Queen post truss construction is used to support pitched roofs where a wider span is needed than a simple king post truss can usually provide. A queen post truss uses two vertical posts, principal rafters, a tie beam, struts, and a straining beam to distribute roof loads safely to the supports. It is commonly used in residential roofs, halls, traditional buildings, and timber roof systems. This article explains its components, benefits, limitations, construction steps, design checks, and common mistakes to avoid before roofing work begins.
Quick Summary
A queen post truss is a pitched roof truss with two vertical queen posts instead of one central post. It is used for medium roof spans, often longer than a king post truss. Proper truss design must account for roof span, load, timber or steel quality, joint detailing, roof pitch, and structural support.
What is a Queen Post Truss?
The Queen post truss is a structural framework commonly used in roof construction. It adapts to the more basic King post truss, but the Queen post truss spans longer distances. It is used in roofing systems that need medium spans; the maximum span of a queen post roof is around 10 meters (33 feet).
Unlike a King post truss with a single vertical post in the centre, a Queen post truss has two vertical posts called queen posts that divide the span into three sections. This results in a lightweight and structurally sound truss that supports the roof’s weight and any external loads like snow or wind. The Queen post truss is used in timber-framed buildings, bridges, and other constructions where aesthetic appeal and structural strength are needed.
Queen Post Truss Construction: Main Components
The strength of queen post truss construction depends on how each member works with the others. The main components include:
|
Component |
Function |
|
Tie beam |
Connects the bottom ends of the truss and resists outward thrust |
|
Queen posts |
Two vertical members that support the internal truss system |
|
Principal rafters |
Sloping members that form the main roof shape |
|
Struts |
Inclined members that support rafters and transfer load |
|
Straining beam |
Horizontal member connecting the tops of the queen posts |
|
Straining sill |
Member placed between queen posts near the tie beam |
|
Purlins |
Horizontal members that support common rafters or roof covering |
|
Joints and fasteners |
Connect members and transfer forces safely |
Gharpedia lists the main parts of a queen post truss as two queen posts, two principal rafters, struts, a tie beam, straining beams, straining sills, and purlins.
Queen Post Truss Design
The Queen post truss is designed using principles of geometry and engineering to efficiently support the loads acting on the roof. The design uses the basic triangular form, which is naturally stable and strong.
Here’s a step-by-step explanation of the factors affecting Queen post truss design:
1. Triangular Framework
Like most trusses, the Queen post truss uses triangles to ensure structural integrity. The triangular shape is naturally rigid, meaning it cannot deform unless one of its sides changes length.
2. Load Distribution
The vertical queen posts divide the top chord into three sections, allowing even load distribution across the truss. The tie beam at the bottom resists the outward thrust produced by the roof’s weight.
3. Forces in the Members
- The top chord experiences compression due to the weight of the roof and any applied loads.
- The bottom chord (tie beam) is in tension as it resists the outward forces exerted by the roof.
- The queen posts are primarily under compression, carrying the loads from the top chord down to the bottom chord.
- The struts are under compression and tension, depending on the forces acting on different parts of the roof.
4. Span Capabilities
While a King post truss is suitable for spans up to 8 meters (26 feet), a Queen post truss can span distances up to 10 meters (33 feet). This makes it a preferred option for medium-sized roofs.
5. Pitch
The pitch (angle) of the roof can vary depending on the application, but it is usually between 30 and 45 degrees for most Queen post truss systems. The steeper the pitch, the better it is for draining rain and snow, but it also increases the forces on the top chord.
Uses of Queen Post Truss
Queen trusses have been used for centuries in various types of structures due to their simplicity, efficiency and ability to cover moderate spans. Some applications are:
1. Residential Buildings
Queen post trusses are used in residential roofing systems, especially in houses with pitched roofs. They balance structural and aesthetic appeal, making them ideal for modern and traditional homes.
2. Bridges
In addition to roofing, Queen trusses have historically been used in bridge construction. The truss can support the weight of pedestrian or vehicular traffic, making it suitable for small to medium-sized bridges.
3. Timber-Framed Buildings
The Queen post roof truss is a popular choice due to its relatively lightweight design for timber-framed structures. Timber trusses also enhance the aesthetic of exposed ceilings, which are often featured in rustic or heritage-style buildings.
4. Agricultural Buildings
Barns and agricultural structures frequently use Queen post roof trusses. These trusses allow for wide-open spaces without the need for interior supports, which is beneficial in buildings that need large, unobstructed areas.
Benefits and Drawbacks of Queen Post Truss
| Advantages | Disadvantages |
| Efficient for medium span distances and medium-sized roofs and other structures. | The queen post truss spans are limited to around 10 meters (33 feet). |
| Cost-effective as they are simple to design and construct for residential and commercial buildings. | For larger buildings, more complex trusses or additional supports may be needed. |
| The exposed truss serves as a decorative element to the interior of a building, making it an attractive option for homes, churches and other buildings. | Constructing a queen post truss involves more joinery and components than simpler trusses like a king post. |
| It has good flexibility as it can be constructed from various materials like wood, steel, and engineered timber. Queen truss is adaptable to different types of construction projects. | The construction time and labour costs are high for queen post trusses. |
| Truss design ensures that loads are evenly distributed across structures, reducing the risk of sagging or failure over time. | Even though queen post trusses are strong, they are not suitable for structures that need to bear very heavy loads, like industrial buildings or bridges with high traffic. |
Queen Post Truss vs King Post Truss
|
Factor |
Queen Post Truss |
King Post Truss |
|
Vertical members |
Two queen posts |
One central king post |
|
Span suitability |
Medium spans |
Shorter spans |
|
Roof complexity |
More complex |
Simpler |
|
Material use |
Slightly higher |
Lower |
|
Interior space |
Better for wider spaces |
Better for smaller roofs |
|
Common use |
Halls, larger rooms, traditional roofs |
Small houses, sheds, porches |
The main difference is the number of vertical posts and span capacity. A king post truss is simpler, while a queen post truss is better when the roof needs to cover a wider distance.
Construction Steps for a Queen Post Truss
The construction process should follow approved drawings. The steps below explain the general sequence.
1. Finalise roof span and pitch
The span, roof pitch, and height must be decided first. These values affect truss geometry, member size, roofing material, and drainage.
2. Select suitable material
Queen post trusses are commonly built with timber or steel. Timber gives a traditional appearance, while steel may be selected for better durability, longer spans, or modern construction needs.
3. Prepare truss members
The tie beam, principal rafters, queen posts, struts, straining beam, and purlins are cut or fabricated as per design. Member dimensions should not be changed at site without approval.
4. Assemble the truss frame
The truss is assembled on the ground or in position, depending on size and site access. Joints must be tight, aligned, and properly connected using bolts, plates, welds, or approved timber joinery.
5. Install bracing and supports
Bracing prevents sideways movement and keeps the trusses aligned. Supports at wall plates, beams, or columns should be level and strong enough to carry roof loads.
6. Fix purlins and roof covering
Purlins are fixed across the trusses to support the roofing material. The roof covering is then installed with proper overlap, fastening, flashing, and drainage details.
7. Inspect before final roofing
Before closing the roof, check alignment, joint tightness, member defects, termite treatment, corrosion protection, and anchorage. Any visible sagging or misalignment should be corrected early.
Material Options for Queen Post Truss
Timber queen post truss
Timber is common in traditional construction. It gives a warm and natural appearance, but it must be protected from termites, moisture, fungal decay, and warping. Seasoned timber and proper treatment are important.
Steel queen post truss
Steel trusses are used where strength, durability, and longer service life are priorities. Steel members must be protected against corrosion, especially in coastal or humid regions.
Hybrid truss
Some projects use timber for visible members and steel connectors for improved joint strength. This option needs careful detailing so the appearance and structural performance both work well.
Expert Note
Queen post truss design should be checked by a structural engineer or experienced roofing professional. The final design depends on span, roof pitch, roofing material, dead load, wind load, support type, joint strength, timber or steel grade, and local building requirements. Site teams should follow approved drawings and should not remove struts, alter joints, or change roofing material without engineering approval.
Conclusion
Queen post truss construction is a practical choice for medium-span pitched roofs where strength, open space, and traditional appearance are important. It offers better span capacity than a king post truss and works well for homes, halls, verandas, and heritage-style buildings. However, its performance depends on correct member sizing, strong joints, bracing, material quality, and roof-load checks. Before construction, confirm the truss design with a qualified engineer or roofing contractor.
FAQs
- What is a queen post truss?
A queen post truss is a pitched roof truss with two vertical queen posts instead of one central post. It includes a tie beam, principal rafters, struts, and a straining beam. It is commonly used where the roof span is wider than what a simple king post truss can comfortably support. - What is queen post truss construction used for?
Queen post truss construction is used for medium-span pitched roofs in homes, halls, verandas, workshops, farmhouses, and traditional buildings. It helps transfer roof loads to the supports while allowing more open interior space. It is especially useful where a strong roof frame and classic timber appearance are desired. - What are the main components of a queen post truss?
The main components are the tie beam, two queen posts, principal rafters, struts, straining beam, straining sill, purlins, and joints. Each member has a specific role in supporting the roof and transferring loads. Missing or poorly connected members can reduce the strength of the truss. - What is the difference between queen post and king post truss?
The main difference is that a king post truss has one central vertical post, while a queen post truss has two vertical posts. A king post truss is simpler and suited to shorter spans. A queen post truss is better for medium spans and wider roof openings. - What is the suitable span for a queen post truss?
A queen post truss is generally used for medium spans, often longer than a king post truss. Many common references place it around medium roof-span applications, but the exact span depends on roof load, timber or steel quality, member size, spacing, and structural design. - Which material is best for a queen post truss?
The best material depends on design, budget, appearance, and exposure. Timber is preferred for traditional exposed roofs, while steel is useful for strength and durability. Timber needs termite and moisture protection, while steel needs corrosion protection. The structural designer should confirm the final material. - Can queen post trusses support heavy roof tiles?
Yes, queen post trusses can support heavy roof tiles if they are designed for that load. Clay or concrete tiles are much heavier than metal sheets, so member size, purlin spacing, joints, and supports must be checked. Do not change roofing material without engineering approval. - Who should design a queen post truss?
A structural engineer or experienced roof-truss designer should design a queen post truss. The design must consider span, roof pitch, wind load, dead load, roofing material, support condition, joint strength, and local rules. Site workers should follow approved drawings rather than making changes during construction.
Sowjanya Siddanoor