Foundation + site work has begun on the island Outpost project and we quickly encountered an important decision after removing the overburden of soil at the building site. In the video below you’ll see the drawings I prepare for the early stages of construction, learn how I choose an appropriate foundation system and join me for a typical site visit as I review progress.
We rely on the architectural drawings to order and organize information and ensure our design decisions are enacted in the field, but they're not fixed instruments as construction always presents unexpected opportunities + challenges. Our initial foundation strategy to use posts + piers and minimize the amount of concrete was thwarted by higher than expected bedrock (ledge) elevations. As a result we had to raise the main level finished floor and connected decks by 6” and we shifted the building eastward - toward the water - to better fit with the underlying ledge profiles. This is one of many reason I visit the site regularly to review + resolve the questions that invariably arise during construction.
Timestamps:
00:00 Building on an island
00:41 Foundation design considerations
01:51 Slab on grade
04:01 Post + pier
06:09 Frost wall + crawlspace
08:47 Making changes
09:40 Drawing the foundation plan
10:51 Locating the building on-site
12:00 What to include on the foundation plan
13:25 Checklists (in Notion)
13:46 Site walk + tour
15:24 An office with a view
16:14 “This is the worst one…”
Transit
Site Benchmark - main level datum
Foundation Plan - 1/4” = 1’-0”
Wall Section Detail - 1”=1’-0”
Importantly, the drawings must also take into account the sequence and order of operations on a construction site. The foundation resolves the gravity and lateral forces acting on the building into the bearing substrate below. It conceals the many utilities entering and exiting the building’s perimeter, keeps groundwater out, and serves as a semi-conditioned space to rough-in plumbing, mechanical and electrical systems. The purpose of the foundation plan is to collate and coordinate the locations of these systems on paper before our field work begins. It must also adequately describe the building’s siting in three-dimensional space on raw land. Note the use of vertical datums and elevation tags on the foundation plan which all reference the site benchmark set by the surveyor early in the construction phase.
Site overview - looking southeast
Luther (our GC) at work in his “office”
Footings scribed to ledge
It’s not unusual for the footing formwork to be scribed to ledge here on the coast of Maine where ledge is always within a few feet of the surface. Our footing - in this case - is acting as a level pad to set our wall forms on and these will all be concealed as we’ll backfill against them. However, there are some locations where the ledge and wall interface will be exposed and in those spots we don’t want to see a footing, so we’ll be casting our wall directly on top of the ledge, scribing our wall forms in the same way. To anchor everything we drill into the ledge and use steel rebar epoxied in place roughly 24” on center. Before backfilling we’ll waterproof and add our subsurface drainage to ensure a dry crawlspace.
Southeast Corner
Detail at Southeast Corner - scribed footing
South pour complete - October 15, 2020
There's nothing more rewarding as an architect than seeing your ideas realized in physical form. It's a complete thrill for me each and every time. I'm honored to be working with such an incredible team of collaborators. Without generous clients (and their willingness to share the process so openly) and skilled craftspeople to assemble the parts, none of this is possible.
More updates soon!