[Greenbuilding] heat treated wood siding

[Dave Boyt]

Maybe I can help a bit here.  I operate a small sawmill in southwest Missouri, and deal with some of these issues.  “Heat treated” is a specific term that assures the wood has been heated to a temperature for a designated period of time to destroy the bugs that could emerge from the wood and cause damage or become invasive.  The USDA has the specifics on this, but it basically requires the core of the wood to maintain a temperature of at least 135 deg F for at least an hour.  Further, this has to be documented.  In the winter, my solar kiln will kiln dry wood to 8% moisture content without reaching 135, so I supplement the heat source to meet this requirement.  Most industrial kilns surpass that temperature, but there is no guarantee, unless it has specifically been certified as heat treated.  Conversely, wood can (and often is) heat treated without being kiln dry.  Heat certainly facilitates the drying process, but is not required, nor does heating wood to a given temperature dry it to a given moisture content.

As regards to the original question, species is the critical issue, as heat treating does not, in any way, prevent the wood from decaying—it just kills the bugs already in the wood.  For example, cottonwood, hickory, or sycamore would be poor choices, since they quickly.  Red or black oak would be much better, and white oak better yet.  Finally, kiln dry wood is the LAST thing you’d want for exterior siding.  It will actually expand as it picks up moisture, and the wood can buckle and pull away.  Lap siding and board & batten are designed specifically to allow green wood to shrink as it goes from green to air dry moisture content (around 12% in NE Kansas).  Kiln dry is only useful for indoor flooring and furniture.  I built our passive solar house out of “green” black oak lumber fresh off the mill over 30 years ago, with no problems of warping or rot.  No heartbreak here!

Dave Boyt
Pottershop Hollow Tree Farm & Sawmill
Neosho, MO


From: RT 
Sent: Thursday, November 12, 2015 5:08 PM
To: Green Building 
Subject: Re: [Greenbuilding] heat treated wood siding

Picture me scratching my ... head ... with left eye turned down in a wrinkle and right side of mouth agape.

I'm wondering why the wood has been labeled as "heat treated" as opposed to the term "kiln dried" that has been in use since long before I was born and I'm OLD, real OLD. (Okay, okay. Just "not so young anymore".)

Using dried lumber for any sort of building task is pretty much always a Good Thing.   It provides a degree ("degree" depending upon degree of drying) of dimensional stability,  less chance of distortion (ie twisting, warping, cupping, bowing etc.) and self-destruction (ie cracking and splitting) due to uneven/uncontrolled moisture loss during drying (from "green" lumber state) ... provided that the dried lumber is kept dry prior to and after installation at all stages (ie storage by supplier, delivery, on-site storage, in situ before finishing if finishing etc.)    

I remember a little book from the olde days when the Whole Earth Catalogue was in vogue extolling the virtues of building with green lumber (in one word "cheap"). I think that the same author came out with a subsequent book with a title being something like "The Heartbreak of Building with Green Lumber"

Using "kiln dried" lumber as opposed to "air-dried" provides a higher degree of assurance that any bugs that were in the green lumber will have been killed, and that's also a Good Thing. (Not such a Good Thing from a cabinetry perspective though, but we're not talking about cabinetry here.)

So if the appellation "Heat Treated" is describing a process that is the same as "kiln drying", then one should be able to expect the same benefits as one would expect in using "kiln dried".   But they don't use the conventional age-old term "kiln dried" which makes me wonder "Why not ?"

The suspicious part of me thinks "because it's not the same and is just a marketing term to make the product appear as though is they have done something done to it to make it better but in reality is just that -- a marketing gimmick that is akin to polishing  a turd.  But perhaps the reality isn't as bad as that.   

(I know that "Heat Treated" is a term that is used in the wooden shipping pallet industry and I probably wouldn't lose a wager if I were to venture that the standards in the pallet manufacturing industry aren't quite at the same level as the home building industry -- or at least, I hope that's the case.)  



On Thu, 12 Nov 2015 16:56:55 -0500, Sacie Lambertson <sacie.lambertson at gmail.com> wrote:



  I am interested in this group's opinion about using heat treated wood on the exterior of a house in NE Kansas?

  Thanks, Sacie




-- 
=== * ===
Rob Tom DT7-64 
Kanata, Ontario, Canada


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