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Under rafters insulation: simple and inexpensive
Under rafters insulation: simple and inexpensive

Video: Under rafters insulation: simple and inexpensive

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Video: Insulating Between & Under Rafters | Loft Conversion Project 4.0 2023, January

The rafters insulation is the perfect solution for do-it-yourselfers who want to modernize their home as simply and inexpensively as possible. Because the additional insulation layer improves thermal insulation, which means you can save energy easily and effectively. With our step-by-step instructions and a little patience, you can easily install the sub-rafter insulation yourself.

Table of contents Table of contents Untersparrendämmung: Insulation simply made by yourself!

  • Under rafter insulation: you should know that!
  • Under rafters insulation: this is how it works!
  • Step-by-step to insulate rafters with mineral wool:

Table of contents Table of contents Untersparrendämmung: Insulation simply made by yourself!

  • Under rafter insulation: you should know that!
  • Under rafters insulation: this is how it works!
  • Step-by-step to insulate rafters with mineral wool:

Do you want to modernize your home or are you currently building your own home? Regardless of whether the structural conditions preclude an intermediate rafter insulation or the existing insulation layer is not sufficiently insulated, the lower rafter insulation offers a simple and inexpensive option for better thermal insulation. Another decisive factor: elaborate roof renovation takes time and is a major burden, especially in occupied rooms. With the rafters insulation you improve the living environment with minimal effort.

Under rafter insulation: you should know that

Before you decide to additionally insulate your attic with a rafters insulation, think about the room height. The rafters insulation is installed under the previous roof insulation. This means that you lose room height with this insulation method. It is therefore important that the room is high enough.

Then check the roof skin. The existing insulation between the rafters and the bricks must be complete and undamaged. To do this, also remove any plasterboard and the vapor barrier of the previous insulation. You install a new vapor barrier as part of the new sub-rafter insulation. This ensures that no humidity from the living room can penetrate the insulation. Defective vapor barriers can lead to mold formation and damage to the insulation.

Under rafters insulation: this is how it works

Before you can start with the rafters insulation, you may need the missing material and tools.




  • drilling machine
  • hammer
  • saw
  • screwdriver
  • Spirit level
  • Cutter knife
  • Folding rule
  • Slats
  • Mineral wool
  • Vapor barrier
  • Plasterboard or

    OSB boards for


  • Screws and nails
  • Staple gun

    Guideline cartridge press

  • safety goggles
  • Gloves
  • any protective clothing

The under rafters can be insulated with various building materials. There are various insulation materials for thermal insulation to choose from: hard foam panels that can be screwed directly onto the rafters, or the significantly cheaper stone or glass wool. You can buy the mineral wool in various sizes on rolls or in a package in the hardware store or in the building materials trade. There are also complete packages for lower rafter insulation, in which the cladding is already included.

Tip: When buying the roof battens, make sure that they later have the same height as the planned insulation layer. You may also have to calculate when purchasing materials that two slats have to be screwed together. You can get roof battens, for example, four by six centimeters thick.

If you are not confident enough to do the work, you will find partners near you here:

Step-by-step to insulate rafters with mineral wool:

1. Start with the base of your rafter insulation. Check in advance whether the ceiling height is the same everywhere so that you can take into account any slopes at the beginning. This is usually the case with older roofs. Here you can attach the slats to measure. You only make corrections on the last crossbar.

Screw or nail the bottom bar, the so-called baseboard, to the existing rafters. The baseboard is attached across the rafters.

Now gradually all rows of roof battens up to the roof top are attached parallel to the baseboard. Pay attention to the exact distance, so that the entire thermal insulation is not accidentally installed wrong.

2. To calculate the exact spacing of the roof battens, subtract one centimeter from the width of the mineral wool. The roof battens are attached at this distance and you can simply clamp the mineral wool panels between the battens without them slipping or falling out. In this way, you not only progress faster with the work, but also save material waste. If, for structural reasons, you cannot maintain the desired distance between the roof battens, simply cut the insulation material to the desired size using the cutter knife.

3. As soon as both sides of the roof are finished with the battens and you would later like to attach skirting boards, attach a 10 cm wide bar to the rafters at the bottom. Since the floor and the sloping roof usually meet at an acute angle, you would otherwise not be able to attach strips. Make sure that the bar is aligned at right angles to the floor. A spirit level and small wooden wedges can be helpful here.

Safety tip: Before starting insulation, you must put on appropriate protective clothing. Safety glasses and gloves as well as appropriate clothing are particularly recommended when working with mineral wool. A face mask can also help to prevent possible irritation of the skin or mucous membranes.


4. Now you can simply press the individual mineral wool insulation boards between the slats. If the spacing of the slats has been chosen correctly, this step is easy. Important: Make sure that there are no gaps in the joints of the mineral wool. This way, the sub-rafters insulation will be perfectly insulated later and is insensitive to the penetration of moisture. To do this, push the insulation boards as tightly as possible against the previous board. There is usually a remaining piece on the last plate that is cut off. To save material, this forms the beginning of the next row of insulation.

5. After you have completely laid the mineral wool, check your work for any gaps that you overlooked at work. Thermal bridges can only be avoided and your insulation ensures the desired energy savings if the insulation material has been installed correctly.

6. Now it goes to the vapor barrier. You can buy these on rolls of one meter wide, for example. This width is also recommended because it is easy to work with. If the film web is wider, get help from a friend or neighbor to align it correctly. Important: So that the vapor barrier closes neatly towards the wall later, make sure that the vapor barrier on the ridge walls protrudes about ten centimeters.

The application of the film is then very easy for two with a tacker. Stretch the film and staple it to the roof battens. The following sheets are also always attached with 10 cm overlapping film. This also applies to the end to the ceiling. You should also seal the chimney under the roof, for example with cuffs and the vapor barrier.

7. Then seal the overlaps of the film without gaps. You can also get the special tape and the adhesive to seal the film to the wall and ceiling from specialist dealers. This work is particularly important because it really has to be done very carefully.

8. Now clad your sub-rafter insulation with plasterboard. These can be easily processed and then simply filled at the joints. The surfaces created in this way can simply be painted after priming. Of course, boards or panels can also be attached as cladding. For this you still need thin battens to be able to attach them horizontally.

Carolin Haist

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