Johns Manville Radiant Barrier Installation Nationwide

Johns Manville Radiant Barrier Installation: The Boerne Owner’s Guide

Johns Manville radiant barrier installation in Boerne typically runs $1,800 to $3,400 for a standard 2,000-square-foot attic, and we stock the full JM AP Foil-Faced and ComfortTherm lines for same-day starts on most residential jobs. Most Boerne homeowners realize their existing radiant barrier is failing when second-floor rooms won’t cool below 78 degrees even with the AC running flat out, or when they notice the original foil has gone dull, torn, or been displaced by wind washing through ridge vents. We see this pattern constantly in the older subdivisions off River Road and in the ranch-style homes south of Main Street, where original barriers were stapled to rafters without proper air gaps or perimeter sealing.

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Which Johns Manville Models This Applies To

We install and replace across the full Johns Manville radiant barrier catalog, including the AP Foil-Faced line (AP-120, AP-150, and AP-200 weights), the ComfortTherm batts with factory-applied foil facing, and the JM Reflective Insulation board products used in some cathedral ceiling assemblies. The critical identifier is the foil scrim kraft (FSK) facing stamp on the product edge, which carries a JM lot number and ASTM C1313 compliance marking. If your existing barrier has no visible label, measure the facing thickness: AP-120 uses a 0.3-mil aluminum layer, while AP-200 steps to 0.5-mil for higher emissivity ratings in Texas solar gain zones.

On the OEM-versus-aftermarket question, Johns Manville’s foil facing is a laminated FSK product with a specific emissivity rating of 0.03 to 0.05, tested to ASTM C1371. Generic reflective films often claim equivalent performance but ship with untested emissivity values that drift after two to three summers of Hill Country UV exposure. We source JM materials direct through our supplier network, same as we do Owens Corning, Knauf, and Rockwool, so there’s no proprietary lock-in, just the part that matches the spec.

Signs Your Johns Manville Radiant Barrier Installation Is Failing

• Surface oxidation or dulling. The aluminized facing on JM barriers oxidizes from the outside in when attic ventilation pulls humid outdoor air across the foil. In Boerne, where summer attic temperatures spike past 140 degrees, this oxidation accelerates after year seven or eight, and the emissivity value climbs from 0.03 toward 0.15, which means the barrier is reflecting less radiant heat than it was designed to.
• Tears, sags, or wind displacement. Staple-only installation, common in homes built between 2005 and 2015 around Boerne, lets the foil flap and tear when ridge vents create negative pressure. Once the barrier loses contact with the rafter bay, the required 0.75-inch minimum air gap disappears and convective heat transfer takes over.
• Hot second-floor ceilings in late afternoon. This is the symptom that drives most calls. When the radiant barrier fails, roof deck temperatures radiate directly through the drywall. We measure this with an infrared camera: a functioning JM barrier should show ceiling surface temperatures within 5 to 8 degrees of ambient air temperature; failed barriers read 15 to 25 degrees hotter.
• Increased cooling runtime with no AC mechanical change. Your thermostat history doesn’t lie. A failed barrier adds 20 to 40 percent to cooling load in a vented attic assembly, which in Boerne translates to compressors running 90 minutes longer per day through August.
• Moisture staining on rafters or sheathing. When JM foil facing is installed upside-down, with the kraft paper side facing the roof deck, summer condensation traps against the sheathing. We’ve found this in several Fair Oaks Ranch homes where the original installer didn’t follow JM’s “foil toward the air gap” specification.

Replacement Cost & What’s Included

For a typical Boerne home with 1,800 to 2,400 square feet of attic floor, Johns Manville radiant barrier replacement runs $1,800 to $3,400 installed. The low end covers removal of degraded foil and reinstallation of AP-120 with proper air gap spacers; the high end includes full rafter-bay retrofit with AP-200, new baffles at soffit vents, and perimeter air sealing before the barrier goes in. We don’t blow insulation over an unsealed attic floor, so every quote includes top plate and penetration sealing as a prerequisite, not an upsell.

The written scope you receive before anyone lifts a tool specifies the JM product weight, the measured attic square footage, the blower-door target (we aim for 35 percent leakage reduction minimum), and the 365-Day Done Right Promise in plain language. You also get a Documented Photo Record of the completed work and, on applicable jobs, before-and-after blower-door numbers in CFM50 and pascals so the performance change is on paper.

DIY or Call Us?

There’s no high-tension danger in radiant barrier work, but there are two ways DIY goes wrong fast. First, working in a Texas attic in summer is genuinely hazardous: heat stress sets in at ambient temperatures above 95 degrees, and a Boerne attic in July runs 130 to 150. Second, the installation detail matters more than the product. JM requires a minimum 0.75-inch air gap, proper baffles to prevent wind washing, and correct facing orientation. We’ve been called to fix homeowner installs where the foil was stapled tight to the sheathing with no gap, which renders it essentially decorative.

What you can safely check: confirm your existing barrier has a visible JM stamp or measure the foil thickness with a micrometer. What you can’t verify without equipment: whether your attic ventilation rate is pulling 2 to 3 CFM per square foot, or whether your top plates are leaking enough to make the barrier irrelevant. Seal the envelope first. Then fill it. Call (830) 529-7780 and we’ll run the diagnostics.

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