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IKO Home Additions & ADU: The San Diego Owner’s Guide
If you’re planning a home addition or ADU in San Diego and want IKO roofing and waterproofing products specified into the build, we install and coordinate IKO-compatible systems on every project we run. A full home addition in San Diego typically runs $53,100 – $153,400, while an ADU (accessory dwelling unit) runs $106,200 – $259,600 depending on square footage, site conditions, and finish level. Most homeowners discover they need an IKO-savvy contractor when their existing roof ties into a new addition and the underlayment, flashing, or shingle integration fails within the first two years because someone cut a corner on the transition.
Penhallow Remodeling San Diego is an independent general contractor. We are not affiliated with IKO, but we specify and install their roofing underlayment, ice-and-water shield, and shingle lines where they make sense for San Diego’s coastal moisture and canyon wind patterns.
Which IKO Models This Applies To
IKO makes a broad roofing and waterproofing catalog, and the right product line depends entirely on the addition’s roofline. For low-slope sections common on San Diego ADUs and single-story additions, the IKO Armourbase and GoldShield lines are the workhorses: self-adhered underlayments that handle the marine layer moisture we get in Point Loma, OB, and Clairemont. For steep-slope tie-ins on the main house, IKO Cambridge architectural shingles (available in dual-laminate profiles) and the Dynasty line with ArmourZone technology are the two most common choices. Where the addition’s roof meets the existing house, the compatibility gotcha is the old roof’s shingle profile: if the existing roof has a 3-tab shingle and you spec a dimensional shingle on the new section, the seam will never look right and the transition flashing becomes a weak point. Most San Diego homes built before 1995 have 3-tab, so we check that first. The other gotcha is underlayment adhesion: IKO’s self-adhered products need at least 40°F surface temperature during installation, which in San Diego is rarely a problem, but in coastal winter mornings the roof deck can be damp with condensation, and that will compromise the bond if the installer doesn’t check. We check.
When an owner is deciding between OEM IKO underlayment and an aftermarket equivalent, the honest answer is that IKO’s self-adhered lines are worth the OEM premium on addition transitions because that’s the exact place where a failed seal shows up as a ceiling stain six months later. On steep-slope shingles, a quality aftermarket architectural shingle will perform well, but you lose the wind-warranty coverage that IKO ties to its full system. For San Diego’s canyon winds in Mission Valley and the 50 – 60 mph gusts along the 52 corridor, full-system coverage matters.
Styles & brands we work with
Signs Your IKO Home Additions & ADU Is Failing
- Water staining at the addition’s interior ceiling within the first year. This is almost always the transition flashing between old roof and new roof, or an underlayment lap that wasn’t pressed correctly on a cool morning. The stain appears at the seam, not the field of the roof.
- Shingle granule loss concentrated at the valley of the new roof. IKO shingles, like all architectural lines, shed some granules early. But if the valley looks bare after two seasons and the rest of the roof is fine, the valley was walked too aggressively during install or the shingles were bent over the valley center instead of cut cleanly.
- Daylight visible through the ridge from inside the attic. On an addition, the ridge vent needs to be continuous across the whole run. If the original roof’s ridge doesn’t match the new IKO ridge profile, you’ll see a gap at the transition. That gap is not just a leak risk; it’s a rat and ash-borer entry point, and in East County it’s an ember intrusion point during fire season.
- Underlayment peeling at the eave edges. IKO’s self-adhered products fail at the eave when the drip edge wasn’t cleaned before adhesion or when the installer didn’t roll the lap with hand pressure. San Diego’s oscillating humidity in spring makes partially-bonded laps lift faster than they would in a dry climate.
- Wrinkling or fishmouths in the underlayment visible from below during construction. If the paper is wrinkled before the shingles go on, the shingles will telegraph that same wrinkle, and every wrinkle is a water channel. This is stopped-in-the-tracks obvious if you inspect before the shingles are set, which we do on every job.
See the difference
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After
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After
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AfterReplacement Cost & What’s Included
When we talk about “replacement” on an IKO-specified addition or ADU, we’re usually replacing a failed transition, a failed underlayment section, or a full re-roof of the new addition’s plane. Here’s what that costs in San Diego:
| Scope | Typical Installed Range |
|---|---|
| Full home addition (design, permits, framing, roofing, finish) | $53,100 – $153,400 |
| ADU construction (full build, IKO roofing specified) | $106,200 – $259,600 |
| Roof replacement on an existing addition or ADU | $9,440 – $23,600 |
| Roof repair (flashing, transition, valley) | $470 – $2,125 |
The range on an addition or ADU is driven by square footage first, then foundation work (pier-and-beam versus raised versus slab on grade – in San Diego you’ll hit all three depending on the neighborhood), then finish level. A 400-square-foot ADU with basic finishes in an El Cajon backyard comes in far below a 700-square-foot addition with a kitchen in Kensington. The roofing portion of any of these projects is a discrete line item, and you get that number in writing before we pull a permit. Every IKO roof we install includes the manufacturer’s system warranty where the full IKO system is used, plus our 365-Day Done Right Promise: if the roof fails inside the guarantee period, we come back and fix it at no charge. Written, not verbal.
DIY or Call Us?
Here’s the honest split. A homeowner who knows their way around a ladder can inspect the ridge transition from the attic side: look for daylight, check for granules in the gutter, and look at the ceiling below the transition for discoloration. That’s a useful check. The actual replacement work on an addition roof is not a Saturday project. Working on a roof’s edge, valleys, or transitions means working at height on a slope, and the specific failure on an IKO addition is usually in the one place where the new roof is still settling against the old house. If you patch that seam yourself, you’ll disrupt the shingle bond and void whatever warranty remains. And pulling up self-adhered underlayment on a hot San Diego afternoon is a good way to tear the membrane under it. Call us at (619) 604-9624 and Trevor will walk the roof with you, tell you exactly what failed, and put the fix in writing before anyone touches a shingle.
FAQs
A properly installed IKO architectural shingle roof on a new addition will run 25 – 30 years in San Diego’s climate, while the self-adhered underlayment should outlast the shingles it’s under; the weak points are always transitions and valleys, not the field of the roof.
Yes, in about 70% of the cases we see, the failure is confined to the transition flashing or a short underlayment lap, and that can be repaired without tearing off the shingles; if the failure has spread into the sheathing at the seam, we’ll replace that section before it becomes a structural issue.
A transition repair is usually a one-day job, and a full re-roof of a 400-square-foot addition takes two to three days once materials are on site; we give a real arrival window and a written price before we start, not after.
We order IKO materials per job so the underlayment rolls have consistent lot numbers, and we’ll bring the exact spec you approved to the site; that also means you’re not paying for half-rolls from someone else’s leftover inventory.
Written by Trevor Nash, Owner, Penhallow Remodeling San Diego at Penhallow Remodeling San Diego, serving San Diego and nearby areas.
