Wil RC Channel eliminate the need for ventilation

[M_Freeman]

We are in plancheck for a remodel and have a problem

Sec 1203.1 2006 IBC states "Enclosed attics and enclosed rafter spaces where ceilings are applied directly to the underside of roof framing members shall have cross ventilation for each seperate space..."
How does the application of RC channel to the framing then applying the gyp bd to RC channel instead of "directly to roof framing" affect this code?
I have a small balcony over living space that is impossible to ventilate the floor joists bays due to firecodes. I would think the RC channel would exempt us as we are not applying the ceiling directly to the framing?

[brian schmitt]

nice try no cigar imho:D

[Jerry Peck]

We are in plancheck for a remodel and have a problem

Sec 1203.1 2006 IBC states "Enclosed attics and enclosed rafter spaces where ceilings are applied directly to the underside of roof framing members shall have cross ventilation for each separate space..."
How does the application of RC channel to the framing then applying the gyp bd to RC channel instead of "directly to roof framing" affect this code?
I have a small balcony over living space that is impossible to ventilate the floor joists bays due to firecodes. I would think the RC channel would exempt us as we are not applying the ceiling directly to the framing?


The entire intent and concept of and for that section is being misunderstood/mis-interpreted/mis-applied in the above.

Let's start over with the basics:

a) The attic space needs to be ventilated. (Notice the "." after that, as in " ... needs to be ventilated PERIOD" :) )

b) When there is no attic (i.e., the drywall is attached directly to the underside of the rafters) but only separate rafter bays between the rafters, those rafter bays "shall have cross ventilation for each separate space" (i.e., each rafter bay shall be ventilated such that it has "cross ventilation" or air in one end of the rafter bay and out the other end of the rafter bay).

Okay, now let's take your design as I understand it: You have living space with a flat roof above and that flat roof area is being, or going to be, used as a balcony/deck area ("deck" is more appropriate than "balcony" in this case by definition of balcony) and the rafter are: c) running with open ends at both ends; d) running with one end closed at the structure's wall.

If c) above, then each rafter bay can be cross-ventilated, however, if d) above, then the rafter bay can only be ventilated from one end - not fitting the requirements of the code. However, being as the code was not intended to be a design limiting factor in cases such as this, the ventilation would be achieved as 'best possible and best practical', which, yes, could include installing vents at the open end underneath the rafter bay at the overhang and installing raised vents at the inboard end of the rafter bay near the wall, thereby creating the cross-ventilation specified.

So ... what's the problem? :D

Brian, how did I do explaining why 'close but no ceegar'?

[brian schmitt]

The entire intent and concept of and for that section is being misunderstood/mis-interpreted/mis-applied in the above.

Let's start over with the basics:

a) The attic space needs to be ventilated. (Notice the "." after that, as in " ... needs to be ventilated PERIOD" :) )

b) When there is no attic (i.e., the drywall is attached directly to the underside of the rafters) but only separate rafter bays between the rafters, those rafter bays "shall have cross ventilation for each separate space" (i.e., each rafter bay shall be ventilated such that it has "cross ventilation" or air in one end of the rafter bay and out the other end of the rafter bay).

Okay, now let's take your design as I understand it: You have living space with a flat roof above and that flat roof area is being, or going to be, used as a balcony/deck area ("deck" is more appropriate than "balcony" in this case by definition of balcony) and the rafter are: c) running with open ends at both ends; d) running with one end closed at the structure's wall.

If c) above, then each rafter bay can be cross-ventilated, however, if d) above, then the rafter bay can only be ventilated from one end - not fitting the requirements of the code. However, being as the code was not intended to be a design limiting factor in cases such as this, the ventilation would be achieved as 'best possible and best practical', which, yes, could include installing vents at the open end underneath the rafter bay at the overhang and installing raised vents at the inboard end of the rafter bay near the wall, thereby creating the cross-ventilation specified.

So ... what's the problem? :D

Brian, how did I do explaining why 'close but no ceegar'?
jp,
very well done my steaming colleauge! if you can't dazzle them with your brilliance them baffle them with your bull$h$t:D freeman should run this by the ahj and get his opinion!

[Robert Hronek]

From an energy efficiency standpoint I think the better option would be to spray foam the cavitiy eliminating the need to vent.

What I am picturing is a 2 story home with a flat roof above a portion of the main floor. If you vent the underside of the decking the interior side of the cavity will need to be air sealed to prevent and air exchange from the flat roof area to inside the building envelope. Also there is a limited space to insulate between the drywall and roof decking. The effects of radiant heat on and from the deck and convection in the insulated cavity with leave the effective R value much lower, maybe 50%, than the stated R value. Plus the effectiveness of venting moisture will be questionable. I think closed cell foam insulation would make sense and eliminate the need for venting.