| Author |
Message |
Nathan Woods, CSI, CCCA, LEED AP
Senior Member
Username: nwoods
Post Number: 681
Registered: 08-2005
| | Posted on Tuesday, July 14, 2015 - 01:41 pm: |    |
I have a project with an indoor pool. We have a dedicated HVAC system for this room, and it includes a huge dehumidifier system, and we are pumping warm air directly on our windows, and have a high number of air changes in the space. We are good on HVAC. However, I need to detail and specify the interior wall and ceiling construction, and running into questions:
1a. Is it better to have a vapor barrier paint coating (such as: http://www.sherwin-williams.com/painting-contractors/products/catalog/moisture-vapor-barrier/) over an Aqua-Tough or DensShield type gyp sheathing, or to have a sheet applied vapor barrier behind the sheathing?
1b. If I went with sheet applied, any recommendations?
2. I have 6" light weight concrete and metal deck roof, with R-30 rigid insulation above the concrete, and capped by a cool roof compliant SBS roofing system. Not quite sure where the dew point would be in that assembly, and not sure where the vapor barrier in that assembly should be located. Thoughts? |
ken hercenberg
Senior Member
Username: khercenberg
Post Number: 927
Registered: 12-2006
| | Posted on Tuesday, July 14, 2015 - 02:27 pm: | |
Where is the project located? What is outboard of the sheathing? How are you handling water (liquid or condensation) that occurs within the assembly? Is there a vapor source on the other side of the walls? Hard to say what to do at the walls without knowing the wall assembly and relative conditions.
Remember that every drainage plane must have a way to drain.
Regardless of geography, I'd be concerned about using lightweight concrete as lightweight aggregates hold moisture. You will already have vapor drive pushing up from the pool below so my guess is that there is a high probability of needing a vapor retarder applied direct to your deck assembly. I'd get in touch with the roof manufacturer for product as they may have specific requirements for this type of application.
How are you going to make sure your metal deck doesn't rust out? |
Nathan Woods, CSI, CCCA, LEED AP
Senior Member
Username: nwoods
Post Number: 682
Registered: 08-2005
| | Posted on Tuesday, July 14, 2015 - 02:53 pm: | |
Ken, this project is in sunny southern California.
One wall of this room is an exterior wall, and it's 14" thick with 8" studs, 3" Continuous insultation, and rainscreen assembly. The other three walls are interior walls. All walls have Ceramic Tile on them, full height.
I am considering use something like this directly over the sheathing, under the tile motar assembly: http://noblecompany.com/products/nobleseal-ts
I currently have a hardlid ceiling, which I assume will be sheathed in DensArmor Plus or Aqua-tough or similar. Perhaps I will then coat it with this: http://www.sherwin-williams.com/painting-contractors/products/catalog/moisture-vapor-barrier/
The concrete deck has 15mil Stego directly below it. The pool itself is a prefab pool sitting on/in a concrete pit. The deck around the pool is an epoxy resin traffic rated material from Dex-O-Tex or Pacific Polymers or similar. |
Phil Kabza
Senior Member
Username: phil_kabza
Post Number: 561
Registered: 12-2002
| | Posted on Tuesday, July 14, 2015 - 05:39 pm: | |
Metals within the room and within the enclosures need extra corrosion consideration due to chlorine. Even 304 stainless steel will corrode in this environment. Door hardware, lintels, window operators, etc. will all need extra attention or will have limited lives.
I share Ken's concern about the roof assembly. An SBS roof is essentially a vapor barrier at the exterior; with excess moisture under it, it will blister. For protection from the moist pool air, the vapor retarder wants to be on the deck as he points out. That creates the heretical dual vapor barrier situation, with the moisture-holding lightweight concrete stuck in the middle. You may want to look at distributed venting across the roof, and you will definitely use a venting type base sheet directly on top of the lightweight. |
ken hercenberg
Senior Member
Username: khercenberg
Post Number: 928
Registered: 12-2006
| | Posted on Tuesday, July 14, 2015 - 06:02 pm: | |
Agreed Phil. Venting may work. Nathan, any chance for an IRMA configuration? Avoids the moisture chamber. Hot-rubberized asphalt systems are very tolerant of vapor drive unlike their mod bit sheet cousins.
For the walls you may be able to get away with a non-vapor permeable membrane on the face of the sheathing under the setting bed. Check with the usual suspects (Custom, Mapei, Laticrete)for your best system. |
J. Peter Jordan
Senior Member
Username: jpjordan
Post Number: 854
Registered: 05-2004
| | Posted on Tuesday, July 14, 2015 - 06:13 pm: | |
Agree with Ken about the metals but consider putting something on the concrete deck around the pool. I have specified FRP doors for these situations (especially the door to the pump room), and I limit these to the ones that are all FRP (not aluminum stile and rail with FRP faces) and that come with FRP frames. These are pretty expensive, but will neet little or no maintenance over the life of the facilty. |
Nathan Woods, CSI, CCCA, LEED AP
Senior Member
Username: nwoods
Post Number: 683
Registered: 08-2005
| | Posted on Tuesday, July 14, 2015 - 07:59 pm: | |
Oddly, Custom, Laticrete, Mapei, etc...all make a variety of waterproofing materials, but none seem rated for anti-vapor permeance.
Ken, no idea what an IRMA configuration is.
So, between the pool and the roof I have a plenum. I have vented metal decking for the concrete roof slab. I have return air in the plenum. HVAC is good. Just trying to figure out the dew point/condensation plane location in the ceiling if I put rigid insulation on the pool side of the plenum, and I'm trying to figure out the right materials for the ceiling and wall membranes. |
ken hercenberg
Senior Member
Username: khercenberg
Post Number: 930
Registered: 12-2006
| | Posted on Tuesday, July 14, 2015 - 11:07 pm: | |
Plenum changes everything.
First, IRMA = Inverted Roof Membrane Assembly: You adhere the membrane direct to the deck and put the insulation on top. Roof acts as both roof and vapor barrier. It's actually a form of waterproofing. Very effective. Membrane is protected from heat and UV while not being subjected to temperature fluctuations. Pretty clever really. Hard part is getting the insulation to stay put in high-wind areas.
Okay, so with the plenum in between, the roof seems like it gets taken out of the picture. With the HVAC system properly balanced, you could very possibly avoid having a dew point occur. I'll leave that for your mechanical engineer to figure out.
When you say you want to put rigid insulation on the pool side of the plenum I presume you mean in the plenum. Not sure if you want to do that or not. If you insulate the top of the ceiling you may lose the benefit you gain from conditioning the plenum. The nice part of all this is once you have established equilibrium in the system, all you have to do is maintain it.
As to the wall, Laticrete has a vapor reduction coating - http://www.laticrete.com/Portals/0/datasheets/LDS5070.pdf that might work. Not really sure it's designed for vertical applications. On the other hand I would think that something like EasyMat by Custom would do it. Unfortunately their product data sheet doesn't address perm ratings. One of the Noble Seal products would probably work as well. Unfortunately the ANSI standard that they're tested to don't seem to include perm ratings. |
Greta Eckhardt
Senior Member
Username: gretaeckhardt
Post Number: 17
Registered: 08-2013
| | Posted on Wednesday, July 15, 2015 - 09:15 am: | |
Many wise comments have been offered already. At the same time, I have heard enough stories about serious problems with corrosion, condensation and air quality surrounding indoor pools that I suggest that the Architect or Owner hire an building enclosure consultant who is well versed in building science and knows how to coordinate building enclosures with HVAC systems. |
Wayne Yancey
Senior Member
Username: wayne_yancey
Post Number: 748
Registered: 01-2008
| | Posted on Wednesday, July 15, 2015 - 11:17 am: | |
Greta has provided the best advice and recommendation in this thread.
This is serious business requiring serious building science expertise.
As Greta noted, the solution goes way beyond the air/water/vapor barrier in the exterior enclosure.
In addition to the exterior enclosure materials, chose the nonferrous metals for use in an interior swimming pool wisely. Chlorine treated swim water attacks Type 304 stainless steel aggressively. Guard railings, handrails, and door hardware are all in danger of corroding prematurely. Select a stainless steel type with extra-low carbon content.
For example:
UNS S32003 lean duplex stainless steel (LDSS) is a molybdenum-enhance, proprietary duplex stainless steel alloy. Cr, Ni, Mo, and N are controlled to give a phase balance similar to that of duplex stainless steel, while reducing costs.
UNS S32003 LDSS can be an economic alternative to Type 316L stainless steel, providing enhanced strength and corrosion resistance.
Don't be penny wise and pound foolish.
That is all I have to say about that. |
Bill Coady CSI, CCPR
Senior Member
Username: billcoady
Post Number: 22
Registered: 06-2006
| | Posted on Wednesday, July 15, 2015 - 11:42 am: | |
Just a caution: If there are any exterior (or interior) insulating glass units (IGU's) on this project you need to confirm with potential suppliers that their insulating glass seal warranty will be valid in this type of installation. Many IGU fabricators have boiler plate exclusions on their warranties for this type of application. As has been noted by others, the chlorine rich environment is hard on materials including sealants used to make IGU's.
Also, even though there is talk about a quality HVAC system with numerous air exchanges and the project is in So. Cal., plan on condensation forming at times on the glass. This isn't a flaw in the IGU but simply a function of humidity and dew points. Triple pane with low E on #2 and #5 and argon fill will provide the warmest inside glass surface (#6), which will allow more relative humidity in the pool area before the dew point is reached. I don't recommend using double pane with low E on #2 (normal) and a fourth surface low E (even if it is my company's product). The 4th surface low E will improve the U value as promised but the inside glass surface temperature is reduced a bit as a result of the 4th surface low E. Lower surface temperature means dew point is reached with lower RH in the pool area which means more condensation on the glass.
If you have exterior glass have your HVAC designer consider vents below the glass to act as "defrosters". |
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