How to Insulate Your Basement: Part 3

In the third and final episode of this series on insulating a basement, Justin Fink explains the why and how of using foam insulation on masonry walls, and demonstrates how to properly insulate the rim joist area with rigid foam and batt insulation.
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[@brianford9522]

Might be the most thorough and well done basement insulation job I've seen done. Nice job! LIke my old man always says, "If you're going to do it, might as well do it well!"

[@AI-00000]

As I was watching this, I kept thinking to myself "damn i'm not sure its possible if i hire someone that they would even do 60% as good of a job..." i'd like to do most of my basement I live in a 72 year old home and the basements like 20 degrees colder at all times than the rest of my house

[@aaronvallejo8220]

This is exactly what I just finished doing in my 1912 old two story house basement. The rim joists were stuffed with old newspapers, potatoes sacks, dirt and insulation. I cleaned and vacuumed each one. Repacked with fiberglass insulation and then cut 2" R10 foam boards for each one screwed in place and spray foamed.

[@TheLatinMass]

The flexible tube on the end of the spray gun for hard to reach spaces is a great takeaway from this video. Thank you!

[@mikekim6374]

Great video! I'm redoing my basement walls with rigid foam insulation to prevent condensation and mold on the fiberglass insulation. My question: with trench drain drain boards that stick out from the floor, where do you position the foam? In front of the drain boards, above our behind?

[@lisav1186]

i've been watching a ton of these videos. Everyone was all tidy. This guy has spray foam everywhere. In my head i'm like the other videos. In reality i'm this guy. I look forward to some more videos so i know what the reality of my projects will look like. I'll be cleaning that foam up too my man.

[@binoshsamuel5893]

How do you put the foam board if you have french drain around the perimeter and have the 3-4 inch plastic lip of the drain. Do you put the foam board over the plastic and then foam the bottom ?

[@matthewblue7839]

great to see thorough quality work.

[@Feelstoramusic]

Nice tutorial! I'm in the process of the insulation stage myself. Unfortunately a recent heavy rain indicated some condensation noticeable on the back wall. I'm going through options of whether to water proof down to the footer with exterior drain tile and piping, but I have an interior french drain in this section already where it's building up condensation. I had to remove a section of the drain mat and piping for plumbing, so I think once I install that once again the moisture will drain into the pump again. Using this foam board, and sealing it with foam at the bottom, and vertical caulk beads, I think things should stay dry.

[@anneharrington7951]

Best video I've ever seen.

[@keshavr9617]

How does this work when you have some interior waterproofing sheet closer to the basement walls?

[@canuckfixit7722]

Some of the top of the sill plate was still exposed after inserting the 2in XPS. You added the Roxul which should adequately cover that part and then some. Inserting horizontal sheets of XPS covers any part of the concrete foundation from the top. Looks good!

[@kylehoyland]

Hi looks great! I'm going to do this, do you think insulating the stud walls with rockwool on top of this would be a good idea? Also if i do would i need to put a vapor barrier or is the foam acting as one? Thank you

[@robertm5969]

Foam board acts as a vapor barrier

[@tomsenft7434]

The rock wool is a good idea if you decide you need the extra r- value. Also, you could use thinner foam sheets and rock wool to hit your r-value goal. Each stud insulates less than the insulation, so continuous foam will outperform your Rock wool assembly for that reason. Polyiso slightly outperforms exp in r-value, and is a lot less flammable.

[@hollahabibi1897]

do you put batting insulation after ?

[@lnavinkumar123]

My basement wall was painted with Dyrlock. I was looking what adhesive to use to stick the foam board. I will test the spray foam to stick the foil faced foam board into Dylock painted basement wall

[@ronh9384]

Great video series. I watched all 3 of them. It might just be the best basement waterproofing, insulation, and air infiltration video I’ve seen. I do have some questions however. 1. Can dimple matt be put on the walls behind the styrene sheets in the event of a future leak from the wall? 2. In the event of a future leak from the wall should the low expanding foam you applied at the bottom of the styrene sheets have some small gaps for the water to weep out of? 3. Doesn’t code require the styrene sheets be covered with a fire resistant material such as drywall or another product? Thank you for your time. Ron

[@doctordutch]

I had same thought. I dont see why not. People put delta membrane on floor and exterior for waterproofing but it probably also gives an air space for drying.

[@larryh657]

To question 3 YES and YES !!!!!

[@tomsenft7434]

@D perhaps the water just stays behind the foam and drains into the sump, evaporates, or gets absorbed back into the concrete and earth as they dry...

[@goodtimes12342]

I've got got a perimeter drain w/sump pump. In my basement there's a skirt that sticks out where the wall meets the floor. I'm using the dimpled membrane system behind the styrene sheets. Using a 4 foot wide roll, I'm installing them vertically with screws or ramset (making sure they are level all the way). Each strip I tuck behind the exposed skirt on the floor so that condensation and leaks will drip right into my perimeter drain. Strips of membrane are overlapped and locked together by stacking the dimples and taping with appropriate seam tape. Then I'll go in and tapcon the styrene boards on top.

[@bretttrentham]

Great video! Understand you had a french drain. Our french drain around the inside perimeter of basement walls has a plastic material that goes up the bottom of the wall 4 inches or so off the ground. should I have the foam board go all the way to the bottom and seal it to the bottom with that plastic material from the french drain between the foam board and the wall?

[@michaelhenrysr.3031]

Any answers for this question?

[@RandomNumber141]

@@michaelhenrysr.3031The foam should cover up the drainage mat and be sealed to the floor.

[@joshrountree]

Will you be showing the stud walls?

[@cecilopez3369]

Do you have a video on how to make the foamboard door you are seen installing him this clip?

[@eagleeye5890]

Excellent video and explanation of the job!

[@bricemadden397]

what about fire blocking?

[@grayboo212]

03:18 Isn't that Owens Corning XPS? From what I've been reading so far, everything states you should EPS board (like R-Tech) as it breaths better and won't trap moisture. I only want to do this once and want to get it right. Any suggestions on this?

[@stonecoldcustoms]

You are correct, 2" XPS is considered a vapour barrier, while 1.5" or below is not. In this case, the 2" XPS is also being used as a vapour barrier. Where you place the XPS though, depends on your climate. In a warm climate, placing it on the outside makes sense, and then using bat or spray foam inside of it. But in a cold climate, it makes more sense to run the XPS from floor to ceiling on the inside as a vapour barrier, then insulate the rim joist behind it with bat or spray foam.

[@tomsenft7434]

Polyiso?

[@Supercharged111]

Polyiso SUCKS in a cold environment. XPS has trouble getting rid of moisture once it accumulates, whereas EPS is much more capable of shedding that moisture. The question though is where does that moisture come from? The video here has a scenario where it comes from the inside and the insulation stops that from happening. A lot of folks here in the comments section (like myself) are far more concerned with when the moisture comes from the outside say during a Spring thaw.

[@toddkilpatrick7871]

Currently doing 2 layers of 2" Foamular on the rim joists of the craw space. I also used UGL Drylock on the walls, 3 coats. Should I go back and put Foamular over the recently Drylocked walls?

[@Lincoln_Hawk]

Great informative video. Thank you!

[@ReyShady05]

so i plan on doing exactly this. using foam board on a cynder block wall. My question is, i am going to install stud walls. I am curious would you recommend using an inch gap between stud wall and foam board? also could i use the rockwool insulation like you did in the upper part of the wall? thanks

[@TheDirtCreature]

Look for This Old House insulating basement wall. It shows everything.

[@robertm5969]

No gap necessary between foam board and insulation batt. Foam board must be the one facing the cinderblock though.

[@damasydia]

What about fieldstone foundations?

[@doctordutch]

does the wall assembly need a vapour barrier/ PE liner?

[@deathmetalfunzone7727]

Good video. I think I’ll give it a try. Thanks!

[@TheShehab12]

Great job. The only thing I have to add here is that if you adding subfloor panels, it would be before the rigid insulation.

[@keshavr9617]

Sub flooring before wall insulation and framing

[@RushWorkingMan]

I would spray the beads of adhesive vertically behind the foam boards. Should any moisture appear it can work its way down and not get hung up and cause mold. Might use a penetrating sealer on the walls first too.

[@jackhayner1990]

Do you really need drylock if you do this. It seems redundant?

[@sholagan]

This is for insulation while drylock is for waterproofing.

[@TheDirtCreature]

You would first test the walls for moisture and seal them, preferably with something better than drylock, such as MasterSeal 583 (Super Thoroseal). If you have a lot of moisture, sealing from the inside is never a solution. You would need to seal from the outside before adding this type of insulation.

[@RandomNumber141]

The DryLok is not needed because the foam creates the vapor barrier. It’s not meant to stop bulk water leaks, though, and neither is DryLok.

[@cotwold]

Very helpful

[@samdaniel5703]

How do I do this if my whole house is concrete and the back wall is underground also anything I need to do different in a bathroom

[@davidchillton1744]

Most building codes require, foam to be covered up whether it be with 1x3 strapping or 2x4 framing and drywall or equivalent

[@JonTheChron]

Correct, this foam is flameable

[@davidchillton1744]

@@JonTheChron so is wood and drywall though 😂

[@mpxz999]

@@davidchillton1744 not as insanely flammable as XPS foam. It lights up and spreads at a frightening pace

[@markprimiano]

what about the fireblocking above at the joist bay? typically a 2 x 6, 8 or 10 on the flat depending on foundation depth would cap off the top of the insulation. the plate (fireblock) would go from exterior sill plate to the furred out 2 x 4 top plate.. so that layer of rigid you put at the top tight to bottom of joists does not really allow for this fireblocking technique.. I believe all XPS needs to be covered and cannot be left exposed (highly flammable)..

[@Shad0wC0mpany2]

Wondered the same thing!

[@bhadz100]

How do you insulate the long joist? It’s the last joist for each side?

[@robertm5969]

Cut a 8' long piece of XPS foam the height of the joist. Jam it in there so the tight fit keeps it pressed against the exterior joist. Foam around it if there's any gaps. Repeat until the entire length of the end joist is covered.

[@AaronPlay]

This is the way I’ve always insulated basements. But the county I’m building in is requiring r-19. Any suggestions?

[@ADVRider78]

I did what he did and framed a 2x4 wall in front of it, then used Roxul for insulation and drywalled it.

[@robertm5969]

2" foam board is R10 then when you frame on top and add fiberglass or roxul batts that's another R13-15. So total is R23-25, you're all set.

[@AaronPlay]

@@robertm5969 Might as well just use r-19 batt then.

[@robertm5969]

@@AaronPlay the foam board also provides a vapor barrier, so moisture doesn't accumulate inside the framing and batts. You lose some space but it's well worth the advantages

[@stoneyj1a1]

@@robertm5969 what happens to the moisture coming from the blocks?

[@MitchOfCanada]

Rigid is the way for basements. Living next to farmland the mice in my lower walls were brutal. Now spray foamed and rigid they cannot freely travel on their old insulated highways

[@Andrico77]

I would’ve used spray foam for top of wall and rim joist area. Like the 200 BF take home kits.

[@mghc7]

Can you leave it as is,and will it help with insulation factor

[@ADVRider78]

Looks like the 2" is R-10 insulation factor. You could leave it as is but where I live you have to fireproof it (like drywall it)

[@mghc7]

@@ADVRider78 Thank you for your reply

[@patty109109]

Not sure I’d use foam for gluing panels. I’m surprised you did since it’s not its intended use. PL300 foam glue is intended for it. Good job overall but that wrap tape has terrible adhesion to foam. I wouldn’t bother.

[@ev1558]

Have a pretreat of termiticide first. I've seen termites travel up (unexpected areas) to reach their food source of cellulose. It's easier and cheaper to do ahead then cover inspection points and find out you have termites after the damage is done.

[@lionintu]

What do u consider a good pretreatment? I love had the termit guys spray everything before i started work

[@georgesobon3977]

No one wants to watch a podcast, as the veiws show, everyone loves visual instruction

[@alexblaska9802]

Just pay someone to spray foam the rim joist. You cant beat it, the walls i did myself with 2in foam board like the video

[@bettergetdave]

I put this up as a DIY and some professional came in and told me i was going to cause mold to grow behind the insulation and ruin my basement.

[@finksoncarpentryandwoodwor4170]

That’s not true

[@stoneyj1a1]

that is correct

[@bettergetdave]

@@stoneyj1a1 thank you both bc i was worried

[@RandomNumber141]

So what if some mold grows behind the insulation? The foam seals off the concrete from the room. Anything happening behind the foam does not impact the living space

[@patty109109]

Did you ask this professional how the heck mold survives without a food source? What exactly is it eating? Foam? Concrete? Some people seem to think mold is a magical organism that exists in moisture and doesn’t need a food source like every other organism on the planet. No you won’t trap mold. Foam against wall is what I did in my last house. On my current one the walls are so darn dry I didn’t bother-just went with the lazy fiberglass blankets that came with the house.

[@stoneyj1a1]

What would be the point of this? What happens when there is moisture? Often there is moisture in the blocks

[@matthewblue7839]

It will naturally ventilate to the outside. So, the point is to turn your basement into a comfortable , warm and non drafts space, with no moist air condensing on interior face causing water to form and pool. You will also be saving money each winter due to reduced heat loss/transfer. It’s a lot of work, but do it once right and then enjoy your basement each year afterwards.

[@johnpeck2316]

That is an outside problem…or an older house that has no, or inferior drainage control.

[@RandomNumber141]

Why does it matter if there is moisture in the foundation wall? Concrete does not care if it’s wet or cold.

[@user-jy6vd3uw1m]

Look up dew point and vapor pressure differentials. Moisture moves through materials directionally based on pressure differentials, temperature, and other factors. The dew point can cause condensation of vapor on a surface when the dew point is hit. Understanding these mechanics is critically important to prevent mold growth, along with other phenomenon like lime leaching among other problems. Materials like walls expel or transport moisture in more than one direction. If weather conditions change or materials like paint, vapor membranes, foam, etc. are added or removed, the way vapor moves from one space to another can change. For example a wall that normally transports vapor inside to out, can transport vapor outside to in.

[@aoreilly1196]

Does the insulation and foam need to be fireproof? Are the materials you used fireproof? Somebody told me that insurance companies will not pay in case of a fire if regular foam is used. Thx

[@huejanus5505]

Foam has to be covered with drywall. It’s very toxic when burnt.

[@davidchillton1744]

@@huejanus5505 many things in your house are toxic if they burn lmao

[@TheDirtCreature]

You need to protect the foam, preferably with drywall. The goal is to help prevent fire ignition and spread since basements often have combustion sources, but it is also principally to allow more time to get out of the house and not be overcome with toxic gasses.

[@Nightl3lade]

@@davidchillton1744 *everything

[@Yoyoyojohn]

Question for you or anyone who knows anything about this. I read something online that said putting insulation against cinderblocks wouldn’t allow them to warm up and they would freeze in the winter causing the mortar to weaken. So they recommended not using this method. Can anyone lead me in the right direction? I have a cinderblock basement and don’t want to glue foam to the walls if that’s a bad idea.

[@edcollier2526]

I just watched an Owens Corning video and they installed their rigid foam board on both, concrete and cinder block, walls. I am also installing this on my cinder block walls, not worried about needing to heat up the block as I'm trying to stop the moisture from the heat to cold. I do have a drain tile and we drilled weep holes at the bottom of my block columns for drainage.

[@seawall90]

You won't freeze below the frost line.

[@RandomNumber141]

@@seawall90But foundations obviously extend above the frost line

[@59seank]

Are you going to insulate the concrete floor?

[@travisreed8244]

Yes I have the same question

[@RandomNumber141]

Not a lot of heat loss into the floor since the deep ground temperature is close to the average yearly temperature.

[@mrrex5682]

2 inch fome board is only r7 that's like not even insulating.

[@RandomNumber141]

2” XPS is R-10. That stops 90% of heat flow. Far from “not even insulating.” This is not an attic where it’s easy and cheap to add R-30+ insulation.

[@mrrex5682]

@RandomNumber141 even r10 doesn't meet new building code for a living space

[@brianvangrinsven5496]

@mrrex5682 You would then put up a stud wall up against the foam core and use either fiberglass bats or rockwool in between the studs to achieve your desired/required R-value

[@RobKingRC]

It's called a serrated knife.

[@JasonEllingsworth]

a couple notes for anyone watching and thinking of doing the same. First, run your foam with a 1/4" air space behind. You need this space for airflow to dry moisture vapor in the concrete. Second, run your foam from 1/4" off the floor, to the plywood deck above. Do this straight up and tooth in between your joists. Seal this foam to your joists with spray foam. DO not spray foam the bottom of the foam board. The way this guy did it, does not allow the concrete to breathe. It will always trap moisture and that condensed water will leak out on to your finished floor. Maintain the 1/4" gap under the foam board, through the back of the board, and up to your floor joists and band board above, where the vapor can be absorbed in to the wood, and wick its way outside. This is the only proper way to keep your basement from having condensation moisture issues

[@JasonEllingsworth]

Then once you have done this, you can consider a product like DMX 1 step floor underlayment and vapor barrier. It has knobs on the bottom that keep your flooring off the concrete and allow vapor/moisture to flow underneath and dry out. In this scenario, you would tape the underlayment to the face of your foam board. This creates a sealed area where your finishes are, and an outer U shaped channel from your joists, down to the floor, across the floor, and back up the other side allowing air flow to dry any moisture/condensation. Frame all interior walls ON TOP of your subfloor.

[@yellowbellybee]

@@JasonEllingsworth How would you recommend to make the 1/4" spacing behind the foam? wood strips? also what do you mean by ". Do this straight up and tooth in between your joists." thank you for your time and help

[@JasonEllingsworth]

@yellowbellybee you should run the foam all the way to the plywood, instead of just to the bottom of your floor framing. The 1/4" spacing is as simple as gluing shims or using expanding foam as an adhesive. There's actually a version of it that you can get that is an adhesive

[@RandomNumber141]

None of that is correct. If you leave an air gap behind the insulation, and allow air to circulate between that cold gap and the room, what’s the point of insulating? That air gap enables heat to flow freely between the concrete and room. What’s the point of even using foam if you’re not taking advantage of the air-barrier and vapor-barrier property?

[@JasonEllingsworth]

Reading comprehension isn't your strong suit. No outside air would be entering the living space. ​@RandomNumber141

[@Thor1O1]

Looks like a mold trap to me. Concrete even when sealed from the outside still pulls some mosture into the basment. You have 2 options use bat insulation leaving a space between it and the concrete. This allows for airflow within the void.Other option is get a professional sprayfoam installer can use CLOSED CELL FOAM. often you will have to use a mild acid to clean the concrete in order for good adhesion to occur. He used open cell foam which is a big issue especially on the floor. It works like a sponge with mosture. Any moisture comming up through the floor slab or any flooding even minor will result in black mold shooting up behind the foam. I am a contractor with 23 years under me, also i just tore a basement clean out for this reason this last summer. Water tank burst and led to only a inch of standing water but lead to mold everywhere and a $55000 dollar renovation.

[@RandomNumber141]

What’s the difference between closed cell foam sprayed onto the concrete, and closed cell foam boards attached and sealed to the concrete with more closed cell foam? Hint: there is no difference

[@Ryan-ge9nt]

Nice. now when the moisure comes through that old concrete wall, like it always does because conrete is porous and these older houses are never sealed well on the outside, it has no way to dry out and the homeowner can rip out all of the foam and hire a mold remediation company.

[@robertm5969]

What would the mold feed on? Doesn't it need organic material? As an alternative would it be better to leave a 1/2" air gap between the foam board and concrete?

[@stoneyj1a1]

I'm thinking this exact same scenario. Do these people not understand the ground and foundations?

[@RandomNumber141]

1) Concrete does not care if it’s wet or cold. See: literally any concrete structure in a northern climate, i.e. bridges 2) The point is to create a sealed room inside the foam, so that any moisture in the concrete has no way of getting into the basement. Any mold or mildew behind the foam stays behind the foam.

[@RandomNumber141]

@@robertm5969No, if you leave an air gap you defeat the point of the insulation. The whole idea is to keep heat from transferring between the room and the concrete wall - an air gap will allow air movement and heat transfer. If the air gap is completely sealed off, then there’s no point of having it.

[@patty109109]

Since when does mold eat foam as a food source?

[@JJJere]

Seems like over kill!

[@brandonfrancey5592]

No one complains about a job done too well.

[@mjleechcontract9030]

Depends on what they want to use the space for, if warmth isn’t a factor could just frame it with a tyvek water paper behind and pink insul in studs

[@Andrico77]

That’s why the channel is called fine home building

[@jim8206]

Won’t mould grow in between the wall and the styrofoam as Condensation will form

[@Ryan-ge9nt]

yes! plus moisture that comes through porous concrete! this is a horrible idea for any older basement that isnt well sealed on the exterior.

[@TheDirtCreature]

You must ensure that your walls remain dry, which means the EXTERIOR of your house has been properly sealed. Sealing from the inside is never a good solution to mitigate moisture. It can reduce it, but not eliminate it.

[@RandomNumber141]

What will the mold feed on? Concrete? Foam? Organic matter in the water (which was already there)? What happens if mold does grow behind the foam, which is sealed to the concrete? How can the mold impact the living space if it’s sealed behind the foam? How can there be condensation (which comes from water vapor touching a cold surface) behind the foam, if water vapor from the basement can’t touch the concrete? The only source of moisture is water from outside which was always there.

[@patty109109]

@@RandomNumber141thank you random. Honestly the scientific ignorance of KZbin commentary in general is stunning. Mold can’t survive by eating concrete or foam.