Disclaimer: Hope I'm not preaching to the choir but here is a serious 
answer because the original question seemed legitimate (although I never 
really know with this group).  Also, all information is non-professional.

While a useful tool, as I understand it, dendrochronology can only tell 
you so much, i.e. dates of some part of the life span of the tree the 
lumber being tested came from.  Unless you have a relatively complete 
trunk (and I have seen early buildings where whole trees with their bark 
still attached have been used as floor joists after the top edge has 
been hewn a bit flat) your information would only be specific to the 
piece of the tree being tested.  It might be from the core and hence 
older, the interior or nearer the exterior and hence younger.  Unless 
you can date the layer that was immediately under the bark (sapwood), 
you can't even tell when it was felled with any accuracy (some use the 
likely life span of a tree to develop a possible range).  Vertical 
location would also make a difference in the dating, the core closer to 
the top being younger than at the base.

Keep in mind, too, it was not uncommon for parts of one building to be 
reused in another.  Even today there are companies actively recycling 
buildings.  I know there are currently 100+ year old barns on Long 
Island that came from New Jersey less than 20 years ago.  What useful 
information would dating one of those barns by dendrochronology give you 
about the building's age and history?

Dating a building using just one technique is kind of like the blind 
men (or are we using visually challenged persons now) and the elephant 
parable, you're not going to get very reliable information from just one 
source.

I think you will find it hard to determine with absolute authority when 
a historic building was first erected unless you have some detailed 
written record available and supporting evidence that what is there now 
is the same as what was first built.  Failing that, you have to use all 
the dating tools at your disposal and then often are forced to take a 
best guess to merely determine a range of dates.

Evidence of saw pit marks was mentioned.  Tool marks can be used to give 
some idea of the age of materials but that method is by no means 
foolproof.  Hand hewn and hand sawn marks are fairly distinct as are 
vertical sawmill marks and all would be expected on timbers produced 
before the Industrial Revolution but there is no hard line when they 
would have disappeared.  Urban areas most likely would have changed 
first but there might have been a surplus of materials that could have 
been used years later.  Also, how does anyone know that the lumber 
you're are looking at was not manufactured more recently, say even by 
some historic reenactor using traditional tools and techniques just a 
few years ago.  Circular sawmill marks from after the start of the 
Industrial Revolution would exclude the possibility of earlier 
construction unless it happened to be a replacement piece in an older 
structure.  Moreover, the more modern planing marks might be mistaken 
for vertical saw marks by an untrained eye.

Design is another dating tool but it too is obviously imperfect as it is 
subject to correct current analysis and interpretation as well as the 
personal and regional tastes of the original builder and yields only 
rather large time span estimates.  Interior and exterior finish 
materials can be used as dating evidence but again are imperfect and are 
only as reliable as the confidence one has that they are original. 
Paint analysis might be useful as long as there has been no removal and 
replacement.  Nails and screws used in the construction can be dated 
but, once again, taken alone, that method is imperfect.

Public records like deed, tax, probate, and wills can list buildings and 
as long as there is some proof of continuity, can be useful in dating 
buildings.

An understanding of the development patterns of the area will also help 
in a limited way to establish likely dates.

So, with lots of study, along with some knowledge and wisdom as well as 
a little luck, you might be able to get a vague idea the age of a 
particular building.  Good luck dating yours.

T. Gale with lots of rings but who's counting.

Cuyler Page wrote:

>>>Dendrochronology will date it with finality.
> 
> 
> 
> Dendrochrono will tell you when the tree died.   When it became a building
> may be something else, like the Chinese versus Anglo way of dating the age
> of humans.   They say you are one year old when born in the Chinese
> tradition, and one year old a year after in the Anglo heritage system.
> Apparently Stradivarius used timbers cured in a salt water harbour for many
> years before making them into violins.   I once lined the inside of my house
> with cedar split slabs from an ancient growth piece of tree long long off
> the stump.
> 
> No slices needed.   Just a nice little bore hole starting at a bit of wain,
> with the core removed.   The hole can be plugged if in an old timber, and
> should be if in a living tree.
> 
> cp in bc
> 
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