Planning a home addition starts by settling the decisions that affect the footprint before choosing finishes. In New Hampshire, the useful order is: define the household need, document site and house constraints, establish a realistic total budget, develop a buildable concept, confirm permit requirements, and then compare construction proposals against the same scope.
That sequence prevents a common planning problem: falling in love with a room layout before learning that setbacks, utilities, roof geometry, drainage, or existing systems require a different solution.
Use a decision brief before requesting drawings
A good addition starts with a one-page brief. It should explain the problem the new space must solve, the rooms it must connect to, and the conditions that would make the project successful. “More space” is too broad; “a first-floor bedroom and accessible bath connected to the main living area” gives the designer and contractor something testable.
| Decision to settle | Questions to answer | Evidence to bring |
|---|---|---|
| Purpose | Who will use the space, and what must happen there every day? | Room list, furniture needs, accessibility needs, five-year household plan |
| Connection | Which existing rooms should the addition connect to? | Simple floor plan, photos, traffic-flow pain points |
| Footprint | Where could the addition fit without creating site conflicts? | Survey if available, septic or well information, utility locations |
| Performance | What comfort, daylight, storage, and energy goals matter? | Cold or hot room history, window preferences, storage inventory |
| Budget | What is the total project limit, including related work? | Funding range, must-haves, deferrable items, contingency approach |
| Timing | Are there move-in, school, weather, or financing constraints? | Target window and decisions that must happen first |
Document the property before shaping the addition
Begin with information you already have: a plot plan or survey, septic and well records where applicable, utility locations, and photos of the yard in wet and dry conditions. A contractor may still need field measurements and further investigation, but an early property packet makes the first concept more credible.
Site questions
- Where are lot lines, setbacks, easements, and access routes?
- Could the new footprint affect drainage, grading, mature trees, or snow storage?
- Can workers and materials reach the proposed area without avoidable damage?
- Are overhead or underground utilities close to the work?
- If the property uses a septic system or well, what areas must remain protected?
Existing-house questions
- How will the new floor height align with the current house?
- Where can the roof tie in while managing snow and water?
- Which walls carry loads, and where can an opening be created?
- Can the electrical, plumbing, heating, and cooling systems support the added space?
- Will construction temporarily affect a kitchen, bathroom, bedroom, or primary entrance?
These questions do not replace design or engineering. They reveal what the design team must verify before pricing becomes dependable.
Define scope in layers
Separate the project into three layers so related costs do not disappear from early conversations.
- The addition itself: foundation, framing, roofing, windows, insulation, mechanical systems, finishes, and built-ins.
- The connection work: structural opening, transitions, relocated doors or windows, and repairs to rooms that meet the addition.
- Property and protection work: excavation access, grading, drainage, temporary protection, landscaping restoration, and any utility changes.
This model gives homeowners a more useful scope than a cost-per-square-foot shortcut. Two additions with the same floor area can demand very different foundation work, roof connections, mechanical upgrades, and interior alterations.
Build the budget around decisions, not a single allowance
Set one total limit, then reserve part of it for investigation, design, permits, construction, related property work, and conditions that cannot be confirmed until work opens the house. The exact reserve should reflect what is known about the building—not a generic percentage copied from another project.
Identify must-haves before design expands. A weather-tight mudroom, first-floor bedroom, or accessible bathroom may be the reason for the project. Custom millwork, an enlarged patio, or premium finishes may be valuable but easier to defer. Labeling those choices early gives the design team room to protect the purpose of the addition.
Develop one buildable concept before comparing bids
Contractor prices are most useful when they respond to the same concept and assumptions. At minimum, the preconstruction package should establish the approximate footprint, floor relationship, roof form, window and door locations, room uses, mechanical approach, and finish level. Depending on the project, architectural or engineering documents may be required before final pricing or permit submission.
New England Home Pros’ home remodeling service describes the wider design-and-construction context for additions and whole-home changes in Londonderry and surrounding New Hampshire communities.
Confirm permits and local review early
New Hampshire law requires a building permit before covered construction, renovation, or alteration begins and allows local enforcement through the municipality. Review the current language in RSA 155-A:4, then confirm how it applies to your address and scope with the local building department.
For Londonderry properties, the town’s residential building permit page provides current application links for additions and remodeling. Ask what plans, site information, trade permits, energy documentation, or other reviews are required. Requirements can change, and neighboring municipalities may use a different process.
Resolve long-lead choices before construction
Once the concept and approvals are clear, identify products that influence framing or rough-in work: windows, exterior doors, plumbing fixtures, heating and cooling equipment, cabinets, and specialty lighting. Confirm selections and acceptable substitutes in writing. A color choice can wait; a window size that determines a framed opening cannot.
Also decide how the household will live through the work. Document parking, deliveries, dust separation, pets, temporary access, work hours, and which utilities may be interrupted. These operating details often determine whether the construction plan is practical.
Compare proposals with the same checklist
- Does each proposal use the same drawings and written assumptions?
- Are design, permits, engineering, excavation, utilities, and restoration included or clearly excluded?
- Does the payment schedule track defined progress?
- Are allowances labeled with the product or scope they cover?
- Is the process for hidden conditions and owner-requested changes written down?
- Who coordinates inspections, selections, and schedule updates?
- What warranty documentation and closeout records will you receive?
The lowest number is not automatically the lowest-risk proposal. A clear scope makes differences visible before construction, when choices are still easier to change.
Turn the checklist into a project brief
Before the first design meeting, assemble your one-page purpose statement, property information, photos, must-haves, deferrable options, budget limit, and timing constraints. That packet gives professionals enough context to test the idea instead of guessing at it.
If you are planning an addition in Londonderry or a nearby New Hampshire community, request an estimate from New England Home Pros to discuss the site, existing house, and next preconstruction step.
