InstaBidsAttic conversion costs?
Portland, Oregon, Brochure 9 attic floor loads: “You must determine if the existing attic floor structure is strong enough to carry the additional weight of people and furniture. It is very common that when tracing floor loads from the converted attic, it is the beam in the basement that will be overstressed.”
Source: City of Portland, Portland Permitting & Development, read 6 November 2026.
Portland, Oregon, attic conversion guidance: “Converting your attic might mean raising the roof. If so, the zoning code height regulations may affect your project.”
Source: City of Portland, Portland Permitting & Development, read 6 November 2026.
Context: all "Added other room or converted existing space to other room" jobs
The survey figure below covers all "Added other room or converted existing space to other room" jobs, not attic conversion alone.
$12,000 was the median homeowner survey figure for data years 2021-2023 in the United States. For all jobs in “Added other room or converted existing space to other room”, the American Housing Survey recorded a typical range (middle half of 126 American Housing Survey data points, the United States, 2021-2023) of $4,500 to $50,000.
Updated 2026-11-06
InstaBids is an AI-run marketplace for homeowners and property managers: describe a home job once, by chat or through your own AI assistant, add photos, and get multiple written quotes on the same scope, compared apples to apples, with no phone calls or home visits before you pick.
For homeowners, property managers, landlords and HOA boards.
| What was measured | Median | Typical range (middle half) |
|---|---|---|
| For all jobs in “Added other room or converted existing space to other room”, the American Housing Survey recorded | a median of $12,000 | the typical range (middle half of 126 American Housing Survey data points, the United States, 2021-2023) was $4,500 to $50,000 |
How measured: hired-out finished jobs, survey-weighted, not adjusted for inflation. Source: U.S. Census Bureau, American Housing Survey 2023, data read 6 November 2026.
These figures are estimates from U.S. Census Bureau, American Housing Survey 2023, data years 2021-2023, read 6 November 2026, for the United States. They are not a quote, and they are not a promise of what any contractor on InstaBids will charge. Your price depends on your home, the materials and the contractor. Get written bids before you decide.
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At a glance
- at least 70 square feetPortland living-space floor areaCity of Portland, Portland Permitting & Development, read November 6, 2026
- 6 feet 8 inchesPortland minimum headroom for new stairsCity of Portland, Portland Permitting & Development, read November 6, 2026
- existing two-by-four studs or raftersPortland framing for the quoted R-15 allowanceCity of Portland, Portland Permitting & Development, read November 6, 2026
For your AI assistant
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- MCP connector URL
https://instabids.ai/api/agent/mcp - Agent API (OpenAPI)
https://instabids.ai/openapi.json - Start-request link
https://instabids.ai/intake?from=cost-attic-conversion&utm_source=us&utm_medium=page&utm_campaign=cost&page_type=cost&job=attic+conversion - Prompt for any AI, with your job
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Every page is plain HTML. Steps for every assistant: add to your assistant.
What attic conversion includes
Portland, Oregon, Brochure 9 dormer framing: “Adding a new dormer or enlarging an existing dormer may trigger structural improvements to the existing structure for the purpose of resisting wind or earthquake load and for floor live loads.”
Source: City of Portland, Portland Permitting & Development.
Source read: 6 November 2026.
Where a quote below names a city or county, it is that office's own rule, shown as one example; the permit office for your home may set different rules.
| What the source says | Where it comes from |
|---|---|
| Portland, Oregon, Brochure 9 attic engineering calculations: “When the scope of work will change the structural load, it is important that you submit engineering calculations that show the continuity of the load path from floors or other affected members all the way to the foundation.” | City of Portland, Portland Permitting & Development, read 6 November 2026. |
On InstaBids, describe dormer framing and the attic load path through the supporting floors in one scope.
Line items a written bid should list
Portland, Oregon, residential stair guidance: “New stairways must be at least 36 inches wide between walls (above the handrail). In a few cases (like if the new stair is the second stairway), the stairway can be 30 inches wide. This exception does not apply to outdoor stairs, like for deck.”
Source: City of Portland, Portland Permitting & Development.
Source read: 6 November 2026.
- Portland, Oregon, residential stair guidance: “Headroom is measured vertically. Measure from the sloped line between tread nosings to the ceiling or any other projection. Minimum headroom for new stairs is 6 feet 8 inches. For spiral stairs, the minimum is 6 feet 6 inches.”
Source: City of Portland, Portland Permitting & Development, read 6 November 2026.
- Portland, Oregon, Brochure 9 sloped-ceiling floor area: “Living space must have at least 70 square feet of floor area. Utility and storage rooms, closets, bathrooms or kitchens may be any size. In living space with sloped ceilings, no more than one half of the minimum required floor area may have a sloped ceiling less than 6’8" in height with no part of the required floor area less than five feet in height.”
Source: City of Portland, Portland Permitting & Development, read 6 November 2026.
- Portland, Oregon, Brochure 9 exposed attic framing: “Exposed framing must be insulated if finishes are removed from the exterior walls or roof. R-15 insulation is allowed between existing two-by-four studs or rafters. If the attic areas can be accessed without removing the finishes, they too must be insulated to the maximum extent possible to meet current code.”
Source: City of Portland, Portland Permitting & Development, read 6 November 2026.
On InstaBids, include stair clearance, sloped ceilings and exposed rafter insulation in the attic scope contractors receive.
How to compare written bids like for like
Portland, Oregon, residential stair guidance: “You may be able to keep the existing stairs without rebuilding them, if they were permitted. Check your permit history. But you still need a permit for both the space conversion and any stairway work.”
Source: City of Portland, Portland Permitting & Development.
Source read: 6 November 2026.
Ask every contractor to bid in writing on the same line items listed above, then compare the written bids line by line.
On InstaBids, describe whether the attic stairs are retained or rebuilt in the scope contractors receive.
What inspections does attic conversion need?
Portland, Oregon, residential inspection guidance: “Under-floor and attic insulation may be done at a later time, but must be in place before the final inspection.”
Source: City of Portland, Portland Permitting & Development.
Source read: 6 November 2026.
Include the attic conversion inspection stages in your InstaBids scope so contractors can describe that work in writing.
Get written bids
Contractors who take part bid on one written scope card, so nobody visits before you see any prices.
Sources for the figures on this page
- U.S. Census Bureau, American Housing Survey 2023, https://www.census.gov/programs-surveys/ahs/data/2023/ahs-2023-public-use-file--puf-.html, read 6 November 2026. U.S. government work; no endorsement implied.
- City of Portland, Portland Permitting & Development, www.portland.gov/ppd/documents/converting-attics-basements-and-garages-living-space-brochure-9/download, read 6 November 2026.
- City of Portland, Portland Permitting & Development, www.portland.gov/ppd/residential-permitting/home-projects/stairs, read 6 November 2026.
- City of Portland, Portland Permitting & Development, www.portland.gov/ppd/residential-permitting/residential-inspections, read 6 November 2026.
- City of Portland, Portland Permitting & Development, www.portland.gov/ppd/residential-permitting/home-projects/attic-basement-or-garage-conversion, read 6 November 2026.