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Wood roof

Why Choose a Wooden Roof?

A wooden roof is an appealing, sustainable, cost-effective, and safe solution. Here’s what it’s made of and why it’s advantageous

For decades, one of the most traditional and widespread construction systems has regained popularity: the wooden roof. Thanks to the consolidation of new technologies (such as laminated wood) and the focus on recyclable and sustainable materials, the wood roof, adequately revised and revisited, is becoming increasingly a winning choice in the construction industry.

Lightness, safety, ease of installation, and energy efficiency are just some of its key features.

But let’s delve into why choosing a wooden roof, what advantages and disadvantages it entails, and how to manage them in the design phase using 3D software for construction.

roof in wood examples

Roof in wood examples

The Characteristics of a Wood Roof

Wood, always appreciated for its ease of processing and availability, strength, and lightness, was gradually set aside, becoming almost “out of fashion,” with the advent of the Modern Movement that exalted right angles architecture and flat roofs, replacing wooden floors with reinforced concrete ones. This phenomenon deeply influenced the way of designing, technical regulations, university research, almost leading to the disuse of wood and its associated construction techniques.

Only since the 1990s has wood roof technology returned to design and construction practice, facing all the challenges caused by the regulatory and training gap consolidated in 50 years of history.

This return to tradition actually makes sense, especially when considering the great qualities of this material:

  • Aesthetic appeal: Wood is appreciated for its natural and warm beauty. A wood roof can give a rustic look to spaces while simultaneously being elegant and welcoming;
  • Versatility: It can be easily adapted to different architectural needs. Beams and slats can be shaped and molded to create curves, arches, and other distinctive structural features. It is easy to shape and can be worked directly on-site for customized solutions;
  • Thermal insulation: Wood is a good insulating material, and a wood roof tends to retain heat during winter and maintain a comfortable temperature inside the building, helping to reduce heating costs;
  • Durability: If built and maintained correctly, a wood roof can last for decades. Wood is a fairly durable material and can withstand weather and climate if treated and maintained properly;
  • Sustainability: Wood is a natural, renewable, and sustainable material. A well-managed wood roof can have minimal impact on the environment, especially if the wood comes from sustainable and certified sources;
  • Construction flexibility: Wood is lighter and more flexible than many traditional building materials, making it easier to construct complex or unusual shapes;
  • Easy maintenance: With regular maintenance, wood shake roofs can remain in good condition for many years. Periodic cleaning and debris removal are often sufficient to maintain the integrity of the structure;
  • Earthquake resistance: In some seismic regions, wood is considered a preferable structural material because it can bend without breaking, thus reducing damage in the event of an earthquake. Additionally, its reduced weight compared to other construction systems makes it less burdensome for the entire structure even in the event of an earthquake;
  • Facilitates air circulation: A ventilated wood roof can allow natural air circulation, which can help maintain a constant building temperature and reduce moisture formation;
  • Variety of finishes: Wood can be finished in many different ways, offering a range of finishing options that can vary from traditional and natural to modern, depending on personal taste.

Before proceeding to delve into some other key aspects, if you need to design a wood roof, we recommend using a 3D software for construction that will be useful for managing all aspects of design: from architectural composition to checking material choices; from creating model renderings and realistic views to presenting the project for obtaining permits and approvals.

Wood Shake Roof | 3D Model created with Edificius

Wood Roof | 3D Model created with Edificius

Structure

In current construction practice, the supporting structure of a wood shake roof is usually made by placing laminated wood beams, on which a double boarding with a total thickness of about five to six centimeters is subsequently laid. It is important to note that the second boarding is laid rotated at a certain angle, previously established in the project, compared to the one below. In this way, it is possible to leave the underside of the floor visible, offering an aesthetic perspective that enhances the wood.

Conversely, in a construction with a concrete-slab floor, the floor is commonly made with reinforced concrete beams and perforated pots, with an overall height of about 20 cm. This structure is then covered with a layer of concrete about 4 cm thick (screed) and internally finished with a thin layer of plaster or drywall. The roof covering, however, can be similar in both wood shake roofs and concrete-slab roofs.

However, a significant difference between the two types of structures lies in their weight.

A wood shake roof, with a laminated structure, weighs on average about 30 kg/m2, while a concrete-slab structure can weigh up to 310 kg/m2. This makes the concrete-slab roof up to ten times heavier than the wood shake roof. This important characteristic makes the wood shake roof especially useful in case of roof refurbishment on existing buildings, additions, and in all those cases where it is preferable or necessary to create a lightweight roof that puts as little strain as possible on the underlying structure.

To calculate a new wood shake roof, or to verify an existing one, you can use specific structural calculation software that allows you to design safely and in full compliance with current regulations.

Insulation

To improve the roof transmittance values, both in the case of a wood shake roof and a concrete-slab roof, it is necessary to use a layer of insulating material. The thickness and characteristics of the material to be chosen depend on the climatic zone and the indications of the regulations.

In terms of thermal insulation in winter, the two roofs behave similarly. Thermal conductivity, indicated by the symbol λ, is the main control variable that influences thermal behavior in winter. Since roof insulation depends on the type and thickness of the insulation, it is reasonable to expect that in both cases, with the same insulation material, their thermal transmittance will be comparable.

Square format

Square format

Air Tightness

Water vapor, a common condition in indoor environments, represents one of the main issues to address when designing wood shake or concrete-slab roofs. In the case of a wood roof, especially if the insulation layer consists of wood fiber, we are exposed to a phenomenon of vapor transport by convection.

This phenomenon occurs when indoor air, generally laden with moisture, enters the floor package, expands into the gaps, and, upon contact with colder points, tends to condense. This cycle of condensation and evaporation, associated with the typical moisture of wooden materials and their behavior during freezing, can lead to a weakening of the mechanical resistance of the structure, causing damage to wooden components, and reducing thermal resistance.

The transmission of vapor by convection is often a cause of structural problems that are difficult to detect immediately. To prevent this phenomenon, it is essential to design the roof stratigraphy so that vapor transmission occurs solely by diffusion, through materials perpendicular to the faces. In this mode, the vapor passing through the stratigraphy is significantly lower than in cases of convection transmission and, with a section designed correctly in terms of thermo-hygrometry, does not cause moisture accumulation problems.

To achieve effective air tightness and minimize vapor transport by convection, it is necessary to place a functional layer of “air tightness” above the boarding and below the insulation layer, to preserve the visual appearance of the wood from the inside. Similarly, attention must be paid to external air penetration, using a windproof membrane above the insulation layer. In this way, the insulation package is protected from vapor convection.

In the case of concrete-slab roofs, air tightness is usually guaranteed by the same internal plaster layer, also used for aesthetic purposes.

To ensure the protection of the wood structure from rain, it is necessary to consider vapor management. Installing a bituminous membrane, which acts as a vapor barrier, above the insulation layer can trap vapor inside the stratigraphy, causing condensation problems. On the contrary, to ensure effective vapor disposal while also protecting against rain, it is advisable to use a functional “ventilation” layer (a characteristic typical of “ventilated roofs“), composed of an air gap and a suitable support for the water-resistant layer.

This layer can be made with a double cross-bracing, on which bituminous membranes or other water-resistant elements can be placed. Lately, these solutions are becoming common even for concrete-slab roofs, which previously had the membrane directly on the insulation layer and, as a roof, tiles fixed with mortar.

Some Disadvantages

Despite its numerous qualities, there are also disadvantages to installing a wood roof:

  • High initial cost: Installing a wood roof can involve higher initial costs compared to materials like concrete;
  • Maintenance: Wood requires regular maintenance to preserve its integrity and aesthetic appearance. This may include periodic painting, repairing any damage caused by wear and tear, inspecting the roof conditions for the presence of fungi, insects, and other biological damages;
  • Vulnerability to weather elements: Despite some treatments that can increase wood’s resistance to weather elements, continuous exposure to rain, sun, wind, and snow over time can cause damage. This may require localized repairs or replacement of some parts of the roof. However, interventions are usually not very costly and are simple to carry out;
  • Combustibility properties: Wood is flammable, which can pose a risk in case of fire. Therefore, houses with wood shake roofs may require more expensive fire insurance and specific treatments to improve fire resistance.

In summary, a wood shake roof can offer a series of advantages, but it is important to carefully evaluate the disadvantages before making a decision regarding the material to use.

Composition of a Wood Roof

Regardless of the type of wood used for construction (laminated or solid wood), a wood shake roof has some recurring elements in its material layers, such as:

  • Support structure made with beams and joists (or rafters) responsible for supporting the building’s roof;
  • Wooden boarding (often made of OSB3 panels) resting on the secondary structure and necessary for housing other layers (insulation, vapor barrier, etc.) and for closing the roof;
  • Waterproof layer, which protects the structure from water while ensuring air passage;
  • Insulation layer to improve the energy performance of the roof assembly;
  • Roof covering often made of tiles (in terracotta or concrete) placed on double wooden battens (tile-bearing battens) to create the so-called ventilated roof;
  • Gutters, flashings, and downspouts to allow rainwater to flow away from the roof.

The roof can be characterized, besides the type of structure and material layers, also by the inclination, shape, and number of slopes. In any case, especially in rainy or snowy areas, it is advisable to exclude flat roofs and create slopes with a minimum of 20%.

 

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