Install Question - Attic Insulation Shield

[Vigil Igne]

The attic insulation shield has a height of 15" before putting on the top collar. Add in that my trusses are only 3-1/2" and I get a total height of 18-1/2". I'm in COLD country and have to blow in 20" of insulation eventually. So what do I do? I'm guessing that the frame I make for the support box could be made with 2x6's or 2x8's to give me a bit more height. Sound right?

 

[DAKSY]

Check to see if the manufacturer makes an extension for his part. Many of them do. If he doesn't,
I would get a piece of sheet metal, the same gauge as your shield & attach it to the existing one.
Roll it to the correct diameter, with a 2" overlap & then cut the top surface to the roof pitch & run it right up to the underside of your sheathing.
Once it's in position, attach them togther using zip screws.

 

[Highbeam]

The purpose of the shield is to hold away the insulation the required 2" or more. The shield itself can be made of plywood so long as it stays outside of the 2" clearance. So, it is possible to frame and build a chase around the chimney of wood as tall as you want it. Some folks use sheets of durock or sheet metal instead of plywood.

In my two attics I used the square duravent insulation shields and when I was blowing in the insulation I just lowered the insulation depth around the chimney and before I was done went back with a vacuum to make sure none had fallen in. Over time, the insulation settles even more.

 

[JabaduGarfunkle]

Fully enclosed chimneys require a rafter radiation shield when installed (at least with Selkirk chimney parts they did). Not sure if framing an attic insulation shield all the way up to the rafters would be considered 'fully enclosed' but something to consider.

 

[Vigil Igne]

Thanks everyone! I'll go ahead and just use 2x8's for the support box.