Hemet's dominant construction risk is hidden in the existing structure — not in the ADU itself. The 1970s and 1980s housing stock that makes up most of Hemet has three consistent upgrade issues that ADU projects trigger: 100A electrical panels that need upgrade to 200A, galvanized water lines that need replacement, and aging sewer laterals that need camera inspection. None of these are problems with the ADU design; they're problems in the existing house that become visible — and mandatory to address — when you add a second unit to the system load.
Risk 1: 100A Electrical Panels
The most consistent infrastructure issue on Hemet ADU projects. Homes built before 1980 routinely have 100A main electrical panels that were appropriate for the original home but are at or near capacity when the original load plus an ADU (adds 40–60A) is considered. California electrical code requires adequate panel capacity for all planned loads — the plan checker at Development Services will flag inadequate panel capacity if it's in the permit plans.
Panel upgrade cost: $2,500–$4,500 for a 100A-to-200A upgrade. This is a fixed cost per project — not optional if the panel is insufficient. We assess panel capacity during the initial site visit and include the upgrade in the project quote if needed. Discovering this during plan check (if the original contractor didn't assess it) causes a mid-process plan amendment and delay.
We see 100A panels on approximately 60% of Hemet projects that involve pre-1985 homes. It's a standard planning item, not a surprise — but only if it's assessed before the project is scoped.
Risk 2: Galvanized Water Lines
Pre-1980 Hemet construction used galvanized steel water supply lines. Galvanized pipe corrodes internally over 30–50 years — rust and mineral deposits restrict flow, discolor water, and eventually fail. Adding an ADU's water demand to an already-degraded galvanized supply system creates real risk of low pressure at fixtures and accelerated pipe failure under increased demand.
The question is not whether to replace galvanized lines — it's which ones, during which phase of construction. We assess the extent of galvanized piping during the site visit. Replacement of main supply lines and those within the construction scope costs $3,500–$12,000 depending on extent. Replacing galvanized lines while walls are already open during construction is $2,000–$4,000 less than replacing them as a standalone project later.
Risk 3: Aging Sewer Laterals
Hemet's sewer laterals — the pipes running from the home to the city sewer main — in pre-1990 construction are often vitrified clay or cast iron. Clay lateral joints can separate or develop root intrusion over decades; cast iron corrodes. An ADU adds wastewater load to a lateral that may already be partially compromised.
A sewer lateral camera inspection ($300–$600) is the right mitigation before a Hemet ADU project begins. If the lateral shows significant root intrusion or joint displacement, lining or replacement costs $3,500–$9,000 — but is better known before construction than discovered as an emergency during or after.
Risk 4: Post-Tension Slab Conditions
Many 1970s–1980s Hemet homes were constructed on post-tension concrete slabs. These slabs require specific construction protocols when penetrating for plumbing — the tensioning cables running through the slab cannot be cut. An inexperienced contractor who saws or drills without a cable locate can damage the structural system, requiring expensive slab repair. We use post-tension cable location tools before any slab penetration on Hemet projects. This is a skill gap that separates experienced Hemet contractors from those new to the market.
Every risk on this page is identifiable during the pre-design site assessment. Panel inspection, plumbing type identification, sewer lateral assessment — we do all of this before any design fees are committed. Surprises happen to contractors who skip this step.
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