Marine Climate Zone

The marine climate presents several challenges for home building.

The marine climate covers a narrow band paralleling the west coast from the Canadian border south to the county boundary separating Ventura and Los Angeles counties in California. The marine climate was designated in recognition of the mild temperatures and moist conditions found along the coast. However, the marine climate borders on the cold climate in the north, and the hot-dry climate in the south and the more extreme conditions of these neighboring climates are found in some inland areas.
The marine climate has moderate conditions most of the time. But weather conditions similar to those found in neighboring climate zones occasionally prevail. Homes in the marine climate are faced with a lot of moisture, often in the form of fog or rain.
The use of full basements and crawlspaces is common in these climates and presents another set of challenges. These design features may bring extra living and storage space, but they also bring their own moisture and temperature management challenges.

Marine Climate Best Practices

Housing types vary greatly throughout the marine climate. Basements and crawlspaces are common in the north. Slab foundations are used throughout the region.

In the face of this diversity, no single set of measures will achieve the 30 percent energy savings in space conditioning and water heating that qualifies a home as ENERGY STAR^®-qualified. The principles included in these best practices need to be adjusted for different circumstances. A building scientist, such as a home energy rating professional, can help homeowners determine which combination of best practices is most appropriate.

These best practices are derived from Building America's research on tens of thousands of homes. Building scientists have tried and tested these measures on actual homes in the field. While not every measure will be right for a specific home, achieving high-efficiency performance and a healthy indoor environment depends on making informed decisions about interactions among all aspects of the building system.

Special Considerations for the Marine Climate Zone

Site Design

Hotter and dryer portions of the marine climate may be dominated by cooling rather than heating. Avoiding summer cooling is more important than encouraging solar gains for winter heating. Planners should do all they can to avoid the entry of solar energy into houses in summer. Site planners have two important tools to help manage solar heat gain: lot orientation and shade trees.

Xeriscaping

Rain is not abundant throughout the marine climate, especially in summer. Although fog may hug the coast, inland summer droughts are common. In dry areas xeriscaping may be important. The term is taken from the Greek xeros, meaning dry, in combination with landscape.

The goal of a xeriscape is to create a visually attractive landscape that uses plants selected for their water efficiency. Properly maintained, a xeriscape can easily use less than one-half the water of a traditional landscape. Once established, a xeriscape should require less maintenance than turf landscape.

By grouping plants with similar water needs together in specific zones, a xeriscape landscape can use water more efficiently. Low-water-use plants should be grouped

together, away from high-water-use plants and turf. Take advantage of warm or cool microclimates (climatic conditions influenced by the placement of walls and shade trees) to create areas of interest and diversity.

A well-planned and well-maintained irrigation system can significantly reduce a traditional landscape's water use. For the most efficient use of water, irrigate turf areas separately from other plantings. Other irrigation zones should be designed so low-water use plants receive only the water they require. Proper irrigation choices can also save water. Turf lawns are best watered by sprinklers. Trees, shrubs, flowers, and groundcovers can be watered efficiently with low-volume drip emitters, sprayers, and bubblers.

The information presented here was adapted from the City of Albuquerque'Web site.

Foundations

Slabs, crawlspaces, and basements are all found in the marine climate. Building foundations should be designed and constructed to prevent the entry of moisture and other soil gases such as radon.

Slabs and Basement Floors

Slabs in this climate should be insulated at the perimeter with one inch of borate-treated foam board insulation or rigid glass fiber insulation.

Walls

Wood Frame Walls

Best practice for frame wall construction involves advanced framing techniques. However, these techniques are not required to achieve 30 percent space conditioning energy savings in the marine climate zone. More information on gaining greater efficiency using advanced framing can be found at the Building Science Corporation's Web site. If advanced framing is to be used, a detailed plan should be developed showing framing placement.

External walls with 2x6 framing are typical in the marine climate. These walls should include the following features:

Exterior sheathing, preferably insulating sheathing with joints taped to provide a water and air barrier. Use insulating sheathing that does not have a film facing.
Insulation may be R-19 friction-fit, kraft-faced fiberglass insulation or blown-in cellulose insulation.
Unfaced or kraft-faced insulation on frame walls between the garage and the conditioned space, including bonus rooms.
Rim joists with kraft-faced R-19 friction-fit batt insulation cut to fit.
Foam sealed or caulked top-plate penetrations and exterior wall penetrations.
Sealed gypsum board to control air leakage through the walls, especially in penetrations to garages and porches, and where the walls meet the ceiling.

Vapor Management

In the marine climate, and especially in the Pacific Northwest, interior and exterior moisture loads tends to be high. Typically interior relative humidity levels around the nation are maintained at 30 to 40 percent on average in the winter. Field testing in the Pacific Northwest show that average interior relative humidity in excess of 55 percent is common in the winter.

Building assemblies need to be protected from getting wet from both the interior and exterior and should be allowed to dry to either the exterior or the interior. Lstiburek (2001) notes three general strategies for managing vapor in wall assemblies:

Installing vapor diffusion retarders on the interior and exterior of wall assemblies to block moisture entry from both directions. This approach is very dangerous if moisture is trapped inside the wall from water leaks, using wet building materials, or vapor transport. Tight construction using OSB (oriented strand board) exterior sheathing and a polystyrene vapor retarder behind the gypsum board may create this situation. Building America teams do not recommend this approach.
Allowing vapor to "flow through" by using permeable materials on both the interior and exterior sides of the building assemblies. This allows water vapor to diffuse through the assembly from the interior to exterior during heating periods and from the exterior during cooling periods. An example of this type of assembly may include plywood sheathing and vinyl cladding on the exterior and interior gypsum board finished with primer and latex paint.
Putting the vapor diffusion retarder roughly in the "middle" of the assembly by installing impermeable or semi-permeable insulating sheathing (such as unfaced, rigid, extruded polystyrene foam insulation) on the exterior of a frame cavity wall filled with permeable insulation. This is the system recommended by Building America teams.

Based on research in multifamily buildings in Seattle, ORNL suggests that if interior relative humidity is maintained below 60 percent, then a latex primer and paint may perform better than the use of a polyethylene sheet (Karagiozis 2002b). Other research suggests that some wall systems with low permeable cladding, such as stucco, may require a class 1 vapor retarder, such as polystyrene sheets, on the interior (Murray 2005). These findings suggest that wall systems are diverse and should be carefully designed to accommodate building materials, local climate conditions, and interior moisture loads.

Insulation

Reflective Insulation Systems

Reflective insulation systems are effective in the marine climate at reducing peak cooling loads, especially if ductwork or cooling equipment is located in the attic. Additional information on reflective insulation systems can be found in the insulation section of this site.

Slab Foundation Insulation

Slabs in the marine climate may be insulated at the perimeter with borate-treated foam board or rigid glass fiber insulation.
Use only insulation approved for below-grade use. Some code officials may require a gap between exterior insulation and wood foundations elements to provide a termite inspection area. Exterior insulation should be applied from the top of the foundation wall to the bottom of the frost line. Cover the exterior face of the insulation exposed to outside air using material such as flashing, fiber cement board, parging (stucco type material), treated plywood, or membrane material.
A shallow, frost protected slab foundation may be used in areas subject to seasonal ground freezing. With this approach, foundation footings need not be placed below frost depth. However, rigid insulation, approved for below-grade use, must be placed vertically on the exterior of the grade beam, and must be placed to extend away from the foundation horizontally at the base of the grade beam for a distance equivalent to frost depth. Rigid insulation is also needed vertically on the inside of the grade beam, and must extend horizontally under the slab, on top of the gravel capillary break, for two feet. Code officials may require that a structural engineer review and approve specific plans.
Slab perimeters may be insulated on the interior side. This approach requires that rigid insulation be placed between the slab and the foundation wall, and under the slab, as required by local code.

For more information on shallow foundations see:

The American Society of Civil Engineers standard (number 32-01), Design and Construction of Frost-Protected Shallow Foundations.

Crawlspace Insulation

Another approach used in the marine climate is referred to as conditioned crawlspaces, or mechanically vented crawlspaces. Within this type of system, foundation side walls are insulated on either the interior or exterior (or both), and no outside air vents tunnel through the crawlspace wall. The floor above the crawlspace is not insulated. These conditioned crawlspaces allow for the placement of ducts and air handlers in conditioned space. Research on this type of crawlspace system is just getting underway in the Pacific Northwest. Conditioned crawlspaces may require a code variance. Building America teams recommend using conditioned crawlspaces.

Basement Insulation

Basements are a common foundation system in the marine climate. Wall insulation in basements is similar to the approaches described for crawlspaces, and basement floors are insulated in ways similar to slabs.