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In my perpetual quest for the ‘perfect’ basement remodelling plan, I came across an article in a magazine that said that you gain very little in energy efficiency insulating the wall below the frost line and that by not insulating below the frost line, you prevent having insulation near the bottom of the wall, where it is more likely to get wet.
I was just curious as to other’s opinions?
Right now I’m leaning towards not using any vapor barrier in the basement and building the walls possibly with some vents. Not having to insulate the lower 2′ would allow me to have a rather open wall cavity at that level allowing greater air-flow, and theoretically, dryer wall cavities. Anyone care to validate/invalidate my theory?
Replies
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Dear Darrel,
Since I'm a real builder and you actually own a house you want to work on yourself, I'm supposed to put you down. Sorry, I'm not up for it, just give me a pass ok?
Now about these magazine articles. You should never trust anybody who writes articles about building. Got that? Good.
Frost lines don't mean anything. We can get 5 feet of frost here in Vermont. This year we got 5 inches. Can't plan on that basis.
As water evaporates off your foundation walls, it must somehow get out of the house. The primary route is through the attic. If the foundation wall is too wet to insulate at the bottom, you should not add insulation anywhere in your house. Especially not in the attic.
Moisture control must precede any insulation attempts. Water requires heat to evaporate, not air movement. If you have water, you must accept either heat loss or accelerated building deterioration from condensation.
Sparing you from my nasty attic and cellar fiberglass photos, Fred
*FredL,We read over your reply a few times to try and make sense of it without success.It seems that you only wanted to mock this poster and that doesn't make sense. Normally, somewhere in most of your postings, however long they may be, there is one line of advise. In this one, only your closing sign off can be construed as positive.What was the purpose?Darrel,Most colder areas do only insulate to below expected frost lines. It's both a cost saving measure as well as taking advantage of the steady ground temperatures below frost.If your basement has that much moisture to soak the insulation, you should investigate this before proceding any further.
*i Moisture control must precede any insulation attempts.Understood. That said, I'm a big fan of contigency plans. The basement walls aren't too wet to insulate...they're dry...I'd just rather not apply insulation to the wall in areas where it is not necessary to avoid ane potential future what-ifs.I don't quite understand the concept of moisture in the basement escaping through the attic, though. How would that affect my planning of the insulation in the basement?The biggest concern isn't really outside moisture. We get a damp spot once, maybe twice a summer in two parts of the basement, and we're doing landscaping this spring to remedy that situation. I'm more concerned about general humidty in the summer. A true vapor barrier would prevent that moisture from hitting the walls and condensing, but I'd rather not use one for two reasons: 1) I doubt we (or anyone) could make a true, continuous vapor barrier, and 2) just 'in case' the worst ever happened and water found its way back in somehow from the outside.BTW, I'm not planning on using any fiberglass insulation, but rather the pink Extruded Poly insulation. I am going to put a layer of that on the wall, then stud out the wall from there.And, just to be clear, I'm absolutely working on making sure the basement is completely dry before doing any remodelling. It's just that I've seen enough basement remodels where even though they were 'sure' the water problem was fixed, there are still musty carpets, soaked insulation, etc.
*Darrel,Using a continuous SM as you indicate will also act as your vb. Use ship lapped sheets instead of the square butt type.Your supplier probably carries Baseclad and this could save you some time, money and space to use.http://www.owenscorning.com/around/insulation/products/insulpink.aspIt comes prepared to accept wall strapping and you tapcon/ramset/gripcon it to the wall.Eleminates the need for studs. You apply the drywall directly onto the straps embedded into the SM.Don't worry about air making it's way into the attic, that's an old wive's tale.
*what is this .. good fred / bad fred ?will you guys come down to earth and talk sense ?most of what you are saying is getting lost in the background noise...Darrell.. basements are peculiar animals.. in the northern tier of states they act like houses on the mason/dixon line.. sometime during the year.. moisture vapor is trying to move in.. and sometime during the year it is trying to move out..you did catch the part from fredl that first you have to make sure you have taken care of water and moisture from the earth... this means proper drainage .. some kind of strategy for either keeping water out or controling it if it gets in....fredl is saying that if the water gets in.. the only way it is getting out is up thru the living space and thru the attic...with occasional detours by way of air leaks into the wall system where it will also condense and cause rot..wether you insulate the walls of the basement or not depends on what you want to do there and how you want to heat your first floor..if i have a heating system OR ductwork in the basement then i like to put either 1" or 2" of 2 lb/cf EPS under the slab and turned up the wall to isolate the slab..over a 6 mil poly vapor barrier against the concrete and under the EPS under the slab... this directs any water leaks.. or any condensate into the crushed stone under the slab...then i insulate the walls with 3"EPS performguard with 1/2 " gypsum bonded to it for firecode...then we blow cellulose into the bandjoist area.. so , the basement becomes part of the conditioned space.. although maintained at a lower temperature...the drainage plane is outside the concrete walls into a crushed stone base under the concrete walls..the vapor drive will be minimal because the eps acts as a vapor barrier/ retarder..also the eps will maintain either surface above the dew point...if you have a well insulated attic , and adequate insualtion in your walls.... energy conserving windows and doors... then the basement becomes your last great heat loss...with the top two feet aproximating ambient air tempthe middle portion half way between ambient and 45 deg. and the bottom portion at apx 45deg. year round...on a 24 hour basis.. that is a lot of heat passing into the earth...so.. you original question.. is it worthwhile insulating your bvasement or crawlspace?depends on your goal.. if your goal is energy conservation and improved comfort, then my answer is yes..b but hey, whadda i no ?
*Not too bad of an answer Mr. Smith but a little over dramatic.2 areas that you're weak in. Sealing and sealing. Spend a little more time learning about this weakness of yours and you will understand and build better houses.
*lfred... two areas yur weak in... communicating and communicating ... or maybe it's just me... hah, hah, hah....i don't think so...
*Mike, how do you blow cels into the band joist bays and keep them there? Blocking of some sort, or mesh...?
*Sorry can't agree with you. I get my point across everytime.
*Uhh...gee...didn't mean to start an argument!Here's a little background. The house was built in 1929. Concrete block foundation. The house sits on a hill and the floor of the basement is about 2 ft. above the street which is about 70 feet above the natural waterline in our neighborhood. The soil is solid clay, so liitle-to-no natural drainage.The previous owners had the yard sloping towards the foundation, so, naturally, in heavy rains, we had damp spots. We re-sloped the yard, re-routed the gutters and pretty much stopped the water problem EXCEPT in extremely heavy periods, where the back-yard doesn't dry. In this case, we have water coming in at one corner.We are resolving this two ways. 1) We're skirting the house and adding a drainage tile to move surface water down the front hill. 2) The problem corner will not be fully finished.that said, it's a beatiful basement to finish...8 1/2 foot ceiling...interior brick walls...full fireplace. The thing is, I'm OK with it being a basement and not having it 'as finished' as the rest of the house. I'd really like to go for a bit of an industrial look and make it the family room (TV, couch, etc...) I'd like to stud out the walls, add wiring and HW radiant heat and sheetrock. The ceiling joists above will be left exposed and stained and the concrete floor cleaned and stained as well. We will be adding a bathroom.So, at this point, I'm really just focusing on how best to build these exterior walls. Even though I plan to eliminate the water issue completely before proceeding, I'd still like to build walls that are a moisture-friendly as possible, and try not to trap any moisture and promote mold/mildew.Local code dictates that we apply plastic directly to the wall before framing. I don't like this idea. I'm now thinking of insulating from the floor joists above down to about two feet from the floor with 2" EPS. The first two-feet of the stud wall will be 2x4 steel studs, with water and electrical. Above that will rest the insulation and 1x1 furrings. Then, I'll sheet rock down to about 3 - 6" to the floor. This gap will then be filled with the floor trim.I figure this makes a fairly water resiliant wall along the first foot or so and the airspace + the occasional vent will allow enough air flow to eliminate any condensation worries.
*i Uhh...gee...didn't mean to start an argument!Dear Darrel,Don't blame yourself. If I had done my job in the beginning to run you off, this never would have happened.I see your concern about developing a highly reliable assembly. You don't want to trap moisture. Would it help to know that 1" extruded foam panels do not qualify as a vapor retarder? Allowing foundation moisture to evaporate into the house is not my way of doing things. But if it is your way, the foam panels will allow any moisture behind them to leave.Mike says a lot of good things and I would differ on just one item here. Band joist treatment is not the best place for cels. Building retrofit containment is too much effort for me. Typically we would loosely install foam blocks and seal them into the floor and wall insulation with a foam gun. It's not that cels could not work. Just that Mike is a fanatic about the stuff and tends to over promote it.It's important to do the whole wall. Even small areas of highly conductive wall will have disproportionately high losses. For example, if your wall is 80% R-6 and 20% R-1, the whole wall would be about R-3.Just having a good time, Fred
*Darrel, I must say that your last details were much clearer.A layer of SM would qualify as a type 2 VB.It has the following ratingswater vapour permeability of 1.4ngm/nswater vapour diffusion resistance factor of 140water absorbtion of 0.3%volumecapillary of nil2 1/2 inches would qualify as a type 1 VBStart off by foaming all pipe and cable penetrations then install foam blocks and seal. Install SM directly on your blocks and strap.Drywall and you're off to the races.
*good point fredl... but our eps 3" panels are 4x8 and form the blocking without much additional work.. so some 1" holes drilled in the subfloor fills the bays in about 1/2 hour....also has the additional benefit of not supporting vermin due to the borates... we've had a lot of bad problems with vermin in foam products so all we'll recommend in our area is EPS Performguard until some of the other foam mfr's address the issue...splints.. hope that addressed your question too
*Dear Mike,Good point yourself. Whenever there is the chance to access the subfloor, I'd drill and blow it too. Also if there was a concurrent siding job, I won't hesitate to drill the band joist. Right on the vermin thing. Did I miss something about that in Darrel's comments. I read too fast sometimes.Regards, Fred
*no.. you didn't miss anything from darrell about vermin.. that was just me... gratis...the things i've seen living in foam....that i installed, or others, convinced me that it is a major problem for me
*OK, i've been thinking and i'm more confused.Mike and Fred,Is there a ceiling in the basement? What holds the DP cels in the bay? The cels need to be packed in the bay, but if you do that, you push the basement outside the envelope. What part don't i see?
*... splints.. if i want to condition the space i make it part of the conditioned box...so i insulate the basement walls... and i extend that 3" foam to the underside of the 1st floor..this forms a 12" wide by apx 12" box all around the top of the foundation wall... in most insulation jobs this (band area )gets stuffed with fiberglass insulation...i blow it with DP cells... i don't insulate the joist bays of the 1st floor, just the band box above the foundation wall
*i Would it help to know that 1" extruded foam panels do not qualify as a vapor retarder?Actually (perhaps erroneously...or naively) I don't want a vapor retarder per se. I'd rather assume that no matter how careful one is in preventing moisture in the basement, I, or some other future owner, will experience some moisture, and, therefore, I'd rather allow the walls to breathe.I'm having the same dilema with the main two floors of the house where we have little insulation on the outside walls, and no vapor barrier what-so-ever. I'd like to put central air in the entire house. In doing so, we'll be completely flip-flopping the 'hot' side of the wall each season (it hits the negatives in the winter and high 90's in the summer). So, one argument I've heard is to pump as much insulation in those walls to prevent heat moving each way, and another argument I've heard is that you can't avoid the heat transfer, so don't insulate at all as you'd trap more moisture in the cavity of the wall.Ah. Building science. So many interesting (and differing) opinions. ;o)
*darrell.. no insulation in the walls ?have you been reading anything here for the past several years ?why would you even repeat that ?
*I knew I should have kicked him out.
*Darrell,The other guys know stuff about building houses. I'm not a real builder or ever a make-believe one, but I do size heating and cooling systems and for the purposes of heat loss through walls below grade, only the top 3 feet is counted for significant heat loss (in northern IL). Below that, except in extremes, the ground is 54-57 degree, and with inside temps of 70 degrees, not a big "driver".
*Mike Fred:You have opinions...but I've found that a LOT of the building industry is just that...opinions. I can have two different contractors come out to my house, and they will suggest I do two totally opposite things.I'm sure both 'things' are correct depending on your POV, but it's tough to just blanketdly accept one's opinion over the other when they both sound reasonably experienced.This is where it gets confusing. I really enjoy the discussion boards here, I learn a lot from all of you pros. That said, my above comment on the insultation is based on DIFFERING opinions I've read on these very forums.So. Mike, that's why I repeated it.If you feel that I'm crazy in saying that (and that's fine...that's why I posted here...to get feedback!) please explain, as that will help me better understand the issues.Is the moisture transfer through the wall in summer a non-issue? How about the moisture transfer in winter? Is one more likely to cause problems than the other? If I DO insulate, should I have a vapor barrier?
*darrell... since you want more than my personal experience and research.. try Lstiburek's "Builder's Guide to Mixed Climates".. & Gene Leger's "Complete Building Construction"personally i don't want to continue a conversation that includes "no insulation" as a viable option
*Dear Darrel,I want to echo Mike's sentiment. My opinions: * Heat and moisture transfers are important year round.* I try to insulate every surface that defines the indoors from the outdoors.* I don't use poly in walls b/c it is too hard for me to capture gas in a site built plastic bag.* I use plastic to keep ground water from evaporating into the house.* I never insulate a building with uncontrolled moisture sources. Patiently, Fred
*Mike:Thanks for the book info. I'm off to hunt them down...Fred: Thanks for the comments. I agree with them all, though I'm maybe a bit confused with the plastic and ground water item.
*Dear Darrel,Happy to oblige. We use a plastic sheet, Tu-Tuf or Shelter-Tuf, to stop ground water from evaporating into the basement. If we cover 90%+ of the foundation, we get a 90% solution to condensation problems all over the house.This strategy does not work with the same membranes placed in the framing. Once water has evaporated into the house, the cat is out of the bag. Air pressure is pushing water vapor against every seal and pinhole in the membrane. Now you have to work to extraordinarily high standards to get mediocre results.Trying to get it done the easy way, Fred
*"If we cover 90%+ of the foundation, we get a 90% solution to condensation problems all over the house."That's the most ridiculous statement that any of us here have ever read. You must be a closet standup comedian.The 10% that isn't covered up COULD BE THE 100% of the problem. Now that's a fact.
*lfred... speak for yourself...the 90% could just be 90%...if the drive is an infinitely damp earth to a dryer basement... then 90% coverage will indeed eliminate 90% of the vapor..if it's ground water and the poly is bypassed , then nothing will save it anyways...ground moisture management is our goal.. what's yours?
*I am speaking for myself, now how about YOU not speaking for FredL.Your explaination is not only weak but totally without merit.Any calculations based on made up percentages cannot be taken seriously.10% of all drivers are drunk and are causing 90% of all accidents.By your calculations, if we take out the first 10 drivers we meet on the road then we will have saved 90% of all accidents.I think you better join the standup circuit as well.
*lfred, your additions to discussions in the form of personal attacks are so irreverent that they are rendered inconsequential and moot. Make your points and loose the vindictive attitude. Everyone else has. You have good points to make but they are totally lost in the noise.
*Father Bill,Thank you for your unsolicited judgement.
*A pleasure, my son.
*Finally!!!!!!!A comeback in kind.Bill you're okay.
*Didn't mean to cause a fight in here!OK, the plastic makes some sense...it'll stop the water from coming into the house, but it won't stop it from coming through the foundation, will it? And, as such, won't there be moisture trapped between the plastic and the foundation wall?
*yup.. there will be moisture trapped between the foundation and the poly.. forever.. just like you wanted ...no poly... no trap.. so where does the moisture go ?
*Mike:Actually, I DIDN'T want water trapped...that's why I wasn't planning on using poly and why I was a bit confused with the suggestion to use it.
*darrell.. yes ,you do want it trapped.. and redirected by gravity down the wall behind the poly into the drainage sysemthat is UNDER the poly under the slab.. if you don't trap it and redirect it ..then either you are ensuring that it never came thru the wall (?) or..you are going to let it come thru the wall into the conditioned space.. can you design a system that will keep it from going thru the wall... or short circuiting by capillary action up thru the bottom of the wall and out thru the interior ?naturally the number of strategies available to you is endless....but the ones you pick have to take all of these moisture sources into account
*Mike:Ah! Yes...I see your point now. Well, that goes back to my thinking that the lower 2 feet of the wall will not be insulated and steel studded. Then, I'd vent this cavity so that any moisture that would come through could make it into the conditioned space and sucked up via the AC or dehumidifier.My aversion to poly at this point is that I DON'T have any way to move that moisture from behind it...so in my case, it'd be trapped with no where to go.I'm sitting on solid clay, so there is little 'sponge' effect. And the house is on a bluff, so the water table is quite low. That doesn't address surface water, but with one side of the house paved, and the other soon-to-be skirted and drainage tiled, I'm not too worried about excess water...mainly just natural wicking and condensation in the summer.Going, back to your method, though, how would one do that? In otherwords how would you create a seal between the poly and the under-slab drainage system? I've looked into the systems that attach to the bottom inside corner of the floor slab and wall, but they seem to only address excess water/leaks...not really natual moisture migration.
*well... gene leger put me onto thinking about capillary action.. so when we pour walls on footings we put a 6 mil poly OR a thick tar base foundation coat on the footing before the wall forms are set....also....unless you're in a desert, the ground, be it clay , or chert, or gravel .. is infinitely wet compared to your basement.. so the vapor will drive into the conditioned space... leaving the bottm of your walls open will do nothing to stop the vapor.. and it will overwhelm your venting or A/C system...if you put 8" of crushed stone in the bottom of your hole you can install a system to manage ground water and vapor.. where do you live ?
*Mike:I'm in Minnesota.With what you said, it basically sounds like no matter what I do, I will have wet walls via normal moisture migration through the wall, and that no amount of AC/Dehumidification will help. In your opinion, should I not even bother with the finishing of the basement? I've seen a handful of basement remodels in old homes areoung the area with the only 'waterproofing' being poly along the wall and under the carpet, are they all doomed?We're definitely not going to be digging up the foundation to waterproof the exterior, but I was hoping the skirting around the house would take care of excess ground moisture around the foudation...but I agree that no matter what you do outside the earth will always be wetter than the inside of the basement.
*.. from the 1st time i read your post , i've been assuming this was NOT an existing foundation.. apparently it is...if i wanted a finished basement... i'd put a vapor barrier on the walls..i'd direct the vapor barrier down to one of the channel systems at the foot of the wall and lead it to a sump....then i'd build my stud walls in front of the channel system..any moisture comming THRU the walls would be trapped and either stay there or condense and go out the channel system.. i'd use a vapor barrier membrane ( liquid ) on the floor and tile or sheet vinyl over it...if i were starting from scratch.. i'd build it on an 8" to 12" crushed stone base
*Mike:Yes, sorry for the confusion...the house was built in 1929, cement block walls, half of them coated with plaster. The outside of the house is solid clay. Our house sits on a hill with the floor of the basement about 2 feet above street level. The entire neighborhood is on a bluff. One side of the house is sidewalk/patio. The other side is properly sloped (our doing) and will have a membrane skirt + drainage tile installed this spring.To be honest, I may NEVER get around to finishing this basement, as it would be so much easier to do it right the first time when we get around to building our own...I like your idea, but I find it hard to believe that I'd EVER have enough moisture to warrant needing a channel system. I did some test-squares of plastic on the walls and floor last summer and I couldn't get any condensation on either side of the plastic. We did have a dehumidifier going. Would running central air draw more water through the cement block than it is currently (just a dehumidfier?)
Darrell,
I have an older house with no vapor barrier/retarder under, around or any where near the poured concrete basement. I have forced, central air, with a few supplies and low returns in the basement. I move about 200 cfm through an 800 sf space. Moisture is not a problem in this basement. Your experience my be different.
Tim:
Thanks for the input. That's basically my (unproven, of course) theory as well...if I get enough airflow, and don't build the walls extremely tight, normal moisture from condensation and natural wicking of the concrete shouldn't be an issue.
May I as what kind of insulation you used (extruded vs. fiber bats?)
I bought the house with the basement finished. It was furred out with 2x4's and had 1" of styrofoam glued to the poured concrete, a 2-1/2" air gap and 1/4" plywood based paneling. The floor was uninsulated with old asbestos type of floor tile. I removed the floor tile to expose the bare concrete, because I use it as a shop and the tiles were getting damaged. The ceiling is exposed floor joists and decking of the floor above.
Something to note is that I live on a well drained, side of a hill some 80 feet above the water table (my well is set at 120'). If the house is real humid, like before I installed a decent forced air system, I would see some minor condesation on the floor tile. The deep ground temp here is about 55, so if my house is 80 and at more than 30% rh I get some condensation on cold surfaces without moving air.