Homes on grades that slope aggressively away from the main entry of the home have unique entry requirements to get good modeling and calibration. This document covers the steps that need to be taken to properly model a home with a walkout basement.

The first section will review the principles on how to parse out the foundation space to properly enter data into the foundation screen. Then, there will be an example project with entries as a demonstration.

To model a walkout basement, the foundation needs to be broken up into two spaces. The first space will represent the part of the basement where the foundation is more than two feet below grade plane, and the second, of course, is the part of the basement that is more than two feet above grade. The section of the basement that is less than two feet below grade will be entered into Snugg Pro as slab-on-grade and the section that is more than two feet above grade is full basement.

To estimate the average height above grade for the foundation, it's necessary to take a weighted average of the three walls that are more than two feet below grade. To do this, first find the area above grade of each side.

The length of a side is measured in linear feet.

The minimum height above grade is measuring the minimum distance between the top of the foundation and the exterior grade.

The maximum height above grade is measuring the distance between the top of the foundation and where the exterior grade reaches two feet above the slab.

To create the weighted average, divide the sum of the area above grade of each side by the sum of the linear feet of each side.

The number of floors above grade should estimate the number of floors that are above the foundation, in half-story increments. For example, if half of the basement is less than two feet below grade, enter 1.5 stories above grade. If only 20% of the basement is less than two feet below grade, enter 1 story above grade.

This can be done with all manner of walk out basements, no matter how complicated the grading is around the foundation. For example, there are homes with nearly two full foundation walls above grade. These strategies can still be applied to split the foundation into slab on grade and full basement - albeit the calculations to do so will become more complicated.

Next, we'll use an idealized example to provide some guidance on how to enter a walkout basement into Snugg Pro.

Splitting the foundation and slab

Start with home with a foundation that is 25x25 feet. Five feet from the back out the house, the foundation falls less than two feet below grade.

To separate the foundation between basement and slab, calculate the area of the full foundation first: 25x25 = 625 sqft. For the first 20 feet of the foundation going to the back of the house, the foundation is greater than two feet below grade. In this example, 20x25 feet = 500 sqft will be considered basement. The remainder, 5x25 feet = 125 sqft, will be considered slab-on-grade. Converting these square feet to percentages, 500/625 = 80% of the foundation is basement and the remaining 20% is slab on grade.

Foundation height above grade

To establish the input for foundation height above grade, it's necessary to determine the average height above grade for the part of the foundation we're calling the basement.

In the front of the example home, we'll assume the 8-foot-tall foundation is two feet above grade and slopes consistently down the sides of the house. When the grading reaches two feet from the foundation, 6 feet of foundation is above grade.

The linear feet of the sides of the home with the grading descending is 20ft (remember - we stop counting when the slab is less than two feet below grade!). The minimum height above grade is 2ft, and the maximum is 6ft. The length in linear feet of the front of the house is 25ft, with the entire width of the house being 2ft above grade. So, the inputs to calculate the weighted height above grade are:

The calculation to get the weighted average of the foundation height above grade is:

As a result, the entry for average height above grade for this home should be entered as 3.2 since only one decimal is allowed.

In Snugg Pro, the "Foundation" section for this example home will be entered like this:

Snugg Pro will model the "wall" of the "basement" that is adjacent to the "slab" automatically, so that "basement wall" does not need to be included when creating a weighted average of foundation height above grade.

This guidance is based on this reference document from OptiMiser: Microsoft Word - Walk Out Basements