How to Build: Attics

When building an ICF home, especially for energy savings, it is important to examine the full envelope of the home, and ensure that all of the efforts put into the walls are not wasted when you get to the roof. 

Attics in an ICF Home

First, there are a couple of options when you get to the attic, which will make or break your home’s energy efficiency. There are two types of attics. The first is a vented attic. The second is an unvented attic. Each has its own benefits and challenges. Additionally, adding a radiant barrier will also increase the efficiency of your home.


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Vented Attic

The first kind of attic we will compare is a vented attic. A vented attic is an insulated ceiling, with an open and vented soffit and ridge, or vents placed on the ends of gables.  The theory behind this design is to encapsulate the home’s heating and air conditioning within the living space only. This keeps the attic as a separate unconditioned space. Building vented attics has been the normal construction practice for years. 

In the summer the heat that builds up in the attic is vented out through the ridge or gable vents, and cooler air is brought in through the soffit vents.  The goal of this design is that this vented area will create a buffer zone between the hot roof and the cooler interior and thus reduce the AC load.  In most homes, the seal between these 2 zones is full of leaks. These leaks can be found around lights, at HVAC penetrations, and anywhere the insulation layer has been moved or compressed. 

Unvented Attic

Second, let’s discuss unvented attics. Unvented attics are built with insulation of the attic is placed at the roof level, and the area inside the attic is a conditioned space. This has several advantages, including less air transfer, and what air does transfer is conditioned.  You can reduce dust buildup using an unvented attic versus a vented attic. There is also a smaller chance of stray or wild animals taking up residence. 

It also places much of the HVAC system into a more temperature and humidity stable environment. This extends the life and efficiency of the system.  You will still have a condenser outside. However, the A-coil and most of the refrigerant lines will be isolated from the drastic temperature and humidity swings of a vented attic.

Gable ends on a vented attic can be built with either stick framing or ICF with little difference really in the efficiency of the system. However, a non-vented attic will see a significant boost to the efficiency with ICF gables.

In this system, with ICF gables and sprayed Icynene insulation at the roof level, the chance of air leaks into the attic space is negligible.

Radiant Barriers

Lastly, radiant barriers are also excellent additions to an attic area to ensure maximum efficiency.  Most radiant barriers are a foil product that is typically adhered to a stronger substrate.  Some newer products have come out which are spray on, as well.  Radiant barriers require an air gap to work.  The size of this varies among barriers but can be anywhere from ¼” to a few inches. 

The main idea behind the radiant barrier is to reflect the heat and prevent it from affecting the insulating material below. You can use radiant barriers with both vented and unvented attics.