Cathedral support box question

[AlexS]

Hello, we are getting ready to install the cathedral support box between the rafters. We marked the pitch (10/12) of the rafter on the box and found that part of the support box will be shorter than the bottom of rafter by at least a few inches. The instructions say that the support box may be installed flush to the lowest side of the ceiling, but is it okay to have the support box above the lowest part of the ceiling as long as the proper 2" clearance around the chimney is maintained below the support box? Any help would be appreciated.

 

[RetsooR]

How tall is your support box? If you bought a kit most come with 12" or so boxes. I remember the one I used said it needed to be installed 2 inches below lowest point of ceiling . They make taller boxes . What brand are you using?

 

[RetsooR]

I believe what will happen is your single wall or double wall stove pipe will not have proper clearance.

 

[AlexS]

How tall is your support box? If you bought a kit most come with 12" or so boxes. I remember the one I used said it needed to be installed 2 inches below lowest point of ceiling . They make taller boxes . What brand are you using?

It's a Selkirk brand, seems to be one of the few brands sold in our area. The support box is approximately 17" in height. Do you know of a brand/company that sells taller boxes in Canada? We're looking for a box that would fit a 10/12 pitch roof with 2x8 rafters.

 

[bholler]

It's a Selkirk brand, seems to be one of the few brands sold in our area. The support box is approximately 17" in height. Do you know of a brand/company that sells taller boxes in Canada? We're looking for a box that would fit a 10/12 pitch roof with 2x8 rafters.

Just don't run it all the way to the top of the rafters.

 

[RetsooR]

Yea with a 17 inch box you should have enough box for 10/12 . Check your angle again. 10/12 should be ready close to 40 degrees.

 

[AlexS]

Just don't run it all the way to the top of the rafters.

Thanks for the information, definitely helpful!

Do you happen to know if it is recommended to add shielding insulation inside the support box to fill the void between it and the chimney? (this would be proper universal shielding insulation (JUSI/SUSI) from Selkirk)

 

[AlexS]

Yea with a 17 inch box you should have enough box for 10/12 . Check your angle again. 10/12 should be ready close to 40 degrees.

Thanks, we'll double check before installing to make sure we haven't gone wrong somewhere.

 

[bholler]

Thanks for the information, definitely helpful!

Do you happen to know if it is recommended to add shielding insulation inside the support box to fill the void between it and the chimney? (this would be proper universal shielding insulation (JUSI/SUSI) from Selkirk)

Check with the chimney manufacturer. But generally no

 

[AlexS]

Just don't run it all the way to the top of the rafters.

Thanks for the information

Check with the chimney manufacturer. But generally no

Good to know, I'll see what they say. Thanks again for the quick reply!

 

[MoDoug]

Do you happen to know if it is recommended to add shielding insulation inside the support box to fill the void between it and the chimney? (this would be proper universal shielding insulation (JUSI/SUSI) from Selkirk)

I went through this last year, same situation and manufacturer, but my roof pitch is only 5/12. I called the insulation manufacturer Selkirk about the safety of using the insulation and she assured me they did extensive testing of it before they had to meet the UL requirements. Even tested it up to 2100 degrees. That is exactly what the insulation was made for. Call their tech assistance, from my experience they've been very easy to get a hold of and provide great customer service.

If you're doing the install yourself, document everything, every step of the way, with photographs. I did my install. the inspector wanted the photos, and my insurance company wanted the inspection.