Therma-Tru Home Additions & ADU Nationwide

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

Therma-Tru entry systems in Sunnyvale home additions and ADUs typically run $45,000-$130,000 for a complete addition with integrated door package, or $900-$2,400 for a direct Therma-Tru door replacement within an existing addition footprint. We stock Therma-Tru-compatible frames, sills, and jamb extensions on our Sunnyvale trucks, and most replacements are completed in a single visit once the model is verified. Homeowners usually discover the failure when the door sticks in summer, gaps daylight in winter, or the multi-point lock no longer draws the slab tight against the weatherstrip - all signs the frame has shifted or the composite jamb has taken on moisture.

Call (650) 405-3637

Which Therma-Tru Models This Applies To

Therma-Tru identifies its product lines by series code stamped on the hinge edge of the door slab and on a foil label inside the frame head. The Classic-Craft, Fiber-Classic, and Smooth-Star series are the three most common in Sunnyvale additions built between 2005 and 2020, though we’ve installed Benchmark and Pulse series in newer ADU builds near Lakewood Village. The critical match is not the slab style but the frame depth and sill type: a 4-9/16″ jamb depth with a composite adjustable sill behaves differently from a 6-9/16″ jamb with an aluminum sill, and the wrong replacement cracks the drywall return or leaves the threshold proud of the finished floor.

We source OEM Therma-Tru frames and sills through authorized distribution, but for certain ADU applications we also spec a quality aftermarket jamb kit when the original series has been discontinued. The aftermarket equivalent must carry the same DP rating (design pressure, the structural wind-load spec) as the original; in Sunnyvale, that means DP-50 minimum for any door receiving a permit under current Santa Clara County amendments. We verify the DP rating on the product literature before quoting, and we keep that documentation in the project file.

Signs Your Therma-Tru Home Additions & ADU Is Failing

• The door drags or binds seasonally. In Sunnyvale, the clay-heavy soils off Mathilda Avenue and north of 101 expand with winter rains and contract through August. That movement transfers to the addition’s slab or stem wall, racking the Therma-Tru frame out of square. The composite jamb resists rot but not racking; once the frame twists, the slab binds against the stop.
• Daylight shows at the top corner or bottom sweep. This usually means the adjustable sill has lost its seal or the multi-point lock hardware is no longer pulling the slab tight. Therma-Tru’s adjustable sills use a composite cap over a foam seal; after seven to ten years of UV exposure on a south-facing ADU, that foam compresses permanently.
• Water stains on the interior jamb or baseboard. The weep holes in the sill are designed to drain to the exterior, but stucco or siding installers sometimes seal them with caulk or backer rod. Water ponds in the track, wicks into the jamb, and the composite material swells - not rots, but swells enough to distort the frame.
• The multi-point lock is hard to engage or the handle feels loose. Therma-Tru’s locking systems are brand-specific; a generic replacement handle from a hardware store will mount but won’t interface with the deadbolt and hook bolts. The failure is often the gear box, not the handle, and the gear box is keyed to the series.
• Finish peeling or delaminating on the slab exterior. Fiber-Classic and Smooth-Star slabs have a thermoset skin over a polyurethane core. Direct afternoon sun on a west-facing ADU in Sunnyvale can exceed the skin’s thermal tolerance after eight to twelve years, causing the bond to release. The door still functions but the weather barrier is compromised.

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Replacement Cost & What’s Included

The range depends on three factors: whether the original frame can be saved (saving roughly $600-$900 in labor and materials), whether the interior trim and drywall return must be disturbed, and whether the door is a standard size or a custom-order unit. Every quote we deliver in Sunnyvale lists these separately - slab cost, frame cost, labor hours, trim repair allowance - so the number is transparent before any work starts. Under Clause 1 of The Haven Standard, that written price is fixed; no change proceeds without a signed change order. The 365-Day Done Right Promise covers the installation and hardware function, and the documented photo record from our visit shows the condition of the rough opening before we close it back up.

DIY or Call Us?

A homeowner can safely verify the model series from the hinge-edge stamp and check whether the sill weep holes are blocked with debris - a toothpick or compressed air will clear them. What goes wrong fast is frame removal: Therma-Tru units are shimmed and fastened through the jamb into the rough opening, but the fastener locations vary by series, and an unseen screw through the composite jamb will split it if pried. Worse, a prehung unit weighs 80-120 pounds; without proper support, the frame racks during installation and the door never seals correctly. The multi-point lock also requires precise alignment of the keepers in the jamb - a 1/16″ error and the deadbolt won’t throw fully. For a door that sees daily use and secures an addition you’ve invested in, we recommend having it handled. Call (650) 405-3637 and we’ll schedule a free estimate with the written line-item quote before any work begins.

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