Dear Pole Barn Guru: Concrete Footing or Not?

Pole Barn Guru Blog

DEAR POLE BARN GURU: I have read much debate about setting the poles in concrete with no “footing” beneath them vs. setting the poles on a concrete footing and back filling with gravel and earth. Seems to be an issue of rot.  What do you recommend? MYSTIFIED IN MAGNOIA

DEAR MYSTIFIED: It seems you and I have been reading the very same posts on advice boards all over the internet!

Let’s start with the “no footing” concept. Typically the soil is not able to resist applied vertical loads when those loads are transferred through the post alone. Therefore, the post is set on some type of a footing, which in the case of post-frame construction is usually concrete.

Footings must be adequate in area (radius squared x pi) to prevent the building from settling under not only the weight of the structure itself, but also the load from snow or minimum live load requirements. They must also be thick enough, to prevent the column from punching through the footing.

Considering even a fairly small span building, with minimum loads requires a footing diameter of 18 inches or more, it is fairly impractical to think of a material other than concrete which could be placed affordably beneath the columns.

On to the “rot” issue. Chapter 23 of the IBC (International Building Code) requires wood in contact with concrete to be either “naturally durable” or pressure-preservative treated. This, in itself, tends to take away credence from the “concrete rots treated wood” faction.

I know every major post frame building company in America. I have yet to have any of them report of having a single “properly treated post” rot off.

The clincher in this is “properly treated post”.

When the first IBC was published in 2000, Section 1805.7.1.2 stated, “Wood poles shall be treated in accordance with AWPA C2 or C4. This language remained the same in the 2003 IBC. The AWPA C2 and C4 standards have been withdrawn, therefore are no longer applicable or referenced standards in later editions of the Code.

In the 2006 IBC, however, things changed. Section 1807.7.1 states, “Wood poles shall be treated in accordance with AWPA U1 for sawn timber posts (Commodity Specification A, Use Category 4B)”. In the 2009 IBC (and repeated for the 2012 edition), the language remained the same, however the referenced section of the Code is now 1807.3.

What this means to you or the average consumer who is shopping for a new pole barn? Everything!

Take a visit to the local lumberyard or big box lumber store. Take a walk through the pressure treated lumber department. Every piece of pressure preservative treated lumber has a tag on it. This tag identified who the pressure treater was, as well as the level of pressure treating. Sadly, most of the pressure treated posts will be treated only to UC-4A…which does NOT meet with the Code requirements for use in pole buildings!

What this means is there are a plethora of buildings which have under treated columns, which is responsible for the rot issues, not the proximity to concrete.

Every time I have someone try to foist the “concrete rots treated wood” story on me, I ask them to show me a single laboratory test, which proves their point. None exist.

The best solution – and my recommendation – use a properly treated post, backfilled with pre-mix concrete in a monolithic pour. Place a minimum of six (and better eight) inches of concrete below the column and eight or more inches up the post (this is known as a bottom collar).

13 thoughts on “Dear Pole Barn Guru: Concrete Footing or Not?

  1. Zane

    Has there been enough history with non CCA treated posts to know if they will last in concrete or dirt? Why not just use a concrete footing and post base since the buried post contributes very little to the stiffness of the building?
    Great website! Thanks!

    Reply
    1. polebarnguru Post author

      In most cases, the chemicals which are used for preservatives are the same as or similar to CCA, just without the arsenate. Most of the compounds have been used for treating for a number of years and have been rigorously tested. The buried column actually provides for the moment (bending) resistance is an embedded system. We’re currently aware of only one bracket which is capable of withstanding those rotation forces, and it is not an inexpensive part.

      Reply
  2. Ashley

    When you pour the poles in monolithically is the shrinkage of the footing below the pole something to worried about? The 1/16″ gap would eliminate end bearing until the load increased to shear the friction from the pole to the encasing concrete.

    Also when pouring the poles in are the blocked up off the bottom to be able to pour monolithic?

    Reply
  3. Randy Briggs

    I am planning on installing a heated therapy pool at our home and want to enclose it for full year use. We live in central PA and code requires a substantial frost depth footing. I am trying to find the least expensive and yet durable way to enclose the pool. I will need to insulate the building and plan to have scissors trusses to allow me to ventilate the structure more easily.

    If I use a pole structure, I am not sure how to ensure the inside floor will not heave with freezes and thaws. I was planning to use a poured concrete floor

    My other option is to install a regular foundation and build up from there. Obviously that will increase costs substantially–6 to 10 thousand dollars I suspect.

    what would you suggest for the best long term option. Thanks.

    Any thoughts on this

    Reply
  4. bobby wayne carlisle

    USING 5FT SLELVES ON BOTTOM OF 6X6 POSTS FOR ROT SET A 10 INCH CONCRTETE PAD AT THE BOTTOM THEN BACK FILL WITH GRAVEL OR STONE IS THAT OK TO USE

    Reply
    1. admin Post author

      The scenario you describe is probably inadequate to prevent uplift. You should confer with the RDP (Registered Design Professional – engineer or architect) who designed your building’s plans to verify adequacy.

      Reply
  5. BOBBY w CARLISLE

    THE POLE BARN THAT I BOUT COMES WITH A PLASTIC SLEEVE OF SOME SORT TO PROTECT FROM ROT SHOULD I SET IT ON A CONCRETE PAD AT THE BOTTOM OF THE HOLE AND BACK FILL WITH GRAVEL

    Reply
    1. admin Post author

      Yes, it should be placed on an adequate concrete footing pad. A provision for uplift also needs to be accounted for. These are items which will be spelled out on the RDP (Registered Design Professional – engineer or architect) sealed plans for your building.

      Reply
  6. Eric Bauer

    Saratoga wyoming Customer is wanting to build a Morton pole barn house wondering about no footings slab on grade with hydronic heat very expensive would hate to see something happen to tubing for heating

    Reply
    1. admin Post author

      Post frame buildings do not require a continuous footing and foundation. Columns do need to extend below the frost line and be adequately concreted in. Most important will be adequately preparing your site to avoid frost heave issues. Search on our website for “frost” and “site prep” for more information.

      Reply

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