Community insights for a straw & steel green build?
We are building a straw-bale house with steel bones in Sacramento, CA in spring 2015 and I'd love to get some insights from the community! We are pretty far along into the design process, but with nothing purchased as of yet I'd love to get some input before we put our money where our mouths are.
Our goal is to have a (mostly) passively heated and cooled home in (relativity) temperate Sacramento, CA. Passivhaus would be nice but it's an aspiration rather than a goal. Our lot has a number of trees for shade that we plan to utilize, especially in the western aspect.
We are building 2 structures; a ~1500sqft guest house (thank you inexpensive steel!) and a ~2100sqft home. Floor plans are attached; further details can be found on StrawAndSteel.com (which is our home build/blog site, as a web developer by trade, it's flashier than it should be ;).
Our structural materials per our current plan are as follows:
The steel structure is pre-engineered and provided by a distributor of OutbackBuildings.com. It will have 12' bays (clearspan) and will be a relativity light structure (in comparison to traditional residential framing). The walls will be straw-bale in-fill making the requirements and code easier to meet (thanks to the steel being the structural element).
We are still debating on if we should encase the steel vertical supports within the straw-bale walls (which isn't a big deal with C-Channel verticals) or butt the bales up against a breathable barrier (not vapor, my bad) on the outside face of the steel. Putting the bales outside of the steel makes for an easier install of the straw-bale in-filled walls and could allow us to not render the inside face of the bales (good idea? bad idea?). It also belays issues with dew point on the steel within the straw-bales walls.
The roofing purlins will be thermally broken from the rest of the steel structure (that is, outside of the thermally broken envelope). Our concrete slab will be thermally broken/insulated.
Thanks to you guys, we are looking to the Canadian manufactures of triple glazed windows for our ~850sqft in windows across the two structures. We have been advised to use SGHC 0.5 and as low a U-Value we can afford. We also plan on using external motorized windows shades to help limit thermal gain (keep the photons out and they can't heat the inside). So uPVC? Fiberglass? Aluminum+Wood? We're looking for performance and price, so ultra-high-spec is likely out (or is it worth it?).
Internally, as you can see from the attached floor plans, we are embracing the clearspan of the steel buildings. Buildings are oriented as laid out in the attached floor plans; N being top, E being right. Ground flooring will be polished concrete for durability, expense and thermal mass. Internal walls and sub-flooring will be MgO board likely over non-structural steel studs.
So... what problems are we likely to have? Are there any materials we should re-think? What pitfalls are we likely to hit?
We very much appreciate your input and feedback!
Posted Aug 26, 2014 12:42 AM ET
Edited Aug 26, 2014 7:38 PM ET
Other Questions in Plans Review
Is it advisable to use nail base insulation panels over a roof insulated with closed cell spray foam?