Large flat roof area with the markings of a measurement grid

Service · nationwide

Radiometric moisture measurement
low-impact — without drilling

Using an isotope probe, we determine the water content in flat roof structures, screeds, and insulation layers — across the entire area in a grid, without a single drill hole and without opening the waterproofing or floor covering. In use for around 30 years, with nationwide approval since 2026.

Request measurement +49 7664 / 50559-0

Initial situation

Moisture suspected — but where, and how much?

After water damage or in the case of a leaking roof membrane, the crucial question at the beginning is: How far has the moisture spread? Without reliable answers, either too much is demolished or too little is dried.

Suspicion without proof

A damp spot on the ceiling says nothing about how far the water has traveled in the insulation layer. Renovation decisions are made on suspicion.

Drilling causes damage

Drill cores and structural openings provide values at exactly one point — and leave behind a spot every time that must be professionally resealed. In occupied rooms and on sealed roofs, this is the actual damage.

Large areas, few points

On several thousand square meters of roof area, point-based measurement is neither economical nor meaningful. The wet spot is rarely where the measurement was taken.

Metal distorts results

Trapezoidal sheet metal, reinforcement, or aluminum lamination interfere with capacitive and resistance methods. The display reacts to the metal, not the water.

The procedure

Low-impact grid moisture measurement with the isotope probe

The probe is placed on the surface — we traverse the area in a fixed grid and measure the water content in the structure at every point, without drilling. The result is not a single value, but a map: It shows where it is wet, how wet, and where the dry area begins. On large roof areas, we measure in a 5-meter grid by default, and in buildings in a 1-meter grid.

Measurement values of a radiometric grid moisture measurement, color-coded from dry to wet — Each measurement point a value, each color a statement: Green dry, Red saturated.

Moisture grid overlaid on the aerial view of the roof area — Overlaid on the area, this becomes the renovation boundary — here a hall in an existing building.

Low-impact, without drilling

Roof membrane, screed, and floor covering remain closed. The grid measurement itself requires no drilling at all — only one or two control points are needed for reference.

Economical over large areas

A measurement point takes seconds. This allows several thousand square meters to be covered in one day — at a fraction of the cost of a structural opening.

Unaffected by metal

The hydrogen in the component is measured, not the electrical conductivity. Trapezoidal sheet metal, reinforcement, and laminations do not distort the result.

Reliable decision-making basis

The moisture distribution plan shows renovation boundaries. It provides evidence to building owners, insurers, and experts — and justifies what can be preserved.

Measurement principle

Why the probe finds water

The probe contains an americium-beryllium source that emits fast neutrons. When these hit hydrogen atoms — which are found in the component practically only in water — they lose energy with each collision and are slowed down. A detector counts the returning slow neutrons: the more there are, the more water is under the probe.

The measured value is initially a pulse count, not a percentage. Only the reference measurement at a known dry spot of the same structure turns this into a statement about the water content. That is why every grid measurement includes a control point — and why the evaluation is the task of someone who knows the roof structure.

We work with the isotope probe from the manufacturer Troxler — in industry parlance, the Troxler probe or neutron probe. The procedure has been established in building diagnostics for decades; in road construction, the same principle is used for density determination.

Display of the isotope probe next to the DÖLCO measuring device during the reference measurement — The count value alone says nothing — only the reference makes it a statement.

Measurement at a marked grid point on the roof waterproofing — Point by point along the previously marked grid.

Comparison of methods

Radiometry or microwave measurement?

Both methods measure in a low-impact manner from the surface, both require no drilling. The difference lies in what they physically measure — and thus in which structure causes them to fail.

Criterion	Radiometry (isotope probe)	Microwave measurement
Measured variable	Hydrogen in the component — which is found practically only in water	Dielectricity of the material
Metal in the structure Trapezoidal sheet metal, reinforcement, aluminum lamination	no influence on the measured value	distorts the measured values, sometimes significantly
Conductive substances Salt load, moisture salts in the screed	no influence	distorts the measured values
Multi-layer structure	measures across the entire structure	boundary layers between the layers interfere with the measurement
Detection depth	entire roof or floor structure	limited per probe head
Large areas	measurement point in seconds, several thousand m² per day	can also be used over large areas
Approval & radiation protection	requires approval — DÖLCO has nationwide approval	not required

In a simple, homogeneous structure, microwave measurement is a good tool — it requires no approval and is available at short notice. Its limit is where the structure becomes real: trapezoidal sheet metal under insulation, reinforcement in concrete, aluminum lamination on the vapor barrier, salts in the screed, multiple layers on top of each other. This is exactly where radiometric measurement continues to provide reliable values — it does not ask about the conductivity of the material, but about the hydrogen within it.

Areas of application

Wherever opening is not an option

Isotope probe on the carpet of an office room during moisture measurement in the screed — Not just roofs: Here the measurement is running over the screed of an office room — carpet and flooring remain in place.

Flat roof

After leak detection and emergency repair, the grid measurement shows how far the saturation extends into the insulation and structure — the basis for the decision between drying and renewal.

Screed and insulation layer

In the building, the extent of water damage in the insulation layer can be determined without opening the floor covering — even under tiles, parquet, and in occupied rooms.

Industrial and hall floors

Large contiguous areas, ongoing operation, reinforcement in concrete: the combination where point-based methods reach their limits.

Expert reports and evidence preservation

Documented measurement values in a grid, before and after drying — understandable for experts, insurers, and courts.

To flat roof leak detection

Radiation protection

Approved, monitored, safe in operation

Handling the radioactive source requires approval under the Radiation Protection Act. DÖLCO has been performing radiometric measurements for around 30 years. In 2026, the approval was renewed and extended to the entire federal territory: Since then, we have been measuring nationwide and no longer just within the jurisdiction of a single authority.

The source is enclosed on all sides and remains in the shielded transport container until it is extended for measurement. Our measurement technicians are instructed as professionally radiation-exposed persons and are monitored dosimetrically.

There is no danger to those present in the building during the measurement: The safety distance of a few meters is maintained, and operations do not have to be stopped.

Approval

Issued by

Regional Council Freiburg
Radiation Protection Authority

Nationwide valid since

2026 — previously regional, for around 30 years

Scope

Federal territory

Procedure

From inquiry to moisture plan

Step 1

Object recording

Clarify structure, area, accessibility, and the question — by phone or based on your documents.

Step 2

On-site measurement

Define grid, determine reference point, traverse the area. For a typical roof, one working day.

Step 3

Evaluation

Moisture distribution plan with marked renovation boundaries and measurement protocol.

Step 4

Recommendation

Drying concept or renovation proposal — with a quantity structure as the basis for your decision.

Measurement technician with the isotope probe on a large flat roof area — Step 2 in practice — and the scale involved: a contiguous hall area.

Frequently asked questions

What clients want to know

Is the measurement dangerous for residents or employees?

No. The source is enclosed, the radiation only penetrates a few centimeters into the component. During the measurement, a safety distance is maintained; rooms do not need to be cleared and operations continue.

How large can the area be?

There is practically no upper limit — especially with large areas, the procedure shows its advantage. Reference project from our practice: a contiguous roof area of 5,000 m².

Does drilling have to be done for the measurement?

Not for the grid measurement itself — the probe measures from the surface. However, to convert the measured values into percentage water content, we need a reference from the same structure: usually one or two control points at a dry spot. Compared to a full-area drilling grid investigation, these are two interventions instead of hundreds.

Does it also work on trapezoidal sheet metal or over reinforcement?

Yes. The procedure measures hydrogen, not conductivity. Exactly where resistance and capacitive measurements react to the metal, the isotope probe continues to provide reliable values.

What distinguishes radiometry from microwave measurement?

Microwave measurement evaluates the dielectricity of the material. Metals, conductive substances, and salts distort the result, and in multi-layer structures, the boundary layers between the layers interfere. Radiometric measurement instead detects the hydrogen in the component and remains unaffected by this. However, it requires approval — we have that approval.

What does a measurement cost?

Every measurement is offered individually — the area and the agreed measurement grid are decisive. Describe the object and the question to us, and we will calculate it at short notice.

Request measurement

Four details are enough for an offer

Area, structure, insulation, and what is on top — these determine grid density, measurement duration, and price. Leave what you don't know blank; we will clarify it over the phone.

1 · Object

Where should the measurement take place? *

Total area in m² *

Desired measurement grid

2 · Structure

Roof or floor structure, if known

Type of insulation

Load on the waterproofing

3 · Request

What is it about?

4 · Contact

Company *

Industry *

First name *

Last name *

E-mail *

Phone *

Street and house number of the object *

Zip code *

City *

How did you hear about us? *

We need the industry and origin information for assignment in the system.

I have read the privacy policy and agree that my details will be stored and processed in order to handle my enquiry. *

I would like to receive information from DÖLCO about products, seminars and the system partnership. For this purpose DÖLCO may contact me by e-mail and telephone. I can withdraw this consent at any time with effect for the future.

* Required field

Our standard grid

5 m

on large roof areas

1 m

in buildings

Tighter grids are possible if a damage boundary is to be precisely defined — this extends the measurement and affects the price.

Why we ask about the structure

The count value of the probe depends on the entire structure. Anyone who knows which insulation is installed and what is on top can correctly set the reference measurement — and convert the measured values into reliable percentages.

+49 7664 / 50559-0 schaden@doelco.de