Checklist for selecting a housing company

Click to enlarge

Housing company selection checklist – minimum requirements

Earthquake resistance grade 3

One of the first questions you should ask to determine if a housing company is reputable is, "Does it have seismic resistance level 3?" While about 80% of major manufacturers meet this standard, more than 80% of smaller companies fail to do so. The importance of seismic resistance level 3 is explained in detail on the page below, so please take a look.

 

If you want to investigate further, ask about the structural calculation method. There are three main types of calculation methods: the simplified "wall quantity calculation ," the proper structural calculation "allowable stress calculation ," and type approval. (*Type approval is a structural analysis method adopted by major house builders.) Allowable stress calculation is mandatory for buildings with three or more stories , but for single-story and two-story houses, more than 90% of housing companies only use wall quantity calculation . Shibaura Institute of Technology once conducted an experiment to collect 100 housing drawings using the simplified calculation method at random and perform allowable stress calculation. The result was astonishing: "Errors occurred in all of the properties." When building a single-story or two-story house, be sure to ask, "Do you perform allowable stress calculation?"

There is a 70-80% probability that the Nankai Trough earthquake will occur within the next 30 years . Furthermore, this probability increases year by year as the timing of the earthquake is delayed. For people in their mid-thirties who are building a house, they will almost certainly be affected by a major earthquake . Looking at major earthquakes such as the Great Hanshin Earthquake, the Great East Japan Earthquake, and the Kumamoto Earthquake, the maximum seismic intensity was 7, and immediately after the earthquake, including micro-tremors, there were about 1000 earthquakes in a week. In Kumamoto, aftershocks with a seismic intensity of 7 were also observed, a first in recorded history. When such a major earthquake occurs, there remains a possibility that houses with seismic resistance of level 2 or lower will be destroyed to a level where they cannot be reinhabited .

This applies to both major earthquakes and massive typhoons: if the same type of damage occurs on a large scale in the same area, even if there is a budget, there is a severe shortage of manpower among contractors, and it is difficult to get them to come and carry out repairs. Seismic resistance level 1 is the standard that will protect lives, level 2 is the probability of becoming uninhabitable with a 20% chance, and level 3 is the standard that will allow you to continue living in the house even if earthquakes of magnitude 7 occur consecutively.

UA value 0.46 or less

The UA value (pronounced "U-A-C") is a common indicator of insulation performance that housing companies can display today . It's a value calculated by law, and the thicker the insulation material used, the lower this value becomes. To use a clothing analogy, it's an indicator of warmth determined by both the material (like cotton or down) and the thickness in millimeters. So, while the housing industry is full of talk about things like "it's warm because it's built with XX construction method" or "it's highly insulated because it's XX insulation," you can ignore it completely without any real harm. When it comes to insulation performance, you can determine whether a housing company is serious about insulation or not by checking the UA value . Companies that rely on empty rhetoric about XX insulation and can't immediately provide the UA value are out of the question.

C value 1 or less

First, this is pronounced "C-value". To use a clothing analogy, it represents how much space is left, including not only cuffs and zippers, but also tears in the garment itself . Just like with clothing, no matter how good the insulation is, if there are lots of gaps, it won't get warm. This isn't measured by calculation; a measuring device resembling a bazooka is set up on-site and the air inside is continuously removed to take the measurement. This is called "air tightness testing". As the second question to determine if a housing company is reputable, I think it's a good idea to ask, "Do you conduct air tightness testing?" Generally, only about 2% of companies do. If they clear that hurdle, then ask, "What is your target C-value?" If it's not at least 1 or less, the air won't flow as intended, so planned ventilation won't be possible (resulting in rooms with lingering odors), and of course, the efficiency of heating and cooling will also decrease.

Windows that do not cause condensation on the bottom frame at 20℃ 50%

In winter, when temperatures reach around 20°C without humidification, you'll feel thirsty while sleeping. Also, if someone contracts influenza or other viruses without proper humidification, it's much easier for the virus to spread to other family members. From a health perspective, a humidity level of around 50% is desirable at 20°C . This is roughly equivalent to humidifying with 10 liters of humidifier per day. While this level of humidification is very healthy and comfortable for humans, it puts a strain on windows. Most residential windows with resin-aluminum frames will experience condensation on the bottom. To prevent this, at a minimum, either resin-only frames or, though very expensive, wooden frames are necessary. Even without considering condensation, windows are the biggest source of heat loss. Companies that don't insulate their windows can be considered to lack both interest in and technical expertise in insulation.

Recommendations

Is the whole house heated?

In the case of cars, you wouldn't be told, "Please have your air conditioner installed at Autobacs." However, in the housing industry, it's almost the same thing; you're overwhelmingly more likely to be told, "Please have your air conditioner installed at an electronics retailer." No matter how good the insulation and airtightness are, the entire house won't be warm if the heating plan isn't properly implemented . Furthermore, when this is outsourced, a much larger capacity is selected compared to when the person who designed the insulation selected the appropriate capacity . The installation method that many people consider common sense, such as "a 6-tatami room needs a 6-tatami room air conditioner," is actually quite excessive in modern new homes, even those that aren't highly insulated. Most electronics retailers' salespeople and housing contractors are unaware of this. The maximum capacity of a 6-tatami room air conditioner, even a mid-to-high-end model, generates 6300W—the amount of heat equivalent to 10 kotatsu tables. However, in a highly insulated house, even at the coldest moment, about 600W (the amount of one kotatsu) is sufficient for heating . That's why, in Matsuo Design Office's houses, one air conditioner can heat the entire house.

Is there a whole-house cooling plan?

It's similar to a heating plan, but it's much more difficult than heating. Underfloor air conditioners have become quite popular among some construction companies. This is because our company published the design method for underfloor air conditioners in the April 2012 issue of the industry magazine "Architecture Knowledge," and the number of companies imitating them has exploded nationwide. If you use an underfloor air conditioner system in a house with a certain level of insulation and airtightness, it's easy to heat the whole house. However, it depends on the skill of the housing company whether you can keep the electricity bill at a level that the general public can accept. The second floor is usually smaller than the first floor, so if the entire first floor is heated, the heat will reach the second floor as well. That's why it's easy to heat the whole house with one unit.

Air conditioning is different. The second floor is different from the first floor, with individual rooms separated. Unless a method is established to distribute cool air effectively to each room, it is absolutely impossible to cool the entire house with just one air conditioner . This is easier said than done, which is why construction companies from all over the country are now coming to study our air conditioning system. Our company is working on a system that cools the entire house as evenly as possible with the minimum amount of energy using just one air conditioner . This method not only reduces the number of air conditioners needed, but also reduces cooling costs so that even if the entire house is cooled 24 hours a day in August, the cooling cost will be around 4000 to 5000 yen . It may be hard to believe, but if you thoroughly optimize sun shading and air conditioning planning, you can achieve such results . To use the car analogy again, even if the manufacturer provides air conditioning as standard, you would never hear something like, "The left rear seat doesn't get any cooling," even in a small car. A house costs ten times as much as a car, is used for more than five times as long (2 hours vs. 10 hours per day), and is used for more than four times as long (10 years vs. over 40 years). It's strange that while this is standard equipment and works consistently well in cars, most companies don't offer it for houses.

One more point to note. Recently, more than 30 whole-house air conditioning systems are being offered to construction companies in the housing industry. However, most of them cost over 130 million yen at cost. If the customer pays for it as an option, it will probably add more than 150 million yen. Not so long ago, these kinds of systems cost more than 250 million yen, so compared to that, they have become considerably cheaper, but they are still a luxury option that can only be installed by people with ample funds . At our company, we believe that having a whole house that is warm and cool should not be a privilege reserved for the wealthy . That's why, instead of expensive whole-house air conditioning systems, we design and plan heating and cooling using our own unique methods. If you encounter a housing company that uses any of these systems, we recommend checking whether they can provide it to all of their houses. Also, the cost of replacing the air conditioner every 10 years, which is its lifespan , is an important point to check.

Is winter solar radiation being obtained?

Many people may think that the warmth of a house is determined solely by insulation and airtightness. While insulation and airtightness are indeed important factors in reducing heat loss, the precise definition of a warm house is one with a low "heat load" (the amount of heat required for heating) . The amount of heat required for heating is the value obtained by subtracting solar heat gain and internal heat generation from heat loss.

Heat required for heating (heating load) = heat loss - (solar radiation gained + internal heat generation)

In other words, to make a house warm, not only heat loss but also heat gain is a very important factor . If direct sunlight hits just one sliding window, which is 165m wide and 2m high and can be found in any house, it will bring in the equivalent amount of heat (600W) of a kotatsu (heated table) . Internal heat generation is determined by the number of people and electrical appliances, so it cannot be controlled by the housing company.

 

Therefore, while reducing heat loss determined by insulation and airtightness is important for creating a warm house, increasing solar heat gain is even more important . The reason solar heat gain is more important is that it doesn't increase construction costs . Improving insulation performance inevitably costs money. Since solar heat gain does not increase costs, it is definitely beneficial to do as much as possible.

Do you have perfect summer sun protection?

Improving insulation and airtightness will definitely make a house warmer. In that sense, winter countermeasures are simple and easy. However, there are countless housing companies that stop there. As explained in the section on "winter solar heat gain," the energy of sunlight is very strong . It is an aid in winter, but a formidable enemy in summer. If summer solar shading is not done "perfectly," the house will be warm in winter, but unbearably hot in summer.

This can be simplified into a rule. For south-facing windows (within a 20-degree angle from due south), is there an overhang of at least 3 units per 10 units of window height, or is there an external sunshade, also known as an outer shade ? (The key point is that it's external. Sunlight can be cut by 8% outside, but even with blackout curtains, only 4% can be cut inside.)

Are the windows on the east, west, and north sides as small as possible (ideally one window per room, no more than 0.5 m²) and made of heat-shielding Low-E glass? If these two conditions cannot be met, external sunshade measures must be in place. There is a deceptive sales pitch that you should be wary of. It is a big lie to say, "It's okay because we're using heat-shielding Low-E glass!" when the windows on the east, west, and north sides are quite large, or when there is no overhang or anything on the south side. No matter how heat-shielding Low-E glass you use, if the area is large, a lot of sunlight will come in . If sun shading is not done properly, you will have to run the air conditioner more than necessary to remove the heat that comes in. This is the worst possible situation in terms of comfort, health, and air conditioning costs, as it is like "the windows are emitting the same amount of heat as a stove, so the air conditioner is turned up high."

In the case of steel and reinforced concrete, is it externally insulated?

For detached houses, the most common structure is wood, followed by steel frame. In apartment complexes, reinforced concrete is often used, but these days, except for ultra-luxury homes, reinforced concrete structures are rarely seen in detached houses.

Steel conducts heat 480 times more easily than wood . Therefore, it was inherently a very disadvantageous structure in terms of insulation. Many major home builders started out with steel frames. The reason why these manufacturers have gradually increased their proportion of wooden construction over the past decade lies here. With energy-saving standards and industry-wide improvements in insulation levels, competing with steel frame construction has become a tough challenge. If you absolutely must adopt such a thermally disadvantageous steel frame construction, you need to wrap it with at least 5 cm of insulation material using exterior insulation . One major home builder is trying to solve this problem by using exterior insulation of less than 2 cm and pretending that they have addressed the issue, but please be aware that this is not enough to compensate for 480 times the heat loss.

Is the plan created by a second-class architect or above?

Originally, the Building Standards Act lists "wooden buildings of 100 square meters or more" as "buildings that must not be designed or supervised by anyone other than a first-class architect, second-class architect, or wooden building architect." Since most houses exceed 100 square meters (30.25 tsubo), the law stipulates that , except for very small houses, unlicensed persons should not be allowed to design them . However, in the housing industry, including major housing manufacturers, this law has become a dead letter. There are countless companies where the task of creating floor plans and elevations, known as "layouts" or "planning," is handled by a 23-year-old salesman with a literature degree. While there are a few exceptionally skilled individuals among them, the probability of finding such a person is extremely low. This is the exact opposite of the medical and legal professions, where even with extensive practical experience, unlicensed individuals cannot handle scalpels or stand in court.

Is there any consideration for durability?

There is no need to worry about this when it comes to major housing manufacturers. On the other hand, many small and medium-sized companies are weak in this area. Unlike insulation and airtightness, there are actually a mountain of items that need to be checked, but it is impossible for the average person to complete them. Here is a simple way to tell the difference.

• Houses without eaves (the ends of the roof that extend to prevent the exterior walls from getting wet and act as a sunshade) (common in simple modern houses) are highly susceptible to leaks, deterioration of the exterior walls, and condensation inside the walls, so advanced technical skills are required to balance durability with these features. However, the majority of companies that build houses without eaves generally do not have this technical ability.
• If the person in charge does not understand the meaning of this one question, ``Have you performed condensation calculations?'', or if the company checks and finds that no one has done so, it means that the risk of internal condensation in walls has not been considered.

The fewer air conditioner outdoor units in the model home, the better.

Walk around the outside of a model home and count the number of air conditioner outdoor units from each company. On average, each company will have 7 to 9 units. This shows that without these, it is not possible to keep the entire house warm or cool. This is because the model home is large, but if you were to install air conditioners using the same design method in a typical home of 30 to 40m², you would need a total of five units: two for the living/dining/kitchen room and Japanese-style room on the first floor, and three for the master bedroom and two children's rooms on the second floor. Even if each unit costs 1 yen, it would come to 2 yen. It would be a huge expense to replace them every 2 years.

If possible, it is better to have as few bumps as possible on the floor plan and roof.

This is an item that depends more on the skill and habits of the designer than on the housing company itself. The closer a house is to a mass-produced home, the more likely it is to be a house where the rooms requested by the customer are simply attached together and a roof is added to complete it. When designed using this method, the exterior shape becomes bumpy and uneven. This is because not only the walls but also the way the roof is constructed becomes complex. Because the bumpy surface increases the exterior wall area, construction costs are higher . Also, because the surface area increases, heat loss is greater . Construction becomes more difficult and the house is more prone to leaks.