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Basement Walkouts
When adding a basement walkout to an existing house, it’s a huge job to underpin the house foundations and footings in the vicinity of the walkout. A more common approach in many areas is to protect the walkout excavation from frost with rigid insulation before the walkout is constructed. This slows the rate of frost penetration into the soil and, if done properly, will help prevent frost heaving problems to the basement walkout and the adjacent house wall.
Basement Walkouts By Alan Carson, Carson Dunlop, www.carsondunlop.com
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ote: This article applies to regions with basements that are subject to freezing temperatures.
Houses in cold climates may have an entrance straight into the basement from the outside. Creating this entrance usually requires soil excavation (except on sloped lots). The walls of the stairwell are retaining walls. A railing is needed to protect people moving up and down the stairs. A guard should be provided around the opening to protect people passing by the walkout. A drain at the bottom prevents the stairwell from filling up with water. The door opening should have a raised threshold to protect against water or snow from entering under the door.
Now let’s look at some of the problems to watch for. Problems with walkouts are commonly related to the following:
Although simple to describe, basement walkouts are tricky to build. Basement walkouts, especially if added after original construction, should be inspected with caution. Basement walkouts typically have to resist lateral soil pressure and frost pressure. You will find few walkouts that are perfect. You will have to use your professional experience and judgment to evaluate the performance and identify what should be corrected. You should inspect walkouts from inside the home as well as outside. The illustration and the photo on this page show what things should look like.
Soil Pressure Soil on one side of a wall exerts considerable pressure against foundations, retaining walls and basement walkouts. Wet soil exerts more pressure. Soils that expand when wet exert even more pressure. When wet soils freeze, the water expands and the soil exerts more pressure still. Hydrostatic pressure and frost pressure in the soil below also can cause heaving. Let’s take a closer look at frost.
A well-constructed basement walkout with no damage to the retaining walls, a drain at the bottom and railings. Note: In new construction, the handrails would return to the walls.
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ASHI Reporter • November 2015
•W alls cracking, leaning, bowing or spalling, due to soil pressure, hydrostatic pressure and frost pressure • Steps, railings and guards • Drains • Door thresholds • Covers and roofs
Watch for evidence of structural damage to the home and the walkout. Look for walkout doors that don’t open and close freely and those that have been trimmed extensively. Look for doors that have buckled or been crushed. Look for cracks around door frames on the inside and outside of house foundation walls. Look at the house foundation walls for evidence of inward movement. This may be leaning or bowing. These often are accompanied by horizontal cracks. Cracks, heaving, bowing. Look for bowing, leaning and cracks in the walls of the stairwell itself. The walls of the basement walkout must be built as retaining walls to withstand the lateral soil pressure. As previously discussed, the pressure exerted on one side of the wall by the soil can increase dramatically if the soil is wet, if the soil is expansive or if it freezes. The more water there is in the soil, the greater the hydrostatic pressure.
Frost Protection Frost goes deeper. In freezing climates, basement walkouts must have adequate frost protection. Frost penetrates deeper where a basement walkout is created. In an area where frost goes down three or four feet into the ground, and the grade level adjacent to the foundation and footing system is dropped five feet by creating a basement walkout, the frost now goes three or four feet down below the bottom of the stairwell. Frost can now get three or four feet below the bottom of the new grade level, below the foundation and footing of the home. Damage due to frost heaving is a significant risk. Frost damage is likely to be most severe where the soil is wet. Good surface water management, including surface drainage and free draining soils, helps to minimize the risk.
This crack is consistent with heaving as a result of frost penetration.
Lowered footings. Including a basement walkout during original construction adds to the expense, but the foundation and footing system can be built lower in this part of the house to account for the greater frost depth.
During the home inspection, you will not be able to determine whether the foundations and footings have been lowered, or whether insulation has been added to protect against frost damage. As with many things in a home inspection, you can’t review the design; you can only evaluate the performance.
The left side retaining wall has a severe vertical crack due to frost pressure.
11November 2015
• www.ASHIReporter.org
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