Log Home Site Planning Basics: Determining the foundation elevation

Have you ever seen a house that sits low in the ground?  It looks like it's sinking and you have to wonder if there are water issues in the basement. 

Part of developing the site plan involves determining the depth of the foundation wall footings in relation to the foundation wall height, terrain, water table level and the final grade.  It's basically a balancing act that factors these elements to get it just right.  Before we dig the hole, we’ll spend a significant amount of time at the building site doing all these calculations to determine the optimal footing depth for the foundation wall.  It’s so crucial to the appearance, performance and overall health of the home.  Since many log homes are built near water or on uneven terrain or both, this challenge becomes even more important when preparing the site plan.  

There are three key areas that we factor when setting the footing depth: 

•          Appearance of the log home with 18-24” of foundation wall showing at final grade.
•          Site water table and if there are hydro-static water pressure issues.
•          Site terrain and final grade on all four sides of the home (water runoff and drainage).

Here are some steps we typically take when working with the foundation contractor.

To determine the water table depth on the building site, we’ll test dig 1-4 holes at least the depth of your basement or crawl space floor and 1-2 holes at least 1-2 feet deeper than the basement or crawl space floor.  Let them sit for 24-48 hours and check them to see if water is in the hole(s), that tells us the water table level.  We’ll measure from the water level to the top of grade to help us calculate footing depth in relation to the foundation wall height and factoring the grade and 18-24” of foundation wall show.  This test also will give us a good idea of the seasonal high water mark based on the time of year of the test. 

Next we’ll meet with the foundation contractor on site prior to the scheduled excavation date to review the overall game plan for site clearing, excavation, location of topsoil pile, seek his opinion on the test hole results, discuss if additional fill sand maybe required and review the our estimated footing depth measurements.

On excavation day we’re there as they dig the foundation hole.  Once the hole is dug for the footings at our pre-determined depth we’ll evaluate the soil conditions (sand is good, clay is bad) and check for water issues if any and if necessary make adjustments to the footing depth.

If there is water or a potential for water issues, we’ll take the necessary steps to insure the foundation will perform properly.  Typically we’ll spec perimeter drain tile around the outside of the foundation at the footings, plus drain tile inside the foundation draining into a sump crock with pump.  We may also spec 6” of pea stone fill inside the foundation under the slab floor which effectively dissipates the hydro-static pressure.  In addition, we may upgrade the foundation wall coating to waterproofing or membrane barriers if there a significant risk of excessive hydro-static water pressure issues.  These steps are inexpensive insurance and will help protect your investment from potential water issues.

Factoring the existing terrain we'll make sure the grade is away from the foundation and we achieve 18-24" of foundation showing with the final grade on all four sides of the home.  This may require additional fill.

Because each new home is unique and presents its own challenges not every foundation site plan will be the same.  We hope this gives you some insight into the many factors used to avoid that sinking log home look. 

By The Leelanau Log Home Company

www.leelanauloghomes.com