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Mass Timber Construction

We have proven firestop systems and the products to meet the needs of this rapidly growing building segment.

Mass Timber Construction

Firestopping for Mass Timber

Mass Timber, which includes Cross Laminated Timber (CLT) among other types, is a category of engineered wood quickly becoming the choice for architects due to its exceptional strength and stability and being a low-carbon alternative. Recent code changes have allowed for mass timber buildings up to 18 stories tall. STI has the 3rd party Certified Systems and products to keep your mass timber projects compliant.

The proliferation of mass timber construction provides many positives to our world. It utilizes biophilic design, which creates a sense of well-being by putting us in touch with nature by encompassing us with the beautiful richness wood surfaces provide. Building with mass timber also has sustainability benefits to the environment.

Where construction with concrete and steel adds carbon to the atmosphere, wood construction absorbs carbon reducing the overall carbon footprint, leaving increasing potential sustainability credits.

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Ascent Project, Milwaukee, Wisconsin
World’s Tallest Mass Timber Project

Changes to Building Codes

Changes to building codes have only reinforced the acceptance of this building material. When mass timber elements are qualified for fire-resistance rating purposes, the designer considers the expected char depth when considering load-bearing capability. Wood converted to char has no structural integrity, and the design load must support the uncompromised wood that remains after a prescribed fire duration.

Code Application 2018 IBC 2021 IBC
Type 4 Construction Subtypes IV-HT IV-HT, IV-A, IV-B, IV-C
Maximum height range depending on occupancy 60 to 85 feet IV-HT - 60-85 feet
Allowable stories depending on occupancy 1 to 6 stories
A-5 occupancy unlimited with or without sprinklers
IV-HT - 1-6 stories
IV-A - 1-18 stories
IV-B - 1-12 stories
IV-C - 1-9 stories
A-5 sprinklered occupancy is unlimited
2018 IBC
  • A-5 occupancies, which are for the purpose of viewing outdoor activities such as a grandstand or stadium the allowable stories are unlimited
  • Surfaces of CLT required to be protected by fire-retardant treated wood, gypsum wallboard, or other approved non-combustible material.
2021 IBC
  • Some types of occupancies are not permitted, unless sprinklered. Primarily this is for H-1 (High hazard) and I-1 (Institutional for individuals requiring custodial care)Unlimited stories for A-5 occupancies as long as they’re sprinklered

Systems & Products

Features and benefits for all Listings:
  • Min. 3-15/16 in (100mm) 3 ply systems for 1 and 2-hour applications
  • Optional gypsum protection for 1 hour
  • Optional gypsum protection for 2 hours with min 5-15/16 inch (132mm) floor or wall assemblies
  • Optional floor toppings for floor applications
Click hyperlink to see systems:
  • Max 4 in PVC, closed or vented
  • Largest plastic pipe penetration system offered currently
  • AC Lineset Penetration
  • Max 1 in copper tube, steel, cast iron, ductile iron pipe insulated with ¾ in. AB/PVC
  • Two control wires
  • Max 1 in copper tube, steel, cast iron, ductile iron pipe condensate line
  • Max 4 inch bundle of multiple cable
  • Percent fill range from 0% to 44%
Application 1 Hour Listing 2 Hour Listing Product
4"" PVC pipe (vented of closed) STI/PF 60-01 STI/PF 120-01 SSWBLU2/
AC Lineset STI/PF 60-02 STI/PF 120-02 LCI
Cable Bundle STI/PF 60-03 STI/PF 120-03 LCI
Metallic Pipe STI/PF 60-04 STI/PF 120-04 LCI
Insulated Metallic Pipe STI/PF 60-05 LCI
4"" ABS pipe (vented of closed) STI/PF 60-06 SSWBLU2/
Blank Opening STI/PF 60-07 LCI
  • Up to 6 in diameter copper tube, steel, cast iron, ductile iron pipe, or conduit
  • Up to 6 in diameter copper tube, steel, cast iron, ductile iron pipe
  • Up to 2 in fiberglass insulation
  • Max 4 in ABS, closed or vented
  • Largest plastic pipe penetration system offered currently
  • Max 5 in diameter blank opening

NOTE: all systems are for floor and wall configurations.


  • SpecSeal LCI Firestop Sealant is a water-based intumescent sealant intended for a wide range of through-penetration and construction joint applications.
More Information
  • SpecSeal SSW Wrap Strips are available in a variety of sizes and types to tackle any combustible penetration. SSW Wrap Strips are available in 12 ft. rolls as well as individually pre-sized strips to minimize waste and speed up installation.
More Information
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