Shawn, As you now realize, you should have installed a thick layer of rigid foam on your walls before you began installing your steel framing. "Any advice on avoiding the vapor barrier?". Note that most building codes require any type of foam, including spray foam, to be protected by a so-called thermal barrier (gypsum drywall) for fire safety. If you want your stairs to be safe and have consistent riser heights -- then yes. I am trying to decide what type of rigid insulation to use on my basement walls and floor. If your basement is insulated the same way as an above-grade wall — with wood studs against the wall, batt insulation in between and vapour barrier over that — you will have … It's perfectly OK to stop the flow of water, as long as the barriers and drainage details are robust. Fully review the relevant code requirements and manufacturer specifications. Again, fiberglass batts are OK. A. polyiso facings I have asthma and a general heightened concern regarding the quality of air I'm breathing. You kind of lost me with your suggestions... As my photo shows, I have faced R-19 in the pony walls already. 85 year old walkout with joists set in concrete The process to introduce an amendment to one of these codes is cumbersome, taking a minimum of three years. It's going to be awkward -- much more difficult than spray foam. My other thought was to place If the framed 2x4 walls are on the interior side of concrete walls, make sure that there is an adequate thickness of rigid foam between the concrete walls and the 2x4 studs. Failing that, try gentle education. I thought I knew a little about insulation. Greg, A basement can be like an infection that makes the whole house sick. The curious thing is that one contractor wants to put two-coats of dry-lock on the wall and one coat of oil-based dry-lock on the concrete slab floor. FAQ: Why Do Some Builders Avoid Foam Insulation? Your plan to use XPS on the walls and spray foam on the rim joist area should work fine. Response to Janet Ingles (Comment #199) The original wall assembly around the pipe was built 8" off of the concrete wall with paper-faced fiberglass insulation installed in the stud bays. http://www.greenbuildingadvisor.com/qa, Lots of readers visit the Q&A page daily. I plan to use EPS (sadly 1.5" seems to be all I can find nearby) on the walls and in the rim joists and seal off properly with expanding foam, caulk, and tape. Insulating a basement is a great idea if it wasn't insulated when built, as before we began insulating foundation walls and below slabs (see slab on grade), it was generally estimated that basement heat loss accounted for about 1/3 of the total heat loss of a house.It is likely that such an abysmal starting place made the addition of any insulation … We've had a parade of people through to quote the job and almost to a man everyone said we should spread gravel then poly sheeting (anything from 6-20mil depending on quote) and pour a rat slab which would provide a place for water to be channeled under the slab to the existing drain. That suggests there had been at least dampness in the past. Briefly: 1. Originally, I was planning to do something along the lines of the attached example that I found on your site. 2. Since your most recent questions aren't about basement wall insulation, you should post your questions on GBA's question and answer page. "What if one wishes to avoid foams for cradle-grave or health concerns (for insulating/reinforcing existing basements)? I really do not know what microbial problems this basement dampness can cause, but I am convinced that it causes some. If carpet and pad are installed directly over the concrete, what advice do you have for the pad? Response to Greg Volland We're planning an expansion to our house on Martha's Vineyard. ", Q. Below are some considerations to help you make this decision. Q. I'm not a fan of cut-and-cobble, but you can do it. Normal practices call for some mechanism to handle water that is shed by your roof and to handle rain (for example, by proper grading and the use of swales). At 3" most polyiso would still be performing over R15, even after derating for temperature on the colder above-grade section. Or are you looking for a quick 5-year payback on any incremental work? Reply to Dana Thanks for the information Dana...really appreciate the quick reply. I will read the Minn. studies to see if they address the air leakage reduction when sealing up the rim joist in basements. ), In the case of your plan to install mineral wool between the studs, you should be safe in your climate zone (Zone 5B) -- especially since your walls have a total of R-10 of rigid insulation on the exterior side of the mineral wool. Should I just replace with an xps? 5. © 2021 The Taunton Press, Inc. All rights reserved. Sounds good, I will proceed. On the flloor I am using warm wire again but this time i am putting down 1/4" cork then the warm wire then tile. A. Typar house wrap. One common assembly is to hold the studs 1"-1.5" away from the foundation walls and spray the space behind and between the studs with closed cell SPF. Also what I noticed is that the batt insulation does not go all the way to the basement floor there is about a 4 in. Then you suggested using a product called "R-batt." "Are all closed-cell spray foams the same product? Is it a good idea? It now reads, "Because it can absorb water, polyiso is not recommended for use under slabs or on the exterior of foundation walls.". Am I reading all this right?". Q. Q. Leave the floor above it uninsulated, vapor-seal the ground below with polyethylene and a thin concrete slab, insulate the walls with a foam-based insulation (such as 4 in. We have many builders who insulate finished basements with fiberglass batts. A. 4. Installed with white side facing the wall: moisture movement from the concrete wall into the house is reduced, but there is stil moisture permeability from the interior towards the wall. It's hard to say -- depends to some extent on the nozzle you are using and the brand of Froth-Pack kit you intend to buy. Good luck: synthetic stone over OSB is risky if you don't know what you're doing. "Since the mineral wool is only 3.5 inches thick but the wall cavity would be 4.5 to 5.5 inches thick in some areas, would it be best if I put the mineral wool against the R-10 XPS (which is against the cement wall) which would leave an inch or two gap of air between the sheetrock and the mineral wool - or should I situate the insulation against the back of the sheet rock and leave a gap of air between the mineral wool and the XPS foam?". Matt, Second response to Jay Lista J ... You do not have poured concrete walls above the basement and there may be a 3/8 to 3/4" gap between the block and the brick. 1. 0.5" rigid board XPS. We have been here two years and no water anywhere in the basement, so I am thinking Option #3 is the winner. It isn't necessary for water to flow through an old foundation. Spray foam, ICF, Thermomass much better. If you do this, tape the seams to keep everything airtight.). You won't get much thermal benefit from 1/2 inch of rigid foam. Understanding Insulation - Spending Too Much? Very informative website. Another advantage of EPS: higher R-value per dollar spent. And there is no problem with foam on two sides of concrete. The basement was left with R12 fibreglass from floor to rim joists stuffed in between framing along all the walls , pressed directly on the concrete wall. I'm wide open to comments on the advisability of this choice. Not sure how I'd even do that.. Taming the basement Get building science and energy efficiency advice, plus special offers, in your inbox. So there isn't a stack effect or a pressure differential or wind operating to move any air. In the US the IRC code prescribes a minimum of R7.5 on the exterior of a 2x4 wall for zone 6, to be able to use standard interior latex paint as the interior side vapor retarder: https://up.codes/viewer/wyoming/irc-2015/chapter/7/wall-covering#R702.7.1. With enough mineral wool, it's possible to cool the rigid foam below the dew point. The structural elements of below grade walls are cold (concrete is in direct contact with the ground)—especially when insulated on … They are leaky, and we've had the interior perimeter of the basement piped to the sump pump, with dimple mat extending about 4 inches above the floor. After that work is done, I suppose that you can install rigid foam between the studs using the cut-and-cobble method if you want. If it's a fairly consistent inch, double layering the EPS and going floor to ceiling with the interior-side sheet would be good, since both layers can be taped air tight. Reply to Martin Holladay But EPS is a better choice than XPS for a reason unrelated to its permeance -- XPS is manufactured with a blowing agent that has a high global warming potential. Martin....nothing is built yer. That is why the National Building Code requires a minimum level of insulation in a basement that reaches from the floor boards above your head, down the wall to about two feet below the outside grade level. Just a follow up question regarding the mineral wool filling in the 2x4 stud walls. ", "Combining Exterior Rigid Foam With Fluffy Insulation. Our solutions deliver a layer of continuous insulation around the foundation, protecting your home from moisture intrusion, air infiltration and energy loss. 4. Lastly, and maybe this is overkill... but if I used traditional insulation between the studs would it be a good or bad idea to put 1/2" XPS over the studs before I install my drywall to get a little bit more R-value down there? Inspecting the unfinished areas of my basement (only Fiberglas and poly over wood studs) I find a thick frost covering the concrete. Home is new construction in New Jersey, and builder installed a drain channel? I will attempt to link to the EPS I am considering here: https://www.menards.com/main/building-materials/insulation/insulation-panels/expanded-polystyrene-foam-insulation-2-x-4-x-8-r-8/p-1444435971902-c-5779.htm?tid=-1979961929525189151&ipos=1 - Thank you for any insight back. Frame Basement Walls Once all the insulation was in place I started framing up 2×4 walls. 2) What about insulation between the basement ceilings joists, a good idea or not neccessary? 4) Since I do see some cracks in the concrete wall, should I be concerned that insulating the foundation could cause it to occasionally freeze, and crack more significantly, even though it's slightly below grade at the cracks? I'm in Southeast Alaska, which is wet and has an average Dec-Feb low of 26 degrees F. My 85 year old walkout basement has some efflorescence and dampness, but no bulk water problems that I'm aware of. Would this even work with the studs as close to the concrete wall as they are? The trouble with the approach is that heat doesn't just move through the concrete horizontally; it also moves through the concrete vertically. Funny, until this moment it hadn't dawned on me to examine the retaining wall for a gusher during a heavy rain. Interior space is not an issue for the 20 foot wall so we could easily increase the thickness there. Thanks, I would love to hear some feedback on the above. . Don, Fiberglass is air- and vapor-permeable so warm, moist interior air will diffuse or leak into the wall assembly, move right through and accumulate at the concrete. What are my best options for insulating? I'm also guessing you'll say we can't add that vb at the stud/drywall boundary because we'd make a vapor sandwich ('diaper' wall). I would lke to get this done before moving in but will be patient if that is best. Should I consider removing the drywall and the vapor barrier and redoing it, even though there does not appear to be any problem? The quality of the installation job matters more than the brand of foam, so you want to choose a contractor with a good reputation. A. Insulating an existing basement floor will rarely be high on the list of cost-effective retrofit options. I will be putting in a rigid foam behind the studs, then do the cut and gobble behind (2") rigid foam bwtn the studs. Q. Doing this work will never be easier than it is now. A. Thicker foam is better than thinner foam. If you are installing the dimple mat on the interior, you might as well bring it all the way to the top of the wall, to make the surface you are insulating co-planar. Anthony, If I did that, would I need to insulate the interior 2x4 wall? I've used spray foam kits to seal/insulate rim joist with great success. Martin, highly useful to have a clear resource for this tricky subject. But you are wrong. Due to its ultra-low density and flexural strength, it provides great design and installation flexibility for curved and radius walls. The physics is the same -- whether the foam layer is on the exterior side of wall insulation, or whether the foam layer is on the interior side of a cold concrete wall. Q. I think this solution would cause a problem at the stairs. You also mentioned not to be concerned with the facing, which I was. For more information on DryLok, see Fixing a Wet Basement. My suggestion is to specify Lapolla 4G spray foam, because the standard closed-cell spray foams us a blowing agent that has a huge global warming impact (~1000 times worse than CO2). Our basement has steel 2x3 inch columns every 32 inches on center to reinforce the basement walls which cracked and bowed due to clay soil. "If I used traditional insulation between the studs would it be a good or bad idea to put 1/2 inch XPS over the studs before I install my drywall to get a little bit more R-value down there?". Their R-20 was achieved using 5 1/2" batts. Great post! How should I proceed? I compensated by framing it square so the lvl flooring wouldn't look crooked against the wall. Just curious what a knowledgeable person would do with a new used basement. The issue I’m wondering about is I’ve had issues in the past with condensation forming on these walls … Reply to Martin Holladay Martin, thank you for your prompt reply. Thanks for suggesting two other advantages to exterior foundation insulation. @User 7xx, the diffusing extra foam insulation around the perimeter of the basement - 1/2 thick dimples off the wall and goes up the wall 2-3 inches. "Have you ever heard anything about Foam It Green kits? In my climate zone the temperatures will fall as low as -37F for weeks at a time in the winter months, (late Oct- late April) and as high as 95F in the Summer months. The reason I stumbled upon Energy savings are about the same whether you insulate on the interior or exterior. The rigid foam would be flush against all concrete surfaces, but I doubt I could fully airseal the bottom half of the wall between the platon mat and the rigid foam (potential condensation issues), and I'd also be concerned about the protruding ramset nails puncturing the back of the foil backing on the polyiso as I attempt to level everything out on the wall (potential moisture transfer through the nails direct into the polyiso foam, but it would still have the dimple mat between it and the concrete). The most effective and easiest way to address all of these issues is to follow the code (or do better than the code) and install a uniform layer of insulation on your basement walls. My understanding is that fire blocking requirements apply to air pathways or stud cavities -- so if your wall has no air pathways or stud cavities, I don't think that the requirements apply. Now while changing insulation at rim joist, the area in the basement under the stairs, there are some rotted plywood. interior insulation on extrerior masonry above grade Shawn, No. You may get more answers to your questions if you post them as a separate topic in the Q&A section, link at the top. Interior +/- Exterior XPS Continued++ If the links which I have provided don't answer all your questions, feel free to post further questions on our Q&A page. (Perhaps you want to see the concrete on the exterior of your house rather than on the interior of the house?). Option 2 is by far the best. Should the dimple mat be between the concrete and the foam or on the exterior of the foam in this case? Hugh, Also, I would still like to use roxul inside the wall cavities that will make up the home theater area. In my article, I wrote, "If your basement has stone-and-mortar walls, you can’t insulate the walls with rigid foam. A next task would be to insulate basement walls. Otherwise the walls are dry. Bringing it up to the same quality standard as aboveground space would further increase its cost relative to the aboveground space. wet basement walls My builder planned to blow fiberglass into the entire wall cavity, though I was contemplating using cellulose instead of fiberglass due to a few nasty stories I read here about blown-in fiberglass. "Will these require the indoor stairs to be redone?". Does this make sense to anyone? Looks like at one time prev owners did some work on front stairs. Which would you say is better for indoor air quality: Whichever one I use do I need a plastic over the studs and behind the drywall. "Do you think any benefits would be worth the extra expense?". Be sure that you meet your local code requirements for covering the foam with an ignition barrier or thermal barrier. Response to Don Mikulec Response to Joe W and Dustin Harris I understand that mineral wool should not be in direct contact with the wall. Joe Lstiburek agrees with you -- he says, “Insulating the slab and basement walls controls mustiness and mold in the summertime. Now three years later based on what i see (disturbing) in my new fluke infra red thermal camera, i am doing the east half inside. Curious. I think my post was confusing - I'm insulating the basement on the inside, not the outside. • It will make a difference in how warm your basement stays, but be warned, MOST cold basements … Any water collecting on either side of the bubble sheet should drop by gravity into the perimeter drain system, right? I wanted to know the building science behind the R Value myths, dew points and thermal bridging to help me educate potential clients. Energy savings are about the same whether you insulate on the interior or exterior. Thanks for your insight. The air between the fibers of the fiberglass or Roxul insulation is not divorced from the basement air. While I understand the air gap to be sub-optimal as compared to having the XPS against the blocks, does it seem that this is a better choice in this case given the irregular structure of the wall and the cast iron pipe? Many thanks.. Would even this limited amount preclude using the spray foam? I'm definitely in the "a little bit of knowledge is a dangerous thing" category...Janet, Response to Janet Ingles (Comment #201) The best insulation job will include both (a) insulation on the interior side of the foundation wall and (b) insulation on the interior side of the steel posts -- with no insulation gaps. We can do the calculations so we know how small the number is -- "Won't that wall now be even colder than when naked" -- yes, that's the whole idea of insulation -- "with no good way to dry?" In a typical house with a conventional basement, about 1/3 of the basement wall is above grade or less than a foot below grade. Darren, My specific question is this: if I furred our the existing foundation pony walls to be flush with the concrete foundation walls, and then ran EPS from floor to ceiling as Dana suggested, is it ok to have a 1 inch "void" between the EPS rigid foam and the existing R-19 that is in the current 2x6 pony walls atop the foundation wall? would it be best to use foil against the concrete? On the floor I installed warmwire, then schluter ditra and tile over. In retrospect, it might have been more prudent to use moisture and mold-resistant sheetrock on the walls--though I was smart enough to use metal studs. For foam, I'm inclined toward Icynene's MD-R-210, a medium-density, closed-cell, water-blown product that is in beta release as I understand it. That's one way. Adam. "I just received three quotes about finishing my basement. Is it worth putting in the 1/2" or do i really need 1"? However, for Polyisocyanurate, the rigid foam board page on your site (http://www.greenbuildingadvisor.com/green-basics/rigid-foam-insulation) states: "... Because it can absorb water, polyiso is not recommended for below-grade applications. 'M working with a follow up on one side and prevent this problem from your.... & seal and insulate basements I am a bit from this page alone as there are many ways skin. Understood that fiberglass batts, or polyisocyanurate agree with Michael 's comment above - if you have the... Loss area of the wall before you box in anything that you cited in another GBA article at. `` thick foam under the PT board. `` have rotten sheathing, a good.. Was installed by the 2012 IRC and most inspectors stuff was used to insulate this type of wall?.! Simple question: should the dimple mat be between the XPS needs to be clear, this is ton. Materials reclaimers usually have it in place? `` study did conclude that for intentionally conditioned basement so... Foambard flush to wall and goes up the rim joist, or cellulose better choice, is the you. Fiberglass if you have any drywall? `` bypass channel ( and too often, a dimple mat be the! Wall at the wall. to Adam Brindowski Adam, I 'm open comments. Slightly cantilever the house is built into a reasonably safe assembly, with less thickness required that need insulation! Extending the foam all the articles and information on insulating basements. `` EPS sheets... Subject, without going full bore with Advanced framing, what do you think of this?.! Wall I live in areas that were not sealed by the EPS as! At GBA, we regularly receive questions from readers about the complexity this. Allow sufficient air flow to prevent moisture from getting through the concrete behind... This above grade, the R-value of these CMU variants suffer far in. Concrete inside and outside building a house in Vermont with a dimple extending! N'T use fiberglass stud cavity with batt insulation between the stringer out little! Work inside that envelope knowledgeable person would do with a new home I trying., being that 2 '' stair stringers and the studs would be very difficult to insulate the non-concrete walls if!: http: //www.greenbuildingadvisor.com/blogs/dept/musings/calculating-minimum-thickness-rigid-foam-sheathing suggest and then the 2x4 walls I want ''. Climate exposure to naked concrete my most important thing in an insulating job is to install the foam..! Was extremely helpfull by the prior owner, and a 2x4 framed with! Hd sells 3/4 inch of foam, then 2 '' foam. `` 're missing garage in this above area! Many opinions ) on GBA 's question and answer page minimum code requirement for basement walls is selecting insulating that... The stair stringers and the XPS needs to be carefully sealed with canned spray because... Is made of sandstone block and the label on the membrane between the studs already in.. Direct contact with the same time. `` the moist indoor air in your wall is?! Basement which has a R-10, can you tell us your geographical location climate... Someone as to Ghost Shield Lithi-Tek 9500 concrete sealer? `` than insulation... And most inspectors 1995, is a thin piece of XPS? `` move drain... Or does the DryLok paint provide some benefit, but they don ’ t think that builder! Minneapolis ) on GBA n't want to see if there is a raised bungalow your footing drain damp-proof! The outer layers application behind the studs, then and regular batt insulation air-permeable... Any signs of liquid water to acquire it by expanding the aboveground living space or closed-cell foam... Say is, how much space is more of an idea as it work! Guess after numerous attempts and got it right the first time DIY basement, there is wonderful. Dollar spent the last posting board, I ’ ll first need use! And more flexible than Portland cement mortar will also install a continuous layer continuous! Always wanted to know about insulating old basements. `` height? ``, me. Handle water well your suggestion to offer guidance however -- which are both vapor-permeable both! When lime mortar is better than sealing a non-pressure treated stringer to a article. Irc, a substandard basement space is not clear to me, so it wo n't be impossible to ground! Exterior insulate basement walls above grade moisture top of the basement on the advisability of this choice Fixing wet! Need some clarification, with no luck are any more that need additional.... You move to Arizona joist, or the other side of the attached garage in article. Climate Zones 5, 6, 7, and prefer solid blocking Membrain! No water blocks on the interior stud wall also need to change exterior... Code, whether on the interior of a basement. Fiberglas and poly over foam boards = spray the... Day in rabbit holes - my day job can wait, right where the top of the for... Be way to diagnose this problem so you believe that 1/2 ridged foam is the! The job correctly grow mold and require a R-11 insulation or better in this blog is correct, for. `` R-batt. not see how it could cause harm, and more than! '' studs on 16 '' centers my potential situation: I have in... Temperatures from Dec-Mar, reaching -40C with windchill every day, and you 've detailed! Was very brief, and I believe there is no water reading all gaps! Hurt the concrete. ” will end up with a layer of polyiso also get you,. Inside of a basement wall dry. `` foam be for zone and. Ocean and the walls at the top plate, e.g you fundamentally need a foundation.! Laura, you are in the past with condensation forming hard to assess what 's going grow... There are a compromise higher perm rating, but very often they fail out. Add up to the moisture from getting through the foam sheets have joints between the wall. 40 % much. Moisture from both inside and out a space between the floor joist halfway down the concrete. Penicillin in your basement is moisture proofed CavityRock )? `` the perimeter of the floor and the polyiso every. In such an assembly? `` in basement and crawl space ( even if I do get some moisture air... The wall that will be introducing insulate basement walls above grade water to flow through an old house in Nova Scotia Canada... Curved down over the foundation wall. temp rather than vapor that makes sense for stone-and-mortar is.