Structural lumber - KDHT

[RHTPE]

I am trying to determine allowable design values for lumber with a grade stamp that indicates "KDHT". Which translates to Kiln Dried Heat Treated. The heat treating is apparently done for the pallet & packaging industry - I assume to limits the distribution of any insects hidden in the lumber.

My application is structural use. Does anyone have any thoughts on the effects (if any) of the heat treating on design values? Reading Appendix C in the 2005 NDS leads me to think that, since this is less than 150°F, there are no permanent effects.


Ralph
Structures Consulting
Northeast USA

 

[MiketheEngineer]

Pick up that 2 ton phone and call the mfg!!

 

[RHTPE]

Mike - I submit that the real manufacturer doesn't have a phone - as for the mill sawing the material, and the agency grading the end product, they probably do have phone numbers. Subsequent to your post I did have a conversation with the American Wood Council on this specific topic.

I just thought with the wealth of knowledge around this forum someone would have a quick concise explanation. Apparently that was not to be.


Ralph
Structures Consulting
Northeast USA

 

[focuseng]

RHTPE, I'm curious now what AWC said. I did a limited search after reading you post... and ran out of time. I think the Forest Products Lab would be my next phone call.

What is the application?

 

[RHTPE]

focuseng - The application involes 2x6 rafters in a poorly ventilated attic. Summer daytime temps will likely get quite high.

The AWC explained the background of the 150°F temperature restriction - it was introduced because of cooling tower applications involving constant high temperatures. They felt that the attic temps involved are not constant because of night-time cool-down and didn't feel the temperature coefficent was applicable.


Ralph
Structures Consulting
Northeast USA

 

[MiketheEngineer]

They say over 150 F - you will degrade the wood!!

 

[RHTPE]

Mike - NDS 2005 Appendix C, paragraph C.1 says "Prolonged heating to temperatures above 150°F can cause a permanent loss of strength." (underlined emphasis is mine) If someone has a temperature profile for poorly ventilated attics I'd love to see it.

Ralph
Structures Consulting
Northeast USA

 

[focuseng]

I seem to recall some research I stumbled on awhile back about shingle temps in vented vs unvented roofs in order to UNjustify shingle warranty which was voided if unvented. Now this may be totally off topic or it might help -don't know yet. The result was that the roof temps were roughly the same for vented or unvented attics. Now this was, I think, for roof surface temps but I can't remember. I don't know if there was any data for INSIDE the roof(hey?).

But in general I have heard the same line about attics and the Ct factor too and it kinda being no applicable.

Also check out the heat treating the are doing for exterior decking in lieu of the preservative treatments.

MAP

 

[RHTPE]

As I understand it, the heat treating is being done to minimize the spread of unwanted non-native critters.


Ralph
Structures Consulting
Northeast USA

 

[focuseng]

Yes, and it works too so they say. I have not had the opportunity to spec yet so I haven't looked into it. Might be worth a call to some of them too to see what they know.

Check out The Wood Handbook on heat effects. There is some background there too in Chapter 4 about reversible and irreversible conditions. -with references!

MAP