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How to install soffits on a roof pediment

When installing new siding on a house, it is common to replace the soffit and fascia at the same time. This doesn’t have to be the case, as they can be done separately, but when completed at the same time, it provides a uniform look in the home. If you can put the siding in place, you can handle the soffit and fascia. Knowing the finest way of doing it will make the work much faster and smoother.

What is a soffit?

A soffit is an aluminum sheet placed under the edge of the roof, the cornice, the perforation of which allows air to enter the attic. You can find the ventilated soffit on sloping roofs since plexes with flat roofs in Montreal do not have one, at least not like suburban homes. Do not confuse the flashing that completes the edges of the plex roofing with the soffit. If your house has a sloped roof with a soffit under the edging, you will need to lay a fascia to cover the wood along the side portion of the edging. Briefly, the soffit use to have a purpose of “ventilation grid”.

To be effective, an air circulation system must have an equivalent inlet and outlet so that air can flow from one opening to the other. There are different types of openings called “vents”: roof overhang, ridge, gable and roof. If air enters under the roof edge, it can exit through the gable vents on the front and back of the house, for example.

The soffit performs a ventilation function by allowing good air circulation in your attic or attic. In winter, when the temperature inside is high, it prevents the accumulation of humidity while reducing the formation of icicles under the roof edge. In the month of summer, it will mark your air conditioner more effectual.

James Hardie

What exactly is a fascia?

The fascia is a fragment of aluminum that makes up the roof. It is an accompanying element of the soffit. They cannot be installed separately. The fascia is also often underestimated for being only a decorative accessory. Yet, it plays a crucial protective role in a home, while sealing the roof with the soffit and gutters.

Covered soffit

If the soffit is already covered then you will be adding the new soffit. This makes the soffit installation simple. You can be sure that you are using a J channel to support the soffit.

Uncovered soffit

Where there has never been an overlap on the soffit, you will need to use a J-channel to support the soffit. This will also be the case if a previous soffit has been removed.


With an aluminum soffit, you will need to leave room for expansion. Typically, a ¼ inch expansion piece at each end of the soffit will be sufficient, although in cooler climates this should be increased to 5/16 inch at each end. This will give ample room to accommodate changes in temperature without bending the soffit.


There are two choices with the soffit, vented or non-vented. Ventilated soffits have small holes to allow air circulation in the attic, while non-ventilated ones are just solid. Maximum people choose a mixture of the two. This will still allow sufficient ventilation in the attic without drawing too much cold air from outside.

Gutters and downspouts


The soffit is sold in lengths. These are not meant to be a long length that spans the entire length of the house. As an alternative, it must be divided to the soffit width, with the pieces lock up together. The type of locking mechanism between the parts will vary from manufacturer to manufacturer, but the end result is the same in all cases.


When the soffit reaches an angle, you have two options. You can either miter the corner at 45 degrees or go with a square cut. While a bolster may look better, most people will find the 90 degree cut much easier to perform. Either way, you’ll have to use a T-channel to make the connection.

What is the fascia for?

The fascia is part of the roof. It is on its surface that the gutter is installed. It therefore creates a sealing barrier between the gutter, the soffit and the house. Being exposed to the elements, its role is to prevent the different elements from entering the house and causing damage to the structure.

Some tips for installing a fascia

Soffit and fascia installation is a task that must be completed with care. If you do not do it the right way, the fascia will not perform its protective role well and installation errors will appear. Those without renovation experience should call in experts to carry out the process.

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