Roof Cornice, Its Types And Purpose, As Well As Calculation And Installation Features

2024 Author: Bailey Albertson | [email protected]. Last modified: 2023-12-17 12:53

If the weather is outside the window, do not let it into your warm house: do it yourself roof cornice

Installation of roofing does not end with the installation of roofing. Now you need to take care of the aesthetic appearance of the roof and, most importantly, enhance its protective functions. And this is the task of the cornices. That is why they need to be installed and hemmed. What are the cornices, what is their role and how to arrange the cornice yourself, we will talk in this article.

Content

• 1 Roof cornice and its purpose

  1.1 Video: how the eaves overhang should look like

• 2 Types of eaves

  • 2.1 The main types of roof overhangs according to the arrangement method

    • 2.1.1 Wall (cornice) overhangs
    • 2.1.2 Gable overhangs
    • 2.1.3 Video: how to make a large gable overhang

• 3 Roof eaves size

  • 3.1 How to lengthen the eaves on the roof

    3.1.1 Video: the formation of the eaves

• 4 Calculation of the eaves of the roof

  • 4.1 Optimal size
  • 4.2 Regulatory requirements for the dimensions of roof eaves

• 5 Installation of the eaves

  • 5.1 Video: a new way of installing the eaves overhang - beauty is in the details

  • 5.2 Do-it-yourself roof cornice

    5.2.1 Video: do-it-yourself roof and gable cornice

• 6 Sewing roof eaves

  • 6.1 Materials for filing

    6.1.1 Video: filing overhangs, which spotlights to choose

• 7 User reviews about the device of roof overhangs
• 8 Video: eaves of the roof of a house - construction and hemming

Roof cornice and its purpose

Roof cornice - the part of the roof that protrudes beyond the vertical enclosing structures of the house and protects them from precipitation. In addition, the cornices provide natural ventilation of the under-roof space, prevent the accumulation of condensate, the formation of fungus, mold and the wetting of the insulation.

Well-equipped roof eaves reliably protect the main structures of the house from moisture

Thus, the role of these small roof elements is very significant. They serve as a guarantee of the longevity of the rafter system and covering material, as well as a comfortable microclimate in the house. And their skillful design with beautiful materials gives a complete attractive look to the entire building.

The design of roof overhangs in harmony with the exterior of the house gives a very beautiful result - the house looks elegant and picturesque

Almost any roof, regardless of its configuration, has cornices. The only exceptions can be roofs equipped with parapets or super stylish designs such as canopies.

On roofs in the form of awnings, roof overhangs are not equipped, because such a structure itself is designed to protect the building from getting wet

Video: how the eaves overhang should look like

Types of roof eaves

The construction of houses has a centuries-old history. At the same time, at all times, each developer not only paid tribute to the fashion trends of a particular era, but also sought to distinguish their housing from the general mass, give it individuality and improve performance.

Therefore, there are many varieties of roof cornices in terms of the way they are designed, but by design there are only two - cornice (horizontal) and pediment. They differ from each other in the technology of arrangement: horizontal (wall) overhangs are formed by the lower part of the slopes based on the rafters, and the pediment cornices - by the lateral (inclined) part of the slopes based on the open ends of the sheathing.

By the method of arrangement, roof overhangs are wall (cornices) and pediment

Moreover, both types are:

• hemmed or not hemmed;

• shortened or box-shaped.

  

  Eaves hemmed in any way give the roof a beautiful finished look

Here you can add another design option - mixed cornices - when a large roof has a different structure in different places. For example, a simple gable shape plus a hip (half-hip) plus a domed one, where shortened overhangs are made. Sometimes narrow overhangs are arranged over the dormer windows in the attic structures.

On complex roofs, mixed cornices are often equipped, using shortened overhangs in some places as decorative elements

Shortened cornices throughout the roof are extremely rare. They are more used as a design element, since such a configuration is good for builders, but does not fully fulfill its protective functions. Namely: does not protect (or protects little) the walls of the building, basement and foundation from moisture.

Eaves with shortened overhangs look stylish, but they do not fully protect the structure of the house from rain, wind and snow

As for the other types, the hemmed cornices are universal for any roofing structure, just like box-shaped ones.

Hemmed cornices give the house a well-groomed and sophisticated look and fit any roof structure

Non-sewn overhangs are ideal for rough, wide chalet roofs or medieval Tudor-style structures. Another option is in modern modern roofs, in which the rafter system is not simply taken out of the house, but a beautifully crafted one is literally displayed.

Unfitted cornices are arranged on wide, rough roofs, when the rafter system also serves as a decorating detail of the house

The main types of roof overhangs according to the arrangement method

Poorly made roof overhangs will nullify all efforts to equip the roof. In order for the costs of expensive roofing materials to be justified, you need to know how to properly install and process the cornices.

Wall (cornice) overhangs

1. Flush eaves overhang. That is, the rafter legs are not brought out beyond the boundaries of the walls. In this case, a drain board is mounted along the edges of the rafters. It serves for fixing gutters and draining water from the roof. Such a roof device allows you to save on the construction of the rafter system - less lumber is required. However, the walls remain unprotected, so you have to take care of very good roof ventilation and facade cladding.

   

   Installation of eaves overhangs flush emphasizes the strict and clear proportions of the house, but requires good ventilation of the roof space and high-quality facade cladding

2. The horizontal overhang of the open type is a lightweight technology and is often used - the rafter legs extend evenly beyond all walls. The gutter system is mounted on the side parts of the rafters or to their upper edges.

   

   Open-type horizontal roof eaves are used mainly on sweeping roofs with a slight slope, while the elements of the rafter system, which remain open, need high-quality treatment with antiseptics and a beautiful design

3. Closed roof cornice - sheathed distance between the walls and the rafter legs protruding beyond them. The device resembles a box with an empty triangular space inside. Closed cornices look neat and aesthetically pleasing, and the cladding matched harmoniously or in contrast to the facade gives the whole structure a special charm.

   

   Closed wall overhangs are most often used, since they hide all the elements of the rafter system and thus protect them well

Frontal overhangs

Gable overhangs are not involved in the ventilation of the roof space. However, for them, it is important to ensure reliable protection against moisture penetration and wind blowing through the sheathing boards. Gable overhangs can be protruding or flush, but must be well sealed.

An example of a house roof with wide gable overhangs that reliably protect the facade and basement from excessive atmospheric moisture

Methods for installing gable overhangs are determined by the weight of the roof:

1. The basis of overhangs is only lathing boards. This is the most common but weakest option.
2. The basis for fastening is a Mauerlat, a ridge bar and girders protruding from the walls by the amount of overhangs. This design is stiffer and is considered the best for the arrangement of overhangs.

Video: how to make a large gable overhang

Roof eaves size

It is difficult for non-professional developers to determine the required size of the eaves, if a house plan has not been drawn up in advance. Too small a ledge will cause the walls and foundations to get wet, as water accumulates near the house.

Then, it would seem, the wider the cornice, the drier the walls. But here, too, there are some nuances - the larger the overhang, the greater the windage, so hurricane winds can undermine the roof. Therefore, you need to look for the golden mean - the optimal size of the eaves for a particular building.

Good eaves overhangs are, in fact, an extension of the roof. Therefore, they are made taking into account the same parameters as when arranging a roof - they take into account the climate of the area, wind and snow loads, the structure of the roof and the house, the type of covering material, the layering of the roof, etc. Basically, you need to focus on:

1. Climatic features of a particular region - the amount of precipitation during the year, the strength of the winds and direction, snow cover. In snowy and mountainous areas, cornice overhangs are made with a width of one to three meters. And where hurricane winds prevail, the cornice ledges are much narrower, but not less than the minimum allowable size - 40-60 cm.
2. Roof slope - the steeper the slopes, the wider the cornice overhangs, which will make it possible to protect the walls and basement from splashing water that will roll off the roof. And, conversely, the flatter the roof, the narrower the eaves, since melt water will leave such a roof far from the walls of the house.
3. The proportions of the building. The wrong size of overhangs can visually distort the proportions of the house. For example, a flat roof with wide overhangs will make the structure squat, and a narrow cornice of a steep roof, on the contrary, will stretch the silhouette of the house.
4. Roof covering. Covering decking made of folded materials or bitumen requires more air circulation in the under-roof space. This means that you will need a larger volume of ventilation holes and, as a result, wider overhangs.

How to lengthen the eaves on the roof

Eaves overhangs in most cases are mounted on the open parts of the rafter legs. However, the length of the rafters is not always sufficient. Therefore, in case of shortage, they resort to:

1. To splicing the rafters with beams of the same section as the rafter legs. This is the easiest way to get the desired overhang length. However, this increases the weight of the frame, which means that there will be a much greater load on the walls and foundation. The rafters are spliced using the butt joint method using a special overlay made of board scraps according to the "oblique cut" scheme, when the contacting ends of the boards are cut at a certain angle. Another way is to join the boards with an overlap of 1 m.

   

   When connecting elements with an overlap, it is not required to observe the accuracy of cutting, and instead of nails, studs with washers and nuts can be used as fasteners

2. To lengthen the rafters with the help of fillies, on which the roof overhang is then equipped. Fillets are made from a thinner edged board, due to which this method is cheaper, and the frame is easier, despite the width of the cornices.

   

   Raising the rafter legs with the help of fillies allows, if necessary, to repair and replace structural parts without disassembling the entire roof

Experienced builders give preference to building rafter legs with the help of fillies, because in this case:

• significant savings on wood are achieved;
• the load on the structural elements of the house is reduced;
• less effort is required to output the eaves overhang line;
• it simplifies the replacement or repair of the structure in case of damage to any of its elements;

• it becomes possible to decorate overhangs.

  

  The use of carved filly for the arrangement of eaves will give the roof individuality, so such a roof and the house as a whole will not go unnoticed

In addition, if necessary, the filly can be installed not parallel to the rafters, but slightly horizontally, which will make the slope broken in this place. The result is a kind of springboard that will throw water away from the walls.

Video: the formation of a cornice overhang

Calculation of the eaves of the roof

The key function of roof overhangs is to protect the walls of the building from water collected on the roof after melting snow and precipitation, as well as falling on the walls during oblique rain. In addition, the overhangs also perform a decorative function, but it does not play a special role in determining the size. It is clear that maximum protection will be achieved with the maximum overhang size for a particular structure.

Optimal size

Calculating a roof overhang means finding a compromise between cost and functionality. The optimum size is achieved when the required value is simultaneously sufficient. A decrease in the optimum is fraught with moistening of the walls, basement, foundation, rotting of the rafter system and other negatives.

Exceeding the optimum value means an increase in snow and wind load, higher costs for building materials. Add one more factor here - icing. In short, an increase in the safety margin of the roof will be required, which, of course, is associated with additional financial costs.

Therefore, most often they rely on the architectural style of the building, taking into account the parameters listed in the section on the size of the eaves. In addition, take into account:

• the height of the house - the higher the structure, the wider the cornice should be;
• the width of the blind area - with a wider and high-quality blind area, roof overhangs can be made narrower;
• building materials (brick, wood, panels). For example, for panel or brick houses, the width of the cornices is considered optimal up to 55 cm, for wooden buildings - from 55 cm and above.

The architectural style can be the main criterion for choosing the length of the overhangs

Regulatory requirements for the size of roof overhangs

Once in the building codes (SNiP) norms for the removal of rafters were spelled out. According to them, for low-rise buildings, protrusions of at least 60 cm were allowed, and with a drainage system it was possible to make a cornice 40 cm wide. These norms were preserved in SNB 3.02.04-03 and are designed for simple structures.

Today, new architectural trends have emerged with more intricate facades and complex roofs, for which standards have not yet been developed. And although many do not know the old standards, they maintain the dimensions, mainly relying on common sense.

Many no longer know about SNiP, but they maintain the dimensions, relying on design features and common sense

According to SNiP II-26–76, the overhang of the roof made of aluminum and sheet steel must be made of a solid plank flooring with a width of at least 70 cm (clause 7.3). In addition, the eaves nodes with an external drainage system should be reinforced with two waterproof layers 40 cm wide (section 2.6).

Therefore, overhangs are needed, and their width should be at least 50 cm. Professional builders, referring to practice, believe that making smaller eaves overhangs would be a mistake. And they give two arguments:

• normal overhangs increase the cost of construction within 0.1–0.3%, but it will be the right house, reliable and solid;
• in addition, in the future, additional cladding or insulation may be required, and then the overhangs will decrease even more.

If, according to the design concept, there are no cornice and pediment overhangs, then to protect the house from moisture, a drain from the roof is still made, but it is hidden behind a hinged facade, which is revetted with modern moisture-proof materials. In this case, the facade of the building itself protects the walls from excessive moisture.

In the absence of roof overhangs, the task of protecting the walls from moisture is solved differently - there is a drain from the roof, but it is hidden behind a hinged facade, which itself protects the walls from getting wet

Roof cornice installation

When arranging cornices, you need to remember that, unlike pediment overhangs, they are involved in roof ventilation. If installed incorrectly, it is on the filing of the overhangs that frost can form, which will impede the flow of air and disrupt its free circulation in the under-roof space. Therefore, before making a filing of overhangs, you need to properly prepare the base.

Video: a new way of installing the eaves overhang - beauty in the details

DIY roof cornice

Eaves are installed according to the following scheme:

1. The rafter legs are trimmed in level strictly at the same distance from the walls.

2. If necessary, lengthen with filly.

   

   Before filing the roof overhangs, the rafter joists are leveled, and if necessary, they are increased with the help of filly

3. A strapping board is fixed at the ends of the rafter legs or filly, which connects the edges of the rafters (filly). It is made of wood and covered with paint or moisture-proof compound. It is on it that gutters are subsequently installed.

   

   The ends of the rafters or filly are tied with a board along the entire length of the cornice

4. On top of the strapping strip, a frontal board is fixed, which is most often steel and is included as an additional element in a set of roofing from metal tiles, profiled sheets, ondulin, ceramic or bituminous tiles.

5. The filly is hemmed with boards to form a horizontal box, which, if desired, is revetted, relying on the style of the house and the preferences of the owners.

   

   Fillets or released parts of the rafters are hemmed with boards, and then revetted as necessary

The pediment overhang is mounted a little differently:

1. Sheathing boards that protrude beyond the lines of the walls are cut strictly parallel to their surfaces and maintaining the distance according to the roof design - the same everywhere or reduced / increased in some zones.
2. Attach an end board made of wood or steel to the cut edges and to the edge of the ridge.

3. It is covered with roofing or finishing material along the entire length of the cornice.

   

   Sheathing boards are cut according to the project of arrangement of overhangs, and then connected with a frontal board

Video: do-it-yourself roof and pediment cornice

Sewing roof eaves

Sewing roof overhangs is not difficult. Such work can be done independently.

There are two schemes for filing a protective lining:

1. Horizontal hemming on steep slopes. For this, a box of beams is constructed, which is attached to the rafters and walls. At the same time, for a good drain, the box is fastened to the walls 1 cm higher than to the rafters. Then the boards are nailed from the corners of the roof to the corners of the building. With a wide overhang, a longitudinal beam is additionally filled in the middle of the structure. This technology allows installation to be carried out quickly and significantly save building materials.

   

   Horizontal filing boards can be nailed with a herringbone pattern

2. Overhangs filing on rafters. It is used for small rafters (40-50 cm) and on roofs with a slope of no more than 30 °. A crate of boards located parallel or perpendicular to the walls is stuffed directly onto the rafters. For such a scheme, it is necessary to have a common plane at the lower ends of the rafters.

   

   If the lower ends of the rafters form a common plane, the hemming can be performed directly along them

The filing method does not matter here. Planks or beams are stuffed directly onto the crate along the pediment, to which the sheathing strips are attached.

Frontal overhangs do not participate in the ventilation of the under-roof space, therefore they are hemmed right along the crate

Binder materials

The modern construction market pleases with a large abundance of filing materials, so that homeowners can choose anyone to their taste and wallet. The main requirement is excellent frost and water resistance.

Traditionally used:

• planed or edged softwood board - the most economical material for filing cornices;

  

  The wood used for filing must be protected from decay by antiseptic compounds and have a permissible moisture content of no more than 40%

• wooden lining, which has undergone a special treatment, which looks more aesthetically pleasing compared to boards;
• galvanized steel sheets (corrugated board) covered with a polymer layer, due to which high-quality metal protection and a variety of colors are provided;

• PVC siding, sheet metal (steel, aluminum and copper), wood boards and, of course, soffits.

  

  The lining with partially perforated copper soffits ensures good air circulation throughout the roof, including overhangs

Video: filing overhangs, which spotlights to choose

User reviews about the device of roof overhangs

Video: eaves of the roof of a house - construction and hemming

Whichever type of cornices is installed, whatever filing materials are chosen, it is important that the roof overhangs provide good ventilation of the under-roof space, additional insulation and effective protection from rain and winds of all elements of the roof structure hidden behind them. Only high-quality overhangs will save the facade, extend the life of the roof and the house.