Wooden buildings and insulation

Quality insulation is fit for purpose and retains its good qualities year after year. There is a wide range of insulation products available, each suited for a specific task. Thermal insulation products vary in their materials and properties, but air leakage in a building needs to be considered regardless of the material used. Airtightness is an important factor in terms of energy efficiency, and the use of insulation also does not preclude the normal need for partitioning firewalls and fire barriers.

This article contains our compilation of information on the standard thermal insulation products on the market, their properties, and how they can be used in a variety of wooden frame buildings. We compiled this information in collaboration with the manufacturers and had experts from Eristeteollisuus ry check the resulting article.  

Text and photographs: Puuinfo, Saint-Gobain Finland Oy, Rockwool Finland Oy, Ekovilla Oy, Finnfoam Oy, Kingspan Insulation Oy

Source: Rakenteellinen energiatehokkuus korjausrakentamisessa– opas. Tuomo Ojanen, Esa Nykänen, Kari Hemmilä. 2017.

Read the article in Finnish here.


Glass and stone wool products are examples of mineral wool that are manufactured by spinning fibres from their raw materials together and adding a binder. Glass wool is often made from waste glass, while stone wool is made from a variety of minerals. The secret to mineral wool lies in the fibre, which both traps air in the insulation and inhibits radiant heat transmission.

Mineral wool works as thermal and acoustic insulation in buildings and is used in exterior walls in particular. This insulation is available in slabs, rolls, and wind barrier panels. Mineral wool can be used in all wooden construction: wooden apartment buildings, detached houses, and public structures.

ISOVER (Saint-Gobain Finland Oy) and Knauf Oy manufacture/sell glass wool in Finland while Rockwool Finland Oy and Paroc Group Oy do the same for stone wool. 

Glass woll

ISOVER building insulation can be used in all buildings, regardless of the frame material. In terms of fire behaviour, these products are suitable for buildings in fire class P0-P3 thanks to their rating of Euroclass A1 or a minimum of A2-s1, d0.

This insulation material does not require separate protective cladding, which means these products can be used to build simple structures with only one insulating material. ISOVER glass wool can also be used for protective cladding, such as K₂10 protective cladding with a wind barrier facing (120 mm ->).

Alongside its thermal insulation capabilities, long-fibre glass wool improves acoustic insulation. This porous insulation material is non-hygroscopic, which means water vapour passes through the homogeneous, diffusion-capable insulation layer. This keeps the load-bearing structures dry. Glass wool insulation can be installed as a uniform, wind barrier type layer on the external side of load-bearing and solid wood frames. This means that supporting rails and studwork are not needed. Rather, a structure with spacers and no thermal bridges provides the best possible protection to the solid wood frame in a changing climate.


The insulation lasts for the lifetime of structures and buildings. Energy efficiency is guaranteed by the good thermal insulation provided in such compact form. This all keeps energy consumption low while the building is in use without adding environmental emissions during construction. Since glass wool is made with recycled raw materials and renewable energy sources, it is already a very low emission material that can reduce the overall CO2 emissions of a construction project. It is of course possible to build energy-efficient solutions with other insulation materials that generate higher CO2 emissions, as long as they effectively reduce emissions during use and the need to purchase energy.

ISOVER offers different kinds of insulation with a variety of properties, including wool slabs that improve acoustic insulation in partition walls and compression-resistant roof and element wool and wool strips. The available products have different thermal conductivity ratings and facings. Options include binder-free, non-shrink blown wool for roof structures, and wool strips for sealing seams in solid wood and element structures and in frame joints.

ISOVER uses recycled glass (about 80% of the raw materials) and emission-free electricity to manufacture its glass wool in Hyvinkää and Forssa. When finished, these products are compressed down to a quarter of their normal volume to simplify transport and save on storage space. Research is under way to create products that are even more low-carbon. ISOVER always conducts carbon calculations for its products and continuously updates this information as products evolve. As an insulation manufacturer, Saint-Gobain Finland is committed to being carbon neutral by 2035. 


ISOVER began collaborating with Revisol in 2022 to launch a glass wool recycling service to collect waste from demolition and the cutting of wool rolls at work sites. There are also various on-going projects to recycle mineral wool for use as a replacement for cement in concrete.

We collaborated with the manufacturers in creating this text. For more information, visit
www.saint-gobain.fi/puurakentaminen, www.isover.fi

Stone wool

ROCKWOOL stone wool insulation can be used in exterior walls, partition walls, subfloors, intermediate floors, and roof structures. In addition to their excellent insulation capabilities, stone wool products are very resistant to fire and can therefore protect structures by inhibiting the fire and arresting its spread. In terms of fire behaviour, stone wool building materials are in Euroclass A1 or A2-s1, d0, depending on the product. In fires, Euroclass A1 products do not burn at all, while Euroclass A2 products burn to a very limited extent. Since it is made from natural stone, stone wool can tolerate temperatures of up to over 1000°C without melting. Stone wool insulation can be used in fire class P0-P3 buildings. Research tells us that stone wool retains its ability to serve as thermal insulation through a building’s lifecycle, meaning for at least 55 years.

Stone wool sheds liquid moisture and does not absorb moisture from the surrounding air. This diffusion-capable material allows water vapour to pass through it, which helps keep structures dry. When you use stone wool insulation in a building’s outer shell structures, you need an air or vapour barrier close to the structure’s inner surface. This prevents moist and warm indoor air from permeating the thermal insulation and structures and also prevents air leaks from one side of a structure to another. Membranes, panels, or the structures themselves can act as an air and/or vapour barrier. Of the various membrane products available, vapour barrier plastic sheeting, air barrier paper, and so-called smart vapour barrier membrane fabrics can be used with stone wool. When choosing a product, you need to consider the resulting structural-physical functionality of the total structure.

The regulations or requirements for fire safety will vary depending on the building’s intended use. For example, fire regulations require that the outer surface of the frame (the inner surface of the ventilation gap) in certain fire class P2 buildings have a protective cladding that lasts at least 10 minutes (K210).


When the insulation is 100 mm thick at a minimum, the ROCKWOOL Redair Flex system meets this 10 minute requirement and can therefore be used for the protective exterior cladding of a fire class P2 building with solid wood/CLT frames . The Redair Flex system is installed on vertical wooden support rails, which makes it a good match for horizontal facade cladding panels. For vertically installable panels, a criss-crossed rails can be used instead.

ROCKWOOL also offers an extensive selection of technical insulation for use in fire, thermal, condensation and acoustic management in various building technology applications. The Rockpanel and Rockfon brands are also part of the ROCKWOOL group. Made from pressed stone wool fibres, Rockpanel facade panels can be used to add design flair to wooden facades. Rockfon acoustic products are intended for building interiors.

After ten years of significant investment in reducing climate impacts, ROCKWOOL has reduced the carbon footprint of the products it sells on the Finnish market by up to 70 percent. In the stone wool production process, stone is melted at temperatures of around 1,500 degrees Celsius. Three of the four Nordic ROCKWOOL factories have already begun to use renewable fuels in their melting furnaces.


ROCKWOOL stone wool insulation is completely recyclable, which creates a so-called closed material cycle. In autumn 2022, ROCKWELL launched its Rockcycle® recycling system. This system makes it possible to recycle leftover stone wool insulation and used stone wool products from demolition and renovation work sites. The stone wool insulation collected is reused as a raw material in the manufacture of new stone wool products. ROCKWOOL is the only Finnish mineral wool insulation manufacturer that offers a closed material cycle-based solution for recycling used insulation.

We collaborated with the manufacturer in creating this text. For more information, visit www.rockwool.fi


Wood fibre insulation has good moisture management and heat storage properties, which suits both new construction and renovation work. Thermal insulation made from wood fibre is an excellent choice for wood construction due to its hygroscopicity. Wood fibre insulation is organic in nature as it is made from wood fibre pulp, recycled paper, or pulp fibre. This insulation operates in the same way as other fibre-based insulation, meaning that the fibre both traps air in the insulation and limits radiant heat transmission.

Ekovilla Oy, Termex-Eriste Oy, and Hunton Oy/Ab manufacture/sell wood fibre insulation/cellulose wool in Finland.

Wood fibre insulation

Ekovilla wood fibre insulation is made from wood fibre that is made from recycled newspapers. This Finnish thermal insulation is well suited for wood construction due to its hygroscopicity. Suited for both new construction and renovation work, this insulation

is mainly meant for use in fire class P3 buildings and class P2 buildings that are no more than 2 storeys tall. You can use this insulation on the roof structures of P1 class buildings up to 28 metres high (with concrete roof structures) and in wooden apartment buildings with a functional fire rating (P0).

Ekovilla is available as blown wool or in slabs. This means that with the exception of fire-safety issues, the design process for insulating a building is not much different than with other conventional insulating materials. These products are usable in all types of construction. Ekovilla insulation breathes, which means it absorbs and releases moisture. It doesn’t require a plastic vapour barrier, rather you can use air barrier paper that creates a fault-tolerant structure that dries on both sides.

Photo: Ekovilla

Ekovilla insulation provides a good level of thermal protection. The insulating air remains in place thanks to the minimum thermal transfer and air flow. In other words, this insulation hinders convection inside structures. Just like other wood materials, Ekovilla has an excellent moisture and heat capacity. This moisture capacity and the ability to absorb and release moisture balances out indoor air moisture levels, while the high heat capacity reduces large temperature fluctuations in buildings.

Ekovilla insulation also has a high level resistance to fire, meaning that it does not melt even at high temperatures. Rather, it chars like solid wood, providing effective protection for the structures wrapped inside. The typical structures used in ordinary row and detached houses (fire class P3) meet the one hour fire resistance rating of REI 60. At Euroclass B-s2, d0, blown wool has the highest possible fire class for natural fibre insulation. Slab wool is in fire class E.

Ekovilla is manufactured from wood fibre recycled from carefully selected, cleaned newspaper and cardboard. Collected near the manufacturing facilities, the material is processed into insulation using only a minimum amount of energy because production consists of grinding the fibre instead of using high melting temperatures. The electricity used in manufacturing is 100% sourced from renewable wind power.

Kuva: Ekovilla

The amount of carbon stored in the raw materials is much greater than that emitted during the manufacturing process, which makes Ekovilla carbon negative. Ekovilla products have a small carbon footprint and a large carbon handprint; for example, blown wool has a carbon footprint of 0.087 kg CO2e/kg and a carbon handprint of -1.34 kg CO2€/kg.

We collaborated with the manufacturer in creating this text. For more information, visit www.ekovilla.com


The term rigid thermal insulation refers to plastic-based products such as XPS, EPS, PU, and phenolic insulation. These insulation slabs can be coated with different materials, such as aluminium laminate, bitumen, fibreglass, or gypsum board, and can be used in wall, floor, and ceiling structures.  Rigid thermal insulation has poor acoustic insulation properties, which means it is not suitable for preventing the lateral transmission of sound in structures.

XPS and EPS insulation are both manufactured from polystyrene. As a closed cell structure, polystyrene’s insulating properties are based on the air trapped within it. The acronym XPS stands for extruded polystyrene. It is manufactured using a continuous pressing process, which results in smaller air pockets and smoother foam. The acronym EPS stands for expanded polystyrene. It is manufactured by placing spherical polystyrene beads in a mould and expanding then with heat and pressure, which fuses them together.

PU insulation is based on polyurethane (PUR) or polyisocyanurate (PIR). Over 90% of the cells in this insulation are closed. To further improve insulation, these cells are filled with a gas that conducts heat less efficiently than air. The product range includes options with aluminium or plastic laminate surfaces, which make the products impermeable to air and moisture.

Phenolic insulation (PF) is a plastic-based product made from closed-cell foam that similarly to PU insulation is filled with a gas that conducts heat less efficiently than air. The space between the closed cells is left partially open. This insulation is laminated on both sides, with either one or both sides typically being diffusion-capable.

Finnfoam Oy, Inora Oy, Jackon Finland Oy, Kingspan Insulation Oy, Porkka Finland Oy, Recticel Insulation Oy, Solupak Insulation Oy and Styroplast Oy sell/manufacture rigid thermal insulation in Finland. The individual product types vary by manufacturer.

XPS- (FINNFOAM), PIR- ja EPS-insulations

Finnfoam (FF) manufactures EPS and PIR insulation, which can be used for all wall structures. Finnfoam’s thermal insulation has been used widely for fire class P1 projects.

FF-EPS thermal insulation is typically accompanied by a separate air or vapour barrier layer because it does not have enough water vapour resistance on its own. In contrast, FF-EPS insulation with aluminium or plastic laminated facings have a very high resistance to water vapour and can serve as a vapour barrier by themselves.

For CLT elements and other solid wood structures, FF-PIR FR flame-proof laminated polyurethane is an excellent choice for exterior thermal insulation. In this case, the CLT wall elements act as the load-bearing structure and have an exterior covering of FF-PIR FR insulation panels with ventilation slots and wood panel cladding. FR flame-proof laminate is a expanding surface laminate in Euroclass Bs-1, d0. The insulation foam is fire class D. When heated, the flame-proof laminate expands to cover the ventilation slot, inhibiting fire from spreading through the structure. This insulation decreases the U value of the structure, making it more resource and energy efficient with significantly improved thermal insulation in comparison to traditional construction techniques with solid wood walls.

Photo: Finnfoam

This all enables a so-called hybrid structure that is both tight and energy efficient. In this case, wind protection panels are installed normally on the exterior side of a wood-framed building’s frame posts, then soft mineral wool insulation is placed between these frame posts, followed by FF-PIR insulation panels on the interior side of the frame posts. The seams in the resulting assembly are sealed with elastic joint foam and taped. The target U value is what determines how thick the insulation needs to be.

Finnfoam has prepared an Environmental Product Declaration (EPD) for its FF-PIR insulation. This document contains a statement on the insulation’s environmental impact, which you can compare to the generic values at CO2data.fi. FF-PIR insulation is completely recyclable, and Finnfoam collects leftover pieces and cutting waste from work sites through its FF recycling bag program. One noteworthy aspect of the company’s recycling efforts is that products from other plastic insulation manufacturers can also be placed in FF recycling bags with the exception of phenolic insulation. The insulation foam pieces collected in recycling bags can be used to manufacture new Finnfoam products. A facility for recycling solvents will open in Salo in 2023, which will further improve the reuse of recycled insulation.

Photo: Finnfoam

We collaborated with the manufacturer in creating this text. For more information, visit https://finnfoam.fi/

PIR and phenolic insulation (Kingspan Insulation Oy)

Kingspan manufactures PIR and phenolic foam insulation suitable for wood construction and sells it under the brand names Therma and Kooltherm. Polycyanurate (PIR) insulation is a polyurethane, but it is an improvement over traditional polyurethane (PUR) with its enhanced thermal insulation and fire resistance. Therma and Sauna-Satu are Kingspan insulation panels with a PIR core and a laminated surface on both sides. Kooltherm series panels are phenolic foam insulation that has a fibre-free core and is laminated on both sides.

Kuva: Kingspan

For the construction of an energy-efficient detached house, Therma and Kooltherm insulation make excellent choices.  Kooltherm insulation can also be used with non-load-bearing wooden structures in fire class P1 buildings and for insulating wooden attic structures in fire class P1 apartment buildings that are less than 28 metres tall.

Kingspan’s efficient insulation can reduce heating costs. All Kingspan insulation materials behave well when exposed to fire, have been thoroughly tested and fulfil local requirements.

Therma and Kooltherm insulation come in rigid and airtight insulation panels and have a dense cell structure. Various facings are available for these products, including low diffusion aluminium laminate, and gypsum board. Moisture management at the work site is also straightforward and safe. The products are lightweight, making them easy to handle, install, and transport. The insulation panels are also easy to work with, as they can be cut to the desired dimensions with handsaws, sharp knives, or circular saws, and they are also dust free.

With insulation panels, the insulation layer in wall, ceiling and floor structures can be made quite thin. This can add additional square metres to the interior or enable a higher ceiling, adding significant value to both new construction and renovation work. For example, a façade wall can be made half the usual thickness, allowing up to 40% more daylight.

Kooltherm insulation is quick to install on the entire building exterior, which means that you can turn the heat on earlier and begin work on the building interior.

Kingspan has introduced its 10-year long plan for sustainable development, called Planet Passionate, to reduce the environmental impact of its production processes. Through this programme, Kingspan aims to reduce its carbon dioxide emissions in production to as close to zero as technically possible and to halve the carbon intensity in its primary supply chain.

We collaborated with the manufacturer in creating this text. For more information, visit www.kingspaneristeet.fi

ProductPurposeMaterialThermal conductivity λD (W/m K)Thermal resistance RD
insulation thickness 100 mm
Carbon footprint GWP
A1-A3, when thermal resistance R=1
Euro fire classCoatingWater vapour permeability coefficientAir flow AFr
(kPa s/m²)
Product type approvals
P0-P3 class buildingsglass wool0,0333,000,543A1noMU118CE, M1, EPD, Finnish Key Flag, suitable for buildings with the Nordic Swan
Flexibatts 36P0-P3 class buildingsstone wool0,0362,750,425A1noMU18,8CE, M1, EPD, suitable for buildings with the Nordic Swan
Ekovilla panelsP3 class buildings, maximum of 2 storeys P2 class buildingswood fibre0,0392,55-0,624Enono information available9CE, M1, EPD, Finnish Key Flag
Therma TP10
insulation board
P3 class buildingspolyurethane (PIR)0,0224,502,57Ealuminium laminate on both sidesno information availableProduct standards do not require an airflow resistance value.CE, M1, EPD, suitable for buildings with the Nordic Swan
K12 framing board
P3 class buildings,
non-load-bearing structures in P1 class buildings, for insulating wooden attic structures in P1 class apartment buildings under 28 m high
phenolic foam0,0214,751,94C-s1, d0aluminium laminate on both sidesno information availableProduct standards do not require an airflow resistance value.CE, EPD, suitable for buildings with the Nordic Swan
FF-PIR FRP1 class buildingspolyurethane (PIR)0,0253,852,20B-s1, d0 (black
coating side)
D-s2, d0 (foam)
fire laminate on one sideno information availableProduct standards do not require an airflow resistance value.CE, M1, EPD
FF-PIR ALAdditional thermal insulation, for insulating wooden attic structures in P1 class residential apartment buildings under 28 m highpolyurethane (PIR)0,0224,552,05E, In insulating part D-s2, d0 (foam)aluminium laminateno information availableProduct standards do not require an airflow resistance value.CE, M1, EPD
Table 1. Properties of different insulation products.
Note! Not all numerical values are comparable to each other as such. Always use structural level calculations, and check with the manufacturers for the values.