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
There are a couple of options when you get to the attic, which will make or break your homes energy efficiency. The two types of attics used in construction are vented attics versus unvented attics. Each has their own benefits and challenges. Additionally adding a radiant barrier will also increase the efficiency of your home.
A vented attic has been the norm for a number of years and is characterized by 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 homes heating and air conditioning within the living space only and keep the attic as a separate unconditioned space.
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. It is hoped 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, around lights, at HVAC penetrations, and anywhere the insulation layer has been moved or compressed.
An unvented attic is built so that the 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. There is less buildup of dust, compared to vented attics, and 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, extending the life and efficiency of the system. You will still have a condenser outside, but 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, but 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 are also excellent additions to an attic area to ensure maximum efficiency. Most are a foil product, 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. Radiant barriers can be used with either vented or non-vented attic designs.
Hear from Michael Drew as he talks about the advantages of an ICF attic.