Therma-Tru Home Additions & ADU Nationwide

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

Therma-Tru entry systems in Los Angeles home additions and ADUs typically run $53,100-$153,400 installed, depending on whether you’re integrating a single door into a new addition or specifying full Therma-Tru systems throughout a detached ADU. We stock Therma-Tru-compatible frames, sills, and jamb components for same-day installation on most Classic-Craft and Fiber-Classic series units in the Los Angeles basin. Most owners discover a problem when the door won’t latch properly after seasonal swelling, or when they notice daylight between the slab and the sill after a few years of Santa Ana wind cycles.

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Which Therma-Tru Models This Applies To

Therma-Tru organizes its residential lines into series families, and the part you need depends on which family your addition or ADU was built with. The Classic-Craft series uses a 4-9/16″ or 6-9/16″ jamb depth with a composite frame that doesn’t rot, but the adjustable sill cap on these units is model-specific and not interchangeable with Smooth-Star or Fiber-Classic lines. Fiber-Classic uses a different door edge profile, so the weatherstrip channel geometry changes even when the rough opening dimensions match.

To identify your unit, check the hinge edge of the door slab for the stamped manufacturing date and series code, or look for the label on the top of the frame behind the trim. We carry OEM sill caps and composite jamb legs for Classic-Craft CCA12 and CCA14, Fiber-Classic FCW12 and FCW14, and Smooth-Star SSW12 and SSW14 series. For QuickShip and Builder’s Choice units common in production ADUs around Inglewood and Baldwin Hills, we stock quality aftermarket equivalents that match the thermal break spec at a lower parts cost. OEM versus aftermarket is a real decision on Therma-Tru: the OEM composite sill cap runs higher but carries the full 10-year system warranty intact, while our aftermarket equivalent meets the same ASTM E330 structural load rating and costs less. We stock both on our Los Angeles trucks and will show you the part before we install it.

Signs Your Therma-Tru Home Additions & ADU Is Failing

• Door sticks or binds seasonally. In Los Angeles, the combination of morning marine layer moisture and afternoon dry heat causes Therma-Tru fiberglass slabs to expand and contract differently than the composite frame. If the binding is worse in October and April, the frame is likely out of plumb or the adjustable sill cap has compressed.
• Visible gap under the sill or light showing at the threshold. The composite sill cap on Classic-Craft units can crush down over time, especially on ADUs built with a concrete pour that wasn’t fully cured before door installation. This gap bypasses the sweep and lets in dust, water, and insects.
• Weatherstrip is torn, compressed, or pulling from the frame kerf. Therma-Tru uses a dual-fin bulb seal in a routed channel. Once the fins lose memory, the seal becomes cosmetic. We see this accelerated on south-facing ADU doors in neighborhoods like Mar Vista where UV exposure is constant.
• Latch doesn’t engage or deadbolt is hard to turn. Frame shift from foundation settlement is common in Los Angeles hillside ADUs. The door isn’t the problem; the opening geometry has changed. A new door on a shifted frame fails the same way in six months.
• Condensation between storm door and entry door. This indicates the thermal break in the frame is compromised or the weep holes in the sill are blocked with stucco debris, a frequent find on newer ADUs where the stucco crew didn’t clear the drainage path.

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Replacement Cost & What’s Included

These are installed prices for Los Angeles, with parts, labor, removal, and disposal included. What drives the range: jamb depth (4-9/16″ standard versus 6-9/16″ for stucco or thick drywall), whether the frame is plumb and square or needs reframing, and whether we’re matching existing trim or installing new. Under Clause 1 of the Haven Standard, you get a written price before any work starts. The 365-Day Done Right Promise covers the installation. We also document with a photo record before, during, and after, included as standard.

DIY or Call Us?

There’s a safe middle ground here. A homeowner can check the weep holes for debris, verify the door closes against the weatherstrip evenly, and confirm the latch strike plate hasn’t wallowed out. These checks cost nothing and tell us a lot when you call.

Where DIY goes wrong: removing a Therma-Tru prehung unit without supporting the header can shift the framing above, especially in older Los Angeles additions with 2×4 headers instead of engineered lumber. The adjustable sill cap looks simple but sets the door’s compression against the sweep, and getting it wrong means water intrusion you won’t notice until the subfloor is damaged. The fiberglass slab is heavy, and the composite frame requires specific fasteners, not standard wood screws, to maintain the warranty. We’re not going to tell you it’s rocket science. We are going to tell you that in our documented photo records, the jobs that went sideways usually started with “I watched a video and thought I could handle it.” Call (213) 652-7670 and we’ll give you a written price. If it’s a five-minute adjustment, we’ll tell you that too.

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