GPR scanning vs as-built drawings. Why scan if you have the plans?

Yes. Even good drawings show design intent and recorded information, not the as-placed reality at the exact point you're about to drill. Reinforcement and post-tension tendons are routinely shifted during placement to clear obstructions, hit elevations, or accommodate other trades — and those field changes seldom make it back onto the record. Drawings are valuable for planning and for telling the scanning operator what to expect, but the core itself must be cleared against what GPR finds in the actual slab.

Wrong enough to cut a tendon. Common failures: the drawings are design issue, not as-built; revisions during construction never got recorded; tendons and bars were shifted in the field; conduit was added that no structural drawing tracks; or the drawings for that era simply don't exist. We regularly scan slabs where the reinforcement sits materially off where the drawing shows it — which is exactly why 'the plans say it's clear here' is not a safe basis for a core, especially on a post-tensioned floor.

Not at all — they're a valuable input, just not a substitute for verification. Good drawings tell the scanning operator what to expect: whether the slab is post-tensioned, how many reinforcement mats, the approximate tendon drape, where services likely run. That context makes the scan faster and the interpretation sharper. The right model is drawings + scan: the drawings plan the work and inform the scan; the scan confirms reality before the bit goes in.

Because the cost of trusting a drawing over a scan on a PT slab is a severed tendon — a 15–20 tonne energy release, a halted job, and a $20,000–$75,000+ repair. Tendons follow a draped profile and are among the most likely elements to be field-adjusted, so a plan tendon location is particularly unreliable. On post-tensioned construction (standard in BC towers and parkades since the 1970s), the clearance standard is unambiguous: locate the actual tendons with GPR at the actual core, every time. See our post-tension scanning guide.

Then GPR isn't just better than drawings — it's the only source of truth, and it's how coring proceeds at all. We scan the slab to establish whether it's reinforced or post-tensioned and map what's there, enabling penetrations that would otherwise be a blind gamble. Many older BC buildings have no usable structural drawings; the scan makes their slabs workable. It's the clearest case of why scanning is a capability drawings can't provide.

No — it informs it. For routine penetrations the scan clears the location directly. For structural work (large openings, de-tensioning, anything affecting capacity) the structural engineer makes the call, and our scan gives them located reality to design from instead of unreliable drawings. Drawings, engineer judgement, and GPR scanning are complementary; the scan supplies the as-placed truth the other two need.