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High-performance insulation in attic refurbished in a room is a guarantee of comfort and economy. The quality of its implementation determines its performance.

Make an insulation in two crossed layers

Difficulty: 3/4
Cost: € 1,800 for 44 m2
Time: 3 weeks to 2 persons (excluding bathroom fittings)
Equipment: hand saws, circular and jigsaw, planer, screwdriver, deburrer, level, ruler, cutter, scaffolding, electric hoist, spatulas, plastering knife, glasses, disposable mask and hearing protectors, nail pullers...

To successfully develop a master suite of 30 m2 with bathroom in an attic, three conditions are necessary.

  • First, the ease of access. It is here ensured by an existing staircase, in good condition.
  • Then a sufficient ceiling height. On this site, the free height under the ridge tip is 3.50 m, which allows the development of a comfortable volume.
  • Finally, the floor must be sufficiently strong and dimensioned to withstand normal loads. It does not require any additional reinforcement here.

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Find the original volume

The first step is to demolish a rectangular room with a ceiling too low. Objective: to find the original configuration.
The clinker partitions and the old ceiling made of thin strips of wood are laid down. A false floor is also removed. The roof is also crossed by a chimney in solid brick: it is also demolished after the implementation of a protective formwork to prevent the fall of rubble in the street.
In the opening left in the roof takes place a snuffbox; it will bring natural light into the adjoining bathroom. An existing half-round window adds to the charm of the cleared volume.

Summer comfort: insulation can do better

The height under ridge (3.50 m) allows to implement a comfortable insulation. The total thickness (21 cm) of the two crossed layers of glass wool ("Isoconfort" in 6 cm and "Monospace" in 15 cm, Isover) ensures a very significant reduction in heat loss in winter.
It also optimizes summer comfort. However, the installation of an air conditioning can cool the room and ensure a constant thermal comfort during the hottest periods.

1 Removal of existing building before insulation work

1 Removal of existing building before insulation work

Clinker partitions are quite easy to demolish with a mass. As dust emissions are important, the use of a disposable protective mask (paper type) is recommended.

Make an insulation in two crossed layers: make

The ceiling to be deposited is supported by a false floor provisionally preserved. To work on it safely, a continuous bastaing decking is fixed in the joists.

Make an insulation in two crossed layers: make

The old flue is demolished starting with the stump. The degraded joints allow almost brick removal by brick.

2 Implementation of the insulation

2 Implementation of the insulation

Measure the center distance between rafters. Check several points, because the space between them is often irregular in the old habitat.

Make an insulation in two crossed layers: insulation

Record the largest spacing on the insulating panels and cut them with a handsaw. The insulation can be compressed between rafters in a limit not exceeding 5 to 8 cm.

Make an insulation in two crossed layers: crossed

Set up the insulation from the top to the bottom.
Compress as you go along the sides to insert it between the rafters (be careful: any swelling should be avoided).

Make an insulation in two crossed layers: layers

Continue laying in successive strips.
In case of connection in the direction of the width (end of roll and beginning of another), take care to treat the junction between strips.

Make an insulation in two crossed layers: make

The first layer completely laid, align the lines perpendicularly to the rafters.
Measure their base, then screw them.

3 Laying the second layer of insulation

3 Laying the second layer of insulation

After carrying out the measurements, cut the sections that will support the drywall and the second layer of insulation (here Placostyl system) with a grinder (or shears). Wear protective glasses.

Make an insulation in two crossed layers: crossed

Clip these rails on the lines. The length of the lines protruding from the rafters must be equal to the thickness of the second layer and the distance between rails corresponds to the width of the plasterboards (here 1.20 m).

Make an insulation in two crossed layers: make

Remove the intermediate rails and lay the insulation between the rails, perpendicular to the first layer.
Secure the insulation under the rails. During this operation, it is necessary to be helped.

Make an insulation in two crossed layers: crossed

To care for the installation of the last panel (measured and cut with precision): it conditions the thermal performances at the ridge.
Once the second layer is laid, replace the intermediate profiles and snap them into the lines.

Make an insulation in two crossed layers: layers

To facilitate the installation of gypsum board, screw the profiles into the frame.

Make an insulation in two crossed layers: insulation

Screw the plates on the rails: their regular spacing, corresponding to the width of the plates, ensures a quick installation.

Make an insulation in two crossed layers: insulation

The cutting of the last row imposes a measurements and a precise cut, for a perfect wedging of the plates between them.

Make an insulation in two crossed layers: insulation

Once all the plasterboard screwed on the frames, it remains to finalize the installation of the strips of calico, stuck in a smoothing coating with a plaster knife. Perform this operation carefully, it determines the final appearance.

Make an insulation in two crossed layers: insulation

On the street side, the load-bearing wall made up of clinker blocks is insulated by means of a lining fixed with glue pads.

Make an insulation in two crossed layers: insulation

After coating and applying an undercoat (to even out the support and block the bottoms), the walls can receive two layers of acrylic paint applied by roller.

Supplies for the realization of this two-layer insulation

• Glass wool (6 cm and 15 cm thick)
• Profiles and lines (placostyl plasterboard system)
• Plasterboard
• Calico and coatings
• Abrasive paper
• Undercoat and acrylic finish paint (here The Little Greene)


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