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A buried room, without opening on the outside, does not allow a good renewal of the ambient air resulting in moisture retention, responsible for mold among others. Well-ventilated air vents are able to clean the air.

Ventilate a basement

Practical advice

The ventilation capacity of a grate depends on its useful surface, indicated on it. For a living room, choose a grid of 100 to 150 cm2, preferably with mosquito net to prevent insects from entering.
● The positioning of the grid in relation to the plane of the wall must take into account the thickness of the coating that will cover it.
● A round grid fits easily to an existing wall. Just drill through and provide a PVC pipe length equal to the thickness of the wall.

Essential ventilation

It is by building a roof extension that this ventilation problem arose. The new basement, deeply buried, emerges only 80 cm from the ground level outside: it already has a low ventilation, common with that of the old building. But to allow a good air circulation, it is necessary to add a ventilation at the top. This is ensured by two mouths, made during the elevation of the load-bearing walls.
■ These two openings (one rectangular, the other circular) are located under the chaining of the basement. They are equipped on both sides with a grid to seal, whose useful surface conditions the supply of air in the room.

The rectangular mouth

At construction, the site is reserved leaving a free space between two blocks. Its dimensions correspond to those of grids increased by one centimeter around the perimeter, for the purpose of sealing. Equipped with a mosquito net, the grids have a useful surface of 150 cm2.

■ To achieve the air passage, the trick is to deposit in the reservation two superimposed polystyrene blocks corresponding substantially to the height of the grid. Two cleats forming formwork are then clamped on each side by clamps, aligning them on the upper edges of the blocks. After having placed two Ø 6 mm concrete reinforcing bars inside this small formwork, the remaining space is filled with a concrete composed of one volume of cement, for two of sand and two of chippings.
■ The concrete is vibrated by patting the cleats with the mallet, then left to "shoot" for two days. The formwork is then removed and the polystyrene removed, to complete the construction of the wall. Grids are sealed only after the masonry is finished.

Round mouth

The method is a little different, because the grids of Ø 100 or 125 mm can fit on a section of PVC tube of equivalent diameter. With a length of 200 mm, it is flared at each end to adapt the collar of the grids. The operation is carried out by heat stripper, with the help of a pot of flowers of suitable diameter and taper. Before cooling, each grid is positioned on its flared end and then sealed directly without formwork.

Install a rectangular mouth

Install a rectangular mouth

After determining the location of the air vent, reserve between the two blocks a space equal to the length of the grid, plus 1 cm on each side to seal it.

Materialize the volume of the mouth

Materialize the volume of the mouth

Place in the slot thus formed two blocks of polystyrene corresponding to the height of the grid. This parallelepiped materializes the volume of the mouth, therefore the passage of air.

Fill with concrete

Fill with concrete

Block on both sides, with clamps, two cleats aligned on the top of the blocks. After having reinforced the formwork (irons Ø 6mm), fill it with vibrated concrete with the mallet.

Disassemble the formwork

Disassemble the formwork

Once the concrete has set, remove the formwork and remove the polystyrene with a sharp tool. You can then finish raising the wall or run the chaining.

Seal the grid

Seal the grid

Seal the grill around its circumference with a cement seal. If necessary, make sure to slightly protrude front to compensate for the thickness of the finishing plaster.

Install a round mouth

Install a round mouth

Cut a piece of PVC tube with the same diameter as the round grid and of length equal to a block of block. Then soften it at each end with a heat gun.

Prepare the pipe

Prepare the pipe

Heat each end evenly and put in a flower pot of suitable shape and size. It must then be able to fit the flange of the grid into the flare.

Fit and push the collar

Fit and push the collar

Before cooling the PVC, push the flange completely into its flare: the junction must be a little tight. You can also fix the grid with a plastic glue.

Seal with mortar

Seal with mortar

Position the assembly at the desired location and seal it as is with cement mortar. Unlike the rectangular mouth, you do not need to wait for the plug to finish the wall.


Video Instruction: How to Properly Ventilate Your Basement