Roof Insulation Air Gap

A boarded roof with plywood sheet providing structural strength over the rafters what all these have in common is.

Roof insulation air gap. At the ridge and also at the bottom either through vents at the eaves or. 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. Water is insulation s enemy. So much information has been devoted to the subject of roof venting that it s easy to become confused and to lose focus.

So i ll start by saying something that might sound controversial but really isn t. 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. Box out light fixtures. The r 0 87 value for the first value in this air r value table subsection.

This gap must be ventilated at the top i e. You literally must have a void nothing in the air gap except air itself. It creates a breeding ground for mold and mildew and ruins the air trapping pockets that block heat flow. Now with explanation of air gap would i be better served to place the radiant barrier on the underside of the roof rafters.

Insulation is technically a solid with a lot of air in it therefore it is not an air gap. An air space between the insulation and the bottom of the roof sheathing is desirable. 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. 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.

With a warm roof the usual process is to split the insulation into two layers. Air gap or air film 3 4 air space insulating properties. 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. 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.

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.