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Water supply conditions in modern homes - Plumbing trends that people renovating should know and points to counter-propose to contractors

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Introduction: What you will learn from this article

When trying to renovate or perform a skeleton remodel of a 20 to 40 year old house, one thing you always run into is the problem of what to do about the water supply. When I peeled off the walls and floor, I found that the steel pipes were red with rust, that the foundation had been cut out to accommodate a drainage pipe, and that there was a large hole in the foundation for the water heater piping - not uncommon in old houses.

However, if the client does not know about ``modern plumbing trends'' and leaves the work to a contractor, they may end up reassembling the building using old construction methods using ``the way they are accustomed to.'' Even if you later realize that ``I should have used the header construction method'' or ``I could have taken a route that didn't require a foundation,'' it is too late.

In this article, we will organize the materials that renovators can make counter-proposals to water contractors and equipment contractors in line with the latest plumbing trends. We present water supply pipe materials, header construction methods, drainage routes, avoidance of foundation defects, piping requirements for each water heater, and finally a "counterproposal checklist" in a table.

If you're wondering "How much renovation or remodeling can I actually do on my own home?" or "Where should I even start?", please visit this page. If you're looking to learn more about specific renovation processes or construction details, don't miss this page as well!

Information on updates to this website will be delivered to you once a month.NewsletterIf you are interested, please register.

Please note that this document is not necessarily accurate, and should be used as reference information only.

So, here you go.

Why do renovation owners need to “know” about water supply now?

Waterworks are a typical example of ``invisible construction''. It has been pointed out that deterioration and accidents in wiring and piping systems that are hidden under floors, inside walls, and foundations often surface after 10 to 20 years of use (Ministry of Land, Infrastructure, Transport and Tourism, n.d.). Renovation is a rare opportunity to rebuild those "invisible parts" all at once.

Additionally, from April 1, 2024, water administration in Japan was transferred from the Ministry of Health, Labor and Welfare to the Ministry of Land, Infrastructure, Transport and Tourism (water supply development and management) and the Ministry of the Environment (water quality standards) (Ministry of Health, Labor and Welfare, n.d.). Although the standards for water supply equipment construction will continue to exist even if the jurisdiction changes, it is important to be aware that the references when following regulatory trends have changed.

It is also clear that ``areas that only qualified personnel should not touch''. According to the Water Supply Law, construction of water supply systems (water supply piping inside buildings) must be carried out by a "designated water supply system construction business operator" designated by the municipality and under the supervision of a "chief engineer for water supply system construction" (Ministry of Land, Infrastructure, Transport and Tourism, n.d.). The owner cannot modify the main pipe downstream of the meter as a DIY project. The right approach is to have a qualified person carry out the construction and the owner to intervene in decision-making regarding design and material selection.

Water pipe trends: Comparison of SGP/HIVP/PEX/PB

In homes from the post-war period to the 1990s, SGP (galvanized steel pipes) and PVC-lined steel pipes were widely used for water mains and branch pipes. However, red water, reduced flow rate, and corrosion of joints due to internal rust are known to be long-term weaknesses (Japan Society of Air Conditioning and Sanitary Engineers, n.d.). The following three systems are generally used in modern renovations and new construction.

  • HIVP (impact-resistant hard polyvinyl chloride pipe): A resin pipe that is often used outdoors, buried around water meters, etc. PVC manufacturers have a lineup (Kubotake Mix, n.d.).
  • Cross-linked polyethylene pipe (PEX): A resin pipe standardized by JIS K 6769. This system is widely used for indoor water supply and hot water supply in houses, and is often combined with the header method (Japan Industrial Standards Committee, n.d.).
  • Polybutene pipe (PB): A resin pipe that has long been used in indoor hot water supply systems. Along with PEX, it is treated as a representative of residential indoor systems.
MaterialMain usesmeritDisadvantages
SGP (steel pipe)Old residential main pipe/exposed pipingHigh strength and impact resistanceRed water due to internal corrosion, problems with long-term reliability of joints
HIVPOutdoor buried/underground mainsShock and corrosion resistant, easy to handle outdoorsIt is easily deteriorated by ultraviolet rays and is not suitable for exposed piping.
PEX (crosslinked polyethylene)Indoor water supply/hot water supplyLight weight, flexibility, and good seismic behavior, compatible with header construction method◎It is sensitive to UV rays and high temperatures, so be careful about the upper temperature limit. Connection quality depends on the installer
PB (polybutene)Indoor hot water supplyStable and durable in high temperature rangeSensitive to exposure and UV rays, construction management is as severe as PEX

It's not like "changing to resin pipes will solve everything." While resin pipes are said to have excellent followability during earthquakes, the quality of the connections (mechanical joints and electrical welding) is an area where the builder's skill is often required. That's why the modern idea of ​​not only ``selecting the material'' but also ``reducing the number of connection points by combining it with the header construction method'' has become mainstream.

Header construction method vs. pre-branch construction method - trade-off between water pressure and renewability

The "header construction method (sheath pipe header method)" is a method in which the main lines for water supply and hot water supply are once consolidated into a header (branch box), and from there one independent pipe is drawn to each faucet. Since the inner tube is passed through the sheath tube (protective tube), a major feature is that only the inner tube can be inserted and removed during future upgrades (Japan Society of Air-Conditioning and Sanitary Engineers, n.d.).

On the other hand, the ``pre-branching method'' is a traditional construction method in which branch pipes are separated from the main line in series in a T-shape, and has the advantage of lower initial costs and shorter total piping length. However, water pressure tends to drop when multiple faucets are used at the same time, and it tends to be difficult to update just one faucet later.

Perspectiveheader construction methodPre-branch method
Stable water pressureStrong against simultaneous usePressure tends to drop when used simultaneously
UpdateabilityOnly the inner tube can be inserted and removed later.The premise is to tear down the wall and replace it.
Initial costHigh (increased amount of ingredients)cheap
Number of connectionsLess (reduced risk of water leakage)Many (water leakage risk is dispersed)

If you wish to use the header construction method during renovation, it is effective for the owner to specify the installation location of the header (directly below the inspection opening for easier future updates). On the other hand, if cost is your top priority because you want to use it for rental purposes in a short period of time, you may decide to branch out. A flat view is that you should make trade-offs in light of the purpose, rather than saying "all headers are right."

Do not destroy the foundation with drainage - rationality of floor drainage and peripheral piping

One of the construction problems that you most want to avoid in houses built using conventional framework construction methods is ``cutouts in the foundation.'' The foundation is a key component that connects the foundation and the superstructure, and it has been pointed out that if it becomes severely indented due to horizontal drainage pipes, it may have a negative impact on vertical load transmission and horizontal rigidity during an earthquake (Ministry of Land, Infrastructure, Transport and Tourism, n.d.). This is an issue related to the evaluation of seismic resistance grades under the Quality Assurance Law and the Housing Performance Indication System (Ministry of Land, Infrastructure, Transport and Tourism, n.d.).

Therefore, in modern renovations, the standard approach is to build drainage from toilets, washbasins, bathrooms, etc. around ``floor drainage'' rather than ``wall drainage,'' dropping from above the foundation to below the floor, ensuring sufficient clearance under the floor, and running it to an external pipe (outdoors) while taking the slope. It is widely known that the drainage slope is set at 1/50 to 1/100 for sewage and gray water as a guideline in the HASS (Heat-Heating and Sanitary Engineers Society Standards) system (Heat-Heating, Air-Conditioning and Sanitary Engineers Society, n.d.). Additionally, double traps should be avoided as they tend to cause water seal breakage and poor drainage, and it is recommended that designs be combined with ventilation components such as Dolgo ventilation valves as necessary.

In terms of both arguments, the under-floor route minimizes damage to the structure at the expense of increasing the trouble of removing the floor for maintenance. On the other hand, in older houses where site conditions are severe and under-floor clearance cannot be achieved, it may be more practical to switch to "floor drainage + perimeter underground piping" in combination with a half-unit bath.

Piping route that does not destroy the foundation - underground piping and half unit bath

If multiple through holes with a diameter of 75mm are drilled in the rising part of the foundation for reheating piping for the water heater or drainage from the bathroom to the external basin, the continuity of the foundation and the thickness of the reinforcing bars will be compromised. This is called "fundamental deficiency" and has been pointed out as a risk to long-term durability (Ministry of Land, Infrastructure, Transport and Tourism, n.d.).

As countermeasures that are often taken in modern renovations, the water heater's outgoing/return piping does not penetrate the foundation but goes around the perimeter with underground piping, the bathroom adopts a half-unit bath and drains into the concrete on the earth floor and flows down naturally to the external basin, and if penetration is absolutely necessary, a foundation sleeve (sheath pipe) is installed at the time of pouring, the hole is made square to circular, and reinforcing bars are installed. Although underground piping does not damage the foundation, it has the disadvantages of ground subsidence, freezing, and long routes. In cold regions, it is necessary to bury it below the freezing depth and cover it with insulation material and anti-freezing band. It is important to make a decision based on both arguments.

Differences in piping requirements by water heating equipment - Eco-Jozu/Eco-Cute/Hybrid

When renovating water heaters to replace them, the plumbing requirements vary slightly for each piece of equipment. As a client, if you understand the restrictions on piping at the equipment selection stage, you can avoid accidents later on such as forgetting to route the drain or not having enough power capacity.

  • Eco-Jozu (latent heat recovery type gas water heater): Acidic drain water is produced to recover latent heat from combustion exhaust gas. Piping must be designed to flow through a neutralizer and then into a rainwater system or combined drainage system (Rinnai, n.d.; Noritz, n.d.).
  • EcoCute (Heat Pump Water Heater): Consists of a two-piece outdoor heat pump unit + hot water storage tank, requiring outgoing/return piping between the hot water storage tank and the bathroom. There are cases where the earthen foundation needs to be reinforced due to the weight of the tank.
  • Hybrid water heater: A combination of gas and heat pump. The piping requirements are closer to EcoCute, but gas side supply piping is also required.

Different models require different piping, power supplies, and delivery routes, so the general rule is to ``redraw the piping design based on the selected model.''

“Counter proposal checklist” to submit to contractors

This is the crux of this article. When a renovation client has a meeting with a water contractor or equipment contractor, if they summarize the information to a level that can be handed over on a single piece of paper, the accuracy of the competitive estimate will immediately increase.

itemContents of counter proposalwhy is it important
Water supply pipe materialI want a PEX+HIVP configuration and want to avoid reusing SGPLong-term avoidance of red water and corrosion risks
Construction methodI want to use the sheath header method.Ensuring water pressure during simultaneous use + future updateability
header positionI would like it to be installed directly under the inspection entrance.No need to destroy the floor or wall when replacing the inner pipe
drainage routeFocus on floor drainage and aim for zero foundation notchesPreserves the structural performance of the foundation
Foundation penetrationPriority is given to underground underground piping for hot water return and reheating piping.Avoiding basic deficits
Prevention of freezingOutdoor underground piping has freezing depth + heat insulation zone specificationsPrevention of freezing accidents in cold regions and winter
ventilationNo double trapping/dolgo ventilation if necessaryPreventing water seal failure and bad odor backflow
DeliverablesI would like a system diagram and material list after the water meter.Information assets for future updates and troubles
qualificationConfirmation of employment of designated water supply equipment construction company/chief engineerEnsuring legal compliance and construction quality

It is more constructive to present counter-proposals with the stance of ``I would like you to tell me the reason for your selection from among them,'' rather than ``Please implement all of them.'' Contractors also have their own circumstances, and there may be constraints unique to the site, such as ``the site conditions make it impossible to turn the perimeter around'' or ``a floor plan that branches off earlier will result in more stable water pressure.''

Points to note/common mistakes

  • ``All resin pipes are OK,'' I thought, causing a short circuit and passing PEX around the UV-exposed parts. As a general rule, exposed parts should be made of steel pipe or HIVP + insulation material.
  • By embedding the header in an invisible location on the wall, you are eliminating the advantage of ``high updateability.''
  • Deciding to change the model of equipment (Eco-Jozu → Eco-Cute, etc.) will require redoing all the piping, power supply, and foundation reinforcement.
  • A piping system diagram was not left before the demolition and removal, making it impossible to know later where the water was being drawn from.

These cases often stem from the owner not sharing the counterproposal checklist with the contractor.

Summary: Next actions

Precisely because waterworks are hidden from view, if the renovator is aware of ``modern standards,'' his or her negotiating power will immediately increase.

  • Water supply: PEX + HIVP + header construction method proposed as the basic line
  • Drainage: Mainly floor drainage, goal of zero foundation notches
  • Basics: Avoid damage by running the hot water supply area underground and around the outside.
  • Equipment: Decide on the model and draw the piping design
  • Contractor: Must perform construction and deliver system diagrams under the supervision of the designated water supply equipment construction company's chief engineer.

If you use this checklist in hand and get mutual estimates, you will be closer to a renovation that was ``designed together'' rather than ``the work was done as instructed.'' Please note that this article is just an overview of ideas, and final decisions should be made based on on-site surveys and designs by qualified personnel.

If you're wondering "How much renovation or remodeling can I actually do on my own home?" or "Where should I even start?", please visit this page. If you're looking to learn more about specific renovation processes or construction details, don't miss this page as well!

Information on updates to this website will be delivered to you once a month.NewsletterIf you are interested, please register.

Newsletter registration/Subscribe to Newsletters

Please note that this document is not necessarily accurate, and should be used as reference information only.

Well, then!

Frequently Asked Questions (Q&A)

Q. Can I do DIY replacement of water pipes by myself?

A. Construction of water supply equipment downstream of the meter must be carried out by a designated water supply equipment construction business operator designated by the municipality based on the Water Supply Law and under the supervision of a chief water supply equipment construction engineer (Ministry of Land, Infrastructure, Transport and Tourism, n.d.). In principle, it is not possible for the owner alone to construct or modify the main pipe or branch downstream of the meter. On the other hand, if you have someone at home who is qualified as a chief engineer for construction of water supply systems, there may be room for you to proceed with a DIY project as long as the requirements are met.

Q. Is it possible to keep all the old iron pipes (SGP) and partially replace them with resin pipes?

A. Partial replacement is technically possible, but if the remaining SGP side continues to corrode, it will eventually become a weak point. If the renovation is close to a skeleton, it would be easier to stabilize long-term maintenance costs by switching to plastic pipes and header construction for both water and hot water supply.

Q. What is the cost difference between the header method and the branch method?

A. Generally speaking, the header method tends to increase material costs because the total length of piping increases. On the other hand, if you take into account the fact that future partial updates can be done without destroying walls and floors, the life cycle costs can be reversed. It depends on the age of the building and the number of years you plan to live in it.

Q. I just can't get enough clearance under the floor. Is it still possible to have zero base notches?

A. This can often be avoided by combining a raised floor + half unit bath + underground piping around the perimeter. If this is still difficult, consult with a structural designer or qualified architect to consider a design that will compensate for the loss on the foundation side with reinforcing hardware and additional beams.

Q. I am concerned about freezing of outdoor underground pipes.

A. In cold regions, it should be buried below the freezing depth and covered with an antifreeze band and heat insulation material. The electrical work required to connect the power source and operate the anti-freezing zone is the work area of ​​those who are qualified as a Class 2 electrician or higher based on the Electrical Contractors Act. If you have a qualified person with you, you can expand the range of DIY, but please avoid wiring without qualification.

References

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