On my fourth property, I set aside 350,000 yen extra for a bathroom remodel and thought I was being generous. Three weeks into the job, a rotted subfloor under the tub pushed the total 90,000 yen past even that padded number. That single project taught me the lesson I now apply to every renovation across my 9 rental units: a contingency budget is not a nice-to-have line item, it is the difference between a job that stays profitable and one that quietly eats your margin.
After more than 15 years of self-managing renovations, I have landed on a system for sizing that contingency that is neither too thin to matter nor so padded that it distorts my numbers. Here is exactly how I calculate it before a single wall comes down.
Why I Never Skip a Contingency Line
ud83duded2 RECOMMENDED ON AMAZON US
Personal Finance & Real Estate Books
The financial mindset shift that made property investment possible on a salary.
Early on I used to quote myself a single number, say 1.2 million yen for a full unit turnover, and treat that as gospel. The problem is that number was really just the visible scope: new flooring, a repainted kitchen, fresh fixtures. It never accounted for what I could not see behind the walls. Now every estimate I write has two numbers next to it: the base scope cost and a separate contingency line, tracked as its own category in my spreadsheet, never blended into the main total. Keeping them separate is what lets me actually measure, project after project, whether my sizing is accurate.
The Percentage I Actually Use
ud83duded2 RECOMMENDED ON AMAZON US
Budget Planners for Property Owners
Track every yen in and out u2014 the foundation of profitable landlord accounting.
My rule of thumb depends on the age and history of the building. For any property built before 1981, when Japan’s earthquake code changed, I budget 15 percent of the base renovation cost as contingency. Older wiring, older plumbing runs, and a higher chance of moisture damage behind walls all push that number up. For a newer property, or a purely cosmetic job like repainting and replacing flooring in a unit I already know well, I drop that down to 8 to 10 percent. Over roughly 40 renovation projects, that 15 percent figure on older buildings has been close enough that I rarely run out, and rarely have much left over either, which tells me it is calibrated correctly rather than just being a scare number.
Where the Extra Money Actually Goes
The same handful of surprises show up again and again once I open up a wall or pull old flooring. Knowing the usual suspects in advance is what lets me size the contingency with confidence instead of guessing.
- Water damage or rot hidden under flooring or behind a tub, often only visible once the old surface is removed
- Wiring that does not meet current code once an inspector or electrician actually looks at it, common in units older than 25 years
- Pipe corrosion discovered mid-renovation, especially in units that still have the original galvanized steel plumbing
- Mold behind wallpaper in north-facing rooms, which I have hit in at least 6 different units over the years
- Price increases on materials between the day I quote the job and the day I actually order, which added roughly 5 percent to my lumber costs on one project last year
How I Calculate the Number Before Demo Starts
ud83duded2 RECOMMENDED PRODUCTS
Tax Guides for Property Investors
Knowing the tax rules turns a good investment into a great one.
Before any renovation begins, I walk through a short process rather than just picking a round number out of habit.
- Get the base scope priced out first, either from my own labor and material estimate or a contractor quote
- Check the building’s construction year and last major renovation date to decide between the 15 percent and 10 percent tier
- Add 5 percent more if the unit has never had flooring pulled up since I bought the property, since that is where the biggest surprises tend to hide
- Round the contingency up to the nearest 10,000 yen so it is a clean number I can track easily
- Write both the base cost and the contingency as separate lines before requesting any materials
On a typical kitchen and bathroom refresh that runs 900,000 yen in base scope, that process usually lands me at a contingency of 120,000 to 140,000 yen. It sounds like a lot until you remember that a single subfloor repair alone can run 80,000 yen on its own.
What I Do When the Contingency Runs Out
Even with careful sizing, I have blown through the full contingency on 3 separate projects over the years. When that happens, I do not just keep spending. I stop and reassess against the unit’s expected rent increase: if the additional repair will not pay itself back within about 24 months through higher rent or lower vacancy, I scale back the rest of the renovation instead of chasing the original plan. On one older unit, that meant skipping a planned kitchen counter upgrade so I could cover an unexpected 150,000 yen plumbing repair without touching my own emergency fund. The contingency protects the project, but the real safety net is being willing to cut scope when the numbers say so.
That is the approach I use across all 9 of my properties, and it is the single habit that has kept every renovation I have run in the black.
Renovation Cost Reduction Checklist (60% Savings Method)
My step-by-step process management template that cut renovation costs by 60% across 3 apartment buildings over 15 years.
ud83cudfe0 More from DIY Father
15 years of landlord experience u00b7 3 apartment buildings u00b7 DIY renovations that saved millions of yen. Browse all articles at diytosan.com
