition. The factor depends on the level of detail: whether stone joints, carpenters’ marks and fixing holes have to be drawn decides the effort. That is why we fix the accuracy level and the extent of detail before the quotation.
2D drawing or 3D model?
The model only where a downstream purpose demands it: structural analysis, shop drawings, complex roof structures. Otherwise 2D drawings plus the point cloud. We build a deformation-accurate 3D model in Rhino, because BIM software is designed for regular geometry and historic components are one-offs.
Can only parts of a building be evaluated deformation-accurately?
Yes, that is the most common case: the roof structure deformation-accurate as a model, the storeys below as ordinary as-built drawings, the point cloud of the whole building as a reference. Because the capture is complete, further areas can be added later without a new site visit.
A monument, a roof structure, a tower?
Send us photographs and the question your designer or authority is asking. You will get an assessment of which accuracy level your project calls for and what that means for capture and evaluation, before anyone travels out.