Attic insulation technology with mineral wool from the inside


The under-roof space is used in different ways; living rooms or storage systems are equipped here. Small in terms of labor costs and financial investments, thermal insulation work makes it possible to obtain additional living space, which will never be superfluous. More than half of developers use mineral wool as a heat insulator. Let’s talk about the process of warming the attic from the inside with your own hands with mineral wool, and the video at the end of the article will help you better understand this issue.

All about the insulation of the attic floor with mineral wool

Pros and cons of insulation

Features of insulation of the attic room

Heat insulator thickness

Stages of work

  1. Preparing for installation
  2. Formation of an insulating layer

Pros and cons of mineral wool

Mineral wool is a heat insulator with a fibrous structure, made from mineral raw materials with the addition of synthetic binders. Depending on what raw material was used, there are three types of material.

Material types

  • Stone or basalt. It is made from the melt of rocks: diabase, basalt, gabbro. Clay, limestone or dolomite are added to them. The binder is a small amount of formaldehyde resin.
  • Slag. Produced from the melt of blast-furnace slag. These are wastes resulting from the smelting of iron and other metals. May be toxic.
  • Glass wool. The raw materials for its production are limestone, soda, sand, dolomite and borax. Broken glass and glass production waste are often used.

Fibrous insulator of all types has a different density. Available in the form of plates, mats or rolls. The last two varieties are less dense. This is not always convenient at work.

Stone wool Rockwool

Stone wool Rockwool


  • Fire safety. The insulating coating does not ignite and does not smolder.
  • Low thermal conductivity values ​​for all types of watts.
  • Resistant to temperature changes. The fibers do not deform when cooled and heated.
  • High vapor permeability, which allows the insulator to «breathe».
  • Biological and chemical stability. Insects and rodents do not live in mineral wool. Exposure to chemicals does not destroy it.
  • Convenient and easy installation.

In addition, the relatively low price of the insulator attracts. But you need to be aware of its shortcomings.


They are few, but they are significant.

  • High hygroscopicity. In conditions of high humidity or when water enters, cotton wool absorbs a lot of moisture. At the same time, its properties change. The thermal conductivity of the wet coating increases. Moreover, the more water got into the cotton coating, the worse it retains heat.
  • Material is heavier than light insulators: Styrofoam, extruded polystyrene foam, etc.
  • All cotton wool is prone to dusting during operation, for this reason protective equipment is required.
  • When choosing a heater for the attic, it must be taken into account that this is a living space. Therefore, a security certificate is required.

It is better to choose stone wool, slag wool can be toxic. Glass wool is safe, but very dusty. Its small fibers are very sharp, their impact is harmful to humans.

Features of thermal insulation of the attic floor

The technology of warming a mineral wool attic from the inside involves creating an obstacle to the outflow of heat and reducing air exchange with a cold street. This is the nature of the isolation process. As a result, warm, moist steam remains indoors. In such conditions, it is necessary to reliably protect the cotton wool from moisture, otherwise it will quickly get wet and lose its properties.

Another problem is dew point drift. If you insulate the attic roof from the outside, the dew point will be on its outer side. In this case, the resulting condensate will evaporate into the atmosphere. But if the insulator is laid from the inside, this does not happen. Therefore, it is very important to leave an air gap of 50-100 mm between the roof and the insulator. It is necessary for the evaporation of condensate.

For effective insulation, a roofing cake of five layers is needed. When viewed from the roof, they are arranged in this sequence.

Stone wool TechnoNIKOL Rocklight

Stone wool TechnoNIKOL Rocklight

Roofing cake layers

  1. Ventilation gap 50-100 mm.
  2. Vapor-permeable membrane, moisture and wind insulation.
  3. The warming layer, keeps within between rafters.

  4. Vapor barrier film or membrane.
  5. Attic ceiling.

For vapor barrier it is best to choose special membranes. They are rough on one side and smooth on the other. Thanks to this feature, condensation does not form on them. If there is no membrane, a film of polypropylene or polyethylene, glassine is laid. For moisture and wind protection, other membranes are chosen: two-layer film, porous and superdiffusion. The last option is considered the best.

Recommended thickness of mineral wool for a mansard roof

What thickness of mineral wool should be chosen for a mansard roof? An exact answer to this question can only be done after the calculations. It is difficult to perform them on your own, since knowledge of the standards and formulas is required. They are given in the set of rules on thermal protection of houses. Having spent time studying it, you cannot be sure that the calculations will be carried out correctly. It remains for a person without special education to use averaged values ​​or determine the thickness using a special program.

The second option is preferable. There are many such offers on the web. There are online versions and applications for PC. It is better to choose an independent product, and not the development of any manufacturer of thermal insulation. To obtain the result, you will need to indicate in the filter table the grades and thickness of all components of the roofing pie, as well as the region where the building was erected. This is the only way to get an accurate calculation.

Stone wool TechnoNIKOL Technovent Standard

Stone wool TechnoNIKOL Technovent Standard

If it is not possible to calculate which layer of mineral wool is needed when insulating the attic, developers use averaged data. This is the simplest technique, it also gives the most errors. So, it is believed that, on average, for the thermal insulation of the attic floor, a layer of material of 280-300 mm is required. But depending on the region, it can decrease or increase.

How to properly insulate the attic with mineral wool

Thermal insulation technology is simple. Sometimes the work is done with their own hands, even without assistants. Let’s analyze the sequence of installation of insulation.

1. Preparing for styling

Before forming a warming cake, you need to protect the wood of the rafters from harmful effects. They are treated with an antiseptic and flame retardants. Strictly observe all the requirements of the manufacturer of the composition, carefully dry the tree. Experts recommend mounting the insulator on the crate, which is nailed under the rafters. So cold bridges will not appear, but the useful area of ​​\u200b\u200bthe under-roof space will noticeably decrease.

Therefore, most often a heat insulator is placed in the space between the beams. It is, as it were, inserted into the frame formed by the rafters. It is important that the thickness of the insulation matches the size of the beams. If it protrudes outward, pre-stuffing of bars will be required to level this difference.

2. Shaping the warming cake

Lay layers correctly. Otherwise, thermal insulation will not be effective.

Moisture and wind protection

Its task is to prevent moisture from the street from penetrating into the heat insulator and at the same time allow steam to escape from it into the atmosphere. Better than others, special membranes cope with this task. On the one hand, small perforations are applied to them. They are laid in a horizontal direction. The strips are overlapped so that the row lying above is superimposed on the one lying below from the outside by 100-150 mm. Joints must be sealed with adhesive tape.

It is advisable to buy all the materials needed for installation from one manufacturer. Otherwise, problems are possible. One brand suggests that the membrane cloth and glue will not damage each other, they will last a long time. Products from different brands may conflict with each other.

Properly laid moisture and wind protection forms a continuous canvas. If moisture gets on it from the side of the leaky roof, it will roll down without getting into the insulating cake.


The next stage is the laying of mineral wool in the space between the beams or the elements of the crate. First, it is cut. If rolled panels are mounted, they are cut into strips corresponding to the distance between the rafters. Be sure to make an allowance for laying, that is, the width of the strip should be 20-30 cm more than the distance between the beams. In this case, the cloth will lie as tightly as possible.

Stone wool Rockwool

Stone wool Rockwool

Plates are cut in the same way. The plates prepared in this way are placed in the space between the rafters. In order for the plate to lie flat, it is inserted with a little effort, pressing on the edges. The panel laid between the beams must be fixed. This will prevent it from sagging. This is done using a thin synthetic cord, which is stretched between the supporting elements.

vapor barrier

From the inside of the attic room, the heat-insulating layer is covered with a vapor barrier. It prevents moisture from getting inside the insulation. A film, glassine or membrane is chosen as an insulating coating. It is laid in the same way as moisture and wind protection. The strips are mounted horizontally with an overlap of 100-150 mm. The top edge covers the bottom.

Particular attention is paid to the joints. They are glued with adhesive tape. There should not be a single gap left, otherwise the steam will penetrate into the insulation layer. Adhesive tape is additionally used at the junctions to structural elements, pipes, cables, reinforcing the fastening. The film is attached to the base with small nails with wide hats or staples of a construction stapler.

Sometimes foiled film panels are chosen for vapor barrier. This is a good solution to save on heating. The metallic side reflects heat back into the room. Lay the foil insulation so that the shiny side is turned into the room. Otherwise, the entire effect of its use will be lost.

ceiling lining

Thermal insulation technology assumes that a crate is mounted on top of the vapor barrier. It is stuffed from bars, the thickness of which is from 15 to 25 mm. They will not only hold the skin, but also form a small gap for ventilation. At the same time, the crate will additionally fix and press the vapor barrier membrane against the insulating coating. This will improve the quality of the roofing cake.

The height of the wooden bars should be the same, so the surface will turn out to be even. Before installing the crate, it is desirable to treat the elements with an antiseptic. The step of the crate is chosen depending on what kind of wall and ceiling decoration is planned in the future. It cannot be more than 500-600 mm. The bars are sheathed with wooden boards, drywall, plywood, etc.

We also offer you to watch a video showing all the stages of the process.

We figured out how to insulate the attic with our own hands with mineral wool from the inside. These are general recommendations that must be followed when arranging the under-roof space. It is possible to turn the attic floor into a warm and cozy living space. And you can do it yourself if you follow the rules.


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