Case Study: Envelope Solution for LA Commercial Multifamily Development Requiring Special Certification

EPRO PreTak waterproofing and methane barrier system being installed.

EPRO’s PreTak waterproofing and methane barrier system was the ideal building envelope solution for a commercial multifamily development by 800 Detroit in Los Angeles, California.

The Project

This three-story building, with two stories of below-grade construction, is situated in an area of LA with methane-rich soils. Typical throughout the LA area, these projects require appropriately designed methane mitigation systems tailored for the site’s unique geotechnical conditions.

These construction sites require the use of products that have attained a special certification from the city of Los Angeles Department of Building and Saftey. And as an added technical challenge, the design for this project included a back lag support for excavation.

A back lag condition is a configuration of soldier pile lagging where the lagging boards are mounted or fixed to the back flange of the piles. While being technically more challenging for waterproofing, this configuration maximizes the interior square footage of zero lot line developments.

Soldier piles with lagging boards behind them.

Specification of an effective building envelope system, especially for back lag and under slab applications in hydrostatic and methane conditions, requires an in-depth understanding of the unique physical characteristics and performance attributes of various manufacturer’s systems. PreTak was accepted for use based on its stated physical performance and overall versatility as both a waterproofing and methane barrier system. 

The Problem and the Solution

Comprised of a thick 32 mils of durable, highly impermeable, chemically resistant high-density polyethylene (HDPE) and pressure-sensitive adhesive (PSA), PreTak is a high-performance environmental barrier sheet membrane, effective at not only preventing the passage of water under hydrostatic conditions but also methane gas and other chemical vapors common on brownfield construction sites.

PreTak’s pressure-sensitive adhesive integrally bonds the durable membrane to fresh concrete, eliminating the potential for lateral water migration. Unique to PreTak is the availability of extra-wide format rolls spanning nearly 8 ft in width. These wider rolls reduce the number of seams in the applied system. Fewer seams mean fewer potential pathways for water or vapors.

Wider rolls are also more productive requiring fewer accessory components such as sealants and tape adhesives while covering more area with a single roll. As a heat weld capable system, PreTak helps ensure the highest level of protection for waterproofing and methane vapor through industry-standard heat weld application procedures and quality control such as smoke testing seams. 

EPRO PreTak heat weld application.

Insights From the Waterproofing Consultant

Back lag wall conditions pose certain challenges for blindside vertical wall waterproofing.

“We really liked the wider width rolls. Not only did they really increase our productivity on the horizontal under-slab portion of the project, but they also fit evenly between the soldier piles on the vertical wall sections and allowed for easy detailing to the face of the flange for our back-lagged SOE. Heat welding the system was a real advantage as well. We were able to field fabricate fitted boots to detail the base of the flanges for a better quality more efficient install,” explains PreTak-approved project applicator Noble Waterproofing and Coatings.

Local LA EPRO representative Brian Miraki provided on-site technical assistance throughout the application working directly with the applicator, GC and designers to ensure a successful install.

“The direct support and technical knowledge that we provide as a company help ensure that our projects are a success. PreTak was the right choice for this project. However, the right system selection is only half the equation to any successful project. At EPRO, we are committed as much to the right product as we are to the right install. We support each project with our technical knowledge, installation know-how and on-site problem-solving experience to make sure we attain 100% success,” explains Brian.

EPRO Can Be Your Next Solution

Despite this project having various barriers including the need for back lag support for excavation, EPRO was determined to make this project a success. The applicator, Noble Waterproofing and Coating, really supported the PreTak solution, along with application of wider rolls.

Because the city of Los Angeles requires different approvals for sites, using PreTak was the perfect solution. Not only is it tough and durable water membrane, but it is also Los Angeles approved as a gas and methane barrier (LARR #26164) and for shotcrete.

To learn more about PreTak, click here. To see how EPRO has helped on other projects, check out our other case studies