Cover Home Additions & ADU Nationwide

Cover Home Additions & ADU: The Sunnyvale Owner’s Guide

We stock and install Cover-compatible home additions and ADU systems in Sunnyvale, with typical installed pricing from $45,000 to $130,000 for additions and $90,000 to $220,000 for detached ADUs. Most Cover-based projects we scope in Sunnyvale can begin within 2-4 weeks of signed contract, assuming permit approval from the City of Sunnyvale. Homeowners usually discover their Cover addition or ADU needs attention when they notice sagging rooflines, water intrusion at the addition-to-existing seam, or doors that no longer square in their frames - signs that the structural integration between the Cover system and the original structure has shifted or failed.

Call (650) 405-3637

Which Cover Models This Applies To

Cover manufactured prefabricated addition and ADU systems in several product lines between roughly 2015 and 2022, including the Cover Studio, Cover One, and Cover Two series. The Studio was their compact single-room module, typically 120-250 square feet; the One and Two scaled to full bedroom or multi-room configurations up to 500 square feet. Identification is straightforward: every Cover unit ships with a metal data plate mounted on the electrical panel or inside the utility closet, listing the model designation, serial number, and manufacturing date. For Sunnyvale properties, we also check the original permit file with the City of Sunnyvale Building Division, since Cover units installed here required a specific structural attachment detail to meet local seismic requirements.

The OEM-versus-aftermarket question for Cover is specific. Cover’s proprietary wall panel system, with its integrated steel frame and closed-cell foam core, means structural repairs or modifications must match the original gauge and thermal bridging specs. We source through Cover’s remaining parts network where available, and where Cover OEM is discontinued, we engineer equivalent solutions using structural steel of matching ASTM grade and insulation values, documented in writing before any work proceeds. Rowan Construction Group Sunnyvale is an independent service provider, not affiliated with Cover.

Signs Your Cover Home Additions & ADU Is Failing

• Gaps appearing at the addition-to-house seam. The Cover system attaches to the existing structure through a bolted steel ledger; if the connection loosens or the original structure settles differentially, a visible gap opens. In Sunnyvale’s clay-heavy soils, seasonal moisture swings accelerate this - we see it most often in properties near Lakewood Village where the alluvial soil holds water longer.
• Doors or windows that stick or won’t latch. The steel frame of a Cover unit is rigid, so any racking or twist in the foundation transmits directly to the openings. This is usually the first symptom owners notice, and it means the structural integration needs inspection before cosmetic adjustment.
• Water staining on interior walls, especially at ceiling corners. Cover’s roof-to-wall flashing uses a proprietary extruded aluminum profile; if the sealant degrades or the flashing pulls away, water enters at the joint. Sunnyvale’s winter rains are concentrated enough that a small gap becomes a visible stain within one season.
• Floor bounce or sag in the addition floor. Cover units use a steel chassis with composite floor panels; if the chassis support points sink or corrode (we see this where drainage was poorly planned), the floor feels springy or visibly dips.
• HVAC short-cycling or inability to maintain temperature. The foam core in Cover wall panels is high-performing when intact, but if panels are punctured or the thermal envelope is compromised at seams, the mini-split or ducted system runs continuously. Energy bills spike before comfort drops.

Before

After

Replacement Cost & What’s Included

For Cover home additions in Sunnyvale, our installed pricing runs $45,000-$130,000 depending on whether we’re repairing structural integration, replacing damaged envelope panels, or rebuilding the addition entirely. ADU construction using Cover-compatible methods starts at $90,000 and ranges to $220,000 for detached units with full utility connections. What drives the range: square footage, foundation condition (retrofit piers versus new stem wall), utility extension distance, and whether the original Cover electrical and plumbing rough-ins are reusable.

Every quote we deliver is flat-priced with written scope - material costs, labor hours, and any subcontractor scope listed separately. Under Clause 1 of The Haven Standard, that written price is delivered before any work starts, and no change proceeds without a signed change order. Our 365-Day Done Right Promise covers the workmanship; manufacturer warranties on materials pass through as documented. We also stock common Cover-compatible structural hardware and flashing profiles on our trucks, so diagnosis doesn’t wait on parts shipping.

DIY or Call Us?

There’s a safe middle ground for Cover owners. You can inspect the data plate, photograph any gaps or stains for documentation, and check that downspouts drain away from the addition foundation - all useful information that speeds our diagnosis when you call. What you should not attempt: loosening or tightening the structural attachment bolts (these are torque-specified for seismic load), cutting into wall panels (the foam core and steel frame require specific fire-sealing when penetrated), or modifying electrical or plumbing rough-ins without permit.

Cover’s integrated system means a fix in one area often stresses another. We’ve seen well-meaning owners seal a roof gap with off-the-shelf caulk, only to trap moisture against the steel frame and accelerate corrosion. If you’re seeing any of the symptoms above, call (650) 405-3637. We’ll schedule a free estimate, deliver a written line-item quote, and if you have a competitor’s estimate already, we’ll review it line by line at no charge.

FAQs