Structural Engineering for Additions That Tie Into What's Already There.
Foundation, framing and lateral design for room additions, second stories and bump-outs — coordinated with your architectural set and the existing structure.
Upload plans, photos or permit comments. Get a defined scope and quote before any commitment.
An addition is two structures pretending to be one. The new work has to carry its own gravity and lateral loads, and it has to connect to an existing building that was built to a different code — often with different footing depths, different wall heights and a roof that was never meant to have a valley cut into it. Good addition engineering resolves both: it designs the new foundation and framing, and it details the interface so the two halves act together under seismic load.
Second-story additions add a further layer. The first-floor walls and foundation now carry a floor and a roof they were not sized for, and the lateral system has to be re-evaluated from the roof down. We evaluate the existing structure from your plans and photos, design reinforcement only where it is actually needed, and produce a structural set that plan check can follow without a second round of questions.
Common projects
- Single-story rear and side additions
- Second-story additions over the existing footprint
- Bonus rooms over garages
- Primary suite and bathroom additions
- Kitchen bump-outs and dining extensions
- Sunrooms and enclosed patios
- Additions on sloped lots with stepped footings
- Attached garage additions
- Additions tying into engineered-truss roofs
What to upload
Submit what you have — we'll tell you what else is needed before engineering begins.
- Architectural plans for the addition: floor plan, elevations and sections
- Existing floor plan or an as-built sketch with dimensions
- Site plan showing the addition location and property lines
- Photos of the existing exterior walls, roof and foundation at the tie-in
- Photos of the crawlspace or basement near the addition
- Geotechnical report, if one exists
- Existing structural drawings, if you have them
- Year built and any known previous additions
Deliverables
What you receive
Every set goes through structural design, drafting and review by the licensed engineer responsible for the work before it is released to your dashboard.
- Foundation plan with footing and slab details at the new work
- Floor and roof framing plans for the addition
- Tie-in details between new and existing framing
- Lateral analysis and shear wall design for the combined structure
- Beam, header and post schedules
- Reinforcement of existing walls or footings where required
- Bound calculations
- Signed and sealed documents where required by the jurisdiction
Example project
Second-story addition over a single-story ranch — Fresno
New 900 sq ft second story with two bedrooms and a bath added over the rear half of a 1970s slab-on-grade home, using the existing exterior walls as bearing lines.
Jurisdiction
City of Fresno
Turnaround
12–18 business days
Engineering scope
- Evaluation of existing bearing walls and footings
- Floor framing over the existing ceiling joists
- New roof framing tying into the existing hip
- Lateral design for the full two-story structure
- Footing enlargement at new point loads
- Calculations and structural sheets keyed to the architectural set
How it works
From Plans to Engineering in Four Steps
- 1
Submit Your Project
Tell us what you're building and upload whatever you already have. Plans, photos, sketches and permit comments can all be submitted.
- 2
Receive Your Scope & Quote
We review the project and send you a defined engineering scope, price and estimated turnaround.
- 3
Engineering Begins
Your project moves through structural design, calculations, drafting and engineer review.
- 4
Receive Your Documents
Final engineering documents are delivered through your project dashboard. Permit comments can be submitted back through the same project.
Frequently asked questions
Can my existing foundation support a second story?+
Sometimes as-is, often with reinforcement. A second story adds floor and roof load to the first-floor walls and footings, and it changes the lateral demand on every wall below. We evaluate the existing foundation from photos, your plans and the era of construction; where footings are undersized, we design enlargement or supplemental footings rather than replacing the whole foundation.
Does an addition need its own foundation, or can it share the existing one?+
The addition gets its own foundation, designed to current code, and is doweled into the existing one so the two act together. Footing depth, width and reinforcing follow the soil conditions and the loads from the new structure — which is why we ask about the site and whether a geotechnical report exists.
Will I need a soils report for an addition?+
Not always. Many single-story additions are designed with the code's presumptive soil values. Sites with expansive clay, fill, slopes or a history of settlement — and second-story additions in some jurisdictions — may require a geotechnical report. We flag this during scope review so it does not surprise you in plan check.
What changes if the addition is on a slope?+
Stepped footings, deeper embedment on the downhill side and sometimes drilled piers with grade beams. Slopes also raise the question of surcharge on retaining elements and of the geotechnical requirements above. Send site photos and a survey or grading plan if you have one.
How does an addition affect the lateral system of the existing house?+
The addition's new walls become shear walls, the roof and floor diaphragms have to connect across the joint, and the existing walls sometimes need strengthening to carry their share of the combined building. Our lateral analysis covers the combined structure, not just the new part.
Do you coordinate with my architect?+
Yes. We work from the architectural set, key structural sheets and details to it, and flag conflicts such as beam depths that clash with ceiling heights or hold-downs that land in door openings. Your architect can be added to the project to upload revisions and see status directly.
Related services
Remodels & Load-Bearing Wall Removal
Beam, post and footing design with a complete load path — engineered from your plans or photos and delivered as permit-ready documents.
Foundation Engineering & Repair
New foundations, underpinning, seismic retrofits and repair details — engineered from your plans, photos and inspection reports.
ADU Structural Engineering
Complete structural packages for detached ADUs, garage conversions and units over garages — sized for California's ADU review process.
Have a project that needs engineering?
Upload what you have and we will define the engineering scope and send a quote.
No commitment required to submit a project for review.