Therma-Tru Home Additions & ADU Nationwide

Therma-Tru Home Additions & ADU: The Campbell Owner’s Guide

Therma-Tru entry systems in Campbell home additions and ADUs typically run $45,000-$130,000 for a complete addition with integrated door package, or $90,000-$220,000 for a standalone ADU with full Therma-Tru specification. We stock and install Therma-Tru-compatible entry systems, sidelites, and transom assemblies for Campbell’s common addition footprints, from compact 400-square-foot garage conversions near the Pruneyard to full second-story additions in the neighborhoods east of Winchester Boulevard. Most Therma-Tru entry components for active projects are available within 24-48 hours through our supplier network; we do not stock complete door slabs on the truck, but we carry weatherstrip, sweep, and hinge hardware kits for same-day service calls.

Call (831) 704-1211

Campbell homeowners usually discover a Therma-Tru entry issue during the framing walkthrough, when the rough opening doesn’t match the spec sheet, or months after move-in when the fiberglass skin delaminates at the bottom rail due to the clay-heavy soil settlement patterns we see west of Highway 17. The symptom is often a door that won’t latch properly, visible gaps at the jamb, or water staining on the interior trim after the first winter rains.

Which Therma-Tru Models This Applies To

Therma-Tru’s entry system lines break into three categories relevant to Campbell additions and ADUs: the Classic-Craft premium fiberglass series (most common on ADUs where the owner wants a front-door aesthetic on a secondary unit), the Smooth-Star paint-ready line (popular on modern additions with flush trim details), and the Benchmark entry-level series (frequently spec’d by builders on cost-sensitive garage conversions). The part you need depends on the manufacturing date: pre-2019 units use a 4-9/16″ jamb depth as standard, while post-2019 production shifted to 5-1/4″ for California Title 24 compliance, and mixing these on a retrofit will leave you with a 3/4″ trim gap that’s expensive to hide.

To identify your unit, check the hinge edge of the door slab for a stamped manufacturing date and series code, or remove the interior trim to find the specification label on the jamb. The critical measurement is the rough opening width, height, and jamb depth, taken at three points each, because Therma-Tru units are factory-built to 1/4″ tolerances and field-cutting the composite jamb voids the warranty. OEM replacement is our standard recommendation for Classic-Craft and Smooth-Star lines; Benchmark units can accept quality aftermarket equivalents from Plastpro or JELD-WEN if the homeowner is not pursuing a warranty claim, though we document the substitution in writing per Clause 1 of the Haven Standard.

Signs Your Therma-Tru Home Additions & ADU Is Failing

• Door won’t latch or requires shoulder pressure to close. This usually traces to hinge screw withdrawal in the composite jamb, common in Campbell’s older additions where the original installer used standard wood screws instead of the longer structural screws Therma-Tru specifies. The jamb leg flexes slightly with each cycle, enlarging the screw holes until the strike plate no longer aligns.
• Visible delamination or bubbling at the bottom rail. The fiberglass skin separates from the polyurethane core when water sits on the threshold, which happens on north-facing ADU entries in Campbell where morning condensation doesn’t dry before noon. Once the core swells, the door is structurally compromised and patching is temporary at best.
• Light visible around the perimeter when closed. Compression weatherstrip loses its memory after 5-7 years in California’s UV exposure, faster on west-facing additions in Campbell where afternoon sun hits the jamb directly. The gap drives conditioned air loss and can spike a mini-split’s runtime by 15-20%.
• Sidelite glass fogs between panes. The insulated glass unit (IGU) seal fails, typically at the spacer edge where Campbell’s temperature swings, 45°F winter lows to 95°F summer highs, stress the butyl sealant. Therma-Tru sidelites use a proprietary IGU size that doesn’t match standard stock; we measure and order factory replacements.
• Threshold cap lifts or separates from the sub-threshold. The aluminum cap traps water if the weep holes clog with construction debris, a frequent find in Campbell garage conversions where the original concrete pour wasn’t sloped properly. The wood substrate rots, and the cap pops loose under foot traffic.

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Replacement Cost & What’s Included

These ranges sit inside the broader addition or ADU project cost of $45,000-$130,000 and $90,000-$220,000 respectively. What drives the spread: Classic-Craft decorative glass upgrades add $800-$2,400; smooth-Star paint-grade units need factory priming plus site painting, which we quote separately; and retrofit installations in existing Campbell additions often require jamb extension or drywall repair that isn’t visible until the trim comes off. Every quote is a flat written price with line-item breakdown before work starts, no exceptions. Under our 365-Day Done Right Promise, if the weatherstrip leaks or the latch drifts out of alignment within a year, we return and correct it at no charge.

DIY or Call Us?

A Campbell homeowner can safely check three things: verify the hinge screws are tight with a #3 Phillips (loose screws are the most common cause of latch failure), confirm the threshold weep holes are clear with a piece of wire, and inspect the weatherstrip for visible cracking or compression set. These checks take ten minutes and require no special tools.

What goes wrong fast: adjusting a prehung unit’s plumb in an existing opening without a 6-foot level and shims of graduated thickness; cutting a fiberglass door slab with anything other than a fine-tooth carbide blade, which melts the skin and voids the warranty; or attempting to reglue a delaminated bottom rail with construction adhesive, which traps moisture and accelerates core rot. The composite jamb material Therma-Tru uses, while dimensionally stable, splits if you overdrive screws near the edge. If your door weighs more than you expected, that’s because a 3/0 x 6/8 Classic-Craft slab runs 85-95 pounds, and managing that alone in a Campbell addition’s tight hallway risks damage to the slab, the jamb, and your drywall. For anything beyond the three checks above, call (831) 704-1211 and we’ll scope it in person, with a written price before any work starts.

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