DOWSIL DefendAir 200 Weather Resistive Barrier (WRB) underlies the Medallion Apartments’ exterior renovations. The apartment building is 6-stories high with 90-unit affordable residential homes, located in Portland’s "Alphabet" Historic District. The Historic Landmarks Commission designated the Medallion Apartments as a non-contributing residential development, because it was built in 1965, well after the historic period. Nonetheless, the building renovation project required Landmarks Commission approval, which concluded:
The proposed exterior alterations and site changes to this existing multi-dwelling development will increase the building’s compatibility with its surrounding historic district and improve and activate the surrounding pedestrian network. The proposed materials are of high quality and the careful details will contribute to the durability of the building.
Increase the Medallion Apartments’ Compatibility with its Surrounding Historic District
Prior to its renovation, a failed, stucco Exterior Insulation and Finish Systems (EIFS) dominated the building’s architecture. The stucco EIFS and uninsulated concrete masonry unit (CMU) around each apartment’s entrance contrasted with surrounding Victorian and Federal-style homes.
After renovation, the building’s exterior will be a blend of sand colored, thin brick tile cladding, earth-colored EQUITONE facade panels on the stairwells and cedar plank-inspired fiber cement panels around each apartment’s entrance. The new variations in texture and color will help to soften the Medallion Apartments’ appearance, thus bringing it into harmony with its neighbors.
High Quality Materials Contribute to the Medallion Apartments’ Durability
The use of CMU to construct the Medallion Apartments significantly influenced its renovations.
First, CMU lacks the strength of modern, post-tensioned concrete construction able to support a heavy curtain wall. This limited the choice of brick cladding to lighter thin brick instead of heavier face brick.
Second, CMU is quite porous and requires a WRB to protect against water intrusion. The weather resistive barrier acts like a one-way street for moisture to travel. Water vapor may escape from the building’s interior via tiny holes in the barrier membrane. These same holes are too small for liquid water to penetrate the interior from the building’s exterior. The result is a drier, more comfortable residence, less prone to mold and mildew.
DOWSIL DefendAir 200 Benefits
The key benefits of applying DefendAir 200 include a water-based formula, ultraviolet (UV) stability, primerless adhesion:
- Water-Based formula enabled easy cleanup of rollers and sprayers using tap water, without gray water retention and disposal, ideal on a space-constrained worksite
- UV Stable composition allowed the barrier membrane to remain exposed to sunlight after its application, while construction proceeded elsewhere, thus eliminating weatherproofing as a scheduling bottleneck
- Silicone formula ensured compatibility with DOWSIL 791 Silicone Weatherproofing Sealant
- Liquid Applied having milkshake consistency using rollers or an airless paint sprayer (Graco® Sprayer or similar);
- Primerless adhesion to clean CMU or CMU covered with thin-set mortar
- Quick Turn-Around Time meaning the liquid dries in 2-4 hours and rainwater will run off, if it were to rain later in the day.
Architects are hungry to learn more about the benefits of the next generation of liquid applied air barriers. These benefits include easy water cleanup, indefinite UV stability, and high moisture vapor permeability. DOWSIL DefendAir 200 delivers all of these and more.
Project Challenge: Residual Cementitious Adhesive
Removal of the failed EIFS cladding revealed a unique challenge: residual cementitious adhesive used to glue polyisocyanurate (polyiso) insulation directly to the CMU walls. Mechanical removal of the adhesive proved unworkable, without damaging the CMU substrate. A layer of thin-set mortar proved to be the best solution to bring the CMU to plane and provide a primerless surface to receive the DefendAir 200 Air and Weather Barrier. Figure 2 shows a section of CMU with residual adhesive on the left, a strip of exposed thin-set mortar in the center and roller-applied DefendAir 200 on the right.
Thin Brick Veneer Curtain Wall Details
The thin brick veneer curtain walls are the dominant visible feature of the renovated Medallion Apartments building and include a hidden, careful detail: a moisture drainage plane missing from the failed EIFS. This drainage plane allows intermittent moisture to escape from behind the curtain wall and drain away via a horizontal opening at the bottom of the wall assembly. Figure 3 shows a cross section schematic of the complete wall assembly comprising the following components:
- CMU Wall
- Thin-Set Mortar to smooth up to plane (when required)
- DOWSIL DefendAir 200 Air and Weather Barrier (WRB)
- RockWool™ insulation mounted on posts and secured with pins
- Metal furring strips or hat channel used to create an open-air space (drainage plane)
- WonderBoard® Lite Backerboard with integrated waterproofing
- Thin-Set Mortar
- Mutual Materials Slimbrick® Thin Brick Tiles
- Masonry Pointing Mortar
- Horizontal Metal Flashing.
The curtain wall, moisture drainage plane and weather resistive barrier work together to ensure the interior CMU wall stays dry.
DefendAir was the right choice for this project because it was able to meet a number of different performance criteria. First, there was the fact that on several elevations, Dow AllGuard had been applied. The DefendAir will both adhere to, and is compatible with AllGuard. The resistance to both air and water infiltration are excellent, and the vapor permeability is right in the sweet spot for our environment. In addition to that, DefendAir offers long term UV exposure, adding flexibility to our schedule, while the water based clean up means we can spend more time installing material instead of cleaning equipment at the end of each day. Finally, we place great value on the partnership and support we receive from both Dowsil and Atlas – they have been long term partners with Walsh in achieving high performance projects for our clients and we knew we could trust them to contribute positively to the team.
DOWSIL DefendAir 200 Air and Weather Barrier For Your Next Project
Dow High Performance Building solutions include proven and innovative materials for structural and protective glazing, weatherproofing, insulating glass, high-efficiency insulation, and window and door fabrication. Experience the benefits of DOWSIL DefendAir 200 Air and Weather Barrier on your next weatherproofing project. Call Atlas Supply at 1-800-347-5767 to speak with your team of local weatherproofing experts. Refer to the DefendAir 200 Technical Data Sheet before using this product.
- Home Forward – Medallion Apartments – 1969 NW Johnson St, Portland, OR 97209
- City of Portland, Oregon – FINAL FINDINGS AND DECISION BY THE LANDMARKS COMMISSION RENDERED ON November 19, 2018 – CASE FILE NUMBER: LU18-234018HRM PC # 18-139301 [PDF]
- Architect – Holst Architecture, Inc.
- General Contractor – Walsh Construction Company
- Dow – DOWSIL DefendAir 200 Air and Weather Barrier
- Dow – DOWSIL 791 Silicone Weatherproofing Sealant
- Atlas Supply – DOWSIL High Performance Building (HPB) Silicone Solutions, Products & Technologies
- Atlas Supply – Sealants Glossary
- Mutual Materials – Slimbrick Thin Brick Tiles
- EQUITONE Facade Panels.
Randy McAdams, Senior Outside Sales, Atlas Supply
Lorne Andrusiak, DowSil-Specialist, Atlas Supply
Last Modified: May 3, 2020