Case Study: Low Profile HVAC for Mid-Century Modern Homes

Have you ever turned a corner in a flat-roof single-story neighborhood and been shocked by the maze of metal ducts and equipment protruding from inconspicuous rooftops? As a flat roof integration and HVAC expert, I regularly receive owner requests to either restore or maintain the sleek low-profile appeal of their Mid-Century Modern homes. The solution is referred to as “Low Profile HVAC”.

Eichler and Mid-Century Modern homes were built with radiant heating systems which typically pump hot water through circuits of metal tubing encased in concrete slab foundations. As these old systems fail, boiler water leaks into floors through cracked foundations and corroded pipes. Meanwhile, the owner is faced with an urgent dilemma of how to restore the home’s heating system. Many turn to forced-air heating as a solution which often result in the aforementioned infamous eyesores.

Even with a functional radiant heat system, other homeowners turn to the same forced air systems in fulfillment of air conditioning and air filtration needs. Other types of HVAC systems that do not require ductwork are available. For example, mini-split systems are a popular alternative as they feature multi-zoned heating and cooling with no ductwork. However, some owners opt-against mini-split systems in objection to the bulky mini-split equipment units located on walls in each major room. Although additional alternatives are available, low-profile solutions for forced-air are the focus of this article.

Traditional homes locate ventilation ducts in attics and between rafters. However, Eichler style homes featue open-beam ceilings which do not provide such spaces for hiding ductwork. Rather than elevating ducts above-the-roof, Dura-Foam systems integrate low-profile rectangular ducts that are installed directly over flat roof’s deck boards. Then, closed-cell polyurethane roof waterproofing materials embed and encapsulate the ductwork. Rather than installing a roof-top packaged HVAC unit (see photo below), the Low Profile HVAC systems usually locate the furnace in the garage or in a utility closet. The air conditioner is a separate component that is typically located in a side-yard at ground level.

Hide HVAC
Move HVAC equipment from the roof into the garage or utility closet

Around the turn of the century, a new style of small duct air systems by Unico and High Velocity began garnering interest with Mid-Century Modern remodel teams. With 2″ diameter branch ducts and trunk ducts of maximum 4″ height, all ductwork can be embedded in 4″ thick insulation board, then encapsulated in a 1.5″ thick Dura-Foam roof layer. Air registers for these small duct systems also sport low profile appeal with 2″ diameter round or 8″ wide thin-slotted apertures. Around that time, I became a Unico-certified installer and began designing and installing small duct systems integrated with Dura-Foam roofs. Before long, our team at Dura-Foam shifted gears as Unico and High Velocity equipment was not becoming widely adopted in the Bay Area. Rather than pushing these new specialty small duct systems, we innovated a standard for integrating low profile ductwork with standard HVAC equipment which proved advantageous for its local availability and industry-wide familiarity among technicians.

When possible, Dura-Foam systems retain existing layers of roof insulation by cutting trenches where recessed ducts are to be located. After the galvanized rectangular ducts are installed, a waterproofing layer of 1.5″ thick closed cell polyurethane is seamlessly applied as a monolithic barrier over the ducts and entire roof surface (see photo below).

waterproof barrier
Galvanized ducts are recessed down to the structural deck, then sealed with Dura-Foam roofing.

Dura-Foam roof barriers are finished with acrylic-based Cool Roof Coatings. As a result, the embedded ductwork is super-insulated from outdoor temperature fluctuations. In addition, the embedded ducts are guaranteed against leaks under the seamless roof system. When installed properly, the entire roof provides a solid walkable surface – including areas over embedded ducts. Well-planned design integration is a must for proper air flow and roof drainage. Installing PV solar over areas of low profile HVAC ducts is also a possibility, but needs to be well-coordinated.

low profile hvac
Low-profile HVAC is encapsulated in a tough and walkable Dura-Foam roof surface.

Stripping the existing roof materials down to the wood deck is often required on major remodels where the roof deck is to be reinforced with plywood decking and fully re-wired. Complete roof removal and replacement of insulation board layers can easily double the roof installation cost. HVAC system cost varies with the efficiency level of equipment, quantity of air registers and add-on features such as hypoallergenic filtration systems. Slim Line outdoor HVAC units are a popular choice for side yards. These AC units are quieter than most other models while allowing maximum side yard access with their narrow profile (see photo below).

HVAC Slim Line
Slime Line outdoor AC units maximize side yard access.

Among forced air alternatives, Low Profile HVAC best maintains the low-profile architectural emphasis of Mid-Century Modern homes by keeping the roof surface clear of ducts, refrigerant lines and conduits. Specialty small duct (e.g. Unico) versus traditional equipment integrated with low profile ducts each have their unique advantages and trade-offs. While all will agree that heating is a must-have, many Dura-Foam roof owners find that cooling systems are not essential in Silicon Valley’s mild climate. Cool Roof coatings over closed-cell polyurethane, the world’s best insulator, efficiently get the cooling job done for the majority.

7/21/2018 written by Jarom Feriante, CEO of Dura-Foam Roofing & Solar Center – LinkedIn

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