- You want to insulate your attic at € 1?
- Thin joint assembly
- Do not forget the future railing fixings...
- 1 Laying the foundation blocks
- 2 Fixing the blocks to the support wall
- Info +
- 3 Formwork of a bay support
- 4 Application of the plaster
- Laying hemp blocks in ITE: do or have it done?
Today, outdoor insulation can be a powerful solution thanks to breathable and natural materials such as hemp, which is light and easy to fix.
Cost: starting from 37 € / m2 (Insulation 10 cm thick and coated, not installed)
Time: 2 to 3 weeks
Equipment: ruler, cord, level, square, handsaw, form hammer, shovel, spatula or notched trowel, concrete drill and drills, pliers, pincers, trowel, scraper, wheelbarrow, concrete mixer, scaffolding and projecting machine (rented)
In the facade, thermal insulation from the outside (ITE) is most often using expanded polystyrene or rockwool. But it also happens to use more natural and breathable materials such as hemp proposed in blocks of several centimeters thick, covered with a coating.
Made from hemp (central part of the hemp stalk) and natural hydraulic binders, these blocks of hemp are available in different thicknesses (10 to 30 cm), with a thermal resistance of 1.4 to 4.2 m2.K / W.
Note however that it takes at least 3.7 m2.K / W (so a thickness of 30 cm) to qualify for the tax credit and possibly eco-loan at zero rates (under conditions).
You want to insulate your attic at € 1?
Test your eligibility by filling out the form below:
Thin joint assembly
In ITE, these blocks are covered with a lime plaster (in two layers with fiberglass reinforcement frame). They are thicker as the walls to be dressed are high: up to 6 m for blocks of 10 cm and up to 10 m for those of 30 cm.
The first row must be placed 15 cm above the ground (on basement profiles or a water-resistant base) and the assembly is done with thin joints with a lime-based mortar (preformulated or not), which can be used to other works such as supports or enclosures of berries.
Do not forget the future railing fixings...
As for the fixings of railings, downspouts, awnings, light fixtures, etc., they are realized in the same way as in the case of polystyrene: it is necessary to cross the insulation and go fix on a sufficiently strong support with suitable fixings (see the Info + box).
Depending on the method used, these new fixing points must be prepared before laying the blocks (legs, supports, etc.) or after the coating (chemical anchors and threaded rods, lag bolts, etc.).
1 Laying the foundation blocks
Trace the cups with chalk and resize the blocks with a handsaw. They will sit here in front of a door at floor / threshold height.
To properly dose the mortar, plan 1 vol. fine sand (0-2 caliber) for 1 vol. of NHL lime 3.5 and ½ vol. of water.
The mixture must be fluid enough to obtain joints 3 to 4 mm thick.
Draw a chalk mark on the laying surface (arase).
Apply mortar with a notched trowel or spatula.
Place the first block in the mortar, closest to the existing wall.
No need to reserve an air space behind the blocks or put mortar between the two walls.
Fix the end of the chalk on one side (scaffolding for example) and unroll it to the second block at the other end of the wall.
Block the cord tight.
For subsequent blocks, also glue the side faces.
From the second row, check the plumb of each block with a spirit level or a plumb line.
2 Fixing the blocks to the support wall
Each row is connected to the masonry by brackets.
Drill the corresponding holes every 1.20 m by shifting them at each row.
The fasteners used here are false ceilings for metal framing, to bend at 90° before use.
Fix the legs (or brackets) in the wall with dowels to hit.
Then nail the fasteners in the hemp blocks with two galvanized tips Ø 3 x 70 mm.
If a plumb bob reveals a defect in verticality, correct it by pulling or retrieving the blocks with the help of a mallet.
Regularly check the alignment with an aluminum mason ruler.
In the corners, the blocks are harped (mounted in staggered rows)...
For a perfect verticality, a plumb line is attached under the eaves and unrolled over the entire height of the ridge.
When an interval of more than 5 cm has been reserved between the blocks and the wall (for example to correct a defect), close it (with pieces of blocks glued to the mortar) so that the air thus imprisoned remains still, therefore insulating.
Measure the remaining height under the eaves and resize the blocks accordingly.
If an interval is to be filled behind these blocks, use hemp or wood wool instead of loose insulation.
In order to perfect the insulation, one can be tempted to join the blocks.
Better to refrain because their connections may reappear through the coating, in the form of "spectra". We leave them open.
And in addition, several hours of work are saved!
3 Formwork of a bay support
To include the masonry and its insulation, clamp a board horizontally on both sides of the opening.
On the outside, the board is 2 to 3 cm lower to obtain a slope of 5 cm / m.
If there is no welded mesh, cut Ø 6 or 8 mm twisted concrete bars.
Spread them on the surface by crossing them to form meshes of 20 x 20 cm approximately.
Ligate their intersections with wire.
Prepare the lime mortar (not too liquid) and partially fill the surface of the formwork.
The frame should rest at mid-thickness of the structure.
Smooth to the buncher or trowel: horizontally inside to the bare exterior of the future carpentry, then slope to the board bordering the formwork outside.
The bay support must extend 5 or 6 cm beyond the blocks.
For this, the board bordering the formwork on the outside side was plated on a 40 x 60 mm chevron.
4 Application of the plaster
Once the installation is complete, the blocks can remain exposed to the weather for several days without any problem.
The tarpaulin is only there to protect the passers-by or the surrounding works (terrace, passages, etc.).
Thin enough (6 mm), the first layer serves both gobetis and plaster body.
The recoil available on the scaffold determines the direction of the passes: vertical or horizontal.
Then pull the mortar up with a large knife (60 cm).
After two days, apply the topcoat, tinted and thicker (10 mm).
The dresser to the rule in order to blur the reliefs.
Finish with the straightener by fairly large movements, in a semicircle.
After 24 hours, the plaster shot enough to be scratched.
It gives it its final thickness (8 mm).
Laying hemp blocks in ITE: do or have it done?
Realize an ITE (external thermal insulation) then apply the corresponding finish is not within the reach of the first comer.
Even renting scaffolding requires working at least two or even three people and having one to two weeks off.
In addition, the application of the coating (manual or machine) requires some practice.
In all cases, in order to benefit from the various financial aids (tax credit, community grants, zero-rate eco-loans, etc.), it is necessary to call on a company for the supply and implementation of the insulation - company that also provides warranty for the work.
• Insulating blocks made from hemp
• Preformulated lime mortar (or 0-2 caliber fine plaster and NHL 3.5 lime)
• Galvanized tips Ø 3 x 70 mm
• VBA screws Ø 5 x 50 mm (fixing on wood) or peg Ø 6 x 50 mm or more (blocks, concrete...)
• Installation accessories (underbody profiles, lintel support brackets, offset shutter hinges, precadres for joinery...)
• 20 x 20 cm welded wire mesh or 6 or 8 mm twisted concrete iron and wire (for bay supports)
• Lime-based finishing plaster
• 10 x 10 mm fiberglass mesh frame