Chimny sprayfoam? | Ask Mason Knowles - SPF Consultant | Spray Foam Technical Questions and Answers | SprayFoam Magazine Q&A Forums

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Brian Hall Posted: Oct 17, 2012 02:56 PM	Chimny sprayfoam? Hi guys, Im not new to foam- but i have a unique foam situation with a chimny. Looking for some thoughts on this. The whole place is foamed (cabin) 12/12 roof- sprayed to the top sheeting. The customer has made a 2foot x 4 foot by 14 feet tall chimny box. The insulated Selkirk chimny will come from the main 12/12 proceed 14 feet up and out this box. Being were in Canada, my concern is condensation, so my plans would be to foam the interior of this box- effectively making the box part of the interior envelop of this cabin. Being there is no air movement in there- would this get too hot? the chimny recommendation is 2 inches from a combustible. were approx 8 inches. The alternative is to leave the box not insulated, terminate the envelope at the ceiling (which you really cant do as you cannot spray foam right to the chimny) then every-time the chimny is used- it warms and cools this box that has moisture from the broken ceiling vapour barrier. Plus not to mention if its doesnt get used- a whole winter of moisture freezing in there. I have full pictures if needed.
mason Posted: Oct 18, 2012 10:48 AM	Sprayfoam's physical properties will become affected at temperatures approaching 200 degrees F. Sprayfoam should not be sprayed directly to any surface that is expected to reach those temperatures. I would recommend another type of more heat resistant insulation for your purposes. One way is to put a heat resistant insulation against the hot surface and then install foam to it. This is the way we insulate hot stacks in roofing applications. See SPFA's AY 104 for design details for hot stacks. It is available at spray foam.org in the technical document section.
Brian Hall Posted: Oct 22, 2012 12:11 PM	Thank you for the reply- this makes more sense in this application. I think i will stay away from foaming the whole enclosure and terminate this at the Roof-line.

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Comments

Brian Hall

Posted: Oct 17, 2012 02:56 PM

Chimny sprayfoam?

Hi guys, Im not new to foam- but i have a unique foam situation with a chimny. Looking for some thoughts on this. The whole place is foamed (cabin) 12/12 roof- sprayed to the top sheeting. The customer has made a 2foot x 4 foot by 14 feet tall chimny box. The insulated Selkirk chimny will come from the main 12/12 proceed 14 feet up and out this box. Being were in Canada, my concern is condensation, so my plans would be to foam the interior of this box- effectively making the box part of the interior envelop of this cabin. Being there is no air movement in there- would this get too hot? the chimny recommendation is 2 inches from a combustible. were approx 8 inches.
The alternative is to leave the box not insulated, terminate the envelope at the ceiling (which you really cant do as you cannot spray foam right to the chimny) then every-time the chimny is used- it warms and cools this box that has moisture from the broken ceiling vapour barrier. Plus not to mention if its doesnt get used- a whole winter of moisture freezing in there.
I have full pictures if needed.

mason

Posted: Oct 18, 2012 10:48 AM

Sprayfoam's physical properties will become affected at temperatures approaching 200 degrees F. Sprayfoam should not be sprayed directly to any surface that is expected to reach those temperatures. I would recommend another type of more heat resistant insulation for your purposes.

One way is to put a heat resistant insulation against the hot surface and then install foam to it. This is the way we insulate hot stacks in roofing applications. See SPFA's AY 104 for design details for hot stacks. It is available at spray foam.org in the technical document section.

Brian Hall

Posted: Oct 22, 2012 12:11 PM

Thank you for the reply- this makes more sense in this application. I think i will stay away from foaming the whole enclosure and terminate this at the Roof-line.

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