Construction glossary · Envelope and finishes

What is soffitin construction?

A soffit is the finished underside of a roof overhang, eave, or projecting element that closes in the space between the wall and the edge of the roof. In estimating it is taken off as square feet of underside area plus the linear-foot edge trim that frames it. Its dimensions come straight from the overhang width and the eave run length.

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Updated August 2026 · Reviewed by the Ruh construction team

Takeoff unit Linear ft x widthVent ratio 1/300 net free areaCommon width 12 to 24 inMaterial Vinyl / aluminum / fiber

Soffit underside of overhang

The definition

Soffit, explained.

A soffit is the horizontal (or sloped) finished surface that encloses the underside of a roof overhang, eave, canopy, or similar projection. On commercial work it may be vented aluminum or composite panel, gypsum board on framing, or a metal soffit panel system, and it ties into the fascia at the outer edge and the wall at the inner edge. The estimator takes soffit off as square feet of underside area, driven by two numbers: the eave run length in linear feet and the overhang width in feet. Because the soffit wraps building corners, each outside corner adds a small square infill equal to the overhang squared, and those corner pieces are easy to drop. Soffit scope also carries linear-foot trim where it meets the wall (a J-channel or receiver) and where it meets the fascia, plus a vented-versus-solid split when half or more of the run needs ventilation. The soffit, fascia, and eave quantities all trace back to the same eave run, so they should be taken off together to stay consistent.

How it is measured

Soffit is measured in square feet of underside area, computed as eave run length (lf) times overhang width (ft), taken from the roof plan for length and the eave-detail section for width. Add the corner infills: each outside corner is the overhang width squared. Then measure the framing edge trim in linear feet on both edges (the inner run at the wall and the outer run at the fascia), which roughly doubles the eave length. Split the run into vented versus solid soffit per the roof ventilation detail, since vented panel and solid panel carry different unit prices. Confirm overhang width and panel type against the wall section before finalizing.

Worked example

A worked soffit example.

Worked example

Take a 2 ft overhang around 200 lf of eave. The base soffit area is 200 lf x 2 ft = 400 sf. The building has 4 outside corners, and each corner adds an infill of 2 ft x 2 ft = 4 sf, so 4 corners x 4 sf = 16 sf. Total soffit area is 400 + 16 = 416 sf. The edge trim runs both sides of the soffit (wall side and fascia side), so trim length is 200 + 200 = 400 lf. If the ventilation detail calls for half the run to be vented soffit, that is 416 / 2 = 208 sf of vented panel and 208 sf of solid panel, each priced on its own unit (illustrative, US market). Every one of these quantities (the 400 sf field, the 16 sf of corners, the 400 lf of trim, the 208 sf vented) traces to the same 200 lf eave run, which is why soffit, fascia, and eave are taken off as one coordinated set.

How Ruh handles it

How Ruh handles soffit.

Ruh reads the roof plan for eave length and the eave-detail section for overhang width, multiplies to get soffit area, adds the corner infills, and splits the run into vented and solid per the ventilation detail. It returns soffit square feet plus the wall-side and fascia-side edge trim in linear feet and prices each on the contractor's own price book. The estimator confirms the overhang width and the vented-versus-solid split and signs off.

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Soffit: frequently asked questions

How do I get soffit area if I only have a plan?+

Multiply the eave run length in linear feet by the overhang width in feet from the eave-detail section, then add a corner infill equal to the overhang squared at each outside corner.

Why does soffit get split into vented and solid?+

Roof ventilation details call for vented panel over part of the run and solid panel elsewhere. The two carry different unit prices, so you take off the vented and solid square footage separately.

Do soffit, fascia, and eave get estimated together?+

Yes. All three trace back to the same eave run length, so taking them off as one coordinated set keeps the area, fascia run, and trim quantities consistent and avoids missed corners.

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Related terms

Eave Fascia Facade Drywall types

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