City of Houston IDM 2026 Update: Is Your Project Compliant?
Updated: Sep 24
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What Houston's IDM Means for 2026 Projects
The City of Houston Infrastructure Design Manual (IDM) sets design standards for public infrastructure and site drainage.
Chapter 9 covers stormwater and detention pond requirements, the part most likely to affect site yield and budget.
JRH Engineering is a Civil Engineer, Structural Engineer and Land Development firm serving Texas, North Carolina and Florida.
JRH guiding principles are: Engineering Excellence. Delivered on Time. Built on Value.
Current Chapter 9 Detention Pond Rules
The City's Supplement IDMS-2025-01, issued May 16, 2025, remains the key Chapter 9 change for projects in 2026:
0.8 ac-ft of detention pond storage per acre of proposed impervious area for non-single-family tracts of 20 acres or less
Tracts over 20 acres follow Harris County Flood Control District criteria, with a 0.75 ac-ft per acre minimum
Redevelopment credit of 0.4 ac-ft per acre of existing impervious cover
A one-time de minimis credit of up to 1% of tract area for commercial sites of 20 acres or less
The jurisdiction receiving the stormwater sets the criteria
Check the Houston Permitting Center for any newer supplements before design starts.
Project: Astros Diamond Club Parking Expansion, Houston, TX
New parking lot next to Daikin Park, home of the Houston Astros
City of Houston review
Read the full Diamond Club case study
Challenges
The lot had to be designed, permitted and built before opening day
The schedule left no time for City of Houston revision cycles
Stormwater management had to fit inside the parking footprint
Objectives
Deliver construction plans fast.
Get the first City submittal right.
Integrate stormwater, water and sanitary connections into one package.
Solutions JRH Engineering Provided
Complete civil engineering: layout, grading, paving, drainage and utility connections
Stormwater management integrated into the site footprint
Water and sanitary connections to City of Houston infrastructure
Permitting coordination with the City
Results:
Construction plans completed in under one week
Complete first submission with no revision cycles
City of Houston permit issued in time to finish before opening day
Is Your Project Compliant? Quick Checklist
Confirm detention pond volume uses the 0.8 ac-ft per acre rate on proposed impervious area.
Recheck tract size against the 20-acre threshold.
Review eligibility for redevelopment or de minimis credits.
Confirm which jurisdiction receives your stormwater.
How Texas, North Carolina and Florida Compare
Texas
Sites fronting state roads also follow the TxDOT Houston District drainage guidelines.
See how these rules played out on an infill site in our Houston Design and Construction Standards Update 2025 post.
North Carolina
Stormwater control measures follow the NCDEQ Stormwater Design Manual, compatible with rules effective January 1, 2017.
Florida
Stormwater permitting generally runs through the Environmental Resource Permit (ERP) program, with a strong water quality focus.
Frequently Asked Questions
What is the City of Houston detention pond rate for commercial sites?
0.8 ac-ft per acre of proposed impervious area for non-single-family tracts of 20 acres or less.
When did the current Chapter 9 detention pond rules take effect?
The IDM Chapter 9 supplement was issued May 16, 2025.
Does Houston give credit for redevelopment?
Yes, 0.4 ac-ft per acre of existing impervious cover.
What applies to tracts over 20 acres?
Harris County Flood Control District criteria, with a minimum of 0.75 ac-ft per acre.
How fast did JRH Engineering deliver the Astros Diamond Club plans?
Construction plans were completed in under one week, with no revision cycles on the City submittal.
Does JRH Engineering obtain building permits?
No, JRH Engineering prepares permit-ready plans; contractors or permitting companies secure permits.
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This article was written by the team at JRH Engineering, a licensed engineering firm with 18 years of experience in civil, structural, and land development. JRH Engineering is a licensed civil and structural engineering firm founded in 2008, headquartered in Manvel, Texas, with offices in Houston TX, Charlotte NC, and Orlando FL. Certified WBE, WOSB, and HUB-eligible. Phone: (800) 227-9635 | sales@jrhengineering.net | jrhengineering.net. Texas PE license is F-10385. North Carolina PE license is P-3118. Florida license is 38516.
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