Footing width and thickness

An explanation of the required concrete footing width. R3 occupancies, the edge thickness is permitted to be 6 inches 152 mm, provided that the footing does not extend beyond a distance greater than the thickness of the footing on either side of the supported wall. An unreinforced footing that is too wide may crack close to the wall, overloading the soil beneath. Minimum thickness of concrete slab, beam, column, foundation.

Guide to foundation footings building code the spruce. As you can see, heavy houses on weak soil need footings 2 feet wide or more. How to determine the thickness of a footing based on the. Footing fundamentals homeowners step 1 homeadvisor. An explanation of the required concrete footing width perplexities. In my specific problem im trying to find a required footing width for a strip footing with axial loads of about 20kips every 10 feet, with qa2000psf. The footing dimensions will largely be determined by the size of the wall.

A poured concrete footing for concrete, block or brick walls should be at least twice as wide as the planned wall. Acceptable tolerances for residential footings for. The break line would be like a 45degree angle flaring outward from the wall of the pier. If footing thickness is inadequate for shear capacity a red warning indicator will appear. Maximum efficiency in the footing sizing is achieved when the plan dimension inc. Footing projections, p, shall be at least 2 inches 51 mm and shall not exceed the thickness of the footing. Ubc recommends minimum thickness of bearing wall to 125 supported height or length whichever is shorter or not less than 102mm. The weight of the house is transferred to the footing, and the foundation wall provides the base for the house framing. Reading down the table, you see that the code calls for a 12inchwide footing under a two. What are the thickness requirements of strip foundations. For every 2 feet of adjustment to the width of the house add or subtract 2 inches of footing width and 1 inch of footing thickness but not less than 6 inches thick. Without reinforcement, codes say the thickness of the footing should be at least as great as the distance it projects next to the wall. Assume that the footings bear on silty sand with an allowable soil bearing pressure of 3000 psf. Size a spread footing for column b3 in the building shown below.

For bending and shear design of the footing, the rebar depth d is taken as footing depth rebar cover. Seismic activity and other severe environmental conditions may also have to be addressed in foundation design. Minimum footing thickness as per aci 318 structural. Footing width and depth this footing is 20 inches wide and the depth will be over 42 inches once the backfill is placed against the finished foundation. Footing thickness 1 footing thickness shall be not less than the greater of a 100 mm, or b the width of the projection of the footing beyond the supported element. Rectangular footing aspect ratio structural engineering. The allowable bearing capacity of the soil under the footing has to equal the load imposed by the structure.

The walls should be reinforced and made thicker if the hydrostatic pressure pressure from soil water is very high. Thats because a footing thats too wide and not thick enough will experience a bending force that could crack the concrete. If you increase the footing width, the code requires an increased thickness as well. Thats because a footing thats too wide and not thick enough will. Depth of footing above bottom reinforcement shall not be less than 150 mm for footings on soil, nor less than 300 mm for footings on piles. Eight inches is the minimum thickness for a footing. The 45 degree angle makes each side beyond the wall equal to the thickness of the footing, and then you have. Followings are two code references aci and bnbc for minimum thickness value of concrete footing.

You can look up the recommended footing size, based on the size and type of house and the bearing capacity of the soil see the table above. Guide for square footing sizing minnesota department of. I dont think ive ever done one less than 18, and something closer to 24 is pretty common. I have added a few fields like length, width, mark, type and elebation at bottom. Where i live, 16 width for a continuous wall footing is very narrow. The walls need to be thick enough to withstand the lateral pressure of the soil bearing against them. Footings should extend to a minimum depth of 12 inches below previously undisturbed soil. Typical spread footing detail when separate reinforced concrete columns or concrete block columns are used they should be supported by square footings not less than 20 square and 12 thick. The footer is extra thick where painted orange because of the sloping ground at the building site. The minimum depth for footing on soil is advised to be 150mm. Minimum requirements are set out in building codes, including foundation wall thickness.

What are the standard dimensions for a footing in a residential building. Concrete footing soil bearing capacity relating to the size. Footing thickness how thick the footing must be from the top of the concrete to the bottom of the concrete. I have created footing schedule by clicking schedule quantities. The design, materials and construction of masonryunit footings shall comply with sec. The 45 degree angle makes each side beyond the wall equal to the thickness of the footing, and then you have the thickness of the wall. The dimensions depend on three main criteria, all of which contribute to how much weightforces the footing will need to resist to keep. The weight of the house is transferred to the footing, and the foundation wall provides the. Allowable load on footings this is the total load that comes down the column to the top of the footing.

Size concrete footings by finding the buildings size, construction materials and the locations soil bearing capacity on a concrete footing width chart. The ontario building code basic footing widths and areas. A footing is the cement slab that is used to support a structure by distributing weight over a defined area. If z is less than y and you over load this pier, the concrete is likely to break along the bottom surface x. Although actual concrete compressive strength psi may vary, it is assumed that at a minimum, plain structural concrete 2500 psi will be used for column footings sized herein. The length and width reported at that point be the most optimum for that thickness. Footing thickness inches footing width inches reinforcing each way 1500 psf 8 12. Five ways to build deck footings size shape depth information.

Determining perimeter footing sizes village of ruidoso. The footing width, w, shall be based on the loadbearing value of the soil in accordance with table r401. Total footing thickness, not including the key depth if used. Chapter 4 foundations 2015 international residential code. How to calculate the depth of footing for a retention wall. Footings may not be less than 8 thick thickness 2 footing thickness formula from. Reading down the table, you see that the code calls for a 12inchwide footing under a twostory woodframe house in 2,500psfbearing soil. If you increase the footing width, the code requires an increased thickness as well figure 6. Requirements for levelness are different for the top and bottom of the footing. Jul 17, 2017 divide the length by 12 to convert it to feet. Footing projections, p, shall be not less than 2 inches 51 mm and shall not exceed the thickness of the footing. The footing width shall be based on the loadbearing value of the soil in accordance with table r401. Jul 17, 2017 determine the planned walls height and width. I have selected a footingrectangular in foundation plan and and edited the family.

Prescriptive method for insulating concrete forms in residential construction by nahb research centre, inc. The thickness of the footing z must always be greater than that distance. If the measurement for the length is 240 inches the result is 20 feet. Spread footings shall be at least 6 inches 152 mm in thickness, t. Ten inches is better and twelve inches is highly desirable. In family type dialog box, i have also highliged thickness. To add to this, minimum thickness above bottom of concrete reinforcement prescribed for concrete footing is. So, if the foundation walls is 8 wide and the minimum width requirement for a 1 story building is 12 in soil that will bear, for example, 2000 psf, and the minimum projection requirement is 2 then theoretically the. The nominal width of blocks for exterior walls and load bearing interior. Thickness requirements of strip foundations thickness of strip foundation carrying light loads. Footings shall be minimum 8 thick, and shall have a width that allows for a.

Youll also want to provide a certain minimum thickness of footing. Footings also must extend at least 12 inches below the frost line the depth to which the ground freezes in winter or must be frostprotected. Footing depth can be confused with the thickness of a footing. A wide footer distributes the building load over a greater area. Footing thickness and projection for fireplaces shall be in accordance with section r1001.

The amount of cement that is needed for the footing is obtained by calculating cubic feet. But the smaller those values, the more the time required to calculate the suitable. Footing projections p shall be at least 2 inches and shall not exceed the thickness of the footing. The projection of the footing on either side of the wall is supposed to be no greater than the depth of the footing. But the lightest buildings on the strongest soil require footings as narrow as 7 or 8 inches. The cubic feet of cement required for the footings is calculated by using the dimensions of the slab. Footing thickness how thick the footing must be from the top of the concrete to the. Without reinforcement, codes say the thickness of the footing should be at least as great as the distance it.

The same value is recommended by international residential code irc 2009 for foundation wall. So what you said and what i said is the same thing. Individual pad footing table tables are shown for fc concrete at 2000 psi and 3000 psi. Determine the depth or thickness that is required for the footing in inches. But when calculating applied pressure to the soil through a rectangular footing, im sure you cant count on your whole footing area to bear evenly if its 2x10 for example. This minimum thickness is imposed to make sure that the strip foundation possess adequate rigidity and consequently be able to bridge weak pockets in soil. If building on a sloped grade, you can step the footing as much as 1. Reinforce footings when the projection on each side of the wall, pier, or. Where clays must be used as the foundation bearing material, the width of the footing should be increased to a minimum of 2 6. Minimum thickness of concrete footing civil engineering. First things first, you should have a soils report which typically gives minimum footing dimension recommendations. Concrete footing soil bearing capacity relating to the.

Width of footing inches thickness of footing inches 1126 2156 3188 l a l a l a l a l a l a l a l a l a l a l a l a l a l a l a l a l a l a l a l a l a l a l a l a soils and foundations 2014. Under an 8inchthick wall, thats the same as saying you have no footing. Chapter 4 foundations 2012 international residential code. Increasing the thickness and strength of the walls is necessary if they must fight both leaks and soil pressure. A poured concrete footing for concrete, block or brick walls should. The average foundation wall, whether poured concrete or block, is 8 to 10 inches. Minimum width of concrete footing for logix walls maximum number of storeys minimum load bearing value of soil 2000 psf 2500 psf 3000 psf 3500 psf 4000 psf 6. The minimum thickness for pier footings is 8 inches or 112 times the length of the footing projection from the pier, whichever is greater. Chapter 4 foundations 2012 international residential. Commonly, the thickness of strip foundation is equal to the projection from the face of footing or the. I have selected a footingrectangular in foundation plan. Basic code requirements for foundation footings include site grading.

Step footings 1where step footings are used, a the vertical rise between horizontal portions shall not exceed 600 mm, and. So, if the foundation walls is 8 wide and the minimum width. The footing should be at least as thick vertically as the walls planned width. The spread footing should be no less than 6 inches thick. Eventually i have to decide the minimum thickness of the footing based on this 200 mm value. Commonly, the thickness of strip foundation is equal to the projection from the face of footing or the wall but it should not be less than 150mm. Footing projections, p, shall be not less than 2 inches 51 mm and shall not exceed the thickness of. Multiply the width by the length and then by the depth. Ubc specified minimum thickness of exterior basement wall and foundation wall to be 191mm. Thats because a footing thats too wide and not thick enough will experience a bending force that could. The walls should be reinforced and made thicker if the hydrostatic pressure. Although actual concrete compressive strength psi may vary, it is assumed that at a minimum, plain structural concrete 2500 psi will be used for column.