I am no expert and actually have been looking for years... The squared, dove-tailed cabins of the southern appalachians has traditionally been hemlock. The problem is aquiring enough tree's large enough reasonably as its a harder slow growth tree in comparison to the pines in these parts... But in VT, I am sure it's probably even better as it probably has real tight rings with your winters...

I would say most the 120+y.o. cabins that I have seen are hemlock. Also there's appalachian log homes that offers it as a material choice in the square dove tailed design...

The Hemlocks are currently being wiped out like the american chestnut was by a blight called wolly adeglia. is sucks the sap out of the trees, and talking with the mills around here, after the adelgia has gotten them, they rot super fast, google wolly adelgia, and see if its up in vermont yet, It has devestated stand here in VA

Stu is correct, the shake in the center of Hemlock is the real problem. That is one reason they don't bring as much at the mill, and then most mills have to ask more for them to make up the differance, there is really no solid middle to them, so the mills can only use the outer layers, thus less wood. therefore most hemlocks are used for wood pulp only. Hemlock also seems to split a lot along the grain. Living here in Appalachian Ky. I've seen two cabins that were built with Hemlock, they both used LARGE (very large) square cut logs, which if I was going to use Hemlock I would suggest using only the very largest ones available, and don't square them off, you may have a harder time getting rebar to really take hold because of the centers being shake (almost like being hollow in the middle) Some hemlock logs will have more shake than others, if you cut a mature hemlock down you'll see what we mean about the shake. If that is all you have, then use them and make sure the rebar goes down 3/4 way instead of half, and seal the ends real well. It should well out last any purpose you may have for it.

The hemlock woolly adelgid (Adelges tsugae) is an aphid-like insect that covers itself with a white, waxy “wool” which acts as a protective coating for the insect. Adelgid infestations are easily recognizable by the appearance of tiny “cotton balls” at the base of hemlock needles. The "wool" is most conspicuous on the undersides of branches from fall through spring.

Some trees have more shake than others, however, you will be able to view the shake when you fall it. I would think a stump diameter of 20" would sound about right. They're very slow growing and will get from 80' + tall, eastern hemlocks (Tsuga canadensis) can grow more than 150 feet tall on trunks measuring six feet in diameter. Some hemlocks in the Great Smoky Mountains are over 500 years old.