Installation of external window sills is an extremely important stage in the process of insulating a building.
Learn how to properly prepare for it: what exactly you should pay attention to during the assembly work. Here are some great tips you should read before mounting exterior window sills.
The window sill must be wide enough to protrude about 4 cm outside the face of the wall and its plane should be inclined at an angle of about 5° so that the water does not accumulate on its surface but flows with the gravity to the outer edge. Thanks to that, falling drops will not dampen the render.
Correctly profiled outer edge of the window sill, called gorge, prevents moistening of the window sill's bottom while draining the water outside the face of the facade. All joints of the window sill and the window frame must be sealed.
The sill tips can not rigidly contact the window opening due to thermal expansion. Temperature fluctuations cause changes in the sill dimensions, which can consequently lead to stresses and cracks in the connection with the thermal insulation system at the corner of the window sills.
So when choosing a sill you have to leave a distance at both ends of the sill, proportional to its length. For a safe setting of the expansion joints, plastic end caps have to be installed at the ends of metal window sills. They are also performing the function of aesthetic finish.
The edge of the window sill facing the window frame should be inserted in a specially designed cut and additionally fastened mechanically with screws. On the other hand, if the window sill overlaps the lower window frame, it is necessary to seal the joint with a butyl adhesive tape and a permanently elastic bond. It is not allowed to cover the moisture vents on the frame.
On the lower edge of the window compartment, an additional strip can be added to the strip of expanded self-adhesive tape. Until the end of the insulation works, window sills should be protected with a protective film.
In the window niches when the window does not face the outer surface of the wall, it is advisable to use a polystyrene foam approximately 2-4cm thick for insulation. It is also recommended to dispose of the old plastering on the wall. In order to minimise the formation of thermal bridges in these locations, thermal insulation with the lowest thermal conductivity, for example, graphite styrofoam, can be used.
What could be the effects of improper installation of external windowsills?