Lesson 6 of 6 · Chapter 6
The Load Path
Every pound in a house has to find its way to the ground, through one member after another, with no gap. This lesson traces that path: gravity from the roof down, the loads that sit on floors, and the sideways push of wind that the sheathing carries.
Step one
Read the material
Six ideas: the path from roof to soil, loads around an opening, point and distributed loads, the foundation, lateral loads and shear walls, and choosing and installing sheathing.
Idea one
A continuous path, member by member
Gravity pulls every load down, and it must travel through a continuous path of members to the ground. A gap anywhere means something sags, cracks or fails.
Roof: shingles and sheathing bear on the rafters; the rafters bear on the top plates of the walls. A ridge board carries none of it; the sheathing ties the rafters together.
Walls: the top plates spread the load onto the studs, which carry it to the sole plate.
Floor and foundation: the sole plate bears on the subfloor and the joists or rim joist below it, which bear on the sill, which sits on the foundation, which spreads it into the soil.
Idea two
The header puts its load on the jacks
An opening interrupts the studs, so the load above it has to go around. The header picks it up and carries it to each side.
The header bears on the jack studs (trimmers), and the jacks carry the load down to the sole plate. The king studs beside them hold the assembly in line; the header does not hang on the kings.
An undersized header sags: the window or door racks, binds or leaks. Size it from the span tables for the width and the load above it.
The same rule applies anywhere a load comes down: it needs something solid directly underneath, all the way to the foundation.
Idea three
Concentrated or spread out
A point load is concentrated on a small area: a kitchen island, a full bathtub, a refrigerator, a post. The members right under it take all of it.
A distributed load (the book calls it continuous) is spread over many members: roofing materials across all the rafters, snow across a roof, a floor’s own weight.
Joists must be sized and spaced for both. Span tables give sizes and spacing for the loads and species. Too far apart or too small, and a point load causes deflection: cracked tile, squeaks, or worse.
Where loads combine, such as a tub on the second floor under a roof, every member in the path must carry its share of both at once.
Idea four
Where every load ends
The foundation must carry the total: the walls, the floors, the roof, and everything the house holds, and spread it into the soil.
Residential foundations are usually concrete: a full basement, a crawl space, or a slab. Each is designed for the weight above it.
The sill is anchored to it, treated against the moisture in the concrete, and the connection must be sound: a weak joint here compromises everything above.
When you add a heavy load, a new post, or a bearing wall, ask where it lands. The answer has to end in the foundation.
Idea five
Wind and earthquakes push sideways
Not every load is gravity. Wind and seismic forces push the house sideways. A frame of studs alone would rack like a parallelogram.
Sheathing nailed to the frame turns each wall into a stiff panel, a shear wall, that resists racking and passes the sideways load down to the foundation. Roof and floor sheathing do the same across the top.
It only works if it is fastened: nails about 6 inches apart along the panel edges and 12 inches in the field, or whatever the nailing schedule calls for, with panel seams staggered so no weak line runs through the wall.
Wall sheathing goes on after the wall is raised and braced. House wrap or a moisture barrier goes over it before the siding.
Idea six
Read the stamp, orient it right
Plywood and OSB are the common sheathing panels. Wall sheathing typically runs 7/16 to 3/4 inch thick, set by local code and the loads.
Choose by the APA stamp: its span rating (and Structural I where required) tells you what the panel can do. CDX is an appearance grade with exterior glue, not a measure of strength.
Orientation: floor and roof panels run their long, strong direction across the joists or rafters. Wall panels may run either way where the code allows; follow the nailing schedule at every edge.
Sheathing is a structural skin and a base for siding. It is not a thermal barrier: insulation does that job.
The whole of chapter 6 is free to read or hear on the Residential Framing reader page.
Step two
Work it with your hands on it
The Load Path Bench. Pick where a load starts. The bench shows the member it is in and asks where it goes next. Choose the member that actually carries it. A wrong choice is refused with the reason. Follow it all the way to the soil.
Where the load starts
The load is in: . Where does it go next?
Hands on it, off the screen. In a basement or crawl space, stand under a bearing wall and look up: find the joists or rim it sits on, and the sill and foundation below.
At any window in an unfinished wall, find the header and put your hand on the jack stud under its end. That is where the load goes.
Step three
Prove you understood it
One question per idea, a new situation every time. Miss one and you are sent back to the idea it was testing.
All six solid. The class is complete.
You can trace any load from the roof to the soil, route it around an opening, tell point from distributed loads, explain what the foundation carries, and choose and fasten the sheathing that resists wind. That finishes Residential Framing.
Residential Framing
Lesson six of six, from chapter six. Written by our founder, Dr. Gene A Constant, and donated to the Foundation. Published by Global Sovereign University Press.
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