2. Floor Systems and Foundation Support
Chapter 32
Floor Systems and Foundation Support

3. Links for Chapter 32 Slab Construction Reinforcing Concrete
Crawl Spaces

5. Three Types of Foundations
Types of foundations.  There are three basic types of foundations.  They are: Perimeter.  A perimeter foundation creates a crawl space under the house.  Most perimeter foundations are made of poured concrete or concrete block, although it is not unusual to find brick foundations in older buildings.  Separate piers support girders and other concentrated loads within the perimeter. Slab.  A slab built on grade functions as both the foundation and floor system.  It is an economical type of foundation but can only be built in areas where soil conditions will permit construction.  The slab must have deep footings under all the perimeter and bearing walls, and should always be at least 8 inches above grade. Basement.  A basement foundation has higher walls than a perimeter foundation.  It is built on a footing and has separate footings for support columns.  The basement floor usually consists of a concrete slab poured after the footings and walls are completed.

6. Block Foundation Type

7. Concrete Slab

8. Foundations

9. Wall Section

10. Foundations Images

11. Concrete Slab Foundation

12. Foundation & ½ Wall Section

13. Sources

14. 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

15. 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

16. Slab Construction

17. Slab Construction 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

18. 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

19. 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

20. 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

21. Reinforcing Concrete

22. 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

23. 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

24. 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

25. Reinforcing Concrete

26. 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 ( fixture kept in Plan)

27. Reinforcing Concrete

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

29. 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

30. Crawl Spaces

31. 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

33. Crawl Spaces

34. Crawl Spaces

35. 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

36. Crawl Spaces

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