What Goes Underneath a Roof?

The underside of your roof protects your home from water damage
Read Time: 2 minutes
Jun 28, 2022

When you look at a roof, you see the shingles, the metal panels, or the tiles. The exterior of the roof isn’t the only part of the roof, however. There’s a lot that goes on underneath the roof to protect your home from the elements. So what, exactly, goes underneath the roof and how does it benefit your home?

What Is the Underlayment?

a contractor laying shingles on top of the underlayment of a roof

The underlayment is the layer directly beneath the shingles, tiles, or whatever roofing material is used on the outermost layer. The underlayment is a water-resistant layer that’s usually made out of rubber, fiberglass, or felt. Water in its liquid form isn’t able to pass through the underlayment, so even though it is water-resistant instead of completely waterproof, it can still protect your home from the rain while allowing moisture to pass through as needed.

What Is the Water Shield?

Underneath the underlayment is the water shield. This layer of your roof sticks onto the roof deck below and is meant to protect your roof from water and ice. This waterproof layer protects your home from water damage by creating a barrier at the eaves where water could get under the top layers of the roof.

What Is the Roof Deck?

roofers laying shingles on top of a roof deck

The roof deck is the lowest layer of the roof and sits on top of the roof trusses. Typically, the roof deck is made out of OSB or plywood.

What Is a Radiant Barrier?

a radiant barrier on the underside of the roof deck viewed from an attic

A radiant barrier is an optional layer that is applied to the side of the roof deck that faces down into the attic. This barrier helps to block UV rays from entering the home and helps to reduce heat and lower energy bills.

What Is Roof Ventilation?

ventilators on a shingle roof

Moisture and heat rise and can therefore get trapped in the attic and cause mold and mildew problems if the attic isn’t adequately ventilated. The ventilators in the roof go through all of the above layers but have to connect to the attic so that hot, moist air can flow through to the outside.

What Are Roof Trusses?

the roof trusses of a home that is in the process of being built

The roof trusses are the wooden beams that form the base of the roof. This is the frame of the house that all other layers of the roof sit on top of.

What Is Roof Insulation?

insulation on the underside of a roof in the attic

Insulation helps to regulate the temperature inside the house by blocking out heat and cold during the summer and winter, respectively. It is placed against the underside of the roof deck where it can prevent heat or cold from entering the attic.

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