Hemp what are the particularities of this insulator? How to install it ?

To be confortable, the house must be perfectly insulated. But a good insulation also allows tosave energy. To do this, we can use hemp, a dicotyledonous plant that belongs to the family of Cannabaceae. Hemp thus enters into the composition of materials used in building, both for construction and for renovation, because it is a thermal and acoustic insulation. Let’s look at its peculiarities and see what is the method of laying.

Hemp: an effective insulator

Plant cultivated for more than ten millennia, that is to say since the Neolithic era, hemp has many particularities which make it one of the best ecological insulators today. By installing hemp in your home, you can therefore benefit from insulation:

  • Acoustic,
  • Thermal,
  • 100 % naturel,
  • Made of strong vegetable fibres,
  • Safe because:
    • Free of allergens,
    • Without emission of Volatile Organic Compounds (VOC),
  • Odorless,
  • Which attracts neither pests nor rodents,
  • Recyclable,
  • Efficient,
  • Long lasting, as hemp does not sag over time (except for loose hemp),
  • Very permeable to water vapour,
  • moisture resistant,
  • Humidity regulator because it absorbs excessive humidity and releases it when the atmosphere is too dry
  • Suitable for both interior and exterior insulation.

It is recommended to buy hemp wool from plants grown without phytosanitary treatment, as in the case of organic hemp. The ideal is to give preference to the French sector.

Hemp as an insulator provides breathable walls. This is why it can be placed on a wooden frame or on plaster, which are materials sensitive to humidity. Perfect in summer and winter, hemp maintains optimal comfort in the home. You can insulate everything with hemp: floors, walls and ceilings of the living area, crawl space, attic, attic, cellar, roof…

It should however be noted that its fire resistance varies depending on its conditioning. Thus, bricks and lime/hemp plasters are poorly combustible (Class B) while hemp wool panels and rolls are highly flammable and spread flames. It is therefore absolutely necessary, if one opts for this solution, to place a fire barrier.

Hemp for the interior and exterior insulation of the house

Hemp as insulation is packaged in various ways, depending on whether it is intended to insulate the house from the inside or from the outside.

Interior insulation: hemp wool

In this case, we use panels or else rolls hemp wool. It takes around €22/m² for a thickness of 16 cm and €26/m² for a thickness of 20 cm. Hemp wool panels also represent a good solution in terms of sound insulation.

Hemp exterior insulation: brick or plaster

The hemp bricks can be used to rehabilitate an old building or when building a house. These blocks are available in different thicknesses ranging from 10 to 30 cm. For information, the m² of bricks 10 cm thick costs on average 35 € while it takes about 100 € for 1 m² of hemp brick insulation 30 cm thick. Note that it is quite possible to build interior partitions with these hemp bricks.

As for thehemp coating, it is mainly used to insulate old walls, whether in earth, brick, concrete or stone, which considerably limits the feeling of a cold wall. To do this, we must turn to the bulk hemp which must then be mixed either with garden soil or with lime – respecting the proportions indicated by the supplier. We recommend a thickness of 10 cm to insulate a concrete wall in this way, and 5 cm to insulate an old stone wall. However, it must be taken into account that the bulk hemp compaction is of the order of 18 to 20%.

Bulk hemp is marketed in bags of different capacities (15, 50, 100 and even 200 kg). The cost price of lime/hemp concrete with a thickness of 5 cm is around 10 to 12 €/m².

Hemp, an easy-to-install insulation

The laying of hemp panels or rolls does not represent no difficulty. This natural plant material does not require any particular protection (neither gloves, nor goggles, nor mask). On the other hand, care must be taken to store its panels sheltered from the rain but also from the sun while waiting to install them.

To can cut the panels to the desired size, it is necessary to have either a circular saw with a diamond blade, or a cutting saw or even a cutting knife which must be sharpened regularly during the work . The cutting of semi-rigid panels and rolls of hemp is quite difficult because these insulations are thick and rough.

The laying method proceeds as follows.

  • Cut each panel to the desired width between two supports to which 20 mm should be added,
  • Place the panel by compressing it enough so that the contact with the uprights is optimal in order to ensure the insulation continuity : the junctions between the walls must be caulked,
  • On the inside, put a vapor barrier also called vapor retarder to ensure the best possible airtightness: the vapor barrier must always be placed on the warm side, between the interior facing and the insulation (here, the hemp),
  • Finish with a finishing siding.

Of course, we can entrust the laying of the hemp to a insulation professional, since you are not used to carrying out this type of work. This allows you to have the guarantee work carried out according to the rules of the art. And comparator online allows you to quickly receive several quotes. All that remains is to contact the chosen craftsman.

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