Roofing material

Felt roof

Felt roofing is the standard solution for flat and low-pitched roofs in Finland. Modern SBS bituminous felt is far removed from the reputation of old felt — properly installed it lasts 20–30 years and is completely waterproof.

Lifespan

20–30 yr

Cost level

Weight

8–15 kg/m²

Min. roof pitch

0° (tasakatto)

Property comparison

Durability

How long the material lasts under optimal conditions.

Weather resistance

How well the material withstands Finland's weather variations: frost, moisture, UV.

Low maintenance

How little regular maintenance the material requires in normal use.

Value for money

The ratio of lifespan to installation cost — how much you get for your money.

What is felt roofing?

Felt roofing consists of layers of bituminous membrane providing waterproofing. It is the only practical solution for flat or near-flat roofs in Finland. Modern felt roofing is very different from the old-world "felt" — SBS bituminous membrane is elastic, frost-resistant down to –20 °C, and ideally suited to Finland's demanding climate.

The term "felt roof" originates from the old oxidised bitumen felt used before the 1980s. Modern SBS membrane roofs are an entirely different product and should not be confused with the old material.

SBS bituminous membrane — the modern solution

SBS (styrene-butadiene-styrene) is an elastomer that gives bitumen its flexibility. Unlike old oxidised bitumen felt, SBS does not become brittle in frost or stretch excessively in heat. The system typically consists of two layers: an underlay membrane and a surface membrane, with the surface layer UV-protected.

Installation is done either by heating the membrane with a gas torch (torch-applied / "welded") or with cold-applied adhesive products. Torch-applied membrane is more common in Finland and provides a completely seamless waterproof layer.

Suitability and limitations

Felt roofing works at any pitch, including a completely flat roof — it is the only common roofing material suitable for a 0° pitch. On steeper roofs (over 10°) a special high-pitch membrane is used, mechanically fastened in place.

Maintenance schedule

Annually Visual inspection, clear drainage routes, check penetration condition
3–5 yrs Professional roof inspection — surface condition, cracks, sealing
20–30 yrs Full membrane replacement (SBS membrane)
Immediately Repair any detected leaks — a flat roof leak reaches the structure quickly

When is felt roofing the right choice?

Felt roofing is the mandatory choice for flat-roofed buildings and low-pitched roofs (below 1:5). It is also the standard solution for row house and apartment building roof decks and terrace roof structures. A builder should invest in quality installation and choose a two-membrane system — if the surface layer is damaged, the underlay still protects the structure.