Concrete block foundations offer numerous benefits. Blocks come in many colours and finishes that make differentiation easy. Their relative affordability and flexibility combine to allow builders to sell houses at lower prices and to make previously unbuildable sites viable for development. They require no expensive, specialised equipment, and a competent crew of mason can lay a typical foundation in less than a day. Concrete blocks allow builders to stagger wall height, so steep inclines or declines are not a problem.
Building a concrete block foundation wall takes diverse materials. The footings require lumber for building forms, rebar for structural support, rebar chairs to support the footings before pouring concrete and ties to bind the rebar to the chairs. The wall itself contains concrete block, mortar, foundation vents and anchor straps or bolts to attach the sill plate (the framing member lying atop the wall) to the block wall.
Grading is an often overlooked part of the building process. Good grading transforms a vacant into a building site. Your grader clears away brush and other debris and prepares the lot for building. Depending on the elevations show on the site plan, he may lower the grade by cutting away dirt, or raise it by adding dirt.He also slopes the site so that water drains away from the foundation.
Footings are concrete structural members that support a structure's entire weight. Footings are two to three times wider than the wall resting on them and at least 12 inches deep. Builders use two types of footings, dug and formed, each with inherent advantages and disadvantages. Dug footings cost less to set-up, but waste more concrete. Formed footings require additional lumber and labour to construct; however, they waste little concrete during pouring. Once poured, footings require 12 to 24 hours to dry.
Laying the Foundation
Accurately laying out the wall prior to applying mortar is essential to building a foundation wall and, ultimately, to the structure you build on it. Follow the building plans exactly, paying particular attention to the corners, which guide the rest of the wall. Lay your courses between the corners, and leave space for doors and foundation vents. On the final course, remember to insert anchor straps or bolts according to local code.
Block wall foundations generally cost more than slab foundations because of the extra labour and material involved. However, they are considerably less expensive than poured concrete walls.
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