by Patricia McDaniel Hamilton
Figure 4. Because homes on pilings are typically quite tall, highlifts are indispensabletimesavers when it comes to moving materials.
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Sheathing
We use 1 /2-inch minimum APA-rated
structural sheathing, following
the engineer's recommended nailing
pattern - typically 8-penny nails on
3-inch centers at the edges and 12-inch centers in field. With multistory
houses, the plan often calls for lapping the plywood over the band joist, tying
the studs below to the studs above. If the plywood breaks right at the band
joist, metal straps like the Simpson LFTA are needed to transfer the uplift
loads from studs above to studs below.
All plywood edges need to fall on solid blocking for maximum shear
strength. We sometimes have to build interior shear walls as well. For interior
shear walls, we've found that plywood or let-in 1x4 bracing provides
much stiffer wall sections than using metal bracing. In some cases, we add
shear walls beyond what the specs call for. Houses on pilings have a peculiar
and disturbing way of shaking or vibrating. Traffic on the steps or breezy
days make the house seem to shimmy. It's better to write a change order
sooner for additional bracing than to deal with seasick owners after they move in.
Figure 5. Metal connectors help resist the
huge uplift forces coastal homes are subjected
to. Hurricane connectors secure joists to
girders, strap ties connect first-floor studs to
second-floor studs, and rafter hold-downs tie
rafters to top plates and studs.
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Up on the Roof
By the time the house is ready for
the rafters, the structure is often quite tall. Local codes limit the height of
the house to 35 feet measured from the flood elevation to the midpoint of
the main roof. Windy days can be dangerous when you're walking plates 30
feet up, so we usually allow some extra down time in the schedule for houses
more than two stories tall.
Roof framing is mostly conventional. Once again, metal framing connectors
are needed to secure each rafter to the studs below. If the rafters don't
align with the wall plates, two connectors are needed - one to tie the rafter
to both top plates and one between the top plates and stud. So we try
where possible to align the studs with the rafters. Since stud spacing is usually
on 16-inch centers, framing the roof 16 inches on-center means fewer
connectors of a lower capacity.
Our typical rafter tie is a Simpson H7, which must be installed before
sheathing the roof. If loads are concentrated by dormers or other roof
openings, special consideration is given to concentrated uplift loads. In
general, uplift loads from high winds are usually figured at about 1,000
pounds per rafter. Concentrated loads (at hip rafters or girder trusses, for
example) can run into thousands of pounds, meaning custom hardware
may be required.
Roof sheathing installs normally (once you wrestle it 40 feet in the
air), but once again careful attention must be given to nailing patterns.
Weatherproofing
Making a house weathertight is difficult in an oceanfront environment.
Along our part of the coast, "Northeaster" storms blow through
about once every two weeks, bringing heavy rains and winds around 80 mph.
It's an understatement to say we have to pay careful attention to caulking and flashing details to prevent leaks.
We use Typar housewrap, lapping it from the bottom up and taping all the joints. Typar holds up extremely well
to the wind and weather, and the gray color is easy on the eyes (when you're building along the beach, you don't need any added sources of glare).
Windows. We use only the highest-quality windows, preferably aluminum clad. We prefer to use at least Grade 60 windows, as rated by NWWDA (National Wood Window & Door Assn.). These are usually casement or awning type. When the client insists on double-hungs, it's necessary to settle for Grade 40. In addition, the cladding and hardware must be rated for seacoast exposure.
We always bed the window flanges in caulk, then tape them to the Typar with housewrap tape. We back all exterior trim at windows and doors with tar paper and use drip cap flashing above (Figure 6).
Storm shutters. Since we are building in a hurricane zone, we recommend that all coastal houses include storm
shutters. The three basic types available are hand-applied modular panels, roll-down shutters, and folding (accordion)
shutters. These are all engineered shutters. None of them is aesthetically pleasing, although roll-down shutters can be hidden in soffits.
For any of these shutters, an extra layer of trim is needed around windows and doors so that the shutter isn't obstructed by the window frame or hardware. With sliding glass and outswinging doors, you have to clear
the door handle. Screen doors can also be a problem. This is best thought through early in the design to avoid reworking the trim later.
Figure 6. Coastal builders must take special care to seal openings against wind-driven rain. To install a window (left), the housewrapped
opening is first covered with tar paper. The window is then installed in a bed of caulk. The author uses only clad windows rated for coastal
conditions. The author recommends storm shutters (right) for all coastal homes to prevent hurricane winds and flying debris from bursting the glass
in windows and doors.
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Utilities. Utilities need to be elevated above the base flood elevation
or somehow protected from inundation. Hvac units are usually built on
separate, elevated decks, and electrical meters and panel boxes may be
mounted higher than normal.
Closing in underneath. Many communities require that pilings be
enclosed. Depending on the budget, we may box in individual pilings with
siding and trim or enclose the entire perimeter with lattice or spaced 1x4s.
In a traditional home, the crawl-space insulation can be left exposed,
but for a piling house it is necessary to install a ceiling underneath. Our
usual choice is a 3/8-inch roughtex plywood, although if there are car-ports or parking areas below the
house, we sometimes use exterior gyp-sum. In crawlspaces, we choose materials
for durability with less concern for aesthetics, typically 3/8-inch CDX or OSB.
Cost Considerations
The overall expense of placing a house on a piling foundation runs
between $5 and $10 per square foot higher than placing the house on a
concrete block crawlspace. The added expenses include the pilings, girders,
bolts, cross-bracing, crawlspace ceiling, lattice enclosure, additional
framing expense, and equipment rental.
Patricia Hamilton is co-owner and operator
of Boardwalk Builders in Rehoboth Beach,
Del. Photos by the author.
