Spray insulation. Advantages and disadvantages of PUR foam insulation

Spray insulation made by applying polyurethane foam, has been growing in popularity for several years. Find out the advantages and disadvantages of polyurethane foam, the competition to polystyrene and wool.

Spraying can insulate many elements of a house, from the foundations to the roof. It is one of the fastest insulation methods. An attic with a usable area of 100 m2 is insulated in a few hours, and a flat roof with an area of about 1000 m2 – in one day.

Polyurethane foam (PUR) is a material manufactured on the construction site from ready components and applied with the use of a special unit. Unlike wool or foamed polystyrene insulation, polyurethane foam cannot be applied by ourselves due to lack of appropriate equipment and unfamiliarity with foam production technology.

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Spray insulation: closed-cell foam

There are two types of spray applied polyurethane foam on the market. Closed-cell foam is made of microscopic closed bubbles. It has properties similar to polystyrene XPS and therefore it can be applied in similar places as traditional foamed polystyrene or polyurethane boards. This foam is light (35-60 kg/m3) and has a very good thermal insulation, compared to other insulation materials (λ = 0.023-0.029 W/(m.K)). It is not vapour-permeable but has high water resistance. When dry, it is hard and rigid, so it is more exposed to the consequences of various stresses.

Spray insulation: open cell foam

Open cell foam, on the other hand, resembles a sponge in its structure. It still has a very good thermal insulation (λ = 0.036-0.040 W/(m.K)), but not as good as closed-cell foam. It is extremely light (8-10 kg/m3, compared to wool’s weight of 10-80 kg/m3) and vapour-permeable, so it will perform well in similar places to mineral wool, cellulose or wood wool.

It is flexible, so when insulating wooden structures it will not detach from beams and boards which naturally work. Open-cell foam is more absorbent than closed-cell foam, so when using it in the attic or when insulating walls and other frame structures, it is recommended to install a vapour barrier on the inside of the building.

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Flammability of polyurethane foam

Polyurethane foams according to EN 13501-1 usually have reaction to fire class E which means flammable, self-extinguishing material. Polystyrene foam, for example, has the same class. Mineral wool, on the other hand, can boast the highest class A1 or A2, which is reserved for non-flammable materials. Is there anything to be afraid of then? Will using polyurethane foam cause our house to burn down completely during a fire?

Such a danger would be more real if the foam was uncovered and directly exposed to fire. Tests show that a plasterboard partition filled with polyurethane foam insulation (i.e. the system as it is in the insulated attic) has a reaction to fire class B-s1,d0, which means very limited participation in fire, almost no smoke and no burning drops.

What should be kept in mind when insulating with PUR foam?

Both types of foam are not very resistant to prolonged UV radiation, so they must be protected from the sun. In the case of spraying on external elements, it will be necessary to protect the foam with e.g. acrylic, bituminous, polyurethane or silicone paint. If you want to insulate the attic without damaging the drywall inside, it is possible to remove the covering and insulate from above. You just have to remember to put the covering back on as soon as possible and protect the foam from sunlight.

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Open-cell foam is applied between the elements of the structure – rafters, joists, mayflies, elements of load-bearing grid to which cladding will be fixed.

Closed-cell foam must be sprayed on a dry substrate.

As the team produces the material on site, it is very important to check that the containers with the ingredients are factory sealed. There are scammers who dilute the ingredients with water so that they get more foam for the same price. After a few days, the water evaporates and the insulation layer shrinks by several centimetres. This obviously makes it less effective than expected. It can also happen that the contractor adds cheaper and inferior ingredients, so that the foam has a poorer insulation performance.

Some companies also boast about the excellent λ coefficient of their open-cell foam, while in reality it is the coefficient of closed-cell foam. Therefore, if these values seem suspiciously favourable to you, it is a good idea to ask for a declaration of performance or a technical approval and check the conformity of the promised values with the values given in these documents.

Insulating with PUR foam

Thanks to its good adhesion and low weight, polyurethane foam can be laid over old insulation or finishing layers. It is therefore suitable for thermal insulation and thermal modernisation of buildings. As the foam expands strongly, it can be used to insulate three-layer walls by filling the air void between the walls. Its advantages are also important for insulation of attics and ventilated spaces in flat roofs. These are places where it would be difficult to lay traditional insulation material. The foam gets into all the nooks and crannies practically by itself. However, we are not able to verify with the naked eye whether the foam has actually filled everything thoroughly, so it is worth carrying out an examination with a thermal imaging camera at the end, which will detect any under-insulated areas.

Does spray insulation get old?

Looking through opinions on the Internet we can come across comments suggesting that polyurethane foam loses its insulating properties after years. This statement is true for closed-cell foams. The loss of properties comes from the fact that in polyurethane there are gases with better insulating properties than air. However, over time these gases can escape and be replaced by air. In open-cell foams the air is mainly responsible for the insulation, so this problem does not occur. However, it must be borne in mind that the procedures for establishing performance are very restrictive and should take account of any changes over time. Therefore, the λD quoted by the manufacturer should no longer be exceeded.

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