PPP Notes - Basement Walls

BASEMENT CONSTRUCTION

 (These notes are compiled from AGS)

BASEMENT WALL CONSTRUCTION

 

• Basement walls may be constructed of various materials, including concrete, masonry and wood.

 

CONCRETE BASEMENT WALLS

 

• Concrete basement walls may be either cast-in-place or precast.
• Cast-in-place concrete basement walls provide a cost-effective means of supporting a floor and resisting soil pressures.
• Commercial and residential applications of cast-in-place concrete basement walls are prevalent.
• Forms are easily placed in the excavation on the footings
• Reinforcing steel may be tied on or off-site, and is placed within the wall formwork.
• Depending on the soil and groundwater conditions, dampproofing should typically be used on foundation walls and waterproofing is generally required on basement walls prior to backfilling.
• Unless lateral bracing is utilized, the top of the basement wall must be supported by the first floor and the base of the wall by the footing or slab-on-grade before backfilling against the wall can begin.
• Keeping the wall heights uniform, as well as reducing the number of penetrations and maintaining a simple plan configuration, will help reduce the final cost of the wall.
• Precast concrete basement walls enable basement walls enable construction in less time than conventional cast-in-place concrete.
• In addition to the time and construction methods other advantages of precast concrete include the ability the ability of the precast supplier to utilize concrete admixtures that focus on ultimate strength, rather than cure time and temperature.
• Precast concrete manufacturers are able to produce mixes that cure to 5000 psi, which is stronger than concrete unit masonry or cast-in-place concrete walls.
• Additionally, better control of the concrete mixture and curing environment allows the use of low water/cement ratios, which results in a dense material that reduces water penetration.

 

MASONRY BASEMENT WALLS

 

• Masonry walls have long served as foundations for structures.
• Today, most masonry basement walls consist of a single wythe, or hollow, solid concrete masonry units, depending on the required bearing capacity.
• The walls are reinforced as necessary to resist lateral loads.
• Generally, such reinforcing should be held as close to the interior face shell as possible, to provide the maximum tensile strength.
• Basement walls should protect against heat and cold, insect infestation (particularly termites), fire, and penetration of water and soil gases.
• If radon is a major concern, the top course of the masonry and the course of masonry at or below the slab should be constructed of solid units or fully grouted hollow units using foundation drain to collect and drain condensation moisture from basements, should be avoided in areas where soil-gas entry is a concern.
• Architectural masonry units may be used to improve the appearance of the wall.
• Masonry units with architectural finishes facing the interior can be used for economical construction of finished basement space.
• Masonry easily accommodates any floor plan, and returns and corners increase the structural performance of the wall for lateral load resistance.

 

TREATED WOOD BASEMENT WALLS

 

• The construction of treated wood foundations and basement is similar to the construction of standard wood light-frame walls except for two factors:
• The wood used is pressure-treated with wood preservatives.
• The extra loading and stress requirements caused by below-grade conditions must be accommodated in the design and detailing of the fasteners, connections, blocking, and wall corners.
• As with standard masonry or concrete foundations, treated wood foundations require good drainage to maintain dry basements and crawl spaces.
• However, the drainage system typically used with treated wood foundations is different from that used with masonry or concrete systems.
• The components of a drainage system suitable for use with treated wood foundation include:
• A highly porous backfill material, which directs water down to a granular drainage layer.
• A porous granular drainage layer under the entire foundation and floor to collect and discharge water.
• Positive drainage of water by means of a sump designed for the soil type.  This drainage system (developed for treated wood foundations) takes the place of a typical porous backfill over a perimeter drainage pipe.
• Benefits of a treated wood foundation include system:
• All framing is standard 2 by construction.
• Treated wood foundations can be erected in any weather and when site access for other methods is difficult.
• Deep wall cavities allow use of high R-value thermal insulation without loss of interior space.
• Wiring and finishing are easily achieved.
• Considerations when working with treated wood foundations:
• Treated wood foundations are not appropriate for all sites.  Selection of the proper foundation for a project depends on site conditions, including soil types, drainage conditions, groundwater, and other factors.  Wet sites in low areas (especially areas with coarse-grained soil) should be avoided if a full basement is desired, although a crawl space type foundation can be used in these cases.  Consult a geotechnical engineer to determine the viability of any foundation system.  Also, refer to the wood deterioration zones in all fifty states.  Lumber and plywood used in treated wood foundations must be grade-stamped for foundation use.  These are typically pressure treated with chromated copper arsenate.  Treated wood products used in foundation construction are required to contain more preservatives than treated wood used in applications such as fencing and decking.  Codes generally call for hot-dipped, galvanized fasteners above grade and stainless steel fasteners below grade.
•  Avoid skin contact and prolonged or frequent inhalation of sawdust when handling or working with any pressure-treated wood product.
• Consult applicable building codes and the American Forest Paper Association’s Permanent Wood Foundation System – Design, Fabrication, Installation Manual for requirements and design guidelines.
• In the early stages of a project, consult with the building code officials for the area or jurisdiction to assess their familiarity with and willingness to approve this type of construction.
• The vertical and horizontal edge-to-edge joints of all plywood panels used in these systems should be sealed with a suitable sealant.
• Correct materials and details of construction are very important for treated wood foundations.  If the contractor to be used for the installation is unfamiliar with this foundation type. The design should include the use of shop-fabricated foundation panels.  Most problems with treated wood foundations can be traced to improper installation by inexperienced workers.
• This type of foundation depends especially on the first-floor deck to absorb and distribute any backfill loads; therefore, backfilling cannot occur until the first floor deck is complete unless lateral bracing is provided.