Expert: Daniel Humphrey - 1/11/2009

Question
Hi! I live in Waco Texas. We have a pier and beam home.We would live to extend our living space.I would like to do a two story Addition on the back of the house. Question is can you  build  an upper level on pier and beam.
     Thank you for your time.

Answer
Dear Tammie,

Yes, you can build two story on a pier and beam--if the footing is substantial and the soil is gravelly and hard packed, or the pilings driven deep, if that's the type, or tied together by a concrete grid. You will want to keep the building as light as possible.

The best thing would be to have a standard foundation supporting the addition, making it so that the new structure can act somewhat independently from the older one.

It is possible to design a pier and beam foundation that will support very tall buildings, but most older houses do not have much more support than a single story requires. Perhaps some pier and beam foundations beneath single story houses are actually strong enough for an additional story, and an engineer could tell. The engineer would look for the bearing capacity of the piers and the strength and rigidity of the floor structure and how the piers are locked together at the ground level or below.

A pier and beam foundation can usually support a great deal of weight straight down, but it cannot resist sideways force as well. When people add more weight onto a pier and beam foundation than the soil can bear or the beams can support, or when they try to cantelever a porch, any of those could lead to structural failure.

In an earthquake prone area, adding a second story to a pier and beam is not advisable without doing some engineering first. Earthquakes exert sideways forces that any added height multiplies.

Daniel