One of the biggest factors that impacts energy efficiency is air infiltration. The movement of air through the building envelope can mean the difference between an over-worked mechanical system with very poor efficiencies and a stable building environment that can be carefully controlled to specific temperature set points. Tilt-up panels are massive, opaque, monolithic concrete elements on average more than 6 in. thick. More than monolithic thickness, however, tilt-up panels offer substantially fewer construction joints around the perimeter of a structure than competing building methods. Where joints do exist, they are insulated to a similar or greater degree than the panels, although they represent a minute fraction of the surface area calculations and are treated with high-performance sealants that prevent both moisture and air from moving through them. With today's precise construction techniques, joints between panels are commonly held at no greater than a half-inch for architectural tolerances – a further reduction in air infiltration potential.
Insulating options integral to design
Insulation is a key component for a large portion of the building market - particularly tilt-up buildings that attempt to closely control interior temperatures and humidity and in areas that have significant climate variations. Compared to other forms of construction, tilt-up offers the optimum placement options for insulation systems balanced with construction economy. Furthermore, insulation systems of the past and in use today are often significantly compromised in attained performance due to thermal conductivity, otherwise referred to as thermal bridging. Metal and concrete are the most common construction materials that frequently penetrate or otherwise separate insulation systems and thus dramatically reduce or even negate the effectiveness of the designed insulation envelope. In today's market, proven insulation systems specifically designed for tilt-up construction provide the ultimate solution by eliminating the occurrence of these thermal bridges and providing the full material R-value of the insulation.
Winning with energy efficiency
Case in point is a recent residential tilt-up project that has received tremendous accolades for achieving high energy-efficiency ratings. The 31,824-sq.-ft. ROWhomes on F, located in a highly visible area of downtown San Diego, was designed as a prototypical urban residential project that addresses both "Smart Growth's" desire for higher density (42 homes per acre) and the homeowner's desire for comfort, energy efficiency and visually unique architecture. Conceived and designed with conservation in mind – from open space to energy – the dynamic and visually exciting urban architecture resulted from the adaptation of the "traditional" East Coast row home to Southern California's temperate year-round climate.
The tilt-up design allowed for an open floor plan with operable windows at each end of the structure without perpendicular walls. Such a design created cross-ventilation, which reduced air-conditioning demand, further reducing utility costs. The concrete also offered significant improvements in the energy conservation performance of the homes, to include the capability for the structures to maintain a moderate temperature of 65 to 78 degrees F. As such, the project was selected for the "Energy Efficiency" residential award from San Diego Gas & Electric in response to being 42 percent more efficient than Title-24 requirements. The project also received the tough-to-obtain "Energy Star" rating.
Yet another example of tilt-up meeting the needs of today's energy-conscious owners is the Gleneagles Community Centre in West Vancouver, B.C. A 2004 Tilt-Up Achievement Award winner, the 23,000-sq.-ft. structure houses a gymnasium, fitness area, art center, childcare facilities and administrative space. Constructed on an extremely tight site in a remote, restrictive and mountainous area, the District of West Vancouver (the owner) and architect chose tilt-up to provide a one-system architectural, structural and mechanical solution.
A tilt-up wall mechanically acts as a passive radiator providing heating/cooling through water piping embedded in the panels, which were structurally required to be a seismic shear wall connected to a timber roof diaphragm. These panels are structurally composite, dual-wythe sandwich panels tied together with welded rebar trusses, which allow an increase in the area available for insulation placement between wythes. By opting for this sandwich panel, rather than a non-structurally composite alternative, the overall thickness is minimized, seismic forces are reduced and costs lowered. Tilt-up allowed for a finished, exposed concrete surface on two sides serving as integral components of the radiant slab cooling system, which uses about 50 to 60 percent less electricity than a forced air system. This project also uses both natural and energy-efficient lighting to reduce the overall energy demand.