The Content Of The Article:

Insulation by the interior is the most widespread, in renovation as in the new one. It is carried out here with a new generation mineral wool, meeting very demanding ecological criteria.

Difficulty: Difficult
Cost: about € 1,400 for 50 m2 crawling (including dubbing)
Time: Three weeks

isolate a room under the roof

Sub-crawling insulation in two crossed layers: crossed

An ecological choice

Track down

Laying the first layer of insulation

Sub-crawling insulation in two crossed layers: vapor

Sub-crawling insulation in two crossed layers: insulation

Sub-crawling insulation in two crossed layers: crossed

Sub-crawling insulation in two crossed layers: layers

Good to know for DIYers:

Placing the second layer of insulation

Sub-crawling insulation in two crossed layers: insulation

Sub-crawling insulation in two crossed layers: crossed

Sub-crawling insulation in two crossed layers: insulation

Membrane bonding

Sub-crawling insulation in two crossed layers: insulation

Sub-crawling insulation in two crossed layers: insulation

Sub-crawling insulation in two crossed layers: vapor

Sub-crawling insulation in two crossed layers: vapor

Sub-crawling insulation in two crossed layers: layers

Sub-crawling insulation in two crossed layers: layers

Sub-crawling insulation in two crossed layers: layers

Sub-crawling insulation in two crossed layers: crossed

DIY tip:

The reinforcement of the thermal requirements inevitably has repercussions on the insulation thicknesses.
The choice of a two-layer installation limits the encroachment on the living space since the first fits between the rafters.
In addition, as the second arises transversely, it reduces the risk of thermal bridges at the joints between panels or rollers.

An ecological choice

The performance to be achieved here is a thermal resistance (R) of 6.
The insulation used ("TI" range from Knauf Insulation) belongs to a new class of mineral wools that are more ecological, more pleasant to handle, odorless and less irritating than conventional wools.
Manufactured using the "Ecose Technology" process, they consist of 60% glass, mainly from the recycling of household waste and windshields from scrapped vehicles.
Another peculiarity of the process, the binder used to agglomerate the fibers is free of volatile organic compounds (VOCs), such as formaldehyde, phenol, acrylic...
The substances of petroleum origin are replaced by plant-based inert polymers, without artificial dyes or pigments of any kind whatsoever. This gives this glass wool its characteristic brown hue.

Stalking "leaks" of air

In winter, the permeability to air flows is a major cause of heat loss and, therefore, energy consumption.
It promotes the condensation of water vapor on framing exposed to cold, with the resulting degradation: wood mold, corrosion of metal elements, etc.
In addition, a moistened mineral wool loses its insulating power. Choosing it in the second layer with a kraft paper vapor barrier is recommended to limit the migration of water vapor from the living space to the outside.
It is then necessary to make sure to seal the areas of weakness (junctions and around the insulation).
These points can be treated cheaply with wide-band adhesive tape, but without absolute efficiency. With flexible insulation, the tape does not always stick well and yawns in places...
By covering all the crawlers with a Knauf Insulation Sd 20 or Sd 30 polyethylene film, the air and water vapor tightness is total, when using the adhesives recommended for fixing the strips and their grouting

Laying the first layer of insulation

  • First mount the metal frame, here with soles and amounts M48 put back to back.
  • Leave a length on hold to facilitate the installation of entire panels.

  • At the back of the right foot (vertical part at the base of the rampant), the triangular space is too small to be exploited.
  • Cover the floor with a thick layer of glass wool roll.

  • The dimensions of the semi-rigid panel "TI 135 U" (R = 4 m².K / W) require two people to insert it without damaging it.
  • Go down the panel to the bottom of the right foot.

  • Complete the framework by placing the two missing M48s.
  • Bring them back to back.
  • Center and fix them to the posts with crimping pliers and screw them together.

  • Garnish the crawling panel after panel, making sure to grout them well.
  • Use size drops to fill gaps and complete rows.

Good to know for DIYers:

  • The Sd value of a vapor barrier indicates its resistance to vapor diffusion.
  • The figure that accompanies it represents the thickness in meters of an equivalent layer of air.
  • The higher it is, the more resistant the membrane is to vapor diffusion.
  • Sd values ​​20 or 30 in attic insulation correspond to a high level of performance.

Placing the second layer of insulation

  • The complement is provided by a wool of the range of 80 mm (R = 2 m².K / W), coated here with kraft paper, to achieve a thermal resistance of 6.

  • To streamline the work, cut rolls 60 cm wide, such as the spacing of the uprights.
  • The mineral wool knife allows cutting without tearing the edges.

  • Insert the insulation horizontally into the framework.
  • Bridging the gaps left, as here, by the reinforcements of the farmhouses of these old lost attics.

  • Where electrical cables are to be connected, cut glass wool with a cutter.
  • Pass the cable through the insulation and pull it out.

Membrane bonding

  • Placed on the "hot" side of the creeper, the airtight polyethylene film is placed with a double-sided adhesive that sticks on the furs.

  • Unroll the ribbon by sticking it well all along.
  • Lift one corner of its protective film with the cutter blade, then gently pull on it to remove it.

  • The membrane is 280 cm wide.
  • It is delivered in roll of 140 cm, folded on itself.
  • Take measurements and identify overlap points from the ridge.

  • Unroll the film on the ground then cut each length to the desired length.

  • Kraft duplicating polyethylene, lacerating its surface to "air" it.
  • The cuts of cutter are given diagonally every 20 cm approximately.

  • Fix the top of the le away from the rampant to avoid sticking too early.
  • Progress down and apply it tight on the adhesive.
  • Ride the pieces 10 cm.

  • Check the adhesion of the film with the edge of the window and cut it to clear the opening.
  • Provide 5 to 6 cm of flap for the dressings of the embrasure.

  • Cut strips to the dimensions of the sides of the embrasure, plus 15 to 20 cm of margin for the recovery.
  • Get help to place and glue them carefully.

  • Finish by covering all fittings with tape for overlaps.
  • There is also a cartridge adhesive to fix the edges of the vapor barrier.

DIY tip:

  • Adhesive sleeves are provided to reinforce the airtightness at the passage of the electric cables.
  • Perforate the center to the diameter of the cable and pass it before sticking the "patch".


Video Instruction: Crawl Space Insulation