# Condensation on suspended ceiling grid



## Yikes (Aug 13, 2014)

I have a client who has a problem with their recent remodel of an existing building (it's not my design, thank God!).  They are getting condensation in the tracks of the T-bar ceiling, and it is staining the lay-in ceiling tiles.  He says the problem is everywhere, not just at the HVAC grilles or near other pipes.

This problem  occurs only at the second story ceiling, which has a hip-roofed attic immediately on the back side of the tile.

When I quiz him further, it appears that they:

(A) removed the old drywall ceiling leaving the old ceiling joists in place to function as collar ties

(B)  insulated and put radiant barrier up on the roof RAFTERS, leaving the eave vents exposed to the attic

© installed a fan-coil system, put in the suspended ceiling system, and put insulated flex duct to the registers in the T-bar ceiling.

I realize that the eave vents are essentially allowing outside unconditioned air to circulate directly onto the suspended ceiling, effectively bypassing all that insulation up in the rafters.  T-bar ceilings are generally leaky - -they don't make for a good air barrier!

At this point, I suspect that the T bar metal itself is getting cool air on the underside of the T, and moist unconditioned air on the top edge of the T.  That said, this is a very mellow climate (Los Angeles coast), and I've never heard of anyone out here having this kind of problem.  When I try to research online, most of the places that have condensate problems are in humid parts of the country.

Thoughts? Any other theories?

If the problem truly is at the lay-in ceiling itself, could we just close off the attic vents and treat the (former) attic like and unconditioned "plenum"?


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## cda (Aug 13, 2014)

Where are the actual hvac units located

On the roof or above ceiling


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## ICE (Aug 13, 2014)

What was used for the radiant barrier and how was it installed?


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## steveray (Aug 13, 2014)

The rafter bays need to be ventilated, not neccessarily the "attic"...keep that air where it belongs and it shouldn't be an issue....


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## Frank (Aug 13, 2014)

Insulate the eaves and close off the attic vents as the attic is now in the thermal envelope.


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## pwood (Aug 13, 2014)

Frank said:
			
		

> Insulate the eaves and close off the attic vents as the attic is now in the thermal envelope.


I agree with Frank.


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## michaelj (Aug 13, 2014)

Is there any source of negative pressure in the building? have seen this a lot in restaurants and kitchens where warm moist air is being pulled in around tile and hits face of cool grid and then condensates.


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## retire09 (Aug 13, 2014)

Frank has got it right. The space above the grid is within the thermal envelope and is not an attic requiring ventilation.


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## Yikes (Aug 14, 2014)

cda: the fan-coils are located above the T-bar ceiling, in what we used to call the attic.

ICE: the radiant barrier was a foil stapled to the underside of the batt-insulated roof rafters.

michaelj: no negative pressure that I'm aware of.  It's just an ordinary office use.

Frank, I'm inclined to agree: if the owner closes off the attic vents then it's functioning more like a soffit located within the conditioned thermal envelope, rather than an unconditioned attic.


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## jeffc (Aug 15, 2014)

I would bet the grid is cold due to the A/c system working overtime to cool the space below. Sounds like the warm exterior air is entering the attic above the grid is hitting the cold metal of the grid and condensing. I agree that closing off the vents would help to solve the problem.


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## ICE (Aug 15, 2014)

Closing off the attic vents will make it worse.  The insulation should be laying on the T-Bar.  The attic should be well ventilated with openings high and low.  If the radiant barrier is wrong in material or installation, it's adding to the problem.


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## Frank (Aug 15, 2014)

ICE said:
			
		

> Closing off the attic vents will make it worse.  The insulation should be laying on the T-Bar.  The attic should be well ventilated with openings high and low.  If the radiant barrier is wrong in material or installation, it's adding to the problem.


The insulation on top of the drop ceiling is not effective and is not counted towards meeting the energy code.   2012 iecc 502.2.1 The described arrangement is a conditioned attic.  http://www.buildingscience.com/documents/reports/rr-0301-unvented-roof-summary-article/view


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## mtlogcabin (Aug 15, 2014)

> The insulation on top of the drop ceiling is not effective and is not counted towards meeting the energy code


It would be effective with  keeping the ceiling grid from condensating if that is the problem.


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## Paul Sweet (Aug 15, 2014)

It will only be effective until the first time somebody goes above the ceiling to change a filter or work on the equipment, and pushes the insulation out of his way.  This was popular 30 - 40 years ago, and after a few years the insulation looked like swiss cheese.


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## jeffc (Aug 16, 2014)

yikes mentioned in the first post, "(b) They insulated and put radiant barrier up on the roof RAFTERS, leaving the eave vents exposed to the attic." They are ventilating the heated space below the insulated ceiling. Installing insulation directly above the grid will only be temporary as this everyone how pulls new wires, adds pipe, replaces tile never puts the insulation back. The IEEC states, Insulation installed on a suspended ceiling tiles shall not be considered part of the mininum thermal resitinace of the roof.


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## ICE (Aug 16, 2014)

Removing the drywall was a mistake.



> Installing insulation directly above the grid will only be temporary as this everyone how pulls new wires, adds pipe, replaces tile never puts the insulation back. The IEEC states, Insulation installed on a suspended ceiling tiles shall not be considered part of the minimum thermal resistance of the roof.


I didn't get the idea that IEEC compliance was the objective.  If the insulation is displaced and the ceiling starts to drip, they should know what to do.  If not, let them call a plumber.


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## tmurray (Aug 18, 2014)

ICE said:
			
		

> Closing off the attic vents will make it worse.  The insulation should be laying on the T-Bar.  The attic should be well ventilated with openings high and low.  If the radiant barrier is wrong in material or installation, it's adding to the problem.


How would it make it worse? The reason there is condensation is that you have warm moist air condensing on the tbar that is cold due to air conditioning.


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