We have made it through the maze of permitting for our house with a relatively new wall system of precast concrete (Ideal Walls- https://www.idealbuildingsystems.com/home.aspx ). Plan review wanted some unusual assurances via engineers before they would let us begin. Though precast foundation walls have been around a long time this is a relatively new company and we are using them for the one level house. The plan reviewer was confused about the footings and the foundation. These walls incorporate the footings with the walls and sit on a 6-inch deep #78 gravel bed. There will be some added depth for the “footers” which are 3-foot wide 12-inch deep gravel to end up below frost. That is 18 inches below finish grade here in Asheville.
On top of that, precast concrete demands accurate window and door sizing and placement. There were a few revisions on our part to get where we are confident with the plan. One of the drawbacks of these walls is the inability to relocate openings as you frame. In our usual stick frame construction we often will have what we are sure is a final version of our window openings and door placement only to move a couple around when we are standing in the space and realize a better option. Precast concrete is a hard change order.
Digging ourselves into a hole has given this project some appreciated momentum. It is an ironic sense of accomplishment to have hole to work from. The lot is .1 of an acre or 4,356 square feet. The hole in this case is shallow compared to our norm at 4 ft deep at the deepest corner. One issue that I had not foreseen is where to put the dirt. Even digging this small house footprint (1200 sq ft) that has an average depth of about 2 ft there are large piles of mostly topsoil. Most of it will be needed for backfilling and final grading but it is hard to store out of the way to have room for the cranes that will set the walls and roof trusses before backfilling can begin. Our excavated area comes within 8 feet of the sides of the lot in some places, which is not a lot of room to pile dirt.
The small infill lot-building plan seems like a good one over all. It makes use of existing infrastructure and is close to work opportunities, necessities and cultural attractions as well as the bus system ART. These should all contribute to a lower carbon footprint. But smallness in lot size as well as house size brings with it some interesting challenges and I will be glad when the momentum carries us past the dirt piles.