Metal Roof Cornice, Its Structure And Purpose, As Well As Design And Installation Features

2024 Author: Bailey Albertson | [email protected]. Last modified: 2024-01-17 22:26

Metal roof cornice, its structure, purpose, calculation and installation

Roof cornice is one of the most important elements of the roof. This structure protects the walls of the house and the blind area from atmospheric precipitation, and it is on it that the gutters of the drainage system are attached. Correctly mounted cornice protects the rafters, battens and frontal boards from moisture. Finishing the eaves box with soffits or other materials makes it possible to organize effective ventilation of the under-roof space, which reduces the likelihood of roof icing. It is important to know the purpose of the cornice, its structure, as well as methods of calculating and installing this part of the roofing.

Content

• 1 Metal roof cornice and its purpose

  1.1 Construction of a metal roof eaves

• 2 Size of metal roof eaves

  2.1 How to lengthen a metal roof cornice

• 3 Calculation of the eaves of the roof from metal

  3.1 Table: effective sheet area of metal tiles

• 4 Installation of metal roof eaves

  • 4.1 How to make a do-it-yourself eaves on a roof made of metal tiles

    4.1.1 Photo gallery: options for arranging the cornice

  • 4.2 Video: installation of spotlights
• 5 Reviews of builders on how to install eaves

Metal roof cornice and its purpose

A reliable roof keeps the house from rain, snow and melt water. Along with the ridge and slopes, the cornice fulfills its part of the protective functions and is an important element of the roofing structure. First of all, you need to understand what a cornice is, and then determine what it is for.

A cornice is a part of the roof slope from the lower edge to the intersection of the rafters with the outer walls of the house

Eaves overhangs are usually hemmed with materials that provide ventilation of the under-roof space and are in harmony with the roofing

There is a concept of eaves overhang, which is the distance from the wall of the house to the lower edge of the metal tile. Its length depends on the snow load, the slope of the slope, the height of the building and the architectural solution and is chosen in the range from 40 to 100 cm.

The cornice performs the following functions:

• protection of the walls of the house from precipitation and melt water;
• ensuring the safety of the blind area of the building foundation;
• protection of the rafter system, lathing and frontal boards from moisture;
• ventilation of the roof space;
• creating a solid, rigid structure between the overhang and the wall of the house;
• provision of drainage using eaves and gutters;
• wind protection of the roof;
• giving the roof an aesthetic, complete appearance.

It is important at the design stage to take into account all the features of the functioning of the cornice elements, since the service life of the house itself and the roofing, as well as the cost of the roof, depend on this

The device of the eaves of the roof from metal

The construction of a metal roof can be made in different ways, the choice of a specific option depends on the needs of the owner. The factors influencing the decision can be cost savings, the need for a living space in the attic, or something else. The cornice is a continuation of the ramp and consists of the same roofing cake as the entire roof, but it also serves other functions. The overhang of the rafter leg, due to the increased load, needs an additional stiffness unit, which is provided by the removal of the brickwork or by the beam of the eaves box. Thus, a metal roof cornice consists of the following elements:

• overhang of the rafter leg with the mounted crate;
• waterproofing film for draining condensate from the inner surface of the metal tile, which is attached under the crate;
• vertical frontal board, which is mounted at the ends of the rafters;

• horizontal and vertical boards of the eaves box, creating a rigid triangular structure between the rafters and the wall of the building;

  

  The frame of the eaves box is a rigid triangle, consisting of a part of the rafter leg, a horizontal filing board and a vertical stand

• curly cornice strip, which is attached to the bottom board of the crate and to the frontal board;
• brackets with drainage gutter;
• metal roofing sheets;
• lathing of the eaves box;

• fastening frontal F-strip and slotted J-strip;

  

  Soffits are installed in grooves of special strips with profiles of Latin letters F and J

• perforated soffit or other finishing material.

There are simpler cornice structures that require less material and, accordingly, are cheaper, but the degree of protection of the walls of the house and wooden roofing elements is much lower. It is important to note that the warranty service life of metal roofing from a number of manufacturers reaches 50 years, which means that a correctly mounted cornice should serve as long.

The size of the eaves of the roof from metal

The length of the eaves is determined by a number of factors that influence the choice of the optimal overhang size. The intensity of precipitation, the annual wind rose, the height of the building and the place of development are important here. For a metal roof, the choice is made on the basis of:

• an architectural solution that determines the general appearance of the house and the configuration of various roof slopes;
• the presence of a residential attic room;
• the prevailing wind direction in the region and the location of the building (forest or open space);
• the amount of rainfall and snow load;
• slope angle;
• width of the foundation blind area;
• the presence of a drainage system.

To select the optimal angle of inclination of the slopes, it is necessary to take into account all these factors, since the smaller the angle of inclination, the longer the length of the cornice should be. In regions with frequent and heavy snowfalls, the length of the cornice reaches 100 cm, and in areas with little precipitation, the width of the overhang is chosen from 50 to 70 cm. SNiP II-26-76 recommends that on metal roofs with an unorganized drainage system, remove the cornice from the outer wall at a distance not less than 60 cm. Such removal of the box ensures the safety of the walls of the building and the blind area of the foundation.

The size of the eaves overhang in areas with heavy snowfalls is made more than a meter, for quieter areas according to SNiP, a length of 60 cm is recommended

The recommendations for the construction of rural houses state that the minimum width of the cornice should be in the range from 450 to 550 mm. This is true for brick houses and all types of concrete blocks. Wooden houses should be equipped with more massive eaves, the length of which should be more than 55 cm.

In any case, when designing low-rise buildings, it will be safer to use the services of professionals who can calculate the dimensions of the cornice according to regulatory documents. In order to preserve the walls, blind areas and for the best wind protection, it is important not to pursue savings, but to make, albeit a more expensive, but optimal choice.

How to lengthen a metal roof cornice

The rafter group is made from standard lumber, the length of which does not exceed six meters. If the length of the roof slope from the ridge to the eaves exceeds this size, it becomes necessary to lengthen the rafters. This is achieved in the following ways:

• installation of broken composite rafters with different angles of inclination of slope sections, typical for residential attic rooms;
• connecting two rafters in the middle of the ramp and reinforcing the joint with vertical beams or corner braces;
• elongation of the cornice by filly.

You can increase the length of the cornice with the help of filly - pieces of board connected to the rafters with an overlap

Variants of split rafters are used on long ramps, and it must be borne in mind that they are heavy and create pressure on the load-bearing walls of the building. Therefore, the load should be distributed evenly using struts, struts and other structural elements. With a small length of slopes, it is more preferable to lengthen the rafters with the help of fillies, since they weigh a little and do not exert significant pressure on the walls of the house.

It is important to provide a rigid fastening of the fillies by a reliable connection to the rafters and using a cornice box to reduce the possible snow load on the cornice structure

Calculation of the eaves of a metal roof

The calculation of the amount of roofing material for the eaves, as a rule, is not done separately and is considered in the context of calculating the total consumption of material for the roof slope. If it is necessary to calculate separately the consumption of metal tiles for arranging the cornice, then it must be borne in mind that the overlap of the next sheet in height is 130 mm. The overlap of adjacent sheets is 80 mm, which, with the standard size of the metal tile 1180 mm, gives a useful width of 1100 mm. The choice of the length of the sheet depends on the wishes of the customer, but the standard sizes are:

• 480 mm;
• 1180 mm;
• 2230 mm;
• 3630 mm.

Taking into account the overlaps, the usable area can be calculated from the presented tabular data.

Table: Effective sheet area of metal tiles

Standard length, mm	Useful area, m 2
480	0.528
1180	1.155
2230	2.31
3630	3.85

It is possible to determine the amount of roofing material required for the cornice by calculating the formula S _k = L _c.s. ∙ (L _d + 2 ∙ L _f.s.), where:

• S _k - cornice area;
• L _c.c. - the length of the eaves;
• L _d - the length of the house;
• L _f.s. - the length of the gable overhang.

It is important to take into account the allowance required for cutting sheets, especially with complex slopes. It is usually chosen in the range from 10 to 20% of the area of the slope, depending on the configuration of the roof.

The rest of the eaves overhangs are calculated as follows:

1. The dimensions of the fillies depend on the length of the cornice and the number of rafters, and the fasteners are selected depending on the method of fixation and are calculated individually for each roof.
2. The length and width of the frontal board are selected so that it covers the overhangs of the rafters.
3. The length of the cornice strip is selected taking into account an overlap of 5–10 cm and is equal to the length of the slope with gable overhangs. The finishing material for the cornice box is calculated depending on the length of the cornice and the distance from the frontal board to the wall of the building, taking into account the installation of fastening strips for various purposes (F- and J-strips).

Separately, it is necessary to dwell on the calculation of the number of brackets for the gutters of the gutter system. Manufacturers, on the basis of SNiP standards, recommend installing them every 50–70 cm, observing a slope of 3–5 mm per running meter of the gutter.

Brackets for gutters, depending on the type of system, are attached to the front board or to the first board of the crate

Installation of metal roof eaves

You need to start the installation of the roofing with the arrangement of the cornice. This painstaking work is carried out from scaffolding equipped with safe handrails and safety ropes. At the beginning of the installation, all the wooden structural elements of the cornice are treated with a compound that prevents damage to the wood from various external influences. Then all the necessary markup is performed and materials, tools and equipment are prepared. When installing the eaves, you will need the following tools:

1. Drawing and measuring tool.
2. Chisel and hammer, hand saw.
3. Stairs.
4. Electrical extension cord.
5. Screwdriver, drill, perforator.
6. Electric saw, jigsaw, metal cutting tool.
7. Additional elements, fastening material.
8. Helmet, overalls, gloves.

The eaves installation works are carried out at a height, therefore, they require compliance with safety regulations, assembly is carried out only with a serviceable power tool, and a fence with warning signs is placed on the ground

If all the mandatory requirements are met, the metal roof cornice can be assembled independently without the involvement of professional personnel, which will provide significant cost savings.

How to make a cornice on a roof from metal tiles with your own hands

Do-it-yourself work brings pleasure and confidence that it was carried out with high quality and in compliance with technology. There is nothing complicated in the device of the cornice, and almost every man can use the tool. It is necessary at the moment of doubt about the correct sequence of installation operations to seek advice from roofers. Work should be performed by at least two people and preferably in calm weather.

Photo gallery: options for arranging the cornice

The waterproofing film is attached to the drip tip with double-sided tape

The drip bar is installed so that it goes into the gutter for a length of 1/3 of its diameter

The ventilation gap between the roofing and the waterproofing film on the side of the eaves slope is closed with a perforated tape

It is necessary to mount the eaves of a metal roof in the following sequence:

1. The rafters are aligned vertically and with the help of corners are connected with a frontal board.

   

   The frontal board is attached to the ends of the rafters using corners

2. An L-profile is installed on the frontal board for facing the lower plane of the roof box.

3. Brackets for gutters are attached along a stretched cord, which sets the angle of inclination of the drainage system.

   

   Brackets for gutters are installed along a tensioned cord with an inclination towards the drainage funnel

4. The waterproofing film is attached with double-sided roofing tape to the drip, mounted on the upper cut of the frontal board to ensure the drainage of condensate from the metal tile.

   

   The waterproofing film is attached with tape to the drip tray, so condensation will drain directly into the gutter

5. A cornice strip is mounted to the bottom board of the crate with an overlap of 5 cm so as to ensure the drainage of moisture from the roof into the gutter.

6. On top of the plank, sheets of metal tile are installed on the cornice, and on them - gable windproof planks.

   

   Gable strips protect metal tiles from wind and water

7. On the wall of the house, at the level of the lower edge of the frontal board, a bar is attached to which the J-bar is mounted coaxially with the L-bar.

8. Perforated finishing material (soffit, corrugated board or other of your choice) is installed between them.

   

   Soffits are mounted in the grooves of the L- and F-planks

9. For greater strength, you can install jumpers 50-70 cm between the frontal board and the wall of the house to prevent the sheets of finishing material from bending.

It is important to treat the places for cutting additional elements and sheets of metal tiles with anti-corrosion mastic

Video: installation of spotlights

Reviews of builders on how to install eaves

When working independently on cornices, the question of ventilation of the under-roof space often arises. The greatest interest on the forums is caused by the topics of the correct installation of waterproofing film and the effectiveness of the use of spotlights as a finishing material. Let's dwell on these popular questions.

As we can see, many novice builders are able to make a metal roof cornice with their own hands, and the lack of experience is compensated by the advice of experienced professionals.

We talked about what a metal roof cornice is, what is its structure, purpose, how to calculate the material and install the cornice overhang, as well as how to lengthen the rafter group. Subject to the safety rules, as well as performing a step-by-step sequence of operations, it is quite possible to cope with the installation of the cornice yourself. Based on the rich experience of professional designers and roofers, we have provided complete information and we hope that it will help you in the construction of a metal roof.