advice for wet attic and rotting sheathing

[fran35]

So, as the title states, I have noticed a problem in the attic with condensation building up on the inside of the sheathing. I have noticed for the last few years, since have lived here, there is a major lack of humidity problem with the home. In the winter, with the wood stove going, we also have to keep the humidifier going as well. Dumps around 4 or 5 gallons per day. I think the major problem is that the upstairs rooms all have tongue in groove ceiling with unfaced insulation above, but no vapor barrier. My belief is that all of my heat and moisture is going fright through the tongue in groove gaps and into the attic. My remedy seems to most likely be to put .5 inch drywall directly over the current ceiling.

My questions are this

-is .5 drywall a decent moisture barrier?

- is there any earthly way to seal the tongue in groove and salvage my do ceiling. I really like it

 

[heat seeker]

You need more venting in the attic, as well as a vapor barrier. Mold can also grow in the insulation if it gets and stays wet.

The previous owner of one house I bought put the attic insulation upside down (vapor barrier on top!) on purpose, because it "looked better that way". He also stapled the vapor barrier to the rafters. I spent a ton of time removing staples so I could flip the insulation over.

 

[kennyp2339]

Either the attic gets treated as a warm space or a cold space, most opt for a cold space. I would take the existing insulation and put that off to the side, install new insulation with vapor barrier in existing joists, then the old insulation on top (if in good shape) for more R value try to hit or exceed R30, I would had more ventilation to the attic either by cutting in a second gable vent, adding a ridge vent along the existing roof peak, or some static vents. Either way that plywood sheathing needs to be addressed before it rots and fails.

 

[DickRussell]

.... we also have to keep the humidifier going as well. Dumps around 4 or 5 gallons per day. I think the major problem is that the upstairs rooms all have tongue in groove ceiling with unfaced insulation above, but no vapor barrier.

That humidifier is much of your problem. You realize by now where most of that 4-5 gallons is going, made that much easier by lack of an air barrier between the upstairs living space and the attic. TIG paneling does not provide an air barrier, with all the joints being more of a sieve than air barrier, and much of the moisture flow into the attic is carried by convection (air leakage). You need to fix this before you end up with serious mold/rot issues.

A house that needs humidification in winter is one that is excessively leaky. Human activity in a house produces humidity, while leakage of outside air in and conditioned inside air out flushes out that humidity. It's no secret that newer homes built to very tight standards need deliberate ventilation to keep interior humidity down in winter. Other homes, older or just built "to code" leak enough air (generally too much) that mechanical ventilation is not needed much of the time. The ultimate remedy for you is to fix the house by doing a good air sealing job, especially between the upstairs and the attic. You can put a poly sheet over the TIG, with overlaps taped, then cover it with whatever makes the ceiling look nice. Or you could just sheetrock over the TIG paneling, with all joints taped and sealed, especially where it meets the walls, then apply a coat of vapor retarder primer before painting. Even just a couple of coats of latex paint likely is adequate for retarding diffusion, provided an air barrier is in place to eliminate convective flow and the attic is properly vented. While sheetrock with joints sealed will provide an air barrier to eliminate the convective flow of moisture, sheetrock alone is not sufficient as a vapor retarder to slow the diffusion of water molecules through it.

As for the attic itself, there needs to be adequate venting, preferrably with ridge vent and continuous soffit venting

 

[fran35]

That humidifier is much of your problem. You realize by now where most of that 4-5 gallons is going, made that much easier by lack of an air barrier between the upstairs living space and the attic. TIG paneling does not provide an air barrier, with all the joints being more of a sieve than air barrier, and much of the moisture flow into the attic is carried by convection (air leakage). You need to fix this before you end up with serious mold/rot issues.

A house that needs humidification in winter is one that is excessively leaky. Human activity in a house produces humidity, while leakage of outside air in and conditioned inside air out flushes out that humidity. It's no secret that newer homes built to very tight standards need deliberate ventilation to keep interior humidity down in winter. Other homes, older or just built "to code" leak enough air (generally too much) that mechanical ventilation is not needed much of the time. The ultimate remedy for you is to fix the house by doing a good air sealing job, especially between the upstairs and the attic. You can put a poly sheet over the TIG, with overlaps taped, then cover it with whatever makes the ceiling look nice. Or you could just sheetrock over the TIG paneling, with all joints taped and sealed, especially where it meets the walls, then apply a coat of vapor retarder primer before painting. Even just a couple of coats of latex paint likely is adequate for retarding diffusion, provided an air barrier is in place to eliminate convective flow and the attic is properly vented. While sheetrock with joints sealed will provide an air barrier to eliminate the convective flow of moisture, sheetrock alone is not sufficient as a vapor retarder to slow the diffusion of water molecules through it.

As for the attic itself, there needs to be adequate venting, preferrably with ridge vent and continuous soffit venting

Thanks so much for the advice. I actually have soffit and a ridge vent, but I have a cape cod and the thing is very leaky. The wood stove dries out the air so much, but I suppose the humidity never has a chance to build up because of the master bedroom ceiling. I just got back from the store with 12 sheets of plywood and will go to work tomorrow. I love the T and G ceiling, but it will be just too much work to salvage it.

 

[DickRussell]

..... The wood stove dries out the air so much, but I suppose the humidity never has a chance to build up because of the master bedroom ceiling. I just got back from the store with 12 sheets of plywood and will go to work tomorrow. ....

The wood stove by itself doesn't dry out the air; it just adds heat to it. It is a combustion device, so it does draw in some air from the room, use it, and send the result up the chimney, and that air must be replaced by outside air leaking in. While that contributes to some extent in flushing humidity out of the house, the actual air use by a woodstove isn't all that big relative to other leakage in most cases, and far less than what an open fireplace would draw. Heating the air in the house above outside temperature of course does produce stack effect leakage - in at the low points, out at the high points. Besides doing your air sealing project at the upstairs ceiling, you ought to continue the air sealing effort by looking for other leaking areas. Of particular importance is the rim joist area in the basement. In cold weather, you can feel where air is coming in and seal the leaks. A FG batt piece stuffed up against the rim board does nothing for air sealing; that stuff is a filter. Use a caulk or can foam.

Over on GBA you'll find a good tabulation of links to various blogs on doing the sort of thing you need to do: http://www.greenbuildingadvisor.com/blogs/dept/musings/how-do-everything

In that tabulation you'l find this one on air sealing the basement:http://www.finehomebuilding.com/design/departments/energy-smart-details/air-sealing-a-basement.aspx.

I'm curious as to why you chose plywood to layer over the TIG paneling. You had spoken of using half inch sheetrock. That you could paint to make it look nice. What will you do with the plywood? Be sure to tape the plywood joints, to prevent leakage there.

 

[EatenByLimestone]

I think I'd remove the t and g if I was going to cover it over. There's no sense to just add weight to the ceiling. Another option would be to caulk every joint and make the t and g your sheathing, but the tubes of caulk would likely add up to more than the plywood you bought to install.

Given the opportunity you have, I'd seriously look into removing the t and groove, foaming the joists, and then covering the ceiling with the material of choice.

 

[fran35]

The wood stove by itself doesn't dry out the air; it just adds heat to it. It is a combustion device, so it does draw in some air from the room, use it, and send the result up the chimney, and that air must be replaced by outside air leaking in. While that contributes to some extent in flushing humidity out of the house, the actual air use by a woodstove isn't all that big relative to other leakage in most cases, and far less than what an open fireplace would draw. Heating the air in the house above outside temperature of course does produce stack effect leakage - in at the low points, out at the high points. Besides doing your air sealing project at the upstairs ceiling, you ought to continue the air sealing effort by looking for other leaking areas. Of particular importance is the rim joist area in the basement. In cold weather, you can feel where air is coming in and seal the leaks. A FG batt piece stuffed up against the rim board does nothing for air sealing; that stuff is a filter. Use a caulk or can foam.

Over on GBA you'll find a good tabulation of links to various blogs on doing the sort of thing you need to do: http://www.greenbuildingadvisor.com/blogs/dept/musings/how-do-everything

In that tabulation you'l find this one on air sealing the basement:http://www.finehomebuilding.com/design/departments/energy-smart-details/air-sealing-a-basement.aspx.

I'm curious as to why you chose plywood to layer over the TIG paneling. You had spoken of using half inch sheetrock. That you could paint to make it look nice. What will you do with the plywood? Be sure to tape the plywood joints, to prevent leakage there.

Not sure where my brain was when I wrote the reply, I bought sheet rock.

As for the basement, I will check into sill plate/rim board seal. As for the close cell foam, is the "Great Stuff" spray foam in the red can fit the bill?

I hung the drywall last night, worked into the wee hours getting it done. Another question: if there is a slight .25 inch seam between adjoining drywall, what must I do to ensure a proper barrier? Will tape and the later multiple coats of latex paint suffice?

 

[EatenByLimestone]

Tape, mud and paint will stop air movement.

I'm not sure if Great Stuff is closed cell, but will work for your application just fine.

 

[spawner]

Another step you may consider down the road is to remove the existing insulation that may likely be moist and a potential problem in the future. Blown in cellulose does not require a moisture barrier, is treated to resist mold, insulates better per inch, and is relatively cheap/ easy to install. also If you have a home depot locally, the machine rental is free w/20 bags and there is a large bulk discount if you buy more than 100 bags. I have no affiliation with HD... but I did just finish a project similar to yours. Good luck!

 

[sportbikerider78]

Make sure no insulation is blocking or restricting your soffit vents. When you are done, insulate your attic floor and then take some temperature readings of the attic vs the outside. They should be almost the same temperature. If there is a big difference, your insulation isn't good enough.
Do your bathroom fans vent to the attic? If so, you should look at having them go through the roof. Not too big of a project.

 

[Highbeam]

When you are done, insulate your attic floor and then take some temperature readings of the attic vs the outside. They should be almost the same temperature. If there is a big difference, your insulation isn't good enough.

Or your ventilation is not good enough.

 

[peakbagger]

I bought a house years ago that had moisture issues in the attic. Someone has insulated and stuffed insulation down all the soffits and had the bathroom fan dumping in the attic. There were soffit vents but with the insulation they weren't doing anything. It was shallow roof so I used to use a pole with hook to pull off the insulation out of the soffits. I then slid proper vents in all the openings and added a layer of insulation over the floor joists up to the proper vents. I hooked a hose to the bathroom vent and wired it up into one do the roof vents. It made a big difference.

Years later a friend of a former girlfriend has a brand new house built. It was timber frame floors and roof with standard walls. The house was quite tight in spots but they installed no insulation in the attic and had a loose attic hatch. I had commented on occasion during the construction on some obvious flaws of the construction but she was conned by the contractor that if they knew how to build $700,000 dollar summer homes that they knew how to build a 200K home. Last thing I knew she had black mold growing off the timbers in the attic. They had tried to do warm roof but went cheap so the attic was cooler than the rest of the house and every bit of moisture condensed on the cold structure in the attic. I expect the house ended up getting foreclosed at some point and someone else got to figure out how to fix it.

 

[sportbikerider78]

Yes. The professionals are so professional that we all end up forming these little help groups all over the internet to fix the mistakes of the professionals.

 

[Highbeam]

They've been doing it for 30 years! yeah, well you've been doing it wrong for 30 years you idiot!

 

[woodgeek]

The OP hypothesis is correct. You don't need a vapor barrier, just an air barrier. Drywall would do it. Airsealing from above is labor-intensive, but possible in principle.