Will treated wood skids last long on gravel?

[Bill Houghton]

Hello All,

Its been awhile.  I could use some advice/opinions.  My progress has been slow.  I am sick of the rules and costs for permits, etc...  Anyway, my lumber yard has .6 treated 6x6 up to 28 ft. in length.  I am working through the details of building a 12 x 24 shed roof structure off site, hauling to my property and plopping it down on a gravel base.  There would be three skids, .6 treated plywood on the bottom of my floor joists and then white wood above that. Here is the question part, how long do you think I can expect to go with no rotting problems on the skids?  I have heavy clay soils but I am considering a frost proctected shallow foundation concept - putting down gravel, then a few inches of styrofoam insulation on top of that and then more gravel with the building sitting on top. I adapted this idea from the FPSF information found online for unheated structures. 

Bill in the U.P.

[rwanders]

Good drainage will be a real plus----if you can keep the skids dry they should last at least 20 years and probably upwards of 30+ years. I would try and build up the gravel base several inches above the surrounding terrain and keep it sloped away on all sides.

[Redoverfarm]

Moisture and insects are the major threat to lumber.  If you can eliminate those it should last a long time.  Even PT lumber will fall prey to water in time so if you can eliminate it standing or soaking you should be good.

[archangel]

I've seen plans where there are gravel filled trenches that the skids sit on for drainage.

Just be sure it will not settle and twist the dwelling.

[Bill Houghton]

I've seen plans where there are gravel filled trenches that the skids sit on for drainage.

Just be sure it will not settle and twist the dwelling.

archangel, 

In the Guide to Frost protected Shallow Foundations there is a section on unheated structures.  (See http://www.toolbase.org/Design-Construction-Guides/Foundations/Design-Guide-Frost-Protected-Shallow-Foundation ).  My plan is to use the proper thickness insulation prescribed for our climate then place well draining gravel above the insulation for the structure to rest on.  In theory it shouldn't shift or move if the ground can't freeze below the structure. Plus, the gravel should allow good drainage, keeping the 6x6's relatively dry.

Bill in the U.P.

[glenn kangiser]

If drainage is good it should be similar to RR ties under the tracks - quite a long time.