Plan Specifications
About This Plan
A 20 foot square cottage ADU, 400 square feet over two levels with one bedroom and one bathroom, under a shallow 3 in 12 shed roof. You receive these 400 sq ft adu plans as a PDF immediately after checkout.
Architectural Style
400 sq ft adu plansFour hundred square feet on purpose400 square feet is a threshold number. It sits under the floor area cap that many jurisdictions apply to accessory dwellings, and under the height limits too, with the ridge kept to 15 feet 10 inches. If you are building in a place with tight ADU rules, this plan is drawn to fit inside them rather than to argue with them.
Living Space
The porch is a third of the buildingThere is 140 square feet of covered porch against 400 square feet of interior. That ratio is unusual and it is the reason the cottage does not feel cramped: for much of the year the porch is simply another room, and it takes the boots, the chairs and the firewood that would otherwise be indoors.
Based on national averages: $60,000 - $80,000
($150-$200 per sq ft × 400 sq ft. Actual costs vary by location and finishes.)Get Personalized Estimate →Floor Plans
Use the zoom controls to inspect the drawing. Fully dimensioned PDFs are included in your plan set download.
What's Included in Your Plan Set
Every plan purchase includes everything you need to build your dream home
Construction Drawings
Complete set of detailed architectural plans including floor plans, elevations, sections, and details.
- Foundation plan
- Floor plans for all levels
- Exterior elevations (all sides)
- Building sections
- Construction details
Structural Plans
Engineering specifications for framing, load-bearing walls, and structural support.
- Roof framing plan
- Floor framing plan
- Beam specifications
- Column schedules
- Load calculations
Electrical Layout
Complete electrical plan showing outlets, switches, fixtures, and panel locations.
- Outlet locations
- Switch layouts
- Lighting fixtures
- Panel box location
- Dedicated circuits
Foundation Options
Multiple foundation types included to suit your building site requirements.
- Slab foundation
- Crawl space option
- Basement option
- Pier foundation
- Site-specific adaptations
Plan Features
Frequently Asked Questions
Everything you need to know about our house plans
What's included in the house plan package?
Every set includes the cover sheet, foundation plan, dimensioned floor plans, exterior elevations, building sections, roof plan, and electrical layouts as PDF. The CAD Files upgrade adds fully editable drawings.
Can I modify the house plans?
Yes. Modification quotes are free and most changes such as mirroring, resizing rooms, or adding a garage bay are quoted within 2 business days.
How long does delivery take?
Instantly. Your download is available the moment checkout completes, and the link is emailed to you as well.
Are these plans suitable for my local building codes?
Plans are drawn to the International Residential Code. Some jurisdictions require local engineering review or stamps; your building department can confirm what applies.
What is your return policy?
Plans are digital files delivered instantly, so every order is final and non-refundable. You confirm this at checkout when you ask for immediate access. If a file is faulty, incomplete, or does not match what its listing described, contact us and we will repair or replace it.
Do you provide construction cost estimates?
A cost-to-build report can be ordered for any plan and reflects your local material and labor costs.
Can I build the same plan multiple times?
A purchase licenses one build. Contact us for multi-build pricing.
Do you offer mirror-reverse plans?
Yes, mirrored plan sets are available at no additional cost. Just mention it when ordering or in the modification request.
Not ready to buy yet?
Three things you can do right now, all free.
Inside the Lean Cottage ADU, 20x20 plan set
This is not a sketch or a concept render. It is a complete, buildable document set your contractor can price and permit from on day one.
- Full construction drawings: foundation, framing, elevations and sections
- Reviewed by a licensed architect before it ever reaches your builder
- Delivered as a print-ready PDF the moment your order completes
From Plan to Home in 5 Steps
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