Fireproofing Material Calculator

Spray-applied fire-resistive material thickness depends on three factors: the required fire rating (hours), the type of structural member (beam vs. column), and the weight-to-heated-perimeter ratio (W/D) of the steel section. Heavier steel sections need less fireproofing because their greater mass absorbs more heat before reaching the ASTM E119 limiting temperature: an average of 1,100 deg F (593 deg C) for loaded beams, and 1,000 deg F (538 deg C) for loaded columns.

These are typical values for cementitious CAFCO 300 / ISOLATEK Type 300 (15 pcf, the density Isolatek calls commercial density) held on the safe side of the UL designs opened for this page. UL S721 prints, for a W6×16 beam, 7/16 to 11/16 in. at 1.5 hours, 11/16 to 15/16 in. at 2 hours and 1-3/16 to 1-7/16 in. at 3 hours; UL X790 prints, for W6×16 and W8×28 columns, 5/8 to 3/4 in. at 1 hour, 15/16 to 1-1/8 in. at 1.5 hours, 1-1/4 to 1-7/16 in. at 2 hours and 1-13/16 to 2-1/16 in. at 3 hours; UL N761 covers the joist ladder for the 12K5, 8K1 and 10K1 series. Where the table sits above a printed value it orders a little more material, never less. Actual required thickness depends on the specific UL design number, the SFRM product, and the W/D ratio of your steel section. Always reference the UL design for the exact thickness — the values above are for estimating quantities, not for specifying fire protection.

Fibrous SFRM is not thinner than cementitious. At identical pipe and tube column shapes, Isolatek's own fibrous dry-mix design UL X827 (Types HP, D-C/F, II and II HS — the design printout carries no trade name) lists 8 to 41% MORE thickness than its cementitious design UL X790 (CAFCO 300), so this calculator applies the same table to both methods and no reduction to the fibrous one.

Columns require thicker SFRM than beams at the same fire rating because columns are exposed to fire on all four sides (4-sided exposure), while beams protected by a concrete floor slab above are typically exposed on only three sides (3-sided exposure). The slab acts as a heat sink on the top flange, reducing the rate of temperature rise in the steel.

The W/D ratio directly determines the required SFRM thickness. A heavier beam (higher W) with a smaller heated perimeter (lower D) has a higher W/D ratio and needs less SFRM. A W14×48 beam (W/D ≈ 0.85) needs roughly 20% less SFRM than a W10×22 beam (W/D ≈ 0.52) for the same fire rating. The structural engineer or fire protection engineer calculates W/D for each member and specifies the corresponding thickness from the UL listing. For the structural sizing of the steel beams themselves, you can check steel beam sizing for span, load, and section selection.

Three methods protect structural steel from fire, each suited to different project conditions and budgets.

SFRM (cementitious or fibrous) is the workhorse of commercial fire protection. A crew sprays the material directly onto the steel surface, building up thickness to match the UL listing requirement. Cementitious SFRM (Isolatek Cafco, GCP Monokote) is the most common: it is cheap ($8-$15 per bag), fast to apply (a crew can cover 3,000-5,000 sq ft per day), and bonds well to clean steel. The drawback is appearance — SFRM is a rough, grey-white coating that looks unfinished. It is standard practice behind drywall ceilings and inside wall cavities where appearance does not matter. SFRM is also fragile; it chips and breaks if struck, which makes it unsuitable for areas with regular human contact.

Intumescent coatings are thin-film paints that swell when exposed to fire, expanding to 20-50 times their original thickness and forming an insulating char that protects the steel. At room temperature, intumescent looks like ordinary paint — smooth, thin, and available in any topcoat colour. This makes it the only practical option for architecturally exposed steel (AES) in restaurants, lobbies, atriums, and lofts. The cost is 5-15 times higher than SFRM per linear foot, and application requires multiple coats with controlled drying conditions. The required dry film thickness (DFT) comes from the product's ICC-ES evaluation report, not from a generic ladder: the two reports opened for this page list 0.173 in. (ESR-4766, FIRETEX FX6002) and 0.187 in. (ESR-4767, FIRETEX FX9502) for a 1-hour W10×49 column, and FX6002 is certified from 16 mils up to 160 mils on wide-flange beams and 420 mils on wide-flange columns. Enter the figure from your report in the calculator.

Fire-rated board systems (gypsum board, calcium silicate board) encase the steel in a box of non-combustible panels. Two layers of 5/8-inch Type X drywall on a steel stud frame provide a 2-hour rating. Board systems are self-installed by drywall contractors (no specialty fireproofing crew needed) and produce a finished surface. The trade-off is bulk — the board enclosure adds 2-4 inches to each side of the steel, reducing usable space. Board systems work well for columns in corridors where the enclosure becomes an architectural element.

The bag and per-gallon prices, the 3,000-5,000 sq ft per day productivity figure, the 5-15 times cost ratio and the 20-50 times expansion at 350-400 °F quoted above are not taken from a published source. This is our own estimate; no published source backs these figures. Check your results against your product data or a licensed professional before acting.

SFRM application is a specialised trade with strict quality control requirements. The fireproofing contractor must be certified by the SFRM manufacturer (Isolatek or GCP), and the work is inspected against the UL listing specification.

Steel surface preparation is the first requirement. SFRM bonds to clean, bare steel — not to oil, mill scale, rust, or paint. For new construction, the steel arrives from the fabricator with a light mill scale that SFRM bonds to adequately. For retrofit work on existing painted steel, the paint must be tested for adhesion and compatibility. If welded connections need to be made before fireproofing, estimate the welding time and filler material first — SFRM cannot be applied over fresh weld spatter or flux residue. Some primers (inorganic zinc, alkyd) are compatible; others (latex, epoxy) are not. The SFRM manufacturer's approval is required before spraying over any existing coating.

Thickness measurement during application uses a wet-film gauge (for SFRM) or a dry-film thickness gauge (for intumescent). The applicator measures thickness at regular intervals — typically every 100 sq ft of coverage — and records the readings. The average measured thickness must meet or exceed the specified thickness. For intumescent coatings, the floor for any single reading is 80% of the specified thickness, as printed in ESR-4766 and ESR-4767, section 4.4.2 (ESR-4766 lists ICC-ES acceptance criterion AC23 in its evidence section; ESR-4767 names a different criterion). The SFRM-side individual-reading rule (AWCI Technical Manual 12-A) was not opened for this page; use the tolerance your UL design and specifier state. These measurements become part of the inspection documentation.

Density testing verifies that the SFRM was mixed and applied at the correct density. ASTM E605 specifies the core-cutting method: a circular punch extracts a plug of cured SFRM, which is weighed and measured. The density must fall within the range specified in the UL listing — 15 pcf minimum average (14 pcf minimum individual) for the CAFCO 300 series and 22 pcf for the 400 series per UL X790, with the CAFCO 300 data sheet printing 15 pcf. Low-density material (under-mixed or over-watered) does not provide the rated fire protection even at the correct thickness, and that is also why the bag yield caps at 46 board feet: Isolatek's own yield chart warns that exceeding 46 board feet per bag drops the density below 15 pcf.

Bond testing (ASTM E736) measures the adhesive strength of the SFRM to the steel substrate. The CAFCO 300 data sheet states a minimum bond of 150 psf over uncoated or galvanized steel; the 200 psf figure sometimes quoted for vertical surfaces was not found in any document opened for this page. Failed bond tests require removal and re-application — a costly rework item that proper surface preparation prevents.

The required fire rating for structural steel depends on the building type, occupancy classification, and height/area. Here is how to determine the fire rating for your project.

1. Identify the building type from IBC Table 601. The International Building Code classifies buildings into Types I through V based on the fire resistance of structural elements. Type IA (fully fire-rated non-combustible) requires 3-hour columns and 2-hour beams. Type IIB (unprotected non-combustible) requires 0 hours — no fireproofing at all. Most commercial steel buildings fall into Types IA, IB, IIA, or IIB.

2. Check whether your building qualifies for a reduced type. Building area, height, and sprinkler systems can allow a less restrictive building type. A fully sprinklered building gets area and height increases (IBC 504, 506) that often permit Type IIA or IIB construction — which requires 1-hour or zero fire rating on the structural frame.

3. Determine the rating for each element. IBC Table 601 specifies hours by element: structural frame (columns, beams, bracing), floor assemblies, roof assemblies, and bearing walls. Columns always have the highest rating because column failure leads to progressive collapse. Roof structures in some building types have no fire rating requirement because the roof is not a means of egress.

4. Check occupancy-specific requirements. High-hazard (Group H), assembly (Group A), and institutional (Group I) occupancies may require higher ratings than the base table. Hospitals and detention facilities typically need the full Type IA construction.

5. Reference the correct UL design number. Every fire-rated assembly has a UL design number (for example X790 for contour-sprayed wide-flange columns, S721 for beams) that specifies the exact materials, thicknesses, and construction details. The architect or fire protection engineer specifies the design number on the drawings, and the fireproofing contractor builds to that specification. Isolatek serves its UL design printouts and per-shape thickness charts free from its own website, so the design for your product can be read before the estimate is made.

Fireproofing costs depend on more than just material quantity. Access, timing, cleanup, and retouching drive the total installed price far beyond the raw material calculation.

Mobilisation and containment represent a fixed cost regardless of project size. A fireproofing crew brings a spray rig, mixer, compressor, and scaffolding to the site. They cover all adjacent surfaces with plastic sheeting to contain overspray — SFRM is messy, and removing it from finished surfaces is expensive. This setup takes 1-2 days for a typical floor plate and costs $2,000-$5,000. On small projects (under 5,000 sq ft), mobilisation can exceed the material cost.

Retouching after other trades is a common cost that gets overlooked. Electricians, plumbers, and HVAC installers damage SFRM when running conduit, pipe, and ductwork through fireproofed steel. Every scrape, dent, and removed section must be repaired to maintain the fire rating. Retouching typically adds 10-20% to the base fireproofing cost and should be a separate bid item so the general contractor can charge it back to the trade that caused the damage.

Height and access affect labour productivity. Ground-floor steel that a worker can reach from a ladder costs less per linear foot than steel at 30 feet that requires scissor lifts or scaffolding. Multi-storey buildings typically see fireproofing costs increase 15-25% per floor above the second storey due to vertical material transport and equipment positioning.

The fully installed cost for SFRM runs $2-$6 per linear foot of structural steel for 2-hour ratings. Intumescent coating runs $15-$40 per linear foot for the same rating at older rule-of-thumb thicknesses; at the DFT an evaluation report actually requires (173 mils for a 1-hour W10×49 column), the coating alone can pass $39 per foot, as the second worked example shows. Board enclosures (two layers of Type X drywall) cost $8-$15 per linear foot including the stud framing. These ranges assume typical commercial conditions with reasonable access and standard steel sizes. Every cost figure in this section, the $11 per bag and $100 per gallon the calculator applies, and the mobilisation, retouching and height percentages are not taken from a published source. This is our own estimate; no published source backs these figures. Check your results against your product data or a licensed professional before acting. For projects that combine fireproofing with broader building upgrades, the energy retrofit cost estimator covers insulation and envelope improvements that complement the fire protection scope.