Rafter system - 4 important elements of its design, types and recommendations for construction

In order for the roof of the house to be reliable and strong, it needs a high-quality and durable truss system. The roof protects the building from atmospheric influences - strong wind, rain, snowfall, hail. It must withstand these loads for many years thanks to the rafter system. I will tell you about the device of this construction, what types of it exist and how to build it correctly.

Elements of the rafter system

The main elements of the roof truss system:

Image	The main elements of the roof
	Mauerlat This support beam is the base of the structure. It allows the loads to be evenly distributed along the load-bearing walls.
	Roofing ridge It is located at the top of the structure, in which two slopes are connected. On both sides of the ridge (along it) a continuous crate is laid, which reinforces it.
	Rafter legs (rafters). This element sets the angle of inclination of the slopes and determines the appearance of the roof, rigidly fixing its individual parts.
	Puffs They connect the rafters from below and do not allow them to diverge.
	Struts and racks Gives the rafter legs an extra level of stability.
	Sill This element is laid from below parallel to the roof ridge. It serves as a support for racks and struts.
	Runs They fix the rafter legs. The ridge run is located at the top, and the side runs are on the sides.
	Filly They are used to build rafters if their length is insufficient to create roof overhangs.
	crate It is installed from edged boards or timber perpendicular to the rafters. It serves as a frame for the roofing and transfers the load from it to the rafters.
	Roof overhangs This element goes 30-100 cm beyond the plane of the outer walls and protects them from precipitation.
	Rafter frames (trusses). This knot has a flat triangular shape. It includes a rafter pair, stretch marks, braces and racks. Farms are placed in such a way that no loads are created on the walls inside the building. The frames are supported by load-bearing walls, while they experience vertical loads.

When the spans are of considerable length, the trusses should consist of several elements.For the attic, the lower part of the frames serves as the ceiling. The distance of farms from each other should be determined using calculations.

Parameter 1. Roof frame

1. High quality building materials. For rafters, you can use wood grades 1, 2 and 3. The material should have a minimum number of knots and cracks. Three knots no more than 3 cm long are allowed per 1 m. Cracks should not go to the entire depth of the beam or board:

• For load-bearing structural elements it is necessary to use wood with a thickness of 5 cm or more. For coniferous timber, boards, the maximum length can be 6.5 m, for hardwood - 4.5 m. For Mauerlat, pillows and girders, hardwood should be used.
• All wooden elements of the system be sure to treat with an antiseptic to protect against harmful microorganisms and a flame retardant to protect against fire.

2. The weight of the roof frame and roofing material must not be excessive. Based on this, the truss structure in the vast majority of cases is mounted from wood. When the mass of the roof is large, then its base should be made of metal.
3. Roof structure should be tough. All elements of its frame and the points of their connections should be securely fixed. They should not be deformed under shearing and bursting effects.

All types of truss systems have a triangle base. This form is for trusses installed in parallel with each other.Their rigid fixing gives the roof sufficient stability.

When the frames are movable, this creates a big problem. Such poor-quality installation of the truss structure can lead to the destruction of the roof and walls of the house.

Types of roof structures

The device of the roof truss system can be different. Choose its type based on the design of the building and its dimensions.

Roof rafters can be layered or hanging.

Parameter 2. Layered system

Slanted rafters are optimal for roofs with a span of 10-16 m. The slope at the slopes can be done in any way. The building must have columns or load-bearing walls. From below, the rafters rest on the Mauerlat, and on top of the run.

Skate run in turn, it is supported by racks or lying (inner wall). Loads in this design occur only vertically, so there is no need for puffs.

If the span length is significant, it is better to change the ridge run to two side beams. They should rest on the racks. So that the rafters do not bend, they are reinforced with crossbars and struts. If you are building an attic with your own hands, you can make the rafters broken or lean them against a wall 1-1.5 m high.

What to consider when building a layered rafter system:

1. All structural nodes must have smooth cut surface. This will reduce the chance of them rotting and becoming infected with fungus.
2. Mauerlat sole should be be placed exactly horizontally relative to the outer walls. The docking of the Mauerlat with the rafters should also be strictly horizontal. Otherwise, the support may tip over.
3. Struts and racks must be mounted with maximum symmetry.

4. To avoid the need to repair the truss system, its elements should not get wet and rot. Therefore, in the under-roof space, effective ventilation is needed. To do this, air is left in the attic roof, and cracks are left in the attic.
5. Those points at which the truss system is in contact with stone, concrete, brick walls, must be waterproofed. Otherwise, due to condensation, the wood will begin to rot.
6. Rafters without struts or supports should not be longer than 4.5 m.

Parameter 3. Hanging rafter legs

The gable roof frame system is most often hanging. At the same time, its span should not exceed 6 m, and the house should not have internal walls.

At the top, the rafters lean against each other, at the bottom - on the Mauerlat. The load of the structure on the walls of the building is reduced by puffs. Beam screeds are laid at the bottom of the rafters and additionally serve as a ceiling. There are also crossbars - these are puffs that are placed higher.

The instruction recommends using support braces and posts when spanning between external walls of more than 6 m. They will support the rafters. The length of the bottom of the legs after the support should not be more than 4.5 m here.

What to consider when building a hanging rafter system:

1. It is not necessary to support the roof overhangs on the bottom of the rafter legsbeyond the plane of the walls. Fillies are best suited for supporting this design. When using them, the rafters will be able to rest on the Mauerlat with their entire plane.
2. On the slopes from the support beam to the ridge, fill the wind bar (frontal board).
3. The slope must start from the attic. So the roof will turn out to be rigid, it will not sway, and collapse from the wind.

When the moisture content of the wood is more than 18%, the gable roof truss system may become loose after shrinkage. Therefore, fasten wet building materials not with nails, but with screws or bolts - they can be tightened.

Roof frame with different shapes

Roof truss systems of different types may differ:

1. Single roof. Her frame has the simplest device. The only slope here slopes at an angle of 14-26°. When the building is small and the span between the walls is no more than 5 m, the best choice is layered rafters.
   They rely on the outer walls of different heights and the inner wall, when there is one. If the span is more than 5 m, it is necessary to build roof trusses.

2. Roof with two slopes. This design is simple, under it is an attic or a residential attic. The slope of its slopes can be 14-60 °.
   If the span between the outer walls is not more than 6 m, a hanging frame system of a gable roof is used. If the span is more than 6 m and there are walls inside the house, layered rafters are used.

3. Quadruple roof. The slope of its slopes can be 20-60 °, the span is up to 12 m. Inside the house there must be supports for the roof frame. There are no gable walls with this design, this saves building materials.
   Building a hipped roof is more difficult than a gable roof. For it, layered rafters or trusses are used.

4. Mansard roof. At a sloping roof below, the slope can be up to 60 °, at the top it is more gentle.Thanks to this, the attic area expands and it is possible to equip a residential attic in it.

The span between the walls of the house here should not be more than 10 m. The rafter system can be layered or frame.

Parameter 4. Fasteners

To ensure that the gable roof truss system is reliable, its nodes must be fixed correctly. Before this, it is necessary to take into account the strength and direction of dynamic and static loads. It is important not to forget about the shrinkage of wood.

Previously, all types of roof structures were fastened with cuts. They are reliable, but not economical. In this case, it is necessary that the wooden elements have a large cross section, which makes it possible to make cuts safe.

Therefore, now the fastenings of the rafter knots are made not with cuts, but with bolts or dowels. Perforated stainless steel overlays are also popular. Their price is quite high, but they are convenient and speed up construction.

The pads are fixed with nails or toothed plates.embedded in wood. They reduce the cost of building materials by 20%, since their use requires timber, boards with a smaller section than with cuts.

Conclusion

The truss system is the supporting frame of the roof. It must fully comply with the shape and design of the roof, be reliable, strong and durable. In this case, the roof itself will serve for many years. The video in this article will reveal the topic clearly. Ask your questions in the comments, if any.

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