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Mansard rafter system: installation rules

This article covers the installation rules and regulations for the Mansard Roof System, which is a unique system designed for providing a sturdy and sheltering roof. The Mansard System offers several benefits, including a flat roof for increased living space, improved rain infiltration resistance, improved energy-efficiency, as well as simplicity and cost-efficiency of installation. The article outlines the main installation rules, such as an adequate roof slope, correct framing, and prefabricated wooden components that receive a protective sealant, among others. These procedures will ensure a safe and long-lasting roof that will increase the value and aesthetics of any home.

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This article describes the options for the attic floor. You will learn about the basic rules for creating an attic rafter system, about the advantages and disadvantages. The text contains tables of dependencies of different indicators of wooden elements.

Mansard rafter system. Installation rules

Note.You can find terms and specific names of elements in this article..

An attic roof is arranged in two cases – during the construction of a new building or during the reconstruction of an existing one. In both cases, the principle of the device, functionality and design are similar. In modern practice, there are three main types of attic floor device.

Straight slope on racks

In this version, the attic is arranged without making adjustments to the gable structure of the roof. The rafters remain straight, the walls of the room are arranged along a series of intermediate racks, and the ceiling – along the rafter tightening (crossbar). In this case, the inner planes of the walls and ceiling can be “broken”, that is, mate at different angles.

Mansard rafter system. Installation rules

Benefits:

  1. The attic device does not affect the bearing capacity of the rafter system.
  2. Side “pockets” keep air and serve as insulation.
  3. With a large overlap area, the room can maintain an even rectangular geometry.

Disadvantages:

  1. Incomplete sale of the area: 50-75%.
  2. The lateral sinuses are either not used, or access to them is difficult (due to tightness). In half of the cases, they are simply “jammed”.

Straight slope on the walls

Houses with such a device are called “1.5 floors”. The load-bearing outer walls of such a building are raised to about half of the second floor and serve as a support for the roof. Roof trusses in this case are made without bottom tightening, only with a rafter girder. The walls of the room above the middle will follow the angle of the slope, but this arrangement allows you to use the area of ​​the second floor by 100%. The under-roof space is heated easier and faster due to the smaller volume.

Mansard rafter system. Installation rules

Benefits:

  1. Capital walls of the second floor (50%).
  2. Possibility to adjust the ceiling height and air volume in the upper room at the design stage.
  3. Possibility to install vertical windows, partially located in the wall *.
  4. Full use of the area.

Disadvantages:

  1. Higher consumption of wall material.
  2. Heavy load on the foundation.
  3. Often the armopoyas is “torn” – the load is transferred to the walls unevenly.

* Vertical installation of windows can weaken the reliability of the building’s armored belt.

“Broken” roof

In this case, the line of the slopes is refracted and divided into two sections – the upper one at the most acute, and the lower one at the most obtuse angle to the horizon. The lower part of the slope is often made almost vertical, up to 80 °. This design is most often resorted to when building a superstructure or on small houses. The overlap is used by 80-85% and this is a good indicator if it is impossible (or unprofitable) to raise the walls up to “1.5 floors”.

Mansard rafter system. Installation rules

Benefits:

  1. Simple and lightweight wood construction.
  2. Relatively high efficiency in the implementation of living space.
  3. Less snow accumulation on slopes.
  4. More convenient arrangement of windows and easier to mount.
  5. Roof trusses for small spans can be made in the landfill or in the workshop.
  6. The possibility of the attic device remains.

Disadvantage: unsightly (standard, recognizable) appearance.

All of the above types have a common feature – only roof windows can be used in attic floors..

Mansard rafter system. Installation rules

Note.There are no unsolvable problems in construction. It is possible to achieve vertical (standard) installation of windows, but this will lead to a significant complication of the design and increase in the cost of work.

When choosing an attic rafter device, the following goals are achieved:

  1. Add-on of a residential floor to an existing building.
  2. Lightweight living space construction.
  3. The combined function (roof and room) saves construction time.
  4. External walls – roofing elements – are made of a rafter frame, which is usually cheaper than wall material.
  5. The relative lightness of the finished structure does not require significant strengthening of the foundation.
  6. The area of ​​slopes located at an acute angle to the horizon decreases, i.e. the area of ​​snow accumulation decreases.

Do-it-yourself roof truss system

Due to the fact that the roof structure directly depends on the location of the bearing walls, the width or asymmetry of the spans, the floor area, we will give only general installation rules. All recommendations on the use of cuts and puffs have already been given in the articles “Rafter system”, “Gable rafter system”, “Do-it-yourself gable roof rafter system”, “Hip rafter system”. The methods of fastening and joining elements are valid for any type of roofing based on a wooden frame.

Rule # 1

With straight slopes, the projection of the working part of the rafters (the distance from the support to the support) should not exceed 2 meters.

Mansard rafter system. Installation rules

Span rate table (rafter length) for different rafter leg thicknesses

Thickness, mm Limit length, mm
40 600
50 800
60 1200
75 1500
one hundred 1800

In this case, the rafter tie (crossbar), which connects the rafters in the middle or upper part, is considered a support.

Rule # 2

The pitch of the rafters of the attic rafter system depends on the thickness and design of the trusses.

Pitch versus thickness table

Thickness, mm Maximum allowable pitch, mm
40 500
50 600
60 800
75 1000
one hundred 1200

Note.All the given values ​​and proportions of dependence are taken from the normative and reference literature..

Rule No. 3

If the span of the flat (upper) part of the slope is more than 3 meters, intermediate supports are required. A gentle slope will somehow accumulate snow, which in spring and autumn has the weight of water. Even a well-secured truss will eventually deform over significant spans under the influence of gravity (from its own weight).

Attention! Do not neglect additional reinforcements. They play a decisive role (after the main ones) in load distribution. The absence of intermediate supports can lead to deformations of the slopes and ridge – sagging and the formation of steps within 5 years after installation.

Rule No. 4

Even short rafter legs should be reinforced with slopes and rods wherever possible. Any rafter system works as one continuous frame and thus keeps its shape. The more elements of fastening, the higher its resistance to deformation. This is especially true for gentle slopes and wall “pockets”.

Rule No. 5

Try to avoid overlapping fastenings, especially if the load is transferred not through friction to the surface of another element, but to the rod intended for tightening.

Mansard rafter system. Installation rules

The purpose of tightening the elements with threaded rods and turboprops is not to reinforce the wooden assembly with metal rods, but to press the planes harder, creating a maximum friction force that will hold them in the bundle. Self-tapping screws and turboprops also work. Ideal if you apply wood glue on a plane.

Install permanent vertical posts on the cut-outs. This will take more time for installation, but will add 5-7 years to the life of the structure. The weakest points of the attic truss are the joints of the slope fractures. They must be vertically supported..

The attic floor is a smart solution for the renovation of any building. Before making such a decision, be sure to check the bearing capacity of the walls. An increase in the living space of a house almost twice will give it a new life, and for little money (in comparison with foundation construction).

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Comments: 3
  1. Teagan

    What are the specific installation rules for the mansard rafter system?

    Reply
  2. Avery Kelly

    What are the specific installation rules for the mansard rafter system?

    Reply
    1. Brooklyn Matthews

      The specific installation rules for a mansard rafter system include ensuring that the rafters are properly aligned and spaced according to the design plans. The rafters should be securely attached to the building structure using appropriate fasteners such as nails or screws. It is important to check the slope of the roof to ensure proper drainage and prevent water pooling. Additionally, the materials used for the rafters should be durable and able to withstand the weight of the roof. Proper ventilation and insulation should also be considered during installation to prevent any moisture buildup or heat loss. Finally, it is crucial to follow the manufacturer’s instructions and local building codes to ensure a safe and sturdy mansard rafter system.

      Reply
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