Demilec Attic Insulation: The San Jose Owner’s Guide
If you have Demilec spray foam or blown-in insulation in your San Jose attic that isn’t performing, we can match it, price it, and install the replacement, usually within the same week. Most Demilec attic insulation repairs in San Jose run between $1,400 and $4,200 depending on square footage and whether we’re doing a partial fill or a full re-spray. You’ll typically notice the problem first as a room that won’t hold temperature, a spike in your PG&E bill, or visible gaps where the foam has pulled away from the roof deck.
We’re Woolsey Insulation San Jose, an independent insulation contractor. We’re not affiliated with Demilec, but we stock Demilec-compatible open-cell and closed-cell foam, plus the matching sealants and prep materials. Glenn Hartley, our owner, has been working with spray foam since it started showing up in California attics in a serious way, and he’ll tell you straight: most Demilec “failures” in San Jose aren’t the product itself. They’re installation issues or moisture problems that went unaddressed.
Which Demilec Models This Applies To
Demilec makes two main spray foam lines you’ll find in San Jose homes: Heatlok HFO (closed-cell, typically 2 – 3 inches on the roof deck) and Sealection 500 (open-cell, typically 5.5 – 10 inches in vented attics). There’s also Polar Foam, which shows up in older installations from the late 2000s and early 2010s. Here’s the compatibility gotcha most owners run into: Heatlok HFO and Sealection 500 use different expansion ratios and different substrate prep. You can’t spot-fill an open-cell void with closed-cell foam without creating a condensation point where the two meet. That’s a moisture problem waiting to happen, and in San Jose’s winter damp season, it happens fast.
If you’re not sure what you have, look for the Demilec label on the foam itself or on the job paperwork from the original install. No label? We can identify it by density, cell structure, and age. For attic floors with blown-in Demilec fiberglass or cellulose, we match the R-value, not the brand name. The honest truth: aftermarket open-cell and closed-cell foams from quality manufacturers perform equivalently to Demilec for most repairs, and they typically cost 10 – 15% less. We’ll quote you both options and let you decide. Get the R-value right, and the house does the rest of the work for you.
Signs Your Demilec Attic Insulation Is Failing
- Rooms directly under the attic run 5 – 8 degrees warmer in summer. Closed-cell foam loses effectiveness when it pulls away from the sheathing, creating thermal bypass channels. In San Jose’s 90-degree summer afternoons, you’ll feel it upstairs first.
- Your energy bill spikes without a change in usage. A 20 – 30% jump in heating or cooling costs often means the insulation barrier has been compromised. PG&E rates are high enough already; failed insulation compounds the problem.
- You can see gaps, cracks, or shrinkage in the foam. Open-cell foam can shrink slightly over time, especially if it was installed during humid weather. Gaps as small as half an inch let conditioned air escape.
- Musty smell or visible condensation on the underside of the roof deck. This is the one that worries us most. Foam that wasn’t thick enough or that has pulled away allows warm, moist air to hit a cold surface. In San Jose’s marine-influenced climate, that condenses and feeds mold.
- Rodent or pest activity in the attic. Rats and squirrels burrow through foam and batts alike. San Jose’s older neighborhoods, especially around Willow Glen and Rose Garden, have mature trees that give rodents a highway straight to your roofline.
Replacement Cost & What’s Included
For a typical San Jose single-family home with a 1,200-square-foot attic, here’s what we actually charge:
- Partial re-foam (spot repair, 100 – 200 sq ft): $1,400 – $2,200
- Full open-cell re-spray (Heatlok or equivalent): $2,800 – $4,200
- Full closed-cell re-spray (Heatlok HFO or equivalent): $3,400 – $5,800
- Blown-in Demilec fiberglass top-up (R-38 to R-49): $900 – $1,600
Every quote includes removal of failed material, site prep, the foam or blown-in product, labor, and cleanup. We use the written-price model: you get an exact number before any work starts, and that number is the number. No add-ons at the door. Every job includes our 365-Day Done Right Promise in writing: if the repair fails within a year, we come back and fix it at no charge.
DIY or Call Us?
Spray foam is not a DIY material. The two-part chemical reaction generates heat, and if the mix ratio is off, you can end up with foam that never cures properly, off-gasses, or worse, smolders during application. That’s not a scare tactic; it’s just the reality of working with expanding polyurethane. What you can safely do yourself: inspect visually from the attic hatch, check for obvious gaps or shrinkage, and look for water stains on the sheathing. That’s useful information to have when you call us.
What goes wrong when owners try to patch foam themselves: they buy single-component cans from the hardware store, which don’t have the R-value or expansion characteristics of a two-part system. The patch looks fine and fails within a season. If you’re seeing failed Demilec insulation in your San Jose attic, call us at (669) 333-3579. We’ll tell you what you’re looking at, and if it’s not a repair job, we’ll tell you that too.
FAQs
Properly installed Demilec spray foam lasts 30 to 50 years in San Jose conditions. Closed-cell Heatlok HFO holds up better against our damp winter cycles than open-cell, but both should outlast your mortgage if the original install was done right. Failures inside a decade are almost always installation-related, not product-related.
Spot repairs are absolutely possible if the failure is localized. We can cut out the failed section and re-spray with matching foam, and that’s what we recommend when less than about 30% of the attic insulation has failed. Beyond that, full replacement usually makes more financial sense. Call (669) 333-3579 and we’ll give you an honest read.
Most San Jose attic replacements take one full day for a partial repair and two days for a full re-spray. We show up in the window we give you, and we leave the jobsite cleaner than we found it. You’ll need to stay off the foam for 24 hours while it cures, then it’s fully inert.
We stock Demilec-compatible open-cell and closed-cell foam on our trucks, along with the prep materials and sealants. We also work with seven other insulation brands, including Reflectix for radiant barrier applications, so the material we recommend fits your attic, not whatever happens to be in our inventory. Most Demilec replacement jobs in San Jose are done within five business days of your call.
Talk to a Real Person
If your Demilec attic insulation isn’t holding up, call Woolsey Insulation San Jose at (669) 333-3579. A live person answers, day or night. We’ll schedule a look at your attic, give you a written price before any work begins, and put the guarantee in writing. Glenn Hartley and our crew have been fixing San Jose attics long enough to know what works and what doesn’t. We’ll tell you straight.
Written by Glenn Hartley, Owner, Woolsey Insulation San Jose at Woolsey Insulation San Jose, serving San Jose and nearby areas.