Chapter 32 Floor Systems and Foundation Support

2 Links for Chapter 32 Slab Construction Reinforcing Concrete Crawl Spaces

3 Slab Construction Most foundation floors are concrete slabs –Usually 5” or 6” thick –Does not support walls –Poured as an extension of the foundation wall and footing

4 Slab Construction Slab joints help control natural expansion and shrinkage of concrete slabs –Control joints are cut 6-8 hours after concrete is poured to be sure cracking occurs along the cut –Isolation joints separate a slab from another slab, wall, column or other structural part –Construction joints are made to support the joint between two slabs

5 Slab Construction

6 Slabs are placed above, below, or at grade level –Above grade slabs are indicated with a note –Below grade slabs are used in basements –At grade level slabs must be at least 8” above the grade to keep away from moisture

7 Slab Construction Slabs are poured after the footings have been set At least 4” of sand or gravel fill is placed under the slab Slab fill is given as a note on the plans

8 Reinforcing Concrete To help resist cracking, welded wire fabric is placed in the slab and noted as: –6 X 12—W16 X W8 6 = longitudinal wire spacing 12 = transverse wire spacing 16 = longitudinal wire size 8 = transverse wire size

9 Reinforcing Concrete To help resist cracking, welded wire fabric is placed in the slab and noted as: –6 X 12—W16 X W8 W indicates smooth wire D represents deformed wire

10 Reinforcing Concrete

11 Reinforcing Concrete To resist expansive soil, steel reinforcing bars are added to the slab –A 3” minimum coverage is needed if concrete is exposed to earth –A 2” minimum coverage is needed in basements –A 1 1/2” coverage is needed when concrete is not exposed to earth

12 Reinforcing Concrete Post-tensioning is used when concrete is poured on unstable soil Steel tendons are placed in the concrete as it is poured About 3 to 10 days later the tendons are stretched creating an internal compressive force that helps the concrete resist cracking

13 Reinforcing Concrete Flat slab and ribbed slab are most common forms of post-tensioned concrete –Flat slab tendons range from 3/8” to 1/2” and are spaced 5’-0” to 9’-0” apart –A ribbed slab uses ribs or beams under the slab to reduce the span of the slab over the soil and increase support

14 Reinforcing Concrete

15 Reinforcing Concrete Slabs are placed on 6 mil polyethylene sheet plastic to protect against ground moisture Depending on the climate, additional rigid insulation is added under the slab Plumbing and heating components are placed under the slab

16 Reinforcing Concrete

17 Reinforcing Concrete Dimensions are added to these components –Outline of slab –Interior footing locations –Changes in floor level –Floor drains –Exterior footing locations

18 Crawl Spaces Crawl spaces are at least 18” from bottom of floor and 12” from bottom of joists Floor joists span the foundation walls –Usually build from 2 X 6 to 2 X 12 or from engineered lumber –Nailed to pressure-treated sill plate or flush to the sill plate

19 Crawl Spaces

20 Crawl Spaces A plywood subfloor is placed on the joists Girders are used if the joist span distance is too great and are supported by a pier

21 Crawl Spaces

22 Crawl Spaces

23 Crawl Spaces Beams are used instead of joists in post-and- beam construction The subfloor is made of 2 X 6 T & G boards or 1 1/8” plywood Subfloor is glued to the beams Beams are supported by posts if span is too great

24 Crawl Spaces

25 Crawl Spaces If the site is sloped the floor and foundation methods can be combined