Grade Beam

BEFORE THE ARCHITECT – CUSTOM HOME DESIGNING BACKGROUND – HOUSE DESIGN ARTICLES

ALL ABOUT HOUSE FOUNDATION PROBLEMS and YOUR HOME DESIGN FOUNDATION PLAN GRADE BEAM

YOU MAY FREELY QUOTE THE AG WITH PROPER ATTRIBUTION

Know your home plans. Hold tight to the e-book. It's not important that you can do what a capable home designer or home builder can do. It is important that you can think like a capable home designer or home builder. Vicarious. Details. Nonlinear. Vicarious. Details. Nonlinear. Ask yourself or someone else and listen hard to the answer. Always on simmer. Otherwise, you won't get where you might have thought you were going and you won't appreciate the difference. The contractor, sub, or supplier can tell, right up front, that you're another moron can take you to wherever. That telling moment is almost always the very first impression. Word spreads fast. You're either a welcome mat or someone with whom to reckon and be respected. Gaw-ron-teed. Before The Architect

QUESTION: WHASSUP WITH HOUSE FOUNDATION PROBLEMS?

ANSWER: PRETTY NEAR NOTHING WITH A GOOD HOME FOUNDATION PLAN.

GRADE BEAM IN A HOME FOUNDATION PLAN

Comment: How Lucky Will You Be?

< What if you did not perfectly prepare the home foundation substrates to a slab-on-grade and then perfectly reinforce and place and joint the slab-on-grade? The best slip sheet on the planet won’t protect your stone floor from displacing its smooth surface plane or garage floor from cracking down at the corners or strip oak from rolling.

You likely needn’t be concerned much about a distorted concrete slab-on-grade if you’re building on marl in the Florida Keys or over ledge limestone north of Austin, TX.

Most don’t get so lucky.

It’s A Dangerous World Out There

This home designer runs into more opposition on this aspect of foundation than any other.

	“Well, I’ve been doing it this way for 10 years and never got a call-back.”
	That’s typical of builders who like what they know.
	As well, that’s not a proof statement; when’s the last time anybody heard of a call-back of the general contractor in regard to foundation problems, notably, cracked-up slabs-on-ground? In 40 years or so, this home designer recalls 2 – 1 leaker, 1 horrid substrate prep - neither remediated.

Extending The Already Been There, Done That

What’s more, Before The Architect’s approach to grade beaming a garage slab-on-grade never, never gets second-guessed.

And we extend that approach to other slab-on-grade elements. 30, 40, 50, 60 linear feet and more of uninterrupted, reinforced concrete 4-5 linear inches thick supported by earth can crack up and deflect in an imperfect world.

	How much?
	Ask an engineer.

Who Cares?

In a well-finished space over a slab-on-grade of sizeable extent,

	You’ll care when the paneling distorts, doors catch.
	Looking across a sea of pricey, terra cotta floor tile or Spanish-red pavers over a slab-on-grade, you’ll care even more when the isolation membrane says “No mas,” and cracks with high-low sides begin their differential journeys.

Engineers to The Left of Me, Engineers to the . . .

In fact, grade beams should, ultimately, be specified by an engineer.

Before The Architect’s approach to grade beam application is one among others, including but not limited to the 2-way flat slab in Basic Concrete Engineering For Builders, Max Schwartz, orig. 1922; Craftsman Book Company, 2000, pp.147-150.

the engineering latitude, these grade beam design variables need address -

	Beam spacing
	Beam width
	Beam depth
	Beam sizing
	Reinforcement
	Pedestal or pier sizing
	Spread footing sizing
	Footing depth
	Substrate preparation
	Bond breaks
	Moisture and vapor permeation

Comment: And never bond a grade beam to the concrete slab-on-grade that it's supporting

Comment: When obliged to withdraw reference to grade beams supporting slabs-on-grade [note: this is different from grade beams supporting bearing walls, which support is commonly and widely accepted], this designer writes on the foundation plan, “Grade beam design done by others with engineering latitude.”

Comment: Beware all ye who pass this way – this is not about post-tensioned slabs, with names, such as, mat slab, stiffened mat, stiffened slab, raft foundation, and, doubtlessly, others.

Grade Beam Foundation Details

A grade beam

Shall not be to a dead end except that it terminates in a spread footing and pier

	Which footing shall not be less than 24 linear inches x 24 linear inches x 12 linear inches
	Which footing shall be reinforced by not less than 3-#5 rebar continuous on long axis and evenly spaced with 3/4 linear inch plus aggregate size cover from top of face and similarly with 3/4 linear inch plus aggregate size cover from beam bottom of face
	Which footing bottom of face shall be on not higher than the bottoms of face of proximate footings
	Which pier shall not be less in its four sides than the ½ grade beam width
	Which pier shall be reinforced with not less than 2-#5 bent rebar on the vertical from the footing, or pier, bottom of face with 3/4 linear inch plus aggregate size cover up to the grade beam top of face 3/4 linear inch plus aggregate size cover to footing bottom of face

Comment: In the illustration Grade Beam with Footing Below Slab-On-Grade, Section in Elevation, notice that the grade beam is drawn to support either a 4 linear inch or 6 linear inch slab on grade, that a bond break is required between beam and slab, and that the “FGL”, or finish grade level, is implied because the owners were, at plan set submission time, still uncertain as to certain site grade levels, particularly at passages between interior and exterior. Note also that tamping of earth includes earth below the footing.

Grade Beam with Footing Below Slab-On-Grade, Section in Elevation

	Which pier with footing shall not be greater than 12 linear feet on center
	Which pier with foot shall be directly below each point, or concentrated, load, bearing on a grade beam
	Which pier shall not be connected to the supported slab-on- grade in any manner or reinforcement or any other material
	Which pier top of face shall have a continuous bond break applied between the top of face and the supported slab-on-grade bottom of face

be tamped the greater compaction of

	Not less than 50 beats per square foot and
	95% density, modified proctor in conformance with not less than ASTM D-1557 (a/k/a American Society for Testing and Materials, “Substrate Tests for Moisture-Density Relations of Soils and Soil Aggregate Mixtures Using 10-Pound Rammer and 18-inch Drop”)

terminate at a continuous concrete stem wall (a/k/a t-wall, a/k/a strip footing, a/k/a strip foundation)

	Which termination shall be by not less than the continuation of lengthwise reinforcement into the stem wall as dowels or
	Which termination shall be by bending and lapping the grade beam and stem wall rebar as specified elsewhere in this document

be applied

	As support to a load-bearing partition interior to a perimeter foundation (though not necessarily in lieu of a t-wall)
	As support to a load bearing partition exterior to a perimeter foundation (though not necessarily in lieu of a t-wall)
	As support to a 6 linear inch thick slab-on-grade floor
	at not greater than 24 linear feet span except
	at not greater than 20 linear feet side-to-side in a garage bay
	As support to a 4 linear inch thick slab-on-grade floor with not greater than 16 linear feet span
	Centered

interior and exterior applications

	Shall not be less than 16 linear inches on a side wide and 12 linear inches high
	Shall be reinforced with continuous and not less than #5 rebars

ü Lengthwise in the top if less than 16 linear inches wide or

ü 3 lengthwise in the top if not less than 16 linear inches wide and

ü 2 lengthwise in the bottom if less than 18 linear inches wide or

ü 3 lengthwise in the bottom if not less than 18 wide, and otherwise

ü Set at 12 linear inches on center both ways, i.e., crossed with not less than #5 rebar at 12 linear inches on center

ü The 2 layers shall have 2 linear inches cover each

Shall be supported at joints to stem walls

ü With a masonry pilaster of concrete, block, or brick

ü In width equal to the grade beam width

ü In depth continuously from grade beam bottom or face to footing top of face

ü In thickness equal to the footing reveal

>Comment: The AG recalls when #3 rebar were the rage in residential concrete reinforcement. Now, it’s #5 rebar.

slab-on-grade, grade beam, footing, raised curb, column, brick or masonry ledge, pilaster, and any other concrete foundation element

not then, for foundations separating exterior and interior space

shall be a continuous sheet of high puncture resistant EPDM (Ethylene Propylene Diene Monomer)

	at all cold joints between footing and wall
	each successive placement

ü When between slab on grade and pilaster top of face and slab on grade and grade beam top of face

be a continuous sheet of high puncture resistant EPDM (Ethylene Propylene Diene Monomer)

	at all cold joints between both pilaster and grade beam and the slab
	each successive slab placement

be supported at joints to stem walls

	a masonry pilaster of concrete, block, or brick
	width equal to the grade beam width
	depth continuously from grade beam bottom or face to footing top of face
	thickness equal to the footing reveal

be supported at joints to stem walls

	a masonry pilaster of concrete, block, or brick
	width equal to the grade beam width
	depth continuously from grade beam bottom or face to footing top of face
	thickness equal to the footing reveal

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