What species of wood is actually best suited for the lasting integrity of an exterior assembly?

There are only a handful of woods with the inherent properties that are genetically resistant to exterior elements.  By genetically resistant, we mean the inherent means of defense against the debilitating infestation of insects and bacteria. Trees, like animals, vary in this regard. A forest deer has few defensive tactics and might be considered as fodder for the animal higher on the food chain, such as the bob cat. The coastal redwood, living to several thousand years, is practically indestructible, given its impenetrable fire-resistant bark and peculiar repellent tannins, to where it's only real enemy is the chain saw.

We will not take into account a bevy of species drawn from the rain forests in a process closer to annihilation than sustainable foresting. Nor Larch, Spruce, Cypress, or even Sugar Pine, all of which exhibit certain properties conducive to withstanding the elements but not all the properties, such as their dimensional stability and their workability to joining and millwork.  If we were concerned with only a wood's gift for withstanding harsh conditions, then Larch alone is worthy of a ransom's prize: For the pilers that have held up much of Venice, Italy for the past 600 years, or the millions of board feet as railroad cross-ties and the engineering marvels of all those magnificent trestles..

When we look to suitable species for exterior joinery, we must go beyond its mere resistance to the elements and consider: 1) It's dimensional stability (Is the trunk straight and branchless and with good girth? 2) Does it expand and contract excessively? 3) Is it workable, as in can it be milled and shaped without splitting and checking and burning the cutting edges?

*NOTE: We interrupt here because it is worth notng that the tannin oils mentioned above as the identifiable properties of both Teak and Redwood are also the potential menace. Glue, as in the woodworker's glue, must have a porous surface to grip or adhere to. Because these tannin oils emanate from the tree's fiber to coat the surface, any glue applied will simply sit on the skin and fail to create the sort ofgl required. Almost immediately after both redwood and teak are milled or a joint is cut, the oils begin rising to the surface to prevent a glue-bond. The answer? Assuming one mills all their componants and then turns to gluing and assemblying, the technique involves a light hand-sanding off the new thin layer of oils that have risen since the milling, and then without delay, apply the glue and clamp the joint air-tight, all before the oils rise to coat the face of even the most freshly milled surface.

Mahogany: There are many species of mahogany--usually denoted by the country of origin, but not always. Santos, Sapele, African, Fiddleback, Philippine, Honduras, and Cuban. They are all exotic and endangered and yet with proper research, available as sustainable with the exception of Cuban.  The mahogany industry has been over harvested.  If a sustainable source can be found, look for full figuring and a deep reddish brown coloring.  Mahogany, although a good species for resisting the elements, does not posses the same ideal characteristics as teak, cedar, and redwood.  It will gray out if left natural.
Retail Cost: Approximately $7/per board foot.

Cedars:
Western Red: The more common cedar found in exterior constructions. Harvested in British Columbia, Canada where it is regulated as a 100% sustainability.  Dimensionally stable with tight growth rings. One of the signature properties is the light and dark colorings, often within a single board.  Excellent resistance to insect and fungi.
Retail Cost: Approximately $5-$8/per board foot in the west and $6-$10 in the east. Retail

Alaskan or Yellow Cedar:A slow growing species with many of the trees in North America between 700-1200 years old. Excellent rot resistanc. Harvested between southern Alaska and southern Orgeon. Because of it's slow growth pattern, Alaskan Cedar is rare, and when it is harvested, it normally suffers the same fate and today's redwoods--harvested so early that the maturity of the growth rings and genetic oils are short-changed. Dimensionally unstable.

Port Orford: Grown and harvested and milled in small, select locations in the Pacific Northwest. Fully matured harvests can be difficult or even impossible to find. A creamy white hue, aging to a stately silvery gray.  Smooth with no raised grain. Due to the pale nature of its coloring, it gives unlimited options when staining.  (Redwood, teak, western cedar, and mahogany are dark and cannot take lighter stain pigments) A unique, strong ginger-like scent, due to the volatile tannin oils.  Denser than other cedars.  Dimensionally unstable, which means that because of the early harvests, there is far more fiber between the growth rings, giving way to a vulnerability for checking and cracking as it dries.   Excellent resistance to insect and fungi infestation.  Although in some areas, the lower grade of Port Orford is available as a green, knotty product sold as decking, the clear, double-kiln-dried grade remains largely unavailable to the retail public.   This is the wood Charles and others used in the 1970's in San Francisco---until it was all gone.  A grove was planted in 1978, and although they are harvesting, as mentioned above, it is a premature harvest falling far short of the old-growth properties

Why doesn't CPW provide fence and gate posts? 
---------------1) Because we do not stock posts and are therefore subject to a similar over-the-counter cost as your local installer through his own preferred lumber yard.
--------------2) If we did stock posts-- in 6x6 and 4x4--there would be an added cost of crating and shipping to the site, resulting in a post per-foot cost that far exceeded what your installer paid locally.

Western Cedar is the most commonly used post preference.  East of the Mississippi, this is a special order item and you should allow two weeks.  For their CPW fence-lines, the vast majority of patrons opt for an STK grade.  This is a tight knotted grade.  For gate posts, the preference is often the clear grade.  A full discussion of post options, including the recommended technique for setting your posts is at the following link: <http://www.prowellwoodworks.com/gate/postholes.htm>

Pressure Treating 
---------------1) A common means of circumventing the expense of teak or affordable access to redwood and cedar to those in the east is the process of treating more affordable woods with a chemical that resist or thwarts bacteria infestation. For the longest time, this was best accomplished with a thick coating of creosote, which might be most recognizable in connection with the railroad ties. When creosote was outlawed in the mid-1980's, the method of pressure treating was adopted. Injected by a series of punctures presuured by a vacuum press to a depth of about 1/4" from the surface, an arsonic-based tonic allowed the use of fir and pine and all sort of affordable species to be used in the construction of decks and fence posts and anything deemed susceptible to rot.

Still commonly used today as a cost saving measure, a number of problems are worth noting.
1) Pressure-treated preservatives do in fact transfer to the touch, as well as drain down into the water table. California recently, finally, prohibited such products from all publicly accessed areas. They should be prohibited everywhere and from all uses.
2) When cut, the fiber is exposed where the arsonic has not penetrated, thus requiring the direct application of a medley of products to coat the raw grain. These are far far more transferable than the pressure-treating process, and a good deal more toxic.
3) The cost savings of pressure-treating may allow one to actually afford a deck, but entertaining on that deck, above the wafting odors of poison that permeate the structural underlay, will make for a far greater problem in time.

And yet it is not uncommon for those sites east of the Mississippi to opt for this solution. We are not stewards of the earth.We are woodworkers, and will not preach a high-minded sermon to those who prefer pressure-treated posts.

Requests:
"We'd like our CPW product in Ipe, please"
--------------- You'll have to shop elsewhere. Ipe continues to be non-certified and culled from the rain forest without restraint. It is also extremely dense and heavy and a strain on normal mortise and tenon joints, as a gate is suspended against gravity.
"We'd like our CPW product in Teak, please"
--------------- Unlikely. Not only is the majority of teak harvested beyond sustainable methods, it is also approximately $29/board foot for certified teak. Because the density and rot resistence is comparable to Port Orford and western cedar, the option of teak, at $29/ft is expensive and unwarranted.
"We'd like our CPW product in Mahogany, please"
--------------- African Mahogany, yes. An affordable option, and harvested with acceptabe standards in certain areas. A rich amber coloring and fine figured grain and working properties. Mahogany is a hardwood and hardwoods are seldom inventoried to standard dimensions. Which means there is a fair amount of waste, which in part explains the higher cost for a CPW gate in Mahogany.
"We'd like our CPW product in Redwood, please"
--------------- If you are adamant, we can inquire for the availability of recycled old-growth.

There are sound reasons for the above restrictions.  Enough reasons to fill a book.  But reading books appears to be a lost pastime.  Writing books of this nature is left to pundits and alarmists and the dooms-dayers who are the watchdogs and activists no one listens to anyway.