Head-of-Wall Joint Calculator

Calculate mineral wool, sealant, and deflection requirements for head-of-wall firestop joints.

Inputs

Joint width (in)

Wall length (ft)

Expected deflection (in)

Fire rating (hrs)

Wall type (1-3)

Tab to move between fields

Results

Mineral wool (sq ft)

6.3

Joint area (sq ft)6.25

Sealant (fl oz)374

Sausage packs (20 oz)19

Deflection ratio (%)50%

Total installed cost ($)$435.35

Packing Depth (in)4

How to Use This Calculator

Enter Joint width (in), Wall length (ft), and Expected deflection (in).
Set Fire rating (hrs) and Wall type (1-3).
Review the Mineral wool (sq ft) result.
Use Joint area (sq ft) and Sealant (fl oz) to inform your decision.

How the result changes with Joint width (in)

Joint width (in)	Mineral wool (sq ft)
1.02	4.3
2.96	12.3
5.29	22
7.23	30.1

What each input means

Joint width (in): Gap between top of wall and underside of floor/deck.
Wall length (ft): Total linear feet of head-of-wall joint.
Expected deflection (in): Maximum expected building movement at the joint.
Fire rating (hrs): Required hourly fire resistance rating.
Wall type (1-3): 1 = Gypsum board, 2 = CMU/masonry, 3 = Curtain wall.

What each result means

Joint area (sq ft): Total area of the head-of-wall joint.
Mineral wool (sq ft): Mineral wool safing insulation needed.
Sealant (fl oz): Firestop sealant volume required.
Sausage packs (20 oz): Number of 20 oz sealant packs needed.
Deflection ratio (%): Deflection as % of joint width (keep under 50%).
Total installed cost ($): Materials plus labor estimate.

How this is calculated

Worked example, using the default values

Identify Input Parameters
4 parameters
Joint width (in) = 1.5, Wall length (ft) = 50, Expected deflection (in) = 0.75, Fire rating (hrs) = 2 = 5 input(s) provided
Calculate Mineral wool
Mineral wool
6.3 = 6.3
Calculate Joint area
Joint area = (jointWidthIn / 12) * wallLengthFt
6.25 = 6.25
Calculate Sealant
Sealant
374 = 374

Engine last updated August 5, 2026.

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