Pier and Beam Foundation vs. Post Tension “PT” Slab

There has recently been a lot of discussion regarding to a Post Tension, or PT slab on grade and a pier and beam foundation. I too, was looking for the best solution for my home; which is the most cost effective, and what are the pros and cons of each type. I reached out to a respected structural engineer in Sonoma County and he walked me through the options.  I’m sharing what I learned from that source to add to the discussion and so you don’t need to duplicate the effort.

Pier and beam-description, pros and cons

A traditional pier and beam is the type of foundation most of Coffey Park’s homes were originally built upon; This means piers are placed deep within the soil, carrying through the clay and into bedrock or stabilized soil. Beams lay across and carry the weight of the house. The clay may raise and lower but the house remains stabilize. With this type of foundation, there is a crawl space under the house and the ground floor is a bit higher than street level. A crawl space provides access to add electrical, move plumbing, etc. One must take care to provide adequate drainage, to eliminate risk of standing water under houses.

What are the pros and cons of pier and beam foundation? Some say it is better insulated choice. Over time, you may get a loose nail or notice a squeaky floor. In general, this is slightly more expensive due to lumber cost and additional labor, although contractor told us there was no added cost to do it this way and another said it would cost significantly more. (Maybe the second contractor just does not want to do them!)

PT slab foundation-description, pros and cons

A PT slab foundation consists of a concrete slab covering the entire first floor. Within the slab are cables, stretched with tension. Once concrete is placed, it provides a very strong foundation.

There are several advantages with a PT slab. If your house sat high on the property and you had a steep driveway, this option might lower the house closer to street level, reducing the incline of the driveway. There might be less of a need to bring in soil. Quicker to build, a PT slab foundation can save on construction time and is usually less expensive. Lastly, without a crawl space, there would never be an issue with standing water under the house.

Drawbacks of the PT slab in a rebuild start with a need for the contractor to excavate around all existing piers on the property a few feet down and remove at least a couple feet of each pier. You would never want any existing pier to ever make contact with your PT slab. After that excavation, the contractor would need to backfill with engineered rock, place a moisture barrier and install the slab. All plumbing under the slab will always remain since you would never want to jack hammer a PT slab; essentially your kitchens and bathrooms on the first floor all remain. Also, a PT slab eliminates the subfloor crawl space so you can no longer access to electrical and plumbing under the house for simple small changes.  Duct work for heaters would be located in the walls up high and not in the floor. Since heat rises it does make it harder to heat a house with high ceilings. Lastly, some people say the solid concrete base can be hard on your back.

Making the best decision

Ultimately, the foundation choice depends on your needs and a negotiation with your builder.  Both the pier and beam and the PT slab have good issues and both have negative ones. But more information will hopefully help you make the right choice for your new home.

-written by Steve Rahmn, Block Captain Coffey Strong Area 4