Role of Insulation in Passive House Design
Well-designed insulation reduces heat transfer, minimizing energy consumption and utility bills. It also provides thermal protection for the life of the building.
A super-insulated building envelope and effective sunshades keep desirable warmth in during winter and undesirable heat out, while a ventilation system imperceptibly delivers fresh air. The elimination of interruptions in the insulation (known as thermal bridges) is also critical to performance.
1. Airtightness
Airtight construction reduces the movement of unconditioned outdoor air that carries pollutants, allergens and moisture into buildings. It also stops heated or cooled indoor air from being pushed outside, even when windows are open for ventilation. Airtightness maximizes the benefit of filtered and balanced mechanical ventilation and reduces energy bills.
In Passive House design, airtightness combines with a continuous layer of insulation to control heat loss and gain and prevent condensation in building components and assemblies. The insulative layer is continuous around the building, minimising thermal bridges such as aluminium or steel framed window frames, drywall, concrete slab edges, and corners.
The insulative layer also keeps the inside face of exterior walls warm, preventing condensation on the wall surface and extending the life of the paint and siding. This enables the use of high-performance, non-toxic and water-resistant finishes.
Achieving Passive House standards requires a major reduction in heating energy and an increase in internal gains from people, appliances and solar power systems. This is only possible by making the building incredibly airtight and highly insulated, with the help of low SHGC windows, a passive solar design and a well-chosen ventilation system with heat recovery. This dramatically lowers energy consumption and carbon emissions, while enhancing comfort and occupant health. The resulting ultra-low energy consumption means that, depending on the climate and site, a home built to Passive House standards may not require any supplemental heating.
2. Insulation
Providing an effective barrier between the inside and outside environment, insulation is vital to achieving optimum thermal balance in passive houses. Proper insulation can significantly reduce energy use, saving money and minimizing carbon footprints.
Insulation keeps heat in during winter and out during summer, which greatly cuts down on the amount of energy needed for heating and cooling. This results in substantial savings for homeowners and businesses, especially with a high quality ventilation system. Additionally, a highly efficient thermal insulation system can recycle the heat contained in the exhaust air to make for a more sustainable system overall.
High insulation standards can be achieved with a wide range of materials, from bulky fiber materials like fiberglass and rock wool to rigid foam boards to sleek foils. All forms of insulation must meet a specified R-value to achieve the passive house standard, and special attention is paid to eliminating thermal bridges (breaks in the insulation). These gaps include framing members, such as studs and joists, as well as areas around components with high conductivity such as aluminum windows, steel doors and uninsulated concrete slab edges.
With a continuous layer of insulation wrapping the building, passive houses maintain stable indoor temperatures that eliminate drafts and prevent condensation, mold and high interior humidity levels. In addition, proper insulation reduces noise transfer between spaces, and can help to dampen high-frequency sounds, such as sirens and horns.
3. Energy Efficiency
Insulation is a key feature of passive house construction. Thicker insulation (up to double in thickness compared to conventional building codes) minimizes heat transfer and keeps buildings comfortable year-round with minimal artificial heating and cooling. Besides thermal insulation, careful attention is given to airtightness, ensuring that warm air cannot escape the building in the winter and cold air does not enter in the summer.
In addition, the ventilation system in Passive Houses continuously supplies filtered fresh air and recovers heat from exhaust air. This combination reduces the energy required for ventilation and for heating/cooling, resulting in significant operational energy savings of up to 90%.
To achieve these energy efficiency levels, a variety of high-performance materials and components are used. ROCKWOOL’s non-combustible stone wool insulation, for example, is ideal for Passive House projects as it fits easily into the wall and roof cavities, stays in shape, allows vapour to pass through, and is long-lasting and fire-safe. It also improves indoor air quality, thanks to its natural anti-dust and allergen properties.
Another important component is solar heat gain management, which ensures that sufficient passive solar heat can be obtained during the day to meet heating and cooling needs without the need for mechanical systems. This is accomplished by using shading strategies — such as overhangs, deciduous trees with bare branches in winter and shade-providing leaves in summer, and architectural elements like windows — to maximize solar gains when necessary while minimizing unwanted radiant heat gain.
4. Natural Light
As energy efficiency is a key factor in passive house design, it should be combined with good daylighting. It allows homeowners to reduce their dependence on artificial lighting, which in turn cuts energy usage significantly.
One of the ways to achieve this is by having a super-insulated building envelope. The insulation in a Passive House must meet very low U-values – typically in the 0.10 to 0.15 W/m2K range – and be placed as close to the building structure as possible to avoid thermal bridges. ROCKWOOL’s non-combustible rock wool insulation meets these requirements and can be used in a variety of construction methods to reach Passive House standards, including straw bale and concrete slabs.
A Passive House’s high level of thermal protection can even be so effective that the air in a house does not need to be heated at all. The air is kept warm through the winter by the insulating materials and internally generated heat from cooking, plug loads, and people, or a combination of all of these. During summer, natural breezes and shade plus the insulating walls and windows keep the heat out of the house.
Besides saving on heating and cooling costs, Passive House design also helps preserve non-renewable resources and minimizes climate change. Buildings to Passive House standards use 40-80% less energy than a typical modern home and help reduce greenhouse gas emissions.