A home's insulation performance is a factor that affects how effectively heating and cooling work and how comfortable the interior feels. In recent years, performance labeling using an insulation grade (dannetsu tōkyū) has become more common, and window and sash specifications are an important thing to check too. Below, we cover the basic thinking behind insulation performance and how to read the key indicators.
- A home's energy-efficiency performance is classified by insulation grade, with higher grades indicating better insulation.
- Insulation performance is heavily influenced by window and sash specifications — windows are considered one of the biggest sources of heat gain and loss in a building.
- Double-glazed windows and resin sashes are said to have better insulation performance than single-pane glass and aluminum sashes.
- The effect on utility costs varies by property, region, and how the home is used, so it's important to treat insulation grade as a rough guide to performance rather than a guarantee.
Conclusion
A home's insulation performance is a factor in how effectively heating and cooling work and how comfortable the interior feels. Checking the insulation grade and the window and sash specifications lets you form a reasonable picture of what everyday life will be like after you move in. That said, actual utility costs also depend on how the home is used and where it's located, so it's important to treat insulation grade as a rough benchmark for comparing performance, not a fixed figure.
What Insulation Grade Means
Insulation grade (dannetsu tōkyū) is one indicator of a home's energy-efficiency performance, with a higher grade number indicating better insulation. In recent years, grades 6 and 7 have been introduced at the top end, making it possible to properly rate homes with higher insulation performance than before. If a property's brochure or performance labeling states an insulation grade, it's worth checking as a point of comparison when considering a purchase.
Why Windows and Sashes Matter
Among all parts of a building, windows are considered a particularly large source of heat gain and loss. Compared to the combination of single-pane glass and an aluminum sash, double-glazed windows (pea garasu), resin sashes, or composite sashes combining resin and aluminum are said to offer better insulation performance. Checking what kind of window specifications a property has during your viewing gives you a useful clue to its insulation performance.
The Relationship Between Building Age and Insulation Performance
Generally speaking, homes built to a newer energy-efficiency standard tend to have better insulation performance. For a pre-owned home, the standard that applied differs depending on when it was built, so it's important to check not just the building's age but what insulation specifications were actually used. Some properties have also had their windows and sashes replaced through renovation to improve insulation performance.
The Relationship With Utility Costs
Homes with higher insulation performance are said to have more efficient heating and cooling and tend to keep utility costs down. However, actual utility costs also depend on many other factors — the unit's orientation and floor, household composition, the performance of the heating and cooling equipment used, the number of occupants — so it's hard to estimate a specific figure from insulation grade alone. It's best to treat insulation performance as just one point of comparison among several.
What to Check During a Viewing
During a viewing, in addition to checking the window and sash specifications, it's worth paying attention to how the room actually feels when you stand inside it — the summer heat, whether there's a chill near the floor in winter, and so on. If possible, viewing a property multiple times in different seasons makes it easier to actually feel the difference that insulation performance makes. Whether the floor or walls feel cold to the touch is also a useful physical clue to insulation performance.
FAQ
Where can I check a property's insulation grade?
For new-build properties, it may be stated in documents based on the performance-labeling system. Pre-owned properties don't always have this labeling, so you may need to infer it from the window and sash specifications instead.
If the insulation grade is high, will utility costs definitely be lower?
The general tendency is for them to be lower, but this also depends on the number of occupants, the equipment used, and the local climate, so it's not a fixed rule.
Can insulation performance be improved even in a pre-owned home?
Yes, it's possible to improve performance by replacing windows and sashes or adding insulation material. That said, there can be constraints from the building's structure or its management rules, so checking in advance is necessary.
Summary
You can get a rough sense of a home's insulation performance from its insulation grade and its window and sash specifications. Since the effect on utility costs varies by property and how it's used, we recommend treating insulation grade as just one point of comparison and also checking how the property actually feels during your viewing.