The Z dimension

The good news first. Judging by the inquiries for new work the local economy, particularly for residential construction, is gaining steam.

The not so good news. I have a commission for a new house on a very steep site; a site the old timers would call a “mule’s nose” (again with the mules!).

The steep site has me thinking about the “z” dimension. If “x” and “y” are the dimensions that describe the plan then the “z” dimension is the one that describes topography.

As the esteemed landscape architect John Broadbooks once said, “X and Y tend to take care of themselves – Z will kick your ass” (Slightly paraphrased for emphasis – sorry John).

Living and working in the mountains forces designers and builders to become intimately familiar with the z dimension. Ignore z at your (and your clients) peril. Z is where the money is. Z insists that you become adapt at reading a topographical survey and understanding the implications of all those squiggly lines.

When the lines get tight, so must one’s focus on the implied dimension get stronger.

The green building imperatives are plenty. Of course these will be obvious to most GBC readers but let’s be clear.

Erosion. Steep sites call for increased focus on erosion control – both during construction and for all eternity thereafter. Double silt fences may not be enough to keep that precious topsoil on the site and out of the creek.

Of course our local inspectors will make sure you meet the minimum legal requirements but with the severity of the rain-events of late even this is not enough.

A few strategies I’ve picked up working with green builders, landscape architects, and civil engineers are:

Keep as much native vegetation as possible, especially downhill (duhh).

Design swales into the rough grading during the construction.

Keep finished slopes to a 2 to 1 slope if at all possible.

Try not to channel water. This is tough as a roof is essentially a water collector (second duhhh).

Write temporary ground covers into the specifications when seasonal schedules keep permanent landscaping out of the picture.

Landform stability. During the “frog chocker’ rains of July 4th, we saw some pretty scary landslides. if nothing else it served to underscore the reasoning for the City of Asheville’s steep slope ordinance. We are obliged to hire and to follow the geotechnical engineers recommendations for keeping the mountain off the building.

Retaining walls and basement walls. Basement walls are relatively in-expensive ways to retain soil. Structurally, basement walls act as vertical beams (pinned by the slab or footing on one end and the floor frame on the other).

Not so for retaining walls. Retaining walls are the gold medal gymnast of the construction world. By requiring that they perform as cantiliver beams held only by the footing these walls are expensive (and require a requisite amount of time, money, and material).

A nice trick with retaining walls is to add some 90 degree bends to them with the corner acting as an inside corner to the uphill load. This can save a lot of steel reinforcing and tends to create more level space for the builder to stage from and for the owner to enjoy once the building is complete.

Vehicular circulation. It is my general sense that we spend as much time and money making it possible for cars to get in and out as we do making the foundation. If we can lessen the amount of space given to vehicular circulation we can lessen the undesirable effects of grading (see prior comments).

A stray thought on vehicular circulation and the previous comment. If the solution to excessive vehicular circulation is having the hardscape come right up to the building we have not really solved the problem. Whenever possible we should try to keep at least 6 feet between the house and the hardscape. This allows for an extremely valuable vegetative zone that does much to soften the effects, over time, of our interventions.

Of course there are other issues, such as staging for materials, parking for construction vehicles, locating the temporary facilities, scaffolding the downhill wall, etc. I’ll leave those topics for our experienced mountain builders to address.

On a closing note, they call what I do an architectural “practice”. I take this to mean one is never done learning. if anyone out there would like to share their insights into the z dimension I would love to hear from them.

Until then,

Steve Farrell