Understanding, not designing
This lesson explains how buildings carry weight, so you can read a plan, talk to a builder and spot trouble.
It does not teach you to design or build a structure. Beam sizes, spans, foundation depths and connections are set by the building code, an engineer or a licensed builder for your site.
Loads
A load is any force a building has to carry or resist.
- Dead load: the weight of the building itself: framing, roofing, walls, floors.
- Live load: things that come and go: people, furniture, stored food, water tanks.
- Snow load: the weight of snow on the roof. It varies a great deal by place.
- Wind load: wind pushing on walls and lifting the roof.
- Seismic load: shaking from earthquakes, in places where they happen.
Snow, wind and seismic loads depend on where you live. The local building department sets the design values for your area.
The load path
Loads have to travel all the way to the ground without a break. That route is the load path.
Roughly: roof covering → roof framing → walls or posts → floor framing → foundation → soil.
If any link is weak or missing, the load finds another way down, often through something that was never meant to carry it. That is when you see sagging, cracking or worse.
Wind adds a twist. It can push sideways and pull upward, so the parts also have to be tied together, from roof to foundation.
Text description
A simplified cross-section of a small house, not to scale. Snow load presses down on the roof. Arrows trace the load down the roof slopes to the walls, down the walls to the foundation, and out into the soil, where it spreads. The parts are numbered in order: 1 roof covering, 2 roof framing, 3 walls or posts, 4 floor framing, 5 foundation, 6 soil. Inside, live load from people, furniture and stored food presses on the floor. On the left, wind pushes sideways on the wall and can lift the roof, so a dashed line shows that the parts must be tied together from roof to foundation. A note says this is a concept only, and that sizes, spans and connections come from the code, an engineer or a licensed builder.
Trace the load path
Snow sits on the roof. Put the parts in the order its weight travels down to the ground.
- Foundation
- Walls or posts
- Rafters or roof trusses
- Roof covering
- Soil
Foundations
A foundation spreads the building’s loads onto the soil and keeps the building from moving.
- Slab: a concrete pad poured on the ground.
- Crawlspace: short foundation walls with a space under the floor.
- Basement: deep foundation walls with a full room below.
- Piers: posts or columns down to firm soil, with the house raised above.
In cold places, water in the soil freezes and expands. This frost heave can lift and crack foundations. Foundations in cold climates go below the local frost depth, or use special frost-protected designs. Your building department sets that depth.
Text description
Four simplified sections side by side, not to scale and with no dimensions. Slab: a concrete pad poured on the ground, with insulation laid out flat around its edge, one kind of frost-protected design. Crawlspace: short foundation walls that reach below the frost depth, with a floor above and a crawl space under it. Basement: deep foundation walls with a full room below ground and a concrete floor. Piers: posts or columns that go down below the frost depth to firm soil, holding the house up above the ground. A dashed line across all four marks the local frost depth, which your building department sets.
Framing
Framing is the skeleton of the building: the parts that carry loads and hold the walls, floors and roof in shape.
- Light wood framing: many small pieces, like studs and joists, close together. Most US houses use it.
- Timber framing: fewer, larger posts and beams joined together.
- Steel framing: steel studs or a steel frame, common in commercial work.
A bearing wall carries load from above. A non-bearing wall only divides space. They can look the same. Never remove or cut into a wall until a professional confirms which it is.
Walls also need bracing so they do not rack sideways in wind. Sheathing panels often do this job.
Warning signs
These signs can point to a structural problem. They do not prove one, but they are worth a professional’s look:
- Doors and windows that start to stick or will not latch.
- Diagonal cracks running from the corners of doors and windows.
- A roof line or ridge that sags in the middle.
- Floors that slope or bounce more than they used to.
- Cracks in the foundation that grow or let in water.
Check
You want to open up a small cabin by removing an inside wall. What should you do first?
Summary
- Buildings carry dead, live, snow, wind and seismic loads.
- The load path runs roof → framing → walls → foundation → soil, with no breaks.
- Foundations spread loads and, in cold places, sit below the frost depth or use frost-protected designs.
- Bearing walls carry load. Never remove one without a professional.
- Structural design and changes need a pro and, usually, a permit and inspections.
Next, you will look at the skin of the building: the envelope that keeps heat and water where they belong.
Go deeper: why codes have prescriptive tables
For simple houses, the IRC includes tables that builders and inspectors use for common framing choices. These tables only apply within set limits of size, shape, loads and materials. Small homes with unusual shapes, heavy roofs, big snow loads, or unusual materials like containers often fall outside those limits. Then an engineer has to design the structure. That is one more reason to ask early whether your plan fits the standard path.