I am a contractor in Ohio and have a general question concerning the most recent issue of Fine Homebuilding.
In the code quiz section (question 7 pg 94 – yellow box lower left) it states “dont ever use plastic in basement walls”. It is common practice for local builders to require I wrap the back of a wood studed wall with plastic over 1/2″ foam insulation (treated bottom plate). I have always questioned the builders concerning the use of the vapor barrier but am told the vapor barrier is needed to protect the wood. I follow up the discussion w/ my concerns w/ mold and moisture permeability. As you might suspect, I install all basements in this manner.
Does anyone know of a better practice for framed basements? Are there other concerns besides mold/ moisture which warrant the comment “dont ever use plastic in basement walls”?
Replies
Are there any other concerns besides death for not canoeing over Niagara Falls? :)
No. Moisture is the reason and it's plenty enough. Magazine is correct. Builders are incorrect. Make sure you have order in writing to avoid liability. Also pass copies of magazine to said ignorant builders.
DG/Builder
HELLO anybody how about dow blue board on inter side of band joist in basement ?? Any kind of moisture problems with this ?
Edited 2/16/2006 9:42 pm ET by workdog
Did you see the article about a year ago about finishing a basement. It went into great details.
And look at http://www.buildingscience.com and the research section.
Thanks for the leed Bill.
I wont bury a junction box and I wont put plastic on a basement wall. You are trapping moisture (potentially anyway).
You guys lost me. Is it FHB's position to not use plastic, or to use it? I'd rather follow FHB than the incorrect builders, especially here in the Atlanta area.
Bill, do you know what issue from last year that was? I wouldn't mind locating a copy and reading it.
#169 Feb/March 2005.http://www.taunton.com/store/pages/fh_toc_169.asp
The 25th Anniversary Addition of FHB contained a discussion on the use of plastic. Look in the code quiz question section..pg?
No plastic in basement walls because it prevents drying.
Andy
"Never try to teach a pig to sing. It wastes your time and annoys the pig." Robert A. Heinlein
"Get off your dead #### and on your dying feet." Mom
You have to help me on this one because logically it doesn't make sense to me, especially in an older home.
Concrete foundation or block wall = avenue for moisture from outside to migrate to inside of basement. If wall is framed out and insulated with batt type insulation, back of insulation and studs are unprotected and absorbs moisture that transmits through wall. Ideal petri dish for mold growth. If poly is installed against foundation wall before framing, insulation and studs are protected from moisture. Correct me if I'm wrong, but mold doesn't grow on plastic since there is no "food source". Mold does grow on wood and drywall.
Where am I missing the point in not using plastic?
If a home is brand new with a sealed system on the outside of the foundation then I can see leaving the plastic out. In an older home, with a vintage foundation, I can't see the logic.
D,You're right that an unprotected frame wall that's up against those conditions is not a good idea. However, the solution is not to put up a barrier of poly, it's to fix the real problem (grading issues, no drainage, foundation cracks, etc.).With poly, you must be 100% sure that you have no leaks, holes, or areas of diffusion. If not, when even 5% of the water on the wall gets through you now have a petri dish that captures the moisture and holds it against the studs, insulation, and GWB.
Jon Blakemore RappahannockINC.com Fredericksburg, VA
Here in Kenora Ont Canada building inspector wants: 1" airspace minimum between foundation wall and 2X4 stud wall with standard R12 fibreglass insulation between studs, 6mil plastic vapour barrier and whatever wall finish you choose. All joints sealed with acoustical sealant or tape and with all electrical outlets/fixtures bagged as normal for and upstairs wall.
Jas
Jon,
Thanks for the reply. But I'm referring to placing poly on the foundation wall, with an air space between it and the framed wall. In fact, the poly never even comes in contact with the framed wall.
I have a small apartment building that was built in about 1925 or so. Concrete foundation effervesces (sp?), and certainly has some moisture migration through it. Eight years ago I framed out a closet in the corner of the basement. About 8' x 8', to store some taxidermy before I had a chance to finishh a display room in my home. I wanted the room to be dust-free and "moisture free", so I poly-ed the underside of the open floor joists, and the two exposed foundation walls with 4 mil clear poly. I framed the other two walls and sheeted them with drywall. I can tell you that I have been in that closet at lease once per month, every month, over the past 8 years (I keep the keys for the rent drop box in there). The building foundation definitely has some moisture transmission through it, especially in the summer months when it is hot/humid. But I have NEVER seen any evidence of moisture buildup or mold/mildew on the backside of this clear ploy which is sheeting the concrete foundation walls.
And lets hypothetically figure that a gully washer of a rain backs up a gutter and water makes its way into this basement, or another, with poly against the foundation wall. The water will be isolated behind the poly, run down the foundation wall and seep under the treated bottom plate into the room (which I had happen in my home on one occasion). The framing and insulation remained dry, I vac'd the water up, and had no further issues.
I can see some logic in both the "with poly"/ "without poly" methods, but my experience dictates that "with poly" is the way to go on old structures.
Doitall,I have to agree with Andy, by using the poly you're creating a perfect environment for mold, mildew, and all sorts of other things you don't want behind your walls.One of the most important issues, IMHO, with building science is knowing how your overall system will cope with a failure in one part of the system. The ability to dry is essential for survival.
Jon Blakemore RappahannockINC.com Fredericksburg, VA
Problem #1 is the bat insulation.Problem #2 is the fact that in the sumer you have warm moist air.That will get through the DW and insulation and hit the plastic that is cooled by the foundation. Condenses and no place to go except to soak the wood and insulation.
Problem #1 is the bat insulation.
Problem #2 is the fact that in the sumer you have warm moist air.
That will get through the DW and insulation and hit the plastic that is cooled by the foundation. Condenses and no place to go except to soak the wood and insulation.
This is exactly what I expect the conditions to be in the Summer around my neck of the woods. Good thing I had not yet installed the plastic.
Andy,
A contractor that I know in the Twin Cities of MN told me that code officials prefer BOTH SIDES of the wall wrapped in plastic.
Now I'm really confused!
Sorry for the delay in replying. It's been busy lately.
Do you have FHB 169? If so, read the article there on basement finishing. In it, the reasons for my approach are explained. Or go to http://www.buildingscience.com.
In short, if you trap water, you will get mold growth. Perhaps there's no food on poly, but I guarantee you there's food on the foundation wall. The idea is to build basement walls so that they can dry both to the inside and to the outside. They don't get much chance to dry to the outside, but a vapor barrier prevents moisture from reaching where it can dry, which is to the inside. The other side of the the equation is air sealing. You don't want air to reach the foundation wall and have its moisture condense. So, air seal with permeable materials and dehumidify.
BTW, in my less than humble opinion, anyone who tells you to add a vapor barrier on both sides of most any wall has just demonstrated an appalling ignorance of building science. Are they on the payroll of the mold abatement industry? That approach guarantees mold and rot. If an inspector told me to build walls that way, I'd either appeal it until I got to someone who knew something, do the job without a permit, tear the vb out as soon as the inspector's tail lights were out of sight, or refuse the job. I wouldn't do it that way.
Also, there are some basements that are simply too wet to finish. If there's ever running water there, I don't finish that basement. Andy
"Never try to teach a pig to sing. It wastes your time and annoys the pig." Robert A. Heinlein
"Get off your dead #### and on your dying feet." Mom
Thanks for the input. It will now dictate the method that I use to address basement framing. Thanks again.
Andy,
I'm a man of a million questions! Don't a couple of coats of latex paint act as a vapor barrier on the front of the ceiling and walls (drywall) in a finished space? As an example, I'm thinking of a roof leak in one of my apartment buildings. The water seeped down to the ceiling of the upstairs unit, and the latex paint on the underside of the ceiling (which was drywall) stretched like a plastic bag. I remember being amazed at how much "latex" is in latex paint.
So, in spite of best intentions in basement wall framing, (poly vs no-poly, etc.) isn't painting the drywall on the inside of the room essentially creating an inpenetrable surface for the migration of moisture?
Thanks again for your response and knowledge.
Excellent question. Latex acts as a vapor retarder, not a barrier. So it will slow down but not prevent moisture movement. Use a shellac based primer, like BINS, and you've laid down a vapor barrier.
Andy
"Never try to teach a pig to sing. It wastes your time and annoys the pig." Robert A. Heinlein
"Get off your dead #### and on your dying feet." Mom
Andy,
Thanks for the great info. I appreciate it.
Tom.
That must be a Cincinnati-wide misunderstanding because I've been told the same thing from various trades people. You'd think that plastic would protect the wood from rot, but in reality, it does end up trapping moisture.