Instruction of Pitched Roof
From the beginning of civilization, roofs are one of the essential structural components, necessary for building construction.
Roofs protect the building structure and the inhabitants from adverse atmospheric and exposure condition and also to enable privacy to its inhabitants.
The design and construction of a roof necessitate the consideration of several design factors among which, the element of drainage holds the most crucial role. Excellent Roof construction requires a careful review of all it’s dependent factors and the use of different roofing materials.
The design of drainage is widely dependent on the slope of the roof to be provided, based on which, the shelters are classified into two categories- Flat Roofs & Pitched or Sloping ceilings. These are the two types of roof structure.
Pitched Roofs are the roofs which generally slopes downwards in one, two or more parts (depending upon the design), at a certain angle from the central ridge (the central ridge is the highest point or peak in a sloping roof).
These types of roofs are visually appealing and have a great look, so it’s also a suitable choice for traditional and modern houses, where there are no financial implications.
The difference of the pitched roof from the flat roof is that the slope of the flat roof is less than 10°, which only enables adequate drainage of rainwater in low to moderate rainfall regions, whereas, in the sloping roof, it generally varies between 45°-60°.
What Is Pitched Roof?
A pitched roof is a roof that slopes downwards, typically in two parts at an angle from a central ridge, but sometimes in one part, from one edge to another.
The ‘pitch‘ of a roof is its vertical rise divided by its horizontal span and is a measure of its steepness.
Types of Pitched Roof
Depending upon the slope, environmental condition, aesthetic view and number of sloping surfaces, the pitched roof are widely categorized in the following types
- Mono-Pitch Roof
- Double-Pitch Roof
- Couple Roof
- Couple Close Roof
- Collar Beam Roof
- Slant Roof
- Purlin Roof
- King Post Roof
1. Mono-Pitch Roof
This is the simplest form of Pitched roof, where the number of the sloping surface is one, I.e. It is a single sloping roof surface often not attached to another roof surface.
This type of roof usually takes the look of an equilateral triangle where one is connected with the central ridge, and the other end, overhangs. It can be denoted by various names such as shed roof, lean-to roof, pent roof & skillion roof.
The slope of the mono-pitch roof is the ratio between its rise (considered from the lowest point of the ridge), and it’s span (considered the horizontal distance the roof covers).
Mono-pitch roofs are generally constructed using a set of principal ties, struts, principal rafters and angle purlins to enable the placing of roof coverings or sheets.
Advantages of Mono-Pitch Roof:
- Being the simplest form of a pitched roof, it requires nominal materials to construct this roof, which is why this type of roofs are widely used for garages, storage rooms and go downs.
- To construct this type of roofs, not much design are to be prepared, so this type of roofs can be very quickly erected and does not cost much.
- Having slope more than 45°, it provides adequate drainage of rainwater and snow falls, making it a suitable choice for heavy rainfall regions.
2. Double-Pitch Roof
This is the most widely used pitched roof, where the number of a sloping surface is two, that is, there are two sloping surfaces in the opposite direction. In other words, it is the combination of two mono-pitch roofs.
The rise of double pitch roof is the same as that of the mono-pitch roof, and its horizontal span is twice the value of the mono-pitch roof.
The structure of double pitch roof is similar to that of a quadrilateral triangle. The material used for this type of roof structure is a single set of principal ties, two sets of principal rafters, struts, angle purlins used to place the roof coverings.
Advantages of Double-Pitch Roof
- This type of pitched roof is widely used nowadays for residential buildings. It provides a very economical solution to the roofing system, and are visually appealing.
- Having a slope in the range of 45° to 60°, it provides effective drainage for houses in heavy rainfall and snowfall regions.
- Design of this type of roofing system does not require much effort, which can be done in a very short time.
3. Couple Roof
Being referred to as the simplest form of roofing system, it is similar to that of the Gable roof or Double pitch roof, the only difference is that couple roof can be constructed at meagre cost and can be erected very fast.
The materials used for the construction of a couple close roof essentially timber.
At first, the wall plates are fixed on both the supporting walls (which most of the case is Masonry Pillar) and a ridge piece is fixed at the central ridge. One end of the principal rafters are placed on the ridge piece, and the other end, on the wall plates.
Sheeting (which are generally A.C, G.I sheets or Mangalore tiles) are provided over the angle purlins, which are placed over the principal rafters.
Couple roof is usually suitable in places, where the maximum span is limited to 3.7 meters.
Advantages of Couple Roof
- Being the simplest form of the roof, it can be used in garages and storage house as well as a residential building having low span between the pillars.
- These roofs are very light and easy to construct.
- Having an adequate slope it provides an effective drainage solution for all types of a residential building.
4. Couple Close Roof
This type of roof is very similar to that of the couple roof, the only difference is that in this type of roof, the legs of the common rafters are connected by a horizontal tie.
The tie provided in the roof runs from the wall plate of one pillar to the other wall plate; in other words, it covers the entire horizontal span of the top.
The tie beam prevents the common rafters from spreading and trusting out of the walls, as the tie beam is connected to the feet of the common rafter.
Advantages of Couple Close Roof
- The most important benefit associated with this type of roof is that it provides additional triangular space as storage spaces to be used as a loft, which is most of the time missing in modern house design.
- This type of roof does not include intricate designs to be made; the designs are effortless and can be drawn out in a short time.
5. Collar Beam Roof
Collar Beam Roof is very similar to that of the couple close roof, the only difference is that in a collar beam roof, a collar tie is provided, instead of a horizontal tie, which runs from one wall plates to the other.
A collar tie is a horizontal structural member between the rafters, which is raised from the feet of the rafters to almost the middle of it.
Collar ties should not be fixed by more than one-third or one-half of the rise of the roof, from the wall plate.
When the clear span of the roof increases, or when weighty loads are applied, the rafters show a tendency to bend. To prevent that, the collar ties are provided, which stops the sagging of the rafter under excessive loading conditions or in high spans.
This type of roof is used where the clear span is between 4.4-5 meters, having the ideal span of 4.8 meters.
Advantages of Collar Beam Roof
- It is structurally safe for long span roofs and prevents the sagging of elements.
- In this type of roof, the first-floor beam can be raised to near the roof, this utilizing the unutilized roof spaces.
6. Slant Roof
A hip, or hipped, the roof is a gable roof that has sloped instead of vertical ends. The gambrel roof is a type of gable roof with two slopes on each side, the upper being less steep than the lower.
Advantages of Slant Roof
- Extra Space. A slant roof creates attic space that homeowners can use for storage or some other activity.
- Reduced Snow Buildup. A slant roof can also effectively manage snow.
- Better Water Flow. A slant roof has the ability to easily and quickly direct rain into your gutter system.
Disadvantages of Slanting Roof
Although not much, there are a few disadvantages of using the Slanting roof, which is mentioned as follows:
- The foundation of the roofs can be very stressed when this type of roofs are being used. Thus this type of roofs can only be used where the existing subsoil is strong to withstand the stress.
- Though having a visually appealing appearance, this type of roofs is very expensive, this making it unsuitable, where financial implications prevail.
7. Purlin Roof
A purlin is a longitudinal, horizontal, structural member in a roof. In traditional timber framing, there are three basic types of purlin: purlin plate, principal purlin, and common purlin.
Advantages of Purlin Roof
- The best part and the advantage of using purlins is that your roof coverings can be given different shapes and designs.
- With the use of purlins, it completely becomes your choice whether you want to give your roof a flat look, cone-shaped or pitched look then use purlin roof.
8. King Post
A king post is a central vertical supporting post used in architectural, bridge or aircraft design applications. A king post extends vertically from a crossbeam to the apex of a triangular truss.
The king post connects the apex of the truss with its base, holding up the tie beam at the base of the truss. Development of the king post structure terminates the central post before it reaches the apex of the roof truss.
Instead, the king post is held in place by a collar beam, a secondary beam parallel to the tie beam. In this structure, the central post is termed the crown post.
The king post truss is used for simple roof trusses and short-span bridges. It is the simplest form of truss in that it is constructed of the fewest number of truss members. The truss consists of two rafters, one horizontal beam, serve as a ceiling joist.
Advantage of King Post
- King Post Walls are fast to construct. King Post Walls can be cheaper when compared to other retaining systems such as sheet piled and concreted piled walls.
- King Post Wall installation is versatile and adjustments can be made in the field easily to accommodate changes.