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?