Defining a better Homestead

We have perhaps a dozen requirements scattered through the discussions in this blog that we have not yet incorporated into the Peak Oil Homestead Project. With the benefit of detailed requirements structure, it’s now an almost enjoyable task to plug them into the project.

In Global Warming meets Peak Oil Design, I introduced several potential requirements. Before I show you where to stash ‘em, I want to make some improvements.

We specified that “The Homestead shall withstand temperatures of 115°F or greater.” with the understanding that we would need to better define “withstand”—I now have a way to do that. Consider this improvement:

The homestead shall withstand high-peak temperatures of less than or equal to 115°F for 7 consecutive days without depletion of reserve resources.

This serves several purposes: it specifies how we want the Homestead to withstand, ensures that it’s a system-wide requirement (rather than solely structural), uses “peak” to indicate temperature cycle, and specifies a time frame for the temporary condition we’re guarding against. Similarly we have:

The homestead shall withstand low-peak temperatures of greater than or equal -30?°F for 7 consecutive days without depletion of reserve resources.
The homestead shall withstand greater than or equal to 10 inches (equivalent) of precipitation per year without depletion of reserve resources.
The homestead shall withstand less than or equal to 4 feet of accumulated snow for 7 consecutive days without depletion of reserve resources. (This differs from the original – specifying a depth rather than mass at this level gives broader applicability.)

“But wait!” you say, “we want to make sure that such weather doesn’t damage the place.”
Ah, say I, but that’s a separate set of requirements:

The homestead shall withstand high-peak temperatures of less than or equal to 115&def;F for 7 consecutive days with a minimum of damage.
The homestead shall withstand low-peak temperatures of greater than or equal -30&def;F for 7 consecutive days with a minimum of damage.
The homestead shall withstand less than or equal to 4 feet of accumulated snow for 7 consecutive days with a minimum of damage.
The homestead shall withstand less than or equal to 50 inches (equivalent) of precipitation per year with a minimum of damage.
The homestead shall withstand sustained winds of less than or equal to 60 mph for 72 consecutive hours with a minimum of damage.

All of these requirements go in the same spot – under Input Requirements (Section 1.2.1) since they indicate how the system should respond to external stimuli. The remaining requirement from that post is actually an output requirement and belongs under Section 1.2.2:

The homestead shall provide shelter for no less than 4 people from tornadic winds (less than or equal to 350 mph).

From our discussion on living space, let’s peg 1700 ft^2 for the requirement. Remember, the assumptions are a budget of $100K and access to heavy equipment – if those assumptions change, we’ll likely need to change to a smaller house. It also may be that this size is too large for our goals of sustainability, maintainability, etc. after Peak Oil, but we’ll discover that as we develop the requirements – that’s the beauty of the Systems Engineering process.

Finally, to show an example of an interface requirement, I included the following under 1.1.3: The homestead shall have a weight distribution less than the maximum supportive capability of the soil.

So now that we’ve pulled in all the orphan requirements, we can get back to writing new ones! (A reminder: If you would like to discuss anything about the Peak Oil Homestead Project as a whole so far, feel free to post in the Community Design Forum.)