Deck construction in Lappeenranta

Regulations and permits

Under the new Rakentamislaki 751/2023, significant changes to the building envelope and extensions that affect safety, townscape or building life cycle require a building permit (rakentamislupa). This includes new decks, extensions of existing ones, balcony decks and roof decks.

Helsinki advises applying via Lupapiste when the deck carries structural elements (roof, canopy, railings) or clearly alters the appearance of the building.

Each municipality refines the thresholds in its building regulations. For example, in Vantaa, a deck up to around 50 cm high can, in some cases, be built without a full permit if distances to the boundary (e.g. 2.5 m) and neighbour impact are respected. Higher decks are typically treated as permit-required structures.

In protected buildings and areas, almost any change that affects facade or roof appearance is subject to stricter review of materials and details.

Deck types and structures

The deck type strongly influences cost, complexity and permit needs. At the simple end is a ground-level platform, at the complex end a roof deck or balcony that is part of the load-bearing frame.

• Ground-level deck: timber or composite boards on concrete blocks or a low foundation. Often the simplest and most affordable solution.
• Elevated deck on supports: decking carried by timber or steel joists bearing on concrete piers, posts or screw piles. Suitable for sloping sites and allows air circulation beneath.
• Concrete slab: a monolithic or prefabricated slab on a compacted sand/gravel base with reinforcement. Ideal for decks by the house, garage or veranda but requires careful sub-base and drainage design.
• Balcony deck: an extension of the interior floor or a deck attached at storey level. Almost always requires capacity checks, strengthened supports and a permit.
• Roof deck: an accessible flat roof. This is a multi-layer construction with waterproofing, rails and drainage, designed by an engineer and inspected by building control.

Foundations and load-bearing capacity

Long-term performance of a deck starts with the foundations. On typical soils, concrete piers or blocks installed on compacted sand are common. They are levelled carefully, and deck joists are supported via blocking or plates.

• Concrete blocks and piers – for light timber decks.
• Screw piles – for clay or problematic soils where stability is critical.
• Concrete slabs – for heavy stone or composite surfaces and covered decks.

On weak or frost-susceptible soils, heavier solutions such as screw piles, bored piles or concrete slabs are used. The aim is to go below frost depth (typically 80–120 cm) or design a structure that tolerates ground movement.

For small decks, 30–50 cm depth with a well-compacted gravel bed can be sufficient if spans between supports are kept to roughly 2–3 m and bearing points are protected from moisture.

Drainage, waterproofing and materials

Water is the most common enemy of decks: it must not be allowed to stand at the foundation, by the plinth or in structural details. Both the sub-base and the deck surface should have a slight fall of 1–3 % away from the house or towards a collection channel.

• Softwood decking boards – economical but maintenance-heavy.
• Composite decking – durable, low maintenance and slip-resistant, with a higher upfront cost.
• Concrete slabs and pavers – extremely durable, but demand a stiff base and accurate falls.
• Stone and porcelain tiles – visually striking and premium, but sensitive to frost and waterproofing errors.

A gravel strip or drainage trench with perforated pipes around the deck helps lead stormwater away. Under the decking, geotextile and crushed stone are often used to prevent weed growth and support filtration.

At the junction with the house, tapes, flashings, sealants and trims protect the base of the wall and facade from splash and seepage. Covered decks require additional attention to vapour control and moisture near heated interiors.

Timelines, costs and insurance

Building a single-level 20–30 m² deck typically takes about 2–4 working days for a two- to three-person crew under normal conditions (excluding design and permitting). Complex elements such as stairs, a roof or integration with an existing porch increase time.

Across Finland, deck projects often fall in the range of roughly €1,800–€9,000, with larger covered decks reaching €15,000–€16,000 or more. Final cost depends on size, materials, foundation type and detailing.

Insurers generally do not cover damage caused by structural mistakes, non-compliant details or unpermitted work. If a deck directs water to the foundation and this causes damage, the case may be considered non-compensable.

Using a qualified contractor, having a documented design and inspection records after completion forms a practical minimum for relying on insurance and satisfying municipal requirements.

How to avoid issues and order a safe deck

Even for a simple deck, it is worth checking municipal guidance and, if needed, asking for advice before starting work. This reduces the risk of tear-outs and disputes with neighbours or authorities.

• Prepare at least a sketch, material description and photos of the current situation.
• Plan waterproofing and drainage: connection to the house, slopes and directing water away from the foundation.
• Provide ventilation under timber decks so that wood stays dry.
• Check your contractor’s deck experience and request handover documents on completion.

Leave a request on our site — our specialists will help design and build your deck turnkey. We will assess the soil and existing structures, check municipal requirements, choose suitable materials and deliver a deck that is level, durable and safe in Finnish conditions.