Tamko Home Additions & ADU Nationwide

Tamko Home Additions & ADU: The Los Angeles Owner’s Guide

If you own a home with a Tamko addition or ADU and something has failed, you need to know exactly what failed, what it will cost, and whether a repair or full replacement makes sense. Rowan Construction Group works with Tamko systems across Los Angeles on a near-weekly basis, and the range that covers most repairs and partial rebuilds is $53,100-$153,400 depending on the structural scope. Most owners first discover the problem through water staining at the roofline, a door that no longer closes square, or electrical interruptions that trace back to the connection point between the original house and the addition.

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Tectonic specificity matters here. Los Angeles sits on active seismic soil, and expansions get baked in direct UV exposure for 300-plus days a year. What fails first is rarely the framing. It is the interface: where the Tamko envelope meets the original structure, where flashing was undercut by a previous installer, or where movement cracked a stucco corner and let moisture into the sheathing. We will explain what we look for, what we stock, and what the numbers come to before anyone brings a tool to your property.

Which Tamko Models This Applies To

Tamko’s residential addition and ADU systems are typically sold through local building material suppliers in Southern California, and the most common lines we encounter in Los Angeles are the Tamko ProLine series for attached additions and the Tamko FlexStep modular systems used in garage-to-ADU conversions. The compatibility gotcha most owners miss is that Tamko’s flashing kits and transition membranes are keyed to the roofing profile they were paired with. A Tamko addition built with tamko Heritage shingles requires the matching transition kit when you are adding a new roofline or changing pitch. Aftermarket equivalents exist, but the $80-$400 you save usually disappears the first time the transition gets a hard rain and the seam opens.

OEM versus aftermarket is not theoretical for this category. Tamko’s in-house transition components are ASTM-tested as a system. We install both, but we show you the cost difference in writing and let you decide. What we recommend: OEM for anything waterproofing-related, aftermarket only for non-structural hardware like vent caps and trim. Before you order anything, check the ink stamp on the underside of the rafter tail or the back of the gable trim. It will list the series name and manufacturing year. That information determines whether your repair is a patch or a teardown.

Signs Your Tamko Home Addition or ADU Is Failing

• Water staining at the addition’s roofline, usually at the corners. This means the transition flashing between your original roof and the Tamko section has separated. In Los Angeles, the culprit is usually thermal cycling: the expansion gap closes, sealant fails, and wind-driven rain finds the opening. If you see staining, you likely have wet sheathing behind it already.
• A door that sticks or a window that will not latch. That is movement. In a Los Angeles addition, movement means either the foundation was under-engineered for the soil type, or the addition’s connection to the main house is pulling. Depending on your area, soil in Los Angeles ranges from clay-heavy (which expands in winter rains) to sandy loam (which shifts in drought). Both move a light addition.
• Electrical flicker or dead outlets only in the ADU or addition. Subpanel wiring for additions is frequently undersized when the work was permitted by an overworked Los Angeles building office, and connections at the main panel may have loosened over time. Do not open the panel yourself. Call us, or call any licensed electrician, before the flicker becomes an arc.
• Musty smell in the knee wall or attic of the addition. This points to a failed or missing vapor barrier at the crawl space or roof deck. In coastal Los Angeles, morning marine layer moisture gets pulled into unconditioned additions and condenses on the backside of drywall.
• Visibly cracked stucco at the seam between house and addition. A classic Los Angeles symptom. The stucco cracks because the addition is settling at a different rate than the original structure. If the crack is wider at the top than the bottom, you are looking at differential settlement, and it is worth an inspection before it becomes a structural issue.

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Replacement Cost & What’s Included

For a Tamko addition or ADU in Los Angeles, full teardown-and-rebuild work lands in the $53,100-$153,400 range depending on the size of the addition, whether the roof gets replaced, and whether foundation work is required. Partial envelope repair (flashing, stucco, weather barrier at the transition) runs from $5,310-$23,600 in most cases. A subpanel or electrical service repair for a failing ADU connection typically lands between $2,360 and $9,440 depending on whether the feeder needs rerunning.

Every number Rowan Construction Group gives you is a flat written price. That is Clause 1 of the Haven Standard. It includes the part or materials, labor for our background-checked and uniformed crew, the documented photo record we take on every visit, and the written warranty on the work. You will know the exact cost before anyone swings a hammer, and no change proceeds without a signed change order. That discipline is why 4,000-plus projects have come in within a few percent of our agreed number since 2007.

DIY or Call Us?

You can safely check a few things yourself: look at the rafter tails for the ink stamp, note where the staining appears and whether it worsens after rain, and test every outlet in the addition with a simple plug tester. What you should not do is open any electrical panel, pull back stucco or flashing, or get on a ladder at the transition seam. Roof transitions and electrical work are the two places where a homeowner trying to save a service call ends up creating a bigger one.

If the issue is water intrusion at the interface, that is a roof-and-wall repair combined, and it belongs with someone who has done it on Tamko systems. If it is electrical, same answer, different trade. If you are not sure which trade is the right one, call us at (470) 298-9650 and describe what you see. We will tell you honestly whether it needs one of our crews or a referral. The call costs you nothing.

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