Therma-Tru Home Additions & ADU Nationwide

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

Therma-Tru entry systems in Palo Alto home additions and ADUs typically run $45,000-$130,000 installed, depending on whether you’re integrating a single door into a modest bump-out or engineering a full Therma-Tru grand entry for a standalone accessory dwelling unit. We stock Therma-Tru-compatible frames, sills, and weatherseal kits for same-day replacement on failed units, and we carry the Classic-Craft, Fiber-Classic, and Smooth-Star series lines on most trucks. In Palo Alto, we see the most calls after winter rains reveal sill rot in additions built during the 2015-2019 boom, when fiberglass doors went in fast but flashing details got skipped.

Call (650) 446-9092

Which Therma-Tru Models This Applies To

Therma-Tru organizes its residential lines by substrate and aesthetic tier, and the part you need depends on which skin sits over the polyurethane core. Classic-Craft (mahogany, oak, and canvas-textured collections) uses a denser frame stock with integrated composite bottom rails; Fiber-Classic (the original fiberglass line) has a thinner profile and a separate aluminum sill pan; Smooth-Star (paint-ready and stainable) carries the most standardized hardware prep but requires specific hinge mortise spacing.

To identify your unit, check the hinge stile for a stamped date code and series mark, or remove the interior trim to find the specification label on the frame rabbet. The critical compatibility gotcha in Palo Alto’s 94024 and 94301 zones: additions built with 2×4 framing often used Fiber-Classic 6’8″ slabs in 32″ or 36″ widths, but the ADU ordinance after 2020 pushed many projects to 2×6 walls and 8’0″ doors, which demand Classic-Craft or Smooth-Star frames with extended jamb depths. OEM sills from Therma-Tru run $80-$220; we also source L.I.F. Industries and Endura compatible sills that match the drain slope and cap seal geometry at roughly half the cost, though we disclose the substitution in writing before installation.

Signs Your Therma-Tru Home Addition or ADU Entry Is Failing

• Water staining at the bottom corners of the interior casing. This usually means the sill pan or end dam has separated from the frame, letting Palo Alto’s driven winter rain migrate behind the brickmold. We find this most often on south-facing additions where thermal cycling fatigues the sealant joint.
• Door sticks at the top or drags at the threshold in summer, then gaps in winter. The composite frame is expanding and contracting beyond its original tolerance, often because the original installer skipped shimming at the hinge locations or used non-composite fasteners that backed out.
• Visible delamination or bubbling on the skin surface. On Fiber-Classic units, this indicates moisture has breached the gel coat, usually from a failed weatherstrip seal at the lock stile. The core will continue to absorb water until the slab warps.
• Draft despite closed door, or insect intrusion at the sill. The compression seal at the bottom has flattened or the adjustable cap has cracked; Therma-Tru’s OEM bulb seal is EPDM, which degrades in UV after 8-12 years in California exposure.
• Lockset misalignment requiring shoulder force to latch. Frame racking from inadequate header support in the addition’s rough opening, common in Palo Alto’s Eichler-style and mid-century ranch additions where the original post-and-beam structure wasn’t designed for a heavy insulated entry.

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Replacement Cost & What’s Included

For a Therma-Tru entry system in a Palo Alto home addition or ADU, expect $45,000-$130,000 for full addition construction with integrated door placement; standalone door replacement with frame, sill, and trim runs $2,800-$6,500 depending on jamb depth, sidelite configuration, and whether we need to rebuild the rough opening. The range driver is almost always the wall condition we find after removing the old unit: additions with stucco exteriors often require weep screed repair and paper flashing integration that interior replacements don’t.

Our quote breaks out slab, frame, sill, hardware, labor, and disposal line by line. Under Clause 1 of the Haven Standard, that written price is fixed; if we find rot in the subfloor after removal, we stop, photograph it, and present a signed change order before continuing. Every Therma-Tru installation carries our 365-Day Done Right Promise, and we document the full opening condition with dated photos before the new unit goes in.

DIY or Call Us?

An owner can safely check the door’s operation, look for visible seal damage, and confirm the model stamp on the hinge edge. What goes wrong fast: removing a pre-hung unit without supporting the addition’s header risks structural settlement, and re-flashing to Palo Alto’s current building code (Chapter 14, weather-resistant barriers) requires integration with existing stucco or siding that most homeowners don’t have the tools to execute cleanly.

We don’t recommend DIY on these. The fiberglass slab is manageable; the frame, sill pan, and head flashing assembly is not. If you’re seeing the symptoms above, call (650) 446-9092 and we’ll schedule a free estimate with a written price before any work starts.

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