INSULATED SHEATHING

GOAL:

To become aware of energy efficient design and construction that will save energy, cost less to operate and have less of a negative impact on the natural environment.

OBJECTIVES:

The student will:

1) Be able to decribe energy efficient construction techniques

2) Develop the ability to use sheathing as a method to increase the insulation value of the exterior wall.

LESSON/INFORMATION:

Many different types of building materials are used as sheathing for a house. Sheathing refers to the material on the outside of the exterior wall. One of the major purposes is to provide stability for the stud framing. It can also help carry the structural load from the floors or roof above. Most of the stability for wind shear can be provided at the corners with full sheets of plywood. Another method of stabilizing the framing system is diagonal bracing at the corners. This can be done with a 1 x 4 let-in for a 2 x 4 stud wall, a 2 x 4 let-in for a 2 x 6 stud wall, or with metal straps. Let-in means the stud is cut back so the bracing finishes flush. Let-in and metal bracing also provides the opportunity to tie the wall system to the foundation by nailing to the sole plate, and this should always be done. In these situations the sheathing is used as insulation to increase the R-value of the exterior wall.

There are many different types of insulated sheathing boards which come in various thicknesses and all have different insulation values (R-value). If the exterior wall is made with 2 x 6 studs, then the need for extra insulation is less justified, but for a 2 x 4 stud wall it can use the added insulation. It is recommended that the R-value for a wall in Louisiana be R-19.

Insulated sheathing boards can have a reflective foil surface (radiant barrier) on one side or both sides. It reflects the shortwave radiant energy from the sun that penetrates the exterior finish. About 40% of the heat that enters the house is radiant heat and the remaining heat gain is from thermal heat moving through the building envelope. A radiant barrier works well to stop or reflect the radiant energy, and insulation is effective in controlling the thermal heat. The radiant barrier is only needed on those walls or roofs that get direct sun exposure, but it must be used with an air space. The ideal wall situation for this is a brick veneer wall where the air space already exists. For sidings, an air space must be provided. The radiant barrier must face this air space. It is also best for this air space to be ventilated and can be provided with 1 x 2 vertical nailers installed over the sheathing.

INFORMATION CHECK:

A. Please indicate whether the statements below are True or False.

1. Sheathing is placed on the inside of the stud wall.

2. Sheathing can provide wind bracing for the wall.

3. Diagonal bracing can provide this same stability against wind shear.

4. Let-in bracing means the bracing is put on the inside of the wall.

5. Insulated sheathing should only be used with diagonal bracing.

6. Insulated sheathing can increase the R-value of the wall.

7. Insulated sheathing comes in only .5" thickness.

8. Insulated sheathing comes in different R-values.

9. A radiant barrier stops radiant heat but not thermal heat.

10. A radiant barrier must face an air space.

B. Fill in the blanks.

1._______ is the exterior cover for a stud wall.

2. Sheathing provides structural _______ for the wall.

3. Another method of stabilizing the exterior wall is with_______ bracing.

4._______ means the stud is cut back so the bracing finishes flush.

5. The foil surface on some rigid insulated sheathing is called a _______ barrier.

6. About_______% of the heat reaching the interior of the house is radiant heat.

7. It is important to have the radiant barrier facing an _______ space.

8. It is best if the air space is _______.

TEACHER'S NOTES:

The sheathing and corner bracing is used to prevent racking due to wind loads. Racking refers to the twisting of the structure by the wind. Therefore, it is not necessary to test the corner sections for gravity leads from above.

ANSWERS TO TRUE/FALSE:

1. False

2. True

3. True

4. False

5. True

6. True

7. False

8. True

9. True

10. True.

ANSWERS TO FILL-IN-THE BLANKS:

1. Sheathing is the exterior cover for a stud wall.

2. Sheathing provides structural stability for the wall.

3. Another method of stabilizing the exterior wall is with diagonal bracing.

4. Let - in means the stud is cut back so the bracing finishes flush.

5. The foil surface on some rigid insulated sheathing is called a radiant barrier.

6. About 40% of the heat reaching the interior of the house is radiant heat.

7. It is important to have the radiant barrier facing an air space.

8. It is best if the air space is vented.

RECOMMENDED READING:

Energy Efficient Florida Home Building. K. Sheinkopt and R. Vieria. Cape Canaveral, FL: Florida Solar Energy Center, 1988.

REFERENCES:

"The Comfort Zone".....E.J. Cazayoux, USL Monthly Press Release.

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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