Technical Due Diligence (TDD): Assessing Building & Site

The expensive surprises in a property transaction rarely sit in the prospectus. They sit in the building line that swallows a third of the building-rights value you were counting on, in the road that turns out to be private and without a registered right of access, and in the square metres that are on record but were never built. A technical due diligence (TDD) is where those errors get caught — before they become yours.

TDD is the discipline that translates a property’s physical and recorded reality into concrete assumptions for a project or an investment. The legal review tells you what you are allowed to do, and the environmental review tells you what is in the ground — but the technical review tells you what you can actually build and use on the site, and what it will cost to make it usable. It is closely tied to the other workstreams, and it is worth viewing it alongside the overall framework for property due diligence before we go deep on the technical side.

What technical due diligence covers — and what it does not

A technical review of building and site is about uncovering the physical and recorded conditions that affect use, building rights and operating economics. In practice it revolves around four groups of issues:

• The buildings’ condition and legality: load-bearing structures, roof, building envelope, technical installations, and whether what was built matches what was approved and recorded.
• The site’s constraints: building lines, building zones, height and setback requirements, protected-forest obligations, protected natural habitats and easements that restrict construction.
• Access and utilities: right of way and road status, connection to sewer, water, heating and electricity — and whether capacity is sufficient for what you intend to build.
• The data quality behind all of it: do the records in BBR (the Buildings & Dwellings Register), matriklen (the cadastre) and tingbogen (the Land Registry) agree with what actually stands on the site.

TDD is professional guidance, not a guarantee. It does not replace a building surveyor’s physical inspection of structures or a consulting engineer’s structural sizing. But a thorough desktop TDD — carried out on public registers before you put people on the roof — determines whether it is even worth proceeding, and where the physical investigations should be concentrated.

Building lines and road conditions: the constraints that move building rights

Building lines are the classic blind spot. A road building line, a watercourse protection line or a high-voltage easement can place a significant part of the site outside the area you are allowed to build on — without it being obvious from a cadastral map at first glance. Two sites with the same area and the same plot ratio can have wildly different real building rights if one of them is cut by a building line.

The sources must be cross-checked. The local plan and the municipal plan in Plandata.dk (the national planning data portal) set out building zones, heights and setback requirements, and the local plan takes precedence over the more general provisions. Easements and covenants are found in tingbogen (the Land Registry) — this is where an old sightline easement or a utility-line covenant can turn up and tie down a corner of the site. Road and nature-protection lines sit as separate layers on top of the map.

Road conditions deserve particular attention, because they concern both physical and legal access:

• Road status: Is the access road a public road or a private joint road? A private road typically means a maintenance obligation and dependence on other landowners.
• Right of way: Does the property have a registered right to use the road? A driveway that is in fact used is not the same as a secured right of way.
• Crossing access: Can a crossing be established or widened for the use you are planning? This often requires the road authority’s permission.

Rule of thumb: If access runs over a private joint road, treat the right of way as unresolved until it has been found and verified in tingbogen — not when the seller says “we’ve always used it”.

Where a building line or an easement blocks an otherwise obvious project, the way forward may be a dispensation. The Planning Act’s dispensation provision allows the municipality to depart from a local plan’s provisions where it does not conflict with the principles of the plan — but it is a possibility, not a right, and the prerequisite should always be clarified with the municipality before it is factored in. Likewise, specific setback and height requirements should be verified in the current local plan and in the building code, since they vary from plan to plan. How to read the binding provisions out of a plan we have covered separately in the guide to reading a local plan correctly.

BBR verification: never trust the recorded areas blindly

BBR is the pivot of the technical review, because almost all of the subsequent arithmetic — plot ratio, rental income per m², rebuilding value — is built on the recorded areas. And BBR is precisely a register of declarations, not a survey. Errors are common enough that a verification can never be skipped.

The typical discrepancies a TDD must catch:

• Areas that don’t add up: footprint, living area and basement/loft areas that diverge from what was built. BBR’s area concepts distinguish between several categories, and it matters which ones count towards the plot ratio.
• Mismatch between recorded and approved construction: extensions that were never declared, or uses that were changed without permission — a latent legalisation case.
• Wrong use code or number of units: affects both the planning assessment and the economics.
• Installations and utilities: heating source, drainage and water supply that do not match reality.

Verification is done by holding BBR up against the other sources and against the physical: aerial imagery, planning basis, the building-case archive and an inspection. A recorded area that cannot be found again on the site is either an error — or an illegal construction that you inherit. Both must be priced before you sign. We have gathered the most widespread traps, and how they arise, in the review of what BBR data shows, and where it gets it wrong.

From register extract to a consolidated technical risk picture

The single error is rarely the dangerous part. The dangerous part is the combination: a building line that cuts the building zone, on top of a BBR over-registration, on top of an unresolved right of way — three conditions that each seem manageable on their own, but together change the project’s premises radically. A structured TDD therefore gathers the individual findings into a single risk picture, where each condition is given a consequence and an action:

1. Identify the condition and the source (Plandata.dk, BBR, tingbogen, matriklen).
2. Verify against an independent source and against the physical, where possible.
3. Quantify the consequence — in lost building rights, in legalisation cost or in delay.
4. Decide whether the condition is a showstopper, a price adjustment or a term in the deal.

The technical workstream must be seen together with the environmental one, because contamination and climate risk are also physical constraints on what the site can bear — see the parallel review of soil contamination, flooding and climate risk. Together the two workstreams form the picture that an investment or project decision actually has to rest on.

How the register review is automated in Arcili

The manual work in a TDD lies in retrieving, gathering and cross-checking scattered public registers — planning basis from Plandata.dk, areas from BBR, easements and title from tingbogen, geometry from matriklen — and holding them up against one another, property by property. That is exactly what the Ejendomme (Properties) module in Arcili does in a single lookup: ten detail tabs with BBR, planning conditions, land registration, economics and surroundings gathered for each individual property, so that discrepancies between recorded and actual stand out immediately.

It does not remove the engineer’s or building surveyor’s physical assessment — that still has to be carried out. But it cuts the hours out of the initial register review and ensures that none of the four groups of conditions is overlooked because a source was not looked up. If you want to see what it looks like on a concrete property, take a look at Arcili or book a walkthrough.