Exterior wall placement (Outside, Center, Inside)
Exterior Wall Placement decides where the walls sit relative to the outline you draw — and that changes your Gross and Usable area. Here's exactly how each mode reads, with the dimension chains.
When you draw a room, you draw a single outline, but a real wall has thickness. Exterior Wall Placement decides where that thickness goes relative to the line you drew: pushed Outside it, centered on it, or tucked Inside it. New designs start in Outside mode; you can switch any time in Plan Settings → Walls (on a computer, Plan Settings is the panel at the top of the left panel; on a phone, the Plan Settings button in the top row).
This one setting decides whether the size you typed is the inside of the room or the outside of the house. It changes the inside measurements on the plan and the Gross and Usable areas. Looking for the inside size of a room you already have? See See the inside size of every room.
Step by step
- 1
First: how the plan measures
Every measurement on the plan runs face to face, like a tape measure held against the walls. The outermost line on each side measures the house to its outer wall faces. The lighter line inside it measures the room from one inner wall face to the other (it shows when Layers → Show interior dimensions is on; the outer line is Show exterior dimensions). The plan never labels a wall's thickness as a measurement of its own. The size you type when you create a room sets your outline, and Exterior Wall Placement decides which face of the walls that outline is.
- 2
Gross Area vs Usable Area
Two readouts sit under the Layout tab of Plan Settings (switch from Walls to Layout to see them update after you change the placement): - Gross area: the floor's footprint to the outer faces of the outer walls. It includes the walls. - Usable area: the floor inside the walls, with every wall's footprint removed. The gap between them is the floor space the walls take up. Thicker walls make a bigger gap.
Gross and Usable area sit on the Layout tab of Plan Settings. - 3
Outside mode: the outline is the inside
In Outside mode (the default), the outline you draw is the inside face of the walls, and the thickness is added outward. The size you typed is the inside size of the room: what you'll live in, and what you measured with a tape inside. For a room created as 16 ft × 12 ft with 6.5-inch walls, the inside lines read 16′ and 12′ and the outside lines read 17′ 1″ and 13′ 1″. Usable area 192 sq ft (your 16 × 12), Gross area 224 sq ft. Best when you're designing to interior room sizes.
Outside: inside 16′ × 12′, outside 17′ 1″ × 13′ 1″. Gross 224, Usable 192. - 4
Center mode: walls straddle the line
In Center mode, the walls are centered on the outline: half the thickness falls inside the line, half outside. The size you typed is wall center to wall center, which is how many architectural drawings are dimensioned. For the same 16 × 12 room: inside 15′ 5.5″ × 11′ 5.5″, outside 16′ 6.5″ × 12′ 6.5″; Gross area 207 sq ft, Usable area 177 sq ft.
Center: the dashed outline runs down the middle of the walls. Gross 207, Usable 177. - 5
Inside mode: the outline is the outside
In Inside mode, the outline is the outside of the building, and the wall thickness is taken inward. The size you typed is the outside footprint, and the room is smaller inside. For the 16 × 12 room: outside 16′ × 12′, inside 14′ 11″ × 10′ 11″; Gross area 192 sq ft (your 16 × 12), Usable area 163 sq ft. Best when you're matching an outside footprint, such as a slab or a building you measured from outside.
Inside: outside 16′ × 12′, inside 14′ 11″ × 10′ 11″. Gross 192, Usable 163. - 6
Putting it together
Same 16 × 12 outline, same 6.5-inch walls, three readings: - Outside: inside 16′ × 12′; Gross 224, Usable 192 - Center: inside 15′ 5.5″ × 11′ 5.5″; Gross 207, Usable 177 - Inside: inside 14′ 11″ × 10′ 11″; Gross 192, Usable 163 Switching keeps your outline where it is and moves the walls, so the inside sizes and areas change. Pick the mode that matches the numbers you typed: inside measurements, Outside; centerline drawings, Center; an outside footprint, Inside.
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After the walls exist: typing a wall's length
Once your plan is drawn, a wall's own length box always shows the same number as the plan: the outside length for an outer wall and the length wall face to wall face for an interior wall, whatever the placement. To change a room's inside size, tap the room's inside measurement along the wall and type the size you want. See Set an exact wall length.
Tips
Set it before you type your sizes
If you measured inside your rooms, stay in Outside and type those sizes. If you measured the building from outside, switch to Inside first.
Wall thickness drives the gap
Gross minus Usable is the area the walls occupy. Thicker outer walls (masonry) widen that gap. Set the default in Settings → Floor plan defaults, or change any wall's thickness after selecting it.
Show the outline you drew
The Outline button next to the heading draws your original outline as a dashed yellow line, so you can see which face of the walls it follows.
Frequently asked questions
Which mode should I use?
Outside if you're designing to interior room sizes (the default), Inside if you're matching an exterior footprint you measured, Center for centerline-style drafting. You can switch any time.
What's the difference between Gross and Usable area?
Gross area is the whole footprint measured to the outer wall faces (it includes the walls); Usable area is the floor inside the walls. The difference is the space the walls take up.
Does changing the mode resize my room?
Your outline stays put and the walls move to the other side of it, so the room's inside size and the areas change. Outside gives the most room inside, Inside the least.
Where do I see the square footage of my plan?
In Plan Settings → Layout: Gross area and Usable area (plus balcony or patio area when you have one). On a computer Plan Settings is the panel at the top of the left panel; on a phone, the Plan Settings button in the top row. Each room's own size and area show on its room label; turn them on in Layers. See See the inside size of every room.
Why doesn't the plan show the wall thickness?
Measurements show the spaces you use and the overall house, never a wall's thickness on its own. Select a wall to see and change its thickness.
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