With that said, I would be pleased to hear any suggestions you might have. I am eager to learn!
Heat pumps are very common here, as we have mild winters. They serve a dual purpose: they exchange the air and heat your home. ..."When a heat pump is used for heating, it employs the same basic refrigeration-type cycle used by an air conditioner or a refrigerator, but in the opposite direction - releasing heat into the conditioned space rather than the surrounding environment. In this use, heat pumps generally draw heat from the cooler external air or from the ground. In heating mode, heat pumps are three to four times more efficient in their use of electric power than simple electrical resistance heaters."
We have only just chosen our GC, who is knowledgeable about green building systems. We have not yet sat down to chat about the details on how to make this home as green as we can, while sticking within our tight budget. So he may come up with ideas I don't even know about yet, such as the hybrid system you mentioned (which I'm not familiar with).
In the meantime I have been intensively researching the topic of building green with stick-frame construction (ecohome.net is providing me with endless information!) and the message I am getting is to build it as airtight as possible, over insulate (while reducing thermal bridges) along the lines of the PassivHaus system, and use an HRV system for fresh air exchange. If one choose the finishes carefully, low VOC paints, concrete floors, etc, there should not be chemicals off-gassing in the interior environment.
As for what kind of vapour barrier, I am currently studying the topic. I've learned that there is a difference between an air barrier and a vapour barrier and I'm still trying to wrap my head around that. Again, I haven't discussed this with our builder yet, but ecohome.net offers some interesting options, such as putting the sheathing on the inside. http://www.ecohome.net/guide/interior-sheathing-air-vapour-barrier
I should also point out that my husband and I have zero DIY skills and not a lot of time to do labour on the house ourselves, which is why things like cob and natural plastering, plus the maintenance involved, are just not in the cards for us.
It's really hard to make these decisions without knowing how it will be to live in the house. I don't know how much the passive solar will work in winter when we don't get much sun, and I don't know how often we'll need to use the wood stove, or how well it will heat the home. I'm a "verbal processor", so talking this out with you people is very helpful for organizing my thoughts.
...initial plan was to do a natural building method...our particular climate, where humidity does not always flow easily out of the walls during our warm and moist winters, these techniques are still considered "under development."... Cob is a poor insulator and plaster needs regular repairing of the cracks that form, straw bales get wet inside ...So after 3 years of research, the overall impression we were left with is that it is still experimental here - enough that we are not willing to risk the biggest investment we will ever make - and simply too expensive for our budget and desired floor space (which I've pared down as far as I'm willing to go).
We also are borrowing money to build this house, so the bank has some say-so in what we build. It must carry a new home warranty, etc. so we are not able to go too far outside the box.
I've done a good deal of research to find the right builders, and as I said there are plenty of examples around here, and its not a big community, so all in all I feel good about who we will go with....
Heat pumps most definitely do work...We probably can't afford in-floor radiant heating. My parents have a baseboard system that uses water instead of coils, which is circulated through the house through various baseboard units. Is this what you are referring to when you suggest using radiant heating?
Yes, the Ecohome site is based on the usual stick-frame construction. But I don't understand why you say that is necessarily unnatural and unsustainable. I live in an area that is rich in wood as a local resource - in fact we will be using some of our own lumber milled from trees felled on our property in the project.
Breathable walls: whenever I read about breathable walls they all seem to leave out my circumstance - a climate where the winters are relatively warm and very humid. A breathable wall only works if there is a humidity gradient.
...if my circumstances were different we might pursue a breathable wall system/natural building...I'm just not there, not in terms of time, resources, etc. And this house needs to be built now.
With that said, our longer term plans are to hand this house over to the kids, whoever has a young family first I suppose, and we'll build a small retirement cottage elsewhere on the property. That is something we could think about doing as a natural build.
...there is nobody around here telling me that I can have a natural-built home within my budget (and size requirements).
I lack the resources to pull off what you call t/n building given the boundaries I have set for the project (eg. cost, size) and the local expertise available to me.
Now, on to questions: you mentioned "natural cellulose and/or high loft matrix (sawdust, wool, mineral wool, light straw clay, perlite, pumice, expanded clay, hemp, etc, etc)" - are these infill materials?
I've seen a variety of natural infill materials, typically with timber-frame skeleton, though I can't see why stick-frame would not work too (timber framing here is for luxury homes and the contractors who do it charge $$$).
Assume a stick-frame exterior wall with some kind of natural infill such as mineral wool or packed cellulose, etc...what would that look like if there is no air or vapour barrier? What cladding on the outside? What is on the inside (you mentioned gypsum and taping, I think? or perhaps that was Bill)? Or perhaps there is just no way to tie in what you are saying with a what we are planning?
As for heating, yes I want to avoid ducts, I really do.
I would love to hear more from you about radiant heating. You say you don't do radiant in-floor heating in "OPC", were you referring to portland cement floors?
So you put them in natural earthen floors, then?
What about putting it in wall systems?
We have talked about doing a wee bit of cob or clay-slip on a few interior walls to soak up the sun if we don't have a concrete floor (I'm much more partial to laminate hardwood flooring, which I'm sure makes you shudder, lol, but hey I like the look!), so perhaps we could run radiant heating tubes through there. I just don't know of anyone who has done that and why you would do that instead of in the floor.
I looked at the Radiantec website and the prices are certainly lower than what I have been led to believe, although they are a US company and we Canadians often have sticker-envy when we see what things cost us up here. Will have to look into this more. I'm supposed to meet with one of the guys this week to take a closer look at cost of radiant in floor heating.