The unsavory mix of salt, strong winds, unknown underground conditions and conflicting local government requirements means that poor design decisions are quickly exposed and the bulk of very expensive design decisions are taken during the pre-design / feasibility stage of a project and are very costly to alter once ‘Locked-in’ prior to submission of permits for approval.
The subsequent phases are detailed step by step with check points at appropriate times to allow trade-off decisions to be made to safeguard numbers throughout the remainder of the project.
Reading the site before you commit to it
Unlike buying a simple block of land, conducting due diligence on a coastal property involves looking at the land through the geotechnical, hydrological and jurisdictional eyes of potential construction of a house on that land.
Consider ordering a geotechnical investigation on the proposed building site prior to purchase of the property. The bearing capacity of dune sand, fills and other estuarine deposits can vary significantly over short distances. Also, consider the cost of providing shallow footings compared with driven pile foundations for a coastal property.
The checks worth paying for up front
- Soil borings at the proposed footprint, not just at the parcel center
- Current flood zone and base flood elevation, plus any pending map revisions
- Setback lines from erosion control structures, dunes, or vegetation lines, which may sit well inland of the property boundary
- Septic feasibility or utility connection capacity, since high groundwater can rule out conventional systems
- Historical shoreline movement data over the longest available record
- Access and laydown area for cranes, pile rigs, and deliveries
Designing for the environmental load, not the brochure
Material selection is typically based on exposure conditions as opposed to visual appearance. Even minor corrosion of fasteners, hardware and reinforcement can take seven years or more to develop and typically occurs after the end of the warranty period.
For the envelope of a coastal home of lasting value, use stainless steel for all fasteners in salt spray areas. Dissimilar metals should also be avoided to prevent corrosion. Detailed rain screen modeling of wind driven rain at design pressure is generally a far better approach than typical attempts to detail flashings.
Orientation and elevation decisions
When considering the plan form structure the Floor Facing Level (FFL) should be set higher than the minimum Floor Facing Level required. Add freeboard early on in the design, it costs little to add extra height at design stage and will get better terms from insurers. The client’s map will always show less freeboard than actually is on the property. Consider the orientation of external walls for the building early on. This will enable you to cast the maximum amount of shade on the western side of the building and use the prevailing onshore wind to protect external exposed areas of the property.
Building a budget that survives contact with the site
As with any project, coastal budgets fail in predictable places, the foundation, site access and the envelope of your building. Anyone preparing to build a custom home in Hilton Head or a comparable barrier island market should put those three items into the first allocation conversation, well before Design Development stage.
| Cost area | Typical inland assumption | Coastal adjustment |
| Foundation | Slab or crawl space | Piles or grade beams, driven to tested depth |
| Structure | Conventional framing | Continuous uplift load path, engineered connections |
| Envelope | Standard windows and cladding | Impact glazing, corrosion-rated hardware and cladding |
| Permitting | Single jurisdiction | Local, state coastal, and possibly federal review |
| Contingency | Five percent | Ten to fifteen percent until borings are returned |
Keep this for known unknowns and do not use as a discretionary fund. Release this to finishings prior to signing off the foundation.
Sequencing permits and construction realistically
Coastal Zone Review and Environmental Assessment events occur in series rather than in parallel and can be scheduled by the client’s representative on their calendar, not in your favor. They can also occur at times that are not favorable to your aggressive construction schedule.
A workable order of operations
- Site investigation and survey, including wetlands delineation where relevant
- Schematic design sized to confirmed buildable area
- Pre-application meeting with the permitting authority before drawings are finished
- Structural and civil engineering coordinated with the geotechnical report
- Permit submission with the environmental review package assembled in full
- Contractor procurement and long-lead ordering, particularly glazing and custom metals
- Construction, with foundation work scheduled outside the primary storm season
The long lead items such as impact-rated openings or special hardware items take months to arrive and must only be ordered once that portion of the drawing has been approved for construction.
Choosing the team that has done it before
Draw upon previous experience designing in similar conditions and gain insight into the prior corrosion and waterproofing detailing used for similar buildings, and see how they’ve performed over time.
Consider either an allowance for the foundation or a cost-plus arrangement for the foundation work on a project where there are uncertain subsurface conditions at the time of signing (e.g. Fill site, poor dune soils).