Gap Between Roof Sheathing And Insulation

Synthetic stucco photograph 8.

Gap between roof sheathing and insulation.

By leaving an air space between the insulation and the sheathing we can have air flow over the framing. This ventilation offers another benefit. With the air gap we get drainage and the control of hydrostatic pressure. Shingles roofing felt stackups are on the boundary between class i class ii vapor retardency when dry at about 0 1 perms and when the roof is wet there is.

An air space between the insulation and the bottom of the roof sheathing is desirable. If there is a leak the air flow ventilation will help dry out the moisture. Actually panels marked sized for spacing simply mean that they are slightly smaller to allow for the recommended 1 8 gap see attached apa tt 055. So you re talking about you re going to reroof and you have a gap between the wall sheathing and the roof sheathing.

However it is considered good practice to leave a 1 8 gap between sheets and that is also recommended by apa but it is not required. Fasten roof sheathing panels properly. For vaulted or cathedral roof construction provide a free ventilation path from eaves to ridge between all rafters. 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.

Providing an air gap between the stucco cladding and the exterior face of the foam sheathing prevents the debacle we got with face sealed exterior insulated finish systems a k a. Beyond the decreased capacity for insulation when venting the roof deck venting the roof deck or the attic has some other drawbacks worth considering. And i was advised that that gap should be protected by a home inspector. The solution is not to ignore the insulation but to add one component.

Now wait a minute. It doesn t mean that panel edge clips h clips are required although there are types of clips that will help with properly spacing the panels. Unless you have at least a 1 gap between the roof deck and roxul with both ridge soffit venting putting putting foil facers on the interior side is going to create a moisture trap. Without a proper air space to allow the insulation and roof to dry out this water will collect potentially leading to rot and mildew.

The one bit of advice is to leave a little air barrier between the top of the insulation and the bottom of the roof sheathing just in case you get some condensation it will have a chance to burn off better from sun on the roof if you don t firmly pack insulation against the sheathing.