Roof decking: definition and importance

Roof decking: definition and importance


Roof decking is the sturdy layer found underneath the roof covering. So if you want a strong roof, you will need a strong deck. If you want to protect your property from the weather and extreme temperatures efficiently, then it is important to install the roof decking in a professional manner.

Here’s what you need to know about decking before you get started, whether you are building a new roof or repairing an older one.

Definition of decking

The roof decking is the set of plywood boards that are placed on the frame and which forms the structure of the roof. The decking is the part of the roof that closes the structure while ensuring its solidity. It is located exactly between the structure and the membrane that will cover the roof.

Before plywood sheets, roof decks were more often made of wooden planks. For buildings built before the 1960s, it is most likely that the deck is made of wood.

What is the purpose of roof decking?

Roof decking is the foundation of any roof and therefore plays a very important role. In fact, it is on the decking of your roof that the coating will be fixed. It is therefore essential to maintain the latter and must be adequate by meeting the standards of the National Building Code (NBC). For example, its thickness must generally be ½ inch to prevent the sheets from sagging.

The decking also serves to reinforce the structure and improves the insulation of the building.

Insulation, ventilation and wood decking

The attic plays an essential role towards the proper ventilation of your home. If your home is not properly ventilated, your deck will quickly deteriorate. Mould, mildew, fungus and contamination of all kinds could occur, and your deck will have a much shorter life span.

Poor ventilation is most often detected by the presence of droplets falling from the ceiling or by the presence of condensation. If your roof is soft, that means your decking is damaged and must be replaced. It is also possible that poor ventilation is the cause of the problem. Good ventilation in the attic will preserve your roofing decking for many years.

A well-insulated roof will not only keep your property at a comfortable temperature, but it will also protect the roofing materials.

How do i install a roof deck?

When rebuilding a roof deck, there are two options depending on its state of repair: adding a layer or replacing it. The first option consists of installing an additional layer of plywood to solidify it or to level it if it presents irregularities.

If you have a wooden frame, adding plywood is an effective way of making the deck stronger without having to replace it. In all cases, the first layer must be sound and solid, meaning there must be no mould, rot, swelling, etc.

If a roof deck is in poor condition, it can be replaced in part or in its entirety, although the second option is more rare. This involves removing the sheets or boards, then nailing plywood (at least ½ inch) to the rafters. You will also do this when installing new decking.

Decking a flat roof

A “flat roof” is any roof with a slope of less than 2/12. These roofs must meet specific requirements. For example, they must have openings of at least 1/150 of the surface area. By comparison, a regular roof only requires openings of 1/300 of the surface area.

When it comes to decking a flat roof, it must be designed in such a way that water does not accumulate on the roof. That means the roof must have a slight incline towards the roof drain. If puddles are forming, the decking is probably inadequate.

Difference between decking and roof structure

When we refer to the structure of a roof, we are talking about its framework. This is most often made of wood. The rafters, to which the decking is nailed, are part of it, as well as several other components such as joints, beams, etc. While the roofer takes care of the decking and the entire roof covering, the structure is the responsibility of the carpenter.

In short, before starting the construction or repair of your deck, it is important to know your type of roof, particularly its slope (flat roof, for example), in order to meet its specific requirements. You will also need to be aware of the National Building Code (NBC) standards.

If you need a helping hand or for any questions, don’t hesitate to contact our team of experts at Toiture FCA: we are always happy to help!

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