INSULATING EXPOSED CEILING TRUSSES

QUESTION FROM GARY OF INDIANA:

We have small cottage that has the trusses visible. we are wanting to insulate between the trusses next to the roof but we want to keep the trusses visable and not cover. What kind of insulation could we use, if anything? Is there something with a back that would fit between the ceiling trusses with a back on it that would not have to be covered?

ANSWER FROM THE INSULATION DOCTOR:

Regarding insulating your trusses ( if they are conventional) between the roof and the top truss core, it is not recommended to install insulation on the underside of the roof deck. Doing so will cause the plywood to rot or mildew. The insulation should be installed on the flat of the truss if it is flat ceiling.

Also another type of truss you might have is part of the roof rafter system (bridge trusses) and if there is enough depth to provide air space between the top of the insulation and the underside of the roof at a minimum of 2", you can do so and meet your requirement to keep the trusses exposed if you use a non-combustible faced insulation. This is commonly referred to as FSK25. This is a foil-backed flame resistant insulation. Standard foil and standard kraft-backed insulation do not meet the FSK25 flame-spread requirement.

Another means to maintain air space between the insulation and underside of the roof would be to install baffles or proper vents from the top to the bottom of the slope before installing insulation. If you are not sure what type of trusses you have and can send me a drawing, I would be glad to take a look at it.

Bruce Jones
The Insulation Doctor