Module 3 - Foundation Systems

Part 3.2 - Concrete Foundation System

Select Content From the Index Below or Scroll Down:

• Introduction
• Concrete Footings
• Strip Footings
• Column Footings
• Step Footings
• Foundation
• Foundation Damproofing
• Foundation Details

Reading Preparation / Review
Page 26-34	WebCT Site Canadian Wood-Frame House Construction Historic Concrete Home in Toronto

Introduction

Concrete foundations consists of footings, foundation wall, concrete slab on grade, weeper tile and damproofing system.

Source: Illustrated Residential and Commercial Construction, Peter Mann, page 5-10

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Concrete Footings

Types of footings (mouse over):

Purpose of footings is to distribute the weight of the house to the soil below.

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Strip Footings

Strip Footings support foundation walls.

Concrete strip footings should be a minimum depth for frost protection.

General rule of thumb for footing width is that footing should project beyond each side of the wall at least 4 in. (100mm). Therefore a 10" (250mm) thick wall will require the following width of footing to support it: 4" + 10" + 4" = 18" = 1'-6" wide (100mm + 250mm + 100mm) = 450mm wide

	Footing Form Layout A nail is installed to locate the corner of the foundation wall. The footings will be off-set by 100mm (4") from this nail. This illustration shows forms, setting-nail and the nail in the footing to be used for setting the foundation wall.
	Strip Footing Forms Lumber is used as forms for the sides of the strip footings. Forms will be leveled and a wood spread used to keep the forms at the right width.
	Concrete Strip Footing Strip footing has been formed, poured and stripped. Mouse-over shows a closeup of the keyway in the footing to be used as a lock for the foundation wall system.
	Concrete Strip Footing -Services Strip Footing forms are in-place and the sewer service is installed under the footing. The mouse-over illustrates the concrete strip footing has been poured and stripped.
	Concrete Strip Footing - Weeper Tile Strip footing intersection. Note the a section of weeper tile is embedded into the concrete. This allows the weeper tile to run around the perimeter of the foundation and pass through the footing.
	Gravel under Concrete Slab Granular base can be placed inside the strip footings where the concrete slab on grade will be placed. Note: Do you think the strip footings look wavy to you?

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Column (Pad) Footings

A Column (Pad) Footing is used to support a point load such as a steel column under a beam.

The size of a pad footing depends on the load (# floors) it is supporting.

	Pad Footing Forms Pad footing forms are built and set-in place. At a close look a red spray painted "x" marks the middle of the location of each pad footing.
	Concrete Pad Footing Concrete pad footings have been poured with concrete and the formwork stripped. (Strip Footing can be seen around the outside perimeter of the foundation.) Mouse-over shows a close-up of 1 pad footing.
Source: Canadian Wood Frame House Construction, page 27	Pad Footing & Post Concrete Pad Footing supports an isolated load such as a steel adjustable post.

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Stepped Footings

Stepped Footings can be used: on steeply sloping sites where unstable soil is encountered or where floor levels are split. The bottom of stepped footings are always on undisturbed soil or compacted granular fill. The thickness of a step footing should be a minimum of 6 in thick (150mm) and same width as footing. On steep slopes, where more than one step may be required, therefore the following applies:

 

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Foundations

The foundation wall is used to carry the floor, wall, roof and other building loads down to the footing.

Concrete as a material for foundation walls is common.

Wall thickness for concrete is 6-12 inches (150-300mm). Foundation wall thickness affected by:

Depth below grade lateral support system provided Unstable soils are present - consult an Engineer

 

Foundation Formwork Foundation formwork must be installed strong enough to hold the concrete Form systems are available in a variety of types. Form-ties are used to hold the forms together as well apart by a specified distance. Form-ties can be snapped or broken off just beneath the concrete surface and patched to make it water-tight.	Source: Canadian Wood Framed House Construction, figure 12, page 30
Form Ties Form-ties serve to spread the forms apart by the desired dimension. They also serve to hold the form together after a steel waler is slid through the form (bar) tie.	Source: Reading Blueprints for Trade Information, page 133
Snap Form Ties Form-ties can be snapped or broken off just beneath the concrete surface and patched to make it water-tight.	Source: Building Construction Technology, F. Hately, page 109

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FOUNDATION DAMPROOFING

When the forms of a concrete foundation wall have been removed the exterior area to be backfilled will have to receive a damproofing treatment. 2 methods of treatment are sprayed and platoon.

Damproofing System Sprayed on asphalt bitumen treatment over concrete surface to be covered with backfill. Weeper Tile c/w sock is installed around the outside of the footing but not yet covered with weeper stone.	Damproofing Platon System of damproofing is installed on the foundation complete with the weeper tile and gravel around the footings. The mouse-over shows this wall backfilled.

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FOUNDATION DETAILS

	Stepped Foundation Concrete Footings and Foundations may be stepped similar to the foundation to the left. This eliminates a lot of exposed concrete wall. Forms may not be great looking but if built straight and strong will serve well. Mouse-over shows the foundation after it is stripped and backfilled.
	Formwork Corner detail of a foundation wall system. Not all foundation formwork is pretty.
	Form Ties The formwork for the concrete footing and foundation wall system have been stripped and the concrete exposed. Once the form ties (also called snap ties) are removed the surface can be sealed with mortar mix. [Mouse-over] After the parging is complete, the entire surface can then have damproofing applied.
	Formwork Foundation formwork in place ready for the concrete. Formwork will be stripped after the concrete has set up. These forms have been, and will be used many times.
	Beam Pockets Beam pockets must be put in foundation walls to allow beams to set into the foundation wall. The beam pocket to the left is made by fastening pieces of lumber to the inside of the forms.
Source: Illustrated Residential and Commercial Construction, Peter Mann, page 4-9	Beams Both steel and wood beams can be embedded into the concrete walls into areas made with beam pockets. Minimum end beam bearing must be maintained.
	Basement Window Cast-in-place wood basement window. Basement windows can also be made of metal.
	Check Checked down area of the foundation will serve as a shelf for the brick at the front of the house.
	Bulkhead Check Concrete foundation is lowered at the garage entrance. The lowered area is called a bulkhead or a check. A small portion of concrete is all that remains in the between 2 checked area.
	Foundation Check Part of the foundation is checked-down to allow a shelve for the brick finish.
Source: Illustrated Residential and Commercial Construction, Peter Mann, page 5-7	Anchor Bolts Anchor Bolts embedded into the concrete are used to attach the lumber sill plate to the foundation wall system. [Mouse-over]
	Concrete Slab Concrete slabs will be placed after the gravel is placed and all the rough in plumbing is completed. Concrete slabs will be finished so they slope towards a "floor drain".
Source: Illustrated Residential and Commercial Construction, Peter Mann, page 5-9	Weeper Tile System Big "O" weeper tile system is installed next to the footings and below the top of the foundation slab. Weeper Stone 10" (250mm) is placed over the 4" diameter (100mm) weeper tile

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