We chose Accurate-Dorwin, of Winnepeg  www.accuratedorwin.com, mostly on the ground that their windows had been used in at least one demonstration energy efficient house in Canada, and their insulated frame, fiberglass windows were both low maintenance and met our energy requirement.  In particular, Accurate-Dorwin offers a triple glaze unit which achieves a U value of .2 (or R5), which is significantly better than any triple glaze unit made in the US.  (Note: we've subsequently heard that at least one manufacturer is making an insulated frame, triple glaze vinyl window, but we didn't want vinyl for two reasons:  it expands and contracts a lot with temperature and its raw ingredients are apparently toxic (see www.bluevinyl.org for more info)).

Fiberglass windows are white in their natural state, but paintable, and we chose to have factory applied paint (which we believe is some kind of hard enamel, that will last long, but is probably highly toxic- we didn't ask questions).  For the inside of the windows, they offer an "oak wrap" which is a veneer of oak applied to the fiberglass that makes the windows look like wood (except when their open!).  We also got some of our windows with a glued on "simulated divided light" in a pattern that is common on older houses here in Seattle.  Their not as convenient as the snap on grilles, but look much better.

Overall we are very happy with the look, and although they aren't as classy as the Marvin metal clad wood windows (used on a previous remodel), they have much better energy performance and were quite a bit cheaper.  Our only problems have been in dealing with a sales person who is two time zones away, and that we are currently having some problems getting some of them to close correctly, even though the frame appears to be plumb and level.  We have been waiting for an adjustment tool from the factory for over two weeks.

Doors
All our commonly used exterior doors are fiberglass, which are filled with a polyurethane foam (a better insulator than polystyrene, but we don't know if its environmentally comparable or not). For doors that are rarely used (such as the ones to our utility room), we used polyurethane filled steel door, because they are cheaper, and supposedly have the same R-value.  While these door have decent performance (about R8), their aesthetics are more "suburban house" than we would like, and a really far cry from the aesthetics seen in natural building.  Most of them have fake wood grain that doesn't fool anyone, and proportions that don't match the way door were traditionally made. If they'd only look at a real door, and then clad the inside of the door with actual wood (as an example, Milgard makes a wood clad fiberglass window that does exactly that), there would be an immediate market for them. 

At one point we considered starting with a two or three inch thick slab of polystyrene board and surrounding it with a frame, and then cladding both sides with wood (ie rails, stiles, panels and all) to make it as authentic as possible.  The problem was that we didn't have the expertise to know how to make sure it would be dimensional stable in all seasons, and even if we did, we didn't know where we'd find door knobs and locks to fit such a thick door.

The only other caveat we have with these windows is that the nailing flange doesn't protrude from the window (in particular at the sill, although in most windows it sticks out all the way around), because it leaves the potential for water to run between the window and the sill, which then leads right down behind the siding.  You'd prefer than some part of the window stuck out enough so that you can tuck the siding underneath it (more details in the rainscreen section below)

Siding
In our view (and many others), there really isn't a good environmental choice for siding.  We chose, Hardi-plank fiber-cement siding because paint lasts on it a long time (much longer than wood), and the reduction in toxics from having to repaint often seemed to us to out weigh any other criteria (and truth be known, we don't really like spending a summer painting).  Economically, fiber cement is also a good choice because we estimate that repainting the house every seven years (which is how often conventional wisdom says you have to paint wood) would cost about $10,000 each time (current dollars).  Vinyl is more durable yet, and doesn't ever need painting, but we couldn't choose it due to toxicity concerns (see www.bluevinyl.org for more info).  Aluminum and steel have gone completely out of favor.  Our sider says that aluminum is available, but expensive, while steel is cost competitive with fiber-cement. For some reason we never really thought of this option, and maybe we should have considered it.

Making a low maintenance exterior
Even if we all chose a simpler lifestyle, most of us still wouldn't put house maintenance high on our to do list, and in most climates the only season you can paint is also the best one for vacations.  In addition to choosing low-maintenance windows and siding, we had the majority of our exterior trim wrapped in pre-painted aluminum (our understanding is that it is a powder coat, not paint, and so lacking the VOCs associated with paint.  We don't know whether it is less toxic.).  Some piece, like the roof knee braces are too complex to wrap, and others, like door casing is too susceptible to being dented.  We'll see when we have to paint them, if we think this is still an OK idea.

Keeping water out- the rainscreen system and drying potential
Siding not only keeps water out of the walls, but it needs to allow any water that gets in them to get back out (see the moisture control section under healthy houses).  Since Seattle is largely a heating climate, most of the year, water moves toward the outside of the house, making it important to let it dry out on the exterior. An unfortunate complication is that plywood is generally considered to be mostly impermeable to water, (due to the layers of glue, the outmost layer of wood will hold water just like any other piece of wood), and so it is unclear how effective exterior drying is at allowing water that has entered via the interior to escape to the exterior.

In spite of this potentially fatal flaw, we decided to install our siding using the rainscreen system to increase our chances that any water that did somehow get behind the siding, it could dry out.  Even if it doesn't halpe much with interior driven water,  it helps with water due to wind driven rain or leaks in caulking). The way it works is that the house is first wrapped in a wind and water resistant barrier, which in our case is just two overlapped layers of tar paper.  On top of the tar paper, strips of plywood (pressure treated) are nailed to create air gaps, where the air can enter where the siding meets the foundation (we make sure that only air gets in, not insects by filling the bottom with a material that is nearly identical to the green scratchy pot cleaners) and exits at the top, under the roof.

There is a lot of vague information out there about rainscreens, but not much in the way of details.

Tar paper .vs. tyvek and others