Beefing up exterior walls

Hello everyone! I've begun the beefup process for my studio, whose basic design can be found here: viewtopic.php?p=62702#62702 The wall that separate the control room from the other exterior wall in the basement is complete with two additional layers of 5/8" between the studs and everything went great. Now that I've moved on to beefing up the exterior walls of the house I've run into a bit of confusion. I've placed two layers of 5/8" into several of the stud bays. I thought everything was going as planned, but today found a layer of frozen condensation on the next bay that was to be completed. Upon further inspection, the first bay that I had done on this exterior wall is showing some signs of moisture. I removed the insulation and let it dry out for a few minutes and the wet spot completely disappeared, so my question is: Should the exterior walls be beefed up in the same manner as the interior walls? I had considered inserting a layer of plastic between the wood wall and the drywall, but I'm under the impression that there should be only one vapor barrier and that it should live directly beneath the drywall layers on the interior wall. If I continue building in this manner, will this moisture still occur there, or will it appear instead on the vapor barrier I put up once the interior wall is finished? If the moisture does still occur will it ever get the chance to dry out? Thanks for any help you might have to offer. This forum is amazing!

Did you have a pre-existing vapor barrier? A vapor barrier in general isn't a hard and fast placement but pertains to how much cold/heat days of weather you have in your area. If you HAD a vapor barrier and it was modified, that was the wrong thing to do. Placing plastic in between the open stud bays will not create the envelope required to operate as a vapor barrier. And may not be part of your wall assembly either. Other things should be considered. Is this space currently heated? If it isn't, and you live in a cold place(like Indy) this can contribute. You speak of placing the beef up against wood(between the wood wall and the drywall) can this be taken to mean that you have wood grade exterior siding and there is nothing in between the siding and your sheetrock? If you have wood siding you should also have a contiguous insulated panel sheathing underneath that. BUT, if you never had panel sheathing underneath then you may have had a contigous plastic barrier placed directly on the interior of the room. So how was it, really?

Hi. Thanks for the reply! The original vapor barrier was a plastic sheet on the inside of the insulation. It is still there on the bays that have yet to be modified. From outside in: Siding, wood, insulation, plastic. In the bays that have been modified it is now: Siding, wood, sheetrock, sheetrock, insulation. I'm building room inside of a room, so there will be another wall with insulation, vapor barrier, drywall, drywall as well. The room is heated to a degree in that it accepts heat from the other side of the basement which is already finished. I thought I had it all figured out and was treating this wall just like an interior wall. I just want to make sure I'm not creating a situation for mold to thrive in the drywall that is placed directly onto the exterior wood.

leadvox wrote:

Hi. Thanks for the reply! The original vapor barrier was a plastic sheet on the inside of the insulation. It is still there on the bays that have yet to be modified. From outside in: Siding, wood, insulation, plastic. In the bays that have been modified it is now: Siding, wood, sheetrock, sheetrock, insulation. I'm building room inside of a room, so there will be another wall with insulation, vapor barrier, drywall, drywall as well.

Did you have existing kraft faced insulation or was it unfaced? Unfaced with a plastic barrier would make sense. Probably what has happened is that the area that is showing condensation did not have the barrier in place and the result was moisture on the interior.

Once again, thanks for the rapid response. It's appreciated! The insulation was unfaced.

Probably what has happened is that the area that is showing condensation did not have the barrier in place and the result was moisture on the interior.

This was the conclusion that I came to as well after seeing it dry out so quickly. I see no condensation on the inside of the vapor barrier that's still in place. I know there must be others here who have built against an exterior wall in a similar climate. Has anybody employed a different technique, or am I doing this right?

The technique is rather simple but depends on the weather and the type or kind of exterior material of the building. If the builder used un-faced insulation then the plastic was installed as the vapor barrier. If you use kraft or paper faced insulation then you do not want to install an interior plastic vapor barrier as the kraft paper IS the vapor barrier. Once you get inside the building it is not recommended to use a vapor barrier.

Yes, the plastic was clearly the vapor barrier. In the end, I plan to have that vapor barrier on the inside leaf just before the drywall goes up. In your opinion and from your experience, is it okay to have these layers of drywall pressed directly up against the wood on the exterior leaf? Sorry, I just want to make sure my question was posed clearly and that I'm not doing something stupid right off the bat...

leadvox wrote:

In your opinion and from your experience, is it okay to have these layers of drywall pressed directly up against the wood on the exterior leaf?

Yes sir.

yes sir....? even without vapour barrier? I'd love to see a diagram of the layers, I not completely following

"In the end, I plan to have that vapor barrier on the inside leaf just before the drywall goes up."

Yup, the vaporbarrier HAS to be facing the INSIDE of the room. Warm on the inside, cold on the outside... u quess what happens. When it's constructed wrong, as in barrier on the outside, moist will soon eat up yer wool...

I would put the barrier back exactly where it was before I opened the wall up - but just without the drywall over it (of course) Even through the new wall will have insulation and then drywall - the cavity itself will stay warm enough that it should never reach dew point. Rod

Thanks Rod. I didn't make myself as clear as I should have.

Thanks Rod, Ro, and xSpace. I'll continue as planned! Here are some more observations regarding the condensation: It occurs only with the pink insulation in place. Stud bays that I kept uninsulated overnight are completely dry, whether the top layer is drywall or wood sheathing. The bays with the insulation are a bit damp, even with the vapor barrier in place. I found another thread on this forum suggesting that Uline poly strapping be used to keep the insulation 1/2" or so away from the cement walls to prevent moisture. Should I do that on this wall as well to prevent the insulation from touching the wall since it appears that it is likely helping to cause the moisture?

"It occurs only with the pink insulation in place. " It could be the un-faced insulation is coming into contact with the plastic barrier. Since you have added extra thickness with multiple layers of mass to the area that used to contain only the insulation, it is now bulging and pressing against the barrier, yes? You need to make this contact between barrier and insulation go away. Compressing the insulation works against you here. So applying a strip of wood to each stud face, thick enough strips to allow no contact between insulation and plastic.

Sorry, I guess I need to clarify. The moisture appears between the insulation and the wall/drywall, not between the vapor barrier and the insulation.

I re-read your thread from the original post. This is a new house right? "Siding, wood, insulation, plastic" Is there something similar to Tyvek or some type of house wrap, felt, any thing considered a drain plane in between the siding and the plywood? I'm still wondering about the temperatures in this area. Water vapor moves from the warm side of the building to the cold side of the building. If this area is mostly cold with limited heat then it stands between the heated side(where the vapor moves from) and the cold side(where the vapor moves towards). This wall assembly was inspected and is a typical procedure for your area?

Hi. Yes, it's new construction. Appears there was no Tyvek between the siding and wood. Yes, this was inspected. It does appear that the vapor is moving from the warm side (basement) towards the cold outside. The vapor barrier was and is currently still on the inside side of the wall. This is typical in this area. The condensation forms on the inside wall surface, beneath the insulation. If I leave the insulation out, no moisture will form. I feel like I might be coming up short in my explanation.

No sir, your not short, I'm try to understand what kind of wall assembly you have and what it is made of. Everything matters in this respect. If the picture you show here is how the exterior walls were treated, e.g. no house wrap or felt or a complete drainage plane with rigid insulation, this can be as much of the problem as the inside. It is cold were you are and cold makes ice and ice is just hard water. It can melt with the sun and get into cracks and siding butt joints, end joints, wick up lap joints, etc. Plywood can absorb and hold moisture as well which is another reason to be able to drain it off or have the wall assembly dry to the outside. This not with standing, if this is a reputable builder and this is his common and accepted practice, then who am I way down here at Exit 4 Alabama to judge, right? So we are back to is the insulation touching the plastic? Doesn't matter where you see the moisture, if this barrier is making contact with the insulation then the vapor has already become water. It can just as easily drip towards the outside as drip down the barrier. And since it is not dripping and making a puddle, then it must be insulation making contact with the plastic. Tell me this is correct so I can go to sleep:)

haha! Don't stay awake on my account! I should really be sleeping as well. Yes, right now the plastic barrier is most certainly touching the insulation. It's not compressed, but it's definitely touching.

Also, xSpace: remember that the moisture was there when the insulation was present, regardless of whether the barrier was in place or not. Should there be a small gap between the insulation ant the drywall? Rod: Would placing the vapor barrier back in its original position not create a 3 leaf type of system once the inner shell is built? It would leave me with (from inside out): drywall, drywall, insulation, airgap, plastic vapor barrier, insulation, drywall, drywall, wood, siding. Can't wait to put this behind me and find the next obstacle!