If you’re thinking about adding an addition, a second story or even remodeling your kitchen or bath with tiles and granite countertops, be sure you consider the extra weight that it is going to be added to the overall structure. Why do most structures settle? Because the weight of the home is greater than the bearing capacity of the soil. Over time this weight deforms the soil and causes the home to settle. In some cases, homeowners or contractors will proceed with a remodeling project without taking that into consideration. The result can be costly.
Different soil types provide different bearing capacity values.
In general, as particle size increases bearing capacity also increases. The bearing capacity of some soils can be extremely variable depending on moisture content.
Many builders follow the USBC / IRC family of codes when building a house. These codes are devised as the minimum building standards that should be applied. When determining what type of structure to place on a particular lot they refer to a table in the Codebook titled Presumptive Load-Bearing Values of Foundation Materials. This important table sets the guidelines for how much weight can be built on a particular soil. The type of soil and its composition must be factored in when designing the footing to distribute the weight of the new home. For instance, the table shows that “Sandy, silty sand, clayey sand, silty gravel and clayey gravel” which is prevalent in this area, can handle a “Load-Bearing Value of approximately 2000 PSI (pounds per square foot).
Other factors such as compaction of the soil, its organic contents, and the moisture levels within it can affect how well the structure will hold up. Our recommendation is to always go a step beyond and get the soil tested by a Geotechnical Engineer.
In the late part of the last century, the Code required new advances in footing design. A combination of continual footing, which spans the parameter of the house, and pocket footing, to support the interior of the house, assures better stability of the structure when the Code is followed. However, up until more recently, Code was not strict on footing design nor soil composition. Thus many neighborhoods in Hampton Roads were built on substandard soil without bearing capacity being considered. And that’s where the problem of a new addition may occur.
Beyond the tables and the engineering calculations, it’s really quite simple. When additional PSI (pounds per square foot) is added that increases the total weight of the structure to more than the soil can support you will have settling problems. A new addition could start sinking and literally take a portion of the original structure with it. A new second floor can push the original first floor down into the soil. Our Inspectors have seen many cases where the symptoms of foundation failure are directly related to a room addition or second story that was added several years earlier.
Now consider another table from the Codebook entitled “Floor Joist Spans for Common Lumber Species”. This table factors the “dead load” and proper spacing of the joists based on the type of lumber being used. In other words, there are a lot of variables that can add weight to your home based on the materials it is built. So, if your kitchen has laminate countertops and you are changing them to granite, there is going to be much more “dead weight” on the soil below. Even changing the Linoleum in the bathroom to ceramic tile adds weight. We have seen numerous examples of cracked tile renovations due to settlement.
If you’re planning a renovation don’t take short cuts. Rely on the opinion of a Professional Engineer or Geotechnical Engineer to assess whether your property can support addition or second story. If the results indicate it can’t handle the extra weight, don’t worry, there is a solution.
If you’re planning a renovation don’t take short cuts. Rely on the opinion of a Professional Engineer.
Push piers can be driven down beyond the poor soils into the load-bearing stratum to compensate for any additional weight that will be added from renovations. This foundation stabilizing product has little disruption of the surrounding landscape does not take heavy equipment to install and has a lifetime transferable warranty. In cases where an addition may equate to a new construction site, helical piers may be an option. Lastly, if interior walls or flooring need to be shored up in preparation for a kitchen or bath renovation, the IntelliJack crawl space stabilizer system can be installed beneath the beams directly under where the work will take place.
Be sure you do your homework in the planning stages of your remodeling or renovation project. You can make the extra investment now to stabilize your home if its needed, or end up paying more to repair a failing foundation problem in the future.
Jesse Waltz, Professional Engineer
Jesse Waltz, a Professional Engineer, and a 1985 Virginia Military Institute graduate is the founder of JES Foundation Repair. JES is a regional foundation repair, crawl space, and basement waterproofing company with locations in Virginia Beach, Richmond, and Northern Virginia.