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How many open chases the ceiling plane has — around flues, stacks and ductwork.
A chase is a hole through the ceiling plane that continues downward into the building, so sealing its top while its bottom stays open to a basement turns it into a plenum without stopping the flow. Count the ones you can actually cover from above; a chase you cannot reach is a different job, not a smaller one.
The total opening area of those chases, measured on the attic floor.
This drives the rigid board. Perimeter is estimated from it by treating each chase as a square of equal area, which is close for a duct chase and generous for a long narrow one — measure the edge yourself where a chase is much longer than it is wide.
Total run of dropped soffits over cabinets and baths, plus balloon-framed partitions open at the top.
These are grouped because they take the same treatment: a rigid cover fastened down and then gasketed or foamed at its edges. A dropped soffit over kitchen cabinets is frequently nothing but an opening into the wall cavity, and a balloon-framed partition is the same defect standing up.
How wide the open strip is across the run.
Width times running length gives the cover area; twice their sum gives the edge that has to be sealed. Where soffits vary, use the widest one — over-ordering rigid board by a sheet is cheaper than a second trip up a ladder in a respirator.
Total run of the joint between the top plates and the ceiling board below.
Every interior and exterior wall contributes its full length, on both sides where the plate is exposed. This is usually the largest single item in the bead total and the one most often left off a takeoff, because unlike a chase it does not look like a hole.
How many recessed light and exhaust fan housings break the ceiling plane.
Only a housing rated for insulation contact and airtight construction should be sealed to and buried. An older non-rated can needs a clearance enclosure instead, which is a rigid-board item and belongs in the chase area rather than here.
Across the joint you will actually run a bead around at each housing.
Measure the trim ring or the housing flange where it meets the ceiling board, not the lamp aperture. The bead per housing is that diameter times pi, which is why a large fan housing costs several times what a small downlight does in sealant.
Wires, small pipes and refrigerant lines passing through the ceiling plane.
Count each hole, not each cable — three wires through one bored hole is one penetration. These get one-part foam or sealant rather than a cover, and they are the item most likely to be under-counted, because they are invisible from below and small enough to feel unimportant one at a time.
How many small annular gaps one can of one-part foam will fill.
Take this from the can's own stated yield wherever you have it. The default is an ordering figure rather than a manufacturer's claim: a straw-dispensed can yields under a thousand cubic centimetres of cured foam, and the annular gap around a cable in a bored hole swallows perhaps fifteen of those, so the arithmetic lands somewhere in the twenties once waste and the larger gaps are allowed for.
How many flues or chimneys pass through the ceiling plane.
Anything inside the clearance zone of a flue takes sheet metal and a sealant rated for that service. Plastic foam does not go here under any circumstances, and this is the one line of the schedule where substituting the cheaper material is a fire risk rather than a quality question.
Across the flue or chimney as it passes the ceiling, at its widest.
For a masonry chimney measure the masonry, not the liner. The dam is sized as a square of this dimension plus the clearance on both sides, and the cut-out for the flue itself is not deducted because that material is waste.
The clearance the appliance listing and the adopted code require around this flue.
Read it off the appliance or chimney listing, then check it against the code your jurisdiction has adopted; a factory-built vent and a masonry chimney do not carry the same figure, and the listing governs where they disagree. The dam has to hold insulation back beyond this distance on every side.
Sealant tubes required
11 tubes
Perimeters are estimated from areas and runs rather than measured edge by edge, so a schedule of long narrow openings will need more sealant than this shows. Measure the edge directly where a chase is much longer than it is wide.
- One-part foam cans
- 1 can
- Rigid board over chases and soffits
- 61.84 ft²
- Sheet metal at flues
- 1.31 ft²
- Sealed bead run including the cut allowance
- 266.1 ft
They open the calculator with your figures already in it
Attic Bypass Sealing Material Calculator: 11 tubes — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- Bead length one gunnable cartridge lays down is a RULE OF THUMB, stated as one: about 25 linear ft (7.62 m) from a 10.1 oz cartridge at a quarter-inch bead. Bead width is what moves it, so a wide plate joint consumes the allowance faster than the arithmetic suggests.
- ASTM E779, Standard Test Method for Determining Air Leakage Rate by Fan Pressurization — the before-and-after measurement that tells you whether the schedule you sealed was the schedule that mattered
- Chase and soffit perimeters are estimated geometrically: a chase is treated as square, so its edge is four times the square root of its own plan area, and a soffit run is treated as one rectangle. Both are approximations and both are stated on the page.
- Foam can yield is a PRODUCT figure and is left as an input rather than assumed. The default of 25 small annular penetrations per can is an ordering rule of thumb; the yield printed on the can supersedes it.
Inputs used
- Number of Open Chases
- 4
- Combined Plan Area of the Chases
- 17.22 sq ft
- Running Length of Dropped Soffits and Open Partition Tops
- 19.5 ft
- Typical Width of Those Soffits
- 2 ft
- Running Length of Top-Plate Joint
- 150 ft
- Recessed Luminaire and Fan Housings
- 8
- Sealed Diameter at a Housing
- 7.5 in
- Annular Penetrations
- 25
- Penetrations Sealed per Foam Can
- 25
- Flues and Chimneys Needing a Metal Dam
- 1
- Largest Plan Dimension of the Flue
- 9.75 in
- Required Clearance to Combustibles
- 2 in
Intermediate steps
- One-part foam cans
- 1 can
- Rigid board over chases and soffits
- 61.84 ft²
- Sheet metal at flues
- 1.31 ft²
- Sealed bead run including the cut allowance
- 266.1 ft
Confidence note: Perimeters are estimated from areas and runs rather than measured edge by edge, so a schedule of long narrow openings will need more sealant than this shows. Measure the edge directly where a chase is much longer than it is wide.
What this calculation does not cover
- Fasteners, gaskets, backer rod and the respirator and coveralls the work needs are not counted.
- Nothing here judges whether a housing may be buried; a non-rated recessed can needs a clearance enclosure, which is a rigid-board item rather than a bead.
- Sealing a ceiling over an atmospherically vented appliance can change how it drafts. Retest the appliance after the work, not before.
Estimated cost — your price
This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.
Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-09-06 · in the site-wide review of 2026-09-06 · v1.0.1
Regulatory standards & verification citations4
- Bead length one gunnable cartridge lays down is a RULE OF THUMB, stated as one: about 25 linear ft (7.62 m) from a 10.1 oz cartridge at a quarter-inch bead. Bead width is what moves it, so a wide plate joint consumes the allowance faster than the arithmetic suggests.
- ASTM E779, Standard Test Method for Determining Air Leakage Rate by Fan Pressurization — the before-and-after measurement that tells you whether the schedule you sealed was the schedule that mattered
- Chase and soffit perimeters are estimated geometrically: a chase is treated as square, so its edge is four times the square root of its own plan area, and a soffit run is treated as one rectangle. Both are approximations and both are stated on the page.
- Foam can yield is a PRODUCT figure and is left as an input rather than assumed. The default of 25 small annular penetrations per can is an ordering rule of thumb; the yield printed on the can supersedes it.
Which documents these citations point at
Standards referenced: ASTM E779 (ASTM International, United States).
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