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  • Microclimatic Landscape Design: Creating Thermal Comfort and Energy Efficiency
    Microclimatic Landscape Design: Creating Thermal Comfort and Energy Efficiency
    by Robert D. Brown, Terry J. Gillespie
  • Understanding Ordinary Landscapes
    Understanding Ordinary Landscapes
    Yale University Press
Bookshelf - Florida Landscape
  • Florida's Best Native Landscape Plants: 200 Readily Available Species for Homeowners and Professionals
    Florida's Best Native Landscape Plants: 200 Readily Available Species for Homeowners and Professionals
    by Gil Nelson
  • Native Florida Plants, Revised Edition: Low Maintenance Landscaping and Gardening
    Native Florida Plants, Revised Edition: Low Maintenance Landscaping and Gardening
    by Robert G. Haehle
  • Natural Florida Landscaping
    Natural Florida Landscaping
    by Dan Walton and Laurel Schiller
  • Sustainable Gardening for Florida
    Sustainable Gardening for Florida
    by Ginny Stibolt
  • Priceless Florida: Natural Ecosystems and Native Species
    Priceless Florida: Natural Ecosystems and Native Species
    by Eleanor Noss Whitney, D. Bruce, Ph.D. Means, Anne Rudloe

 

Elements of Intelligent Design - Landscaping

 

Introduction

It is the functional role that landscaping plays that is most relevant in Intelligent Design, with aesthetics & privacy being important, but secondary objectives. Again, geographic location and associated general climatic conditions dictate what approach is taken in creating a landscaping plan and how appropriate applications of landscaping affects the microclimate of a building site and the air movement in and around buildings.

Typically, the following objectives are used to guide the development of landscaping in various regions:

Temperate Regions

  • Maximize warming effects of the sun in the winter.
  • Maximize shade during the summer
  • Deflect winter winds away from buildings.
  • Funnel summer breezes toward the home.

Hot + Arid Regions

  • Provide shade to cool roofs, walls, and windows.
  • Allow summer winds to access naturally cooled homes.
  • Block or deflect winds away from air-conditioned homes.

Warm/Hot + Wet/Humid Regions

  • Channel summer breezes toward the home.
  • Maximize summer shade with trees that still allow penetration of low-angle winter sun.
  • Avoid locating plants that require frequent watering close to a home.

Cool Regions

  • Use dense windbreaks to protect the home from cold winter winds.
  • Allow the winter sun to reach south-facing windows.
  • Shade south and west windows and walls from the direct summer sun, if summer overheating is a problem.

For purposes of this project, aspects of creating effective landscaping schemes in Florida (and appropriate to other Warm/Hot + Wet/Humid locations) will be explored in more detail.

Landscaping the Hybrid Home

In Warm/Hot + Wet/Humid regions, sheltering a structure from wind is not the prime objective, though, as described later, it does become important at certain times of year when living in hybrid (using both passive and mechanical cooling) homes. Conversely, increasing the frequency and velocity of breezes during appropriate seasons is advantageous in creating comfortable spaces.

Living in tropical and subtropical Florida provides a range of opportunities for using landscape materials to control home environments. There are several effective planting methods that increase the amount of breeze a home receives as well as others that help limit the amount of heat or moisture which enters a structure. Using trees, shrubs, grasses and other ground covers to channel winds, create shade, and reduce moisture near buildings can be highly effective in controlling these elements.

As pointed out in other sections of the Intelligent Design discussion, creating comfortable living conditions in Florida requires adapting to a wide range of conditions that sometimes present conflicting and contrasting situations and, thus, somewhat opposing design solutions. Creating landscaping plans present such a challenge, as conflicts arise between approaches that promote breezes for passive cooling and those that discourage breezes that decrease the efficiency of mechanical cooling.

 

Landscaping for Passive Cooling

Encouraging Airflow
  • To encourage and enhance passive cooling, houses should be landscaped to direct breezes into the home. Trees located parallel to the building’s perimeter walls should be spaced far enough apart that breezes are able to pass by with minimal interference. Shade trees can be used around buildings without affecting ventilation too much if the trees are tall, the trunks are kept bare, and the trees are kept close to the building. [Diagram to come]. Dense hedges should not be placed so that they inhibit airflow through building openings, including below a structure that employs a raised floor.
  • To enhance passive cooling, landscaping efforts should be concentrated on directing breezes toward windows and doors and below the building when appropriate. To use these winds effectively, cross ventilation is necessary, and openings should be positioned opposite each other on the north and south walls.
  • Although shade plants should be placed close to the structure, they need to be far enough away so that they do not restrict air flow. Because they interfere with wind motion, avoid using low-branching trees (or remove low branches) on the southeastern and or southwestern exposures where breezes generally come from when passive cooling is most appropriate.
Directing Airflow
  • Rows of trees and hedges can be situated to direct air toward a building to enhance ventilation [Diagram to come]. It is generally best to orient rows perpendicular to the window walls to channel airflow towards openings, provided that solar control is also maintained.
  • Dense hedges can be used in a manner similar to solid building wingwalls to deflect air into the building openings. Vegetation may be used to create positive and negative pressure areas to assist ventilation or to increase the windward area of the building. While vegetation may not be as efficient as solid wingwalls in producing these effects, it can be more cost effective because larger features can be created at a lower cost.

 

Modifying Wind Velocities
  • Vegetation can create areas of higher wind velocities by deflecting winds or by funneling air through narrow openings [Diagram to come]. Narrowing the spacing of the trees used to funnel air can increase the airflow 25 percent above that of the upwind velocity. A similar effect occurs at the side edge of a windbreak.
  • Wind barriers on the north and northwest sides of the home that block colder winter winds can help push breezes from the south back toward the house during the summer. Shrubs placed near the windows can also be effective in directing air into the house.

 

Landscaping for Mechanical Cooling

During Florida's humid summers, most residents find it impossible to stay comfortable without air conditioning. In order to keep air conditioning costs to a minimum, outside air infiltration must be minimized. Wind movement around the home during warm weather can increase mechanical cooling loads and attendant energy costs by allowing warm, humid air into the home through unsealed spaces around windows and doors, and through any structural cracks. Thus, to control winds encountered during the summer months, mechanically cooled homes need windbreaks to the south to deflect and/or slow breezes.

 

Landscaping to Provide Shade

Maximize Summer Shade / Allow Winter Solar Penetration

  • In a hot, humid climate, air conditioning is likely going to be used during the summer. Natural breezes are good, but not as important as in a temperate climate. Shading is most important.
  • Large plants not only shade the ground below them, keeping it cooler; but will keep the temperature lower by not trapping and radiating heat in the same way as other surfaces, such as rock, paving, metal or glass. Plants also lower temperatures in their immediate vicinity by releasing water vapor from their leaves, a process called evapotranspiration.
  • Existing vegetation can dramatically modify temperature over a large land area. Vegetation will buffer the temperatures by keeping air slightly warmer in winter and cooler in summer.
  • Some materials will absorb and/or store, and radiate heat more than others. Materials such as metal, stone, glass, and paved areas can contribute to increased heat in a garden. The more these materials are used, the more likely a space is to warm up, and stay warm.
  • Avoid an overabundance of plantings which will raise the humidity level and reduce the cooling effect.

 

Trees

Landscaping with trees can be highly effective in shading buildings and the surrounding ground surfaces by reducing direct solar gain to the building and indirect radiation reflected upward into the building from the ground.

Using shade effectively requires knowing the size, shape, and location of the moving shadow that a shading device casts. 3D modeling allows one to look at the building/landscape arrangement prior to committing to a scheme and make design changes accordingly.

In Florida, shading for east and west windows and walls should be given top priority. During most of the cooling season, these surfaces receive about 50% more sunshine than those facing south.

When planning a landscape design, keep in mind that trees are more effective at shading when planted close to the home. A tree planted ten feet from the west wall will shade an area four times longer than a tree planted twenty feet. A tree's shape also influences the duration of the shade. Spreading, round, and vase-shaped tree canopies will provide shade for the longest time.

Heat absorbed through windows and roofs increases solar gain. Incorporating shading concepts into a landscape design can help reduce this solar heat gain, reducing cooling costs. Trees can block up to 70 percent of the direct solar radiation and also filter and cool surrounding air through evapotranspiration.

Shading and evapotranspiration from trees can reduce surrounding air temperatures as much as 9° F (5°C). Because cool air settles near the ground, air temperatures directly under trees can be as much as 25°F (14°C) cooler than air temperatures above nearby blacktop.

Research indicates that shade has a dramatic effect on ground temperatures. When shaded, ground temperatures were found to drop an average of 3 - 6°F in only five minutes. Studies have also shown that temperatures on a forest floor can be as much as 25°F cooler than those recorded at the tree tops.

Home comfort levels and energy costs can be also dramatically affected by shade. Creative landscape planning with trees, shrubs and vines will help alter the climate outside your home and modify indoor temperatures.

Trees can be selected with appropriate sizes, densities, and shapes for almost any shading application.

 

TREE TYPES
  • To block solar heat in the summer but allow the warmth of the low-angled winter sun to penetrate, use deciduous trees.
  • Evergreen trees are used to provide continuous shade or to block heavy winds.

 

TREE SIZE
  • A properly-placed 6-foot to 8-foot (1.8-meter to 2.4-meter) deciduous tree will begin shading windows the first year. Depending on the species and the home, the tree will shade the roof in 5–10 years.
  • If large trees need to be planted, it is best to select trees that have a moderate growth rate rather than fast growing varieties. Moderate growing varieties are sturdier against storm damage, can be more drought resistant, and are generally more resistant to insects and disease. Although a slow-growing tree may require many years of growth before it shades a roof, it will generally live longer than a fast-growing tree.
  • Mature tree height should also be considered when selecting plants. In general, small- or medium-sized trees (26 - 30 feet) are preferred for shading sidewalls.

 

TREE PLACEMENT
  • The best locations for deciduous trees are on the south and east sides of a house. When these trees drop their leaves in the winter, sunlight can reach the house to help in heating the home. Note: Even without leaves, trees can block as much as 60% of the sun, making placement of trees critical to effectiveness.
  • Deciduous trees with high, spreading crowns should be located on the south side of a home to provide maximum summertime roof shading. If deciduous trees are located on the west side, choose trees with crowns lower to the ground to provide shade from lower afternoon sun angles.
  • Trees near the southeast and southwest ends of the home should have their lower branches pruned to allow in more winter sun. 
  • Trees directly south of a home should be located near the house. During summer months (in the northern hemisphere) the sun is higher in the sky and the shadow cast by a tree will fall directly under it. Planted too far away, shade from trees on the southern side will miss a home to the north entirely. In winter, the low angle of the sun will cause the tree's shadow to fall directly on the house, cooling it the entire day. Therefore, the best place to plant trees for shade is on the west (best) and east (second best) sides of the house.
  • Trees can be planted within 20ft of windows and should optimally grow 10ft taller than window height.
  • A tree that will reach a medium to large size should be located 15 to 20 feet from the side of a house and 12 to 15 feet from the corner. 
  • Smaller trees can be planted closer to a house to shade walls and windows.
  • Evergreen trees on the north side afford the best protection from cold winter winds.
  • Evergreen trees on the west side afford the best protection from the setting summer sun.

 

TREE SHAPE
  • A broader crowned tree casts a much larger shadow than a pyramidal shaped tree of the same height.

Shrubs

  • When planted a few feet away from the house, shrubs provide extra shade and control humidity without obstructing air currents.
  • Shrubs will fill in rapidly and begin shading walls and windows within a few years. However, avoid allowing dense foliage to grow immediately next to a home where wetness or humidity are problems. Landscaping in wet areas should allow winds to flow around a home, keeping it and the surrounding soil reasonably dry.
  • Avoid placing shrubs in locations that will inhibit airflow under a raised floor.

Vines

  • Trellised vines can be used to shade windows where space is limited, since they can grow in more confined spaces than trees or shrubs.
  • Evergreen vines are a good choice for providing shade along the east and west sides of the house. To take advantage of the winter sun, deciduous vines - such as wisteria - should be planted on southern exposures.
  • When trees are young and not providing much shade, vines can be used to provide shading on walls and windows.
  • Some vines will cling to any wall surface. This can harm wood surfaces.
  • Trellises placed close to the walls can be used to support vine growth without touching the walls.
  • Vines can also shade walls during their first growing season. A lattice or trellis with climbing vines, or a planter box with trailing vines, shades the home's perimeter while admitting cooling breezes to the shaded area.
  • Using vines which lose foliage in the winter can be used for summer shading as long as vine stems do not significantly block winter sun.
  • Evergreen vines will shade walls in the summer and reduce the effects of cold winds in the winter.

Arbors

  • Arbors along the sides of the house, attached or detached, will reduce temperatures, as air can pass through the arbor and be cooled by evaporation at the plant’s leaves.
  • The shade created by the arbor is also beneficial.
  • The arbor is a traditional cooling method used worldwide.

SHADING AIR CONDITIONING UNITS

  • To keep air conditioning costs to a minimum, shade the outside condensing unit. Be careful to allow sufficient room for air to move around the condenser so that it can operate at peak efficiency. Shading air conditioning units can increase their efficiency by up to 10%.
  • Shrubs or small trees can be used to shade split air conditioning or heat pump equipment that sits outside. This will improve the performance of the equipment. For good airflow and access, plants should not be closer than 3 feet to the compressor.

Managing Ground Reflectance

Heat waves rippling over a sunbaked parking lot is a familiar sight during the summer. Paved surfaces absorb the sun's heat and radiate it back into the immediate environment. Research has shown that temperatures may be 15°F to 25°F hotter over asphalt or concrete. Paved areas also store heat, radiating warmth long after sundown. Paved surfaces around the home can contribute substantially to summertime heat loads. Planting groundcovers around paved areas can help reduce these temperatures and provide a unifying element in a total landscape planting.

Natural ground covers tend to be less reflective than bare soil or manmade surfaces, thereby reducing ground-reflected radiation. Ground-reflected light represents 10-15 % of the total solar radiation transmitted on the sunlit side and may account for greater than 50% of the total radiations transmitted on the shaded side. Some portion of this radiation can provide desirable daylighting within the building, but glare and total solar gain are usually greater problems in hot climates. In general, trees, shrubs, and other irregular vegetation have lower reflectivity than planar vegetated surfaces such as grass.

Trees, shrubs, and groundcover plants can also shade the ground and pavement around the home. This reduces heat radiation and cools the air before it reaches your home's walls and windows. Use a large bush or row of shrubs to shade a patio or driveway. Plant a hedge to shade a sidewalk. Build a trellis.

 

Landscaping to Provide Shelter

WINDBREAKS

Windbreaks are typically used in cold climates to reduce the effect of winter winds, and are used in Florida to minimize the effects of winter frontal winds that come from the northwest. Additionally, windbreaks are also beneficial during Florida’s summer months as they can aid in reducing the effects of warm, moist breezes around a mechanically cooled  house.

During colder months, a windbreak can lower the wind chill near a building. Wind chill occurs when wind speed lowers the outside temperature. A windbreak will reduce wind speed for a distance of as much as 30 times the windbreak's height. However, for maximum protection, windbreaks should be located at a distance from a building of two to five times the mature height of the trees. [Diagram to come]

The best windbreaks block wind close to the ground by using trees and shrubs that have low crowns. Dense evergreen trees and shrubs planted to the north and northwest of the home are the most common type of windbreak. Trees, bushes, and shrubs are often planted together to block or impede wind from ground level to the treetops. Evergreen trees combined with a wall, fence, or earth berm (natural or man-made walls or raised areas of soil) can deflect or lift the wind over the home.

In addition to more distant windbreaks, planting shrubs, bushes, and vines next to the house creates dead air spaces that insulate your home in both winter and summer. Plant so there will be at least 1 foot of space between full-grown plants and the home's wall.

 

Windbreaks can protect both buildings and open spaces from hot or cold winds. Vegetation is more effective at absorbing wind energy than solid objects, such as buildings, which primarily deflect the wind. A windbreak of vegetation creates areas of lower wind velocity in its lee by:

  • Deflecting some of the wind over the windbreak and the zone immediately to the leeward of the barrier
  • Absorbing some of the air's momentum
  • Dissipating some of the air's directed momentum into random turbulent eddies.

The characteristics and resulting effects of windbreaks should be considered both when a windbreak is a desired design component as well as when they present undesirable conditions that inhibit airflow around a building.

 

Effect of the Dimensions of a Windbreak on Sheltered Areas
  • The leeward sheltered area varies with the length, height, depth and density of the windbreak. As the height and length of the windbreak increase, so does the depth of the sheltered area. The sheltered area also increases with windbreak depth, up to a depth of two windbreak heights (2H). If the windbreak depth is increased beyond 2H then the flow "reattaches" to the top of the windbreak and the length of the sheltered area decreases. [Figure 10 to come] An area of slightly lowered velocity also exists for 10H in front of the shelterbelt or windbreak. [Figure 11 to come]
  • The effective zone of protection for a windbreak can be 30 times the height of the trees. However, the maximum protection occurs within 5 - 7 times the tree height. For example, if the windbreak will be 25 feet tall, it should be placed from 125 to 175 feet from the house. [Diagram to come]

 

Effect of the Porosity of a Windbreak on Sheltered Areas
  • The extent of the sheltered area produced also varies with the porosity of the barrier. Porous barriers cause less turbulence and can create a greater area of total shelter (reduced speeds) than solid barriers. The more solid the barrier, the shorter the distance to the point of minimum wind velocity and the greater the reduction in velocity at that point. The velocity, however increases more rapidly downwind of the minimum point providing less sheltered area than behind a more porous barrier.[Figure 11 to come]
  • If a sheltered area is desired for a hybrid house, it is recommended that the landscaping be designed to allow for reduced velocities without large scale turbulence. To achieve this, windbreaks should be at least 35 percent porous. The windbreak is most effective when the building it is to protect is located within 1-1/2 to 5 heights of the windbreak.

 

Wind Incidence Considerations
  • The incidence angle of the wind also affects the length of the sheltered area.
  • Tree and hedge windbreaks are most effective when the wind is normal (perpendicular) to the windbreak.
  • If the wind approaches a windbreak at an oblique angle, the sheltered area is reduced. [Figure 12 to come]

 

Types of Vegetation used for Windbreaks
  • Full evergreens with low branches provide the greatest protection from the chilling northern winds.
  • Hedges provide a more pronounced sheltering effect than trees because they have foliage extending to the ground level. In fact, the flow beneath the branches (around the trunks) of trees can actually be accelerated above the free wind speed upwind of the tree. [Figure 13 to come]

 

Characteristics of an effective windbreak:

  • The windbreak extends to the ground.
  • Foliage density on the windward side is optimally 60%.
  • Two to three rows of evergreen trees in staggered order should be used. If using deciduous trees, there should be five to six rows.
  • The length of a windbreak should be 11.5 times the mature width of the stand of trees.
  • The tree heights within the windbreak should be varied. 

 

OTHER GENERAL CONCEPTS APPROPRIATE TO ENCLOSED LANDSCAPED SPACES E.G., COURTYARDS

  • Increasing the biological mass within a garden, will tend to decrease high temperatures.
  • Incorporating material that does not retain heat will also tend to reduce temperatures (e.g., wood furniture or pavers will keep a courtyard space cooler than masonry or metal).
  • Creating ventilation helps take heat from a space (i.e., if air can move freely through a garden, cool air will move in to replace hot air). Larger, more open spaces allow better air flow.
  • More psychologically than functionally in humid regions, water is useful in cooling an area. The sound of splashing water induces a perception of cooler environments.
  • Consider using other objects to provide shade, including pergolas, shadecloths, umbrellas, etc.

WATER CONSERVATION

First and foremost, native plants have adapted to natural water supply conditions and should be used whenever possible to effectively and efficiently control water use.

Xeriscaping is a landscaping system that promotes water conservation. It is typically thought of and used in arid regions, but its principles can be used in any region to help conserve water. The seven principles upon which it is based are:

  1. Planning and design: Provides direction and guidance, mapping your water and energy conservation strategies, both of which will be dependent upon your regional climate and microclimate.
  2. Selecting and zoning plants appropriately: Base plant selections and locations on those that will flourish in the regional climate and microclimate.
  3. Limiting turf areas: Reduces the use of bluegrass turf, which typically requires an inordinate amount of supplemental watering.
  4. Improving the soil: Enables soil to better absorb water and to encourage deeper roots.
  5. Irrigating efficiently: Encourages using the irrigation method that waters plants in each area most efficiently.
  6. Using mulches: Keeps plant roots cool, minimizes evaporation, prevents soil from crusting, and reduces weed growth.
  7. Maintaining the landscape: Keeps plants healthy through weeding, pruning, fertilizing, and controlling pests.

A local region’s evapotranspiration (ET) rate determines the amount of supplementary watering a landscape requires. Evapotranspiration is the amount of water that is evaporated from the soil and transpired through the plant's leaves. The local water district or cooperative extension service can provide the ET rate. However, particular microclimates will also affect evapotranspiration in different areas of a project. Typically, it is best to water or irrigate in the early morning when evaporation rates are low. This also provides plants with water before mid-day when the evaporation rate is the highest.

 

For a list of Florida-native plants that might be considered for a local landscaping project, click here