Basement Insulation

Basement insulation is a common feature on newer homes.  If you’re finishing your basement you’re probably wondering “what should I do with the insulation that is already on my basement foundation walls?”  The big silver padding that you see nailed to the wall of your basement is the insulation.

Should you remove the existing basement insulation before framing your basement walls?   My opinion on this topic is purely that, an opinion.  This really is an “it’s your choice” decision.  I left my basement insulation up and framed the walls outside of it.  Today I’ll walk you through my thought process so you can make the best choice for your basement project.  It really was a decision making process, this question bugged me for about 4 or 5 days.

Will I save some space?

If I take my basement insulation down and then frame the walls right up against the foundation will I save some space?  The answer, is yes. But not much.

Silver Basement Insulation

Basement insulation attached directly to the basement wall.

Going purely by the numbers you will save about 3 inches on each side of the room as the insulation more or less puffs out at about 3 inches depending on the brand of insulation.  That’s 6 inches in total. However…

There’s always a however isnt’ there?   Why can’t it just be that’s it.  That’s the answer.  It’s not.  The space where your basement foundation wall meets the basement floor is likely not perfectly clean and square.

In my brand new basement floor there are all kinds of concrete bits and mortar overrun that creeps out of the seam.  This is a good sign because it tells me that it’s well sealed from critters and bugs but it also means that I can’t exactly build my framed wall straight up against the foundation wall.  I’m going to have to come out an inch or so to ensure my wall will be flat against the floor.

Click to enlarge and see wall goop detail.

Aha!  You say. I will just clean up all that mortar goop and then frame my wall.  Very well and good luck to you, but make sure that the lumber you are buying is perfectly straight.  Because if that framing lumber has the slightest bow in it then you’ll have to face that side out towards the room.  This will make your drywall guys cry in their pillows.  Which in turn will cost you more money or worse, leave you with wavy walls.

You probably still want that extra inch of room so that you can turn the bowed side of a stud towards the foundation wall, thus keeping your drywall side of the wall even.

You will save about 4 inches by removing your basement insulation

So now you know that you are likely going to have to give back and inch on each side, that’s 2 inches in total for two sides of a room.  So let’s see, now we’re down to a total of 4 inches of extra space.  I mean 4 inches is 4 inches.  In a heated ping-pong match or game of pool that can make a difference.   To me though, that’s not enough of a difference to go through all the hassle of tearing down the insulation and putting it back up.  But, my basement was pretty big to begin with, in a smaller basement that could be a bigger deal.

Amount of space saved by removing your basement insulation


Do I need this insulation?

If you decide to tear it down do you need to put it back up?  Yes,  you should insulate.  Granted, the walls you are going to frame will also act as an insulator but have you ever touched drywall that isn’t insulated on a cold winter morning…. It’s cold baby, ice cold. I would either cut up your old insulation into strips and then put it back into the stud cavities or trash it and buy some new insulation that’s already pre-cut to the right width.

If your basement doesn’t have any insulation to begin with there are several options that you can consider. This website does a good job of explaining how to insulate your basement with extruded polystyrene foam.

What if I frame over it ?

Badger - my nemesis

Badger – my nemesis

I know what you’re thinking, I thought the same thing.  When I frame my basement walls I will just squish the wall in over top of the insulation to save an inch or two. Bad idea.  If you compress basement insulation (or any insulation) then it loses it’s “R” value.  It is no longer an effective barrier of cold and heat. The framed wall studs can touch the insulation but don’t let them crush it.

Oh, and if you see any holes in your insulation go ahead and cover them with some duct tape before you close in everything.  My cat “Badger” used our basement insulation as a ladder to get to the basement window, so that was kind of a problem for me.

basement finishing jasonHopefully that sheds some light on this issue, it’s a very common question.  I’ll have a different post about insulation for sound control – plus a very long post about sound abatement, so look for that in the coming weeks.

Cheers,

Jason

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Comments

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  1. Thank you Jason.

    Today the seller accepted my offer on their house, almost, I have to pay half the closing, but I want to counter by asking for their riding mower. Anyway, the basement has that bulky silver insulation as you described. I’d like to finish it. I can handle a hammer and I know it would take me ten times as long as a carpenter, but I am considering doing it. Is this something I can do?

    • Robert – In my opinion, yes, it’s something you can do. If you’re moving soon it may not be the best time to learn though. If you have some time then yes, go for it! And I would definitely go for that riding mower. – Jason

  2. Jon Hayden says:

    Stupid question…My home is being built and it will have the insulation on the walls already just like you mentioned. Is that all the insulation I’ll need than? For example, if I keep the insulation up and frame outside it, that means I won’t need to add insulation between the studs, right?

    Thanks,
    Jon

    • Not stupid at all, very common question, that’s why I knew a post on this topic would be helpful.

      You are correct. You will not need any additional insulation between the studs. The insulation that’s installed will be more than sufficient. I did had some insulation between the studs around my HVAC room but only to knock down some of the noise. – Jason

      • Jon Hayden says:

        Thanks Jason! That’s great news because that will then allow me to make niches between the studs.

  3. Jason,
    I am having a home built with a basement. The basement will have the exterior walls studded and insulated with fiberglass insulation between the studs, all included with the base cost of the basement. Is it safe to assume that these exterior walls will be ready for drywall? (except for electrical, of course) I hate to ASS-U-ME anything.
    Thanks for all of the helpful info!

    Jeremy

    • Jeremy – You should be good to go. Add electrical, which will mean removing and then reinstalling your insulation (not a big deal), and you’re half way there. – Jason

  4. Jason – the previous owners of my house framed & insulated the basement & hung this awful paneling. I took it down, then got an estimate from a contractor to see how much money I’d save doing it myself. He said that he’d reframe the basement because the studs were up against the concrete wall and they should be several inches out. Is this true? Also – what about a sub-floor or floor? Is that something I should do before walls? Did you put any additional HVAC in your basement? Sorry to load you with questions. Your site is awesome but I’m worrying about details I don’t see. Thanks – Jon

    • Jon – No problem. Unless the studs have mold or other issues (cracking, or something) I can’t think of any reason you would need to reframe. It doesn’t matter if they’re up against the wall. You can do the floors last. You should only need a sub-floor if you plan to put in real hardwood (which I wouldn’t recommend for a basement) or if you have serious moisture issues. I added two HVAC extensions, no new “lines” I just tapped into the existing branch (I’ll be posting about that soon). Thanks for commenting, you’re questions help me know what to write about next! – Jason

    • Matt Rogers says:

      I agree with Jon Tyler’s comments above, I love this site and have gained so many practical tips to prepare for my foray into basement finishing, but a big gap is the lack of information about properly preparing for framing — namely, insulating. Jon is correct that you should NEVER have the studs up against the concrete — this is old thinking, and it is now accepted that this can lead to mold and moisture damage.

      The only mention I found here about prepping for framing was the one line that links out to http://www.homeconstructionimprovement.com/how-to-insulate-basement-walls/ . This step isn’t really considered optional anymore, as alluded to here. The old way — framing against the concrete, then insulating and covering with a vapor barrier — definitely has been shown to lead to mold. The vapor barrier traps the moisture from the concrete inside the walls, with your studs and batt insulation, and it’s a nice little mold factory. The foam is the safest and most cost effective way to avoid that, and gain some R-value in the process.

  5. Jason-
    I would like to add a few things to this topic if I may? First off, we all know that basements that are not insulated correctly will certainly cause an extremely dreaded MOLD issue. So here’s my take on a basement…hold your framed walls off of the concrete by 1/2″ all the way around, then you can have a contractor spray foam a closed cell foam between the studs. This will give you a super tight basement, provide a vapor barrier, as well as fill any cracks that may form down the road. The foam is water resistant, moisture resistant, and “environmentally friendly”. Also, by holding the framing off the wall a 1/2″, it will allow the foam to expand behind the studs “gluing” your framing to the foundation. If you want more tips on basement finishing…I’ve got a slew!

  6. I forgot to mention that they need to use a CLOSED CELL…NOT open cell. Big difference in material. Keep in mind this as well..IF you ever did get a flooded basement and you have fiberglass insulation, you will now need to remove drywall and insulation. With foam, you pull the drywall off…let the area dry out completely, and re-drywall. With foam, you’ll never throw away old insulation, I know this because I’ve seen it happen.

  7. Hi Jason,
    We have a newly built home, and in the basement they draped fiberglass insulation over the walls, and taped the seams. It is only nailed right above the poured basement walls, and just hangs down. It also doesn’t go to the floor, its about 4″ above the concrete. The fiberglass faces the concrete, would this cause a moisture problem since it is open at the bottom? Or is it OK to wall over that?
    Thanks!
    Trent

    • Trent – This should not cause a moisture problem. You should be able to frame right over, exactly as I did with mine (same situation). If you already have a moisture problem, then you have a issue to deal with – but the insulation installation itself won’t create a problem on its own.

      Cheers – Jason

      • My basement has the same set up as Trent’s with the fiber glass insulation not going all of the way to the floor. Would I need to finish insulating the rest of the wall to insure complete insulation and minimize heat loss?

        • Hey Bryan – So usually the reason they don’t insulate all the way down is because you only need the insulation for the parts of your basement that are above the frost line. The space below the frost-line will stay at a constant temperature. The temperature will vary depending on where you live but is most commonly around 55 degrees.

          This is the long ass way of me saying… you don’t need to add additional insulation. At least, I don’t think you do. If you still wanted to, I would frame the wall first, then add insulation between the studs.

          Hope that helps – Jason

  8. I’ve seen a double 2X4 plate with the bottom one being pressure treated lumber. It seems logical since I am doing my basement and who knows what the future will bring with regard to moisture, but where do you stand on this method?

  9. So, what if I cut the insulation at the 16″ so the studs can slide in between? The floor plate is already going to be close to the cement wall, so this would allow me to push the stud in without crushing/compressing the insulation, am I correct?

  10. Hello,
    Great website. I want to begin framing my basement but I am stuck between what to do with existing insulation. Presently, there is insulation only on the top half of the wall with poly wrap. What are my options?

    Do I insulate lower half first and frame in front? Frame in front first then insulate between full height of frame and double up at bottom to match the top? All options except pulling out insulation first seem like it will result in varying “R” values throughout the height of the wall.

    Jason

    • Jason – Insulation on just the top part of your basement wall is a fairly common scenario. They do this because the bottom part is more than likely below the frost line, wether the temperature change isn’t has great. My suggestion is to leave it as and proceed with framing. I wouldn’t bother adding additional insulation nor would I take down what’s already there. Good luck with your basement finishing project! – Jason

  11. Jason,

    Great info, thanks for the insight. I have a brand new home with an unfinished basement that has pre installed insulation that is covered with plastic wrap pinned to the walls. I am thinking of just framing right to it. My question is what is the best way to frame up to the insulation. How do you measure it up and ensure that the wall is good with moisture and such. I know how to plumb/square the wall. I just want to make sure I get close to the wall. I don’t know if this makes sense. Thanks again for your help. Also i am using metal studs for 90+% of all walls.

  12. I just finished framing my basement and left the blanket fiberglass insulation on. My questions is if I add m ore insulation In between the studs and then add a vapour barrier will I get moisture. Should I leave the batt insulation without a vapour barrier?

    • Noah – I would not add an additional vapour barrier unless you currently have a moisture problem. Leave the batt insulation without the barrier. Have fun finishing your basement, thanks for coming by. Cheers – Jason

  13. Assuming based on what I’ve read in this post that I know the answer, but will ask anyways. The builder insulated, vapor barriered (is that even a word?) and drywalled all exterior walls of our basement. I’m assuming that I should just leave them as is, and take it as a bonus that I’ll only have to frame interior (and non-load-bearing) walls??? Looking forward to getting a start on my basement. I’m an RN, so being ‘handy’ and working with real tools/wood isn’t exactly “up my alley”. Did do a lot of work with my dad on our backyard deck last summer though. Just hoping that I can please my wife/it looks how she thinks it should (ha ha!) when all is said and done…

    • Rob – You got it. HUGE bonus! Leave the existing walls as is and commence finishing the rest, sounds like you have all the skills and drive to do it. Good luck! – Jason

  14. Hi Jason, great site, learned a lot over here.

    Have a question though. What insulation should I use for the Basement ceiling ? I plan to make a media room in the basement, this will be directly below the kitchen on the main floor. I would like to reduce noise both from kitchen to media room and vice versa. I was thinking of putting fiberglass insulation in between the ceiling joists. My question is, is fiberglass the right insulation material to use in my scenario? Also, what R value should I target, and wether I should use faced or unfaced insulation. If using faced, I presume the paper side will be “towards the basement”, so I can staple them to the joists. If unfaced insulation should be used, please comment on whether a vapor barrier needs to be installed.

    Thanks.

    • Hey Chet – Ok, lot of good questions here. I’ll do my best to give you my opinion.

      Yes, I think insulation between joists help in noise reduction, especially for a media room. Face or non, doesn’t really matter, I used faced, either orientation is fine, mine was face towards the basement. Instead of stapling I recommend cutting it to fit with just a touch extra, then just push it up into the joists. This way you keep a nice clean plane for the drywall to be installed against (no staples). You shouldn’t need a vapor barrier in the ceiling.

      There’s a bigger problem though, the joists. Sound will travel up to the drywall, through the joists and into the kitchen and vise-versa for the footsteps above. For a legit media room I recommend using drywall clips or special drywall glue which will keep the drywall from directly touching the joists. At first you’ll think you don’t need it. Because with the insulation in and no drywall ceiling, it’s very, very quite. But as soon as that drywall is nailed to the ceiling the sound is amplified quite a bit.

      I need to do a post on this, there a ton more to consider – but hopefully that helps you along.

      Cheers – Jason

      • Hi Jason,

        Thanks for your ultra quick and clear response. I will check into the drywall clips and/or glue you mention for the ceiling.

        I (we all) also await your post about the ceiling. I am sure you will have other aspects in there that I have not even considered yet …

        Regards,
        Chet.

  15. Jason,
    I am using Metal studs and i had to build one of my walls approximately 1 foot away from the concrete wall, due to my plumbing in my basement. I currently have zero water issues in my basement and I have never had my sump pump turn on. Should I glue Foam boards on my concrete walls? Should I do fiberglass batts?

    Great website by the way.

    Thanks! Russ

    • Hola Russ – Well, I’m a little slow, but I’m not sure what the fiberglass batts for foam board have to do with the water issues??? If you haven’t seen any moisture issues, I wouldn’t worry too much about moisture problems if that’s what you’re getting at. Some basements are just bone dry, due to their particular location, soil type and drainage situation. Lucky you! – Jason

      • Sorry, let me explain a little better…I wrote that is a hurry last night!
        Since I have framed a wall 1 foot from my concrete wall, is there a chance that could cause a problem with mold, in the area behind there? Should I put Drylock on the concrete walls or anything else, just as a precautionary ?

        My next question is what type of insulation would you recommend for metal studs? kraft fiberglass batts? unfaced batts? Foam boards?

        • Gotcha – now I can picture it. In my opinion, Drylock would be a worthwhile peace of mind investment. I don’t think mold would be an issue, but that’s because you’re saying your basement doesn’t currently exhibit any moisture issues. My don’t have an insulation preference, I used faced batts on mine. I’m not sure that the metal studs make a difference (if someone knows otherwise please comment). Adam has a post on XPS board coming out this week – I’ll try to remember to link to that here once is live. – Jason

  16. Hi Jason – great advise on the existing insulation. I planned on leaving mine up as well. My walls are insulated three feet below ground level and I plan to carry the insulation to the floor.
    My big question is should I frame with 16 inch centres or can I get away with 24 inch centres?
    It would be a big savings on lumber and I will have no load-bearing walls so I am thinking I should be good.
    Thoughts?
    Thanks,
    Jim

    • Hey Jim – Yes, you’re good with 24 inch on center, as long as your local building department allows it. Double check. 16″ on center would be my preference though. – Jason

  17. Have you ever looked into soundproofing for a basement? One of the things I want to consider is that I have a kid that plays the drums and another that plays the guitar, some day in the not too distant future I image a band practice going on in my basement. Is this something I should be handling with insulation?

    • Hi Dave – If you’re still in the design phase, the best thing is to design a distinct room for drum / band practice, something that will have four walls and a door. Insulation between the ceiling joists can definitely help but the biggest impact you could have is to hang your drywall with some suspension clips so that it’s not directly in contact with the joists. Sound travels to the drywall then to the joist and up into your first floor.

      Rugs of course help a ton and then furniture will absorb sound if it has cushions and fabric, finally you can hang rugs on the wall or go really crazy with sound insulating foam blocks, which when framed in actually don’t look to bad.

      Good Luck!

      Jason

  18. Hey Jason,
    Me and my wife recently bought a house that has the insulation already on the walls. What would you suggest for below the windows for framing, as it is insulated below those as well? The windows are about 4 feet off the ground and are surrounded by wall that are drywalled. Also the windows sit back a good 6-8 inches from the front of the insulation already.
    Advice would be helpful. Thank you in advance,
    Anthony

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