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It’s common practice and Code required to have preservative-treated wood in contact with masonry or concrete.

However, after double checking the Code, (ICC 2304.11.1,) I See it actually says, “naturally durable wood or preservative-treated wood”.

What species is “naturally durable wood” in reference to this application? I’m sure it’s NOT cedar or redwood, which is what we use for exterior decks, siding, etc. where I live.

  • Well it's not the local cheap stuff, no. Hardwoods get pretty exotic. So do their prices. – Harper Nov 24 '17 at 20:34
  • Why is it not Cedar or Redwood? – Paul Logan Nov 24 '17 at 21:42
  • @PaulLogan I don’t know of a Building Code Agency that allows the use of cedar or redwood for sill plates. Cedar and redwood are “softwood” and tend to rot if they don’t dry out completely between “wettings”. When bolted to a concrete wall, the moisture penetrates the wood (from the concrete) and it develops dryrot. Can you find an agency that approves cedar or redwood? ...or any species of wood without preservatives? – Lee Sam Nov 25 '17 at 0:02
  • What you say may be true, however I, non-the-less believe these species are what they are referring to. They will last 10 to15-years at a minimum and many time longer. Maybe that is all the individual needs and at the same time has some particular aversions to the 'Penta' products used in pressure treated lumber. You, of course know that the pressure treated lumber is a soft wood. Have you lately inspected the condition of a house that was sided with redwood say 60-years ago? – Paul Logan Nov 25 '17 at 2:30
  • @PaulLogan Siding is fine. My house (54 years old) has cedar siding and is fine, but My sill plates are PT. I don’t think 10-15 years life expectancy is acceptable for sill plates. – Lee Sam Nov 25 '17 at 2:50
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Here is a study done in 1995 that looks like the heartwood of Douglass Fir, and the heartwood of redwood hold up the best for outdoor exposure. It may not give an indication of what you are looking for with regards to contact to concrete, but it at least gives insight.

In my years in the trade and having a curiosity about how houses were built, how they last, or fail in areas always has intrigued me. I have noticed a great number of homes over time that have D. Fir plates, directly on concrete AT ground level, in a 60+ year old home and the wood is still viable.

I would imagine that there will be this "list" that the gov't relies on to determine the "naturally durable" wood specie somewhere.....

I read/heard that poplar, when super heated becomes surprisingly rot resistant...

None of this may not directly answer the question, but I would like to mention black locust has been used for fence posts that would last for decades. I am sure there is no milled lumber of black locust available, but it sure would make the list.

  • Interesting study. I doubt if the Building Department where I live would allow untreated lumber with a life span of 22-25 years (considered long-life in a “moderate climate”). Even the heartwood rated at an “estimated >30 years” is not that great. Also, I don’t know if I’m smart enough to select the best heartwood for sill plates, etc. We do a lot of restoration and the most difficult (and most expensive) work is replacing sill plates. No wonder treated wood is so popular. – Lee Sam Nov 25 '17 at 20:20
  • Somewhere I gathered over the years that 20 years is an accepted life expectancy. For example, some approved pressure treated wood is labeled or perhaps guaranteed to last 20 years for what it is rated for, ie: above ground or ground contact. If a non pressure treated wood can last that long..... – Jack Nov 25 '17 at 21:23
  • Maybe 20-30 years is all we can expect for sill plates and ledgers. I guess we are a “throw-away” society. It’s so hard to fix that kind of stuff, it seems like we should demand better. I’m glad I live in a “moderate” climate. Folks in a “severe” climate must really get frustrated. Maybe somebody will develop a hybrid tree that’s cheap to grow, cheap to harvest, lasts forever and creates a zillion jobs. Yeah...right. It’s probably more likely the Building Department will allow the cheapest thing possible and it will be somebody else’s problem in 20 years. – Lee Sam Nov 25 '17 at 23:52

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