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Lower Your Basement Floor for More Usable Space

Jun 23, 2015 • By Matthew Stock.

Lower Basement

The American homeowner is on a quest for space – living space – that has been going on for decades and shows no signs of stopping.  But for a brief setback during the Great Recession, the American home has been growing steadily in size since the 1970’s.

Don’t believe it?  In 1973, the average American home occupied only 1,660 square feet.  In 2013, the most recent year with statistics available, that average had climbed to 2,679 square feet, an increase of more than 60%!

Additionally, when taken into consideration that the size of the average household has declined during that same period of time from 3.01 persons to 2.54, the average amount of living space per person has jumped, from 506.6 square feet to 980.7 — an increase of an incredible 94%!

Of course, not everyone wants or can afford a large house but almost every homeowner can use a little extra living space.  One easy way to obtain some is to lower your basement floor to make it possible to remodel it into rooms with full 8-foot ceilings.

How to Lower a Basement Floor for More Living Space

Many homes have been built with 8-foot deep foundations which, when the basement is left unfinished, leave a suitable amount of headroom.  However when floors and ceilings are installed, particularly when mechanical systems must be accommodated, those eight feet will shrink pretty quickly.  This can leave the homeowner with a claustrophobic space to which tall friends can never be invited and can even run afoul of building codes.

For example, the International Building Code requires a minimum of 7  feet of ceiling height in a habitable room and many cities, including Chicago, require 7 ½ feet.

Because the aboveground structure can’t be raised without a huge amount of work and expense, the alternative to creating a basement hobbit hole is to lower the basement floor.  Here’s how it’s done:

The first step in lowering the basement is to remove the concrete floor, breaking it up with sledge hammers or jackhammers.  Then, soil under the floor is excavated to the desired depth and all debris is removed.  When the foundation footings have been exposed, small sections of the soil, typically four feet wide, are dug out in an alternating pattern to the depth of the new footings and floor.

These spaces are used to pour new concrete foundation walls below the footing.

Once the extended foundation walls have been installed, an additional knee wall is poured inside the perimeter of the foundation, overlapping the footings at the top.  This forms what is called a “bench ledge.”  The knee wall and bench ledge add strength to the structure and serves as a retaining wall for outside soil.

When the new extended walls are finished, it’s time to install basement waterproofing, typically interior drain tile to prevent future seepage.  A dewatering channel may be installed on the bench ledge to capture seepage through the original foundation and channel it to the sump pump.

A layer of crushed stone is then poured and leveled and covered by a vapor barrier and reinforcing grid.  A new basement floor can then be poured.

Lowering a basement floor is a practical way of way enabling the addition of much-needed space in a home but it must be done by a qualified foundation repair contractor that uses proper engineering data and state-of-the-art construction methods.  At U.S. Waterproofing, our foundation repair experts have the skills, experience and engineering support to extend foundation walls and lower basement floors to create more headroom safely and cost-effectively.  Why not ask for our free advice?

If you have questions about lowering a basement floor, please post them in the Comments box below.

Tags: lower basement floor, lower foundation floor

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