Tag Archives: expansive soils

Barndominium Building on Solid Ground

For many, a new barndominium is looked upon as being a ‘forever’ home. This is an opportunity to have a floor plan custom crafted to meet all sorts of family wants and needs – whether it is a huge country kitchen or shop space big enough to house a fleet of classic vehicles.

It is yours.

It is YOUR hard earned dollars going to pay for this lovely new home.

While I encourage everyone who can to at least act as their own General Contractor (https://www.hansenpolebuildings.com/2020/02/does-my-barndominium-need-a-turn-key-general-contractor/), not everyone feels confident in doing this. In some instances lenders require a General Contractor’s involvement. For others, their new barndominium and their current home and careers are geographically not close enough to allow for this to occur.

Scary things can happen when turnkey General Contractors are left to their own devices. I have penned previously (okay hunt-and-pecked) on how to avoid General Contractor challenges (https://www.hansenpolebuildings.com/2019/11/a-contractor-for-your-new-barndominium/).
Crucial to long term success with your new barndominium is having a solid base to build upon. Those doing work DIY have an advantage – you get to supervise (or do) site preparation and any needed compaction.

drywall crackHaving a barndominium built? You may anticipate a few things going wrong, but you’d expect your builder to erect your house on solid ground, right? Don’t be so sure.
Population growth and urban sprawl mean there’s not much residential land left in many areas. “What’s left is not very good,” says Daniel G. Knowler, a senior engagement manager at Navigant Consulting, specializing in construction disputes. A lot of homes are being built on expansive soil — it swells when it rains — without adequate safeguards.

One family moved into their new home in Highlands Ranch, Colorado, and long cracks started showing up in walls, then their porch started pulling away from their house. After badgering his builder for a soils report, this homeowner learned their lot was a hot spot for potential swell! Eventually a court found for these homeowners and ordered restitution from said builder.

(for extended reading on barndominiums on expansive soils please see: https://www.hansenpolebuildings.com/2020/07/barndominium-on-expansive-soils/)
Problems besides swelling soil can occur. In Laguna Niguel, California four hillside homes built on an ancient landslide site toppled after unstable soil gave way. Besides these four homes collapsing, they landed on top of other dwellings below – destroying them!

Do not assume a turnkey General Contractor will make all potential problems go away, sadly they can cause more than they solve.

Barndominium on Expansive Soils

Post Frame Barndominium Building on Expansive Soils.

When I was a 1990’s post frame building contractor we trained our sales team to be diligent in looking at soil cuts near where our potential clients were considering erecting new post frame buildings. These cuts could tell us much about what was happening below the surface and potentially impacting digging conditions and ultimately performance of a new building.

Reader STACY in BERTHOUD writes:

“Hello.

My wife and I are looking at building a pretty large Barndominium on some lake front land that we have owned for more than 20 years but we are on expansive (high clay content) with a tested swell of 8-9%. 

Background Info:

The house portion would be approximately 2800 sq’ and the shop/garage portion is about 8000 square feet. The shop portion will store vehicles, Large RV, boats and leave recreational space for gym, Pickleball Court and an enclosed area for dusty work such as wood working and metal fabrication. 

We have a Morton out building there currently that is 42/75 with a fair amount of slab cracking. Although not hindered the function for a non heated barn, I would want the home to perform better. No Over Excavation was done but probably should have been. 

I cannot seem to find advice on if this is doable with a pole barn structure given the soils. They feel that deep cassions setting on a full perimeter grade beam is required which will totally blow the budget on a structure this size. I am trying to find out if this is true or is there a Over Excavation strategy that would be reasonable and how that perimeter detail might look for a tight, well insulated structure?

Any advice or specialist you could point me towards is greatly appreciated. 

Thank you!”

Mike the Pole Barn Guru responds:

My lovely bride and I live in an 8000 square foot, 44 foot tall post frame shop/house in NE South Dakota (we look across Lake Traverse at Minnesota). Minnesota is known as the land of 10,000 lakes. Many of these lakes resulted from glacial erosion causing physical and chemical changes creating small particles required to form clay soil. This clay sediment is both very fertile and makes for excellent lake bottoms!

Our particular building site had significant amounts of clay and we chose to excavate it out (over excavate) and replace with compactable fill. Our site is also built up, so any rain or snowmelt runs away from our home. After 15 years of service we have only minimal hairline cracks in our slab on grade – even though we have been through winters of seven feet of frost! Our building has no perimeter grade beams and our columns are embedded in concrete six feet below grade.

Most Building Departments in your area require engineered soils reports prior to construction. A qualified geotechnical engineer can determine a best course of action to avoid or limit adverse reactions from clay soils.

Here is some further reading: https://www.hansenpolebuildings.com/2019/06/post-frame-construction-on-clay-soils/

and https://www.hansenpolebuildings.com/2020/07/barndominium-on-expansive-soils/

Barndominium Building on Expansive Soils

Barndominium Building on Expansive Soils

Expansive soils in many United States areas pose a significant hazard to foundations for barndominiums. Swelling clays derived from residual soils can exert uplift pressures of as much as 5,500 PSF (pounds per square foot) and can do considerable damage to barndominiums, shouses and post frame homes.

Insurance companies pay out millions of dollars yearly to repair homes distressed by expansive soils. 

Expansive soils owe their characteristics to swelling clay minerals being present. As they get wet, clay minerals absorb water molecules and expand; conversely, as they dry they shrink, leaving large soil voids. Swelling clays can control behaviors of virtually any type of soil if the percentage of clay is more than about five percent by weight.

Soils with smectite clay minerals, such as montmorillonite, exhibit most profound swelling properties. In real life, expansive clay soils can be easily recognized in dry seasons by deep cracks, in roughly polygonal patterns, in ground surfaces. This zone of seasonal moisture content fluctuation can extend from three to forty feet deep. This creates cyclic shrink/swell behavior in upper portions of soil and cracks can extend to much greater depths than imagined by most engineers. 

The most obvious way expansive soils can damage foundations is by uplift as they swell with moisture increases. Swelling soils lift up and crack continuous strip footings (as in typical stick frame construction), and frequently cause distress in floor slabs. Because of different building loads on different portions of a structure’s foundation, resultant uplift will vary in different areas. Exterior corners of a uniformly-loaded rectangular slab foundation will only exert about one-fourth of normal pressure on a swelling soil as compared to central slab portions. As a result, corners tend to be lifted up relative to the central portion. This phenomenon can be exacerbated by moisture differentials within soils at slab edges. Such differential foundation movement can also cause distress to a structure’s framing. 

Drilled pier foundations (like isolated widely spaced post frame building embedded columns) have been used in California, Colorado and Texas since the late 1950s to reduce expansive soil damage. However, these types of foundations can also be adversely affected by expansive soil behavior if piers are not sufficiently deep.

When the rainy season begins, piers are still supported by soil friction. When it begins to rain, water enters deep into soil through cracks. After five to 10 large storms, soil swells, lifting buildings and piers. In the dry season, groundwater table falls and soil dries and contracts. As tension cracks grow around piers, skin friction is reduced and effective soil stress increases (due to drying). When building loads exceed remaining skin friction, or effective soil stress increases to an all-time high, adhesion is broken by this straining, and piers sink. Frequently, corner piers of a pier-supported structure are lifted up during swelling in wet season, and then break their skin friction bond with ground when soil shrinks away from the pier in following dry seasons. Loss of this “skin friction” decreases the pier’s ability to support building loads. This straining to soil can become great enough to cause pier failure. To prevent this style of damage, piers must be drilled well below the zone of seasonal moisture fluctuation, and they must be designed with an assumption upper pier portions will lose contact with adjacent soil. 

Expansive soils pose greatest hazard in regions with pronounced wet and dry seasons. This annual cycle of wetting and drying causes soils to shrink and swell each year. Thus, arid regions are much more susceptible to damage from expansive soils than regions maintaining moist soil conditions year around. Biggest problem in expansive soil areas is differential water content. Sources of water in developed areas are not limited to temporal weather cycles, but can be introduced by people. A frequent source of damage is differential swelling caused by pockets of moist soil adjacent to dry soil. For example, lawn and garden watering creates a moist zone on foundation exterior, whereas interior is dry; this creates differential swelling pressure on foundation elements. There is frequently a moisture differential between soils beneath a house and those more directly exposed to changes in the weather.

Best way to avoid damage from expansive soils is to extend building foundations beneath zones of water content fluctuation. This is twofold: first, to provide for sufficient skin friction adhesion below the zone of drying; and, second, to resist upward movement when surface soils become wet and begin to swell. Successive drought years have demonstrated this zone of seasonal fluctuation can extend much deeper than previously believed. Piers extending to depths of six feet can withstand normal annual fluctuations, but do not appear adequate when taken over long hauls, such as a two-year drought followed by an extremely wet year. Another way of mitigating expansive soil problems is to collect surface runoff and to limit surface infiltration during rainy winter months.

Expansive soils cause major damage to light foundations and associated structures. However, engineers have an ability to recognize swelling clay soils and to design structures able to withstand their effects. Enlightened design of deep foundations (where depth of columns is five times or more than footing diameters), and effective drainage of landscape irrigation and swimming pool leakage could dramatically reduce damage to new barndominiums.