Insulation is a central part of Passive House design. Its performance depends on the bulk insulation material, and the building envelope’s airtightness. It also requires eliminating thermal bridges where other materials bypass the insulation (like around windows and doors, and recessed lighting fixtures).
A continuous layer of thick insulation keeps Passive Houses optimally cool in summer and warm in winter. With a high quality ventilation system that recovers heat from exhaust air, this results in significant operational energy savings.
Energy Efficiency
One of the most important aspects of passive house design is energy efficiency. By super-insulating the building envelope and creating an airtight construction, passive houses need much less active heating and cooling systems to maintain comfortable indoor temperatures.
Passive houses also utilize high-performance glazing, which reduces heat loss and maximizes light transmittance. As a result, they need very little electric lighting, which further reduces energy consumption.
In addition to reducing energy costs, insulation provides many other benefits such as noise reduction and improved durability. The focus on airtight construction also minimizes moisture infiltration, which prevents mold growth and structural damage.
There are a number of insulation materials available, from bulky fibers like fiberglass, rock wool, and cellulose to rigid foam boards and sleek foils. The best insulation materials have a high R-value, which measures the resistance of the material to the flow of thermal energy. R-values range from 0.0 to 4.0, with 1.0 having the highest resistance and 4.0 the lowest.
Passive houses also aim to avoid thermal bridging, which is the bypassing of insulation by other components such as metals. This can reduce the benefits of a super-insulated building envelope. As such, passive houses try to avoid repeating thermal bridges as much as possible, particularly in interface details like the way windows attach to walls and doors meet at corners.
Indoor Air Quality
With the COVID-19 pandemic, indoor air quality has become an important issue for many people. In Passive House buildings, the ultra-tight building envelope coupled with ventilation with heat recovery (MVHR) helps to ensure a healthy and stable indoor climate.
Poor indoor air quality causes many health issues, including respiratory infections, allergies, and increased fatigue and stress levels. Air pollutants can be a result of human activities, such as fuel combustion and cleaning chemicals, or from a variety of other sources.
Ventilation systems in Passive House buildings continuously introduce fresh, filtered air while exhausting stale indoor air. This helps to reduce allergens, volatile organic compounds (VOCs), and excess moisture which can promote mold growth and condensation.
Adding foam insulation to the building envelope is an excellent way to improve the ventilation system. This type of blown-in insulation provides better R-values than batt insulation and also creates an air barrier, helping to reduce the number of invasive weatherization tasks required during construction, such as caulking, applying housewrap or vapor barriers, and taping joints.
The MVHR in passive house buildings must be correctly designed, installed and commissioned to ensure it performs as intended. In addition, the air tight building envelope must be sealed properly to avoid unnecessary energy losses. The best solution for achieving both is working with design and construction teams that understand Passive House requirements. This can help to eliminate finger-pointing during the drafting of a project scope, and ensure that all stakeholders are aware of the high performance goals that are expected from the project.
Thermal Comfort
A high level of thermal comfort is one of the primary goals of passive house design. It is achieved by combining insulation with other passive strategies including natural daylighting and ventilation.
Insulation helps to keep a building at a comfortable temperature throughout the year, reducing the need for air conditioning and heating. It does this by preventing the escape of heat through conduction in winter, and slowing the intrusion of heat from outside in summer — all while maintaining an airtight, energy-efficient envelope. Well-designed and installed insulation keeps a building at its desired temperature with little or no energy input – and does so for the life of the building.
Passive House designs also consider climate specific insulation and the elimination of air leaks, a prerequisite for an airtight building. Often, a simpler building form makes it easier to achieve Passive House air tightness and performance. However, a complex building shape has more potential for thermal bridges and requires more insulation to overcome them.
The super-insulated envelope of a Passive House building is like a warm coat, with an uninterrupted layer of air-tight insulation that prevents the flow of heat in and out of the building. ROCKWOOL’s non-combustible stone wool insulation is ideal for achieving passive house standards, as it fits easily into the envelope, maintains its shape over time, allows water vapour to pass through and is long-lasting and fire-safe. The envelope is also designed to be thermally bridge-free at interface details where different architectural features meet, such as windows or walls.
Sustainability
Insulation is a key ingredient for energy-efficient passive houses. By preventing the transfer of heat from outside to inside, it can optimize energy savings and maintain comfortable temperatures all year round. The insulating layer also helps keep windows and doors warm in winter and cool in summer, helping to reduce air movement. Combined with high-performance glass and shading, this can help control the amount of solar energy entering a building and reduce the need for mechanical heating and cooling systems.
The insulating layer also keeps the interior surface of walls warm, which can protect paint and exterior siding and extend their lifespans. It also prevents moisture build-up and condensation within the building envelope, which can lead to mould growth and poor indoor air quality.
Good insulation materials are available at a competitive price and can be applied in a variety of construction methods. This includes timber construction, formwork element technology and steel construction as well as solid and monolithic concrete construction. The required insulation thickness can even be achieved with straw bale construction, providing a cost-effective option for passive houses.
The insulating layer in a Passive House building is also very airtight, allowing it to be verified with a blower door test. This unbroken air barrier is key to the energy efficiency of a Passive House and its durability. It is achieved through a combination of sheet membranes, fluid-applied membranes, tapes and sealants that transition seamlessly between different components of the building envelope.