Building Foundations
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Transcript of Building Foundations
Building Foundations
Foundation Walls
Footings
A base
Monolithic construction
Independent construction
Foundation-Wall Footings
Spread footings
Undisturbed soil
Footing Design
Prevent settling or cracks
Minimum of 12” below grade. Below frost line
Thickness = thickness of foundation wall
Width = 2x thickness of foundation wall
Footing Reinforcement
Rebar embedded 2 lengths of ½”
diameter (#4) rebar
Positioned minimum of 3” above bottom
Footing Forms
Form steel, lumber, or
combination of lumber & plywood.
Keyway
Other Types of Footings
Pier and post
Stepped Footings
Footing Drains
4” diameter pipes at base of footing
Carries water away from house.
Sloped at least 1/8” per foot
Landscaping Fabric
Poured-Concrete Foundation Walls
Durable & water resistant
Most building sites Support any type of
house 8 –10” thick Min. compressive
strength 2500 psi Most 8’ high
Full Height Walls
Formwork
Reusable forms
Wales
Standard Wall Forms
Wood or metal Built on site Prefabricated
forms Snap-ties 3 –7 days
Insulating Wall Forms
ICFs (Insulating Concrete Forms)
Permanent Basic
components planks, sheets, or
hollow blocks Standard wall Grid wall
Placement
Poured continuously without interruption
Cold joint Water content Remove Air pockets Concrete vibrator
(stinger)
Crawl-space Walls
Advantage – reduced cost
Soil cover Ventilated Insulated Piers support
Reinforcing Concrete Walls
Rebar centered in wall
Lintel
Sill Plate Anchors
Anchor bolts
Metal strap anchors
Sill sealer
Foundation Wall Details
Special features:Brick-veneer
sidingUtility Sleeves
Foundation Vents And Windows Metal vents
Rust-resistant steel frame windows
Wood framing (pressure treated)
Beam Pockets
Girder flush with top of sill plate
Stripping and Maintaining Forms Wood wedges (no
metal pry bars)
Stiff bristle (not wire) brush
Form-release agent – Bio-slick
Moisture Protection
Bituminous (tar) coating
Top of footings to finished grade level
Backfilling
Filling in excavation area
Too soon, push in foundation walls
First floor framing Temporary
bracing
Concrete Block Walls
Popular for foundation walls
No formwork Blocks
inexpensive Work stopped
and started
Concrete Block Basics
Concrete Masonry Unit (CMU)
Head Joint Bed Joint Common bond Pilasters Protect from
freezing & moisture
Cutting Block Brick hammer
and chisel
Portable masonry saw
Mortar Mortar bond
strength depends on: Type & quantity Workability, or
plasticity Surface texture
bedding areas Rate at which
masonry units absorb moisture from mortar
Water retention Skill of person laying
block
Mortar Mixtures
Portland cement, hydrated lime, sand, & water.
Prepackaged mortar mix Type N Type M Type S Type O
Mixing and Placing Mortar
Evaporation Hydration 2 ½ hour when air
temp is 80ºF or higher
3 ½ hours when air temp is below 80ºF.
Laying Block Foundation Walls
Skilled masons
Corners built first
Story pole (course pole)
Intersections
Control joint
Tooling the Joints
Weather tight joints & neat block walls
“Thumbprint hard” Tooling compacts Head joints, then
bed joints
Completing the Walls
Hollow block walls capped
Strengthened with rebar
Moisture Protection
Damp proofed or waterproofed
Parging
Radon
Colorless & odorless radioactive gas
Extremely toxic Lung cancer Soluble in water 9X heavier than
air
Radon-Resistant Construction
Gas-permeable layer
Soil-gas retarder Sealants Vent pipe Cap course
Review1. What is the minimum depth required for an
exterior-wall footing?2. Describe the type and position of reinforcement
that is commonly added to strengthen a footing.3. What is a keyway and how is it formed?4. For nearly all poured-concrete foundation walls,
formwork must be constructed for each wall face. What holds the formwork together?
5. What creates a cold joint?6. Why are the joints in a concrete block wall
tooled?7. When using mortar, why is it helpful to know the
differences between hydration and evaporation?