Soil Requirements for Minor Construction Projects


The information contained herein must be used in conjunction with the most current county soils maps and Description and Interpretive Guide to Soils in Fairfax County. Questions on these requirements may be directed to the Site Code Research and Development Branch at 703-324-1720, TTY 711, or the Site and Addressing Center at 703-222-0801, TTY 711.

  1. This table contains the main design and inspection requirements related to soils that are necessary for building permit approval for minor projects. For details contact Site and Addressing Center at 703 222-0801, TTY 711.
  2. All construction projects requiring a building permit, regardless of land disturbance area, must comply with the applicable sections of the Virginia Uniform Statewide Building Code. For details, contact the Permit Application Center at 703-222-0801, TTY 711, or visit www.fairfaxcounty.gov/buildingpermits.
  3. Excavations in all soil types must comply with OSHA Excavation Standards 29CFR Part 1926, Subpart P, Appendix A.
  4. The underlying bedrock in certain parts of the county can be shallow, typically 10 to 15 feet deep, and can contain naturally occuring asbestos (NOA). However, the overlying soils are not considered to contain NOA. It is necessary to check the Health Department's Orange Soils Map, via www.fairfaxcounty.gov/hd/asb/ to determine if the site is underlain by NOA bedrock and soils. For sites underlain by NOA, personnel working in or around this geological area shall be alerted of the potential health risk. If earth excavation and/or moving is needed during the course of construction, special precautions for the handling of the underlying soils and rock (through dust control, worker protection, etc.) are required to be followed per OSHA regulations and enforced by the Virginia Department of Labor and Industry. Special guidance by the U.S. EPA can be found at www.epa.gov/asbestos/pubs/clean.html.

Directions: Use the top row to identify your soil type and use the left column to identify your project type. In the intersecting cell, are the corresponding codes for the construction requirements. Soil code definitions are listed below the table.

Residential Type of
Addition or Modification
Involving Less Than 2,500 Square Feet of Land Disturbance
Undisturbed Natural Non-Problem Soils
 Class I

Nos.: 11, 28, 33, 38, 39, 76, 79, 80, 81, 84, 85, 87, 88, 90
Undisturbed Natural w/Shallow Water Table, Fluctuating or Prolonged
 Class II

Nos.: 2, 7, 9, 31, 75, 77, 78, 92, 93
Disturbed Soils or Previously Developed Land
Class IVB

Nos.: 3, 4, 5, 6, 12, 14, 16, 18, 19, 22-25, 40, 41, 45, 46, 50, 66, 67, 68, 70, 72, 95-102, 104, 105, 107, 108
Undisturbed and/or Disturbed Soils w/Expansive Potential, Unstable Slopes, Shallow Water Table, Etc.
Class III and Class IVA
Nos.: 1, 8, 10, 13, 15, 17, 20, 21, 26, 27, 29, 30, 32, 34-37, 42-44, 47-49, 51-57, 55, 59-65, 69, 71, 73, 74, 82, 83, 86, 89, 91, 94, 103, 106, 109
Building addition with crawl space at/or above the existing grade. FF , CI FF , CI EDR*, FFE, CI EDR, F4, PEI
Building addition with crawl space  below the existing grade. FF, WP, BF, CI EDR*, FF, FDR, WP, BF, CI EDR*, FFE, WP, BF, CI EDR, S2, F4, FDR, WP, BF, PEI
Building addition with floor slab  at/or above the existing grade. FF, CI FF, WP, CI EDR*, FFE, CI EDR, S2, F4, CI**
Building addition with part of floor slab below the exterior grade. FF, WP, BF, CI EDR*, FF, FDR, WP, BF, CI EDR*, FFE, FDR, WP, BF, CI EDR, WP, FDR, S2, F4, BF, CI**
Convert crawlspace to basement. EDR, FF, FDR, WP, BF, PEI EDR, FF, FDR, WP, BF, PEI EDR, WP, FDR, PEI EDR, WP, FDR, S2, F4, BF, PEI
Garage or shed attached or detached, w/living space at/or above the existing grade. FF, CI FF, CI EDR*, FFE, CI EDR, S2, F4, CI**
Garage or shed attached or detached, w/living space below the existing grade. EDR, FF, FDR, WP, BF, PEI EDR, FF, FDR, WP, BF, PEI EDR, FFE, FDR, WP, BF, PEI EDR, S2, F4, FDR, WP, BF, PEI
Shed, garage or barn, one-story, no living space (detached only) FF, CI FF, CI FFE, CI F4, S2, CI
Fences (Height over six feet) FF, CI FF, CI FFE, CI F4, CI
Retaining walls with no surcharge loads using Fairfax County typical details FF, BF, CI FF, BF, CI FFE, BF, CI CANNOT USE COUNTY DETAILS IN PROBLEM SOILS EDR, FF, BF, CI**
Retaining walls at any height and not using Fairfax County typical details EDR, FF, BF, CI EDR, FF, BF, CI EDR, FFE, BF, CI EDR, FF, BF, CI**
Areaways (Height above 5 feet) FF, FDR, BF, CI FF, FDR, BF, CI FFE, FDR, BF, CI EDR, FF, FDR, BF, CI
Foundation repair or underpinning with entire floor slab at or above exterior grade EDR, PEI EDR, PEI EDR, FFE, WP, PEI RSR, EDR, S2, F4, PEI
Foundation repair or underpinning with part of existing floor slab below exterior grade EDR, WP, BF, PEI EDR, FDR, WP, BF, PEI EDR, FFE, FDR, BF, WP, PEI RSR, EDR, S2, F4, FDR, WP, PEI
Swimming pools CI PRV, SPW, CI EDR, PRV, SPW, CI EDR, PRV, SPW, CI
Decks, porches, screened porches, private foot bridges, etc. that are pier-supported FF, CI FF, CI EDR*, FFE, CI EDR*, F4, CI

 

Commercial Type of
Addition or Modification Involving

Less Than or Equal to 250 Sq. Ft. of Land Disturbance OR 500 Sq. Ft. for ADA Improvements (ZO 17-104-16)
Undisturbed Natural Non-Problem Soils
 Class I

Nos.: 11, 28, 33, 38, 39, 76, 79, 80, 81, 84, 85, 87, 88, 90
Undisturbed Natural w/Shallow Water Table, Fluctuating or Prolonged
 Class II

Nos.: 2, 7, 9, 31, 75, 77, 78, 92, 93
Disturbed Soils or Previously Developed Land
Class IVB

Nos.: 3, 4, 5, 6, 12, 14, 16, 18, 19, 22-25, 40, 41, 45, 46, 50, 66, 67, 68, 70, 72, 95-102, 104, 105, 107, 108
Undisturbed and/or Disturbed Soils w/Expansive Potential, Unstable Slopes, Shallow Water Table, Etc.
Class III and Class IVA
Nos.: 1, 8, 10, 13, 15, 17, 20, 21, 26, 27, 29, 30, 32, 34-37, 42-44, 47-49, 51-57, 55, 59-65, 69, 71, 73, 74, 82, 83, 86, 89, 91, 94, 103, 106, 109
Signs less than 10 feet in height FF, CI FF, CI FFE, CI EDR*, F4, CI
Signs more than 10 feet in height EDR, FF, PEI EDR, FF, PEI EDR, FFE, PEI EDR, F4, PEI
Dumpster enclosure, privacy wall, etc. less than 10 feet in height FF, CI FF, CI FFE, CI F4, PEI
Dumpster enclosure, privacy wall, etc. more than 10 feet in height EDR, FF, PEI EDR, FF, PEI EDR, FFE, PEI EDR, F4, PEI
Equipment pad FF, CI FF, CI FFE, CI F4, PEI
Pedestrian and golf cart bridges for public use EDR, PEI EDR, PEI EDR, FFE, PEI EDR, F4, PEI

  * Only when a foundation bearing pressure of more than 1,500 psf is used in the structural design of the spread footings.

** County inspections of foundation elements may, in some cases, also require professional engineer inspection (PEI).


BF = Walls must be backfilled with non-expansive soils that correspond to the lateral pressure used in the design of the wall as listed below. The top of the backfill shall be adequately sloped to prevent water from accumulating around the structure.

  • Basement and areaway walls: 60 psf/ft = SC, ML-CL and Inorganic CL
  • Basement and areaway walls: 45 psf/ft = GM, GC, SM, SM-SC and ML
  • Basement and areaway walls: 30 psf/ft = GW, GP, SW and SP

CI = County inspections required. Customers may alternatively use Professional Engineer Inspection (PEI) for foundation and soil related inspections.See the New Home Inspections publication or contact the Inspection Request Center at 703-222-0455, TTY 711 . Please note: Customers may also use the Fairfax Inspections Database Online, FIDO, or the automated telephone line 703-222-2474, 24 hours a day, seven days a week, to schedule and cancel inspections. Requests made prior to 11:59 p.m. can be scheduled for the next workday.

EDR = Engineered design required for building foundation in problem soil. The engineered design must be shown on the construction plans (in the form of drawings and/or notes) and must bear the date, signature, and seal of a licensed PE in the Commonwealth of Virginia experienced in soil and foundation engineering. NOTE: An Architect, Surveyor, and/or Landscape Architect Seal is prohibited. The design shall be in accordance with the current Virginia Residential Code (including chapter 4) and Virginia Construction Code (including chapter 18) for residential and commercial projects, respectively. The design must consider the following problems associated with soils and specify the design assumptions that are to be field verified during construction:

  • High water table
  • Expansive clays
  • Unstable excavations and slopes
  • Low bearing capacities
  • Footing depth and size
  • Backfill materials, lateral pressure and drainage
  • Frost heave potential, etc.

FDR = Foundation drains required, per the Virginia Residential Code. Details of drains and backfill must be shown on plans.

FF = Footings and/or piers must bear placed on competent undisturbed soils.

FFE = Footings and/or piers must be extended (or deepened) through previously disturbed soils and bear on competent undisturbed soils.

F4 = Footings must extend at least 4 feet below the nearest exterior grade or to the end of the expansive soils, whichever occurs first, and bear on comptetent, natural soils.

PEI = Foundation and soils-related inspections must be performed by a professional engineer experienced in soil and foundation engineering as required by Article 4 of the Public Facilities Manual.

PRV = Pressure release valves should be provided for the release of hydrostatic pressure when pool is emptied.

RSR =  Remediation soil report is required for foundation damages caused by problems soils. Such repairs require the expertise of a geotechnical and/or structural engineer. Examples of repairs that would require RSR are: underpinning of foundations, cement grouting, chemical grouting, replacement of backfill/installation of foundation drains, wall bracings to prevent deflection, excavation sheeting and shoring and any repair work that could jeopardize the safety of the existing structure or repair crew. The RSR must address at a minimum the following:

  1. Visual and/or laboratory classification of backfill on foundation walls or soils supporting the distressed foundation such as uncontrolled fill or expansive clays.
  2. The engineer's opinion regarding cause of distress or failure, e.g., improper backfill, hydrostatic pressures, swell pressures, slope creep, adjacent grades, settlement, frost heave, effects of weather, tree roots, structural weaknesses, etc.
  3. Remedies and construction procedures.
  4. Drawings showing plan view/cross section of recommended design with details.

The report must bear the date, signature and seal of the preparing engineer. Two copies of the report and plans will be submitted to Building Plan Review.

SPW = Swimming pool bottom slab and wall must be underlain and backfilled with non-expansive materials. Alternatively, an engineered design of the bottom slab and pool wall must be provided. Either designs shall consider all lateral forces on the swimming pool wall (including lateral earth pressures, swelling pressures, hydrostatic pressures, surcharge, etc.). In no case shall equivalent fluid pressure for expansive soils be less than 90 psf per linear foot of the wall height. The structural design of the wall shall be subject to approval of Building Plan Review.

S2 = Undercut expansive soils at least two feet below bottom of floor slab.

WP  = Waterproofing of foundation wall is required in accordance with the Virginia Residential Code.


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