All articles · 6 min read

How do I find north orientation on a floor plan?

Use the north arrow on the drawing, lay the plan over a map with north pointing up, or measure the facade's bearing with your phone's compass — and write the result down as a number of degrees, not as "south-west".

Why north orientation is the figure everything else hangs on

The sun's path across the sky can be worked out exactly from the address's latitude, the date, and the time. There is no uncertainty in that part. But the calculation cannot say anything about your home until it knows which way the home is turned. North orientation is the link between the astronomy and the house.

Getting it wrong is not an academic problem. Rotate a house 20 degrees the wrong way in a sun calculation, and the shadow edge shifts across the floor, the hours the terrace has sun change, and you can end up promising winter sun to a room that never gets any. That is why north orientation is the one figure worth measuring twice, by two different methods.

Method 1: the north arrow on the floor plan

Most floor plans from an estate agent's listing, a building project, or the public building register have a north arrow. It is the fastest source — with three caveats:

• The arrow rarely points straight up. The drawing is usually rotated so the house fills the page as well as possible. It is the arrow that counts, not the edge of the paper.
• Sales material is not always accurately scaled. A floor plan can have been edited, mirrored, or drawn from memory. Check it against a map before you calculate sun from it.
• Check that the arrow matches reality. If a terrace sits on the drawing's "south side", and you know that terrace is in shade all morning, something does not add up.

If there is no north arrow, or it looks wrong, move on to method 2.

Method 2: lay the floor plan over the map

The most reliable method needs neither a compass nor good weather. Find the address on a map or aerial photo with north pointing up — that is the default on nearly every map service. Zoom in until the house's footprint is clear.

1. Find one unambiguous edge of the house — the long facade facing the road, for instance. Pick an edge that is easy to recognise both on the map and on the floor plan.
2. Read off that edge's angle relative to vertical on the map. Vertical on the map is north. The angle can be measured with a protractor held against the screen, or by counting off the map's grid.
3. Rotate the floor plan in your head until the same edge points the same way. Now you know which way north is on the floor plan.
4. Write the figure down. For example: "the house's long axis runs 65°/245°, the street facade faces 155°."

This method has the added benefit of showing what is actually around the house at the same time: neighbouring buildings, trees, garages and terrain. Those are exactly the things that later decide how much sun actually gets in.

Method 3: the phone's compass against the outside wall

If you are standing in the home, the direction can be measured directly. Stand with your back to an outside wall, hold the phone level, and read off the direction you are facing — that is the direction the facade faces.

Three traps with a compass reading:

• Metal and current pull the needle. Reinforced concrete, radiators, steel beams, fuse boxes, car keys and magnetic phone cases can all cause large errors. Measure outside where possible, a couple of metres from the building, and repeat the reading somewhere else.
• Magnetic north and true north are not the same thing. Magnetic north differs from geographic north, and by how much depends on where on the globe you stand. For daylight purposes the difference is usually small, but many compass apps can be set to show true north — use that setting if it is offered.
• Note down a number, not a word. "South-west" covers everything between 202° and 247°. Write down 218°.

Method 4: use the sun itself

The most robust check needs nothing but sunshine and a clock. The sun sits due south at solar noon, so shadows point due north at that moment.

Solar noon rarely falls exactly at 12 o'clock on the clock. It shifts depending on how far east or west you are within your time zone, and daylight saving adds another hour on top. On top of that there is a drift of up to a quarter of an hour over the course of the year, because Earth's orbit is not a perfect circle.

The good news is you do not need to hit the minute exactly. Push a straight stick vertically into the ground, mark the shadow around midday, and see which way it points: north. Compare that with the house's facade, and you have north orientation with good accuracy — a reading that no metal door or reinforced wall can throw off.

How to write north orientation down so it can actually be used

There are two equally good ways to record the result. Pick one and stick with it:

• Facade bearing: "the garden facade faces 187°" (that is, almost due south). Bearings are measured from north, clockwise: north = 0°, east = 90°, south = 180°, west = 270°.
• The house's offset from north: "the floor plan's up-direction is rotated 23° east of north". This is the form most drawing tools and sun calculators use.

Also note which edge of the house the figure applies to. "187°" with no edge to anchor it to is useless three months later.

How precise does it need to be?

For an ordinary assessment of daylight and sun in a home, an accuracy of a few degrees is plenty. That kind of error shifts shadow edges a little, but does not change the conclusion about whether a room gets morning sun.

Large errors are a different matter. Swap two facades around, or rotate the house 90 degrees, and the whole sun study goes wrong in a way that does not look like an error — it just looks like a house with different light. That is why it is worth taking two independent readings: the map method at your desk, plus either the compass or the shadow on site. If they agree within a couple of degrees, you are done. If they don't, one of them has an explanation you need to find before you calculate anything further.

North orientation in a digital floor plan

A digital floor plan has one advantage over paper: north orientation can be stored as a property of the home rather than as a drawn arrow, and every calculation can then draw on the same figure. That removes the classic error where the floor plan, the sun study and the garden plan each carry their own idea of where north is.

In HouseSense, north orientation is set by placing the home's footprint on the map — you rotate and move the house until it sits the way it does in reality. From then on the app knows both the address's latitude and the house's rotation, and sunlight in the 3D model is calculated for that exact combination, on whichever date and time you choose. The north arrow on the finished floor plan is therefore derived from the same placement and cannot contradict the sun calculation.

Whatever tool you use, the order is the same: find north orientation first, write it down as a number of degrees, verify it with a second method — and only then calculate the sun.