Home addition cost in St. Louis, MO
Local estimate from BLS wage data and BEA price levels. Reviewed Nov 4, 2026.
- Typical range (300 sq ft)
- $41,800 – $84,600
- Per sq ft
- $138 – $276
- before permit
- Versus US midpoint
- +10%
- US $57,500
- Rank of 300 metros
- #43
- 1 = most expensive
St. Louis homeowners pay roughly $41,800 to $84,600 to build a home addition at 300 sq ft, or $138 to $276 per sq ft (permit not included). Against the US midpoint, St. Louis is 10% higher. Carpenters earn a median of $34.13 an hour in the St. Louis area, 17% above the US median of $29.12.
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Estimated cost for 300 sq ft in St. Louis, MO, standard level
$54,600 to $71,700
About $179 to $234 per sq ft before permits. Labor is about 70% of the bill.
| Part | Low | High |
|---|---|---|
| Materials | $15,600 | $20,400 |
| Labor | $38,100 | $49,900 |
| Permits and fees | $900 | $1,450 |
| Total | $54,600 | $71,700 |
Cost breakdown for 300 sq ft in St. Louis, MO
| Part of the job | Low | Midpoint | High | Share |
|---|---|---|---|---|
| Materials | $12,000 | $18,000 | $24,000 | 28% |
| Labor | $29,300 | $44,000 | $58,700 | 70% |
| Permits and fees | $480 | $1,200 | $1,900 | 2% |
| Total | $41,800 | $63,200 | $84,600 | 100% |
What is behind the St. Louis number
The wage side of the estimate leans on carpenters, who do 50% of the hours on a typical job. Their local median is $34.13 an hour. Add the other trades involved and the blended wage index for St. Louis is 1.15 (US = 1.00), which puts labor at 70% of the total.
On the materials line, the BEA goods price index for the St. Louis metro is 100.0 (US = 100). The midpoint materials bill for 300 sq ft comes to $18,000, compared with $18,000 at national prices. Permit and inspection fees are scaled by the broader index (95.1) and land at $480 to $1,900.
When to schedule home addition in St. Louis
We use NOAA's 1991-2020 climate normals for St Louis Sci Ctr (in the city). These are 30-year monthly averages, not forecasts.
March through June and August through November are the stretches where digging, grading and setting material in the ground runs into the fewest weather problems in St. Louis (8 of 12 months). January, February and December have an average overnight low at or below freezing (32°F); July has an average daytime high of 90°F or more.
In January, February and December the average low is at or below freezing, which means frozen ground and slower digging, compaction and sod or stone placement. NOAA counts about 79 days a year with a low at or below 32°F at this station.
St. Louis gets about 44 inches of precipitation in a normal year. The wettest months are April, May and June (4.9 inches in May). Inside the workable window, September and October are the driest, at 3.4 and 3.2 inches. The station averages about 47 days a year at 90°F or above.
Does the season change the price? Probably, but we do not have a sourced seasonal price curve, so the estimator shows a year-round figure and does not adjust by month. When you collect quotes, ask whether scheduling in a slower month gets a better rate.
| Month | Avg high °F | Avg low °F | Precip (in) | For this job |
|---|---|---|---|---|
| Jan | 41 | 25 | 2.7 | Cold |
| Feb | 46 | 28 | 2.3 | Cold |
| Mar | 56 | 38 | 3.6 | Workable |
| Apr | 68 | 48 | 4.8 | Workable |
| May | 77 | 59 | 4.9 | Workable |
| Jun | 86 | 67 | 4.7 | Workable |
| Jul | 90 | 72 | 4.2 | Hot |
| Aug | 89 | 70 | 3.8 | Workable |
| Sep | 82 | 62 | 3.4 | Workable |
| Oct | 70 | 50 | 3.2 | Workable |
| Nov | 56 | 39 | 3.7 | Workable |
| Dec | 45 | 30 | 2.6 | Cold |
Local wages behind the labor line
Wages are the part of this estimate that changes most from town to town. 6 trades carry the job here, and each is compared with its US median. The weighted result for St. Louis is 1.15 times the national level.
For carpenters (47-2031, weighted 50%) the local median is $34.13 an hour, which is 17% above the national $29.12. The middle half of them earn between $25.32 and $44.28 an hour. BLS counts 7,210 of them working in the area, 53.8 for every 10,000 jobs (US: 43.1), so the local bench is deeper than average.
For cement masons and concrete finishers (47-2051, weighted 10%) the local median is $31.09 an hour, which is 13% above the national $27.41. The middle half of them earn between $27.37 and $39.47 an hour. BLS counts 2,550 of them working in the area, 19.0 for every 10,000 jobs (US: 13.3), so the local bench is deeper than average.
Electricians (47-2111), 10% of the weighting: a median of $37.10 an hour, 22% above the US median of $30.38. The middle half of them earn between $26.13 and $47.45 an hour. About 5,920 work in the metro. That is 44.1 per 10,000 jobs, compared with 48.7 nationally, so the supply of crews looks typical.
For plumbers, pipefitters and steamfitters (47-2152, weighted 10%) the local median is $37.02 an hour, which is 21% above the national $30.67. The middle half of them earn between $27.61 and $49.92 an hour. BLS counts 4,060 of them working in the area, 30.3 for every 10,000 jobs (US: 30.0), so the local bench is about average.
Drywall and ceiling tile installers (47-2081), 10% of the weighting: a median of $28.97 an hour, in line with the US median of $28.33. The middle half of them earn between $27.34 and $38.74 an hour. About 250 work in the metro. That is 1.9 per 10,000 jobs, compared with 5.3 nationally, so expect fewer local crews to bid.
For roofers (47-2181, weighted 10%) the local median is $28.25 an hour, which is 6% above the national $26.65. The middle half of them earn between $21.87 and $37.84 an hour. BLS counts 1,110 of them working in the area, 8.3 for every 10,000 jobs (US: 8.7), so the local bench is about average.
Quotes come from real crews, not medians. If the carpenters on your job are paid at the 75th percentile ($44.28 an hour) instead of the median, the labor line grows by about $6,650. At the 25th percentile ($25.32) it shrinks by about $5,800. The total moves by 10.5% or 9.2%, so wages alone rarely explain a quote that is far outside our range.
For context on the local economy, BLS counts 1,341,320 jobs in the St. Louis area. That makes it the 23rd largest of the 300 metros we cover, with 0.86% of US employment.
| Trade | Weight | 25th pct | Median | 75th pct | US median | Ratio | Level used |
|---|---|---|---|---|---|---|---|
| Carpenters (47-2031) | 50% | $25.32 | $34.13 | $44.28 | $29.12 | 1.17 | metro |
| Cement masons and concrete finishers (47-2051) | 10% | $27.37 | $31.09 | $39.47 | $27.41 | 1.13 | metro |
| Electricians (47-2111) | 10% | $26.13 | $37.10 | $47.45 | $30.38 | 1.22 | metro |
| Plumbers, pipefitters and steamfitters (47-2152) | 10% | $27.61 | $37.02 | $49.92 | $30.67 | 1.21 | metro |
| Drywall and ceiling tile installers (47-2081) | 10% | $27.34 | $28.97 | $38.74 | $28.33 | 1.02 | metro |
| Roofers (47-2181) | 10% | $21.87 | $28.25 | $37.84 | $26.65 | 1.06 | metro |
| Blended | 100% | 1.15 | |||||
Pick a size, pick a tier: home addition pricing in St. Louis
Three bands are cut from the same cited range and localized for St. Louis wages and prices. They overlap on purpose: a good standard job and a modest premium job can cost the same. The grid below prices the same bands at 3 common sizes.
Basic
$41,800 to $58,900
Bump-out or simple room without plumbing
Standard
$54,600 to $71,700
Standard room addition with HVAC and electrical
Premium
$67,500 to $84,600
Large addition with bath or kitchen and a new foundation
| Size | Basic | Standard | Premium |
|---|---|---|---|
| bump-out (100 sq ft) | $14,300 – $20,300 | $18,800 – $24,900 | $23,400 – $29,500 |
| 20x20 room (400 sq ft) | $55,600 – $78,200 | $72,600 – $95,200 | $89,500 – $112,000 |
| large suite (600 sq ft) | $83,200 – $117,000 | $108,500 – $142,000 | $133,500 – $167,500 |
Specs and site conditions that change a St. Louis bid
Permits
Construction permits run $500-$2,000, or $5-$21 per $1,000 of project cost (HomeGuide).
Foundation
A foundation, framing, roofing and matching exterior finishes all have to be built before the interior work starts.
Type of addition
A new room is $125-$250 per sq ft; a bump-out $85-$200; an attic conversion $50-$150; a garage conversion $50-$200 (HomeGuide).
How St. Louis compares
Contractors rarely work more than an hour or two from home, so the neighboring metros set a rough ceiling and floor for your quotes. Midpoints for 300 sq ft range from $54,200 to $66,800 across St. Louis and its five closest metros.
| Area | Range | Midpoint | vs. here |
|---|---|---|---|
| St. Louis, MOthis page | $41,800 – $84,600 | $63,200 | |
| Springfield, IL85 miles | $44,200 – $89,400 | $66,800 | +6% |
| Jefferson City, MO95 miles | $36,500 – $73,900 | $55,200 | −13% |
| Columbia, MO120 miles | $35,900 – $72,600 | $54,200 | −14% |
| Bloomington, IL145 miles | $43,000 – $86,900 | $64,900 | +3% |
| Peoria, IL150 miles | $43,700 – $88,300 | $66,000 | +4% |
| Missouri (statewide) | $37,800 – $76,500 | $57,200 | −10% |
| United States | $38,000 – $77,000 | $57,500 | −9% |
Across 300 US metros, St. Louis comes in at #43 from the top. The priciest is Honolulu, HI at $79,600; the cheapest is Brownsville, TX at $44,300 (midpoints, 300 sq ft). Statewide, St. Louis is 11% above the Missouri figure.
Other Missouri metros
| Metro | Size | Range | Midpoint | vs. here |
|---|---|---|---|---|
| Kansas City, MO | 1,096,110 jobs | $38,400 – $77,700 | $58,100 | −8% |
| Springfield, MO | 223,030 jobs | $34,700 – $70,200 | $52,400 | −17% |
| Columbia, MO | 107,680 jobs | $35,900 – $72,600 | $54,200 | −14% |
| Joplin, MO | 87,190 jobs | $34,300 – $69,400 | $51,900 | −18% |
| Jefferson City, MO | 80,220 jobs | $36,500 – $73,900 | $55,200 | −13% |
Cities with a workforce like St. Louis's
Big cities and small ones price differently, so here is St. Louis against the 4 metros with the closest total employment.
| Metro | Size | Range | Midpoint | vs. here |
|---|---|---|---|---|
| Baltimore, MD | 1,356,680 jobs | $38,100 – $77,300 | $57,700 | −9% |
| Austin, TX | 1,293,690 jobs | $33,800 – $68,700 | $51,300 | −19% |
| Charlotte, NC | 1,358,370 jobs | $33,900 – $68,800 | $51,300 | −19% |
| Portland, OR | 1,208,410 jobs | $46,600 – $94,300 | $70,500 | +12% |
Planning more than one job in St. Louis?
Because every project leans on different trades, St. Louis's wage level does not move all prices equally. Against the US midpoint, detached garage runs +10% and kitchen remodel +3%.
| Project | Size | Range | vs. US |
|---|---|---|---|
| Kitchen remodel | 120 sq ft | $19,100 – $32,500 | +3% |
| Bathroom remodel | 45 sq ft | $5,100 – $25,300 | +9% |
| Detached garage | 576 sq ft | $31,800 – $63,800 | +10% |
| Roof replacement | 2,000 sq ft of roof | $6,550 – $13,200 | +6% |
Get 3 local quotes
Tell us about the job and we will try to connect you with up to three local contractors for written quotes. It is free and you are under no obligation to hire. Your estimate of $54,600 to $71,700 for St. Louis, MO is attached.
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Multi-page report for St. Louis, MO: low, typical and high cost, a line-item breakdown of materials and labor by trade, permit notes, the best months to schedule, a quote comparison sheet, red flags, questions for contractors, checklists and every source. Save your estimate above, preview page 1 free, and unlock the full report for $9 one-time, or get every report with CostLocal Pro.
Home addition in St. Louis: your questions
+How much does it cost to build a home addition in St. Louis?
For 300 sq ft, expect $41,800 to $84,600 in the St. Louis area. A standard-spec job lands at $54,600 to $71,700. Small jobs usually cost more per sq ft and large ones less.
+What is the price per sq ft for home addition in St. Louis?
About $138 to $276 per sq ft for materials and labor, plus $480 to $1,900 for the permit if one is needed. The US range is $125 to $250.
+Is home addition cheaper in St. Louis or Springfield?
Springfield is 85 miles away. The midpoint for 300 sq ft there is $66,800, which is 6% more than St. Louis ($63,200). Wage and materials indexes both feed that gap.
+How much of the bill is labor in St. Louis?
About 70% at the midpoint, or $44,000 out of $63,200. Materials are 28% and permits 2%. Nationally, labor is 67%.
+What would 20x20 room (400 sq ft) cost in St. Louis?
$55,600 to $112,000. Pick a different size in the estimator above to get your own number.
+Does home addition need a permit in St. Louis?
Often, but rules are set by your city or county building office, so call before you hire. Budget $480 to $1,900 for fees in the St. Louis area (our national range of $500 to $2,000 scaled by the local price level).
+Is St. Louis expensive for home addition compared with the rest of Missouri?
St. Louis is 11% above the Missouri statewide estimate ($57,200 at the midpoint). We cover 6 metros in Missouri; see the state page to compare them.
+What do carpenters earn in St. Louis?
The BLS median is $34.13 an hour in the St. Louis area, compared with $29.12 nationally. The 25th to 75th percentile range is $25.32 to $44.28.
+What do basic and premium home addition work cost in St. Louis?
For 300 sq ft, basic work runs $41,800 to $58,900 and premium work $67,500 to $84,600. Basic means: bump-out or simple room without plumbing. Premium means: large addition with bath or kitchen and a new foundation.
+When is the best time to build a home addition in St. Louis?
Based on NOAA 1991-2020 normals, the comfortable months for this kind of work are March through June and August through November. September and October are typically the driest of those months. Local contractors' schedules matter as much as the weather, so book early for the busy months.
Home addition near St. Louis
Where these numbers come from
Base prices are national ranges from the sources below. We scale labor by local BLS wages, materials by BEA goods prices and permits by the BEA all-items price level. Full method on the methodology page.
- HomeGuide: How Much Does a Home Addition Cost? (2026) (accessed November 4, 2026)
- Cost to Renovate: Renovation Labor Report 2026: Where the Money Goes (accessed November 4, 2026)
- HomeGuide: 2026 Building Permit Costs | Fees & Cost Calculator (accessed November 4, 2026)
- BLS Occupational Employment and Wage Statistics, May 2025
- BEA Regional Price Parities, 2024
- NOAA NCEI U.S. Climate Normals, 1991-2020
Note on derived figures: Materials = 32% of the installed price, from Cost to Renovate's mid-range 'Structural' category split (56% labor, 32% materials, 11% permits and design). It is a category average rather than an addition-specific figure.