Building Concrete Masonry Homes: Design and Construction
August 1998, 43 pages
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Concrete rises above grade.
Sure, you've seen concrete masonry units (CMU) used for foundation walls. But unless you build in the South, you--and your local code official--may not be as familiar with using CMU in above-grade walls. The strength, durability, fire-resistance and energy performance of CMU make it an attractive material for residential construction.
This document identifies the major issues related to the design and construction of a home with above-grade concrete masonry walls, focusing on two case study homes. It presents different approaches to construction details including the installation of insulation, floor framing, and doors and windows.
The case study homes illustrate several different techniques for detailing building elements such as floor decks, insulation, windows and doors, flashing, and gypsum wallboard.
- The design method used to provide compliance with the local building codes (empirical design vs. engineered design) affects the efficient use of the material. The empirical design method is often used for single-family dwellings for reasons of simplicity, as well as the elimination of engineering costs. The engineered design approach does introduce additional costs, but can help reassure skeptical building officials who may be unfamiliar with residential block construction.
- Local suppliers can be integral and supportive players in the development of plans. A high level of support may be required before some conventional stick-frame builders convert to concrete masonry construction. Home builders considering concrete masonry above grade should seek support from their local supplier.
- The weight of concrete masonry blocks requires consideration during the construction of both single- and multi-story walls.
- Lateral support of walls was not a design issue/barrier with the two case study homes, nor will it be an issue for many low-rise residential structures. Because the clear span distance between floors and roof is typically 8 or 9 feet in most single-family detached homes, the masonry walls rely on lateral support in the vertical direction (floors and roofs) and not the horizontal direction. Buildings with tall, unsupported exterior walls or high ceilings, e.g., "great rooms" and entry foyers, as well as buildings with 6-inch thick block (which limit the spacing between lateral support) will require special attention.
- While the concrete masonry industry offers recommendations for controlling cracks in masonry walls, the model building codes do not include prescriptive requirements for crack control. For typical residential construction crack control has not necessarily been "proven" to be a problem. However, the uncertainty surrounding the need for bond beams, horizontal joint reinforcement, and control joints results in decisions made on an individual basis.
Content updated on 1/5/2007