Free written scope consultation - allowances, timeline, and change-order rules on paper before a single trade is scheduled
IKO Home Additions & ADU: The San Antonio Owner’s Guide
IKO home additions and ADU construction in San Antonio typically runs $45,000 to $130,000 for a complete addition, and $90,000 to $220,000 for a detached accessory dwelling unit. We stock IKO-compatible roofing, decking, and underlayment materials on our trucks for addition and ADU projects across San Antonio, and we can usually start the structural phase within two weeks of a signed scope. Most homeowners don’t discover an IKO product problem until water shows up where it shouldn’t be: a stained ceiling corner, a buckling seam in the decking, or an underlayment that’s quietly deteriorating under a roof that still looks fine from the street.
Mason Remodeling Co San Antonio is an independent general contractor, not affiliated with IKO. We work with IKO products because they’re specification-grade and hold up to South Texas heat, but we also stock compatible materials from GAF, CertainTeed, and Owens Corning when a project calls for them. Our kitchen and bath work leans on KraftMaid, Cambria, and Silestone, which matters when an addition includes a new kitchen or bathroom.
Key Takeaways:
- Home additions in San Antonio: $45,000 – $130,000 installed
- Detached ADUs: $90,000 – $220,000 depending on utilities and finishes
- We deliver a written price before any work starts, on every project
- Every crew member is name-and-photo verified before they reach your door
Which IKO Models This Applies To
IKO’s product line breaks into three categories that matter for additions and ADUs: asphalt shingles (the Cambridge and Dynasty series are the ones we see most often on San Antonio roofs), synthetic underlayment (StormShield and GoldShield), and decking materials. The compatibility gotcha most homeowners run into is this: IKO’s Cambridge shingles are a metric-size product with a different exposure spec than standard three-tab or some competitor architectural lines. If your addition is tying into an existing roof, the roofline transition needs to be measured carefully so the new IKO material meets the old material cleanly.
On the OEM-versus-aftermarket question for IKO specifically: IKO’s underlayment system is engineered to work with their shingle spec, with specific fastener patterns and overlap requirements. When we’re adding square footage to a home or building a detached ADU, we use IKO’s full system rather than mixing in generic underlayment, because the warranty language actually requires it. The practical difference in San Antonio is heat performance: a mismatched underlayment under IKO shingles fails faster when attic temperatures hit 140 degrees in August.
Styles & brands we work with
Signs Your IKO Home Additions & ADU Is Failing
- Water staining at the roofline transition. When an existing roof meets a new addition, the seam is where failures start. If the original roofer didn’t install proper flashing or used a mismatched underlayment, water gets in slowly and shows up as a faint brown line months before it becomes a drip.
- Shingle granule loss in the first three years. IKO shingles shed some granules during install and the first big storm season, but if you’re seeing bare asphalt patches or granules collecting in gutters after year one, the shingles were likely improperly fastened or walked on in high heat.
- Wrinkled or bubbled underlayment visible at the eaves. San Antonio’s heat cycling causes cheap underlayment to delaminate. IKO’s synthetic products resist this, but if the installer used a generic felt product to save money, you’ll see ripples at the drip edge within two summers.
- Sagging decking or soft spots around the ADU’s plumbing vents. Detached ADUs with small baths and kitchens concentrate moisture around vent penetrations. If the decking wasn’t sealed properly there, you’ll feel give underfoot before you see water inside.
- Doors and windows binding in a new addition. This is a framing or foundation settlement issue, not an IKO product failure, but it often shows up at the same time as roof problems. A properly engineered addition shouldn’t shift enough to bind a door in its first five years.
See the difference
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AfterReplacement Cost & What’s Included
Here’s what real San Antonio addition and ADU pricing looks like line by line, so you can self-qualify before you call:
- Home addition (300 – 600 sq ft, finished): $45,000 – $130,000
- Detached ADU (400 – 800 sq ft, with kitchen and bath): $90,000 – $220,000
- Garage conversion to living space: $30,000 – $80,000
- Roof replacement on addition (IKO Cambridge/Dynasty): $8,000 – $20,000
- Structural repair to existing addition framing or decking: typically 15 – 30% of the original addition cost, depending on what’s compromised
Every project gets a written price before a single tool is unpacked. That number includes all permits, all labor, all materials, and the written guarantee. What drives the range is foundation work, utility runs (especially sewer and electrical for a detached ADU), and finish level. A kitchen rebuild inside an addition runs $14,000 – $45,000 on its own; a bath adds $9,000 – $28,000. Our 365-Day Done Right Promise covers every addition and ADU we build: if the work isn’t right within a year of completion, we make it right at no cost to you.
DIY or Call Us?
What you can safely check yourself: granule accumulation in gutters, visible underlayment at eaves, caulk condition around vent pipes, and whether doors and windows open smoothly. None of that requires a ladder.
What you should not do yourself: the structural and roofing work on an addition or ADU is genuinely dangerous. Roof tear-off on a two-story addition means working at height on a surface that’s already compromised. Underlayment replacement requires pulling shingles without damaging the decking. And any framing or load-bearing work inside a converting garage involves temporary support walls and engineering. This is not a weekend project. If you’ve got a failing IKO component in an addition, call us at (254) 269-5071. We’ll send someone to look at it, give you a written price, and explain exactly what’s failing before you spend a dollar.
FAQs
An IKO Cambridge or Dynasty roof installed to spec on a new addition should last 20 – 25 years in San Antonio’s climate, with proper attic ventilation. The two things that shorten that: poor ventilation (attic temps above 150 degrees bake shingles from underneath) and hail. We’ve seen roofs fail in 8 years when a builder skipped ventilation and used the wrong underlayment. Call (254) 269-5071 if you suspect your addition’s roof is aging early.
Repairs are viable if the failure is localized: one vent boot, one section of flashing, a small area of granule loss. If the underlayment is failing across a large area or the decking has rot, full replacement is cheaper than a patchwork of repairs over five years. We’ll tell you which one you need and put it in writing.
A detached ADU build takes 4 – 8 months depending on foundation type, utility trenching, and permit review timelines with the City of San Antonio. A garage conversion runs closer to 8 – 12 weeks when the existing structure is sound. We’ll give you a real timeline in your written scope of work, not a salesperson’s guess.
We keep IKO Cambridge shingles in the most common San Antonio colors, along with IKO underlayment and decking, in our local supply. Custom colors or larger Dynasty orders take 5 – 10 business days. For additions that also involve kitchen or bath work, we can source KraftMaid, Cambria, and Silestone materials through our supplier partnerships at the same time, so you’re not coordinating three different deliveries.
Know who’s coming, know what it costs, know it’s covered – that’s the whole job before the job starts.
If your IKO addition or ADU is showing signs of failure, or if you’re planning a new build and want a contractor who puts everything in writing, call (254) 269-5071 for a free estimate. Isaac Pruett and our crew have been working San Antonio jobs for years, from gut renovations near the King William Historic District to new ADUs in neighborhoods across the city. A real person answers the phone, day or night.
Written by Isaac Pruett, Owner, Mason Remodeling Co San Antonio at Mason Remodeling Co San Antonio, serving San Antonio and nearby areas.
