What does the north arrow on a floor plan mean?
The north arrow shows which way the home actually faces. Without it you cannot tell which rooms get morning sun, evening sun or no direct sun at all — and you must never assume that north is up.
Short answer: the north arrow is an arrow — often inside a circle, marked N — that shows which way north lies on the drawing. It is the one thing on a floor plan that ties the lines to the real world, and it is what makes the light readable: east = morning sun, south = midday sun, west = evening sun, north = almost no direct sun. Never assume north is up on the drawing — it often is, but far from always. If the north arrow is missing, the direction can be found on a map or with a compass app on site.
What the north arrow is, and where it sits
The north arrow is a simple arrow, usually drawn inside a circle and marked with an N or an arrowhead that is half filled in. It typically sits in a corner of the drawing, or right next to the title block in the bottom right.
The north arrow belongs to the drawing, not to the sheet of paper. Rotate the page and the north arrow rotates with it. That is exactly why it exists: so the house can be drawn however is most practical to draw it, while the true direction can always be found again.
Why "north is up" is a dangerous assumption
Many drawings are oriented with north up, because that is the habit maps have taught us. But architects often rotate the plan so the house sits well on the page — a house that sits at an angle on its plot takes up less room and reads more clearly if the plan is turned 20 or 40 degrees.
The result is that a floor plan without a north arrow cannot be used to judge the light. If you guessed that north was up, and the house was in fact rotated 90 degrees, you have swapped morning sun and evening sun across the entire home. It is a mistake you feel every single day in the kitchen you thought got the morning light.
Be especially wary of estate agent particulars. Here the floor plan is often oriented so the picture looked best in the listing, and the north arrow is frequently left out altogether.
How to read the light from the north arrow
Once you have the north direction, you can read the whole day's light straight off the plan. The sun rises in the east, stands highest in the south at midday, and sets in the west — and each of the four compass points gives its own kind of light:
- East: morning sun. Low, warm and sharp early in the day; gone again by mid-morning. Good for a kitchen, a breakfast spot or a bedroom.
- South: sun from mid-morning to mid-afternoon, and it stands highest here. In summer it climbs so high that a roof overhang can shade it out; in winter it sits low and reaches deep into the room. The classic orientation for a living room.
- West: afternoon and evening sun. A low sun that dazzles, and that heats a great deal in summer, because it hits the glass almost head-on late in the day. Good for a terrace, demanding for a home office with a screen.
- North: almost no direct sun. Only at the height of summer, when the sun rises in the northeast and sets in the northwest, does it graze north-facing windows early and late in the day. In return it gives an even, stable daylight with no glare and no hard shadows — which is why artists and studios have favoured north-facing windows for centuries.
Put a finger on the north arrow, turn the drawing over in your head, and walk through the rooms one at a time. It takes two minutes and tells you more about daily life in the home than a whole set of photographs.
What the north arrow cannot tell you
The north arrow gives you the direction — not the sun itself. There are two things it cannot account for:
- The sun's height above the horizon, which changes through the year. At the summer solstice the sun stands high in the sky at midday; at the winter solstice it stands very low. The same south-facing window therefore gives quite different light in summer and winter — in winter the sun reaches far into the room, in summer it stops at the window.
- Shadows from the surroundings. A neighbour's house, a tree, a carport or a hill can take all the morning sun, even though the window faces due east. This does not show on the floor plan, only on a site plan or in person.
So the north arrow alone gives the best possible light, not the actual light. To know exactly when the sun will reach the living room on 15 November, you need the sun's path for the site's latitude, the date, and the shadows, all worked out together.
True north, grid north and magnetic north
There are three kinds of north, and on a home floor plan the difference is rarely decisive — but it is worth knowing them:
- True (geographic) north points towards the North Pole. This is what a north arrow on a building drawing means as a rule.
- Grid north is the north of the map projection — the direction the grid lines on a map run. It usually differs from true north by less than a degree.
- Magnetic north is what a compass needle points to. It differs from true north by a few degrees — how many depends on where in the world you are — and the difference shifts slowly over the years.
For judging daylight in a home, a few degrees of difference makes no practical difference — the sun moves 15 degrees an hour, so an error of a few degrees corresponds to under ten minutes. If instead you are placing solar panels or settling a boundary dispute, the direction needs to come from an actual survey, not from a phone.
How to find north if the arrow is missing
- Look the address up on a map (an aerial photo works well). Find the outline of the house, compare the length of its facades with the floor plan, and see how the plan needs to be turned to match. This is the most precise method, because the map is already oriented to north.
- Use a compass app on site. Stand with your back against an outer wall and read off the direction. Keep the phone away from radiators, refrigerators and reinforced concrete — magnetic interference is the most common source of error indoors.
- Use the sun. At midday the sun sits due south if you are in the northern hemisphere. The shadow cast by a vertical stick then points north. It is rough, but it can never be badly wrong.
- Write the arrow on. Once you have found the direction, add it to the drawing straight away. Otherwise you will have to find it again next time.
North direction in HouseSense
HouseSense uses the north direction as the very foundation of the daylight study: once the home's position and north direction are set, the sun's path is calculated for that address and that date, and the light falls into the 3D model exactly where it would actually fall. You can wind the time forward and back through the day, change season, and watch the patches of sunlight move across the floor.
Precisely because of this, the north direction is not something the app guesses at. If the home's location or north direction is missing, the sun cannot be placed correctly — and HouseSense says so, rather than showing a daylight study that looks right but is not. A sun that stands in the wrong place is worse than no sun at all: it looks like an answer.