04 — Service
Home Additions
Sunrooms, master suites, second stories — we add the space your family needs.
Typical Investment
$145,000 to $790,000
Based on 153 completed MOSS projects. Median investment: $250K.
02Our Process
How Home Additions works at MOSS
Explore, Research and Evaluation
Learn about the Moss approach, our projects, cost, selections and process.
Create a Solution for your Vision
Virtual discovery, in-home consultation, and a project presentation to bring your vision to lie.
Get Started With Your Team
Sign your contract, meet your team, and begin project development.
Enjoy a Superior Design Experience
Design your project and make real-time selections with our MOSS 360 Architects and Project Designers.
Develop Your Customized Project Plan
Receive a formal project plan covering schedule, communication, and safety.
Start Constructing Your Dream Home
Construction begins under the supervision of a dedicated Project Manager.
Enjoy Customer for Life Perks
Join the MOSS family for life with ongoing support after project completion.
- 01
Explore, Research and Evaluation
Learn about the Moss approach, our projects, cost, selections and process.
- 02
Create a Solution for your Vision
Virtual discovery, in-home consultation, and a project presentation to bring your vision to lie.
- 03
Get Started With Your Team
Sign your contract, meet your team, and begin project development.
- 04
Enjoy a Superior Design Experience
Design your project and make real-time selections with our MOSS 360 Architects and Project Designers.
- 05
Develop Your Customized Project Plan
Receive a formal project plan covering schedule, communication, and safety.
- 06
Start Constructing Your Dream Home
Construction begins under the supervision of a dedicated Project Manager.
- 07
Enjoy Customer for Life Perks
Join the MOSS family for life with ongoing support after project completion.
03Common Questions
Everything you want to know about home additions
How much does a home addition cost in the DC metro area?
Home additions in the DMV typically cost $150–$350 per square foot, with most MOSS projects ranging from $150K to $500K depending on size and complexity.
Single-story bump-outs (200–400 SF) start around $100K. Two-story additions and pop-tops run $300K–$600K+. The biggest cost drivers are foundation type, structural complexity, and finish level.
How long does a home addition take?
Most MOSS additions take 4–7 months from permit to completion.
Foundation and framing take 4–6 weeks. Roofing, siding, and MEP rough-in add 3–4 weeks. Interior finishes run 4–8 weeks depending on complexity.
Do I need an architect for a home addition?
MOSS handles design and engineering in-house, eliminating the need for a separate architect.
Our design team creates schematic layouts, 3D renderings, and full construction drawings. For structural work, we engage licensed engineers as part of our standard process.
What types of additions does MOSS build?
MOSS builds bump-outs, sunrooms, second-story additions (pop-tops), garage conversions, and in-law suites.
Each addition type has different structural requirements, permit implications, and cost profiles. Pop-tops require temporary roof removal and structural engineering. Bump-outs are the most cost-efficient way to add square footage.
What does MOSS's design-build process include for a home addition?
A MOSS home addition is engineered and built by one in-house team from first sketch to final inspection. We resolve how the new space ties into your existing floor plan, roofline, and foundation, then produce structural drawings and manage permitting. Our crews handle excavation, framing, and the connection to your home's systems, so the addition looks original to the house rather than bolted on.
Keeping structural design and construction under one MOSS roof is what makes an addition read as original architecture instead of an obvious add-on.
04Materials Guide
Compare your options
Top 4 Addition Types for DMV Homes
Pop-Top (Second Story)
Doubles livable space without expanding the footprint.
Rear Bump-Out
The most cost-efficient way to expand a kitchen or family room.
In-Law Suite
Self-contained living space for multi-generational families.
Sunroom/Four-Season Room
Year-round outdoor living with climate control.
3 Things to Know Before Your Home Addition
Setback requirements limit your options
Every jurisdiction has setback rules. Check before you design.
Foundation type affects everything
Slab, crawl, or full basement — this decision drives cost and timeline.
Tie-in is the hardest part
Where new meets old is where craftsmanship matters most. Rooflines, siding, and interior transitions require expert execution.
Our pop-top gave us three bedrooms and a bathroom we didn't have. The kids finally have their own rooms.
05Portfolio
Home Additions projects
How does home additions look in real homes?
Viola Street Springfield Home Addition
Springfield, VA
Silverleaf Drive Home Addition
Fairfax Station, VA · 2026
N. Columbus Street Arlington Home Addition
Arlington, VA · 2023
Windsor View Terrace Home Addition
Potomac, MD · 2023
Gerken Avenue Second-Story Addition
Vienna, VA · 2023
N. Highland Street Home Addition
Arlington, VA · 2022
Nestlewood Drive Home Addition
Herndon, VA · 2022
Halterbreak Court Home Addition
Herndon, VA · 2022
Preston Court Home Addition
Ashburn, VA · 2022
S. Oakland Street Home Addition
Arlington, VA · 2022
Lowry Drive Home Addition
Chantilly, VA · 2022
Copper Creek Road Home Addition
Herndon, VA · 2022
Other Services
Other ways MOSS transforms your home
06FAQ
Frequently asked questions
- How much does a home addition cost in the DC metro area?
- Home additions in the DMV typically cost $150–$350 per square foot, with most MOSS projects ranging from $150K to $500K depending on size and complexity. Single-story bump-outs (200–400 SF) start around $100K. Two-story additions and pop-tops run $300K–$600K+. The biggest cost drivers are foundation type, structural complexity, and finish level.
- How long does a home addition take?
- Most MOSS additions take 4–7 months from permit to completion. Foundation and framing take 4–6 weeks. Roofing, siding, and MEP rough-in add 3–4 weeks. Interior finishes run 4–8 weeks depending on complexity.
- Do I need an architect for a home addition?
- MOSS handles design and engineering in-house, eliminating the need for a separate architect. Our design team creates schematic layouts, 3D renderings, and full construction drawings. For structural work, we engage licensed engineers as part of our standard process.
- What types of additions does MOSS build?
- MOSS builds bump-outs, sunrooms, second-story additions (pop-tops), garage conversions, and in-law suites. Each addition type has different structural requirements, permit implications, and cost profiles. Pop-tops require temporary roof removal and structural engineering. Bump-outs are the most cost-efficient way to add square footage.
Start your home additions project
One conversation reveals exactly what your project will involve and what it will cost.