What is a Building Insulation Performance Grade

The insulation performance grade of a building is an indicator of heat insulation performance as stipulated in the "Act on Promotion of Housing Quality Assurance" (commonly known as the Housing Quality Assurance Act).

Specific Grades

There are four insulation performance grades, from 1 to 4.
Grade 1, the lowest rank, indicates no insulation.
Since Grade 1 was established, it has been updated frequently, and in 1999, Grade 4 was established.
Grade 4, the highest rank, has strict requirements such as "double-glazing must be installed."
As a result, energy savings of approximately 60% are now possible compared to Grade 1.
Incidentally, a new higher rank, Grade 5, is scheduled to be established in April 2022.

Judgment method for heat insulation performance grade

How is the insulation performance grade determined?
The criterion is the "average heat transfer coefficient (UA value)."
First of all, the heat transfer coefficient is an index that expresses the degree of heat transfer from indoors to outdoors.
Then, the average heat transfer coefficient is the value obtained by dividing the amount of heat loss from the entire house by the total area of the exterior layer, such as walls and windows.
The lower the UA value calculated by this method, the higher the insulation performance.
The UA value also differs depending on the regions in Japan. Each region or area has its own standard based on climate.
The UA value is compared with the standard value of the corresponding region to determine the insulation performance grade.

Is a Grade 4 Heat Insulation performance sufficient?

To make a long story short, even a heat insulation performance of grade 4 is not sufficient.
It is true that many people feel secure with a heat insulation performance grade 4, as it is also a standard for obtaining certifications for long-term excellent housing and Flat 35 home loans (which have stricter housing performance standards than usual home loans).
However, it is by no means the highest level of performance in light of modern technological advances.
For example, Grade 4 requires 90 mm thick insulation for ceilings and floors, but there are now insulation materials in circulation that are thicker than that, and new construction methods are being developed.
Those who are particular about insulation should look for higher insulation performance.

What is the ZEH standard for building insulation performance

So far, we have focused only on the insulation performance of buildings and have provided you with the criteria.
Of course, there is nothing better than high insulation performance, but these days, consideration for the environment is also extremely important.
The "Certified Low Carbon Housing Standard" and the "ZEH Standard" have been attracting attention as well.

What is the Certified Low Carbon Housing Standard?

The Certified Low Carbon Housing Standard is a standard that focuses on carbon dioxide emissions while providing the same level of insulation as a Grade 4 building.
The standards applicable to certified low-carbon housing are as follows:

●Heat insulation performance grade 4 or higher
●Primary energy consumption grade 5 or higher
●Achievement of at least two of the following: water conservation, energy management, "heat island" phenomena counter-measures, and low carbon footprint

The Primary energy consumption grade is calculated by adding up the energy efficiency of lighting and equipment, including heating and cooling, as well as insulation performance.
Thus, we can see that items related to energy conservation have been added, and the requirements have become more stringent.
Incidentally, there are five primary energy consumption grades from 1 to 5.

What is ZEH Standard?

The ZEH standard is a higher grade than the Certified Low Carbon Housing Standard.
ZEH stands for Net Zero Energy House.
ZEH is defined by the Ministry of Land, Infrastructure, Transport and Tourism as "a house that aims to achieve an annual primary energy consumption balance of zero by significantly improving the insulation performance of the outer layer and introducing highly efficient equipment systems to achieve significant energy savings while maintaining the quality of the indoor environment, and by introducing renewable energy."
The ZEH standard is defined as "a house that aims to achieve a zero annual primary energy consumption balance by introducing renewable energy and achieving significant energy savings while maintaining the quality of the indoor environment."
The following four conditions apply to the ZEH standard.

●Must meet reinforced outer layer standards of the area
●At least 20% reduction in base primary energy consumption
●Renewable energy sources such as solar power must be used
●100% reduction in primary energy consumption by the above three

Thus, the ZEH standard aims to create homes that require as little energy as possible by strengthening insulation standards, and to generate what is needed by using renewable energy.
There is also a ZEH+ standard as a higher grade of the ZEH standard, which has these four conditions made more stringent.

Deferred compliance with energy conservation standards

Energy conservation is attracting a great deal of attention, as evidenced by the revision of the "Building Energy Conservation Law," which requires architects to explain to customers the energy-saving performance of their homes.
Although the mandatory insulation rating of 4 scheduled for 2020 was postponed, it is highly likely that it will be implemented in the near future.

What is HEAT 20 and how does it work to improve the insulation performance of buildings?

So far, we have explained the various insulation performance grades.
Although new standards have been established over the years and overall housing performance has been improving, it is still low compared to global standards.
To improve this situation, an organization called HEAT 20 was organized.

What is HEAT 20?

The official name of the committee is "Committee for the Development of Highly Insulated Housing Technologies for 2020."
The purpose of the committee is to promote the improvement of thermal insulation performance and to educate the public about insulated houses in order to promote further energy conservation in housing.
Many members of the committee are housing manufacturers and researchers, all of whom participate in the committee on a voluntary basis.

Characteristics of HEAT20

One of their key features is that they have their own standards for energy conservation.
Specifically, there are G1, G2, and G3 performance grades.

Conditions for determining the grade

HEAT20's emphasis is on the indoor sensory temperature.
The temperature can be calculated as (average temperature of floor, ceiling, and walls + room temperature) divided by 2.
The standard of the temperature for each grade is as follows:

●G1: Performance of not less than 10°C
●G2: Performance of not less than 13°C
●G3: Performance not exceeding 15°C

The top-of-the-line G3 boasts a performance level that is comparable to international housing performance standards.

HEAT20's goals for housing

HEAT20 claims to "set the direction for tomorrow's homes, embody technology, and make recommendations to promote it."
The three key elements of the project are as follows:

Facility Elements
We will reduce power consumption by installing high-efficiency systems such as energy-efficient air conditioners and LED electricity.
The introduction of such environmentally friendly equipment is essential to simultaneously improve insulation performance and save energy.

Energy-Creating Elements
Energy creation means that the house itself creates its own energy.
By using solar power generation, etc., the house becomes self-sufficient in creating the energy it needs on its own.

Health Factors
The effects of poor insulation on the human body can be very significant.
In recent years, many people have lost their lives in their homes due to a phenomenon known as heat shock.
Heat shock is a sudden change in temperature that causes symptoms such as stroke.
We will work to keep the temperature in the building as constant as possible.

In conclusion

In this issue, we have explained insulation performance in buildings using various indices.
Insulation performance in Japan is still inferior to global standards.
Therefore, Japanese standards will become increasingly stricter in the future.
When purchasing a house in the future, we recommend that you consider these future factors and choose a building that pays attention to housing performance.