Moisture in sandwich panels – how to find it before it causes damage
Sandwich panels are one of the most common ways to build offices, warehouses and data centres. They are relatively cheap and quick to install, and Iceland is no exception: you see them on industrial and commercial buildings all over the country.
But the Nordic climate, and especially Iceland's, is hard on any building envelope. Constant rain, high humidity and strong wind mean it is very difficult to guarantee that panels are never exposed to moisture, whether during transport and storage on site, during installation, or over the building's life through joints and flashings.
Why sandwich panels are a special case
Building science describes four control layers a wall needs, in order of importance (Lstiburek, The Perfect Wall, BSI-001):
1. rain
2. air
3. vapour
4. heat
In the panel itself, the two steel skins act as the rain, air and vapour control, and the stone wool core is the thermal layer. As a single element, that works very well. The weak points are the joints, flashings, penetrations and base details, where these layers have to connect from one element to the next.
Two features make panels unforgiving once water gets in:
No second line of defence. Insulated metal panels are face-sealed, not drained, systems (Commissioning Building Enclosure Notebook, p. 290). There is no cavity behind the face to carry away water that gets past a joint.
No drying path. With steel on both sides, a panel is a double vapour barrier by design. Building science guidance warns against double vapour barriers precisely because an assembly needs to be able to dry in at least one direction (BSD-106, Understanding Vapor Barriers, p. 4). Water that enters the core has almost no way out.
How to detect water in the panels
We don’t need to wait for rust stains. NIBS Guideline 3 (Exterior Enclosure Technical Requirements for the Commissioning Process, Annex U) describes the field methods. Used in sequence, they form an effective survey.
Infrared thermography first. An IR survey of the façade, carried out under the right conditions (a temperature difference between inside and outside, with the interior heated evenly, according to ASTM C1060), shows where wall assemblies are damp, often in places that would otherwise be impossible to find. Wet insulation holds and conducts heat differently from dry insulation, so it appears as an anomaly in the thermal image.
Moisture measurements second. The suspect areas from the IR survey are then checked with moisture measurements. Moisture meters are calibrated for specific materials such as wood, concrete and gypsum, so on other materials they mainly show which areas are wet and which are dry relative to each other. With steel faces on both sides, the most reliable confirmation is often a small inspection opening or core sample at the suspect spot, or a relative humidity probe inserted into the core.
Visual inspection. Stains, rust and other signs of earlier water leaks at joints, flashings and the bottom of the panels show where to look.
Make it part of commissioning
The best time to do this is during construction and before handover, not after the first problems appear. An IR survey followed by targeted moisture checks should be part of the building envelope commissioning plan, with particular attention to:
- panel joints
- bottom flashings
- openings
- anywhere water could collect and stay
At Norcom, we work with building envelope commissioning in Iceland and understand how local weather conditions affect sandwich panel buildings. We help to plan and carry out thermography surveys and moisture measurements, review critical details such as joints and bottom flashings, and make sure the envelope is dry and performing as intended before the building is handed over.
References
J. Lstiburek, The Perfect Wall (BSI-001); Hockey Pucks and Hydrostatic Pressure (BSI-057); Punched Openings (BSI-104); Understanding Vapor Barriers (BSD-106). Building Science Corporation.
US EPA, Moisture Control Guidance for Building Design, Construction and Maintenance.
NIBS Guideline 3, Exterior Enclosure Technical Requirements for the Commissioning Process, Annex U.
Commissioning Building Enclosure Assemblies and Systems (course notebook).
