How to Isolate a Habitable Loft

The best solutions to insulate it, to cover the floor and to cover beams.How to Isolate a habitable loft

1. Tools

  • Saw
  • Rule
  • Drill
  • Meter
  • Cutter
  • Hammer
  • Gloves
  • Mask
  • Stapler
  • Scotch tape
  • Wood plank

2. Criteria for choosing the insulation

Before starting, and in order to choose the most effective insulation solution, it is convenient to analyze the characteristics of the attic and to evaluate the following aspects.

Using the loft

Weather in the area

Each type of insulation has a coefficient of thermal insulation depending on its composition (R) and another as a function of its density (?).

There are isolation ratios depending on the area and altitude of the population.


The insulation and laying technique was chosen to fix it will depend on the spacing, thickness, and alignment of the roof truss beams (these beams are also called rafters).

Space utilization

When it is necessary to make the most of the available space in the attic, it is possible to use insulators which, with an equivalent thermal coefficient, are thinner than traditional insulation materials.

Placement inside or outside

In the reforms, as a general rule, the insulation is done in the traditional way, placing an insulation under the skirts of the roof reinforcement.

In new construction, special insulation panels can be placed on the reinforcement and fix on these same panels the tiles that serve as support for the covering of tiles, slate …

NOTE: The insulation products on this sheet are just a few examples of insulation. Nowadays, there are many effective roof insulation solutions that fit all needs.

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3. Preparation

  1. Check the condition of the roof reinforcement and treat it according to the needs, once the insulation has been placed, it will no longer be accessible.
  2. Where a single mineral wool panel is used, it is essential that one of its faces be covered with kraft or aluminum paper acting as a vapor barrier, ie to prevent condensation from Fibers reducing the thermal resistance of the insulation. As you can see in the diagram, the steam barrier must always be directed towards the hot part of the house.
  3. When using two mineral wool panels, it is essential to remove the vapor barrier of one of them, because if this barrier is placed “sandwich”, the product will lose its insulation capacity.
  4. Leave an air gap between the insulation and the roof covering to prevent the reinforcement from rotting and deteriorating the tiles (at least 4 cm between the tiles and the insulation).
  5. Do not compress the mineral wool or its thermal resistance will be reduced.
  6. Insulating panels should be well placed, edge to edge, to prevent heat from escaping (use paper or aluminum tape).
  7. To obtain optimum insulation, it is necessary to distribute ventilation holes through the roof reinforcement. These vents open in the upper, lower and vertical, by reason of a ventilation for every 15 m2 of the roof.

4. Installation

On regular beams

  • Fix the panels on the beams every 30 cm, using galvanized or stainless steel wide head screws or nails.
  • Position the first panel and present the clips with galvanized wide head screws.
  • Place the second panel by fitting it into the first panel.
  • Screw in a clip to secure the second panel.
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Fixing with glue:

Bonding of panels with glue for extruded polystyrene. Leaving a tube of air with the roof.

About irregular beams

1st layer: the panels of rigid mineral wool are cut in a triangle to facilitate their adjustment between the beams.

Use panels of thickness 2 cm. Lower than the beam. (These 2 cm difference will allow air to circulate behind the panels).

Slide the panel triangles between the beams, as shown in the drawing, leaving a 1 cm slot between them. Cut the protruding peaks and keep them.

Hitting the hammer on the top panel edge until it is fully tightened against the bottom panel.

Interpose a small wooden board to prevent the hammer from damaging the wool.

If there are any cracks, use the remaining peaks to cover them.

2nd layer: rigid panels of coated mineral wool are used.

Screw the fixing legs to the beams every 59 cm (this is the correct distance to place the gypsum boards later).

The wool panels are inserted into the fixing legs from above. It starts by placing the row of panels that is in contact with the floor and ascending towards the top of the roof. Do not forget that the vapor barrier must always be oriented towards the interior of the house.

Cover all joints with tape.

Using scissors, cut strips of insulation. The width of the strips will be the spacing between beams plus 3 cm margin on each side. This margin allows stapling the sides of the strips to the beams.

Once the insulation is placed, the rafters are fixed on the beams every 40 or 60 cm. These strips serve simultaneously to support the material used as the roofing of the attic (frieze, plasterboard, etc.) and to keep said insulation liner separate and to circulate the air.

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Before installing the rails, it is necessary to check the level of the assembly. In the case of irregularities, correct them by placing wooden wedges behind the rails, before fixing them.

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