How a house is built
Why there is no arch
An arch works in compression and pushes outward. This wood house uses bending members instead.
Arrow keys turn the house. Plus and minus, or the zoom buttons, change the zoom. A horizontal drag turns it after you tap the drawing. Reset view returns to the step camera.
The drawing needs WebGL. The notes on the page still stand.
An arch carries load by compression along its curve. The curve wants to flatten, so each support is pushed outward. Those thrusts need heavy abutments or a tie across the opening. A vault is that idea extended into a roof. Masonry arches and vaults are old, and they still explain why a curved structure cannot simply sit on a thin wall.
This house does not use an arch. Its floors and roof are beams, joists, rafters, or trusses, which work in bending and deliver mostly vertical load when they are tied. The comparison is here so the wood frame has a contrast, not because the model is hiding a vault.