Douglas Fir VS. Pressure Treated Wood

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Posts: 70
Joined: Fri Oct 19, 2012 3:24 pm

Fri Jan 30, 2015 5:21 pm

Hi All,

so I replacing the three 6 x 6 x 8foot wood posts that hold up an attached awning on my trailer. The ones I'm replacing are circa 1977. They were pressure treated but suffered from lots of 'dry' rot. I live in the hot as Hades California desert. We get sun and heat but very little rain yet these posts have all this dry rot. The posts were always painted.

So now on replacing them.
The posts come as either Douglas Fir or Pressure treated. Which should I use?
Home Depot only carries the pressure treated ones.
Fancy, expensive lumber yard only carries Douglas Fir.
Since each place only carries different products, they don't know enough about the differences to make recommendations.
Thanks in advance.

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Joined: Wed Feb 28, 2007 8:01 pm
Location: Weedsport, NY

Fri Jan 30, 2015 5:42 pm

Since ground moisture doesn't seem to be an issue, I would go for whatever is cheaper.

"If I can't fix it, I can screw it up so bad no one else can either."

Posts: 52
Joined: Fri Dec 20, 2013 1:12 pm

Fri Jan 30, 2015 7:25 pm

In California HCD requires all lumber that contacts any concrete or the ground be pressure treated or of such make up as to not rot or decay. Douglas Fir is what is pressure treated, redwood cedar or oak would survive, pine most likely would be gone in a couple years.
Pressure treated lumber is to protect from insects and mold it can still get dry rot.

" To withstand the elements, wood is chemically protected through a process called pressure treating, which wards off insects, microorganisms and fungal decay. The most common types of chemical used to treat wood are Alkaline Copper Quaternary (ACQ), Copper Azole (CA), and, the newest type, Micronized Copper Quaternary (MCQ). Pressure treated lumber can last 20 years or more, and most pressure treated wood comes with a limited lifetime warranty.

You also will need special fasteners in treated-wood

As a side note here in Ca. we can not use a mobile home to support a shade structure unless you obtain an engineering report from the manufacturer. All carports and shade structure attached to a mobile home require aluminum or the report as stated

I have a shade over my deck it is free standing and it constructed from redwood, very expensive but no chemicals. We did not have it built it was here when we moved in.

Posts: 342
Joined: Fri Apr 06, 2007 9:14 am
Location: Delaware

Fri Jan 30, 2015 9:56 pm

What are the length of the post? It cost a little more but you can look into the PVC type that have an aluminum center in them that are structurally sound.