OWNER BUILT | TP OF THE MONTH

May

Building Pads

Why do some lots require a building pad when others don’t? An average subdivision lot does not require the construction of a pad, typically it will be flat and level. The finish floor elevation (finished height of the homes floor) need only be 12” higher than the curb. Irrigated lots will almost certainly need a pad that raises the finish floor elevation from 18”-20” above the yard, some developers will sell these lots with the pads already installed. Lots that are situated on sloping grades as found in the foothill areas around Phoenix normally require pads, these type lots can benefit from a “cut & fill”. A cut and fill is where the higher portion of the lot is cut down below grade, that material (if suitable for compaction) can be used to raise up the lower section of the lot. On more severe grades retaining walls will also be used.

Compaction Tests

Once a pad is completed a soils engineering company will be called to test the pads compaction rate. The engineer will test the pad in 2-3 different locations. Most cities require a pad have a compaction rating of 95% or better, a letter will be issued listing the compaction rate. When calling for a house footing inspection the city inspector will ask to see the compaction report before approving the footing inspection.

Certified Pads

Recently more cities are requiring a pad to be certified by a soils engineering company before allowing the house to be built. The compaction test as previously mentioned only tests the soils upper layer, apx. 12” down, so if your pad is 4’-5’ high (as measured from native soil) there is no guarantee how well the soil is compacted below. With a certified pad, a soils report is used to determine the characteristics of the existing native soil. Most developers will have completed this report and have it available for the engineer, if not you must hire the engineer to go to the lot with a backhoe or drill rig and perform various tests and create a soils report, this will usually cost about $1,800. The engineer uses the information from the soils report to determine requirements for how the pad should be built.

During pad construction its typical for the engineer to come to the site and perform compaction tests on every 12” of soil added to the pad (these are called “lifts”) Following a final compaction test and verification that the pad was built correctly the engineer will issue a letter certifying the pad. The on-site testing and certification letter will run between $600 and $1,200 depending on the size and scope of work

Civil Engineer

Most cities will require that a civil engineer create a grading and drainage plan on all but the very basic of pads. This plan typically will have a topographical survey, a flow study on any washes that cross your lot, and a plan to take the runoff water safely through and away from your lot. The cost of a grading and drainage plan can run between $2,500 and $4,000. It’s always a good idea to meet with the cities civil engineer to find out if this plan will be required. If not in a city but in a county area you can call the Maricopa county flood control for assistance.

* The information contained in this “tips” section is to be used as a general guide only. When making decisions about your project a professional should be consulted using the specific information that is unique to your project.