Home Addition Drawings · Longmont, CO
Permit-Ready Home Addition
Drawings for Longmont, CO
Expand your home with a permitted room addition, second story, or family room extension. We deliver complete, code-compliant drawing sets for Longmont's building department — in 10 business days, starting at $1,497.
14-day money-back guarantee · 10 business day turnaround
Local Intelligence
What Longmont Homeowners Need to Know Before Submitting
Size & Zoning Rules
Any new square footage added to your Longmont home counts against the same zoning envelope that governs ADU size, meaning large additions may affect your ability to add a future ADU. Longmont's current ADU size cap is 800 sq ft — within the typical range for most floor plan configurations.
Longmont does not impose an owner-occupancy requirement, so you can rent both the main home and any ADU or conversion as investment units.
If the addition creates a second unit or is later converted to a rental, Longmont's ADU market supports approximately $1,798/month for a 2-bedroom unit.
Permit Process & Fees
Building Services Department permit fees for this project type typically range from $5,000 to $10,000 depending on project valuation and scope. Plan check runs approximately 6 weeks — though each correction cycle adds 3–6 weeks, which is why code-compliant drawings matter so much.
Addition permit packages submitted to Building Services Department must include a site plan, floor plans, all four elevations, an electrical plan, and energy compliance documentation — plus stamped structural drawings are always required for any load-bearing elements, second-story work, or new foundation.
Visit Building Services Department ↗Construction Cost Context
Longmont's home addition construction costs run $200–$280 per square foot — a moderate range driven by labor markets, local code complexity, and finish level. Our drawings are priced at a fraction of what a full-service architect would charge to produce the same permit set.
⚠ Common Pitfall in Longmont
Longmont's Building Services Department requires a separate sewer tap fee study for most ADUs, since many older lots (especially in the original townsite grid) were platted with single-service lines that can't legally support a second unit without upsizing — this often means an unexpected $4,000-$9,000 tap fee plus a utility locate delay before your permit even gets scheduled for review. On top of that, Boulder County's shared floodplain mapping along the St. Vrain corridor catches more lots than homeowners expect, so if you're anywhere near Fairgrounds Park or the older north-side neighborhoods, plan on an extra elevation certificate step that generic ADU guides never mention. Since STRs are allowed citywide, expect your neighbors to get a mailed notice during permit review — and in practice, that notice period is when most design changes get demanded, not after construction starts.
Expert Verdict — Marcus Reid, Licensed Designer
"In my experience, that $220/sqft and 6-week timeline are Longmont state-level estimates, not gospel — I'd get quotes from two or three local contractors and call the Building Services Department directly before penciling in a budget or start date. I've also seen plenty of "6-week" submittals stretch to 10+ weeks once a plan set comes back with corrections, so build in a cushion, especially if you're relying on that STR income to pencil out the project financially. — Charlotte Pemberton"
Market Context
Longmont has a median home value of $508,000. Comparable renovation projects in this market typically add 23% to resale value.
Neighborhoods in Longmont with the strongest home addition and resale value potential include Loomiller, Longmont Estates, Sunset, McIntosh, Central Business District (Downtown). Established single-family lots close to downtown make Loomiller ideal for detached ADUs.
Permit Process
Permit applications are reviewed by the Building Services Department, with a plan check timeline of approximately 6 weeks. Permit fees in Longmont range from $5,000 to $10,000 depending on project scope. Design review: Yes - in historic districts only.
Longmont falls within Seismic Design Category Seismic Design Category B, which affects structural requirements for any new addition tying into the existing structure.
Local Financing Resources
Local Home Addition Lenders in Longmont
These lenders offer HELOC, construction, and renovation loans for home addition projects in Boulder County. Compare terms before committing.
Offers HELOCs with variable APRs (rates shown starting at 6.99%) and has branches serving Longmont.
Visit Lender ↗Provides land & construction loans including construction-to-permanent options with locally underwritten terms in Colorado.
Visit Lender ↗Offers construction-to-permanent and renovation loans (Fix-It First) to finance building or renovating projects in Colorado, with branch in Longmont.
Visit Lender ↗HELOCs for home renovations with maximum loan amounts cited (example: up to $500,000 / up to 90% CLTV on some products).
Visit Lender ↗Fintech platform (not a direct lender) that partners with credit unions nationwide to offer renovation/ADU financing; check local credit unions for RenoFi-backed products.
Visit Lender ↗Build With A Plan is not affiliated with these lenders. Always compare rates and consult a mortgage professional.
Local Build Partners
Vetted Home Addition Contractors in Longmont
We draw the plans. These contractors build the addition. Independent — no referral fees paid or received.
Build With A Plan provides drawings only. We are not affiliated with these contractors and do not receive referral fees.
Drawing Package Details
What's Included in Your Longmont Home Addition Package
Transparent Pricing
Longmont Home Addition Drawing Packages
One-time fee. No retainer. No hourly billing.
- ✓Site plan
- ✓Floor plans (existing + proposed)
- ✓All 4 elevations
- ✓Electrical plan
- ✓Title 24 energy compliance
- ✓PDF + DWG delivery
- ✓10 business day turnaround
- ✓Everything in Starter
- ✓Stamped structural drawings
- ✓Foundation plan
- ✓Roof framing plan
- ✓Window & door schedules
- ✓1 round of revisions
- ✓Everything in Standard
- ✓3D rendering
- ✓Cross-section details
- ✓Material specifications
- ✓HOA submission package
- ✓2 rounds of revisions
- ✓Priority 5-day turnaround
After You Order
Your Addition Drawings in 3 Steps
Submit Your Project Details
Share your property address, existing floor plan (if available), and the addition scope. We assign your project coordinator within 4 business hours.
We Draft Your Drawings
Our team designs your complete addition drawing set — engineered for Longmont's building department requirements and CO CBC code. Delivered in 10 business days.
Submit to Your Building Dept
Download your complete package and submit to Building Services Department. We support plan check corrections at no extra charge.
Common Questions
Longmont Home Addition FAQs
Do I need a permit for a home addition in Longmont? +
Yes — any structural addition to your home in Longmont requires a building permit. This applies to room additions, second-story additions, sunrooms, and attached garages. You'll need permit-ready drawings before the building department will accept your application. Our packages are formatted specifically for Longmont's submittal requirements.
How much does a home addition cost in Longmont? +
Home additions in Longmont typically cost between $168.0–$320 per square foot depending on the scope, finishes, and structural complexity. A 600 sq ft addition ranges from $100,800 to $192,000. Second-story additions cost more than ground-floor extensions due to structural requirements. Our drawing packages start at $1,497 — a fraction of local architectural fees.
What drawings are required to permit a home addition in Longmont? +
Longmont's building department requires: a site plan showing the addition's footprint and setbacks, floor plans for all affected levels, all four exterior elevations, an electrical plan, and energy compliance (Title 24 in California). Structural plans stamped by a licensed engineer are required for any load-bearing elements — included in our Premium package.
How long does the permit process take for a home addition in Longmont? +
Plan check in Longmont typically takes 6 weeks for home additions. Additions with structural components may require additional review. Complete, code-compliant drawings significantly reduce correction cycles — each cycle adds 3–6 weeks. Our drawings are engineered to pass on the first submittal.
What setbacks apply to home additions in Longmont? +
Longmont enforces minimum setbacks from property lines for all additions: typically 4–5 ft side setbacks and 5 ft rear setbacks, though these vary by zoning district and lot size. Your addition must stay within the buildable envelope. Our site plan documents existing and proposed setbacks and flags any zoning variances required.
Do I need structural drawings for a home addition in Longmont? +
Yes, for most additions. Any load-bearing walls, new foundations, second-story construction, or roof structure changes require stamped structural drawings from a licensed engineer. California's CBC (California Building Code) and seismic requirements make structural plans mandatory for most addition types. Our Standard and Premium packages include stamped structural drawings.
How much do home addition drawings cost in Longmont? +
Our permit-ready home addition drawing packages for Longmont start at $1,497. Local architects and designers typically charge $3,000–$10,000+ for comparable drawing sets. Every package is engineered for CO code compliance and formatted for Longmont's building department. Turnaround is 10 business days with a 14-day money-back guarantee.
Will a home addition increase my home's value in Longmont? +
In Longmont, where median home values are approximately $508,000, a permitted home addition adds square footage that appraisers value as part of the home's gross living area. Return on investment varies by addition type — master suite additions, family room expansions, and additional bedrooms typically recoup 50–75% of project cost in appraised value in CO markets.
Can I add a second story to my home in Longmont? +
Second-story additions are permitted in most Longmont residential zones, subject to height limits and design review requirements. California generally requires ministerial permit approval, but some cities impose design compatibility or neighborhood compatibility review for second stories. Our drawings cover all levels including foundation upgrades, shear walls, and roof framing required for vertical additions.
Nearby Cities
Also Available in Longmont
Adding an ADU instead? See our ADU design service.
Next Steps
Ready to Move Forward With Your Longmont ADU?
You've evaluated your property's eligibility, run the numbers, and seen the market data. The next step is getting permit-ready architectural drawings to submit to Building Services Department.
Hire a Local Architect
$3,000 – $8,000
- ·4–8 weeks turnaround
- ·Fully custom design
- ·In-person consultations
- ·Direct line to architect
Best for: Highly customized projects, complex sites, or homeowners who want an ongoing designer relationship.
Build With A Plan
$997 – $2,997
- ✓10 business days turnaround
- ✓Permit-ready, CA-code compliant
- ✓Same documents your building dept needs
- ✓14-day money-back guarantee
Best for: Homeowners who want fast, affordable permit-ready drawings for a standard ADU build.
Both options produce permit-ready architectural drawings accepted by Building Services Department. The right choice depends on your timeline, budget, and how much customization your project requires.