Attic insulation with blown glass wool: the right idea?

Are you considering blow-in insulation in the attic of your home? Excellent choice. This solution is in fact ideal for effectively insulating unused attics and saving energy. 

All that remains is to find the best material for this work: and why not glass wool? This insulation is one of the most used, but how effective is it? 

Does it meet your needs and the characteristics of your home? I gives you all its good advice on glass wool.


Table of Contents

Choice of insulation: reminder of the different criteria to take into account

How to find the best material for blown insulation? I reminds you of the main criteria to study to choose the ideal compromise:

  • Expected thermal performance: winter comfort, but also heat resistance
  • Sound insulation qualities to prevent the propagation of external noise in the house
  • The level of resistance and lifespan: resistance to fire, humidity, rodents, or even insects
  • The budget: the price of the insulating material per kilo or per m² as well as the cost of labor, essential for blown insulation
  • The environmental impact of the material, if the ecological aspect is important to you.

What are the reasons for using glass wool in blowing?

Glass wool has several advantages for insulating attics by blowing and saving energy. It is no coincidence that it is so often used in insulation, both in new construction and in renovation. 

Good to know: glass wool is a versatile insulator. It also exists in roll form, to insulate walls or the roof from the inside, for example.

Glass wool offers excellent value for money

This is the major advantage of glass wool for insulation work, especially in unused attics. It is indeed very effective in terms of thermal insulation at an affordable cost.

  • The thermal conductivity of glass wool ranges from 0.032 to 0.046 watts per kelvin meter (W/mK). These figures make glass wool one of the most interesting materials on the market for improving the thermal comfort of a home. Thus, it protects you from the heat in summer and from the cold air in winter.
  • Glass wool is very common and easy to find, including in flakes for blown insulation. This explains its low price.
  • Bulk glass wool costs between 2 and 5 euros per kg (1). Allow between 15 and 35 euros per m² for the work, labor included (1).

Glass wool is a lightweight material that is easy to install in attics

Frequently used in blown insulation, glass wool does not represent any particular difficulty for professionals. It is easy to transport, store, and handle. This argument also explains the economic aspect of this material.

Finally, the physical characteristics of glass wool mean that it adapts perfectly to any type of space: a real strong point for the sometimes cramped corners of attic spaces.

Glass wool is non-combustible

Fire resistance is another advantage of glass wool. It is non-combustible, which means that it prevents the spread of a possible fire in the house.

Glass wool resists rodents

A quality to take into account for attic insulation! Glass wool resists pests such as rodents and insects well, and does not require additional chemical treatment.


The disadvantages of glass wool

Any insulating material has its limitations, and glass wool is no exception. Here are its weak points, to know well for an informed choice.

Glass wool is not very effective in sound insulation

Although glass wool has very good thermal insulation qualities, it is not as effective when it comes to noise insulation. If your house is very exposed to noise pollution (on the side of a busy street for example), this may not be the ideal solution.

It is less resistant to humidity and compaction

Although generally resistant, glass wool has some weaknesses when it comes to water. It tends to settle over time, especially in humid conditions.

Also, glass wool can only be installed in perfectly sealed rooms and attics. A professional will advise you to apply a vapor barrier for better humidity regulation.

She is irritating

Handling and installing glass wool requires wearing appropriate protection: clothing, masks, gloves, and glasses. Otherwise, this material is extremely irritating to the eyes, skin, and respiratory tract.

It is not (always) an ecological material

The manufacture of glass wool requires a significant amount of energy and involves non-renewable resources, which has a negative impact on its environmental impact.

Nevertheless, the sector seems to be making progress in this aspect, with ranges of glass wool partly derived from recycling and with a better carbon footprint.


Alternatives to blown glass wool

Glass wool is not the only insulation suitable for the blown method. You can also look at rock wool, cellulose wadding, or cork.

Rock wool

This other mineral wool has similar qualities to glass wool, with a slight advantage in sound insulation and winter comfort. On the other hand, it offers a less effective shield against the heat. So many characteristics that can make a difference when choosing insulation.

Cellulose wadding

This may be the wadding you prefer. Made from recycled paper, cellulose wadding is one of the biosourced insulating materials. In blown insulation, its performance is equivalent to that of mineral wool, plus the ecological aspect. Its weak points: are less resistance to compaction, insects, and fire.

The cork

In the form of flakes or granules, cork can also be blown into attics to insulate them. It stands out thanks to its excellent performance in terms of sound insulation: real added value compared to glass wool. On the other hand, the price of cork is relatively high and does not suit all budgets.


Reminder: how is blown insulation carried out?

Blown insulation is a technique used exclusively in unused attics: attics that are not fitted out or heated. It uses insulating materials packaged in bulk, in the form of flakes in the case of glass wool.

Implementing blown insulation requires several steps, regardless of the choice of material.

site preparation

  • Before starting the work, the craftsman observes the condition and configuration of the attic: the height under the roof, the condition, and solidity of the floor, the location of any openings, the presence of joists at ground level, waterproofing, etc.
  • It then estimates the thickness of insulation necessary to ensure optimal thermal and sound comfort. He places markers in the attic to lay the right amount of glass wool (or other selected material).

Work execution

  • The professional installs the blowing machine (or blower). This has two pipes: one to suck up the insulating material and a second to blow the glass wool flakes into the attic.
  • When everything is ready, he begins to project the glass wool into the attic. Another craftsman is responsible for checking that the blowing machine is constantly supplied with insulation.

End of construction

Once the flakes are distributed in a uniform layer on the attic floor, the craftsman insulates the attic access hatch. Before leaving the house, he ensures the quality of the work and cleans the site.

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