A Pitched Roof is a roof that has slopes downwards, typically in two halves at an angle from a central ridge, but sometimes in one part, from one edge to another.
A roof can be classified as a pitched roofs when the pitch of the roof is greater than 10°.
But, it should not be more than 70°, else it will be counted as a wall.
The roof is the uppermost part of a building constructed in the form of a framework so that the building is protected from heat, rain, snow, wind, and other climatic factors. The roof also aids in maintaining the internal environment of the house by resisting heat loss.
There are different pitched roof types like gable roofs, Couple Roof Truss, hip roofs, Queen Post Roof Truss, gambrel roofs, dome roofs, and mansard roofs.
Pitched roofs construction is used in workshops, factories, cinema halls, auditoriums, go-downs, warehouses, hangars, villages, and in hilly regions.
For thermal insulation, a false ceiling is also constructed in pitched roof design.
Types of Pitched Roof
Depending upon the environmental condition, slope, aesthetic appearance, and nos. of sloping surfaces, the pitched roof types are widely classified as follows
1. Single Pitched Roof | Mono Pitch Roof
In This types of roof the common rafters are provided as the top chord.
No intermediate support is given to these common rafters in a single roof.
There are four types of single roof as follows that is explained afterwards.
- Lean-to roof
- Couple roof
- Closed couple roof
- Collar tie roof
- dual pitched roof
2. Double-Pitch Roof
In this roof span of the roof increases above 2.4 metre, the section of common rafters becomes heavy and it makes the roof uneconomical.
Originally, in the single roof, the entire load of the roof is transferred to the walls through the end of the rafters only which makes the section bulky.
In purlin roof, intermediate support in the form of purlin is introduced so that some of the load is transferred through this purlin. This reduces the net load at the leg of the rafter and allows the section to be lighter.
We already know that the load from the roof can be transferred only by purlins as the roof only transfers the axial load.
The Double-pitch Roof can be economically adopted up to a span of 4.8 metre.
Advantages of Double-Pitch Roof
- These pitched roof types are widely used for residential construction. Its become an economical solution for roofing systems and its visual appearance is really good.
- A double pitch roof has a slope in the between of 45° to 60° and which is sufficient for effective drainage for houses in heavy rainfall and snowfall regions.
- Designing this type of pitch roof system does not require much time s and effort.
3. Triple/Trussed Roof
When the span is increased, the first solution is to introduce purlins or take support over partition walls.
But, if the span is much more or if the intermediate supports are not possible, then truss is introduced.
A truss is a framed structure that carries a ridge piece and provides support to purlins. In the construction of roofs different materials can be used for truss-like timber, steel, etc.
Wooden truss supports a span of 3 metres.
4. Lean-to Roof
Other names: Pent roof or Aisle roof or Veranda roof
Lean-to Roof is the simplest form of the pitched roof in which slope is provided on a single side only.
In this type of roof, the slope required for the pitched roof is provided by the wall itself.
One of the walls over which the roof is to be supported is raised higher than the other wall. This gives the pitch or slope.
Over these two unequal walls, roofing material is laid to obtain a lean-to roof.
Usability: Sheds, outhouses, veranda attached to the main buildings
It can just support a span of 2.4 metres as it is supported only on a single side.
5. Couple Roof Truss
It is an advanced type of lean-to roof. Here, both the walls on which roof is to be supported are kept at the same level.
Then, roofing is provided leaning upwards towards each other.
At the middle, they intersect at a horizontal beam called a ridge.
This types of pitched roof provided for a span of up to 3.6 metres.
6. Closed Couple Roof
It is similar to the couple roof in structure except it has a tie beam joining the legs of the two common rafters near the support wall.
It is named as closed couple roof as the tie-beam closes the couple roof structure.
The provision of a tie beam prevents the common rafters from being spread outwards. It also prevents overturning of the walls on which the roofing system is supported.
It can be adopted for a span of about 4.2 meters or less.
7. Collar Tie Roof
It is a modified form of a close couple roof.
In collar tie roof, the tie beam that is provided at the leg of common rafters in coupled roof truss is raised above and it is known as collar beam.
The provision of a collar beam enables the roofing system to utilize the space economically. As the beam is raised, the height of the room is increased.
It can be adopted for a span of about 4.8 metres.
8. Simple Roof Truss
Simple roof truss can be adopted for Span 6-9 m.
9. King Post Roof
In this roof truss, a central post is introduced that joins the ridge point to the main tie. This central post is known as the king post.
The two common rafters spanning from the ridge to eaves are called principal (main) rafters.
King post supports the ridge and holds both the principal rafters together at the ridge or apex at the top.
It also provides support to the main tie and prevents it from sagging.
As this truss is provided for longer spans, there is a possibility that the principal rafter may bend from the middle. To prevent this, inclined members called struts are provided.
Struts connect the middle of the principal rafter to the middle of the main tie. Here it forms a joint with the king post and the other strut.
Most of the time, king post roof truss is made up of wood, or a combination of timber and steel can also be used.
Usability: Sheds, porch, garage, small houses, etc.
King post roof truss can be economically adapted for a span of 5-8 meter.
10. Queen Post Roof
This is a modified form of king-post roof truss. As the span increases, the tie beam will experience sagging.
Instead of one post at the center, the queen-post roof truss has two vertical members aligned horizontally across the span.
These two vertical posts are called queen posts. The queen posts are placed at one-third distance from the support.
A horizontal member called a straining beam connects the upper two ends of the queen posts and also holds them in position.
A straining sill connecting the bottom of the queen posts is also laid over the main tie. This straining sill prevents the feet of the queen post from coming closer.
The inner square formed by queen posts and straining beam can be braced diagonally to impart rigidity to the truss.
Purlins are provided on queen posts so that they aid in load transfer. This makes the queen-post roof truss lighter than the king post roof truss.
It may be adopted for a span of 8-12 metre.
11. Combination of King Post and Queen Post Roof Truss
Queen post roof truss cannot be provided for spans exceeding 12 meters. To strengthen its structure, both king post truss and queen post truss are combined to obtain this truss.
An upright vertical member at each side is provided to this type of truss that is called princess post.
It may be adopted for a span up to 18 metres.
12. How Roof
How bridge was first designed by William Howe long back in 1840. He was an American architect.
Its design resembles M-shape in which a vertical post is also installed at its center. The general idea of this roof truss is obtained from the combination of king post and queen post roof truss, in which the queen posts and straining beams are eliminated.
The diagonal members slope outwards from the center (opposite to Pratt roof truss). Hence, the vertical members experience tension in the case of how to truss while the diagonal members are in compression.
It is made up of steel and timber. This combination imparts elegance to this truss. The entire truss is constructed of timber except the members carrying tension. The tension members are made up of steel.
It was used for steel bridges. But sometimes, it is even used in houses.
It can span up from 6 to 30 metre.
13. Double How Roof
If an extra pair of the vertical and diagonal members are provided on both sides of the truss, the truss is called a Double How roof truss.
It can be used for a variety of structures as it can be adopted for a span of 18 meters economically.
14. Fink Roof
A central post connects the bottom main tie to the ridge. On either side of this central post, strut members are arranged in a double V shape.
As the members slope downwards from the center, the size of V is considerably reduced while moving away from the center of the truss.
Fink types roof truss relies on diagonal members and transfers the load efficiently to the support.
Usability: Home, pedestrian bridge.
It can be economically adapted for spans 6-9 metre.
15. Double Fink Roof
It is a modified form of a fink roof truss. Instead of double V, the strut members resemble a double W shape in a double fink roof truss.
The same pattern of fink roof truss is repeated on both sides. However, the central post is eliminated in this truss.
Thus, the struts are arranged in a pattern that resembles ‘W’.
This roof can be economically adapted for spans up to 16 meters.
16. Fan Roof
It is also a steel truss with a simple design.
It is a modified form of fink roof truss in which the strut members fan out from the joints provided at the bottom member of the truss. Even vertical members are provided for more stability.
The top chords are split into small-length members so that more purlins can be supported over it.
This fan roof truss can be adopted for a span of 10-15 metre.
17. Raised Chord Roof
In this truss, the bottom tension member is raised a bit and the apex is formed in this member too. Thus, the main tie in raised chord truss is made up of two members instead of a single member.
Raised Chord Roof truss can be adopted for a span ranging from 4-6 metre.
18. Raised Heel Roof
It is primarily constructed of timber; however, some additional materials are required to support the truss structurally.
The construction of raised heel roof truss is easy and not much complicated as it is a conventional type of truss.
The insulation property of this truss is quite good, so it is energy efficient. Moreover, as the tie is raised, even the attic ventilation is greatly improved.
It even creates a vapour barrier that solves the problem of mold and condensation.
But, the construction cost is comparatively higher.
19. Scissors Roof
The upward-sloping top chord members meet at the ridge.
In the scissor roof truss, even the bottom chord members are inclined. Even the bottom chords slope upwards and meet exactly below the ridge. And this point is joined to the ridge by a vertical post.
This makes the truss appear like an open scissor and hence it is named as scissors truss.
Additionally, a horizontal and a vertical member are also provided on each side of the truss.
In roof truss no beams or bearing walls are required in its construction.
But, at the same time, it consumes too much space, and hence insulation is not possible. This increases energy consumption and reduces efficiency.
However, since the ceiling is vaulted, a spacious attic is obtained in this truss.
Usability: Scissors truss is mostly installed in Cathedrals.
It can be spanned economically for over 15 metres.
20. Pratt Roof
Pratt roof truss came into existence in 1844. It was first presented by Thomas and Caleb Pratt.
It is one of the widely used steel trusses as it is economical.
The vertical members of this truss resist tension while the diagonal members resist compression.
The diagonal members slope down towards the center in a pratt truss, just opposite as in the case of how to truss.
It is costly as compared to the fink roof truss.
Pratt roof truss can be adopted for spans ranging from 6 to 10 metres.
21. North Light Roof
It has large, a wider set of lattice girders in which trusses supported at right angles are also included. This very characteristic makes its construction cheaper.
This is one of the oldest trusses available and it exhibits durability and versatility.
It even helps in providing ventilation, as its design allows light to enter inside the room if kept facing north. Hence, its name is a north light truss.
The shorter vertical side of the north light truss is often glazed so that this part faces the north and reflects a good amount of light inside the structure.
Usability: Drawing rooms, industrial buildings, workshops, and other large places.
North Light roof truss can be adopted for a span ranging from 20 – 30 meter.
22. Hip Girder Types Roof
The top pointed apex is converted into a flat apex in the hip girder truss.
The flattening of the apex allows a hip girder truss to bear more loads. It also imparts stability to the roof truss.
The structural design is adopted from how roof truss, or more precisely double how roof truss. The top chord rafters are flattened between the first vertical members from the center.
It is provided at places where high winds and hurricanes are a frequent event as truss has great resistance to them.
Hip Girder roof truss can effectively span over 5-8 metre.
23. Step Down Hip
It is a variant of a hip truss while its design is inspired from the double fink roof truss. Also, it is the most versatile type out of all the hip trusses.
The slope of a step-down hip truss is kept similar to the standard roof trusses. But, the apex is flattened down.
Step down hip roof truss can effectively span about 10 metres.
24. Bow String Roof
It is also known as Belfast roof truss.
The upper member is in the form of an arch without apex, i.e. a rounded top chord is used as the top chord.
A chord is set out from upper end sloping downwards. Then the next chord starts from where the previous chord ends but it slopes upwards now. This is repeated throughout the entire section.
Bow string roof truss enjoyed great fame in the 1900s.
Bow string roof truss can be utilized for a span of about 20-30 meter.
25. Alternative Bow String Roof
This is a modified form of bowstring truss.
Here, the same chords as provided in bow string roof truss are repeated in the opposite manner too as shown in the figure. The vertical chords are also provided.
Alternative bowstring roof truss can be utilised for a span of about 20-30 metre.
26. Quadrangular Roof
A quadrangular roof truss is like a two-trussed rafter. A central T-tie holds these two rafters in place. The corresponding members of both the top and bottom chords run parallel to each other.
The vertical chords run parallel to each other that carry compression force. To resist the tension force, diagonal members are provided between the vertical parallel chords.
Usability: Railway sheds, auditorium, etc.
It can support a large span.
27. Gambrel Roof
Its design idea is derived from the design of gable and mansard roof trusses.
Two planes slope in an inclined downward direction from a common point- the top ridge.
As in the case of the mansard roof truss, one of the planes has less pitch than the other one. This offers a considerable space in the attic. This attic space is so large that even a bedroom can be provided!
The construction cost of this gambrel roof is lower too. And it is also one of the factors for its widespread usage.
However, it does not much strong enough to resist high winds or heavy snowfalls. Hence, it should be avoided in the areas susceptible to heavy wind currents or a large amount of snowfall.
Usability: Barns. It is quite suitable for barns that it is even called a barn roof. It is even used in residential construction.
Gambrel roof truss can be spanned for over 30 metres.
28. Inverted Roof
Inverted roof truss in structure is a how truss upside down.
This truss allows additional natural light to enter inside the room.
This truss also gives a vaulted ceiling.
Inverted roof truss can be provided for a span up to 12 metres.
Double inverted roof truss: Two inverted trusses are joined at the top.
Four bearings support this truss and a steep angle is formed at the interior ceiling in the central portion of the room.
The span is extended up to 24 metres.
29. Parallel Chord Roof
As indicated by its name, the truss has both horizontal and vertical chords that are parallel to each other. Also, the pitch of both the top and bottom chords are identical.
A typical characteristic of the parallel chord roof truss is that it creates a vapor barrier. And as the vapor is prevented from penetrating the interior of the house, condensation and mold problems are resolved.
This truss can be constructed under a low budget as it can be made out of timber. They do not need any beam or bearing wall in their design.
But, it does not support a larger span as this truss made out of timber.
However, if more stability is needed, then this truss is braced with steel members increasing the cost too.
Quadrangular types of pitched roof truss can be utilised for a span of about 30-60 metre.
30. Double Cantilever Roof
In a double cantilever roof truss, two horizontal beams are provided that extend beyond the supports on either side.
It has cantilever portions over both sides. The truss extends beyond the bearing on both sides.
This truss adds on to the overall height of the structure.
Besides this, a double cantilever truss also adds an aesthetic value to the structure.
Usability: High-rise buildings, it can also be used to create a porch without introducing posts
31. Mansard Roof
This truss is named after French architect Francois Mansard. To accomplish the municipal laws, he gave the design of this truss.
Here, a room can also be provided at the intermediate level. This results in the economy of space in the room.
Mansard truss lies in-between the king post truss and queen post truss. It is constructed by adopting the structural design from the king post truss and queen post truss.
The lower part of this two-storeyed truss resembles queen post truss and the upper part resembles king post truss.
There are two pitches in the Mansard truss– the upper pitch of the king post truss is 30-40 ° and the lower pitch of the queen post is kept 60-70 °.
Dormer windows can be installed on this roof with flat roofs to facilitate lighting and ventilation.
This roof truss has now become obsolete. Its odd and ugly appearance resulted in this truss becoming obsolete. Also, the introduction of steel truss discouraged its usage.
32. Truncated Roof
It is similar in structure to the mansard roof truss. But, the top of the truss is finished as a flat surface and a gentle side slope.
This roof truss provided when a room is to be provided on the roof.
Truncated roof truss can be used for span up to 30 metres.
33. Latticed Roof
Its structure resembles a bow. The top cord consists of timber sections and it is curved.
It can be efficiently used for large spans up to 30 metres, but light roof curing is to be provided.
34. Composite Roof
A combination of wood and steel is used in a composite truss.
Here, the high yield strength of steel is utilized and steel members are provided in place of tension members.
Special fittings are required where the timber sections join with the steel sections.
Types of Pitched Roof Truss and Their Characteristics and Span Length
|Sr. No.||Types of Pitched Roof Truss||Characteristics||Span|
|1||Lean-to roof/ Veranda roof||=> The simplest form of a pitched roof.
=> Supported on walls, one is higher than the other.
=> Sheds, outhouses, veranda attached to main buildings.
|Up to 2.4 m|
|2||A couple of Types of Pitched roof||=> Both the walls are at the same level.
=> Common rafters are provided sloping
upwards from the support
|Up to 3.6 m|
|3||Close couple roof||=> The design similar to a couple of roof except-A tie is
provided near the support.
=> This tie prevents the rafters from spreading out.
|Up to 4.2 m|
|4||Collar tie Types of Pitched roof||=> A modified form of a closed couple roof truss.
=> The tie beam is provided between the rafters at a higher
level from the supports.
=> This rise in the collar beam leaves more space in the room.
|Up to 4.8 m|
|5||Simple truss||=> No central post is provided.
=> Struts are arranged in a diagonal manner.
|6||King post roof truss|| => Centrally located King post joins the ridge to the main tie.
=> The two common rafters sloping downwards from the
ridge is called principal rafters.
=> Inclined members- struts originating from the joint of
king post to the main tie prevent these principal rafters
=> Sheds, porch, garage, small houses, etc.
|7||Queen post roof truss||=> Modified form of king-post roof truss.
=> Two queen posts are provided at one-third distance from support.
=> At the upper end of the queen posts, a staining beam is provided
while staining sill is provided at the bottom.
=> Purlins are provided over queen posts.
|8||Combination of king and queen post roof truss||=> The upper part resembles a king-post roof truss while
the lower part is similar to a queen-post roof truss.
=> The upright member provided is called princess post.
|9||How roof truss||=> Introduced by an American architect William Howe in 1840.
=> Design resembles an M shape with a vertical post at the centering
and queen posts and straining beam and straining sills are eliminated.
from the combination of king and queen post roof truss.
=> Vertical members take tension while inclined members take
=> Steel bridges, houses.
|10||Double how roof truss||=> An extra pair of diagonal and vertical members are provided to
increase the span.
=> Utilised in a variety of structures
|11||Fink roof truss||=> A central post is provided connecting the main tie to the ridge.
=> Strut members slope downwards from the center in V-shapeHome,
|12||Double fink roof truss||=> Modified form of the fink roof trussBut, strut members are
arranged in W-shape as the central post is eliminated.
|13||Fan roof truss||=> Has a simple design.
=> Made from steel.
=> Modified form of the fink roof truss.
=> Strut members fan outwards from the joint in the main tie.
=> Top chords are split into smaller ones to support more purlins.
|14||Raised chord roof truss||=> Bottom main tie is raised a bit by forming an apex with
the help of two members. Both the members of the
main tie are parallel to the corresponding members of the
|15||Raised heel roof truss||=> Conventional type of truss.
=> Construction is simple.
=> Insulation property is quite good.
=> Attic ventilation is also enhanced as the tie is raised.
=> Vapour barrier formation prevents condensation and
mold problems Higher construction cost
|16||Scissors roof truss||=> The bottom main tie is raised a bit by forming an apex
with the help of two members.
=> Both the members of the main tie are parallel to the
corresponding members of the principal rafter.
=> The apexes of top and bottom chord members are joined
by a vertical post.
=> A horizontal and vertical member is provided on either side.
=> No beam or bearing walls are required.
=> Vaulted ceiling results in a spacious atticUsed in Cathedrals.
|17||Pratt roof truss||=> Introduced by Thomas and Caleb in 1844.
=> Widely used truss Vertical members resist tension while
the diagonal members resist compression.
=> Costlier than fink roof truss
|18||North light roof truss|| => Larger, wide set of lattice girders are provided.
=> One of the oldest truss type.
=> Durable and versatile.
=> Ventilation is enhanced as light is allowed to befall
in the roomShorter vertical side is often glazed for
=> Drawing rooms, industrial buildings, workshops, and
other large places
|19||Hip girder roof truss||=> Top pointed apex is flattened.
=> This flattening allows the truss to bear more load.
=> At places where high winds and hurricanes are a frequent event.
|20||Step down hip roof truss||=> A variant of the hip truss, while its design is inspired by
the double fink roof truss.
=> similar to the standard roof trusses.
=> Apex is flattened.
|21||Bow string roof truss||=> Belfast roof truss is its another name.
=> Rounded top chord is used in the form of an arch.
=> This truss used to be quite popular in the 1900s.
|22||Alternative bow string roof truss||=> Modified form of a bowstring roof truss.||20-30 m|
|23||Quadrangular roof truss||=> A central tie holds the two rafters in place.
=> Vertical chords carry compression force.
=> Diagonal members carry the compression force.
=> Railway sheds, auditorium, etc.
|24||Gambrel roof truss||=> Design is inspired by gable and mansard roof trusses.
=> The pitch reduces while moving upwards in the top
chords Construction cost is lower.
=> High winds or strong snowfall cannot be resisted by this truss.
=> Barns commonly use gambrel roof truss.
|25||Inverted roof truss||=> Its structure is similar to how truss turned upside down.
=> A vaulted ceiling is created.
=> Additional natural light is also introduced in the interior room.
|26||Parallel chord roof truss||=> Both horizontal and vertical chords run parallel.
=> Vapour barrier is created.
=> Condensation and mold issues are resolvedLow-budget trusses.
=> Steel bracing is provided to enhance its stability
|27||Double cantilever roof truss||=> The truss is extended beyond the bearing on both sides.
=> Overall height of the structure is increased.
=> Aesthetic value of the building is enhanced.
=> Porch is formed as posts are omittedHigh-rise buildings
|28||Mansard roof truss||=> French truss in which a room can be introduced at an
=> Its structure is the combination of king post and queen
post roof trussUpper pitch is kept 30-40 °Lower pitch is
kept 60-70° Dormer windows can also be provided to
facilitate lighting has become obsolete
|29||Truncated roof truss||=> The structure resembles a mansard roof truss.
=> A room can be provided over the roof.
=> A gentle slope is provided in the top chord member.
|30||Latticed roof truss||=> The structure resembles a bow.
=> Top chord timber members are curved.
=> Light roof curing is to be provided
|31||Composite roof truss||=> Steel and timber combination is used.
=> Steel is provided to carry tension as it has a high yield strength.
=> Special fittings are to be provided at the junction of timber and steel sections
Pitched type roof having a slope greater than 10° is used for various purposes like residential buildings, industrial buildings, sheds, garages, warehouses and other structures.
To overcome the stability problem arising as the span increases, various types of trusses are constructed in which the arrangement of diagonal and vertical members is modified.
Besides this, the economy is also a deciding factor while selecting the type of truss.
Lean to the roof, coupled roof, king post roof truss, queen post roof truss, how roof truss, fink roof truss, fan roof truss, scissors roof truss, and north light roof truss are the most commonly used roof trusses.
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