Checklist for selecting a housing company

Click to enlarge

Housing company selection checklist – minimum requirements

Earthquake resistance grade 3

The first thing to ask to determine if a housing company is legitimate is"Is it earthquake resistance grade 3?"You need to ask. 8% of large manufacturers are okay, but on the other hand, more than 8% of small and medium-sized companies are not. Please also see the following page for a detailed explanation of the importance of earthquake resistance grade 3.

 

If you want to check further, ask about the structural calculation method. The types of calculation methods are simple calculations,"Wall amount calculation", the original structural calculation"Allowable stress calculation"(※ Type certification is a structural review method adopted by major home builders.)Allowable stress calculations are mandatory for buildings with three or more floors.However, in single-storey and two-storey houses,More than 9% of housing companies only calculate the wall volumeIn the past, Shibaura Institute of Technology randomly collected 100 simplified house plans and conducted an experiment to calculate the allowable stress. The results were shocking: "Errors occurred in all of the plans." If you are building a single-storey or two-storey house, be sure to try this."Have you performed allowable stress calculations?"Please check.

There is a 30-70% chance of a Nankai Trough earthquake occurring within the next 80 years.It is said that the later the time of occurrence, the higher the probability of this happening each year. For those who are building a house in their mid-thirties,It is almost certain that a major earthquake will strike.When we look 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 if we include minor earthquakes immediately after the earthquake, there are about 1000 earthquakes in a week. In Kumamoto, an aftershock of seismic intensity 7 was observed for the first time in recorded history. When such a major earthquake occurs,If the earthquake resistance rating is below 2, the building will be destroyed to the point where it will be impossible to re-inhabit it.The possibility remains.

This applies to both major earthquakes and massive typhoons, but when 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 they are slow to come and carry out repairs.Earthquake resistance grade 2 is the standard that can only protect lives, grade 7 means there is a XNUMX% chance that the house will become uninhabitable, and grade XNUMX means that the house can continue to be inhabited even if a series of earthquakes of magnitude XNUMX occur..

UA value 0.46 or less

The current indicator of insulation performance that can be commonly displayed by housing companies is thisUser Account Value(pronounced U-H). It is a value determined by calculation, and the thicker the better the insulation material used, the smaller this value will be. If we liken it to clothing, it is an index of warmth that is determined by both the material (like cotton or down) and the thickness in millimeters. So, the housing industry is full of talk like "it's warm because it's made with XX construction method" or "it's highly insulated because XX insulation is used," but there is almost no harm in ignoring it altogether. When it comes to insulation performance, thisBy checking the UA value, you can determine whether or not a housing company puts effort into insulation.. 〇〇Relying on the poem "Insulation"A company that cannot immediately answer UA values is out of the question..

C value 1 or less

First of all, this is pronounced "shichi." If you compare it to clothing, it includes not only the cuffs and zippers, but also the tears in the clothing itself.How big is the gap?It represents the airtightness of a house. No matter how good the insulation is, if there are many gaps, it will not keep you warm, just like with clothes. This is not a calculation, but rather a measurement is made by installing a measuring device like a bazooka on-site and gradually removing the air inside. This is called an "airtightness measurement." The second question to determine whether a housing company is legitimate is:Have you carried out airtightness measurements?I think it would be best to ask yourself, "What is the point of taking a test?" Generally, only about 1% of people take the test. Once you've cleared that hurdle,"What is the target C value below?"Please ask. If the number is not set to at least 1, the air will not flow as expected.Planned ventilation not possible(This will leave a room with a lingering odor.) Of course.Heating and cooling efficiency also worsens..

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

In winter, when the temperature reaches 20℃ without humidification, you may feel dry throat while sleeping. Also, if the room is not humidified properly, if someone in the family becomes infected with a virus such as influenza, the other family members may easily become infected.From a health perspective, you want a humidity level of around 20% when the temperature is 50°C.This is the place.Humidify 1 liters per day for the perfect amount of humidity.This level of humidification is very healthy and comfortable for humans, but it is harsh on windows. The resin-aluminum framed sashes used in most homes cause condensation on the bottom frame. To prevent this, the frame should at least be made of resin only.樹脂サッシOr, although very expensive,The last thing I wantEither of the above must be used. Even if you ignore the issue of condensation,Windows are the biggest source of heat loss.Companies that do not have high-insulation windows are companies that have neither the interest nor the technical ability to insulate.It is safe to take it that way.

Recommendations

Is the whole house heated?

When it comes to cars, you would never hear someone say, "Please ask Autobacs to install your air conditioner." However, in the housing industry, it's almost the same thing, that is, it's overwhelmingly more common to hear people say, "Please ask a home appliance store to install your air conditioner." No matter how good the insulation and airtightness are,If the heating plan is not done properly, the entire house will not be warm.In addition, if you outsource in this way, the cost will be much higher than if the person who designed the insulation had selected the appropriate capacity.A much larger selection of skills will be conducted.The installation method that everyone thinks is common sense, "a 6-tatami room with a 6-tatami air conditioner," is actually excessive in modern newly built homes, even if they are not highly insulated. Most salesmen at electronics retailers and home builders are unaware of this fact. The maximum capacity of a 6-tatami room air conditioner for a mid- to high-end model is 6300W, which is equivalent to the heat generated by 10 kotatsu tables. However,If you have a well-insulated house, you can get enough heat even at the coldest moment with just 600W (the power for one kotatsu).That's why Matsuo Design Office's homes can heat the entire house with just one air conditioner.

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.

However, the air conditioning is different. The second floor is divided into separate rooms, unlike the first floor.Unless you establish a method for effectively distributing cool air to each room, it is impossible to cool the entire house with one air conditioner.This may seem simple but it is actually very difficult, so construction companies from all over the country are now coming to study our cooling system.A system that cools the entire house as evenly as possible with a single air conditioner while using the minimum amount of energy.This method not only reduces the number of air conditioners required, but also cuts cooling costs by August.If you cool the whole house 24 hours a day, the cooling costs will be around 4000 to 5000 yen.It may be hard to believe, butThis is the result you can achieve by carefully planning your solar shading and cooling.To use the car analogy again, even if the manufacturer provides air conditioning as standard, saying "it doesn't work in the left rear seat" is not possible even for a light vehicle. A house costs 10 times as much as a car, is used for more than five times as long (1 hours vs. 2 hours a day), and lasts more than four times as long (10 years vs. 5 years or more). And yet, while cars come equipped with air conditioning as standard and work evenly, housesIt's strange that most companies don't support this.Please be aware of this.

Another thing to note: Recently, the housing industry has seen a rise inWhole building air conditioning systemare offered to construction companies. However, the cost price of most of them exceeds 130 million yen. If you pay for it yourself, you will probably have to pay an additional 150 million yen or more for options. A long time ago, this type of system cost more than 250 million yen, so it's much cheaper than that, but stillA luxury option that only those with deep pockets can afford.That is what we can say.We believe that keeping the entire home warm and cool is not just a privilege for the wealthy.That's why we don't use expensive central air conditioning systems, but instead use our own unique method to design and plan heating and cooling. If you come across a housing company that uses one of these systems,Is it available to all homes?We recommend you check that as well. Also, the lifespan of the air conditionerHow much does it cost to replace it every 10 years?is also an important checkpoint.

Is winter solar radiation being obtained?

Many people may think that the warmth of a home is determined solely by insulation and airtightness.Insulation and airtightness are key factors in reducing heat lossHowever, the exact definition of a warm home isA house with a small amount of heat required for heating (heating load)The amount of heat required for heating is the heat loss minus the solar radiation gain and internal heat generation.

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

In other words, to make a house warm, it is not just heat loss that is important.Heat gain is also a very important factorIt is a 165m wide, 2m high structure that can be found in any house.If direct sunlight hits one sliding window, the amount of heat entering the room (1W) is equivalent to that of a kotatsu.Internal heat generation is determined by the number of people and electrical appliances, and cannot be controlled by home builders.

 

Therefore, in order to create a warm house, it is important to reduce heat loss, which is determined by insulation and airtightness, but at the same time,Increasing solar gain is even more importantThe reason why solar radiation acquisition is more important isConstruction costs will not increaseThis is because it costs money to improve insulation performance. It is definitely more profitable to do as much solar radiation as possible without increasing costs.

Do you have perfect summer sun protection?

Improving insulation and airtightness will definitely make your house warmer. In that sense, winter measures are simple and easy. There are many housing companies that stop there. As explained in the "Winters' solar radiation acquisition" section,The energy of solar radiation is very strongIt's a help in the winter, but a tough enemy in the summer. If the summer sun protection isn't "perfect," the house will be warm in the winter but unbearably hot in the summer.

This is a fairly simple rule to formulate.On the south side (when the angle is within 20 degrees from due south), are there eaves of at least 10 for every 3 cm of window height?or called outer shadeIs there any external sun protection?(The key point is that it is external. Outside, it can block 8% of the sunlight, but inside, no matter what kind of blackout curtains you use, it can only block 4%.)

The windows on the east, west and north sides are as small as possible.(Preferably one space per room, no more than 0.5 mXNUMX) andHeat shielding Low-EIf these two conditions are not met,External solar shading measuresThere is a sales pitch that is a lie that you should be careful of. If the windows on the east, west, and north sides are quite large, or if there is no eaves on the south side, it is a big lie that "It's fine because we use heat-shielding Low-E glass!!"No matter how much heat insulation Low-E is used, if the area is large, a large amount of solar radiation will enter.If the windows are not shaded, the air conditioner will need to be turned on extra hard to remove the heat that has entered. This is the worst possible situation in terms of comfort, health, and cooling costs, as the windows emit the same amount of heat as a stove, making it hot, so the air conditioner has to be turned on harder.

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 is a material that conducts heat 480 times more easily than wood.Therefore, it was originally a structure that was very disadvantageous in terms of insulation. Many of the major housing manufacturers started out with steel frames. Herein lies the secret behind why these manufacturers have gradually increased the proportion of wooden construction over the past 10 years or so. With energy-saving standards and insulation standards within the industry constantly improving, it was a tough reality to compete with steel-frame construction. If one was to absolutely use steel-frame construction, which is very disadvantageous in terms of heat,The exterior insulation must be wrapped in at least 5cm of insulation.A certain major housing manufacturer is trying to solve this problem by installing less than 2cm of external insulation, but please be aware that this is not enough to compensate for a heat loss of 480 times.

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

Originally, the Building Standards Act listed "wooden buildings over 100 m100" as "buildings that should not be designed or supervised by anyone other than a first-class architect, second-class architect, or wooden building architect." Since most homes are over 30.25 mXNUMX (XNUMX tsubo),Unqualified people must not design anything other than tiny houses.This is especially true legally. However, in the housing industry, including major housing manufacturers, this law has become a mere formality. There are many companies where 23-year-old arts graduates are in charge of salesmen who draw up floor plans and elevations, which are called "floor plans" or "planning." There are very few of them who are good at it, but the chances of this happening are very low. This is the exact opposite of the medical and legal professions, where unqualified people cannot hold a scalpel or stand in court, no matter how much practical experience they have.

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 ability and habits of the designer than on the housing company. The closer to a pre-built house, the more likely it is that the house will be completed by simply attaching the rooms requested by the customer and putting on the roof. If you design using this method, the exterior shape will be uneven and bumpy. This makes not only the walls but also the way the roof is put on complicated. The bumpy shape means that the exterior wall area increases, soConstruction costs are highAlso, the surface area increases.The heat loss will also be large.Installation is also troublesome.It also becomes easier for rain to leak..