What exactly is the FCAB map?
FCAB (Funderingsrisicokaart) is an independently published, national map that visualizes foundation risk for buildings across the Netherlands. It's an established, publicly accessible source that many municipalities, buyers and estate agents already consult as a first indication. PlotSense doesn't use FCAB as a replacement, but as a cross-check alongside its own address-specific assessment: when the two clearly diverge, the Foundation Report explicitly flags that as a point of attention.
Why can two "official" sources differ so much?
It comes down to the fact that FCAB and PlotSense measure at a different level of detail. FCAB is typically modelled at building-type and area level: it clusters similar homes within a neighbourhood or street and assigns a risk profile to that cluster. That's a sensible approach for a nationwide overview, but it inevitably averages over differences between individual addresses. PlotSense's address-specific assessment uses parcel-specific input: the exact construction year from the BAG, local peat thickness from BRO GeoTOP at roughly 100-metre resolution, and current groundwater and subsidence figures from Deltares for that specific location. Two neighbouring houses with a slightly different peat thickness or construction year can therefore end up further apart in the address-specific assessment than in the FCAB, which might place them in the same area cluster.
Divergence runs in both directions
In practice, an address-specific assessment regularly comes out higher than the FCAB map for that area would suggest — for example when an individual property has a less favourable construction year or a thinner peat layer than the neighbourhood average. The reverse also happens: an area with a high FCAB score can contain a specific address that, based on construction year and local soil data, scores more favourably than the area map suggests — for example a more recently renovated or more solidly founded property within an otherwise higher-risk block. Neither source is "wrong" as a result; they simply measure at a different scale.
What does a clear difference mean for you?
When the address-specific assessment and the FCAB map clearly diverge, that's not an error — it's a signal that the two data sources reach a different conclusion and extra caution is warranted. Concretely, this means:
- If the address-specific assessment is higher than the FCAB map, take the parcel-specific risk indicators seriously, even if the area map looks reassuring. That assessment is based on more granular, current input for your specific parcel.
- If the FCAB map is higher than the address-specific assessment, this can mean the area map accounts for building-type or area characteristics not fully represented in the per-address source data — reason not to ignore the broader context of the area.
- In both cases, a clear difference is an extra argument, especially in a purchase decision, to consider a physical foundation survey rather than sailing on a single source.
What FCAB does and doesn't do
FCAB is valuable because it's an independently published, standardized reference that doesn't depend on a single private provider. It's less suited if you want a precise, current estimate for one specific address, simply because it's built at a coarser spatial level. An address-specific assessment is the reverse: strong on accuracy and currency of the source data for that one parcel, but without the broader area context that FCAB sometimes captures.
Practical advice: what to do when they differ
- Look at both sources side by side in the Foundation Report rather than ignoring one.
- Check the reliability note on the address-specific assessment — with low reliability, the FCAB map should weigh relatively more heavily.
- With a clear difference combined with a purchase decision: consider a physical foundation survey (€600–1,200) as extra assurance, especially for a pre-1975 construction year.
- Use the difference as a talking point with the seller or estate agent — it's a concrete, objective thing to ask about.
Check the FCAB cross-check and the address-specific assessment for your own address in the Foundation Report (€35), or search directly at plotsense.app/zoek.