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Chapter 34

Chapter 34. Floor Systems and Foundation Support. Introduction. Common types of floor systems used in residential construction: Floor systems built at grade level Floor systems with a crawl space or basement below the floor system. On-Grade Foundations.

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Chapter 34

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  1. Chapter 34 Floor Systems and Foundation Support

  2. Introduction • Common types of floor systems used in residential construction: • Floor systems built at grade level • Floor systems with a crawl space or basement below the floor system

  3. On-Grade Foundations • Concrete slab is often used for floor system • Provides a firm floor system • Little or no maintenance • Generally requires less material and labor • Poured as extension of foundation wall and footing • Monolithic construction • 3 ½" is the minimum thickness allowed by the IRC for residential floor slabs

  4. On-Grade Foundations (cont’d.) • Slab joints • Used to prevent cracking

  5. On-Grade Foundations (cont’d.) • Slab placement • May be placed above, below, or at grade level • Residential slabs are often placed above grade for hillside construction • Slabs built below grade are most commonly used in basements • When used at grade, the slab is usually placed just above grade level

  6. On-Grade Foundations (cont’d.) • Slab preparation • Slab is built at grade • About 8" to 12" of topsoil and vegetation is removed to provide a stable, level building site • Excavation extends about 5' beyond building size • Most codes require the slab to be placed on a 4" minimum base of compacted sand or gravel fill

  7. On-Grade Foundations (cont’d.) • Slab reinforcement • If slab is placed on 4“ or more of uncompacted fill, welded wire fabric should be specified • Spacing and sizes are identified by style and designations • Refer to the text for ACI placement guidelines

  8. On-Grade Foundations (cont’d.) • Post-tensioned concrete reinforcement • Allows concrete slabs to be poured over unstable soil • Flat or ribbed slab

  9. On-Grade Foundations (cont’d.) • Moisture protection • Slab must be placed over 6-mil polyethylene sheet plastic • Slab insulation • Depends on location • Insulation can be placed under the slab or on outside of stem wall

  10. On-Grade Foundations (cont’d.) • Plumbing and heating requirements • Ducts must be placed under the slab before concrete is poured • For residential plans, plumbing is usually not shown on foundation plan • Drawings for commercial construction include a plumbing plan and a mechanical plan

  11. On-Grade Foundations (cont’d.) • Changes in floor elevation • Floor level may be required to step down to meet design needs

  12. On-Grade Foundations (cont’d.) • Slab foundation • Refer to the text for: • Common components shown on slab foundation • Common components specified by note only on a slab foundation

  13. Crawl Space Floor Systems • Crawl space • Area between floor system and ground • Building codes require a minimum of 18" from the bottom of floor to ground • 12" from the bottom of beams to ground

  14. Crawl Space Floor Systems (cont’d.) • Joist floor framing • Floor joists span between foundation walls • Plywood floor sheathing is installed to provide a base for the finish floor • When distance between the walls is too great for floor joists, a girder is used for support • Concrete pier is placed under intermediate girder supports to resist settling

  15. Crawl Space Floor Systems (cont’d.) • Joist floor framing (cont’d.) • Refer to the text for: • Common components shown for a floor joist system • Common components specified by note only for a floor joist system

  16. Crawl Space Floor Systems (cont’d.) • Post-and-beam floor systems • Built using a standard foundation system • Series of beams support subfloor • Once the mudsill is bolted to foundation wall, the beams are placed flush with the mudsill top • Beams are supported by wooden posts • Each post is supported by a concrete pier

  17. Crawl Space Floor Systems (cont’d.) • Post-and-beam floor systems (cont’d.) • Refer to the text for: • Common components shown for a post-and-beam system • Common components specified by note only for a post-and-beam system

  18. Crawl Space Floor Systems (cont’d.) • Combined floor methods • Floor and foundation methods may be combined depending on the building site • Typically done on partially sloping lots when part of a structure is constructed with a slab and part with a joist floor system

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