CLIMATE AND SITE CONDITIONS
VEGETATION / LANDSCAPE

GOAL:

To become aware of the importance of vegetation/landscape when designing an energy efficient home.

OBJECTIVE:

The student will be able to list ways that vegetation and landscaping can increase the energy efficiency of a structure.

GLOSSARY:

Venturi Effect - When moving air is channeled to pass through a smaller space or opening, the velocity of the air will increase.

Permeability - The ability to allow liquids or gases to seep through small openings.

Deciduous - The ability of a tree to lose its leaves in the fall.

LESSON / INFORMATION:

When designing an energy efficient building, a clear understanding of the environmental factors that affect the building site is needed. These factors will differ from summer to winter. The fall and spring are similar and provide the third climate season. The design should incorporate those positive elements the environment has to offer and protect against those that are detrimental to comfort.

Vegetation is one of the greatest assets of the site for a natural, energy-efficient design. Not only is the existing vegetation useful, but it can be added to, transplanted, or eliminated. Even though it might take time to mature, the landscape is fairly flexible. Selective planting, in terms of growth rates, can reduce the time element.

Vegetation reduces the temperature while providing protection against glare, dust, and erosion. Care should be taken to avoid placement where roots can damage foundation and clog drainage lines, where leaves can block gutters and trap moisture, and where desirable air movement can be drastically reduced or directed the wrong way.

Summer.

Shading is one of the most important advantages of landscaping. The existing landscape can be drawn directly on the sun path graphs in Appendix C. This will indicate the shading pattern at that location, and the need to add landscaping to maximize shading. Generally, keeping the sun off the building for the warmest months of the year will be most beneficial. The need for the sun during the colder months for the additional heat should also be considered. Deciduous trees work best since they will grow leaves in the summer and lose them in the winter.

For shading on the south side, the tree placement would have to be too close to the building because the sun is high in the sky. Vegetation functions best when used on the east, northeast, west and northwest sides, and away from the building. The west side is more critical because the skies are usually clear in the afternoon, providing the greatest opportunity for heat gain. Morning skies are often overcast or foggy, and it may be 10:00 a.m. before skies are clear.

A parking lot should be shaded, especially if it is on the side where natural ventilation will be introduced. Shading the parking lot will reduce the surrounding temperature. Newer porous structural pavement allows grass to grow up through the surface, thereby reducing temperatures.

Ventilation can be greatly enhanced with the use of vegetation. Strategies to increase ventilation could be better understood if the building was operated through one cooling season. Prior to designing the landscape patterns, actual condition assessment of the building site environment will provide greater insight into landscaping potential.

The air introduced into the building should pass under a high canopy cover or at least over a grassy area. This will provide cooler air for ventilation. Air passes through and over a heavily wooded area in various patterns. The air movement closer to the ground is 25 to 50 percent less than that above the trees. A small cut or clearing will create eddies that can make the air movement near the ground move in the opposite direction as those of the prevailing winds. Similar effects can occur in an urban area because of the variation in building forms.

Vegetation can be used to redirect the flow of air and channel it to specific areas or locations on the site. The "Venturi effect" can also be created to increase the velocity of air movement in the area of the structure.

Winter.

Vegetation should not block the sun during the heating season. Try to keep all trees out of the winter sunpath, but if tree use cannot be avoided, use deciduous trees. Vegetation is best used in the winter to protect the building from the cold winds that remove heat. A difference exists between the protection offered by windbreaks composed of plants and that offered by solid screens, fences, walls, or other buildings. The extent of shelter depends not only on height but also on the degree of permeability. Plant materials, which permit a certain amount of air to pass through, cause less turbulence than solid screens, and they result in a greater total area of shelter from the wind.

The shelter zone just behind the windbreak gives the greatest protection. The lowest wind speed will occur at a distance of about three or four times the height of the screen, depending on its density (see Figure 1). The more penetrable the screen is, the shorter the distance to the point of maximum wind velocity and the lower the protection. Care must be taken so winter windbreaks do not prevent the breezes desired in the summer, spring, and fall.

Figure 1.

ACTIVITY:

1. For the site plan given, locate vegetation around the house to provide for summer sun protection (shading) and winter wind protection. Remember that during the winter the house should not be shaded, but receiving heat from the sun.

INFORMATION CHECK:

Indicate whether the statements below are TRUE or FALSE.

1. Vegetation reduces temperatures but does not protect against glare and dust.

2. Ventilation can be greatly enhanced with the use of vegetation.

3. Care should be taken to avoid placement of vegetation where roots can do damage to the foundation of a building or clog drainage lines.

4. To keep the sun off the building during the summer but all the sun through during the winter, plant evergreen trees near the building.

5. Vegetation reduces the erosion of soil.

6. Air introduced into a building should pass over concrete before entering the building.

7. Vegetation can be used to redirect the flow of air and channel it to specific locations on the site.

8. Vegetation is best used in the winter to protect the building from the cold wind that removes heat.

9. The shelter zone just behind the windbreak gives the least protection.

10. The air movement closer to the ground is 25 to 30 percent more than above the trees.

TEACHER'S NOTES:

1. You can create other site plans in addition to the one given.

2. Have the students display their solutions so each can see what the others have done.

3. Have a discussion with the students about what works best and why.

ANSWERS TO TRUE/FALSE:

1. False

2. True

3. True

4. False

5. True

6. False

7. True

8. True

9. False

10. False

RECOMMENDED READING:

Natural Louisiana Architecture. Cazayoux, Hebert and Winn. Baton Rouge, LA: Louisiana Department of Natural Resources, 1991.

Site Analysis. E.T. White, Tucson, Arizona: Architectural Media Ltd. (Published), 1983.

REFERENCES:

Natural Louisiana Architecture. Cazayoux, Hebert and Winn. Baton Rouge, LA: Louisiana Department of Natural Resources, 1991.

Comments or questions to: TechAsmt@LA.GOV

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