Moisture problems in Victoria, BC studio

This is my first post to the forum that has given me so much valuable information. Thanks to all for that. About 1 year ago we completed our new home that includes a combination studio/home theatre. I have attached a portion of the original sketchup model of the house to highlight the studio area. The studio is located below the garage and is completely encased in concrete with one doorway leading to the rest of the house. If you unhide all on the sketchup you will see the garage and roof above the studio. There are basically three structurally separated rooms (the entrance, the control room, and the live/theatre room). Note that the entrance was not built as shown in the sketchup but was built as a third room within a room structurally separate from the other two rooms. All walls and ceilings were done with 2 layers of 5/8 drywall. I have to say that I am very happy with the sound isolation. Now to the problem. I believe I made at least two mistakes. The first was to allow the builder to use tar paper attached to the concrete side of the framed wall. This was apparently standard practice for them and helped hold the insulation in place and away from the concrete. The second mistake (possibly) was not providing venting anywhere for the dead space between the concrete and framed walls. The interior space is adequately ventilated with an HRV. After one year of occupancy I noticed a musty smell coming from an electrical box on the end wall farthest from the entrance. After some preliminary investigation I decided to pull some drywall and found that the tar paper was wicking moisture from the concrete and had what I believe is mold in some places. The exterior of the concrete walls was coated in the usual foundation spray and then covered with dimple board. The garage floor was coated in a waterproof product called stonecraft (http://www.stonecraft.ca/). The house is located on the top of a hill on a very rocky site and I see no evidence of direct water penetration. At this point I am prepared to remove all drywall from the walls facing the concrete and remove the tar paper and replace with nylon strapping. Here are my questions: 1. Am I correct in thinking that the moisture vapor that is penetrating the concrete wall is being trapped inside the dead air space due to zero venting? The concrete bunker is sealed up tight as a drum and the moisture vapor has no where to go. 2. Do I need to provide venting and how would I calculate sufficient venting? 3. Is there a better approach than venting the dead air space? What about coating the concrete walls with a layer of spray foam?

Sorry to hear about this. You would do better uploading actual pictures of the incident rather than a sketchup file since seeing can make a difference. Still the installation of a material designed to shield against water as saturated tar paper ( roofing felt in the US) is, amounts to a barrier. In a typical installation of a typical barrier, the barrier goes to the side of the wall assembly that will have the longest duration of heat exposed to it of a full year. For most of us, that means it will be placed directly on the face of the studs towards the innermost part of the room. In effect, they have placed a barrier in the middle of this wall. What happens with the vapor is that it moves from the warmer side to the colder side of the wall assembly. When you think about this, in your part of the country, it means that the interior of the room is going to be the warm side. So when the vapor moves to the colder side, it will condense on this barrier, the felt or tar paper. The chances of the insulation being soiled I suspect are high. What seems like mitigation from the exterior to the interior most likely is not the case. But pictures prove more than words. You could have an issue with the concrete wall but it is second to the improper placement of this material.

Thanks for the reply xSpace. Here are a few photos showing the progression of events. The tar paper is HAL-Tex building paper meeting "CAN 2-51.32 - Breather Type Sheathing Paper". Apparently it is what the inspectors here are looking for. It is on every new home built in this area. This paper does not preclude the use of a vapor barrier on the inside of the framed wall. I think my situation is unique though in that I basically have a room within a completely enclosed concrete bunker. Funny, I thought this would be the easiest way to go for maximum sound isolation and it does perform well in that regard. I first noticed the moldy smell as I was connecting some wires at the white junction box. I pulled the box out to have a look behind. The pre-demolition photos doesn't show it but I had enclosed the white box for sound isolation reasons by placing a piece of plywood at the back of the studs and sealing the enclosure. Looking at the plywood I thought it seemed discolored due to moisture. A moisture meter registered about 24%. I then looked at the plywood in the box to the right which was not discolored and it measured 15%. I drilled a hole in the back of the first box and found that the building paper had some moisture content and there was very little room between th back of the plywood and the concrete wall (unlike the other box). I concluded that the paper was wicking moisture from the concrete and onto the plywood. I didn't notice any actual mold on the plywood however. I then proceeded to remove drywall to see what else was going on. I didn't find any excessive moisture on the studs or sill plates but the moisture content rose the closer I measured to where the paper was fastened to the wood to as much as 18%. The insulation did not feel moist at all and there is no discoloration on it. The far left corner was where the paper felt the most damp and this is where I think I see mold on the paper. The mold seems to be mostly on the concrete side. This is also where the concrete has some honeycomb. There is no evidence of direct water penetration there however. Keep in mind that the inner room is completely sealed with vapor barrier and the outer walls and ceiling are all concrete. Moisture has no where to dry once it gets it. I have been doing a lot of reading for the last couple of days and it appears that current thinking is that construction techniques should allow basements to dry from the inside. I see recommendations like the following paragraphs from "BSC Information Sheet 511 for All Climates" "The best insulations to use are foam based and should allow the foundation wall assembly to dry inwards. The foam insulation layer should generally be vapor semi impermeable (greater than 0.1 perm), vapor semi permeable (greater than 1.0 perm) or vapor permeable (greater than 10 perm) (Lstiburek, 2004). The greater the permeance the greater the inward drying and therefore the lower the risk of excessive moisture accumulation." "Up to two inches of unfaced extruded polystyrene (R-10), four inches of unfaced expanded polystyrene (R-15), three inches of closed cell medium density spray polyurethane foam (R-18) and ten inches of open cell low density spray foam (R-35) meet these permeability requirements." My current thinking is I will have to remove any drywall adjacent to concrete (including the ceiling) and spray 3 inches of closed cell medium density foam. I will need to treat the areas where the rooms meet specially so as not to defeat the structural separation. I'll then replace the insulation where I can and then drywall this time with no vapor barrier. Am I off track here? Thanks for the help.

http://www.halind.com/assets/pdf/Breath ... eWalls.pdf This paper is used, in standard practice, underneath exterior siding, which you do not have ;) Your interior vapor barrier (the plastic) isn't in the way as it does not allow vapor the opportunity to get behind it and wet the structure. Your hvac is designed to extract the vapor/moisture from with in the room. Or should be. If you have only an area that you are thinking is actually getting wet, I would go outside the house and inspect that area first. If this concrete is cracked or below ground it will be subject to moisture penetrations. The honeycombed area, as you mentioned. Ideally, the cavity should not develop enough moisture to generate mold. Mold needs water to grow, so , I would look towards the outside of the structure first to examine all possible water entrances. Also, if this building paper on the backside of your framing is coming in >direct< contact with the concrete this is a simple bridge that can allow the passage of moisture. This wicking, as you said, can allow high amounts of moisture to gather. Even if the paper is rated for 30 minutes, as you can see, the nail hole areas are just enough to allow vapor access to the interior side of the paper. This is a sad thing to have to deal with I am sure, especially so early after completion. Best of luck, Brien

Thanks xSpace, Again, there is no evidence of direct water penetration. It rained hard all day long here and nothing. I believe there is a natural migration of water vapor going on and the paper is exacerbating the situation be wicking wherever it comes into contact with the concrete. Most of the paper has a somewhat damp feel. Not super wet but noticable. Since the space is sealed tight, there is no place for the moisture to go.

It isn't water penetration , per se, that you are looking for. It is the means for vapor to migrate into the cavity. It could actually be coming from the inside of the room, finding cracks in the vapor barrier and gaining an exit point from there towards the concrete. I think you really can only do what you are faced with first. Removing the sheetrock in the suspect areas. And find a way to get rid of the building paper that is between the framing and the concrete wall. Keep your eyes open to all avenues of bridging or cracks or what have you, potential holes in the vapor barrier, etc.

Does one need to mud the moisture proof drywall that is hidden behind the shower walls and if so, do I need special mud that is resistant to moisture? I am laying the plywood floors, placing the basin, erecting the drywall and then securing the shower walls. How's it sound so far... [ SPAM SIGNATURE REMOVED BY MODERATOR ]

erecting the drywall and then securing the shower walls.

You are going to have a shower inside your studio? :lol: :roll: :!: :poke: :shock: That'll be a first, for sure! - Stuart -