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I’m framing/finishing an 11×20 basement area – separated from the remaining basement area by a door. The basement sits one third above grade abd the room has 2 windows for cross ventilation. The block walls are treated with water seal and have appearance of moisture/leakage, but they are cold to touch. The walls will be drywalled with standard half inch product.
Question 1:
Am I better off framing out with 1x firring and infilling with foan insulation? Or should I go with 2x’s and fiberglass insulation? Should the framing touch the wall or should I allow a space between the wood and the block wall?
Question 2:
Should I apply poly – and if so, against the block or on the outside of the framing and insulation?
Question 3:
Should the insulation be unfaced batts or kraft or foil faced?
Looking forward to some input!
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Replies
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Ed
Before you cover anything up be sure that you have NO seasonal moisture infiltration. Look into using Expanded Polystyrene (XPS-Styrofoam R5/")and the board that has grooves already preformed to accept strapping/furring. It can be attached with a Power Hammer, eliminates the framing and will save interior space, also doesn't deteriorate with moisture. If you decide to use F/g use friction fit, not Kraft Krap! Framing should stand off wall 2"+/- and I would use pressure treated or cedar as a bottom plate and you should poly the f/g on the warm side because of the area that is above grade.Don't forget to fabricate & insulate returns at the windows.
-Patrick
*Patrick,I am in the midst of finishing my basement, much like Ed. Previous owners had nailed 2x2 furring strips to the block. I intend to remove the 2x2s, paint the block with Drylok sealer (even though the walls are dry) and erect stud walls to give me more room for fg insulation. Given my plan, can you elaborate on the need for separation between studs and block. Is this recommended even if the walls are sealed? Would I accomplish the separation by building the walls using 2x2s with 2x4 plates?Thanks,Dan MacD
*DanAs a general rule Wood framing should never be in direct contact with Masonry because of moisture inducing rot. Any exterior basement wall can theoretically leak in its lifetime, and, in certain circumstances, will 'sweat'. For that same reason F/g should be kept away from direct contact with masonry. . . it makes a great sponge, and f/g has a habit of expanding (lofting) several inches in depth when not tightly enclosed. The 2" standoff I recommend is somewhat arbitrary but should be a minimum I would think. I wouldn't recommend your 2x2 on 2x4 plate idea if you are planning to insul with f/g, if space is so tight go with the XPS system,the material cost is more but labour is less.-Patrick
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In regards to question #2: Don't install vapour barrier against the block. If vapour barriers are installed on the cold side of a wall's dew point it turns into a condensation collector.
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... or do install the vapor barrier but be sure to keep the interior wall vapor permeable -- an "inward drying wall". Insulate well to keep the interior wall surface from cooling to the dewpoint, too.
*Since there's much more moisture originating on the cold side - through the masonry - how will putting the plastic on the warmer and dryer side help the insulation stay dry? All the moisture will condense on the masonry and not be able to dry because of the plastic, won't it?
*If you poly on the warm side, what hapens to all the moisture form the wall below grade? Won't it mix and significantly dampen the insulation and - because of teh poly on the dryer side - keep the cavity continually wet?
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Isn't it always suggested to place barrier on warm side because thats where more moisture is present?? It would seem you want the barrier on the side with the most moisture to block infiltration of moisture into the F/G insulation.
So, if your have a house and you are finishing the basement as follows:
Foundation is 8" poured concrete (no block cavity, drain tile w/gravel backfill and perimeter
drain, 7 of 8' below grade, sump-pump.
Building 2x4 wall with F/G insulation, will be adding forced air heating and cooling.
Now for the question: From which direction do you get more moisture?? Through the wall or
from normal living conditions.... I get the impression its from normal living conditions and
therefore you put the barrier on the interior side..
Anyone know of a study that answers??
My question. posed here before, is why not two barriers to stop infiltration from either direction?
Anyone ever tried this and followed up on results?
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Patrick - Thanks for the info, particularly the polystyrene. I also need to run some outlets - do you just run you romex behind the polystyrene or do you can a channel into it? I get anal about wiring - in an application like this I would be prone to run the romex through a piece of 1/2 inch plastic pipe for protection from wayward nails, picture hooks, etc. Any ideas?
Ed
*EdThe downside of the XPS wall is in hiding the wiring, about all I can suggest is using surface mount wiring chases (several brands out there-none particularly pleasing cosmetically) and mounting their boxes on the strapping. There is a system that Stress Skin Panel installers use but they are dealing with much deaper wall thicknesses. Some other contributors might have good ideas. . . also try your local electrical supply outlet for newest products for surface mount applications.
*WalterYou've identified the biggest problem with basement finishing. Building finished living space below grade presents several unique problems. Idealy, in a well drained, properly waterproofed basement the greatest amount of moisture will come from the inside living space, although given normal convection how much of that is likely to try to pass through the insulated basement walls rather than migrate up through the building is also questionable. At present you may have a well sealed exterior basement wall with good drainage systems in place, but many factors can be introduced that can change that. Dealing with those 'possible' future problems is complicated. The very best design that I have ever seen involved building partition walls 4'-6' away from the foundation walls along the three walls that were below grade, a room within a room, with the narrow perimeter area being used for utilities and storage. The floor in the utility/storage area was sloped to drains and if there had ever been a breakdown in the exterior below grade waterproofing/drainage system it would have taken a major flood to reach the fancy carperting in the finished basement area. This particular house was a sprawling backsplit ranch style so there was a large basement area to play with.In houses of more modest basement area it is always a gamble to assume that no exterior moisture will ever enter, and then build finish walls tight to the foundation. In new houses, for example, you just have to hope that settling doesn't introduce masonry cracks 1 or 2 years later. At the very least, close attention must be paid for ever more to sloping the grade, and maintaining the gutters.I've seen below grade masonry walls that had plastic sheeting draped on the inside from ceiling to floor that were spalling badly, but don't know if the spalling was under way before the plastic was installed or not.
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Bill;
I'm assuming that this building does not have a basement seepage problem. When warm, moist interior air meets a cold source, it collects and condenses. If you can block the moisture from entering the wall, there should be no condensation. Cold air is very dry, so unless moisture is entering through the block wall or from the interior space, the framing and insulation should stay dry. If the basement wall is seeping, vapour barrier is not the solution.
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Kelly - I based my question on the original problem which included "The block walls are treated with water seal and have appearance of moisture/leakage, but they are cold to touch."
I understand your theory - but from my experience s and observations there is more moisture from the walls and floors of a basement than from the "warm, moist interior air" overwhelmingly.
I believe that the this started with the idea of putting poly - I think the politically correct term now is VDR - behind drywall and instead of saying "put it on the moist side" someone figured that more people would understand "warm" than "moist", never intending for the practice to be carried into basements. There are too many soaking, moldy, mildew laden, basement "walls" to not automatically assume the moist side is the exterior side and then adjust if you have some reasons to believe that the exterior might be drier.
*Use foam insulation.Only PT wood touching concrete.No plastic. Forget the term vapor barrier.If you're not heating this space from the baseboard up all the time and its not naturally warm and dry, prepare for mildew, musty smells etc.Visit Building Science CorporationBelow grade living spaces are not the best for human habitation. Yes people make it work and its a shame to waste the space but....There is a magic company called Alternative Energy Homes that does the impossible and can build homes with warm dry basement space. I have toured their homes and they are amazing. Warm and toasty from cellar all the way to the top floor with no noticable stratification. No standard building methods employed though. 4" foam with taped seams all outside the structure completely enveloping all but openings. Its under the slab, outside walls and ceilings, just under roofing and siding etc. Time for a walk in the "Park"...Jack : )
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Bill; Perhaps I am making too many assumptions, but my thinking is that if the walls are to be insulated, this building is located in a cold area and would have seen a fair amount of condensation on the uninsulated basement walls during winter which may have caused staining.
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I agree - your diagnosis could be right.
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Here's another possibility. What we do up here in Canada is apply Tyvek or Tyrar (writing facing the concrete) before we frame the basement walls. This allows moisture trapped inside the wall cavity to escape but prevents moisture from the concrete from contaminating the wall cavity. The typar wraps under the wall and is caulked to the vapour barrier. On new construction it continues under the sill plate and right up the house. Now thats a continuous air barrier!!! At least my local inspectors like it!
SteveM
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Fred
How would your suggested form of construction allow the walls to "dry to the inside?" If the "interior sheathing must be made air tight" to stop condensation emanating from the warm side, why will it allow drying in the reverse? And with poly against the masonry, and air tight walls to the inside where's da moisture coming from, or is this just diffusion wandering back & forth?
Also, I have seen serious spalling in some basement walls that were sheathed in poly against the masonry, but don't know if this spalling was already under way before poly, or if so, whether it worsened significantly after poly. . . ever witnessed such goings-on?
A litle furry, but not mouldy
-Pat
*Steve,Have you ever seen all the stuff that grows on wet plastic?I'm just not a fan of any plastic sheet use whether it breathes or not.When plastic seems to be working there is either no water problem (might be your case) to begin with, not enough time has passed, it's hidden in the wall, or you're just lucky.Plastic, humidifiers, cold objects, and tight houses are a tough combination that needs as many Joe L's and their Doctorate studies as we can ever hope for.Have a good day,Jack : )
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Fred;
I don't know if you can repair a leaking basement from the inside. Basement leakage has to be handled from the exterior with proper sealants, pourous backfill, an efficient drainage system at the base, and good landcaping. If a vapour barrier is applied to the inside of the basement wall you are not stopping the moisture from entering the building. Moisture will collect on the vapour barrier and run to the base plate and that is where the decay will start.
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Steve
What some of the rest of us do up here in Canada is not use housewrap for anything, except maybe for wrapping the fish heads in. Why do you beleive that housewrap which is supposed to allow moisture to wick through in one direction is so sophisticated that it knows enough not to let it wick through in the other direction??? Do you suppose there's little microprocessors built in that can read which side the advertising is printed on. It's great stuff. . . really. . . fish heads love it!!!
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Fred,
I like your thought process. Let me throw this at you.I have had good luck with the hydraulic cement based paints in drastically slowing the passage of moisture in masonry walls. Assuming exterior drainage is proper and functioning here is a method i have not tried but think is a workable system. Given that the basement walls are not load bearing, useing 2x2 framing shimmed 1/4 to 3/8 off the floor , staple 4 mil poly to the backside of the studs to the top of the mud sill,wrap poly around the bottom of stud wall,stand wall leaving one inch gap beween cm wall and stud wall insert closed cell foam insul, pull poly up and staple in place. The poly would be a continuos barrier to protect the studs, then sheetrock and finish. Or just give the kids at a birthday party magic markers and let them decorate the concrete walls and live with it.
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I have been responding to this very same topic on other forum sites only to be argued against,much the same way this discussion is going.I am in agreement with FredL,the framing should be kept away from the foundation wall with no contact of any kind from any material.P.T. plate,6mil.vp stapled to the floor joists at least 1" away from foundation wall.Bottom plate is then secured to floor 1"-2" away from foundation,vp stapled to plate (keeping it pulled tight),then frame with studs & top plate.I use 3 1/2" fg in the stud cavities,pushed up tight to the vp(which is now pulled up tight to the back side of the framing),then finish with drywall.The way I look at it is,if there is moisture condensing on the walls because of inside air,then isn't the sheetrock going to get wet as it passes through? I think not.The moisture is coming through the foundation wall from the outside(not leaking),just passing through from ground moisture.Doesn't it make sense to keep that moisture from passing through the framed walls?FredL,thank you for the technical jargon as I am not good at putting my thoughts on paper or words. By the way, this is only my opinion and honest experiences that I can speak on the subject.It is just like any other construction detail,there are 6 ways to accomplish the same task,not any one of them is wrong,just the way that works for you.As for me,I also agree about the finished basement syndrom,no matter how you do it,it WILL be damp,musty,and unhealthy.But what is a person to do when someone is paying you to do a job for them?I think I will do the best job that I am capable of with the knowledge I have at hand.That is why I love these forums,as I have already changed numerous ways of thinking on many topics.
*Poly sheeting; 2mil, 4mil, 6mil, or more.Not for covering your Austin Healy...Not for tightly wrapping your lumber piles...Not for home building; Except between soil and concrete...b No plastic, no plastic, no plastic,b Plastic is the problem, not the solution.If you are b "Adrift" at sea, you need plastic.Why?Read the book.Have a good day,Jack : )
*The book? I guess the title of the book is "Adrift"Amazon.com lists two books titled "Adrift". Who wrote the one you are referring to?Is all of this a less than subtle plug for a book you enjoyed?Just wondering.Rich Beckman
*Adirondackjack,keep talking,you're starting to convince me!!!!I too have been questioning the benefits of plastic vapor barriers.I believe we can get a house too tight,thus trapping moisture and reducing air quality in the house.Unless you spend $$$ on air handling equipment,the house is stuffy and damp.What sense is it to spend thousands of $$$$ in the beginning only to save hundreds of dollars in the long run.I believe a good job of insulating(whether it be fg or cel.) along with a layer of rigid foam around the exterior,this is sufficient.I'm just curious,as I'm a new contractor looking to do the best job I can for my customers.
*Rich,Seventy Six Days Lost At Sea.....Jack : )
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I've just gotta weigh in on this topic. I am an architect & former contractor who used to specialize in energy issues. Maj is mostly right on how to build his wall, but it is incorrect to trash plastic or basement spaces. You can always build a good basement living space.
Plastic is great because it has low EMISSIVITY. It will, in reality prevent vapor (moisture) from passing through it. Of course, you have to lap your joints and seal penetrations very well. With a good vapor barrier no condensation of moisture being generated on the inside of the house will be able to occur within the wall. If some does penetrate, you can predict where it will condense by some simple calculations but you will find it ends up within the fiberglass. This will be due to some natural leaks here and there and it will evaporate itself off eventually and not rot out the wall framing. Moisture condenses when it gets cold enough (reaches the dew point) if you don't add insulation, it would condense on the outside face of the wall board (a bad situation) or the outside face of the vapor barrier (too close to the wall board for my taste). So, put 3 1/2" of fiberglass in to be safe and energy efficient.
Mildew and moisture are real issues, but so is radon in some areas of the country. What is usually done is to add small vents to the outside of the wall cavity above the foundation wall to allow some air exchange of moisture and radon in the air near the foundation wall. If you believe that exterior ground moisture will find it's way into the building, then add some return air (fresh air) ducts leading into the basement and you will then have fresh air with only a slight impact on your heating bill. A vapor barrier towards the living space will also protect exterior moisture from ever harming the wall board.
If you have any worries about all this, I would use MR board (moisture resistant) instead of regular gyprock. I would only do this if I knew there was ground water problems. If you really have ground water problems, then you need to excavate the exterior and add drainage.
Another point, pressure treated wood is not needed in this environment unless you have ongoing leakage problems. It would be an over reaction to issues of only occasional dampness.
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gary,
I disagree with 100% of your post.
The re-occurring theme hear is, "since you built it this way, this is how to add the next layer, to properly mitigate this problem, or that."...A sure sign of "credentials" from the semi-current "old school" of thinking. It takes time, sometimes a generation or two, but things are a changin. Houses will not be built to "70's dated" building methodologies forever.
You're promoting "Severals wrongs to make a right" type of thinking. Extra layers cause extra costs, need extra attention, leaking out bad air also leaks out good air...you forgot about the moldy baseboards...ahhh!... I know of one way to make cellar space really habitable, which a user of heated slab methods stated about his comfortable space.
I Like the "lets get it right the first time" thinking posted throughout Breaktime by the likes of Fred L, etc. Building can be done without all the comprimises found today, I'm sure of it.
Respectfully disagreeing forever. Don"t bother trying to sway me on this.
Jack : )
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I'm framing/finishing an 11x20 basement area - separated from the remaining basement area by a door. The basement sits one third above grade abd the room has 2 windows for cross ventilation. The block walls are treated with water seal and have appearance of moisture/leakage, but they are cold to touch. The walls will be drywalled with standard half inch product.
Question 1:
Am I better off framing out with 1x firring and infilling with foan insulation? Or should I go with 2x's and fiberglass insulation? Should the framing touch the wall or should I allow a space between the wood and the block wall?
Question 2:
Should I apply poly - and if so, against the block or on the outside of the framing and insulation?
Question 3:
Should the insulation be unfaced batts or kraft or foil faced?
Looking forward to some input!