The information contained herein must be used in conjunction with the most current County Soils Maps and the publication entitled Ratings of Soils for Urban Development in Fairfax County. Questions on these requirements may be directed to the Code Analysis Division at 703-324-1720, TTY 711 or the Site Permits Section at 703-324-1510, TTY 711 .
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. Click on each code to view the specific requirement.
| TYPE OF ADDITION OR MODIFICATION |
Soils w/Prolonged High Water Table Problem Class "A" Nos.: 1, 2, 3, 5, 8, 11, 12, 13, 15, 30, 31, 33, 39, 68, 84, 89, 117, 152 |
Soils w/Fluctuating/Perched Water Table Problem Class "B" Nos.: 6, 10, 14, 20, 26, 32, 34, 37, 38, 44, 46, 47, 51, 53, 56, 65, 70, 86, 90, 91, 92, 110, 112, 113, 120, 273 |
Expansive Clays Typically w/Perched/High Water Table Problem Class "A" or "B" Nos.: 40, 41*, 42, 48, 50, 52*, 59*, 69*, 76, 78, 79, 80, 85, 141, 148, 232 |
Expansive Clays w/ Unstable Slopes or Uncontrolled Fill Problem Class "A" |
Unmapped Sites Soil may be mapped in accordance with Fairfax County Soil Series and the preceding columns used to determine the requirements, otherwise apply the following requirements. |
| Building Addition: CRAWL SPACE at/or above the existing grade. | FF, CI | FF, CI | FBC, FF, CI | EDR/SRR, F4, PEI | Over 100 square feet - EDR/SRR, F4, PEI. Less than 100 square feet - FF |
| Building Addition: CRAWL SPACE is below the existing grade. | EDR, DP-WP, FDR, BF, FF, CI | DP-WP, FDR, BF, FF, CI | EDR, FBC, FF, FDR, BF, S2, CI | EDR/SRR, S2, F4, PEI | Over 100 square feet - EDR/SRR, S2, F4, PEI. |
| Building Addition: FLOOR SLAB is at/or above the existing grade. | DP-WP, FF, CI | DP-WP, FF, CI | DP-WP, FBC, FF, S2, CI | EDR/SRR, S2, F4, PEI |
Over 100 square feet - EDR/SRR, S2, F4, PEI.
|
| Building Addition: FLOOR SLAB is below the existing grade. | EDR, DP-WP, FDR, BF, FF, CI | DP-WP, FDR, BF, FF, CI | EDR, DP-WP, FBC, FF, FDR, BF, S2, CI | EDR/SRR, S2, F4, PEI |
EDR/SRR, S2, F4, PEI
|
| GARAGE attached or detached, at/or above the existing grade. | DP-WP, FF, CI | DP-WP, FF, CI | DP-WP, FBC, FF, S2, CI | EDR/SRR, S2, F4, PEI | EDR/SRR, S2, F4, PEI. |
| GARAGE attached or detached below the existing grade. | EDR, DP-WP, FDR, BF, FF, CI | DP-WP, FDR, BF, FF, CI | EDR, DP-WP, FBC, FF, FDR, BF, S2, CI | EDR/SRR, S2, F4, PEI | EDR/SRR, S2, F4, PEI. |
| SHED (attached only) | EDR, FF, CI | FF, CI | EDR, FF, S2, CI | EDR, F4, CI |
Over 100 square feet, EDR, F4, CI.
Less than 100 square feet - FF |
| RETAINING WALLS UNDER 5' HIGH, NON-LOAD BEARING USING FAIRFAX COUNTY DETAILS | BF, FF, CI | BF, FF, CI | BF, FF, CI | BF, FF, CI | BF, FF, CI |
| RETAINING WALLS ABOVE 5' | EDR, FF, BF, PEI | EDR, FF, BF, PEI | EDR, FF, BF, PEI | EDR, FF, BF, PEI | EDR, FF, BF, PEI |
| FOUNDATION REPAIRS DUE TO SOIL PROBLEMS | RSR, DP-WP, PEI | RSR, DP-WP, PEI | RSR, DP-WP, PEI | RSR, DP-WP, PEI | RSR, DP-WP, PEI |
| SWIMMING POOLS | PRV, SPW, CI | PRV, SPW, CI | PRV, SPW, CI | EDR, PRV, SPW, PEI | EDR, PRV, SPW, PEI |
| DECKS | FF, CI | FF, CI | FF, CI | FF, CI | FF, CI |
| FOOT-BRIDGE | FF, CI | FF, CI | FF, CI | FF, CI | FF, CI |
BF = Backfill on walls must be non-expansive, free draining material adequately sloped to prevent ponding of water around the structure. Typically, soil type should classify as silty sands (SM) or coarser material.
CI = County inspections required. See the publication entitled "New Home Inspections" 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. will be scheduled for the next workday.
DP-WP = Damp Proofing/Water Proofing required in accordance with the current building codes.
EDR = Engineered Design Required for minor structures. A minor structure is considered (for soil purposes) an improvement less than 50 percent of the footprint area of the existing structure. An engineered design is required for minor structures when indicated on the chart, in lieu of a detailed geotechnical report as required under Chapter 107 of the County Code and Article 4 of the Public Facilities Manual. The engineered design must be shown on the construction plans and must bear the date, signature and seal of a licensed professional engineer experienced in soil and foundation engineering. The design must consider problems associated with these soils such as:
- High Water Table
- Expansive Clays
- Unstable excavations and slopes
- Low Bearing capacities
- Footing depth and size
- Frost heave potential, etc.
A detailed exploration is not required to establish these parameters except if the engineer determines otherwise (see Soils of Fairfax County, General Ratings for Urban Development).
The design may be provided in form of drawings and/or notes on the construction plans.
FBC = Footings Below Clays. Footings are required to extend below any zone of expansive clays and silts to firm underlying bedrock or saprolite.
FDR = Foundation Drains Required. Details of drains and backfill must be shown.
FF = Foundation on Firm Subgrade. Footings, piers must be placed on competent material.
F4 = Footings must extend at least four feet below exterior grades to minimize differential settlement due to shrinkage and expansion of marine clays.
PEI = Inspections must be performed by a professional engineer experienced in soil and foundation engineering as required by Article 4-0402 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. A 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: slope stabilization, underpinning of foundations, cement grouting, chemical grouting, replacement of backfill/installation of foundations drains, wall bracings to prevent deflection, excavation sheeting and shoring and any repair work that could jeopardize the safety of the existing structure/occupants or repair crew. The RSR does not have to be a report as detailed as soil reports prepared for new construction; however, it must address at a minimum the following:
- Visual and/or laboratory classification of backfill on foundation walls or soils supporting the distressed foundation such as uncontrolled fill or expansive clays.
- 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.
- Remedies and construction procedures.
- Drawings showing plan view/cross section of recommended design with details.
The report must be as brief as possible and must bear the date, signature and seal of the preparing engineer. Two copies of the report/plans will be submitted to the Plan Control Section. There are no fee requirements for such reviews. Adjacent property owners notifications may be required in accordance with Article 107-1-2(b) of the County Code. A written response will be forwarded to the design engineers/owners or contractors regarding the acceptance/approval of the engineer's recommendations from the Code Analysis Division. Structural aspects of foundation repair require the review of Building Plan Review or Critical Structures Section.
SPW = Swimming Pool Wall must be backfilled with non-expansive material. In lieu of such material, an engineered design of pool wall must be provided. The design shall consider all lateral forces on swimming pool wall which include; lateral earth pressures, swelling pressures, hydrostatic pressures, surcharge, etc. In no case shall equivalent fluid pressure for clays be less than 90 psf per linear foot of wall height. The structural design of the wall shall be subject to approval of Building Plan Review after the Code Analysis Division's review of soil and hydrostatic pressures.
SRR = Soil Report must be provided in accordance with Chapter 107 of the County Code for major structures. A major structure is considered an improvement more than 50 percent of the footprint area of the existing structure. The report must be prepared in accordance with Article 4 of the Public Facilities Manual "Geotechnical Guidelines." In lieu of the submission of a soil report, a waiver may be requested. There is a charge for soil report waiver (see current fee schedule). The waiver can only be granted by the County Executive (see Chapter 107-1-5 of the County Code). Approval has to be recommended by Land Development Services. Average processing time is 3-4 weeks.
S2 = Undercut plastic clays at least two feet below floor slabs.
* = Soil/Bedrock may contain asbestos minerals. The applicant/owner/contractor must ensure compliance with the regulations of the Health Department. Contact the Air Pollution Control Division of the Health Department at 703-246-2541, TTY 711.
Other Notes:
1. Building additions, modifications or repair with or without habitable space must comply with all applicable sections of the building codes adopted by the commonwealth of Virginia.
2. Excavations in all soil types must comply with OSHA Excavation Standards 29CFR Part 1926, Subpart P, Appendix A.
3. The above requirements are not the only requirements necessary for Building Permit Approval; however, they address most of the requirements for construction in problem soils. For details of other requirements for your project contact the Permits Applications Center at 703-222-0801, TTY 711.