Stetten Home Services arrived on a hot summer morning, installed a wireless relative humidity device, and thoroughly inspected the floor of the house from the interior and the crawlspace by crawling through every last foot. It was noted that the home has two package units and a 3rd split system for the 3rd floor. It was noted that both package units have 4″ Fresh-Air intakes.
1) Venting – The crawlspace was built without vents which is very common. When I build new homes, I also skip the vents. Because there is an extended period of time, during construction, where the crawlspace has no active drying mechanism, crawlspaces can get moldy prior to completion of construction if the home is built during the summer months. One strategy to reduce the risk of this, is to install 2 crawlspace doors on opposite sides of the crawlspace to allow for cross ventilation during construction. The closer the crawlspace door is to the top of the space, the better it allows the hottest most humid air escape, but no door allows the top 12″-16″ of air to escape, which is why cross-ventilation is a great temporary strategy, because air can really blow through under the right windy conditions.
2) Insulation – The insulation strategy used on this home is a rare one. CORE-FILL low-expanding-foam was forced(squirted or poured) into the center of each hollow concrete block through holes drilled from the inside of the crawlspace. It appears that the top 1 or 2 courses of block are actually solid blocks, which is why in some areas, but not all, there is a 2″ thick strip of foam board insulation affixed to the top 4″ of the wall. The foam board strips were attached with a Hilti Brand Concrete Nailer, which is the best method available, and it is a mystery as to why this same method was not used to affix the wall liner to the walls and piers of the crawlspace. The band-joist has properly installed friction-fit fiberglass batts.
3) Design – A sealed crawlspace requires at least a 6mil vapor barrier, 100% coverage of dirt, penetrations in the wall to be sealed, a drying mechanism, and a reliably air-tight door, in addition to either R-19 in the floor of the home, or R-10 on the walls and R-13 in the band-joist. So the crawlspace would pass code in most areas in NC even now. Building code does allow “HOUSE AIR FANS” to be used as drying mechanisms. I am not sure why the fans sold for this purpose are not HUMIDISTATICALLY CONTROLLED. If the fan runs 24/7, it will not last as long, it will cause the maximum amount of noise, use as much energy as possible, and it could potentially depressurize the interior, which is the opposite of what most building scientists would recommend. The danger, if there is any, is that air would be pulled IN through furnace flues, chimney flues, water heater exhaust pipes, or from the garage/crawlspace, which is not safe, healthy, or ideal. Also, using glue for sealing the liner is very inconsistent, and not as durable or reliable.
4) MOLD – The actual temperature was about 74 degrees and the relative humidity was 50%. All the mold that was visible in the crawlspace was dormant, and this is pretty easy to figure out. The mold was dry, similar to dust, or DORMANT everywhere i could find it, and in many areas there was actually no mold. The mold seemed to be worse further away from the crawlspace door, which leads me to believe that during construction the crawlspace got funky and remained less funky near the crawlspace access door, which during construction was the ventilation strategy. The further from the door, the higher the moisture must have been. I don’t normally recommend dealing with mold directly, but in this case, it would be interesting to clean all the floor joists where mold is visible, and see if it ever returns.
5) Condensation – When moisture is in the air, it is attracted to and moves to cold surfaces. Moisture moves from Hot to Cold. The coldest temperatures in the crawlspace are the areas nearest the supply side trunks. This means, that any moisture in the air will be drawn to the duct-work, and if the temperatures of the duct-work are below dew-point, the moisture will condense, turning from vapor into liquid, and run down hill until it puddles, at which point it will re-evaporate, or drain into some other location, such as dirt, or out a drainage tube. [note on dew-point: the difference between a high-performing sealed space and poorly performing sealed space can be as little as a 1% change in humidity. The lower the dew-point the better in the summer, and the higher, the better in winter, depending on ere you are and what you are looking at compared to ambient conditions, and desired conditions. So both of the HVAC supply trunk-lines were totally saturated with water at the lowest point right before the 14″ duct goes through the crawlspace wall. the one on the left had a big rip that i made bigger, and the one on a right had no rip at all, and then i punctured the outer liner slightly and took a video of about a gallon coming out of the duct, right before I got bit by a spider on my arm and then my camera ran out of memory. I was able to delete some pictures and finish, and my arm is fine.
0) 1st thing is already taken care of! 🙂 We have installed a monitor which allows us to know real-time how the CS is doing.
1) DUCT-SEALING, – Recommended not to save you money, but rather to make sure we don’t have any condensing surfaces, or at least as few as possible. “Duct-Sealing” is not as easy when the ducts appear rather perfect, but in fact are not, in an ideal situation, someone would carefully cut out the duct-insulation at every single joint that feels cold to the human hand, or where you can tell there is moisture, and cover it with closed cell spray-foam, this is a ridiculous proposition unless a spray-foam rig is needed for other purposes. In other words, you wouldn’t pay the daily minimum or $2000 simply for duct-sealing, because you could probably pay $2,000 dollars to have the entire foundation wall properly insulated and sealed along with the floor penetrations, band-joist, etc.
Sealed duct-work in a sealed crawlspace is a little redundant, but I still recommend it, even when I install a Supply Air-Inducer, because I like having ADJUSTABLE DRYING rather than 24/7 or brute force drying. If you can measure the performance and adjust the input factors, at least you have a chance at figuring it out. The other way that one could seal the duct-work, would be to cut the insulation carefully seal the inner joints with mastik, and then carefully re-apply the insulation, adding more as needed, and taping it all up to keep air out of the liner/insulation.
2) Taping – When we provide DELUXE SEALED CRAWLSPACES we use about $75-100 dollars(3-4 rolls) worth of 4″ super sticky 6m white plastic tape per $1,000 Square Feet and about 30 Minutes of Labor per roll. This crawlspace is HUGE, has about 30 PIERS, and the plastic has about 5 times the amount of joints than I would expect. I think it would require about 8 Rolls of Tape and 4-6 man hours to full seal all the seams in the vapor barrier. Specific care should be taken around the main plumbing drain pipes, where they penetrate the liner, and in areas where water would flow if a pipe busted or whatever, so that you could install a future water-leak alarm in the low-point that would trip if any water water inside the crawl.
3) Disable the House Fan Drying Mechanism and Install Adjustable Supply Side Drying Mechanisms with Back-Flow Dampers.Done Properly, the intake vents would be plugged at the floor, with bags of fiberglass insulation.
3b) DRYING CHANGE – Find a convenient way to disable the fresh-air intakes, and also how to enable them easily as needed. I suggested having a fully taped filter that could replace the one that actually filters the ventilation air, but the box itself isn’t completely tight or perfectly shaped to make 100% sealing easy. It definitely is a huge penalty to have these operating when the delta-T is high. Winter/Summer pulling in ambient air in not ideal. The drying mechanism for a sealed crawlspace might already be ventilating the house even though that is not the intention.
4) Mold Wipe Down – I almost never recommend this, but I think someone should wipe down, with a box of damp disposable rags, (with hazmat suits). The more mold spores we get out, the more moisture is would take to have a mold bloom. This work makes sense, because someone down the road could hire an inspector who diagnoses the dormant mold incorrectly and causes a problem in a transaction. This work makes sense because it will allow use to clean the slate and monitor the extent of the mold, or change in mold over time.
5) Automatically Closing Door, or door that can be closed from the inside as well as it can be closed from the outside.
6) Additional Wall Insulation – I firmly believe that Closed Cell Spray Foam is the best foundation wall insulation in NC. As little as 1″ would perfectly seal the wall, stopping all the thermal bridging where the joints in the CMU’s are, and while you are at it, you may as well hit all the other leakage points.
Click on the link below for a short video showing the condensation issues related to too much humidity and surfaces below dew-point.
Information on Mold/Moisture/RH Monitors, etc.: