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Excerpts from the 1994 Uniform Building Code TM, copyright © 1994, are included in this guide with the permission of the publisher, the International Conference of Building Officials.

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Footings And Foundations

The City of Palo Alto has minimum footing requirements for all residential construction one or two stories in height. The footing must be 14 inches wide by 20 inches deep (below grade), continuous concrete with #4 (minimum) steel reinforcing bars (1/2 inch). It must extend a minimum of 6 inches above grade. It can be formed as a "Tee" or "Batter" type footing, or poured with a slab. Drawings which depict these two types follow the "Slab on Grade" section. Single story detached accessory buildings, such as garages and carports, may have a smaller continuous footing which is 12 inches wide by 12 inches deep below grade with one #4 (1/2 inch) bar.

Prior to pouring any concrete the bottom of the footings must be cleaned out; removing any loose soil, wood or debris. Roots must also be removed. All reinforcing steel must be held away from contact with soil or forms. (Note: The use of steel bars driven into the ground to support rebar is prohibited.) Three inches of clearance is required from reinforcing bars to sides and bottom of unformed footings (cast directly against the dirt surface), and 2 inches clearance is required from sides where forms are used.

Reinforcing steel when spliced must have a minimum lap of 12 inches for #4 bars and 15 inches for #5 (5/8 inch) bars. Where a new footing intersects an existing footing the new reinforcing must be doweled at least 6 inches into the existing footing.

Precast girder pier blocks must be set in a concrete footing 18 inches square by 6 inches deep. The pier excavations should be present at the time of the footing inspection.

Wooden form work located in the ground, or between the foundation sills and the ground, must be removed after pouring concrete.


Slabs On Grade

Concrete slabs supported directly on the ground may not be less than 3 1/2 inches thick. A continuous perimeter footing as described above is required. Any piping (such as radiant heat piping) must have a minimum cover of 1 1/2 inches. Electrical conduit, if used in a slab, must have a 2 inch minimum cover. This will require a slab thickness of 5 inches or greater. Any reinforcement in slabs on grade must have 2 inches of clearance from soil. If fir sill plates are to be used for interior partitions, a vapor barrier of 6 mil visqueen minimum is required.

Residential Footings


Floor Joists, Girders And Posts

Wood joists, or the bottom of wood floors closer than 18 inches, or wood girders closer than 12 inches to the ground in the under floor areas, must be redwood or pressure treated lumber. Girders entering masonry or concrete walls must have a minimum bearing of 3 inches and have a minimum of 1/2 inch air space on top, sides and ends unless they are of redwood or pressure treated lumber. Posts supporting girders must fully bear on redwood plates set in or on the pier block. The bottom of posts must be a minimum of 6 inches above grade.

Girder splices must occur over posts and must be provided with a splice gusset of wood or steel to connect their ends.

Solid 2X nominal blocking is required at ends of joists and over all bearing points. Blocking may be omitted where ends of joists are nailed to a header or rim joist. Joists 2 x 12 or larger must be blocked at intervals not to exceed 8'-0". Joists must be doubled under parallel bearing walls above.

Trimmer and header joists at openings must be doubled when the header span exceeds 4'0".

Span tables are included in this booklet for conventional framing methods, based on uniform loads. The tables follow the section on Roof and Ceiling Framing.

Joist framing from opposite sides of a beam, girder or partition shall be lapped at least 3 inches or the opposing joists shall be tied together in an approved manner.


Notches And Holes

Sec. 2326.12.4. Notches and holes. Notching at the ends of rafters or ceiling joists shall not exceed one sixth the depth and shall not be located in the middle one third of the span, except that a notch not exceeding one third of the depth is permitted in the top of the rafter or ceiling joist not further from the face of the support than the depth of the member.

Holes bored in rafters or ceiling joists shall not be within 2 inches (51 mm) of the top and bottom and their diameter shall not exceed one third the depth og the member.

Notches And Holes In Joists


Under Floor Ventilation

Under floor areas must be ventilated either by mechanical means or by openings in the exterior foundation walls. The openings must have a net area of 1 square foot for each 150 square feet of under floor area and should be located so as to provide cross ventilation. Openings must be screened with corrosion resistant wire mesh with openings of 1/4 inch dimension.


Plywood Subflooring

Plywood floor nailing is required to be 6 inches on center on all edges and 10 inches on center on intermediate supports. The thickness of plywood will be determined by your joist spacing and the panel identification index of plywood selected for use. All plywood flooring edges must be tongue and groove joints or must be supported with blocking.