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Therma-Tru Home Additions & ADU: The Santa Clarita Owner’s Guide
A Therma-Tru home addition or ADU project in Santa Clarita typically runs $45,000 to $130,000 for a full addition, or $90,000 to $220,000 for a detached ADU, and we can usually get a written price in your hands within a few days of the first walkthrough. Most owners reach this page because they’ve already started looking at floor plans or their in-law unit has reached the point where the existing footprint no longer works. The Therma-Tru name usually enters the conversation around the entry doors and weather sealing, because a poorly hung exterior door on a new Santa Clarita addition means July heat finds its way inside before the drywall dust settles.
We’re an independent remodeler in Santa Clarita, not a Therma-Tru dealer, and we install Therma-Tru entry and patio doors on additions and ADUs where the homeowner wants a door that holds its reveal through three-digit summers. We also work with KraftMaid cabinets, Cambria and Silestone countertops, and Kohler or Moen fixtures when the project calls for named brands a homeowner can research by name.
Key Takeaways:
- Installed pricing for a home addition in Santa Clarita runs $45,000 to $130,000; ADUs run $90,000 to $220,000 depending on size and site conditions.
- We give you a written price before any work starts, and the price on the paper is the price on the invoice – Graham Stein puts that in writing every time.
- Crews use shoe covers and drop cloths on every visit, and quiet tools during nap and school hours where the job allows.
- Every project carries the 365-Day Done Right Promise – if it’s not done right after completion, we make it right.
Which Therma-Tru Models This Applies To
Therma-Tru entry doors fall into a few families, and the compatibility picture changes depending on whether you’re adding a single door to a new addition or pairing a patio door with an ADU footprint. The Classic-Craft and Fiber-Classic lines remain the most common choices we see on Santa Clarita additions, because both hold their shape through the dry heat of the Santa Clarita Valley and the cooler winter nights up in Canyon Country or Saugus. The Smooth-Star line is a budget-aware fiberglass option, and it’s often specified when the addition is a rental suite where the finish needs to survive tenants.
Therma-Tru builds doors in standard widths of 30, 32, and 36 inches, with the 36-inch width being the right call for any exterior door on an addition or ADU in Santa Clarita, because building code requires a minimum clear opening width. The compatibility gotcha most homeowners don’t know: Therma-Tru frames are factory-mulled with their own sill pans and corner seals, and swapping in a different manufacturer’s slab after the fact usually voids the weather-seal fit. We order the full Therma-Tru system when the addition calls for it, rather than trying to make a slab work in a frame that wasn’t built for it. OEM parts are the way to go for Therma-Tru-specific hardware like the adjustable sill cap and the corner weatherstrip. For hinge hardware and lock sets, quality aftermarket pieces from brands like Schlage or Baldwin fit cleanly and hold up as well as the factory kit.
If you’re not sure which Therma-Tru model you have on an existing door, the label is typically on the hinge edge of the slab, a small white tag with the model name and manufacturing date. We can read that label when we’re on site and save you the guesswork.
Styles & brands we work with
Signs Your Therma-Tru Home Additions & ADU Is Failing
- Door binds at the latch or rubs the jamb. Our dry summers and cooler winters make the framing under the door move a little. When the reveal around a Therma-Tru slab goes uneven, the hinges and strike plate are the first things to tell you. It’s usually a shim adjustment, but left alone it turns into a latch that won’t catch.
- Sweep is worn or light shows under the door. Once the bottom sweep loses its contact with the sill, Santa Clarita dust and heat move through every day. If you can see daylight under the door from inside the addition, the sweep is beyond adjustment.
- Sill cap is cracked or pulling away from the frame. Therma-Tru sills are composite, but years of direct sun on a south-facing ADU wall in Stevenson Ranch or Valencia can eventually make the cap brittle. Water then bypasses the frame corners.
- Condensation or fog inside the door’s glass insert. The sealed insulated glass unit has failed. Therma-Tru doors with decorative glass can have the insert replaced without replacing the whole slab.
- Lock set turns but deadbolt doesn’t engage cleanly. The lock body is fighting a sagging slab. The fix is often realigning the door, not a new lock, but if the strike plate has been badly worn, both need attention.
See the difference
Before
After
Before
After
Before
AfterReplacement Cost & What’s Included
If the Therma-Tru issue is a failed door component on an existing addition or ADU, the repair is a much smaller number than the full project cost. A new Therma-Tru entry door system, installed, typically runs $1,800 to $4,500 in Santa Clarita, depending on the model line, glass options, and whether we’re also rebuilding the rough opening. Replacing just the weatherstripping and sweep can run $120 to $350. Replacing a glass insert runs $300 to $750 depending on size and pattern.
The big dollars on this page are the addition and ADU numbers: $45,000 to $130,000 for an addition, $90,000 to $220,000 for an ADU, and $30,000 to $80,000 if you’re converting an existing garage instead. The price we give before you spend a dollar includes everything, and you’ll see the breakouts: materials, labor, permit fees, and the Therma-Tru door package if it’s part of the project. We don’t change order our way through a job. The 365-Day Done Right Promise covers every project we complete, including doors we hang and additions we build.
What drives the price range:
- Foundation scope and soil conditions – some Santa Clarita lots in areas like Newhall or Castaic need more excavation than others.
- Roof complexity and tie-in to the existing structure.
- Therma-Tru door package: single entry, double entry, or a patio slider addition.
- Interior finish level: paint-grade versus stain-grade trim, cabinet quality, countertop material.
- ADU utility connections: sewer, gas, and panel work can add materially depending on the lot.
DIY or Call Us?
There are a few things an owner can safely check. You can read the Therma-Tru label on the hinge edge of the slab. You can look at the sweep to see if it’s visibly torn or compressed. You can run a dollar bill under the door when it’s closed and feel whether the sweep holds it. If the door binds through the arc of its swing, you can note where it rubs and when it started. None of those cost you anything.
What we’d rather you not do is pull hinges off a full-size fiberglass slab that weighs 80 to 120 pounds, or try to re-shim a door while it’s hung. A door that drops off its hinges will break a toe, a floor, or both. The threshold is also not a beginner job – the sill cap has to be bedded the right way or water finds the subfloor inside a year. If the issue is just a worn sweep or a loose strike plate, that’s a reasonable Saturday job. Anything structural, let us handle it. Call (661) 542-4056 and Graham will walk the site with you, note what’s actually failing, and put the price on paper before any work starts.
FAQs
A properly installed Therma-Tru fiberglass door should last 25 to 30 years in the Santa Clarita climate, with the weatherstripping and sweep replaced every 5 to 7 years. South-facing exposure without a porch shortens the life of the sweep and the sill cap more than anything else. Call (661) 542-4056 if your door is older than 15 years and showing signs of sag – a fresh sweep buys years, but a cracked sill means it’s time to budget the replacement properly.
Yes, in most cases. The sweep, weatherstripping, glass insert, hinges, and lock set are all serviceable parts on a Therma-Tru door, and none of them require replacing the slab. We replace the whole door when the frame is compromised or the slab has taken impact damage. Call (661) 542-4056 and we’ll tell you which one you’re actually facing after we see it.
A single entry door swap takes one day. If we’re doing a full addition or ADU, the door installation happens at the right point in the sequence so we don’t have a finished door up while drywall dust is still moving through the house. For any project, the written price includes the schedule, so you’ll know before we start which days the crew is on site and what happens in what order. Call (661) 542-4056 for a free estimate on your specific job.
We keep common weatherstripping, sweeps, and threshold components on the truck for same-day small fixes. Full Therma-Tru door systems are ordered per project with the exact sizes, glass, and finish you choose, which usually takes a week or two depending on the factory. If your existing door is a standard size, we can often get the replacement in faster. Call (661) 542-4056 and we’ll check current lead times while you’re on the phone.
Written by Graham Stein, Owner, Elmstead Remodeling Santa Clarita at Elmstead Remodeling Santa Clarita, serving Santa Clarita and nearby areas.
