Multi-Wythe Composite Walls vs. Cavity Walls
Are Multi Wythe Composite Walls simpler and better than Cavity Walls?
Prior to the '60s, composite barrier walls were used with little concern for details. Specifications were
very detailed with few changes from job to job. Problems related to masonry construction were
virtually nonexistent.
With the development of cavity wall systems, problems with water leakage, efflorescence, cracking,
and movement increased dramatically.
Now a masonry wall can be highly dependent upon the technique of the mason. It requires intense
supervision to assure that all of the elements are installed and in the proper order.
When circumstances permit, should you build an exterior wall without an insulated
cavity and provide the insulation, vapor barrier, and plaster on the inside wall surface?
Multi-wythe walls stopped the inward migration of water by absorbing water or providing many
barriers to water penetration. The walls could absorb considerable water without causing damage.
They typically were not insulated and did not contain vapor barriers so moisture entering the walls
would dissipate either to the interior or to the exterior. Providing insulation and a vapor barrier on
the interior face of such a system could cause problems in some climates. Without a cavity, these
walls will take more time to dry out and could result in freeze/thaw or efflorescence problems. Such
walls would still require properly designed flashings. The vapor barrier must be designed to shed
water into this flashing. Weep holes must extend through both wythes. If these details were not
addressed, water leakage problems would likely occur. Leakage would be most severe after long
periods of rain when walls become saturated. If flashing systems are designed properly and installed
carefully, cavity walls provide an excellent means of resisting wind-driven rains.
Are there any additional problems with returning to a masonry system?
Both solid walls and cavity walls have advantages and disadvantages and the use of either type
depends on what the designer is trying to accomplish. Features generally stressed for cavity walls are
their resistance to rain penetration. Solid walls generally have higher strength. Neither type rates
highest in all respects.
There is a concern that the cavity wall is too hard to build and has problems with cracking, water
leakage, and efflorescence. But a properly designed wall with good workmanship should not have
any of these problems. Solid walls, not well constructed, leak as much as poorly constructed cavity
walls. The industry evolved the insulated cavity wall to overcome moisture problems inherent in the
solid wall. Both types of walls need good workmanship to be successful, but the cavity wall provides
better water resistance, thermal insulation, and sound transmission.