Building roof

1. Roof function

The roof is an integral part of the outer protection system of the building. The roof generally refers to the surface of the roof of the building, and the plane refers to the area surrounded by walls, gables or eaves. The roof should have the following functions.

(1) Block the wind and rain

The most basic function of the roof is to be able to protect against wind and rain and prevent wind, frost, rain and snow from invading the room. Therefore, the roof must be waterproofed, which is the main measure to ensure the basic function. Rainwater should be discharged from the roof smoothly to reduce the difficulty of waterproofing, so roof drainage is an important supplement to roof waterproofing.

(2) Keep warm and heat to reduce energy consumption

Modern architecture requires a comfortable living and working environment to reduce the impact of the outdoor environment on indoor temperature and humidity, which is also the basic functional requirement of the roof. The roof is directly exposed to heat and rain. In summer, the surface temperature of the roof can reach more than 70℃ when exposed to the sun. In winter, the surface temperature of the roof is very low when there is snow, and the surface temperature in the northern cold areas is as low as minus 30℃. Modern buildings have HVAC systems to regulate temperature and humidity, so improving the insulation requirements of the roof and ensuring the effectiveness of the insulation function of the roof can improve the thermal resistance of the roof and reduce the energy consumption of the HVAC system, which is one of the main measures to save energy.

(3) Protect the structure and extend the service life of the structure to protect against wind and rain

In addition to waterproofing and heat insulation, the roof also assumes the protective function of the roof structure. Whether it is a reinforced concrete structure, a wooden structure or a steel structure, it will cause serious diseases under the erosion of fluid seepage. Reinforced concrete structures will accelerate the carbonization of concrete and alkali aggregate reaction to shorten the service life of concrete. Rebar rust and expansion will cause concrete to crack; wood structural components will rot; steel structural components will rust. The final result will shorten the service life of the component and reduce the bearing capacity of the component. The waterproof and thermal insulation functions of the roof can play a good protective role on the structure.

(4) Use and beautify functions

Nowadays, more and more roofs provide auxiliary functions for buildings and become used roofs, such as roof parking lots, roof gardens, roof sports venues, etc.

In addition, modern architecture has higher and higher requirements for aesthetics. As the fifth facade of the building, the roof also has the requirements to beautify the building and the environment. Most of the roofs of low-rise or multi-storey buildings are exposed to the vision of users of high-rise buildings, and the requirements for beauty are higher.

2. The structural hierarchy of the roof

In the roof with reinforced concrete as the structural plate, in order to realize the basic functions of the roof, there will be a waterproof layer and an insulation layer on the roof structure layer. For the necessity of drainage, the non-structural slope roof needs to be set up; in addition, there will be auxiliary structural layers, such as leveling layer, protective layer, isolation layer, and steam insulation. Layers, etc.; there will be use surface layers on the roof, and there will be planting layers on the planting roof, etc. The waterproof layer and the insulation layer are the basic functional requirements, which are very rich in content and need to be introduced in detail separately. The following only introduces the functions and practices of other structural levels.

Find the slope

(1) Find the slope

Anti-discharge combination is one of the basic principles of roof waterproofing. Smooth drainage is the basic requirement of waterproofing, which requires the roof to have a certain slope. The roof slope should give priority to structural slope, which can reduce the structural level and is conducive to the realization of roof function. If you can't find the slope of the roof with complex plane shapes and the ceiling in the top floor, etc., you can use lightweight materials to find the slope. Lightweight materials are generally made of cheap and easy-to-get materials, such as slag, cement expanded perlite, cement expanded leech, ceramic grain concrete, aerated concrete, etc., but these materials are all materials with a high water absorption rate. The stirring water and rainwater accumulated in the construction are easy to produce bubbles in the slope layer, which needs to be separately Set up an exhaust steam structure to solve it.

Find a flat floor

(2) Find a flat layer

The purpose of setting the level layer is to ensure the construction and engineering quality of the waterproof layer or insulation layer. It is not the structural layer that must be set on the roof. When it can be set or not, it is better not to set it. For example, when making a flexible waterproof layer on the cast-in-place reinforced concrete roof panel, it is appropriate to directly pound and wipe it. When paving the plate-shaped insulation material, it can also not Set up a flat floor.

When you need to set up a leveling layer, you should set up a C20 fine stone concrete leveling layer on the soft or cracked base layer, and add rebar mesh if necessary to improve the integrity. Cement mortar leveling layer is generally set on other grass-roots, and the matching ratio is generally cement: sand = 1:2.5 to 1:3, or M15 premixed ground mortar is used.

Protective layer

(3) Protective layer

The purpose of the protective layer is to extend the service life of the waterproof layer and the insulation layer, reduce the erosion of waterproof materials and insulation materials by ultraviolet rays, ozone, acid and alkali and other media, and prevent the damage of the waterproof layer and insulation layer by external forces. The roof should be reinforced with reinforced concrete or block materials as the protective layer. Light-colored paints, aluminum foil, mineral granules, cement mortar, etc. can be used as protective layers for the roof according to the type of waterproof layer, and block materials or fine stone concrete can be used for better protection.

(4) Isolation layer

Steam barrier layer

(5) Steam barrier layer

The purpose of setting up a steam barrier layer is to prevent indoor moisture and condensation of the roof structure from invading the moisture-absorbing insulation layer to reduce the insulation effect. Therefore, a large amount of water vapor is often generated indoors. For example, the roof of public bathrooms, large kitchens and other buildings should be equipped with a steam insulation layer; in severe cold and cold areas, condensation may occur between the roof insulation layer and the structural layer. A steam barrier should be set up at the same time. The steam barrier layer can be selected with waterproof coils or waterproof coatings with good watertightness and airtightness.

(6) Use the surface layer

There are different methods of using the roof according to the purpose. When used as a parking lot, the surface layer should be reinforced concrete with a thickness of about 80mm. Only when used as a superior, floor tiles, outdoor wooden floors, etc. can be laid as needed. Plastic can also be laid on a reinforced concrete protective layer with a thickness of about 80mm, which can be used as a runway and a stadium. It can also be designed as a roof garden, which can not only beautify the environment, but also allow people to rest.

Planting layer

(7) Planting layer

There must be flowers and plants in the roof garden, so there must be a planting layer. In fact, the planting roof is a system, and it is not enough to have a planting layer. In addition to the slope layer, insulation layer, leveling layer, waterproof layer, protective layer and other layers, the planting roof also needs to have drainage layer, filter layer, planting soil layer and vegetation layer.

The function of the storage and drainage layer is that when there is abundant rain, it can drain most of the rainwater to avoid the planting layer being blistered and causing plant roots to rot; at the same time, it has a certain water storage capacity, which can provide some of the water needed for plant survival on consecutive sunny days; the storage and drainage layer generally adopts a mesh-like intertwined or concave and convex storage and drainage plate; there are also Graded crushed stone or ceramic grains with a particle size of 10mm to 25mm and pebbles with a particle size of 25mm to 40mm are used, and the paving thickness is not less than 100mm. These practices have almost no water storage capacity and are only used as drainage layers.

The function of the filter layer is to prevent the planting medium from being washed away by rainwater. Generally, polyester non-woven fabric with a mass of not less than 200g/m2 per unit area is used.

The planting soil layer includes pastoral soil, improved soil and inorganic planting soil, etc. The thickness of the planting soil is determined according to the plant type. The planting lawn and vegetation is 100mm to 200mm, the planting shrub is 300mm to 600mm, and the planting tree is not less than 600mm.

Roof vegetation should be planted with lawns, ground covers and dwarf shrubs, and should not be planted with tall, fast-growing trees and plants with well-developed roots.

The planting roof must have root blocking measures to prevent the puncture of the plant root system, such as setting up a root-resistant waterproof layer under the storage and drainage layer, or setting up a separate root blocking layer to avoid leakage caused by the plant root system penetrating the waterproof layer.

The above are the common structural levels in the roof. These structural levels do not necessarily appear on every roof. Some levels, such as the leveling layer, may also appear many times in one roof. When designing the roof, the designer should select and combine according to the nature, use function, roof form, climatic conditions and other factors of the building to form a reasonable roof construction practice.