Retrofitting Posts is a Waste of Money
Many engineers and contractors recommend strengthening post to floor and post to pier block connections. As we shall see, this is a complete waste of money.
This what it looks like under your house. The bottom of the posts are sitting on concrete piers and the tops of the posts hold up beams. Floor joists rest on top of the girders and the floor you walk on sits on top of the joists. The building code makes no distinction between posts that are 2 feet tall or 10 feet tall and only requires one nail to attach the bottom of the post to the concrete block and NOTHING (such as pier caps) is required to attach the top of the post to the girder. None of the seismic retrofit guidelines
As shown below, sometimes the posts support beams that the floor is nailed to and there are no joists.
THESE POSTS IN THE CRAWL SPACE HOLD UP THE CENTER OF THE FLOOR WHILE THE PERIMETER FOUNDATION HOLDS UP THE OUTSIDE EDGES. THE BUILDING CODE DOES NOT REQUIRE ANYTHING SPECIAL BE DONE WITH THESE POSTS.
Below are photos of some metal post connectors. Our first alert something might be wrong here is that this is not recommended by any seismic retrofit codes and guidelines.
STEEL CONNECTORS ATTACHING THE TOP OF A POST TO A BEAM THAT SUPPORTS THE FLOOR AND THE BOTTOM OF THE POST TO A CONCRETE BLOCK.
A DIFFERENT TYPE OF CONNECTOR KNOWN AS A “T” STRAP ATTACHING THE TOP OF A POST TO A BEAM.
LOWER ARROW POINTS TO A BOLT THAT ATTACHES THE STEEL CONNECTOR TO THE CONCRETE BLOCK.
A TYPICAL HOME WHERE THE CONTRACTOR OR ENGINEER BELIEVED POST CONNECTORS WERE IMPORTANT.
What Does the Building Code Say?
The purpose of this requirement is clearly stated in the International Residential Code.
Quoting directly from the IRC R407.3 commentary: “To minimize the chance of accidentally displacing columns supporting beams or girders, a means of mechanically anchoring a column is required.”
The Director Of The Construction Codes & Standards For The
National Association of Home Builders had this to say:
“The IRC R407.3 requirement is literally about providing a minimal connection so you can’t elbow or hip-check a column off its footing or dislodge it by running into it carrying a heavy box.” This connection has nothing to do with providing lateral resistance to earthquakes.
Engineer Details
Here are three examples of drawings given to contractors to show what the engineer wants to be done to this unimportant connection. In the drawing to the left, the red box contains the steel “T” strap post connector we showed you earlier. The blue box shows the post to block connection. The arrows point at the hardware and bolts connecting the post to the concrete block. The image to the right from a different engineer shows the exact same thing.
The drawing at the bottom requires a new steel-reinforced concrete foundation. It is buried in the ground and is 18″ wide and 18″ deep. It also has two types of steel connectors at the top of the post and one steel connector at the bottom. This contraption is so complex it would probably cost $1200 or more to build.
Here are some comments from someone who disagrees with this.
To me, your online post about connections of posts at piers and girders is misleading. To say that “one nail” at the bottom a post will provide lateral stability, and that the code requires no “connection at all” to the girder seems to ignore section 502.9 that says “positive connections shall be provided to ensure against uplift and lateral displacement.” The IRC does not specify how the connection must be fastened, but references the fastening scchedule in Table 602.3 (1). That shows, for example, that a single joist requires 4 8d toe nails to attach it to a girder (#22). A post to girder connection would clearly require a stronger connection. That is why “approved framing anchors” are often used (as referenced for example in section 502.6.2).
