Moisture management during construction: requirements and practice 2026

Why does moisture management matter so much in modern construction?

Today's energy-efficient structures are airtight and do not forgive a soaking during construction: trapped moisture cannot dry out and damages materials. Neglected moisture management is among the commonest root causes of mould damage, and Finland's Healthy Premises 2028 programme keeps the topic on the agenda. Moisture management is not expensive – it is mostly planning and the right order of work.

What does the law require of moisture management?

The Building Act (rakentamislaki, 751/2023), in force since 2025, carries forward the earlier moisture-performance requirements. A project proceeds in three stages: a moisture management report at the permit stage, a site plan derived from it before work starts, and documentation in the inspection record at commissioning. The report describes the moisture risks, the countermeasures and who is responsible.

In larger projects the client appoints a moisture management coordinator at the project planning stage; the coordinator is named in the permit application and oversees risk control throughout. Many municipalities offer small-house builders a simplified plan form – check your own building control office's template. The paperwork is light; what matters is that someone on site monitors that the plan is followed.

Kuivaketju10 handles the report for you

Kuivaketju10 ("dry chain 10") is a model maintained by RALA covering a project's ten most significant moisture risks. The process: the client appoints a coordinator, the commitment is written into the contracts, the designers tailor the risk list, and the contractor implements and documents the countermeasures. Building control accepts the model widely – following Kuivaketju10, separate reports are usually not needed. It includes a digital documentation system and ready-made risk lists for small houses, blocks of flats and offices.

As a small-house builder you are the client: ask the contractor at the quotation stage how they will handle weather protection, materials storage and moisture measurements – and get the answers into the contract.

Weather protection in timber construction

A timber frame getting soaked on site is an unnecessary risk. On demanding timber projects the whole frame is enclosed in a tent-like weather shelter – a practice spreading to log-house sites too. For a small house the minimum is getting the roof on quickly: a panel delivery is weathertight in 1–3 days. Unfinished structures are covered, with ventilation so moisture does not condense under the covers. A weather shelter costs money but removes weather-related risks and delays. Tarpaulins demand constant supervision: a cover torn loose in a storm soaks the structures in a single night.

Solid timber gives a head start: a log frame tolerates site moisture better than multi-layer structures and involves no wet pours. Factory-dried logs and correct storage are still a precondition – settling and drying must be kept under control.

Storing materials on site

• Timber off the ground on bearers, sheltered from rain but ventilated.
• Plasterboard and insulation indoors or in dry storage.
• Wet batches are neither accepted nor installed.
• Moisture measurement before installation if a material's dryness is in doubt.

Storage is the cheapest part of moisture management: bearers and proper covering cost a fraction of replacing a soaked batch.

How long does concrete take to dry?

Longer than the schedule would suggest. An 80 mm ground-bearing slab typically dries to covering condition in 2–4 months, a 100 mm slab in 3–5. Drying depends on the water–cement ratio, temperature, air humidity and ventilation – a 100 mm slab cast in August is ready at the earliest towards the end of the year.

The decision is made not by the calendar but by measurement: borehole moisture testing and material-specific limit values determine when the floor may be covered. Covering too early is a typical and expensive cause of moisture damage – construction dryers can speed drying, but the measurement result decides. Timber structures are likewise moisture-checked before boxing in or finishing.

Factor concrete drying into the schedule: if floor covering sits on the critical path, the casting date dictates the whole back end of the timetable.

Builder's checklist

• Draw up the moisture management report at the permit stage – Kuivaketju10 is accepted as-is in most municipalities.
• Name a person responsible for moisture management before work begins.
• Get the roof on quickly, or use a weather shelter over the whole frame.
• Store materials off the ground, covered but ventilated.
• Measure the concrete's moisture before covering – an 80–100 mm slab dries in 2–5 months.
• Document the measures in the inspection record for commissioning.

• The construction permit requires a moisture management report; a site plan derived from it is drawn up for the works.
• Following Kuivaketju10 is generally accepted by building control in place of a separate report.
• For small houses, many municipalities use a simplified moisture management form.
• Get the roof on fast – a panel delivery is weathertight in 1–3 days.
• A concrete slab (80–100 mm) dries to covering condition in 2–5 months; the decision is always made by moisture measurement.
• Solid timber tolerates site moisture better than multi-layer structures, provided the logs are factory-dried and correctly stored.