What we estimate
Addition & ADU Estimating
Addition and ADU estimating prices new square footage attached to, or on the lot of, an existing home. The defining cost driver is the tie-in: matching the existing structure, roof, and systems. K2E scopes that connection explicitly instead of pricing the addition as if it stood alone.
Additions and accessory dwelling units look like small new builds, but they are not. The hard part is where the new work meets the old: the roof tie-in, the panel upgrade, the matching, the disruption to the existing home.
What the estimate includes
- Foundation and framing for the new footprint
- Roof and envelope tie-in to the existing structure
- Electrical service and panel-capacity check
- Matching existing finishes and rooflines
- For ADUs: separate utilities, kitchen, and bath
| Description | Qty | Unit | Material | Labor | Total |
|---|---|---|---|---|---|
| Site prep and excavation | 1 | LS | - | 3,850 | 3,850 |
| Concrete slab on grade | 576 | SF | 4,320 | 3,168 | 7,488 |
| Framing, walls and trusses | 576 | SF | 7,200 | 5,760 | 12,960 |
| Roofing, architectural shingle | 14 | SQ | 2,380 | 2,940 | 5,320 |
| Siding, fiber cement | 1,120 | SF | 4,928 | 5,264 | 10,192 |
| Overhead door and opener | 2 | EA | 3,180 | 940 | 4,120 |
| Electrical, rough and finish | 1 | LS | 1,240 | 2,760 | 4,000 |
| Subtotal, 7 of 34 line items | 47,930 | ||||
The tie-in is the estimate
Price an addition as a freestanding box and you will be low every time. The cost lives in the connection: cutting into the existing roof, matching siding that is no longer made, confirming the existing panel can carry the new load.
We estimate the tie-in as its own scope, so the number reflects the real work of joining new to old, not just the square footage of the new room.
FAQ
Common questions
Do you estimate detached ADUs and garage conversions?
Yes, both. Detached ADUs get priced like a small new build plus their own utility runs. Conversions get priced like a remodel, with existing-conditions allowances for what is behind the walls.
Can you flag whether the existing panel needs upgrading?
We flag it as a scope item to verify. A load calc is an engineering determination, but we make sure the panel-capacity question is on the estimate, not discovered mid-project.
See the work before you commit
A real, itemized, bid-ready K2E estimate for a detached garage build. The same document a paying contractor received.