DIY Renova: Self-renovation support site JP

Basic laws, strengths, weaknesses, and characteristics related to architecture in Japan and countries around the world (with thorough explanations and quotations from a self-renovation perspective)

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Introduction
``Are Japan's building standards strict?'' ``Are they more reasonable overseas?'' These are questions that always come up when you're doing a self-renovation project. This article summarizes the "basic architectural legal systems" and "strengths, weaknesses, and characteristics" of Japan and major countries (USA, Canada, UK, EU/Germany, France, Australia, New Zealand) in a way that is directly relevant to the decision-making of DIY practitioners. As the original source of laws and standards, the main points will be clearly marked with literature. Assuming that the reader is working in Japan, we have included the minimum points to keep in mind "in Japan" in various places.

Please note that this text is general information, and please be sure to consult your local government's building guidance department, confirmation inspection agency, or qualified person for final decisions.

So, here you go.

Japanese laws and rights you need to be aware of if you are building a house [Self-renovation].

Table of Contents

Basics of Japan's legal system (Why start with "Japanese law")

The foundation of Japan is the Building Standards Act, its enforcement orders and notifications, related laws (energy saving, barrier-free, etc.), and standards such as JIS. The purpose is to "define minimum standards for building sites, structures, equipment, and uses to protect life, health, and property." This idea of ​​"minimum standards" is the basis for making DIY decisions.Japanese Law Translation

Regarding energy conservation, the Building Energy Conservation Law provides the framework and establishes rules such as compliance obligations and certification systems. In recent years, revisions have progressed and the scope of compliance obligations has expanded (check the Ministry of Land, Infrastructure, Transport and Tourism page for the latest information).Ministry of Land, Infrastructure, Transport and Tourism

JIS standards are the basis for materials such as roofing and waterproofing. For example, the performance of modified asphalt roofing is specified in JIS A 6013, etc. (the basis for choosing an under-roofing material for DIY).Standard navigation

America (IRC for residential, IBC for commercial, IECC for energy saving)—a treasure trove of “rationality and textualization”

In the United States, states and cities adopt and operate ICC (International Code Council) model codes (IRC/IBC/IECC, etc.). From the perspective of self-renovation, it is very easy to learn that ``specifications, fitment, and acceptable conditions are presented in detail in text''.codes.iccsafe.org+2codes.iccsafe.org+2

For example, IRC R905.1.2 specifies "ice barrier measures for eaves" on roofs. The practice of continuous self-adhesive underlayment (equivalent to so-called Ice & Water) from the eaves to the inside line of the exterior wall has become standardized.codes.iccsafe.org+1

In terms of energy conservation, IECC 2021 systematized matters such as envelopes, airtightness, equipment, etc. in the Housing Chapter (RE). When considering energy-saving renovations in Japan, you can refer to it and use it to check for omissions.codes.iccsafe.org+1

The physics and countermeasures for ice dams (the mutual complementarity of airtightness, insulation, ventilation, and eaves waterproofing) are explained in an easy-to-understand technical note by Building Science Corporation, which is also useful for DIY decision-making.buildingscience.com+1

Canada (NBC) — Strong in dealing with cold, snow, and ice dams

Canada's NBC (National Building Code) is a national standard that covers everything from new construction, renovation, change of use, and demolition, and has accumulated at the implementation level the concept of exterior skin and roof detailing in cold regions.NRC+1

North American industry organizations (NRCA, ARMA, etc.) have repeatedly sounded the alarm regarding ice dams, and have clearly stated that ``water can back up under eaves.'' In DIY, failures can be reduced by prioritizing ``fast water wrap, additional tension position, adhesion of self-adhesive layer, and continuous coverage of valleys.''nrca.net+1

United Kingdom (Building Regulations + Approved Documents)—Performance regulations and “easy-to-read practical guide”

In the UK, performance regulations (building regulations) are specified in "Approved Documents" published by the government. Guidance is provided in each field such as structure, fire protection, insulation, ventilation, etc., and diagrams and text are provided that are easy to understand even for DIYers.GOV.UK+2GOV.UK+2

EU/Germany (Eurocode + GEG + DIN)—Secure insulation, airtightness, and moisture design through “stacking”

The common language for structural calculations in Europe is Eurocode (EN 1990, etc.). The basic design concept and safety factor framework will be organized and operated in the national annex for each country.dl.azmanco.com

Germany's Building Energy Act (GEG) covers energy conservation and renewable energy use. It stipulates the upper limit on primary energy demand for new buildings and the securing of renewable energy ratios, and is currently being revised.climate-laws.org+2Renewable Energy Foundation+2

DIN 4108-7 (airtightness) and DIN 4108-3 (moisture design) are often used in the field of skin construction. From a DIY perspective, the trick is to translate the principles of "airtightness of penetrations," "continuous insulation," and "dew point control" into Japanese and apply them.dinmedia.de+1

France (RE2020) — Driving greenhouse gases and comfort through “law”

In France, RE2020 replaces RT2012 and comprehensively evaluates primary energy, life cycle carbon, summer comfort, etc. Phased application has progressed for each new construction and use. The feature is that it can reach the carbon of the material.Jones Day+1

Australia (NCC) and New Zealand (NZBC)—A good example of performance standards and climate adaptation

Australia's NCC is a performance code that outlines minimum requirements for safety, hygiene, amenities, sustainability, etc. Design consideration has been developed for high solar radiation, strong winds, and termite risk.ncc.abcb.gov.au

There are a lot of termite problems in Japan...

New Zealand's building regulations are supervised by the MBIE, and construction activities, regardless of their size, must comply with the NZBC (even small construction projects that do not require confirmation are still obligated to comply).building.govt.nz+2building.govt.nz

Overview of “positioning of laws/strengths and weaknesses” by country/region (quick reference table useful for self-renovation)

The "characteristics" in the table are summarized from a perspective that is directly related to DIY decisions (see the source of each section for detailed rationale).

regionBasic law/codecharacter of lawStrengthsWeaknesses/CautionFeatures that are useful for DIY
JapanBuilding Standards Law + Energy Saving Law + JIS, etc.Minimum standards national laws + standardsWorld-class implementation for “earthquakes, fire prevention, and typhoons”Complex procedures/differences in local government interpretationsRenovations that touch on "structure, fire protection, and equipment" require prior consultation. Materials are selected based on JIS etc.Japanese Law Translation+1
USIRC/IBC/IECC (adopted by state/city)Model code (legal effect upon adoption)Specifications and fittings are converted into text, rationalized by climate zoneEarthquake response varies by state and adopted versionSpecific details include the ice barrier and outer skin of the roof. When importing into Japan, check for "fire protection/rain protection compliance".codes.iccsafe.org+1
CanadaNBCFederal national modelKnowledge of outer skin design for cold and snowy conditionsThere are regional enforcement differences.Thoroughly ensure valleys, eaves, ventilation, and airtightness. The actual damage caused by ice dams is clear.N.R.C.
ukBuilding Regulations＋Approved DocumentsPerformance regulations + official guideFull of illustrations and practical examplesHistorical buildings are subject to individual judgment. Also, be careful in Japan, as the selection of materials does not take earthquakes into consideration.Detailed guides on openings, rain closures, and insulation can be easily translated into Japanese specifications.GOV.UK
EU/GermanyEurocode＋GEG＋DINEuropean common framework + implementation in each countryA combination of insulation, airtightness, and moisture designThe design information is technical and difficult to understand. Also, be careful in Japan, as the selection of materials does not take earthquakes into consideration.We have optimized and introduced "continuous insulation, airtightness, and dew point control" to Japan's warm and humid environment.dl.azmanco.com+1
BuddhaRE2020Covers carbon as part of legislationComprehensive LCA/comfort/energy savingThe design burden increases. Also, be careful in Japan, as the selection of materials does not take earthquakes into consideration.Useful for decision-making regarding material selection and summer countermeasures.jones day
AustraliaN.C.C.Performance regulations | State applicableStrong practical knowledge of wind, solar radiation, termites, and rainwaterThere are regional differences.The concept of natural ventilation and solar radiation control is a reference.ncc.abcb.gov.au
New ZealandNZBCNational legal systemObligation to comply even with small construction workRequires ingenuity to balance earthquakes and airtightnessMake use of the ``obligation to comply even if confirmation is not required'' as a commandment.building.govt.nz

Minimum checklist to follow “in Japan” (safely transplanting good ideas from overseas)

Step 1: Understand the current situation
Collect and inspect drawings, confirmation certificates, inspection certificates, and deterioration (leaks, rot, termites). We first classify whether it touches the three areas of "structure," "fire protection," and "equipment" (subject to the minimum standards of the Building Standards Act).Japanese Law Translation

Step 2: Assess the legal implications
Building inspections tend to be involved when building extensions, changing uses, relocating load-bearing walls, etc. Energy-saving renovations are related to compliance with the Building Energy Conservation Act and the labeling system (revision status updated from time to time).Ministry of Land, Infrastructure, Transport and Tourism +1

Step 3: Principle design of the outer skin (order of rain, wind, heat, and humidity)
The roof uses ``sunsui lap'', trough lining, and continuous waterproofing of the eaves. In cold weather, heavy snowfall, and low slopes, self-adhesive underlayment is added to key points. The best way to deal with ice dams is to use a combination of ``cooling the roof area,'' ``airtightness,'' ``insulation,'' and ``waterproofing the eaves.''codes.iccsafe.org+1

Step 4: Have a basis for materials and construction methods
The underlayment material is compliant with JIS A 6013, etc. Check the ``overlap width, crimping, and connection with draining'' according to the manufacturer's instructions. For DIY, it is easy to read the construction guidelines of the Japan Waterproofing Materials Association and industry groups.Standard navigation +1

Step 5: Partial mockup and quick test
Check weak points with water spray, smoke generation, thermostat, etc. In particular, "opening corners, valleys, eaves, and verges" are areas where errors are likely to occur (these are also points for backflow of ice dams as pointed out by NRCA and ARMA).nrca.net

Practical points for each part of the roof, exterior walls, and windows (with quotations)

Roof (underlayment, ice dam, capillary prevention)

Top priority is to ``leave the valleys'' and ``sunsui the eaves and integrate them''. Self-adhesion at the eaves (equivalent to Ice & Water) is a standard practice in North America to suppress backflow during ice dams. When transplanting to Japan, choose a JIS-compliant underlayment with an adhesive layer, and adjust the adhesion and overlapping dimensions with the draining hardware as specified.codes.iccsafe.org

The physics of an ice dam is that ``outside air 0℃ x snowfall'' causes meltwater to refreeze at the eaves and create a dam. Countermeasures include "strengthening the airtightness and insulation of the ceiling," "continuously waterproofing the eaves," and "optimizing attic ventilation."buildingscience.com

External wall (ventilation/permeable/waterproof/openings)

The rainscreen (ventilation layer) idea is common in Japan, Britain, and Europe. If you follow the basics, such as the stacking direction and width of the moisture-permeable waterproof sheet, fastener hole preparation, drainage at the bottom, and exhaust at the top, the yield rate of construction will immediately increase. The UK Approved Documents group has plenty of illustrations of the arrangements around windows, making them suitable for use in translation.GOV.UK

Windows (thermal insulation, solar radiation, airtightness)

In Europe, it is common to use a combination of high-performance glass and heat recovery ventilation (HRV). In Japan, the goal becomes clear by determining the target room temperature by referring to guidelines such as HEAT20 while maintaining a balance between "insulation (U value)" and "heat shielding (η)" based on regional classification and orientation (e.g., the relationship between grades 6-7 and G2-G3).Home building school +1

Comparative perspective of energy saving and insulation (Japan and overseas)

In Japan, the legal system is the Building Energy Saving Law, and grades are operated under the framework of the Quality Assurance Law. Insulation grades 6 and 7 will be introduced in 2022, and the scope of mandatory insulation will be expanded from 2025 onwards. The trend is approaching to strengthen "energy-saving performance regulations" like in Europe (GEG/RE2020) and the United States (IECC).. Ministry of Land, Infrastructure, Transport and Tourism

Table: Rough comparison of energy saving systems (guide for DIY planning)

systemWho determines it?What do you want?DIY interpretation
Japan Building Energy Conservation LawLaws and government ordinances under the jurisdiction of the Ministry of Land, Infrastructure, Transport and TourismOuter skin standards/primary energy/compatibility/labelingCheck whether it is mandatory or voluntary and the target scale. Tracking revisions is important.Ministry of Land, Infrastructure, Transport and Tourism +1
US/IECCModel code (legal effect if adopted by state)Housing RE chapter covers, airtightness, and equipmentAbundant specification sheets. Convenient for checking for leaks in insulation and airtightness.codes.iccsafe.org
Germany・GEGFederal law (continuously revised)Primary energy upper limit, renewable energy ratio, etc.LCA-oriented. It goes well with stacking airtight, heat-insulating, and moisture-proof designs.climate-laws.org+1
France・RE2020national regulationsEnergy, carbon, summer comfortDirectly connected to decision-making on material selection and summer overheating countermeasures.jones day

Tips for transplanting “good ideas from overseas” to Japan (practical recipes)

Recipe A: Strengthen the waterproofing of the eaves (snowy/cold regions)

  1. The valley section is made up of sakibari (about 1000mm wide) → general area → ridge in the order of "under water → above water."
  2. Attach the eaves to the draining hardware according to the instructions. Adhesion may be reinforced with double-sided adhesive tape.
  3. If there is a concern about ice dams, install self-adhesive underlayment continuously from the eaves to the point where it straddles the inside line of the exterior wall.
  4. Water spray test and visual inspection before finishing. Use a strip to flatten the steps and gaps at the edge of the verge.
    ——Based on: IRC R905.1.2 (ice barrier), Japan Waterproofing Materials Association's construction guidelines, ARMA/NRCA's ice dam materials.codes.iccsafe.org

Recipe B: Airtight/waterproof taping around windows

  1. Wrap the moisture-permeable waterproof sheet in the order of "bottom → side → top."
  2. The four corners of the opening on three sides of the sash are attached with an L-shaped tip → integrated with wide tape.
  3. Airtight tape on the indoor side and waterproof tape on the outdoor side to make it airtight inside and waterproof outside.
  4. The tape is adhered with a pressure roller. Carefully remove peeling, wrinkles, and floating terminals.
    ——Based on: UK Approved Documents Practical Guide Group, European DIN 4108-7 (Hermetic).GOV.UK

Recipe C: Prioritize “continuity” of insulation and airtightness

  1. Insulation is not a “point” but a “surface”. Bridge the heat bridge of beam victory and pillar victory and make it continuous.
  2. The moisture barrier layer does not span the temperature/humidity position (assuming summer condensation).
  3. DIY Renova, DIYRenova, wood house, self-renovation, DIY, reform, renovation, renovation, renovation, renovation, Japan, Asia, real estate, used housing, used condominium, wood, repair, architecture, housing, detached house, The penetration parts of equipment piping are doubled with airtight packing + butyl.
    ——Based on: DIN 4108 (airtightness/moisture), IECC (enclosure performance).ResearchGate+1

Q&A with failures (with links to evidence)

Q1: “Does double-walled eaves make it easier for water to flow back?”
A: The main causes of backflow are ``reverse wrap,'' ``insufficient overlap,'' ``stagnation at steps,'' and ``insufficient crimping.'' The combination of correct hydration, layering, crimping, and self-adhesive layers will reduce the number of capillaries and, in fact, reduce the risk. Self-attached sheets such as ice barriers are effective for providing backup water in the event of an ice dam.codes.iccsafe.org

Q2: “Since it is a small-scale DIY project, do building inspections and standards matter?”
A: As in New Zealand, even if construction does not require confirmation, the obligation to comply with the Building Code (NZBC) remains. Even in Japan, we cannot escape the responsibility of meeting minimum standards.building.govt.nz

Q3: “Will condensation not occur if the insulation is made thicker?”
A: Condensation is "movement of temperature and humidity x surface temperature". A set of moisture barrier layer position, airtight continuity, and ventilation plan is required. DIN 4108-3 presents a moisture design method.Research Gate

A mini-table of “Materials and Standards” to take a step further (selection basis)

UsesDocuments based on JapanSupplementary information (DIY friendly explanation)
Under-roofing material (modified asphalt)JIS A 6013 (modified asphalt roofing)"Nail hole sealability" and "dimensional stability" are stipulated. For ensuring the performance of primary waterproofing of roofs.Standard navigation
Under-roofing construction (valley/eaves)Japan Waterproofing Materials Association Construction GuidelinesYou can see the steps such as ``tiling the valley edge'' and ``adhering to the eaves drainer'' with diagrams.aspdiv.jwma.or.jp
Energy saving (Japan)Building Energy Conservation Law (latest information page)Click here to check the revised points. DIY insulation and opening renovations also influenced the design policy.Ministry of Land, Infrastructure, Transport and Tourism
Energy saving (US)IECC 2021Just looking at the table in the Housing RE Chapter (Renewable Energy Chapter) will help prevent omissions.codes.iccsafe.org
Basic knowledge of ice damsBuilding Science Digest / InsightIdeal for grasping the overall picture of physical mechanisms and countermeasures.buildingscience.com
EU/German airtightness/humidityDIN 4108-7/-3Learning the concepts of ``airtightness of penetrations'' and dew point control will dramatically reduce failures.dinmedia.de+1

Summary: “Thinking in principle and translating it into Japanese”

Rather than just copying overseas methods, the shortcut to successful self-renovation is to ``translate into Japan's minimum standards and product system'' the principles of ``rain moves from top to bottom,'' ``air moves by pressure differences,'' ``heat moves by temperature differences,'' ``humidity moves by steam pressure differences,'' and ``fire is stopped by coverings and compartments'' and then implement them. Legally, we always use Japan's Building Standards Act and Energy Conservation Law as a starting point, and use US, UK, and EU guides as training wheels. Base your materials on JIS and industry standards, and prioritize the roof's ``valleys, eaves, and openings'' to improve construction quality.Japanese Law Translation

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!

Well, then!

Reference materials/original documents (respect)

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