The earthship books detail how to build the front structure which is made of wood, holds up the front section of roof and takes the glazing for the geenhouse area.
This structure is either angled depending on your latitude so it's perpendicular to the winter sun, therefore capturing the maximum amount of heat in the winter. Or vertical if you're in an area where winter sun is strong and heating is not such an issue. We're going to have a vertical structure.
As this part involves precise carpentry as it needs to take the glass we employed a local carpenter to do this. We also had to use squared off sections of wood instead of the lovely round beams. We think that the two actually work quite well together, they add a nice contrast.
I always thought glass was glass, double glazing was double glazing, how wrong I was. Dave has been reading up on it and there are a multitude of options available these days. All sorts of differences to do with heat gain, light penetration, strength, it's amazing the advances that have been made. Cost is obviously a factor but the differences in those pesky R-values is substantial between a basic unit and a jazzed up version. There's even a glass now that lets heat in but doesn't let it out again. We still have a lot of research to do which will probably involve a trip to the local glazing factory so no decisions have been made yet.
As an aside, we've just put a double glazed window into my studio in our current house. Just a basic unit, with basic specifications. This window faces directly north and is about 2m x 1m. We are so amazed by the difference it's made to the warmth of the room that we're taking this glazing business very seriously indeed.
Wood versus uPVC
The main structure has to be wood for strength, this sits on a row or two of tyres. Non-opening windows might as well be put straight into this wooden structure as detailed in the books. However we would prefer the opening windows to slide rather than be hinged so they won't impede on the front growing/seating area. Sliding wooden windows are not really an option so we've been looking at uPVC... Eeeek, I hear you cry! I know, I know, uPVC is not exactly environmentally friendly in all sorts of ways, but nor are the chemicals we've been using to seal and protect the wood for the roof. I guess it's all a matter of degrees. So, deep breath, we are seriously thinking of putting in a uPVC unit as the centre opening window section. We'll be interested to hear any comments on this subject.
( Sep 08) We've been talking to our local carpenter/metal worker. He says that uPVC is being phased out here in Spain because of environmental issues and suggested we use aluminium frames for the sliding section. This produced an eek! in me as I've had experience of aluminium windows from my childhood - condesation, mould and cold are all words I associate with it. But, he says, big improvements have been made since all those years ago (cheek!!). But seriously, he showed us a section which has been designed with a barrier to stop the cold transferring inwards, which means no condensation. So another option has been given to us - decisions, decisions.