How Much Does Room Addition Cost in St. Louis, MO?
St. Louis pricing is 12% below the national average. Updated for 2026.
Based on local labor rates, varied climate conditions, and St. Louis's diversified economy.See our methodology
Room Addition Pricing in St. Louis, MO
St. Louis is one of the more affordable markets for room addition, with costs running about 12% below the national average. The city's diversified economy and balanced labor market create favorable conditions for competitive pricing. Getting multiple quotes from the 295K-population metro area is straightforward.
Local climate plays a direct role in room addition costs here. Harsh winters and hot summers mean year-round service needs; freeze-thaw cycles affect foundations.
Market-specific factors matter in St. Louis: moderate cost of living keeps contractor rates affordable.
St. Louis has moderate permitting requirements. Depending on the scope of your room addition project, you may need local permits. A licensed contractor will handle the permitting process as part of the job in most cases.
St. Louis vs National Average
What Affects Room Addition Cost in St. Louis?
Size
Small (100 sq ft): $15,000-$25,000. Average (200 sq ft): $30,000-$50,000. Large (400+ sq ft): $60,000-$100,000+
Room Type
Basic bedroom: $20,000-$40,000. Bedroom + bathroom: $35,000-$65,000. In-law suite: $50,000-$100,000+
Per Sq Ft
Budget: $80-$150/sq ft. Mid-range: $150-$250/sq ft. High-end: $250-$400+/sq ft
St. Louis Market Conditions
moderate cost of living keeps contractor rates affordable
Local Climate Impact
harsh winters and hot summers mean year-round service needs; freeze-thaw cycles affect foundations
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Tips to Save on Room Addition in St. Louis
- 1.A bump-out (extending an existing room 2-4 feet) costs $5,000-$15,000 — much less than a full addition
- 2.Building over an existing garage or patio saves on foundation costs
- 3.A dormer addition (expanding attic space) costs 30-50% less than a ground-floor addition
- 4.Act as your own general contractor if you have experience — save 15-25% on management fees
📈 Room Addition in St. Louis Cost Trends (2020–2024)
Prices have increased +17.7% over the last 5 years
| Year | National Avg | YoY Change |
|---|---|---|
| 2020 | $33,636 | — |
| 2021 | $35,049 | +4.2% |
| 2022 | $37,327 | +6.5% |
| 2023 | $38,372 | +2.8% |
| 2024 | $39,600 | +3.2% |
Based on national averages adjusted for annual inflation. Actual costs vary by location and project scope.
💬 What Did You Pay?
Real costs reported by homeowners for Room Addition in St. Louis
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Frequently Asked Questions
Does a room addition increase home value?
Yes, though ROI varies: 50-65% for a standard room addition, 60-75% for a bedroom + bathroom addition. The value also depends on whether the addition fits the neighborhood — over-improving for your area yields lower returns.
How long does a room addition take?
Typical timeline: 2-4 weeks for permits and planning. 8-16 weeks for construction. Total: 3-5 months. Complex additions with full bathrooms or custom features can take 6-12 months.
Why does room addition cost different in St. Louis than other cities?
St. Louis's costs reflect local labor rates driven by the diversified economy, varied climate conditions that affect materials and scheduling, and moderate permitting requirements. The balanced labor market also influences competitive pricing.
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