COLUMN BUILDING SCIENCES FIGURE 8 Capillary Breaks Below Grade. Capillary suction in concrete foundation walls is traditionally controlled by dampproofing the exterior surface of the wall where it is in contact with the surrounding damp soil. Capillary Break On Exterior Foundation Wall PHOTO 4 (Left) Footing Capillary Break. Fluid-applied capillary break located over the top of concrete footings prior to the construction of perimeter foundation walls. PHOTO 5 (Right) Footing Capillary Break. Membrane-applied capillary break located over the top of concrete footings prior to the construction of perimeter foundation walls. Capillary Break Under Slab Capillary Break On Top of Footing dampproofing FIGURE 9 Monolithic Slabs. Polyethylene ground covers should extend under FIGURE 10 Capillary Control Above Grade. The the perimeter grade beam and upward to grade. Additionally, the exposed paint film seals the capillary pores on the surface films are usually portion of slabs should be painted with latex paint to reduce water absorpof the wood. Additionally, the siding should be poor waterproofing tion, and a capillary break should be installed under perimeter wall framing. installed over an air space behind the siding to act membranes. as a receptor for capillary moisture. Wood Baseboard Capillary suction Wood Flooring Concrete Slab under concrete floor Siding Perimeter of Slab slabs is traditionally Protected Above Air Space Created by controlled by placing Grade Furring Strips the floor slab over Sub-Slab Vapor Building Paper Water Perimeter Edge of Slab Barrier large-pore gravel Control Layer Protected Below Grade (3/4 in. [19 mm] Sheathing crushed stone with Ground Saturated With Water fines removed). Insulation in Since the pore size in Wall Cavity the granular pad is too large to support capillary suction, the granular pad between the top of the foundation walls and framing to acts as a capillary break (Figure 8). A sheet polyethylene prevent construction moisture in the foundation wall layer installed directly under the concrete floor slab in from migrating into the floor framing. direct contact with the concrete floor slab can also act as Capillary control also applies to slab-on-grade cona capillary break. struction and crawlspaces. Monolithic slabs need polyCapillary suction in masonry block foundation walls is ethylene ground covers that extend under the perimeter traditionally controlled by coating the exterior surface grade beam and upward to grade (Figure 9). Additionally, of the masonry blocks with a thin layer of mortar (parge the exposed portion of slabs should be painted with coat or rendering) and then applying a dampproof coat- latex paint to reduce water absorption, and a capillary ing over it. Applying a dampproof coating directly on the break should be installed under perimeter wall framing. masonry blocks has not always proven successful, as the Capillary Suction with Rainwater as the Moisture Source pore size of the mortar joints and the pore opening in Capillary suction in porous cladding materials can be the masonry block surfaces themselves can be too large controlled by sealing or filling the pores. One of the most for a fluid-applied dampproof coating to span. common examples of this is the application of a paint Capillary breaks can also be located over the top of film on wood-based siding to reduce the absorption of concrete footings prior to the construction of perimeter deposited rainwater. The paint film seals the capillary foundation walls (Figure 8, Photo 4 and Photo 5) as well as N OVEM BER 2020 ashrae.org ASHRAE JOURNAL 67https://www.ashrae.org/