Builders may construct a foundation wall with solid, filled, or sealed block tops for several reasons, including termite-proofing, energy conservation, distribution of weight of the structure, and radon resistance. The NCMA28 recommends that a solid or grouted top course be installed to distribute the loads of joists and beams. Some building codes require solid tops to block hidden termite entry. In spite of this, the block tops in many residences are left open except at anchor points. Houses have been observed in which block tops were generally sealed, but cores were left unsealed at access doors to crawlspaces, around ash pit doors, and other openings. Sealing hollow cores at or near their tops can prevent soil gas from entering the basement, but more importantly might make the building easier to mitigate in the event that it has elevated radon. Sealing the bottom course might prevent air beneath the slab from entering the block wall, but if the wall cores are used as part of a water control method this may not be possible.
It is recommended, for potential radon control, to seal open blocks at the time of construction. Block tops have been successfully sealed using
1. Mortar mixed with plastic binder to fill the top cores (quality control and shrinkage can be problems).
2. "Termite caps"—cored blocks with a 2-in.-thick solid cap as the top course.
3. Solid or lintel blocks to seal one of the top courses.
When solid blocks or termite caps are used, anchor bolts must be placed in the joints between the blocks. Lintel blocks and grouted top courses allow for more flexible placement.
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