Parapets Capping and Windows Sill

Parapet is an extension of wall at top roof, balcony, stairs or a walkway, used as a guard rails. As the parapet function is guard rails, then it hasn’t been less than 80 cm. or it has to install handrail over it. Parapet is covered with capping to protect plaster, stone cladding, curtain wall or any other wall finishing material from water leaking. For same reason windows sill is used for the bottom side. The windows sill and parapets capping could make in different details and from different materials. This post will discuss capping and sill materials, details and recommendations for well installation.

Parapet capping for flower box, made of Palestinian marble, Gaza 2020
Parapet capping for flower box, made of Palestinian marble, Gaza 2020

Design Details

There are several design details for parapet capping and windows sills. There are different designs however they all have the same functions. Here we will introduce some of the parapets capping and windows sill design details.

sill and capping types : straight, round edge, double edge, round double edge, By Zahi Alrayyes 2020
sill and capping types : straight, round edge, double edge, round double edge, By Zahi Alrayyes 2020

Straight: simple but need to chamfer the corners to make the sharp edges safe.
Round edge: for better appearance and for classical style use a round edge capping and sills.
Double: for larger scale use double marble pieces to have thicker sill. This suite residential and commercial modern buildings.
Double round edge: for lavishness or large scale, use double round edges, it has extra cost than previous choices. Typically used for villas and high quality residential buildings.

Double marble emperador meduim sill
Double marble emperador meduim sill, Gaza Alhelou Station 2018

How to Select the Capping and Sill Materials 

Parapet capping and sill material has to have a low water absorption ratio and to resist weathering. So marble, granite, aluminum and concrete are suitable materials to use. 

Marble is a suitable material for parapets capping and windows sill. Select marble with low water absorbing ratio, also order pieces with more length to have fewer connections between marbles, usually it cut into 150 cm length. The connection will be filled with cement or marble adhesive. Marble is cheap, easy to install and to decorate. Marble effecting from weathering, marble veins and pores will enlarge. Tiny veins will allow water to enter through the marble sill and capping. This problem fixed by either filling the pores and veins by cement or marble adhesive.

Marble capping has defect veins and pores from weathering that accrue water leaking, Gaza 2020
Marble capping has defect veins and pores from weathering that accrue water leaking, Gaza 2020

Granite has low water absorption ratio and can resist weathering more than marble. But usually granite colors are dark and light colors have a high price. Also granite doesn’t have many pores that’s perfect with water absorption but cement mortar won’t bond well it. Therefore there are some chemical products we use for granite backside in order to make it rough for better bonding with mortar. This problem appears more after installing fixtures over the granite sill and capping, like handrail. Where opening a hole in granite after installation or even screws will shake the sill and disassemble it from cement mortar. Therefore we recommend to open holes in a method that won’t shake the sill and capping like, water jet.

Double round edge from Rosa Betta marble, Gaza 2020
Double round edge from Rosa Betta marble, Gaza 2020

Mosaic and terrazzo is a white cement material that cast in place. This will give more bonding to the parapet capping and sills. In my view point it looks nice when it has a light large stones like Perlato size 5. Mosaic and terrazzo is cheap comparing to marble and granite. Also it fit stairs and curved parapet. Long length sills requires expansion joint, it’s made from glass as shown in the following photo.

handrail parapet capping from mosaic, by Almamoura Company, Gaza 2020
handrail parapet capping from mosaic, by Almamoura Company, Gaza 2020

Installing Parapets Capping and Windows Sill Recommendations:

  • Install parapets capping and windows sill after the block works, and stone wall cladding and before plastering works. Paint the sills with lime and sand to avoid cement stick to marble during plaster and painting works.
  • Sill size, for width leave a cm or two for plaster works thickness, and leave 3 cm for tiles works. For the outside, leave two more centimeters to have a cantilevered sill. The cantilevered sill will allow water to slide away from the walls to prevent water dripping the wall. Also prevent water dripping by a grove in the bottom surface of the sill or capping. 
  • The capping or sill length has to be straight leveled. For the width make few millimeters slope toward the outside to allow water slide outside instead of leaking.
  • For corners use 45 or diagonal connections, they look nice and will bond together better than any other connection.
Parapets capping corner connections, Gaza 2020
Parapets capping corner connections, Gaza 2020

FAQs

What capping to use for curtain walls?

For curtain walls and aluminum composite panels  facade use aluminum capping. Aluminum capping can be done by a certain profile or customized from ACP. Remember capping and sill function is to prevent water leaking and the material has to prevent weathering, then aluminum is perfect.