Ceiling Space conditions

[carlosgw]

Any source or experience with conditions in a ceiling space of a wood frame multi-family building. (Northern United Sates) The ceiling space is open web wood joists. Each apartment has a ducted split system with the duct installed in the ceiling space. the question is - do the conditions warrent duct insualtion to prevent condensation?

 

[imok2]

To Answer that question you would need to know what conditions are I should think!

 

[cdxx139]

Whats the temperature inside the duct?
Whats the temperature in the cieling space?
Whats the temperature on the outside of the duct?


knowledge is power

 

[ChrisConley]

Bah, who needs numbers. Yes. Conditions warrant duct insulation to prevent condensation on the duct.

Unless you expect the dewpoint in the attic to never exceed the surface temperature of the duct. Even then, why waste energy 'cooling' the attic. Duct insulation will save energy and help prevent condensation.

 

[carlosgw]

I am not refering to an attic. It is a space between a drywall ceiling and the floor above (or insulated roof above).

 

[ChrisConley]

Same comment as previous then, but replace the word attic with ceiling space.

 

[MechEngNCPE]

Insulate the duct, geez.

 

[DrRTU]

Which code(s) are you working to? IMC requires insulation for attic space duct - review the zone for the r value of the insulation required. Most codes will allow un-insulated duct if the duct is contained inside the conditioned space. You may have an issue of max TD of 15F between duct and space. This system will sweat if the system is starting from a large TD as in the case of occupied from unoccupied. In my region, (Chicago) the external wrap will cost about $2.25 /ft2 so insulation is not cheap from the contractor point of view. I normally do not insulate the interior duct unless required.

 

[lma1]

If this is a Part 3 building according to our BC Building Code or the Vancouver Building Bylaw, ASHRAE 90.1-2007 would be applicable. For our climate zone (#5) and an unconditioned floor space, insulation is not required for heating-only ducts, R-1.9 for cooling-only ducts and return ducts are not required to be insulated. For combined heating and cooling supply ducts, R-3.5 is required and again return ducts are not required to be insulated.

Even if this standard does not apply, it is still good practice to follow from an energy efficiency point of view.