Drainage, Insulation, and Concrete Slabs

Transcription

1 Drainage, Insulation, and Concrete Slabs UNIT Drainage After the foundation walls are erected and before the excavation outside the walls is backfilled (filled with earth to the finished grade line), footing drains, if indicated, must be installed. Footing drains are usually perforated plastic pipe placed around the footings in a bed of crushed stone, Figure If the site has a natural slope, the footing drains can be run around the foundation wall to the lowest point, then away from the building to drain by gravity. In areas where there is no natural drainage, the drain is run to a dry well or municipal storm drain. At one time, clay drain tile was the most common type of pipe for this purpose. However, perforated plastic pipe is used in most new construction. Plastic drain pipe is manufactured in 10-foot lengths of rigid pipe and in 250-foot rolls of flexible pipe, Figure An assortment of plastic fittings is available for joining rigid plastic pipe. When footing drains are to be included, they are shown on a wall section or footing detail, Figure A note on the drawing indicates the size and material of the pipe. If the floor drains are to be included in concrete-slab floors, they are indicated by a symbol on the appropriate floor plan, Figure If these floor Objectives After completing this unit, you will be able to perform the following tasks: Locate and explain information for control of groundwater as shown on a set of drawings. Locate and describe subsurface insulation. Determine the dimensions of concrete slabs and the reinforcement to be used in concrete slabs. FILTER FABRIC CRUSHED STONE OR GRAVEL Figure Footing drain. PERFORATED PLASTIC PIPE PITCHED TOWARD STORM SEWER, DRY WELL, OR SUMP Drainage, Insulation, and Concrete Slabs 89

2 Openmirrors.com Figure The floor drain is shown by a symbol. (Notice that the floor is pitched toward the drain.) Figure Plastic drain pipe. Figure Footing drains are shown outside the footing. 90 Unit 14

3 drains run under a concrete footing, the piping had to be installed before the footing was placed (see Unit 11). The riser (vertical part through the floor) and drain basin are usually set at the proper elevation just prior to placing the concrete floor. The floor plan may include a spot elevation for the finished drain, or it may be necessary to calculate it from information given for the pitch of the concrete slab. Pitch of concrete slabs is discussed later in this unit. Vapor Barriers Another technique often used to prevent groundwater from seeping through the foundation is coating the foundation wall with asphalt foundation coating. At this point, subsurface work outside the foundation wall is completed, but backfilling should not be done until the superstructure is framed. The weight and rigidity of the floor on the foundation wall help the wall resist the pressure of the backfill. If the backfilling must be done before the framing, the foundation walls should be braced. To retard the flow of moisture from the earth through the concrete-slab floor, the drawings may call for a layer of gravel over the entire area before the concrete is placed. A polyethylene vapor barrier is laid over the gravel underfill. The thickness of polyethylene sheeting is measured in mils. One mil equals 1/1,000 of an inch. For vapor barriers, 6-mil polyethylene is generally used. Insulation In cold climates, it is desirable to insulate the foundation and concrete slab. This insulation is usually rigid plastic foam board placed against the foundation wall or laid over the gravel underfill, Figure Like all materials, concrete and masonry expand and contract slightly with changes in temperature. To allow for this slight expansion and contraction, the joint between the concrete slab and foundation wall should include a compressible expansion joint material. Expansion joints can be made from any compressible material such as neoprene or composition sheathing material. This expansion joint filler is as wide as the slab is thick and is simply placed against the foundation wall before the concrete is placed. Concrete Slabs When the house has a basement, the floor is a concrete slab-on-grade. The areas to be covered with concrete are indicated on the foundation plan or basement floor plan. This is usually done by an area not giving the thickness of the concrete slab and any reinforcing steel to be used. To help the concrete resist minor stresses, it is usually reinforced with welded wire fabric. The specifications for welded wire fabric are explained in Figure Where Figure Rigid plastic foam insulation may be laid under the perimeter of the floor or against the foundation wall. Drainage, Insulation, and Concrete Slabs 91

4 Openmirrors.com Figure The callout for welded wire fabric explains the size and spacing of the wires. the slab must support bearing walls or masonry partitions, it may be haunched, as discussed in Unit 12. When floor drains are included or where water must be allowed to run off, the slab is pitched (sloped slightly). A note on the drawings indicates the amount of pitch. One-quarter inch per foot is common. When there is any possibility of confusion about which way the slab is to be pitched, bold arrows are drawn to show the direction the water will run, Figure When floor drains or forms are set for pitched floors, it is necessary to find the total pitch of the slab. This is done by multiplying the pitch per foot by the number of feet over which the slab is pitched. (See Math Review 8.) For example, if the note on a concrete apron in front of a garage door indicates a pitch of ½ inch per foot and the apron is 4 feet wide, the total pitch is 2 inches. The proper elevation for the form at the outer edge of the apron is 2 inches less than the finished floor elevation. Slab-on-grade installations may require electrical raceways to be installed in or just below the concrete slab in the crushed or gravel fill. These installations must be made so that they do not reduce the structural integrity of the concrete slab. An oversized raceway in the concrete slab may cause the slab to crack and settle unevenly. An electrician should be present during concrete placement to observe and correct any damage to these electrical raceways. All underground utility systems must be coordinated prior to starting installation, especially in commercial and industrial buildings, as discussed in Unit 11. The service entrance section may have up to six subdistribution sections or panels located throughout the building. Electrical feeders are required from the electrical service entrance section to these subdistribution sections or panels. This requires detailed coordination between the electrical installer and the other utility installers prior to starting the installation of the utility systems. The electrical installation must be laid out around the other utilities, with the other utility layouts normally having priority. The other utilities to be coordinated may include plumbing, fire sprinkler, heating and air conditioning, and specialty systems. This coordination must be done for both the underground and aboveground systems. 5" CONC. FLR. PITCH 1/8" PER FOOT Figure A bold arrow indicates the way that water will run off a pitched surface. 92 Unit 14

5 Some of the concrete work in the Lake House is of particular interest, because it is part of the passive solar heating system the Lake House uses. Section 1/4 and the lower-level floor plan 1/2 indicate that the area under the living room and dining room floors is a heat sink. A heat sink is a mass of dense material that absorbs the energy of the sun during the day and radiates it at night. The living room and dining room are on the south side of the Lake House. In the winter, when the leaves are off the deciduous trees, the sun shines in the large areas of glass in these rooms and warms the heat sink. At night, this heat is radiated into the house to provide additional heat when it is needed most. The floor over the heat sink is a concrete slab similar to that used in the playroom. Detail 2/5 helps explain this concrete slab. CHECK YOUR PROGRESS Can you perform these tasks? Describe the footing drains shown on a set of construction drawings. Name the material and its thickness when foundation insulation is shown. Describe any vapor barriers or foundation coating to be applied to the foundation or under concrete slabs. List the dimensions of any concrete slab floors shown on the drawings. Describe the reinforcement to be used in concrete slabs. Explain the pitch of a concrete slab to provide for drainage. ASSIGNMENT Refer to the Lake House drawings (in the packet) to complete this assignment. 1. What is the thickness of the concrete slab over the heat sink in the Lake House? What is the largest raceway (conduit) that could be installed in this slab? 2. Describe the reinforcement used in the concrete slab in the playroom of the Lake House. 3. How many square feet of 2-inch rigid insulation are needed for the Lake House heat sink? 4. What prevents moisture from seeping through the concrete slab floor in the Lake House? 5. What is the finished floor elevation of the Lake House garage? 6. What is the elevation of the floor drain in the utility room of the Lake House? 7. What is the purpose of the 8-inch-thick concrete haunch in the middle of the Lake House slab? 8. How many cubic yards of concrete are required for the garage floor? The basement floor? Drainage, Insulation, and Concrete Slabs 93