Prior setup: Before creating dwelling inputs, users need to choose a local folder that will act as their workspace. See Setting up Vulcan Software.
Menus in the Geometry screen
The Geometry section allows creation of HEM inputs on a top-down visual representation of a dwelling. Elements drawn onto this canvas can also be selected and edited. The user can use keyboard or mouse controls to move or zoom the canvas.
This data is saved into a CSV format 'geometry file', which is merged with a JSON format 'defaults file' when you click Save. The geometry file captures the minimal information needed to describe the geometry of a dwelling, and any differences from a default set of system and fabric properties. This helps minimise the inputs required for a HEM simulation.
Dwelling inputs can be created, edited and saved with the following menus. All menus can be dragged to other parts of the canvas (the area of the screen where the dwelling is drawn). Menus are described in an order that corresponds to how you may interact with them when creating inputs:
File Bar: Choose a CSV input file from your workspace (or import dwelling inputs from CAD tools), edit file names, edit global settings, save files, and import SAP data.
North Offset: Edit global orientation, enabling elements to be drawn orthogonally.
Draw: Add elements to a floor. Includes controls and overlays.
Canvas: Used to view, select, and directly manipulate elements.
Editor: Make edits to the properties of elements or zones: location, shape, thermal properties, and relationship with other elements. When multiple elements are selected, different controls appear.
Viewer: View and select elements or zones for editing. View validation for inputs.
Quick solve: Run a fast preview calculation from the Geometry screen and see headline results without moving to the Scenarios section. This can be used to calculate either Primary Energy Rate or PV Generation (with a guide comparing PV to FHS functional requirements)
File Bar
This menu, typically at the top of the canvas, is used to open, name, and save input files, control global properties, request a review, and use SAP data to create or validate inputs.
Files dropdown
Interface to manage geometry input files (saved in the user workspace under input/base_models):
File dropdown, accessed with File button in File Bar
Search through all files by name,
Open the workspace that contains the files;
Updating the view of files in this workspace (for example after adding new files);
Delete a file (visible when hovering over file);
New Model: Create a new file.
Upload IFC: Upload IFC4 format files exported from CAD tools.
File name field
Edit the name of the currently open file. We suggest renaming all files from the default, to something that is distinctive and searchable.
Saving a file under a new name creates a new file and preserves historic saves, and overwrites any files that previously had that name.
Save button
This button saves the current contents of the canvas into a CSV format geometry file. This can be found in your selected workspace folder, under input/base_models.
This is required before you can simulate the dwelling or submit it to ECaaS, and is important to ensure that updates made are not lost. The shortcut Ctrl + S can also be used to save.
Save status and build status are shown separately:
Save success: The geometry CSV has been written to your workspace.
Build errors: The CSV saved, but Vulcan could not create or validate the HEM input JSON. A Build Error button will show the issues to fix. These are usually missing or inconsistent fields rather than a failure to save your drawing.
Save errors: The CSV itself could not be written. Clicking the warning symbol reveals more information about the cause.
Global Settings
The Global Settings button opens the Global Settings menu (below). If there is a red validation dot on this button, there is likely an issue - e.g., the default file, or a required value for HEM simulation, is missing. This can be resolved within the menu.
This can be used to view and update settings across two tabs:
Defaults files tab: Change or edit the HEM JSON file that contains default schedules, controls, and inputs required by HEM, and that the geometry file created by the canvas merges into. Note that many of these defaults may be overwritten by wrapper defaults.
Global settings tab: This includes the following:
Compliance settings: Controls whether the model is being prepared for FHS-compatible export, and records inputs such as Part O/G requirements, bedrooms, wet rooms, ground floor area, heating control type, location, and related compliance assumptions. FHS-compatible export is currently required for the main compliance workflow. Some values can be derived from the geometry, but should be checked before using the file for a calculation or review.
Air tightness: Controls airtightness test result, as well as derived pressure. The Ventilation Zone height is also here. By default, this is calculated from the summed average height of BuildingElementOpaque (external walls) or BuildingElementAdjacent* (party walls) for each floor of the dwelling.
Ventilation environment: Controls location settings that affect the ventilation calculation, including wind exposure, terrain type, and altitude. Settings that affect the ventilation properties of windows can also be controlled, including noting if cross ventilation is possible, and if windows cannot open due to noise nuisance risk.
Thermal bridging: Controls the single global default thermal bridge (y value). This is used by default if zone-level or individual thermal bridge elements are not defined. You can also update the thermal bridge table used for common junctions, so calculated or selected junction values can be reused consistently.
Default assemblies: Choose default wall, roof, and ground-floor assemblies for newly drawn fabric elements. This helps apply consistent fabric assumptions without editing every element individually.
Default files
'Default files' are HEM input files in JSON format. They provide the foundation that geometry files merge into.
A sample default file is part of the Sample Parameter Library, and stored in the user's workspace at input/batch_parameters/base_json/defaults_template.json.
If using another input file as a default, pay attention to validation flags next to the file. These indicate missing data that may make it unsuitable as a general base for models.
Import SAP Data
SAP data in the PDF Worksheet format, or an XML format, can be imported (via Upload) to support creation and validation of HEM building elements within Vulcan. Once a SAP PDF or XML is used for one input file, it will be available to link to any other file (via Link Existing).
Once a file is uploaded, the raw file (PDF or XML) or the extracted data (JSON) can be reviewed. The selected file can also be removed (Clear) or replaced by another file (Replace).
Under Advanced, the pipeline to compare extracted data to the current HEM inputs is visible:
Merged JSON represents the combination of the PDF and XML sources
Mapping JSON links the building elements in a SAP XML to the HEM input file
Diff JSON represents the difference between the current HEM input file and the SAP data described in the Merged JSON and linked by the Mapping JSON.
Validation provided by the SAP file is visible in the form of a blue validation badge in the Elements Viewer, and blue dots or chips within the Elements Editor (see below). Validation can indicate both that a HEM element contains a value inconsistent with the SAP files, or that a specific named element in the SAP file is not in the HEM file. Missing elements can then be drawn or created with properties aligned to the SAP file.
Draft Review
The menu can be used to quickly:
Draft a request for calculation using the MHCLG HEM Calculator (ECaaS), and
Request that this draft is reviewed by the Vulcan team
This functionality is also accessible from the Calculate section of the app. Its inclusion within the Geometry section is to encourage users to get support where helpful.
Vulcan reviewers will have access to evidence for the review including:
The HEM input file, as well as the CSV geometry file and defaults file used to create this
Any uploaded SAP PDF or XML files
Any uploaded floorplan overlay
Element-specific evidence. This evidence can be uploaded and linked to specific element properties in the Element Editor.
We will prioritise users that are Members or Early Adopters in completing reviews. Please reach out directly if your request is urgent. We can only advise on whether an assessment fits provided evidence.
North Offset
This sets the global orientation, which applies an offset to the orientation value of all dwelling elements. This can be edited by either dragging the arrow, or clicking the central number to directly edit the offset number. Note that North = 0; East = 90; South = 180; West = 270.
Drawing Tools
The menu is used to choose dwelling elements to draw, and how and where they are drawn. Drawn elements can be seen in the Viewer, and properties of selected elements edited in the Editor.
2D/3D toggle
This switches between 2D (default; required to draw elements), and a 3D mode which supports visual checking of elevation. 3D mode is view-only and still in development.
Element Selection
Choose which element to draw from a dropdown:
External Wall / Door / Roof
External Window
Ground Floor
Internal elements (walls, ceilings)
Wall adjacent to an unconditioned space (such as an unheated garage or stairwell)
Party elements (walls, ceilings), which are only partly included in a dwelling's energy model
Thermal Bridge (Linear)
Thermal Bridge (Point)
Window Shading (must be assigned to a window)
Lighting
Ventilation Ductwork (must be assigned to a mechanical ventilation unit)
Water Pipework
Heating System Distribution
Electric Appliance
Hot Water Point
External Shading
Infiltration Vent (which can be assigned to a parent to inherit pitch and orientation)
Mechanical Ventilation
Solar Panel
Electric Battery
System (including Product Characteristics Database product selection where available)
Water Pipework and combustion appliances are not currently drawn when the model is being prepared for the FHS compliance path. Use systems/defaults where relevant, and check the validation messages for any missing inputs.
Preset
This can be used to select a saved element of that specific type. Presets can be saved from existing elements using the Element Editor menu.
Floor Selection
Choose which floor to draw the element on. New floors can also be directly added or removed in this menu.
Shape Selection
Choose how the element is represented with a top-down view. After choosing a Shape, the next click on the canvas will start drawing. Shapes can also be quickly selected by using the keyboard shortcut shown, or de-selected with Escape. The Shapes available will depend on the Element Selection.
Line (vertical panel) - when placing note that the arrow indicates the externally facing surface of the element - Shortcut: [ L ]
Polygon (flat plane) - click the original point to close - Shortcut: [ P ]
Slope (angled plane) - when placing note that the first two points are the lowest edge of the slope, with the arrow indicating the externally facing direction of this edge - Shortcut: [ J ]
Room (vertical panels enclosing a polygon) - when placing note that the arrow indicates the externally facing surface of the "walls" of the room - Shortcut: [ K ]
Orthogonal Room (vertical panels enclosing a rectangular polygon) - click and drag to place, and then tweak dimensions in the post-room-creation menu - Shortcut: [ Q ]
Dormer - add dormer geometry to a roof where available. This can then be configured to select a hip / gable / shed dormer. Only available for 'External Wall / Door / Roof'
Thermal bridge line modes - thermal bridges can be drawn as plan, vertical, or sloped lines.
Point - click to place - Shortcut: [ O ]
Hold Shift while drawing to force orthogonal snapping. Hold Alt/Option while placing repeated elements, especially lines, if you want to keep drawing the same shape.
Overlay
Enables selection of an overlay file (PNG, JPEG, or PDF) that can be traced over in the canvas. This can allow faster creation of inputs from a floor plan.
Select overlay image: Choose an image as an overlay. This will be saved into your workspace, and form part of the evidence package for assessments lodged with ECaaS.
Calibrate image: This is done by placing two points onto the canvas, and defining the distance between these points. This is automatically prompted on loading a new image. Overlays can be re-calibrated at any time.
Replace overlay image: Choose another image as an overlay
Remove overlay image: Remove the currently selected overlay image.
Move image: When selected, the image can be dragged to move it around the canvas.
Change opacity: Changes visual transparency of the image.
Controls
Provides information and toggles to effectively use the canvas:
Mouse and Keyboard Controls: Reiterates controls above and provides other options:
[ S ] when hovering over edge of polygon to add a vertex
[ + ] or [ - ] to zoom in or out (also supported by touchpad)
[Ctrl + S ] to Save the current inputs
[Ctrl + Z] to Undo last draw
[ Ctrl + Y ] or [ Ctrl + Shift + Z ] to Redo
[ Delete ] to delete element or selection
[ Escape ] to clear drawing tool or current selection
Click + Drag to select multiple elements (to edit, duplicate, move or delete as a group)
Snap and Label options: Controls when drawn or adjusted elements snap to a grid, each other or potential parent elements, whether snapped vertices stay joined when moved, and whether labels are always visible or only show on hover.
Canvas
Used to view elements, select them (so they can be edited), and move around the model. Panels can be dragged around the canvas, collapsed, or hidden where controls provide that option, so you can create more drawing space.
Quick sim / quick solve
The Quick sim panel can run a preview calculation for the current saved model and show headline results such as FHS primary energy rate or annual solar generation. Use it as a fast sense-check while building the model. It is not a substitute for a full ECaaS submission or a reviewed assessment.
Editor (single element)
Used to edit elements individually
Name: A human-readable name that has no impact on its properties.
Type: Controls Element properties. Note that Element Shape is constrained based on its Type.
Floor: Change the element to another floor by inputting directly, or select from available floors.
Preset: Where available, select a saved element preset or save the current element as a reusable preset. This is useful for repeated walls, windows, and other elements that share the same assumptions.
Assembly picker: For fabric elements, choose a saved assembly or build up layers from materials, cavities, and repeating bridges. Vulcan uses this to estimate fabric values such as U-value, construction resistance, and thermal mass. You can apply the result to the element and keep an auditable record of the assumptions.
Ground U-value tools: For ground floors, Vulcan can help estimate U-value using the element area and perimeter, wall thickness, floor type, and relevant insulation or ventilation inputs. Suspended floors can also use underfloor insulation resistance and ventilation assumptions.
Thermal resistance of unheated space tool: For elements adjacent to an unheated space, Vulcan can help calculate the extra thermal resistance of that space (R_u) and write it back to the element. Use this where a wall, floor, or roof separates the heated dwelling from an unheated garage, loft, stairwell, or similar space. Pitched roofs can also be marked as unheated where the internal heat-transfer surface should be treated differently from the external roof pitch.
System and PCDB inputs: System elements can use product data from the Product Characteristics Database where available. This helps populate system inputs from a selected product, but users should still check that the selected product and linked system assumptions match the dwelling.
Validation flags: "Critical" (red) errors that prevent HEM runs, or "Warning" (orange) errors that may indicate gaps or inaccuracies. Note flags are horizontally scrollable.
Standard fields: Shown below the element, these are usually what is required to model the element in HEM's core methodology. Hovering over the label provides guidance on each field.
Advanced fields: Less commonly available fields the user can optionally set:
From Defaults: Set by the default file (view via the Default button in the File menu); if a value is provided this will override the defaults for this specific element.
No Defaults, Schema Shown: The typical form of this field is shown from the schema; if a value is provided it will be added to the HEM JSON for this specific element.
Duplicate: Creates a copy of that element.
Delete: Deletes this element (after user confirmation).
Editor (multiple elements)
Used to edit multiple elements at once. Only visible when multiple elements are selected (Shift+Click to select each element in canvas or Element Viewer, or click and drag to marquee select)
Floor: updates the floor for all elements
Batch properties: Updates specific properties for all elements. The current value of this property for selected elements, and the number of elements with this value, is shown below the inputs. Properties are not updated until Apply is clicked; other transforms work immediately.
Snap: Extends linear elements so that they snap to nearby vertices. The snap distance is indicated (in metres) in the Snap input field to the right of the button.
Trim: Removes any part of linear elements that extend beyond another linear element. The trim applies to the portion of the element furthest from the centre.
Right align: Adjusts the angle of linear elements to orthogonal (multiples of 90 degrees), if they are within a range. This range is indicated in the Angle input field to the right of the button.
Apply: Applies batch property changes. Not required for other transforms (e.g., Snap, Trim, Align, Duplicate, Delete), which work independently.
Duplicate: Creates a duplicate of this group of elements.
Delete: Deletes this group of elements (after user confirmation).
Viewer
Surfaces all elements and zones in an input file. This panel can be moved, resized by dragging edges, or reset to its original state by double clicking the same handle.
Element and Zone pills
Can be clicked to select and edit the element or zone (via the Element Editor); a double click focusses the element in the centre of the screen. A single zone is created by default when elements are drawn, additional zones can be added (but may be merged in compliance assessments).
Search bar
Elements can be searchable by name or type.
Validation badges
Badges displayed next to the search bar indicate validation issues:
"Warning" (orange validation dots / badge) will not block a run
"Critical" (red validation dots / badge) will prevent a HEM core run
"SAP differences" (blue validation dots / badge) indicate a difference to SAP inputs
Validation is also visible inside the Element Editor when an individual element is selected, and in an element's label on the canvas. Clicking on a validation badge in the Element Viewer filters to elements with that issue type.
Note that when FHS Compliance validation is active in Global Settings, gaps against the FHS schema will be Critical.
CSV file format for HEM inputs
Most visual inputs in the Geometry screen are saved as CSV files in input/base_models in the user's workspace. This folder can be opened from the File Bar file selection dropdown. The CSV format can be reviewed in spreadsheet tools and integrated with local workflows. When saved, it is merged into a HEM JSON file using the selected defaults file.
For day-to-day use, most users should edit geometry through the canvas and use the CSV file as an auditable record of the model.
For integrations or spreadsheet workflows, see the Geometry CSV contract.