Demilec Radiant Barrier Installation: The San Marcos Owner’s Guide
We stock and install Demilec-compatible radiant barrier systems in San Marcos, with most residential attic retrofits running between $1,800 and $3,400 depending on attic square footage and whether the existing insulation needs to be cleared first. Same-day installation is available when we have your attic dimensions and a few photos by 10 a.m. Most San Marcos homeowners figure out something’s wrong when their summer electric bill jumps $80-$120 from one month to the next, or when the upstairs hallway feels like a different climate zone than the living room below it.
Which Demilec Models This Applies To
Demilec’s radiant barrier line centers on their Heatlok HFO and Sealection 500 open-cell foam systems, which are often paired with foil-faced radiant barrier sheathing or retrofit foil rolls in attic applications. The critical compatibility point is whether your original installation used Demilec’s spec-grade foil laminated to polypropylene scrim, or a generic aftermarket equivalent that degrades faster in Central Texas heat. Check the foil edge for a Demilec lot stamp, or the spray foam tag on your rafter bays for a date code between 2012 and 2023. Those are the vintages we see most often in San Marcos homes, particularly the 2016-2019 builds near the Blanco River corridor where builders spec’d Demilec for code compliance but skipped proper attic ventilation pairing.
We carry both OEM Demilec barrier material and a commercial-grade equivalent from Reflectix that meets the same emissivity spec, 0.03 or lower, at a lower per-square-foot cost. The OEM carries Demilec’s material warranty; the Reflectix equivalent carries our 365-Day Done Right Promise. We will walk you through the tradeoff on site.
Signs Your Demilec Radiant Barrier Installation Is Failing
- Hot spots on your ceiling during afternoon hours. The radiant barrier’s emissivity rating has degraded, meaning it’s re-emitting heat into the living space instead of reflecting it back toward the roof deck. In San Marcos, this typically shows up first on west-facing rooms where attic temperatures peak near 140°F.
- Dust accumulation on the foil surface that won’t wipe clean. Once airborne attic dust embeds in the foil’s top coat, the reflectivity drops permanently. This is common in homes near I-35 construction zones or agricultural areas where particulate load is higher.
- Sagging or torn sections, especially near the ridge vent. Demilec’s original stapling pattern in some 2014-2017 installs used too few fasteners for the 24-inch on-center spacing common in San Marcos tract homes. Gravity and thermal cycling do the rest.
- Moisture staining on the rafter bays beneath the barrier. This means the barrier was installed without adequate venting, a code issue we see repeatedly in slab-on-grade homes near Texas State where the builder treated the attic as an afterthought.
- Your HVAC runs continuously from 3 p.m. to 8 p.m. in July. The barrier isn’t doing its job, and your condenser is compensating. We verify this with a quick attic temperature reading, anything over 110°F with the barrier installed indicates failure.
Before
AfterReplacement Cost & What’s Included
| Scope | Price Range (San Marcos) |
|---|---|
| Partial retrofit, 800-1,200 sq ft attic, barrier only | $1,800 - $2,400 |
| Full replacement, 1,200-2,000 sq ft, including old barrier removal | $2,400 - $3,400 |
| Add attic air sealing at top plates and penetrations | +$400 - $700 |
| Blower-door test, before and after | Included on all full replacements |
The range depends on three things: how much old material we are removing, whether your attic has safe decking for crew access, and whether we find unsealed air leaks that need addressing first. Under Haven Standard Clause 1, you get a written price before any work starts, no exceptions. Every job closes with a Documented Photo Record and, on full replacements, a printed blower-door report showing your before-and-after air changes per hour. The R-value tells you how slow heat moves through the material, the blower-door number tells you whether any of that matters.
DIY or Call Us?
There is no high-tension danger in radiant barrier work the way there is with garage door springs, but there are genuine pitfalls. A homeowner can safely verify the symptoms above and snap photos of any Demilec labels for us to review. What goes wrong in DIY: working in an unventilated attic in July, installing barrier with the reflective side facing the wrong direction, or stapling through electrical wiring hidden by blown insulation. We have found live knob-and-tube buried in San Marcos attics more than once, particularly in the 1960s ranch homes off Hopkins Street. If you are up there with a staple gun and no voltage tester, you are gambling.
Our crew carries thermal imaging to spot wiring, respirators for fiberglass dust, and the correct fasteners for your rafter spacing. Call (737) 337-8049 and text us your attic photos. We will tell you whether this is a same-day fix or a larger envelope issue.
FAQs
In Central Texas conditions, a properly installed Demilec radiant barrier maintains effective reflectivity for 15 to 25 years. The lower end applies if your attic ventilation is marginal or if you are near construction dust or agricultural particulate sources. Call (737) 337-8049 for an attic assessment, estimates are free.
Spot repairs work only for isolated tears or fastener pops in otherwise intact material. Once dust embedment or widespread sagging has occurred, partial patching creates thermal bridges that defeat the purpose. We will show you the thermal camera image so you can see exactly where the heat is getting through. Call (737) 337-8049 for a free second opinion on any repair-versus-replace question.
Most residential retrofits in San Marcos are completed in one day, four to six hours for a standard 1,500-square-foot attic with crew access. Jobs requiring old insulation removal or extensive air sealing at the top plates add a second day. We publish a written schedule with your price, and a named technician arrives with a text when they are en route.
We stock both Demilec-spec foil and Reflectix equivalent on our San Marcos truck, and we carry the full fastener assortment for 16-inch, 19.2-inch, and 24-inch rafter spacing. Same-day installation is available when we have your attic dimensions and photos by 10 a.m. Otherwise, we schedule within 48 hours. Call (737) 337-8049 to confirm current truck stock.
Topside Attic Insulation San Marcos is an independent service provider, not affiliated with Demilec. We source materials from Demilec, Reflectix, and other manufacturers based on what fits your specific attic conditions and budget.
Written by Wes Okafor, Owner, Topside Attic Insulation San Marcos at Topside Attic Insulation San Marcos, serving San Marcos and nearby areas.