Exterior Foundation Wall Design

All foundation wall studs shall be designed for axial loads, bending moment and stresses due to shear. Both bottom and top plates shall be designed for axial load bearing of the studs on the plates. Joints in footing, top and bottom plates shall be offest by two feet from each other. Stud framing shall be designed with adequate capacity for concentrated point loads.

Plywood wall sheathing shall be designed to resist bending moment and shear between studs due to soil pressures.

All wall connections in foundation wall shall be adequate to transfer all axials and horizontal forces to the lumber/gravel footing and into both upper and lower floor systems.

All foundation walls are subject to racking loads. Differential soil pressure, wind loads and earthquake may require adequate shear strength to resist the most severe racking load or combination of loads, but wind and earthquake forces shall not assumed to act simultaneously.

Foundation wall studs shall be designed for the applied axial load and bending moment. All live and dead loads shall be considered in the stud design.

Foundation wall studs shall be designed for shear forces due to lateral soil pressures.

The foundation bottom plate shall be designed to resist bearing forces from studs and point load post supports.

Foundation plywood shall be designed to resist soil bending and racking shear forces.

Fasteners used in foundation must be corrosion resistant. Type 304 or 316 staimless steel nails are recommended below grade for attaching treated plywood to treated lumber.

For most above-grade used, plywood may be attached with hot-dipped or hot-tumbled galvanized nails, or stainless steel. (CCA treated lumber only).

Lumber to lumber fasteners above grade can generally be hot-dipped galvanized nails. Stainless steel type 304 or 316 nails generally required below grade, frost wall stud nailing, for all knee wall assemblies, and some wood floor connection.

Earth Pressure Diagram Used in Calculation Moment and Shear in Foundation Walls Resisting Earth Pressure Loadings.

w = Design lateral soil load, lbs./ft.3
W = Total lateral load, lbs./ft.(linear foot of wall)
h = Depth of fill (Bottom of stud to finish grade), ft.
H = Height of wall (from bottom of stud to top of top plate), ft.
R = Reaction st top of wall (top of top plate), lbs./ft. (linear foot of wall)
R1 = Reaction at base of wall (bottom of stud), lbs.ft. (linear foot of wall)
V = Maximum shear, lbs./ft. (linear foot of wall)
M = Maximum moment, ft.-lbs./ft. (linear foot of wall)
x = Location of maximum moment below ground level, ft.

35 lbs. Soil load. Wall height 9'- 0" or 103 1/2" Studs.

w = Equivalent-fluid weight of soil, lbs/cu. ft. = 35 psf.
W = Total lateral load, lbs/linear foot of wall
c = Location o W below finished grade
R = Reaction at top of wall
R1 = Reaction at base of wall
x = Location of maximum moment below ground level, feet.
M = Maximum moment, foot-lbs/linear foot of wall

Minimum Framing Requirements For 9' Basement wall- one-story with clear-span roof trusses and center-bearing floors

Note: Basement walls figured at 35 soil pressure psf.

Table 1.

Table 2.

Table 3.

Minimum Framing Requirements For 9' Basement wall- Two-Story With Clear-Span Roof Trusses And Center-Bearing Floors

Note: Basement walls figured at 35 soil pressure psf.

Table 4.

Table 5.

Table 6.

Troubleshooting Panel Wood Foundations

The foundation wall is bowed, out of plumb, or deflecting inward.

Causes:

a. There is not enough bearing against the floor by the bottom edge of the studs.

b. The grade for the species used for studs is too low.

c. The spacing of the studs is too great.

d. Insufficient number and/or size and diameter of nails used to nail bottom top plate to studs.

e. The grade for the species used for top plates are too low.

f. Nail spacing is too far apart and/or size and diameter of nails used to nail the two top plates together.

g. Nail spacing is too far apart and/or size and diameter of nails used to nail band joists to top plates.

h. Floor joists not adequately attached to the band and the top plates (this may be done with pwf framing straps, joist angles, or joist hangers---The number of nails, size, and diameter is significant for each type of framing anchor).

i. Shear wall(s) may be needed.

j. The length of the shear wall(s) may be too short.

k. The nail spacing at the plywood panel edges of the shear wall(s) may be too far apart at the plywood panel edges, and/or the nails are the incorrect length or diameter.

l. Horizontal blocking may be left out at a horizontal plywood joint in the shear wall.

m. Holes were drilled in the tension half of the stud or near the point of maximum moment.

n. At end walls where the floor joists run parallel to the foundation wall, blocking between the 1st, 2nd, etc. interior joist space(s) may have been left out or removed for ducts, pipes, wires ,etc. The block spacing is significant.

o. In all blocked joist spaces the minimum joist spaces must be at least as wide as the blocks are high.

p. The sub-floor above the foundation may not have been nailed to the 1st, 2nd,etc. interior joists at the correct nail spacing; or the correct number of nails were not used to nail the sub-floor to the blocks; or the nails are not the correct length or diameter.

q. The sub-floor is not a rated sheathing.

r. When a stairwell or other opening is in the floor-ceiling diaphragm, adjacent to and less than 4 feet from a foundation wall with a backfill, the top plates of the wall become a horizontal beam. Depending on conditions, the beam is constructed by adding plates to the top and thru-bolting all the plates together. The lateral load on the beam is blocked into the floor/ceiling diaphragm through headers to the inside of the opening. If this is not done correctly the top of the foundation wall will deflect into the opening. The grade, species, and size of the top plates are significant in determining the number of pieces to us for the beam. The size of the bolts are important in order to determine the spacing of the bolts. All bolts used in wood foundations should always be hex-head machine bolts with washers. (Never use carriage bolts).

Help Desk 810 955-4305

For more information:

www.pwfs.com

www.woodfoundation.com

www.woodbasement.com

Note: Panel foundations can be site built or made in a shop. When made so it cover up items that need inspection by the Building Inspector. Third Party Inspection may be required. (inspect for grade stamps, treatment stamps, stud spacing, insulation, nailing, dip of saw cuts, plywood requirments are some of the item that a third party inspection will note.

All Panel Wood Foundations must be designed and installed in accordance with:
All current Building Codes Standards

While wood foundations are easy to build, this is only true if one is building from an accurate well designed plan. When such a plan is incorrect, or if something is left out of the plan or absent, or if a design is made using a guide manual (these are not design manuals); major mistakes can be made during the construction process. These errors cause problems for the owner, builder, and the building department.

PermanentWoodFoundation.com a service of Permanent Wood Foundation System (PWF), supported by Southern Pine lumber users affiliated with the training and installation of wood foundations.
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