Cedar vs. Pressure Treated Posts

[FJ88]

Does anyone have any experience with or knowledge regarding the durability and structural strength of Cedar vs. Pressure Treated wood posts? I can not find useful information comparing the structural properties of both types of wood. The typical application I am looking for would be wood posts for decks and small elevated backyard structures such as tree houses.

I know pressure treated wood is more durable but are there other factors to consider? Which post can I enclosed in concrete?

 

[civilperson]

Neither wood is good in concrete without a metal skin or covering. The pressure treated wood has the same properties as the type of wood used. Cedar is not very good timber, Douglas Fir is much preferred.

 

[msquared48]

Cedar is weak in bending in relation to either Dopuglas-Fir or Hem-Fir, and Douglas-Fir is hard to pressure treat. Most pressure treated lumber where I practice is Hem-Fir and it takes the pressure treating well.

Mike McCann
McCann Engineering

 

[prost]

A non structural consideration is environmental--the stuff in treated wood is poison. Depending on when, who, where it was treated, it may have arsenic in it, which will leach into the soil when the wood gets wet.

 

[concretemasonry]

Build a properly designed deck with concrete fillrd Sonotubes to the desired depth, appropriate galvanized fasteners and then appropriate sized posts of your choice of wood.

The concrete will last, give greater lateral and vertical strength, so you can replace the temporary wood as necessary.

 

[boffintech]

The trouble with concrete footings for decks is that you have dig the hole, dispose of the spoils from the hole, buy the quikrete, haul the quikrete, mix and pour the quickrete, buy and place a post anchorage device, etc.

An alternative to concrete footings for decks in the Oz Post.

Check it out:

http://www.oz-post.com/html/videos.php

 

[Compositepro]

I live in rural Tennessee where Cedar logs are traditionally used for corner fence posts and pole barns. Its use is being replaced by pressure treated. Cedar is more rot resistant than almost any other untreated wood. The purple heart wood is far more rot resistant than the outer wood.

 

[concretemasonry]

boffintech -

Are you actually serious about using a real estate "for sale" sign base for vetical loads? You will probably need 1 for every two square foot of loaded area.

 

[RARWOOD]

I would use CCA or ACQ pressure treated Southern Pine for any application where the wood is embeded in the ground or concrete, or exposed to the weather where long term durability ia desired.

Only the heart wood of cedar is decay resistant. Cedar posts embeded in the ground may show serious signs of deterioration in as little as 8 years. If the material is only exposed to the weather, and I didn't want to use pressure treated wood, I would use all heart wood Redwood.

 

[boffintech]

concretemasonry - good one... on the one for deck posts it appears that a base plate is added for additional stability and bearing. For low, smaller decks it's probably a good product.

 

[civilperson]

All heart redwood or cypress are both desirable for resistance to weather and moisture decay and unaccessible. Thus the use of pressure treated wood.

 

[SlideRuleEra]

http://fcg.cof.orst.edu/rc/rc26.pdf

http://www.fpl.fs.fed.us/documnts/fplrn/fplrn068.pdf

http://www.SlideRuleEra.net

 

[concretemasonry]

AAJ216 -

The previuos are good studies for fences. The older one is almost as old as my diploma and registration.

Decks and playhouses have different loadings, verificationability, constructability and code requirements that do not apply to fences.

From what I have seen for more permanent structures, the best solution to use is a concrete column/
Sonotube below grade with or w/o a bell-shaped bottom. This gives you a predictable support that complies with codes and keeps the permanent part of the structure in the ground (or a few inches above).

Insert a a suitable metal connection compatible with the chemistry of the wood (if necessary), and attach the wood post/column that is a part of the structure. This keeps the semi-permanent material out of the soil, permits an accurate of the necessary height of the structure and permits the replacement of the post in case of deterioration or change in structure use. - Not a moment connection, but what can you really rely on with most wood?

The choice of wood will be determined by the species LOCALLY available and the preservative methods and concentrations.

For fence posts (and similar applications), usually, most wood should not be encased in concrete unless you have severe lateral or corner/anchor loadings that require the extra area. There are many methods that minimize the wetting/drying exposure of the wood in concrete. These typically involve having the concrete project several inches with a top that slopes to shed water.

For decks, embedded wood posts and sheet metal driving points are usually not approved, or verifyable. For temporary structures, it is a matter of what is permitted for the application. - Narrow line between DIY and engineeres structres that are geared for constructability and life safety.

Dick

 

[FJ88]

I would like to thank everyone for their responce.

Where are you drawing your information from? Is it personel experience or are there actual articles and reference materials I can use for my own research?

The links provided are for fence posts but I am looking for structural applications.