Layers of the Roof and Their Job

The top surface of a roof goes a long way to provide its main characteristics whether you’re talking about the sleek dispersal of rain from a metal roof, being indestructible against wind like a slate tile roof, or being environmentally friendly as wood shakes and cedar shingles are. It should be noted though that while the surface material of a roof plays a large part in the durability and life span of the area, the products and layers below that material ultimately decide how the roof stacks up in inclement weather and years of wear.

One of the main reasons to hire a roofing contractor that comes with a strong reputation is so they hopefully won’t skip corners on your project. The layers below the roof surface need to be installed meticulously but they also cost valuable labour time and material costs. Since the underlay is going to be immediately covered up by the roofing material, it can be tempting for the contractor to skip steps they may deem unnecessary. Although those workarounds won’t be visible to the naked eye at first, they’ll soon be noticeable when the starts to fail due to a poor installation.

It’s important for consumers to understand these various layers and the job they perform. It’s then wise to check with the roofing contractor to make sure these products are quoted, supplied, and installed so that the home owner gets the maximum life out of their new roof.

 

Rafters / Joists

Trusses and Joists

In your home the rafters and joists perform some very important tasks. First of all, the angle at which the rafters are built are what gives the roof its pitch and thus determines what type of material needs to be installed (tile, slate, etc.). If a heavier roofing material is used, the rafters need to be reinforced to support the extra weight demands needed. Straight joists are used in place of rafters on flatter roofs. Joist construction usually requires a specific type flat roofing decking and membrane as tiles and slates will allow water ingress below manufacturer’s minimum pitch (profile tiles 10 degrees and above, small plain tiles 35 degrees and above & slate 20 degrees and above).

 

Insulation

Actis Hybris Insulation

Insulation is installed between the roof joists as a way to lower utility bills inside the house. The insulation provides year-round effects such as reflecting the heat in the Summer and keeping warm air confided to the house in cold months to reduce heating bills.

 

Breathable Roofing Felt

Monaperm 700 Breathable Felt

Roofing felt or underlay, is the first layer of material that is installed to start prevent moisture exposure. If the surface material is installed correctly, felt should never have to do its job – never coming into contact with leaking water. It’s an extra barrier to prevent water coming in which can happen during severe storms or if the tiles or slates are damaged by flying debris or slip from their position. Breathable Felt has the unenviable job of being both breathable, yet water-resistant which is why it’s important not to skimp on poor quality materials in this layer of roofing.

 

Batten

Roof Batten

In countries where asphalt shingles are the most popular roofing choice, plywood or OSB sheets are laid on top of the roof rafters to serve as a nailing surface. This adds to the weight of the roof incredibly and becomes a fire risk as well as creating a much hotter attic. In the UK battens are used to support our preferred roofing material of tiles. The battens are small wood strips installed perpendicular to roof joists on top of felt. The battens serve as an area to fasten the tiles to while also providing support. It’s therefor important to choose a good quality batten. Fully graded batten to BS5534 is the best and safest option. Tiles typically sit vertically across three rows of batten which prevents them from sagging and bowing.

 

Flashing

Lead Flashing Detail

Lead flashing performs many versatile roles within a roof. The material is extremely durable and can last Up to and exceeding the lifetime of the building. Lead is also very flexible especially witnessed by its uses on a roofing install. Flashing is sold in lead rolls which can be used to provide a weatherproof gulley or valley within a roof. The material can also be cut and bent into smaller pieces to create step-flashing around brickwork, windows, and where two sections of home meet at different levels. Flashing creates a seamless mesh between two surfaces, sealing up gaps and providing a waterproof joint. It can also be used for bigger area like loft conversion dormer cheeks and flat roofs. In these instances its important to follow guidelines set out by the lead sheet association to ensure the correct thickness (known as the ‘code’) and in panels of the right dimensions( to avoid thermal splitting caused by building movement

 

Vents

Plain Tile Vent

Ideally a roof needs to function much like a combustible engine with an equal amount of intake and exhaust. Fresh air is important to cool the roof to help prevent algae growth and condensation. The air must also have somewhere to exhaust through so that a circulation is present. Intake ventilation is created with vents in the fascia. A breeze enters through this spot under the eaves, permeates the interior of the roof, and exits through vented tiles on the surface. Ventilation is important to expand the lifespan of the roofing materials and also to help control utility bills within the home.

Roofing Material

Tiles, slates, metal and shingles are materials that provide two important tasks – 1) protect the top of the home from weather related damage and 2) to provide aesthetic appeal. Each type of material has its advantages and disadvantages in this regard:

  • Tiles – clay and concrete are available in a variety of styles and colours. Tiles sold in the UK must meet frost requirements to deal with the wet, freezing, and thawing cycles so they are a durable material.
  • Slate – a stone, but one that is easier to work with than traditional hard materials. Better served in simpler roofs with less curves but offer varieties of colours from grey to purples to greens.
  • Metal – aluminium, zinc, copper, and more materials that can be installed on pitched or flat surfaces.
  • Shingles – commonly constructed of a Western Red Cedar that weathers in a rustic manner. Significantly less life span than other materials.

Each layer of roofing performs an important role in the overall performance of the entire structure. No layer should be skimped and each section should be properly installed as to not compromise surrounding components.

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