HomeTwin Studio

Levels

Draw each floor on its own level. The floor below shows through the plan so walls and stairs line up; in 3D the whole house stacks. Stairs are in the furniture catalog under Structure and carry you between floors in walk mode.

Floor below shows through35%

In 3D, fade the floors above the one I am on

Furniture

Click a piece to drop it in the middle of the view, then drag it into place. R rotates, Delete removes.

Airflow & ventilation

A 2D potential-flow solve across the floor. Openings facing the wind push air in; the rest pull it out.

Wind directionSW

Wind speed7 mph

Overlay Flow arrows Speed heatmap

still

breezy

Room	ACH	Flow

Estimates only. ACH = CFM x 60 / room volume, with window CFM from 88 x area x wind speed x 0.25 cross-ventilation effectiveness. Not a substitute for a Manual J or a code ventilation calc.

Illumination

Place fixtures with the Light tool (key 8), then solve. The map shows footcandles on a work plane 2'6" above the floor, the same way the airflow map shows air speed.

Sky

Count the fixtures Count daylight through windows Show the coverage map

dark

bright

Room	Average	Coverage

Footcandles on a 2'6" work plane. The shape of the map — bright under a fixture, dim in a corner, falling away from a window — comes from inverse-square falloff with walls blocking the ray. The level in each room is then set by the standard methods: the lumen method for fixtures (coefficient of utilisation 0.55, light loss factor 0.85) and split-flux for daylight, so the averages are figures worth quoting. Targets are for general lighting; task lighting over a counter, desk or mirror sits on top and runs higher. A screening estimate, not a photometric study.

Sun position

Sun position from date, time, latitude and how the house sits against true north.

Time of day14:00

DateSep 20

Latitude37.0°N

Plan rotation vs. north0°

Ceiling height9 ft

Sun

Solar position uses a standard declination and hour-angle approximation, accurate to roughly a degree. Good for shadow direction, not for solar panel yield.

Design suggestions

The engine reads the plan and proposes changes — walls to open, arches, windows, ventilation, lighting, furniture — and scores each by running the airflow, lighting, structural and cost models on a copy. Hover or tap Preview to see it on the plan.

Press the button, or turn on Suggest in the top bar.

Every structural line here comes from the load-path screen, not from a language model. "Engineer required" means what it says: this app screens, a licensed structural engineer certifies, and no wall comes out on a screen.

Assistant

Optional. A language model that explains the engine's proposals and turns a request like "open up the kitchen" into the matching ones. It runs where you choose — by default Ollama on your own PC, so nothing about your home leaves your network. It is never asked whether a wall is safe.

Runs on

Structure & load

Screens which walls carry load and sizes a preliminary header. Set the joist direction first — it decides everything below.

Joists span

Show joist direction on the plan These walls also carry the roof

Floors above this one0

Floor live load40 psf

Ground snow load20 psf

Framing lumber

Wall	Trib.	Load

Preliminary screening only. These numbers come from the geometry you drew and the assumptions above, using IRC residential loads and NDS-style bending and deflection checks. They are not a permit calculation and they do not account for point loads, headers above, soil, foundations, or anything hidden inside a wall. A licensed structural engineer must confirm any wall removal, and your locality will almost certainly require a permit.

Configurations

One home, many arrangements. Save the current layout, then try another and switch back.

Cost estimate

A quantity takeoff straight off the model, priced at national averages.

Pricing--

Regional multiplier1.00x

Item	Quantity	Cost

Refinish-everything scope: the takeoff assumes all floors, walls and trim in the plan are new. Unit costs are national averages and swing widely by market and finish level. Treat the total as a range, not a quote.

Maintenance

Generated from what is actually in the model.

Task	Every

Learn the app

A two-minute walk through every part of HomeTwin, and the list of what changed in each build.

Version & updates

The installed app updates itself: it checks on every launch, reloads when a new build lands, and falls back to the copy on the phone when there is no signal.

Checking…

If a phone ever gets stuck on an old build, Force a fresh copy clears the offline cache and pulls the current one. Saved projects are kept.

Self-test

Runs every part of the app against this browser and this plan, and says what broke. Run it here if something misbehaves, then send the report.

Import existing home data

Bring in a home you already captured. Drop a file anywhere on the canvas, or pick one here.

Scan or plan file

Site from an address

Looks up the building footprint from OpenStreetMap and lays it out true to north, so the sun and the outside of the house are right.

Address

Footprints come from OpenStreetMap, which has most US buildings but not all. Outbuildings and additions are often missing or out of date — treat the outline as a starting tracing, not a survey.

Format	Comes from
HomeTwin JSON	this app
RoomPlan JSON	iPhone / iPad LiDAR scan
OBJ, GLB, STL, PLY	any LiDAR scanner app
Wall CSV	x1,y1,x2,y2 in feet
Floor plan image	below, as an underlay

Imported geometry lands in feet, recentred on the origin. Scanned rooms usually need a pass with the wall tool before the airflow numbers mean anything.

Scan mesh underlay

Drop in an OBJ, GLB, STL or PLY from any LiDAR scanner app. It gets sliced at waist height into a floor plan you can trace or auto-detect walls from.

Mesh file

Blueprint underlay

Drop in a floor plan image, set its scale with two clicks, then trace over it with the room tool.

Floor plan image

Opacity55%

Scale1.00 ft/px

Save & load

The plan autosaves in this browser. Copy the JSON to move it elsewhere.