Some relevant literature on earth-walled and post-supported house structures:
 
A useful survey of the ethnographic literature on the abandonment of
vernacular structures in villages is:
 Cameron, Catherine (1991) "Structure Abandonment in Villages" in Schiffer,
Michael (ed)  Archaeological Method and Theory, Vol. 3, pp. 155-194.
University of Arizona Press, Tucson.
 
Also, archaeologists working with post-supported pitstructures in early
Pueblo sites (ca. A.D. 600-900)  in the Four Corners area of the Southwest
have concluded from a variety of lines of evidence that the support posts
in these structures probably need replacement after 10 years or so of use.
Juniper wood is usually selected for such uses, because it is more
resistant to rot and termites than are other commonly available woods.
Locally, juniper is the preferred wood for fenceposts for the same reasons.
Pitstructures are often re-roofed at the same time that the main support
posts are replaced, or are simply abandoned.
 
The lower walls and floors of these early Pueblo pitstructures are usually
comprised of the sediments into which the structure was excavated.  There
are ordinarily four main support posts which support a rectangular
framework of beams which in turn supports a roof of smaller poles covered
by brush or bark and then a layer of dirt.
 
A couple of sources that provide references to relevant literature on rates
of post and roof replacement in such post-supported pitstructures are:
 
Lightfoot, R.R. (1992)  Architecture and Tree-Ring Dating at the Duckfoot
Site in Southwestern Colorado.  Kiva 57(3):213-236 (see especially page
227)
 
Schlanger, Sarah (1987)  Population Measurement, Size, and Change, A.D.
600-1175.  In Dolores Archaeological Program: Supporting Studies:
Settlement and Environment, compiled by Kenneth Lee Petersen and Janet D.
Orcutt, pp. 569-613.  U.S. Bureau of Reclamation, Engineering and Research
Center, Denver.  (see especially pp. 579-589)
 
Bill Lipe
 
==========
 
>Carl Steen said:
>We get earthfast houses up to about the turn of the 19th century it
>seems, but post in ground farm structures are still in use today. Bugs
>do eat the poles, but they [the posts] seem to get replaced as
>necessary...
>
>Carl makes an important point. Posts, even locust, eventually succumb to
>rot and insect infestation. No doubt some colonists used assorted
>remedies such as charring or tarring posts before setting them into the
>ground. With or without treatment, one could expect to replace posts. A
>relatively simple matter involving one or more blocks and levers, a
>short handled shovel, and a suitable replacement post upon which to rest
>the building frame.
>
>I am always puzzled by the distinction made between permanent and
>impermanent architecture. All architecture is impermanent, whether it be
>masonry, frame, timber, or a cardboard box. Virtually any building,
>however, also can be permanent in the sense that it could last several
>generations if properly maintained. Any homeowner today knows that if
>you don't keep the gutters clean, the water drained away from the house,
>the roof tight and--yes--the termites kept under control, that a
>substantial investment could become inhabitable.
>
>The distinction between permanent and impermanent architecture, useful
>nearly 20 years ago, distracts us from the important questions: how long
>was a particular building occupied (notwithstanding the '20 year rule'
>often applied to earthfast structures)? Is there evidence of repair?
>Replacement? Was a particular site abandoned because the buildings fell
>down? Or was the site abandoned because of worn-out crop land, land
>disputes, political or religious tensions, 'carpet-bagging,' a failing
>local economy, merchants diverting ships to other parts, or simply
>greater opportunities to achieve desired goals elsewhere?
>
>Perhaps we could push the functional/environmental explanations into the
>background for awhile and try to understand what the 17th century
>colonists were trying to do and how, and perhaps how they identified and
>solved problems with different architectural approaches.
>
>Jim Gibb
>The Lost Towns of Anne Arundel Project
>Annapolis, MD