A home's quality is decided, even before the drawings, by the materials that arrive on site. Structural materials require acceptance inspection and confirmation of JIS/JAS certificates; finish materials require sample approval; site-mixed materials require a mix-design report. Stop and inspect before anything is hidden, and leave an evidence trail in photos and records — that is the rule we hold to.
1. Why material inspection decides quality
However good the workmanship, if the material itself is out of spec, quality will not follow. Rebar one size too thin, concrete short on strength, timber too high in moisture — caught at delivery, rework is zero. Inspection is done not to "doubt" but to "prove."
2. Acceptance items for key materials
- Rebar: lot number, mill sheet (composition certificate), diameter and count
- Concrete: delivery slip, design strength, mix-design document, slump at pour
- Windows: serial number, glass spec, thermal performance
- Timber: moisture content 15% or less, JAS certification mark
3. The acceptance-inspection flow
| 1. Delivery | Match the slip and order for quantity and spec |
| 2. Visual inspection | Check for deformation, rust, cracks, wetting |
| 3. Certificate check | Mill sheet, mix-design document, JIS/JAS |
| 4. Record and store | Photograph and store properly (rain cover, off the ground) |
4. The absolute rule of pre-concealment checks
Three stages are "always stopped and inspected before being buried":
- Rebar → before the concrete pour
- Waterproofing layer → before protective mortar and finishing
- Plumbing and electrical conduit → before plasterboard and mortar finishing
5. Why construction photos matter
At least 10 photos per concealed stage. "However much doubt arises later, the photo tells the truth." For rebar, record spacing and cover thickness with a ruler in shot; for waterproofing, always shoot the joint detail at the edges.
6. Inspection acceptance criteria
| Pass | Within spec and tolerance / continue as is |
| Minor (repair) | No effect on function or durability / repair and record |
| Serious (rework) | Bears on strength, waterproofing, structure / redo |
7. Responding to a failure
Rebar pitch off, concrete strength test below value, a defect in the waterproofing layer. Minor means repair; serious means rework. The deciding axis is always "the effect over the next 30 years."
8. Using third-party inspection
For structure, waterproofing, and insulation, adding a third-party inspection on top of the supervising architect brings peace of mind. The fee is around 200,000 to 400,000 yen for structure, but the insurance value of an independent eye is immense.
9. Document control and traceability
Mill sheets, mix-design documents, inspection records, photos. Keeping it possible to trace "which lot of material was used where" after the fact is the greatest weapon when trouble strikes. At handover we present it to the owner as a construction photo album.
Concealed work is invisible once complete. Holding that "photos and inspection records are the truth of the house," we keep document control absolute.