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Concrete is one of the most durable, versatile materials in construction, but it’s also one of the most misunderstood when it comes to moisture management. While it may look sleek and solid, concrete is inherently full of pores that act like a sponge, soaking up and holding moisture long after it’s poured.

Why concrete holds moisture

When concrete is first poured, it contains a high percentage of water. Over time, some of that water evaporates as the concrete cures, but a large amount remains locked inside its porous matrix. As building scientist Dr. Joe Lstiburek puts it, concrete is a “reservoir cladding.” Left unmanaged, this moisture can become a liability.

The issue becomes even more pronounced in construction systems that use permanent formwork or precast concrete panels. These assemblies often lack a ventilated cavity or drainage path, leaving nowhere for moisture to escape once it accumulates.

Where it goes wrong

The real trouble begins when hot, humid indoor air migrates through the building envelope in winter and hits the cold, vapour-impermeable surface of internal concrete walls. Moisture condenses on the cold concrete, often behind the plasterboard or insulation, and has nowhere to go.

In many documented cases, litres of water have condensed inside walls, running down into slabs, leaking through the bottom plate, and soaking carpets. Mould and indoor air quality issues soon follow.

Photo credit – Villy Yordanov, Pro Clima

What’s the solution?

Fixing the moisture problem in concrete buildings isn’t about treating symptoms, it’s about designing assemblies that prevent condensation in the first place. Here are three approaches:

1. External insulation (best practice)
   The ultimate solution is to put all the insulation on the outside. This keeps the concrete warm year-round, allowing it to act as true thermal mass while avoiding the cold surface condensation problem entirely. This is standard practice across Europe and aligns with Lstiburek’s “Perfect Wall” philosophy: put your thermal, vapour, water, and air control layers on the exterior.

But there’s a catch. Many architects and developers want the exposed concrete aesthetic, which is lost when insulation and cladding are added externally.

2. Vapour-impermeable internal insulation
   An alternative is to insulate from the inside using closed-cell insulation such as extruded or expanded polystyrene (XPS/EPS), which acts as a vapour barrier. This stops humid indoor air from ever reaching the cold concrete.

However, this method has limitations:

• Fire safety: These materials are combustible and not allowed in buildings over 10 meters tall without specific fire engineering approval.
• Precision required: Every board needs to be carefully sealed with vapour-tight tape. Even small gaps can lead to big problems, still allowing moisture in behind the boards to condense on the cold surface of the concrete without drying capacity.

3. Intelligent vapour control layers
   Pro Clima’s own innovation, the Intello Plus membrane—is a smart solution for those wanting to keep the concrete exposed or internally insulated without vapour issues.

In winter, this intelligent membrane acts as a vapour barrier, preventing humid indoor air from reaching the concrete. In summer, it becomes vapour-open, allowing any trapped moisture within the concrete or insulation to dry back to the interior. This dynamic performance reduces the risk of condensation year-round—if it’s installed with airtight precision.

Climate matters

Not all regions face the same risks. According to hygrothermal simulations, Brisbane and areas north can often get away with internal insulation, as the concrete doesn’t get cold enough to trigger condensation problems. But south of Brisbane, including Adelaide, Melbourne, and even Perth, condensation on internal concrete is a serious concern.

In those cooler zones, external insulation is the safest and most robust strategy. And when in doubt, follow the “perfect wall” principle: put your control layers on the outside.

Final thoughts

Concrete is not going anywhere, developers love it, builders know it, and architects often choose it for aesthetic reasons. But building with concrete requires understanding its physics. Moisture can and will find its way in, and without a well-thought-out design, it may never leave.

If you’re designing or retrofitting concrete buildings, take the time to consider the building envelope holistically. Plan for condensation control, not just waterproofing. Because in the world of building science, a little foresight can prevent a very soggy and expensive mistake.

As usual, we’re always up for a good building science conversation so please call or email whenever you like.

Jess