Ducts Between Attic Floor Joists

[Michael Thomas]

Ducts embedded in insulation and compressed to fit between joists - it's so dumb I can't seem to find documentation explicitly prohibiting it from either a installation or energy efficiency standpoint - anyone have any links or code cites?

(Last pic is a bonus fro' slapper: baffles laying around in moldering attic, none installed at eaves.... )

[Jerry Peck]

Ducts embedded in insulation and compressed to fit between joists - it's so dumb I can't seem to find documentation explicitly prohibiting it from either a installation or energy efficiency standpoint - anyone have any links or code cites?

How much insulation is below the duct and what is its R-value?

If the insulation is compressed, not only is it no longer not the specified thickness, its R-value is GREATLY reduced, making it no longer the required R-value.

The duct insulation does not count as thermal envelope insulation. The correct amount of thickness/R-value would need to be present above or below the duct, the duct is nothing but air and does not count.

I believe you now have your energy code reference - what is the minimum insulation required for ceiling/attic?

[Ted Menelly]

Ducts embedded in insulation and compressed to fit between joists - it's so dumb I can't seem to find documentation explicitly prohibiting it from either a installation or energy efficiency standpoint - anyone have any links or code cites?

(Last pic is a bonus fro' slapper: baffles laying around in moldering attic, none installed at eaves.... )


Well as far a properly insulating the attic floor the thin wall duct is not doing that great a job. you cannot compress the duct just about at all, just like when they are hung up (which is what they should be) and the straps crimp them off.

It also looks like you have a moisture problem in that attic with all the sheathing blackened. Was any of it soft or rotted. WHen you walked on it did it fell like you were going to go thru.

[Michael Thomas]

t also looks like you have a moisture problem in that attic with all the sheathing blackened. Was any of it soft or rotted. WHen you walked on it did it fell like you were going to go thru.

Moisture problem was why I was there, - lot's of problems in this attic: poor vapor retarder, sloppy insulation installation, obstructed soffit vents, compressed ridge vent, bathroom exhausting into soffit, many unsealed penetrations between conditioned/unconditioned space, condensing furnace w/o intake pipe (required by manufacturer) depressurizing attic, etc etc etc.

Where possible I like to include links in reports to articles discussing specific defects, none of my articles on duct installation specifically discuss those ducts, I'm hoping someone will post a link with a cross-section of compressed duct and compromised insulation with a big red X through it. :D

[Dan Harris]

Moisture problem was why I was there, - lot's of problems in this attic: poor vapor retarder, sloppy insulation installation, obstructed soffit vents, compressed ridge vent, bathroom exhausting into soffit, many unsealed penetrations between conditioned/unconditioned space, condensing furnace w/o intake pipe (required by manufacturer) depressurizing attic, etc etc etc.

Where possible I like to include links in reports to articles discussing specific defects, none of my articles on duct installation specifically discuss those ducts, I'm hoping someone will post a link with a cross-section of compressed duct and compromised insulation with a big red X through it. :D

Does site help?
http://www.flexibleduct.org/download/ADC~Inst.pdf

Duct tape question on another post. It also address's type of tape...

[Jerry Peck]

Michael,

Maybe this will help.

From the Florida Building Codes: (bold red text is mine)
- 1.0 General requirements.
- - 1.2.2 Insulation R-values.
- - - Insulation R-values shall be determined as follows:
- - - - a. For insulation that is not compressed, the rated R-value of insulation shall be used.
- - - - b. For calculation purposes, the effective R-value for insulation that is uniformly compressed in confined cavities shall be taken from Table B-3.
- - - - c. For calculation purposes, the effective R-value for insulation installed in cavities in attic roofs with steel joists shall be taken from Table B-18.
- - - - d. For calculation purposes, the effective R-value for insulation installed in cavities in steel-framed walls shall be taken from Table B-17.

Okay, so it is not "uniformly compressed" and not in "confined cavities", but how else would one be able to apply a number without something be "uniformly compressed" and "confined"?

Table B-3 is attached.