Ultimate Guide to Passivhaus Insulation

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Passivhaus Insulation

Passivhaus Insulation is essential given that our homes are responsible for around 20% of UK carbon emissions due to poor insulation, a lack of airtightness and general inefficiency. Modern building regulations aim to address the problem by implementing thermal targets and airtight standards in new and existing buildings that reduce carbon emissions. Passivhaus Insulation standards take this a step further by targeting zero emissions. Ultimately, Passivhaus standards help to make the living environment more comfortable for occupants whilst using very little energy for heating and cooling.

In this Ultimate Guide, we look at various ways our homes can be built to Passivhaus Insulation standards by adopting a whole-house approach that ensures the building’s fabric is energy-efficient and healthy.

What’s On This Page About Passivhaus Insulation?

  • What is a Passivehaus?
  • What special features help make a Passivhaus?
  • Is Passivhaus insulation expensive to achieve?
  • How can spray foam insulation help achieve Passivhaus standards?

Enverge Spray foam insulation used in a Passivhaus construction to achieve airtightness and thermal performance.

What Is Passivhaus Insulation?

Passivhaus is a German principle that developed methods to enable homes to achieve maximum energy efficiency. It has become the gold standard in modern building construction. The methodology behind a Passivhaus Insulation building differs from some carbon-neutral buildings, which use a combination of energy efficiency and clean energy generation to offset any energy use.

A Passivhaus building aims to use less energy by effectively sealing against the elements rather than seeking methods to offset energy loss. Behind every successful Passivhaus home is a high level of insulation installed to airtight standards to reduce or eliminate air leakage. 

The actual construction methods of Passivhaus buildings will vary depending on their size, design and orientation, but typically, common principles will include:

  • A greater insulation level than typical UK properties or Building Regulations requirements.
  • Triple-glazed windows and doors with insulated frames.
  • Impressive airtightness levels at around 20x better performance than a standard build.
  • Mechanical ventilation with heat recovery to minimise air leakage.
 

To meet Passivhaus insulation standards, the building will usually adopt the following criteria:

  • U-Values for walls, floors and roofs are between 0.10 and 0.15 W/m2K.
  • Airtight vapour control layers and sealing tapes should be used to reduce air leakage.
  • Reduced thermal bridging through structural elements.
  • An airtightness target of no greater than 0.6 ACH (air changes per hour) at 50 Pascals of pressure.
  • Energy-efficient ventilation strategies should be used to minimise air leakage and introduce heat recovery.

What Special Features Help To Make A Passivhaus?

The core elements of Passivhaus are Insulation, Airtightness and Ventilation. Insulation and airtightness will help to reduce or eliminate air leakage through buildings, but some form of ventilation strategy that handles internal moisture and air quality is always required. Passivhaus Insulation standards are worlds apart from how we used to construct our buildings. Insulation was never a primary consideration before the 1990s when energy was cheap and carbon emissions weren’t considered a problem. This meant that we used to build single-glazed windows and ventilation openings in the roof, eaves, and wall cavities where used internal air could escape whilst fresh, unheated external air could enter.

As energy costs have risen significantly over the last quarter of a century, insulation levels have become essential in managing heat loss in existing homes. However, when we increase insulation levels in existing buildings, ventilation needs to be implemented to offset the reduced airflow, and this can sometimes compromise the home’s health by introducing dampness, mould and condensation. Some insulation materials like spray foam have been blamed for structural roof degradation when retrofitting existing homes. However, the reality is that the material isn’t the cause; the lack of ventilation is more likely to be the problem because improving energy efficiency within existing homes is challenging.

Passivhaus standards fly in the face of what Building Surveyors and Construction Professionals are used to seeing. Professionals must remain updated as new construction methods and modern materials are introduced. A common misconception from construction professionals and surveyors is that natural ventilation openings are crucial to help buildings breathe, and they often overlook that natural airflow can be replaced with modern, mechanical ventilation strategies. The structural elements of new buildings are better-protected thanks to modern construction materials and principles, which can change how they are built.

Roof, floors and walls are insulated using airtight Enverge Sucraseal Open Cell spray foam insulation to reduce air leakage and running costs.Roof, floors and walls are insulated using airtight Enverge Sucraseal Open Cell spray foam insulation to reduce air leakage and running costs.

Passivhaus Insulation

Generally, the more insulation used in a building, the lower the heat loss, and to meet Passivhaus standards, the U-Value of floor, wall and roof constructions should be between 0.10 and 0.15 W/m2K. Of course, the thickness and type of insulation materials used can significantly impact the structural assembly and construction materials used. For example, thicker roof insulation will require deeper rafters, which adds to the cost of constructing a Passivhaus. Choosing the lowest thermal conductivity per inch of insulation material can positively affect the depth of the structural assembly of walls, floors and roofs. Although the insulation may cost more, the structural assembly may cost less and take up less space. Insulation doesn’t just come in the form of a material that slots into floor, wall or roof cavities; choosing windows and insulated frames is also essential. Triple-glazed windows are generally required to help achieve Passivhaus status.

Passivhaus Airtightness

Insulation slows heat loss but may not prevent it in its entirety. Additionally, most insulation types are cut to size and fitted into place, which can cause small penetrations where air leakage may occur. Airtight tapes and membranes cover any joins between insulation and structural elements to reduce air leakage. Almost every pre-manufactured insulation material will require airtight tapes and seals to boost performance. In contrast, spray foam insulation is the only insulation material manufactured “in situ”. The spray foam is applied as a liquid before rapidly expanding and filling every millimetre of the cavity void to reduce air leakage. Spray foam insulation can achieve heat loss efficiency and airtightness in a single application, making it one of the most effective insulators for Passivhaus construction methods.

Passivhaus Ventilation

With high levels of insulation and airtightness required to achieve Passivhaus standards, ventilation becomes a crucial element that manages the moisture and air quality within buildings. Sealing up every air leakage point within the building will increase humidity and moisture content within the air. This air must be removed from the building while fresh air is introduced to reduce humidity and moisture levels. Passive extract ventilation fans in bathrooms and kitchens may effectively remove moisture. Still, they are also sources of air leakage points and aren’t deemed suitable options in Passivhaus construction. 

Mechanical Ventilation with Heat Recovery (MVHR) is the choice for Passivhaus insulation builders and provides a whole-house, room-by-room approach to ventilation and healthy indoor air quality. Activated by air quality and humidity sensors, the MVHR system will extract moist air from the “wet zones” of a building, such as bathrooms, kitchens and utilities. The MVHR heat exchanger recovers up to 98% of the heat from this air, and it is reintroduced to the fresh, filtered air intake, which re-pressurises the building and ensures that moist, stale air does not attack the insulation and structural assembly.

The net result of these elements can help the building meet Passivhaus standards and should be a priority over all other energy efficiency solutions and green technologies. Passivhaus standards prioritise energy conservation over clean energy generation strategies, which can lead to exceptionally low running costs and a reduction in energy demand.

 

Is Passivhaus Insulation Status Expensive To Achieve?

The answer is yes; the initial cost of achieving Passivhaus insulation standards will be more than simply meeting the targets of the Building Regulations. However, the results should pay for themselves long-term, with Passivhaus homes costing virtually nothing to heat and cool. This can reduce the size of heating systems such as boilers, air-source, ground-source or solar PV, reducing the initial technology cost.  

The structural design of the building will generally require additional materials that will add to the initial cost. For example, the depth of roof rafters to achieve a 0.16 W/m2K U-value is very different from the depth needed to meet a 0.10 W/m2K U-value and will cost more. Where double-glazed windows may have been used to tick the box of Building Regulations, triple-glazed windows with insulated frames are a must in Passivhaus construction.

Heat recovery ventilation is also essential for the whole house. Although new homes must meet the minimum standards of Part F Building Regulations for extract ventilation, Passivhaus buildings require a holistic approach to ventilation. This means extract ventilation is fitted to bathrooms, kitchens, and utility rooms, while the system is balanced with intake airflow to other rooms such as the bedrooms, lounge, and office. The initial investment cost of an MVHR system will be higher. Still, over time, the system’s efficiency will pay for itself financially, and with improved internal air quality, airborne pollutants and viruses will be reduced.

Airtight Enverge Sucraseal open cell spray foam insulation used to provide pitched roof insulation in a Passivhaus project. Airtight Enverge Sucraseal open cell spray foam insulation was used to provide pitched roof insulation in a Passivhaus project.

How Spray Foam Insulation Can Help To Achieve Passivhaus Insulation Standards

Spray foam insulation and Passivhaus work together. They were unconsciously designed for each other! No other pre-manufactured insulation materials achieve the natural airtightness of spray foam in a single application. Where pre-manufactured insulation materials range from mineral wools to Polyisocyanurate (PIR) boards and require cutting to size and fitting into place, spray foam insulation is spray-applied as a Polyurethane liquid that expands and fills the cavity into which it’s installed. This helps to reduce the time and expense of using airtightness tapes, and due to the strong adhesion of the spray foam to the substrate, joists, studs and rafters, a complete seal is achieved.

There are many other benefits of choosing spray foam insulation, not least the fact that it is manufactured and installed in situ, which reduces labour time, off-cuts, and wastage. It can also be spray-applied directly to low-resistance building materials, which negates the requirement for air gaps that waste space within the structural assembly. Open-cell spray foam insulation has a comparable thermal conductivity to mineral wool insulation. It can provide good sound attenuation, whilst closed-cell insulation is more thermally efficient, requires less space, and can add structural integrity thanks to its dimensional stability. 

When undertaking a Passivhaus build, the choice of insulation is one of the primary considerations for success. Spray foam insulation is one of the few insulation materials that never shrinks or degrades, making its long-term thermal performance stable. If you’re investing in achieving Passivhaus status, it’s essential to approach the build as one that you build tight and ventilate right. ThermoFoam provides robust specifications that achieve Passivhaus standards whilst complying with Building Regulations. Our Enverge Sucraseal Open Cell and Enverge Nexseal LE Closed Cell spray foams are BBA-certified for UK construction.

Closing Summary

Undertaking a Passivhaus project requires careful planning and consideration. Insulation and airtightness are key components, which means the structural assembly needs to be constructed carefully and with the right choice and depth of materials. 

Building to Passivhaus standards will be initially more expensive, but the long-term results should yield better energy efficiency and, therefore, lower heating and cooling costs. We recommend that you conduct extensive research before committing to a Passivhaus project. The Passivhaus Trust can help you navigate the pros, cons and requirements of meeting the gold energy efficiency standard.

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