Here at the TOH Modern Barnhouse, homeowner/designer Amy Matthews was mulling over flooring options when inspiration struck. “I was already pouring a concrete slab to be heated, and since I love the minimalist look of concrete floors, I thought, ‘Why not leave it as it is, and just burnish the concrete for a modern industrial look instead of adding another material—and another expense—on top?'”
Concrete floors are incredibly durable, easy to care for, and make a sleek style statement. And thanks to in-floor hydronic radiant heat, these floors will be toasty to the touch.
Planning stage
Shown here, Amy Matthews, site supervisor Jeff Mears, and plumber Nick Dusek review the plans to determine the location of trenches for the plumbing and electrical that needs to live within or below the slab.
What lies beneath
First, a sand and gravel base is laid atop the dirt infill and leveled.
Insulation and PEX tubing
Next, rigid foam insulation is set down on top of the sand and gravel base, and flexible cross-linked polyethylene, or PEX, tubing is snaked around the room and fixed in place with staples. Rebar adds structure and prevents the foam and PEX tubing from rising when the concrete is poured.
Pro Tip: This Old House plumbing and heating expert Richard Trethewey explains why PEX is the right choice for an in-slab application: “This tubing is actually a super plastic called PEX, and it won’t get brittle over time. And that’s really important to be able to put it in the slab and not have to worry.”
From there, the PEX loops run back to a manifold, which distributes heat to several separate circuits of pipe in the floor. As Richard Trethewey notes, “A single circuit would not provide enough heat for the entire garage”—so each loop gets its own home run back through a conduit down to the manifold location in the basement.
PEX tubing: Uponor
Hydronic heat route lines
Tucked out of sight, but easily accessible in the ground floor mechanical room, these manifolds are the heart of the radiant heating system. A carefully laid out system of PEX tubing distributes supply water from the heat source (a high-efficiency natural gas boiler) to smaller pipes that circulate hot water throughout the system.
How the PEX delivers heat to the floor: In retrofit applications, the This Old House team often pairs PEX with aluminum transfer plates fastened to the underside of the subfloor. As plumbing and heating expert Richard Trethewey has explained, “Plastic like PEX is not a good transfer medium. So the aluminum sucks the heat out and conducts it to the subfloor.” The tracks also keep tubing evenly spaced at 6 to 8 inches to prevent cold spots.
PEX tubing: Uponor
Zoning for comfort
Hidden within an access panel in the walk-in closet off the main hallway on the first floor, the manifold gauges monitor and regulate the temperature and water pressure for separate zones. Heated to 80 to 85 degrees F, the floors will feel warm underfoot in winter.
Pro Tip: As This Old House plumbing and heating expert Richard Trethewey puts it, the best heating system a house can have is “the one you don’t realize is there”—no clanking radiators, no whooshing vents, no dusty ductwork, “just an even blanket of heat, right where you want it.”
Hydronic heat system: Uponor
Pouring, leveling and troweling the slab
Concrete trucks poured the 1,900-square-foot slab in just two hours, and a crew quickly levels or “screeds” the floor to keep it from drying unevenly. Once it’s partly hardened, laborers supported on kneepads smooth out rough spots with trowels.
Burnishing the floor for a beautiful finish
With the floor hardened just enough to support a workmen without leaving deep footprints, a troweling machine runs over the surface at high speeds buffing and burnishing it to a smoother, harder, and silkier surface with each pass.
The finishing touch
A sealer is applied to protect the rich, variegated patina.
Watch the Hydronic Heat System Come Together
To learn more about the hydronic radiant heat and cement floors at the 2021 Modern Barnhouse, watch Episode 2 of our Idea House video series.
