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In an old house, windows are often small or insufficient in number. To maximize the light input, the solution is to drill the front wall to integrate a French window...

Install a French window in front

Difficulty: 4/4
Cost: € 2,000 (excluding carpentry)
Time: 3 days (to 2 people)
Equipment: plumb bob, spirit level, measuring tape, mallet, chisel, pencil, trowel, mortar laying, trowel, mason ruler, form hammer, props, hammer chisel, large diameter grinder or grinder, wheelbarrow, mason trestles and planks wood, concrete mixer

The creation of an opening in the facade of an old building is not always easy when the wall is thick (60 cm). It implies to be well informed (do not hesitate to seek the advice of a professional) and get the appropriate tools (jackhammer, grinder, was sufficient in number...) to work in good conditions. Otherwise, it is always possible to rent the appropriate equipment (professional rental or equipment rental sites between individuals).

Create an opening: a prior approach

Before starting the work, it is necessary to deposit a building permit in town hall since the opening creates a modification of the original facade. The house dates from the seventeenth century, the owners wanted to keep here the architectural style of the region (the frame is stone country).
The period of instruction passed or the authorization obtained, it is necessary to think of posting the sign of building site in limit of property to make run the period of recourse to the thirds. After this period (one month), work can begin.

Create a bay window in a stone facade: facade

Learn more about this theme?
Find a special file in System D n° 858 (July 2017)
Check it out

Opening in the rules

The removal of masonry generates noise, dust and rubble. In the case presented here, it is carried out at the beginning of the renovation of the house so as not to interfere with the interior fittings.
After a reflective shoring to create points of support and load reports, the facade is open to the drill and chisel, the dimensions required by the future French window (260 x 255 cm). The stones bordering the table of the future bay are cut to the desired dimensions to integrate the limestone blocks of the frame, placed alternately vertically then horizontally.

Opening of the facade wall

open a stone facade

After shoring, remove the masonry from the chisel or jackhammer.
Start at the top and remove the rubble as you advance.

sitting with cement mortar

On the previously poured concrete slab, make a cement mortar base at each end of the opening to receive the first stones.

build right

Check alignment and plumb.

use a telescopic rigging rule

On each side of the opening, place a telescopic wedging rule vertically, taking care to check its position on the level.

grinder grinder to cut stone

At the grinder, make cuts in the existing stone respecting the pre-set pattern.

enlarge an opening in a stone wall

Advance carefully to the chisel to the lines of the bleedings. These were made taking into account the future position of the stones: vertical or horizontal.

finishing with a hammer and chisel

Treat the finish with the mallet and chisel.

Assembly of tables

to mount the paintings of a window frame

Prepare cement mortar in a trough and then coat the base with a trowel.
Place the first stone vertically on the edge with the aid of the chocking rule.

fill the gaps in a window frame

Fill the gap between the existing façade wall and the stone installed with cement-cut demolition stone pieces.

place a window frame in a stone wall

Coat the cement mortar with the horizontal slice of the second stone and place it on the first stone.
Check the plumb and alignment.

coat a stone window opening with mortar

After preparing lime mortar in a trough, trowel the following reservations.
Coat the third cement mortar stone on its edge and place it.

mount a stone window frame

Continue assembling the frame as before, alternating the horizontal and vertical installation of the stones.
Proceed simultaneously on each side and check the alignment and gauge regularly.

Installation of the stone lintel

shuttering for window opening

Make the formwork of the future stone lintel.
Use props and planks held by masonry nails and clamps. Be precise in measurements and cuts.

formwork boards

Place on the vertical boards a horizontal board. Check that its thickness is 3 mm above the framing stones of the ends.

Create a bay window in a stone facade: window

Locate the pencil axis and place the center stone on the board.

Create a bay window in a stone facade: mortar

Coat the slice of the first stone with cement mortar and then place it on the shuttering board against the central stone.

Create a bay window in a stone facade: stone

Continue laying the lintel stones as before. These being numbered, there is no risk of being mistaken.
Repeat the operation on the other side of the central stone.

Create a bay window in a stone facade: window

The stones thus sealed to each other create a rigid section (keystone) which allows to hold the entire lintel.
Check the alignment over the entire length with a large ruler.

Create a bay window in a stone facade: mortar

With stones from the demolition, fill the top of the lintel by creating a reservation for the threshold.
Use lime mortar, making sure to cross the joints for a good hold.

Pose the window sill

Pose the window sill

At the grinder, cut to size the stone used to support the opening of the first floor.

Create a bay window in a stone facade: facade

Fill the height above the lintel with stones, then make a bed of lime mortar for sealing the threshold.

Create a bay window in a stone facade: stone

Place the stone ledge on the mortar bed and then adjust it so that it is level with the floor of the floor.
After drying, grout the stones between the lintel and the support.



When assembling the framing stones, if it is difficult to get a plumb, insert a small wooden wedge with a hammer and adjust the stone.
Before the lime mortar is fully dried, use a piece of wood to dig the peripheral joints a few centimeters to subsequently grout.


• Cement mortar
• Hydraulic lime grouting mortar
• Local career sand
• Yellow limestone stones of the country
• Wooden wedges
• Formwork boards

Video Instruction: How to Create Custom Stone Window Sills