Demilec Attic Air Sealing: The Los Angeles Owner’s Guide
If you have a Demilec spray foam attic and you’re looking at this page, chances are you’ve spotted gaps in your air seal, felt a draft, or watched your cooling bill climb in the San Fernando Valley heat. Here’s the direct answer: we stock and install Demilec-compatible attic air sealing products across Los Angeles, and the typical installed cost for a full attic air sealing job runs $1,200 to $2,800 depending on attic size and how much of the existing foam barrier needs addressing. Most jobs are completed same-day once we’re on site. You’ll usually find the problem the hard way: a hot upstairs, a musty attic smell, or a foam line that’s peeled back from the sheathing like old caulk around a bathtub.
Which Demilec Models This Applies To
Demilec makes two families of spray foam that end up in Los Angeles attics: the Heatlok HFO series (that’s their closed-cell workhorse, now in HFO Pro and HFO High Lift formulations) and the Sealection 500 open-cell line. The air sealing failure patterns are different for each. Closed-cell Demilec tends to crack or delaminate from the roof deck as the house breathes through LA’s hot-dry to cool-damp cycles. Open-cell Sealection is more forgiving structurally, but it’s hyper-sensitive to moisture intrusion around roof penetrations: a single loose plumbing vent boot lets water wick through that foam and silently degrade the air seal behind it.
If you’re not sure which Demilec you have, look for the stamp on the foam surface or hunt for the yellow Demilec product sticker near the attic hatch. No sticker? Here’s the gotcha: you can usually tell by pressing the foam. Closed-cell feels like a hard foam cooler and won’t dent with a thumb press. Open-cell feels like a firm sponge and springs back slowly. When we quote a Demilec air sealing job, we’re also matching to what’s already in the attic. Mismatching product families (spraying an open-cell patch over a closed-cell barrier, for example) creates a weak seam that’ll fail again within a couple of Los Angeles seasons. We use Demilec product for Demilec attics, and for the small accessory gaps around hatch frames and can lights, we’ll pair it with Reflectix or a compatible sealant as needed.
On the OEM-versus-aftermarket question: Demilec doesn’t sell “parts” in the traditional sense, the way a garage door company sells a spring. What they sell is the chemical system, and the air sealing comes down to the gun, the technique, and whether the installer actually knows how to tie new foam into old cured foam. There’s no quality aftermarket that outperforms Demilec’s own product when you’re repairing a Demilec ceiling. We’re an independent Los Angeles insulation contractor, not a Demilec dealer or affiliate, but we stock their open-cell and closed-cell systems because we’ve seen how much better a same-family patch holds up in a South Bay or Pasadena attic.
Signs Your Demilec Attic Air Sealing Is Failing
- Your upstairs runs 8-10 degrees warmer than downstairs in summer. Air sealing gaps at the roofline let the superheated attic air circulate where it shouldn’t. When the seal fails, that LA sun load on the roof deck pushes straight through into the living space.
- You can smell the attic from the hallway. That musty, slightly dusty odor means air is migrating from the unconditioned attic into the conditioned house. Demilec foam that’s peeled from the sheathing leaves a direct path for that air.
- Your energy bill spikes in July and August even with the same thermostat settings. An intact Demilec air seal is the difference between your AC cooling the house and your AC cooling the neighborhood. We see this pattern in older Los Angeles homes where foam was installed a decade ago and never inspected.
- Visible cracks or gaps in the foam along roof rafters and around can light boxes. Closed-cell Demilec shrinks slightly as it fully cures over the first two years. If the installer sprayed too thin or in the wrong conditions, those shrinkage cracks become permanent air highways.
- Condensation or water staining on the attic-side drywall near bath fans and plumbing vents. A failed air seal at a penetration lets warm moist air from the living space condense against the cooler roof deck. Over time that rots the sheathing and can turn a $400 seal repair into a $4,000 deck replacement.
Replacement Cost & What’s Included
For a Demilec attic air sealing job in Los Angeles, here’s where your money actually goes.
- Inspection and seal assessment: $75 (waived when you book the repair with us)
- Targeted air seal repair (single penetration or seam, 1-2 cans of Demilec foam): $250-$450
- Partial attic air seal (problem areas only, up to 300 sq ft of foam work): $600-$1,100
- Full attic air sealing (complete heat boundary, typical 1,200-2,000 sq ft LA attic): $1,200-$2,800
Every quote includes the Demilec product matched to what’s already in your attic, the labor to open access where needed, cleanup, and disposal of any loose failed foam we encounter. What drives the range is attic height (crawl through a low-pitch Silver Lake attic and you understand why labor increases), the number of recessed lights and vent penetrations that need boxing and sealing, and how much of the old foam has to be removed before we can lay a clean seal line. Every job gets our written price before work starts, and the workmanship is covered by our 365-Day Done Right Promise. If the seal fails within a year, we’re back at no charge.
DIY or Call Us?
There’s a real split here, and I’ll be honest about it. If you’ve spotted a quarter-inch crack in the foam near your attic hatch, and you’re comfortable on a ladder with a can of Demilec single-component foam, you can clean the seam with a stiff brush and fill it. That’s a $25 fix and there’s no shame in doing it yourself. What you cannot safely DIY is a full air-seal restoration. The two-part Demilec systems require mixing equipment, ratio calibration, proper surface prep, and PPE that includes respirators and full skin coverage. Additionally, if you’re working around knob-and-tube wiring or old recessed lights in a pre-1980 Los Angeles house, spraying foam over compromised electrical is a legitimate fire hazard. If a second-story attic or a low-slope roof is involved, the ladder risk alone justifies the call. If your attic is working against you, let’s just fix it – no upsell, no mystery pricing. Call (361) 315-4177 and we’ll tell you over the phone whether it’s a $25 can or a $1,800 full reseal.
FAQs
Done right, a Demilec air seal should hold for 20 years or more, but the reality in Los Angeles is that installation quality matters more than the product itself. We routinely see Demilec jobs from the early 2000s that are still airtight, and we also see five-year-old jobs with foam peeling off the sheathing because the surface wasn’t prepped or the ambient temperature was wrong on install day. The single biggest factor is whether the installer controlled for LA’s summer heat during application. Call (361) 315-4177 and we can tell you from a photo whether your foam looks typical or like it’s failing early.
Yes, and in most Los Angeles houses that’s exactly what we recommend. If the majority of your foam is sound and you’ve got one or two failure zones, say around a bath fan or an old can light box, we can tie new Demilec foam into the existing barrier without stripping the whole attic. The repair bond is every bit as durable as the original spray when we’re able to prep the seam correctly. We’ll always tell you if the seal is too far gone to patch, but we’d sooner fix 40 square feet than sell you a full attic rebuild.
Most targeted repairs run two to four hours from driveway to cleanup. A full attic air sealing on a 1,500-square-foot Los Angeles home usually takes one full day. The foam itself cures in under an hour, so the timeline is really about prep, masking off areas we’re not spraying, and making sure the seam line between old foam and new foam is clean before we pull the trigger.
We do. Our crews run with both Demilec closed-cell and open-cell systems on board, plus the single-component cans for small cosmetic fills, and a supply of Reflectix for penetration boxes where a foil-faced barrier makes more sense than raw foam. That means we can match your Demilec product family on the first visit, not the third. Call (361) 315-4177 for a free estimate, and we’ll have a written price in your hand before any foam leaves the truck.
Chase Whitaker has owned Laurel Attic Insulation for the better part of a decade, and he’s the first to tell you that a Demilec attic with a failed air seal isn’t a product problem. It’s an installation problem. We fix those problems every week across Los Angeles, from Highland Park to Westchester, with the same simple promise: a written price, a fixed appointment time, and a seal that holds. Call us at (361) 315-4177 and we’ll get you on the schedule.
Written by Chase Whitaker, Owner, Laurel Attic Insulation at Laurel Attic Insulation, serving Los Angeles and nearby areas.