Trusted Attic Air Sealing for San Marcos Homeowners
Attic air sealing in San Marcos typically costs $1,200-$2,800 for a complete job and takes one to two days. Most homes we seal in the San Marcos area show blower-door reductions of 30-50%, meaning conditioned air stops escaping through gaps you cannot see from inside the living space.
We’ve sealed and insulated over 9,000 homes since 2016, every one starting with a written price and ending with a documented record. In San Marcos, we regularly find attic floors that were insulated decades ago without sealing first - the fiberglass or cellulose sits directly over leaky top plates, recessed can lights, and plumbing penetrations that let San Marcos summer heat and Hill Country winter cold straight into the conditioned envelope. Our crews are background-checked and uniformed, and a live person answers (737) 337-8049 around the clock. Same-day appointments are often available for San Marcos homes in neighborhoods like Willow Creek, Blanco River Village, and the historic district near downtown.
What Our Attic Air Sealing Service Includes
Attic Floor Air Sealing
The attic floor is the primary pressure boundary in most Kyle and San Marcos homes, and it’s rarely airtight. We seal the plane between your living space and the vented attic above, focusing on the gaps between drywall and framing members, around wire penetrations, and at partition wall intersections. In San Marcos, we see a lot of 1970s and 1980s construction with minimal top plate sealing and batt insulation that has shifted or compressed over forty years of Hill Country temperature swings. Our crew uses Owens Corning Foam Sealant and Knauf Ecoseal for the bulk of attic floor work, applied after we remove existing insulation to expose every leak path. You get before-and-after blower-door numbers and a photo record showing each sealed location.
Top Plate & Penetration Sealing
Top plates - the horizontal framing members where interior walls meet the attic floor - are the single largest source of attic air leakage in most homes. In Lockhart and San Marcos, we regularly measure top plate gaps of 1/8 to 1/4 inch running the full length of partition walls, which adds up to the equivalent of a square foot of open wall to the attic. We seal these with low-expansion foam and fire-rated caulk where required by San Marcos building code, then address every plumbing vent, electrical chase, and HVAC penetration. The work is tedious and invisible once insulation goes back, which is why most contractors skip it or do it poorly. We don’t blow insulation until this step is complete and verified with a smoke pencil or thermal imaging.
Can Light & Duct Boot Sealing
Recessed can lights installed before 2015 are almost never airtight, and in San Marcos’s cooling-dominated climate, they act like chimneys pulling 140-degree attic air down into your living space every summer afternoon. We install Rockwool fire-rated covers over non-IC-rated cans, then seal the cover perimeter with mastic and foam. For duct boots - the metal transitions between flex duct and ceiling diffusers - we seal the drywall-to-metal gap with fiberglass mesh and mastic, then verify with pressure testing. Duct boot leaks are especially common in San Marcos homes with flex duct systems installed during the 1990s building boom; the boots were often cut oversized and never properly sealed to the ceiling plane.
Attic Hatch Sealing
The attic hatch is the most frequently accessed opening in the ceiling plane and usually the leakiest. We build rigid foam hatch covers with weatherstripped edges and latch mechanisms that compress the seal, or we upgrade to insulated attic ladders with factory-built gaskets. In San Marcos’s climate, an unsealed attic hatch can leak as much air as a four-inch hole in the wall, and it’s the one opening homeowners disturb regularly. Our hatch upgrades include a written R-value label and installation date, part of the documented record you receive at job completion.
What happens when you call
- 1
A real person answersNo phone trees - you reach a local pro.
- 2
You get an upfront price rangeHonest numbers before anyone is dispatched.
- 3
A background-checked tech heads outLicensed & insured, dispatched right away.
- 4
You approve before work beginsNothing starts until you say go.
Brands We Service for Attic Air Sealing
We specify materials from Johns Manville, Knauf, Rockwool, and CertainTeed based on what each job requires, not what we have excess inventory of. Johns Manville air-sealing tapes and vapor retarders see heavy use in our San Marcos attic jobs for their adhesion to OSB and dimensional lumber in high-temperature conditions. Knauf Ecoseal and insulation products are our standard for attic floor sealing in homes where chemical sensitivities are a concern - the bio-based binder performs well in the humidity fluctuations common to the Blanco River watershed.
Rockwool fire-safe insulation and cover products are specified for every can light sealing job we do; the 2,150-degree melting point matters when you’re enclosing electrical fixtures in a vented attic. CertainTeed’s air barrier accessories and membrane products round out our specification set for complex top plate and kneewall situations. Whether your San Marcos home was built with these brands or any other materials currently in the attic, we can assess, seal, and document the result. We carry no proprietary product lock-in.
Before
AfterSigns You Need Attic Air Sealing Right Now
- Your upstairs rooms are 8-12 degrees hotter than downstairs in July. This is the classic pattern in San Marcos two-story homes with unsealed attic floors. Conditioned air escapes through ceiling leaks, the upstairs HVAC system cannot keep up, and the temperature stratification worsens as outdoor heat radiates through the roof deck. We measure this with blower-door testing and thermal imaging to pinpoint the worst leak paths.
- Your energy bills spike every June and stay high through October. San Marcos cooling loads run long - May through October is typical. If your summer electricity usage is 40-60% above winter baseline and your insulation depth looks adequate, air leakage is the likely culprit. Conditioned air you’re paying to cool is escaping to the attic, and replacement air is being pulled in from the crawl space, garage, or wall cavities.
- You feel drafts near interior walls and ceiling fixtures even with windows closed. These are not “normal house noises.” In a properly sealed home, interior walls should not produce measurable air movement at the baseboard or outlet level. The draft you’re feeling is attic air being pulled down through top plate gaps by the stack effect, especially strong in San Marcos homes with high ceilings and vented attics.
- Your attic insulation is discolored or dirty on top. Clean insulation is a uniform color. When you see gray or black streaking, especially near the eaves and around penetrations, that’s filtered air - your conditioned air - carrying dust and particulate through the insulation on its way to the attic. The insulation is doing its job of filtering, but it’s not stopping the air movement that matters.
- You’ve had rodent activity in the attic. Mice and rats follow air currents to find entry points, and they widen small gaps into highways. After we seal and rodent-proof your attic, the air sealing work prevents new scent trails from forming. We do this combination frequently in San Marcos’s older neighborhoods where mature trees and established populations meet aging construction.
Our Attic Air Sealing Process - Step by Step
- 1
Written price and scope before any work starts. Haven Standard Clause 1: you receive a flat price, written scope of work, and written warranty before anyone enters your attic. For San Marcos attic air sealing, this typically follows a free site visit where we assess access, insulation depth, and visible leak paths. We do not start work on a time-and-materials basis, ever.
- 2
Insulation removal and attic preparation. We remove existing insulation to expose the full attic floor, top plates, and penetrations. This is non-negotiable - air sealing cannot be verified visually through six inches of compressed fiberglass. The removed material is bagged and documented with photos. If your insulation is in good condition, we may set it aside for reinstallation; if contaminated or degraded, we discuss replacement options before proceeding.
- 3
Blower-door testing and leak detection. We run a blower-door test - a pressurization reading that shows, in one number, how much air your building envelope is losing. Typical pre-sealing numbers for San Marcos homes built 1980-2010 range from 3,500 to 6,500 CFM50. We combine this with thermal imaging and smoke pencils to map leak locations, prioritizing the largest flows first.
- 4
Systematic air sealing from largest to smallest leaks. Crews seal top plates, penetrations, can lights, duct boots, and the attic hatch using foam, caulk, mastic, and rigid covers as appropriate. Every sealed location is photographed. We do not install insulation until this phase is complete and inspected. In San Marcos’s climate, skipping this step means your new insulation will perform at 40-60% of its rated R-value due to wind washing.
- 5
Post-sealing verification and documentation. We run a second blower-door test and deliver the before-and-after numbers, plus a photo record of every sealed location and the written warranty. Most San Marcos attic air sealing jobs show 30-50% reduction in CFM50. You leave with physical documentation, not a promise.
How Much Does Attic Air Sealing Cost in San Marcos?
A typical attic air sealing job in San Marcos runs $1,200-$2,800 depending on attic square footage, accessibility, and whether insulation removal is required. Here’s how that breaks down for common scenarios:
| Scope | Typical Range | What Affects Price |
|---|---|---|
| Attic floor sealing only (no insulation removal) | $1,200-$1,800 | Attic size, number of penetrations, hatch accessibility |
| Attic floor + top plates + penetrations | $1,600-$2,400 | Linear feet of interior wall, plumbing/electrical density |
| Full seal including can lights and duct boots | $2,000-$2,800 | Number of cans, duct system complexity, need for fire-rated covers |
| With insulation removal and replacement | Add $800-$2,500 | Insulation type, contamination level, square footage |
What moves the price: attics with 12-inch or greater joist spacing that require crawling; recessed cans that need Rockwool fire covers; HVAC systems with multiple trunk lines penetrating the ceiling plane; and rodent damage requiring repair before sealing. What does not move the price: we do not charge extra for the blower-door testing, photo documentation, or written warranty - these are included on every job.
How to avoid overpaying: get a written scope that specifies what is being sealed, with what materials, and how verification will be performed. A quote that says “seal attic” without itemizing top plates, penetrations, can lights, and duct boots is not comparable. We provide a Free Second Opinion on any written estimate - bring us a competing quote and we will read it with you line by line. Call (737) 337-8049 to schedule.
Attic Air Sealing Near San Marcos - Our Service Area
We run attic air sealing crews throughout the San Marcos metro and into surrounding Hill Country communities. Typical response times are same-day to next-day for San Marcos proper, including the neighborhoods along McCarty Lane, the Blanco River corridor, and the RM 12 corridor toward Wimberley. We also serve Kyle and Redwood with regular routing, plus Lockhart, Buda, and the Austin metro area including Shady Hollow, Lost Creek, and Lakeway. For homes in Bastrop, Lago Vista, Hornsby Bend, or the outer Austin ring, we typically schedule within two business days. All service areas receive the same Haven Standard: written price before work, documented record after, and before-and-after blower-door numbers on every applicable job.
Serving San Marcos, TX - Our Local Coverage Area
We’re based in the San Marcos area and know this community well. Use the map below to see our service coverage - if you’re nearby, we can almost certainly help.
Frequently Asked Questions - Attic Air Sealing in San Marcos
Attic air sealing is the process of closing gaps, cracks, and penetrations in the ceiling plane and attic floor that allow conditioned air to escape into the vented attic space. In a typical San Marcos home, these leaks occur at top plates where interior walls meet the ceiling, around plumbing and electrical penetrations, at recessed can lights, and at the attic hatch - adding up to the equivalent of a two-foot square hole in your ceiling. We seal these with foam, caulk, mastic, and rigid covers, then verify the result with blower-door testing.
Most attic air sealing jobs in San Marcos are completed in one to two days. A single-story home with straightforward attic access and no insulation removal typically takes four to six hours; two-story homes, complex rooflines, or jobs requiring full insulation removal and replacement may extend to two days. We schedule a specific arrival window, text you when the technician is en route, and leave you with documented completion before we depart. Call (737) 337-8049 for availability - same-day starts are often possible.
Attic air sealing in San Marcos typically costs $1,200-$2,800 depending on attic size, accessibility, and whether insulation removal is needed. Can light sealing with fire-rated Rockwool covers, extensive top plate work, or duct boot sealing push toward the higher end. Every job begins with a free, written estimate - no work starts without a flat price in writing. Bring us any competing written quote for a Free Second Opinion.
Yes. We specify Owens Corning foam sealants and air barrier products, Johns Manville tapes and membranes, and Knauf Ecoseal and insulation based on what each San Marcos job requires. We also use Rockwool and CertainTeed products where their specifications fit. We carry no exclusive arrangements - the material choice is driven by your home’s conditions, not our inventory. Call (737) 337-8049 to discuss what we’d specify for your attic.
We do not treat air sealing as an emergency service - it is planned work that requires dry conditions and proper attic access. However, a live person answers (737) 337-8049 24/7, and we can often schedule next-day service for San Marcos homes where comfort or energy costs have become urgent. If your situation involves active water intrusion, we will refer you to a remediation specialist before air sealing can proceed safely.
All attic air sealing is covered by our 365-Day Done Right Promise - if it’s not done right, we make it right. The specific warranty terms are written and delivered before work starts, per Haven Standard Clause 1. Coverage includes material failure and workmanship defects; it does not cover new damage from roof leaks, rodent re-infestation, or homeowner alterations to the sealed envelope. You receive the written warranty as part of your documented job record.
Clear a path to the attic hatch and remove any stored items within four feet of the opening. We need stable ladder access and headroom to bring equipment and removed insulation through. If you have pets, secure them in a separate room during the blower-door testing - the fan noise and temporary pressure change can distress anxious animals. We handle everything else: floor protection, lighting, ventilation, and cleanup. Call (737) 337-8049 to schedule your free estimate and we’ll confirm any site-specific preparation.
Schedule Your Attic Air Sealing Service in San Marcos Today
Call (737) 337-8049 to speak with a live person - no voicemail, no callback queue measured in business days. We’ll schedule a free site visit, deliver a written price before any work starts, and leave you with before-and-after blower-door numbers and a photo record you can verify. Same-day and next-day appointments are available throughout San Marcos and surrounding communities.
Written by Wes Okafor, Owner at Envelope Insulation Co., serving San Marcos since 2016.