Lloyd Hamilton's words on the pool bubble
We have a new participant at TWL - Lloyd Hamilton. Here's his (unedited) take on the pool:
Cheshire Pool Evaluation and Remediation Report
I evaluated the current operation of the Pool Complex this spring prior to the pressurized dome being removed. Currently, the functionality of the building is extremely problematic and the building has deteriorated significantly. The leakage of warm moist air from the pressurized dome into the permanent structure creates a high vapor pressure within the permanent structure and the inner surfaces of the roof and exterior walls constantly condense the vapor during the winter. The rain inside the permanent structure during warm days in winter is from condensate that froze on the underside of the roof deck that melts in the warmer ventilation air. This condensate creates ideal conditions for the growth of mold. All of the sheetrock was removed from the building due to mold damage and contamination. The roof needs replacement due to rot.
The permanent structure can be made able to withstand the high vapor pressure without mold growth and without structure failure. I began the design process with the assumption that the building must be able to withstand wetting without damage as elimination of the moisture is not possible. I then addressed the vapor load and designed a significant reduction of the leakage rate through the existing pressure barrier while providing a direct route out of the building for the rest of the leakage. This will lower the daily vapor pressure while making the building able to withstand blasts of high leakage, such as during a swim meet. The net result will be a building that is able to function with the pressure dome while reducing energy consumption and increasing comfort.
My first task was to design a roof system that would withstand the moisture while keeping the inner surface warm enough to prevent condensation. I chose Advantech sheathing for its ability to withstand repeated wetting without failure. (The first time I saw it used on a job it was used as sub-flooring that remained exposed to the weather, without a roof, for three years with so little deterioration that it did not have to be leveled for installation of the wood floor.). On top of the Advantech Carlisle CCM-705 air and vapor barrier will be installed to create an impervious layer that also serves as a drainage plane for the roof. The moisture from within the building will be stopped by this layer with only a few molecules able to squeeze through. On top of the impervious layer, R-60 of insulation will be installed to keep the roof deck warm and keep the condensation point well away from the deck under all conditions. The moisture will go elsewhere to condense.
The roof intersects with metal stud knee walls on top of the inner masonry walls. In the lobby area these stud walls are more extensive, but built the same. These walls are currently draining their internal condensation down between the inner and outer masonry walls. The exterior walls are showing a lot of effervescence, a tell tale sign of excessive moisture movement through the wall. With the roof system no longer condensing most of the moisture, the walls will condense much more so my next task was to make the framed walls able to withstand the conditions. Again, preventing condensation is the key design criteria. The wall/roof interface is a critical point so I paid close attention to it. There are short knee walls, built of metal studs, where the barrel roof crosses over the inner masonry wall and by insulating them on the outside I can bring the insulation up to the roof and seal the interface with caulk and tape. I have specified Dow Metal Building sheathing for this air/moisture/thermal barrier.
The lobby has large framed walls with windows in them. These will need to have the windows and outside finish removed down to the metal studs. The side walls that are currently covered with metal, on the ends of the barrel roof, will also need to be stripped down to the metal studs. The Dow system will be installed over the metal studs, the same as the short knee walls and then a STO exterior insulation and finish system will be installed over all ofthe Dow product to complete the wall assembly.
The advantage to this make-over is that the building will no longer rain inside during the winter. Condensation will still occur at times, but it will be limited to the exterior masonry walls where the moisture can do little damage. This way the building can withstand any level of moisture intrusion from the pressurized dome without component failure and the condensation that does occur can be easily dealt with. If the existing masonry cladding system was also removed and the STO cladding system was installed, along with new windows, with insulation down to the footing, then none of the walls will ever condense.
However, simply making the building withstand the moisture is not a full solution to the problem. Reducing the amount of moisture intrusion must also be accomplished. This requires sealing up the existing pressure barriers so that they will not pass the huge quantities of air they now do and providing a direct vent to the outside to create a ducted route out of the building for the air and moisture. The air lock on the lifeguard side of the building will have a duct installed to the outside to vent the airlock and the center hinge door needs to be replaced. The walls and ceiling also need to be sealed at every seam. This will eliminate most of the air coming in through this opening in the concrete wall. On the public side, the revolving door needs to have a much better air seal and the wall and ceiling area that separates the pool area from the permanent structure will have to be sealed up air tight. The main corridor doors need to be repaired and have weather stripping installed. This will create an inner air lock that can be vented to the outside through a duct. The result will be that almost all of the leakage will be removed or vented which will keep most of the moisture from the building interior.
I have also discerned that the pressure inside the dome is kept at a 1.25”-1.5” of water column (wc) all of the time, when it only needs this pressure during a storm. The dome remained fully expanded at .75” wc and did not start to sag until the pressure was less than .5”wc. The pressure can be reduced most of the time which will also reduce the total leakage through the pressure barrier and help keep the permanent structure dry while reducing the energy used to keep the dome pressurized and warm.
The lobby area will still be susceptible to moisture at times, such as a swim meet, and therefor needs a vent to the outside. Because the need for this vent will vary based on the use of the building, it will have a manual control to vary the speed of the fan. The lifeguard side also needs have a vent with the same properties as the lobby vent. These vents, in conjunction with the existing locker room vent, can be operated to put the lobby and lifeguard areas in slight negative pressure relative to the outside, which will bring in dry outside air to replace the moist air from the dome and will help keep the building dry. When the building becomes too wet, the existing portable commercial dehumidifier can be used to remove the moisture.
The surfaces that were covered with sheetrock will be recovered with DensArmor Plus mold resistant interior drywall panels from Georgia-Pacific. Mold resistant paint will be used. This will make sure the drywall is not able to grow mold, no matter what the moisture load of the building is.
It is through a combination of making the building able to withstand moisture, reducing the moisture load by closing the leakage paths between the dome and permanent structure and providing ventilation in the right places that will make the permanent structure work with the pressure dome. This is not a band-aid approach, but rather a comprehensive, building science based, re-engineering of how the building functions to allow it to work with the pressure dome. The energy savings from this comprehensive approach should be at least 30% due to the reduction in outside air used to keep the dome pressurized and a reduction in the energy load of the pool and permanent structure, combined with better operation and utilization of the energy control system already installed.
Respectfully submitted,
Lloyd Hamilton
President
Verdae, LLC
90 Primrose Hill Road
Rhinebeck, NY 12572
845-597-7369
www.Verdaellc.com
Comment away! And as I mentioned about ten days ago, I have very little time for the blog right now... so back to my paper on the economic meltdown... fun, fun!!! Currently debating if I should address the symptoms (Wall Street) or the disease (Washington, DC).
Tim White