Roof Insulation Air Gap

An air space between the insulation and the bottom of the roof sheathing is desirable.

Roof insulation air gap.

Does not consider internal convection effects does not consider presence absence of reflective barriers does not consider directions of heat flow up or down nor winter summer conditions. It creates a breeding ground for mold and mildew and ruins the air trapping pockets that block heat flow. Water is insulation s enemy. Air gaps larger than this work well too they promote ventilation on the foil and help keep the air dry and the air temps lower.

You literally must have a void nothing in the air gap except air itself. It is important that air is allowed to circulate between the roof covering and the insulation to avoid condensation a gap of at least 50mm 2 inch must be left between the insulation and the inside of the roof covering. At the ridge and also at the bottom either through vents at the eaves or. The r 0 87 value for the first value in this air r value table subsection.

A vented attic where insulation is placed on an air sealed attic floor is one of the most underappreciated building assemblies that we have in the history of building science. A cold deck flat roof. Box out light fixtures. Air gap or air film 3 4 air space insulating properties.

So i ll start by saying something that might sound controversial but really isn t. With a warm roof the usual process is to split the insulation into two layers. A boarded roof with plywood sheet providing structural strength over the rafters what all these have in common is. This gap must be ventilated at the top i e.

If 180mm is to be installed then 100mm board might be introduced between the rafters there has to be a minimum 25mm air gap between the insulation and the underside of the tiles or slates with an 80mm board running across the rafters. Let s start with the only situations with between rafter insulation where you do actually need a 50mm ventilated air gap over the insulation a loft conversion where there is a bitumen felt in place. I had originally thought on top of the insulation and under the attic plywood flooring to reduce the heat on the underside of the roof shingles. In the winter humidity from the house s interior will get past the insulation and come in contact with the cold roof sheathing where it will condense into water.

Now with explanation of air gap would i be better served to place the radiant barrier on the underside of the roof rafters.