Identifying, designing and verifying critical design decisions in a coastal lot design to avoid large unknown risks that could cost an arm and a leg after the warranty period has expired.
Decisions made when designing your new home to last a long time on a coastal lot will also impact decisions regarding site investigation, a house design or house specification and selection of builder.
Start With The Site Investigation, Not The Floor Plan
The geotechnical and hydrological conditions of a coastal site can vary greatly over short distances. A sandy profile may support a load bearing structure at the front of a site but deteriorate to a low bearing soil at the rear. Perched water tables need to be taken into account when designing basements and crawl spaces. The presence of acid sulfate soils needs to be taken into account when excavating and disposing of soil and can affect the method of excavation as well as the cost of a project.
Due diligence worth completing before design
- Confirm the flood zone designation and required lowest floor elevation, then add freeboard above the minimum.
- Obtain a geotechnical report with borehole logs, not a desktop assessment.
- Identify coastal setback lines, dune protection overlays, and any erosion hazard mapping that applies.
- Check utility access and whether on-site wastewater treatment is viable given the water table.
- Review access for heavy vehicles, crane positioning, and material storage on a constrained lot.
All unknowns must be identified prior to Schematic Design completion and the Client must understand that 2 complete sets of drawings will be required to adapt the design to any of the site unknowns that are identified after Schematic Design completion.
Match The Specification To The Exposure Category
Note that the set Exposure Categories will influence corrosion severity with distance from the breaking surf and of exposure, that airborne chloride deposition will cause premature failure of standard galvanized fixings and medium grade stainless steel in exposed conditions within a quarter of a mile from the breaking surf. Also wind speed and internal pressure classification increase with distance from the breaking surf on exposed headlands and over open water fetch.
Where the Money is Best Spent
| Component | Common failure near the water | Stronger specification |
| Fasteners and connectors | Surface rust within two years, structural loss by year ten | 316 stainless for exposed work, hot-dip galvanized minimum concealed |
| Window and door hardware | Seized rollers, pitted frames, seal failure | Marine-grade anodized or powder-coated aluminum with documented coastal warranty |
| Reinforced concrete | Chloride ingress and spalling at slab edges | Increased cover, lower water-cement ratio, supplementary cementitious materials |
| Cladding | Coating breakdown on the windward elevation | Fiber cement, masonry, or fully reversible panel systems |
| Balustrades and railings | Weld-line corrosion and staining | Composite, treated hardwood, or electropolished stainless |
Note that Set Exposure Categories need to be included in the contract documents so that your contractor can choose alternative products to meet the exposure category without downgrading to lowest cost items, which is one reason it pays to work with established custom home builders in Hilton Head and comparable coastal markets who price to the specification rather than around it.
Orient The Building For Wind, Salt, And View In That Order
Note the coincidence of best view with prevailing wind direction and highest salt concentration. A buffer will be needed and this could take the form of a deep covered terrace or ‘veranda’, of operable louvered screens or additional glazed layers which can be replaced for wallpaper like failure before it causes primary envelope damage.
Practical layout moves
- Place service areas, laundries, and storage on the most exposed corner where finish degradation matters least.
- Use cross ventilation along the prevailing breeze axis to cut mechanical cooling load during shoulder seasons.
- Keep roof forms simple and hips shallow, since complex junctions concentrate uplift and leak paths.
- Detail generous eaves where wind allows, and omit them where uplift pressures make them a liability.
- Design drainage so salt-laden runoff is directed away from fixings and column bases.
Plan Maintenance Into The Design, Not Around It
After the home has been completed it is a ‘maintained asset’ and can be compromised by the inability of all surfaces to be washed regularly to remove chloride before it concentrates and commences to cause damage. Safe access must be provided to gutters, upper glazing, rooftop plant etc. For regular cleaning and to ensure that items such as these are not left to deteriorate until problems arise and are then treated as afterthoughts and retrospectively added as anchor points and walkways etc.
It is sensible to view items that don’t last the life of a house on a coastal lot as consumables. Establish a replacement schedule for items like deck boards, external fixings, joint sealers and surface finishes and ensure that the Client has a clear understanding of what they can expect to need to replace and when.
Choose A Builder With Verifiable Coastal Projects
Note that for experienced coastal builders “local” work refers to projects of similar exposure to weather to that which they have completed elsewhere, often not even in the same county. Seek completion addresses with at least 5 years elapsed and go and have a good look at how the finish of the fixings has lasted, how the various cladding types have joined together and how the windows and doors have performed.
Questions that reveal real capability
- How are different metals separated to prevent galvanic corrosion at contact points?
- What protection is provided for exposed steel and timber during the build itself?
- Which subcontractors have worked on comparable sites, and are they under the same specification?
- How are substitutions approved, and who signs off on equivalence?
The points a wise builder needs to be concerned with in a coastal environment as opposed to a builder who views a coastal lot as simply another pretty location with great views.
