I have been building Encapsulations from Knoxville Tn to Kingsport Tn for 15 years. Refreshing to hear a completely accurate report. You are truly better off with nothing, rather than fiberglass batts. The rim joists is where 20% of all heating and air conditioning loss comes from because , like he said, nothing is there but a 2 x 10. In almost 1/3 of all homes, you can see the sunlight in and around the band joists (same as rim joists) because the 2" board is too hard to cut (and there's a lot of cuts) , we use 1" Owens Corning board. We pop a 1-1/4" roofing nail in the middle of the board to hold it in place while we foam around it. It's time consuming, but if you pre-cut the boards at the shop, it goes faster. There are lots of non-standard spots and many places where pipes or wires go through. It's best to get accurate measurements for those, and cut them at the shop and write on the PM with a marker. Last two hints. 1) Leave a space above the foam board to shoot the foam into. Foam doesn't have anything to sit on if you don't, and if you're going to drive a roofing nail (a box at Lowes is $3.88) you can't get a hammer into that area. Poke the nail into the foam board first and use something as an extension to hit with a hammer. We have a one inch round lead pipe that's 10 inches long. Very last hint. Major cities Home Depot and Lowes will rent a Fogger and both sell Concrobium Mold Control ($37 gallon, or $9.50 for 16 oz spray bottle) It kills every mold spore instantly and no mold can grow on that lumber again.....EVER !!!! I can't say enough about this product. Whole families were seeing the allergy doctor until we fogged their crawlspace . Angie Hicks of Angie's list made a video BLASTING allergy doctors for NOT telling their clients to atleast have their crawl space looked at. They must have made her take it down. Lastly, an air quality specialist costs four hundred and fifty dollars, you spend seventy percent of your life inside your home breathing God knows what.... these dudes are good and they have the instruments..good luck with your home,

Thanks for the visuals. Seeing quite a few bad takes here in the comments. Simple summary: the fiberglass does not stop air movement. Moist air from inside the crawl space moves through the fiber glass bat and condenses on the cold rim joist. It's not likely to dry, and that's where the wet and black staining comes from. The solution here is to remove the fiberglass, cut and cobble rigid foam and seal the perimeter of the rigid foam blocks with spray foam. Care should be taken to choose the right rigid foam thickness for the climate zone to ensure the inside face of the foam remains above the due point. There are simple tables to find the proper thickness for your climate zone. This topic has been covered repeatedly on the green building advisor website and fine home building podcasts.

Thanks! You have pointed out some good points to ponder( for each) region n weather types!

Thank you for confirming what exactly what I was thinking of doing in the basement

Exactly. Also 1 1/2” strip to fill space below joists up to sill plate especially if it’s a block foundation. And zip tape the seams. Also at that point you can put the fiberglass back in.

You literally read my mind with this video!!! Thank you. I’ll be adding foam board to the rims. 👊

Great input never heard this side of the story before this is used almost every new home I've plumbed unless they spray foam but I've drilled pipes through the closed cell and the vapor fumes are unbelievable

I live in a cold climate and agree your summation is correct. Here we also need a poly (Visqueen) barrier anywhere low density foam or batting is used. We do not need or want to leave a strip of sill plate exposed for termite check because no termites here. Guess u don’t hv them either. I like your commment about being able to remove foamed-in sheet foam versus urethane sprayed foam. Good point. Cutting and can foaming is very labor intensive. You show a good example of how a good job looks. In a cold climate it would take 4 layers of 2 inch rigid foam to make me happy, with each layer can foamed. So I would bring in the urethane foam truck for almost all bays. I know u pointed out the batting moisture problem likely caused from vapor. I think u also mentioned the need to air seal the rim joists. In a multi story house there is a big stack effect with any air path from the basement. The man who built our house urethaned some sill bays, but in some bays he meticulously cut rigid foam blocks. Very neat precise cutting. Must hv had a hot wire. He did not can foam the cuts. During a remodel of ours we found his work. His hand custom cutting with no can foam was a BIG mistake. Terribly drafty. Found dead flys and yellow jacket small nests in locations one would swear a bug couldn’t get to. Harmless enough but the drafty issue I am sure stole much of the R value of his work. Thx for your vid. Good commentary from you.

When I insulate a band joist I start by caulking to stop the air infiltration as much as possible. I caulk the seam where the sill plate sits on the foundation, where the band joist sits on the sill plate, where the floor sits on the band joist, also there the floor joists hit the band joist (the nail holes leak). When you pull the pink insulation out you can see stains in it from all the air leaks. I used mineral wool the last time I did this because if a termite inspection is needed, they can move it out of the way without damage.

My house was done 35 years ago with the fiber glass, I pulled them out and didn't see any problems. I live in Wisconsin, that might make a difference.

You're braver than me. I wouldn't touch fiberglass barehanded if I could help it. Especially if I suspect there's any kind of mold.

Taping around vent box to reduce leaks into the space behind the drywall is a great tip!

I love your adding the comment about removing the glass batt rim insulation and installing the Extruded Polystyrene rigid insulation with the spray foam sealing. To put it mildly, “you have your shit together”. I’m a semi-retired professional roofing and waterproofing consultant with over 40 years of actual field experience.

The contractor used fiberglass in my home's rim joists and I found mildew-ish growths in some, plus the Northeast corner in the master bedroom would form ice on the wall. I tore out all the fiberglass and paid to have proper foam in place. Cost for my 1800 square foot home was $750.

Use Rockwool type bats and cut them to fit very very snug. Do around R25 to R30. You need the joists to breathe a little or trapped moisture will mold the joists. If the exterior is not Tyvek'd or sealed you will always have moist air intrusion.

Fantastic this is exactly the way they did on my new house, bat insulation in my rim joists guess I need to redo it

We have rim joist batts in our 35 year old home and do not have any problems with moisture, mold, or other. The outside of the rim joist and side walls is covered with 1 inch Tuff-R foam, then Tyvek sheeting, then 1/2 inch t-111 siding. Works for us.

If you want to avoid spray foam/foam board, rockwool batts do allow air transfer through the entirety of the batt unlike fiberglass.

I have tried to explain this to people doing bad basement renovations. Run that foam board straight up in to each cavity to the plywood above, and spray foam around. Then you have even vapor transfer along the backside of the foam to the outside. Then your crawlspace or basement will stay fairly warm and dry compared to the outside air temp. In basements, you are essentially building a "bucket" with no leaks that your framing and finishes will sit inside, and you leave the outside area with the concrete and above grade wood to transfer moisture up and out. I recommend DMX 1 step for floor surface prep and then install tongue and groove wood sheathing over that. Then you will be giving yourself a little insurance when you have moisture events in your house.

Good tip, never knew that, will be removing mine!

Spray foam or Styrofoam (blue board) to insulate the rim joist cavities (RJC), not a chance! Maybe you can get away with that Ohio or in the North but that’s a huge mistake in the mid-Atlantic and southern states where a risk of termites exist. Stay away from the blue board, use something of a better quality such as Hunter brand for the walls (it has dual sided fiber reinforced vapor barrier). Take the Hunter board up to within 2” of the top of the block/brick/cast wall and leave the 2” gap for a termite reveal. Next use RockWool insulation for the RJC to limit heat transfer, this allows for easy removal for termite inspection and it doesn’t absorb moisture as fiberglass will. You want to take it to to the next level then insulate the ground 24” horizontally in from the wall around the full exterior perimeter of the wall. Cover the entire ground with a class 1 vapor retarder (20mil) with 6” overlap at the seams and tapped with 4” vapor tape. Install an appropriate sized dehumidifier that will remove around 80-100 pints of moisture per day on a dedicated GFCI outlet. Upgrade your access door to seal tight with weatherstripping and insulated on the inside. Biggest take away for anyone reading this is to limit the use of spray foam in a crawlspace. I’ve seen spray foamed 6x6 beams with 80% rot because of trapped moisture. I’ve seen rim joists and joist tails completely decimated by termites and you could only tell by probing the wood with a wood probe (could actually stick a pencil through the lumber). Save the spray foam for inside the structure. Moisture in the RJC is not from “air transfer” as suggested, it’s a dew point issue. The exterior framing, if constructed properly, should have house warp with taped seams such as Tyvek for a vapor barrier over all exterior sheathing.

When we finished our basement, I used batts in the rim joist, then cut plastic to fit over the batts. Embedded the edge of the plastic in acoustical sealant then even added staples to hold it all in place. About 5 years later we noticed one of the basement rooms was abnormally cool. Started investigating and removed from suspended ceiling tiles in the basement and noticed that the acoustical sealant which was supposed to remain flexible had hardened and let loose in some areas leaving gaps between the plastic and floor joists. Pulled the plastic and batt insulation away to find a 1” thick layer of ice on the rim joist. 😕. Ended up taking the entire ceiling down near the rim joist and pulling plastic and insulating everywhere from the rim joists luckily only found a few more problem spots. Ended up cleaning up what mold had appeared, dried everything out then spray foamed the whole perimeter. Should have just spent the money on spray foam in the first place, way quicker install and complete air tight.

That dampness is shocking! I'll remember this lesson.

Last time we remodeled, I had access to the crawl space and attic rim joists. Use airless to spray paint a good quality exterior paint (with mildewcide) the rim joist cubby hole area, including the end sections of the joists. Took about couple of hours and then went back and give it a second coat (dried pretty fast in the hot summer), sealing the seams and crevices. When the paint's all dried, came back to spray foam the seams and cracks. (spray foam cans) Then cover the entire rim joist area in attic with 6 mil clear plastic as moisture barrier, before sheetrock. The airless spray painting took about a half day; I used the other half day to spray paint the redwood fencing, so only had to clean the airless at the end of the day. For the rim joist paint, used OOPS paint where color doesn't matter; a $300 high quality exterior paint 5 gallons for around $30.

Foam board gets frost/condensation behind it too. Seen it myself on a partially exposed basement in Wisconsin. The wall is better to breath.

Absolutely true. Speaking from personal experience

Cold-climate-liver (love it). Stack effect is real (and powerful). Vapour barrier is difficult to install as a defence at the rim joist (ten tubes of acoustic sealant later). I'm still assessing whether well-installed spray-foam will work better. As the house flexes from warm-humid to cold-dry I'm fairly certain cracks have been opening that I cannot see. Part of the problem is we over-"air condition" in hot weather and over-heat in the cold. We've only had a few decades to see what happens. Also...properly installed exterior insulation if you are doing a new-build (but investigate HVAC air exchange). In most districts these things are code where I live. If I were able to build a new house, I'm interested in insulated concrete forms...but you need a competent contractor. I'd also be happy with a tiny cabin and a wood stove, windows that open in the summer. Where I live it takes a century of shameful neglect before those things decay. I am fond of modern cooking/laundry appliances however..so get your electrical together..

Our house had the fiberglass batt insulation at rim joist in our basement when we moved it. The house is 40 years old. The wood at the rim rotted and we got mice and wasps making nests in that insulation, entering from the rotted outside overhang.

Carpenter ants love rigid foam insulation. Nothing sucks more than hearing chrunching sounds coming from the wall and finding waste piles on the floor of chewed rigid board insulation.

It seemed like to me the way those bats are folded is indeed a problem, but you identified that it being there at all is bad. This is fascinating.

The problem is not with the fiberglass bat, but with improper installation and the lack of vapor barrier. If you're using fiberglass bat it should be cut to fit the space snuggly and a vapor barrier installed and sealed with acoustic sealant. No more air transfer.

I have an older house with a basement that has no sill plate. The wood sits directly on top of the blocks. Three sides are below grade and one is exposed to the elements. How do I insulate for that?

The problem is high RH in an area with leakage, not batt insulation. Batt gets a bad rap because it’s in the right place at the wrong time (when air leaks and temp differentials are greatest. Too much humidity inside will result in condensation anywhere there is air leakage. Windows are no different. The rim leaks air just as any other area of a wood framed home. If you’re going to put any type of insulation in a joist pocket you need to make sure you first seal it so the batts can do their duty via thermal barrier. Batts are not sealers or vapor barriers, and when installed in a spot where it’s surrounding environment has high humidity with leakage, wahla you have condensed.

Good pointing thanks

you need vapor barrier. the wood is the coldest in winter since the outside of the house is way below 55F which is the temperature of the ground inside. the moisture will condense on the cold wood surface. use plastic to block the moisture, then the fiberglass should work well.

Up in Defiance! Toledo, my old neck of the woods.

As far as Air Transfer - I caulk around the ends of joist to where the rim is AND top of mudsill to rim - all around. The Rockwool.

Should mention whether this is an encapsulated crawlspace or a vented one, dirt floor or poured concrete. All factors to consider as moisture control is key in crawlspace. If encapsulated you will need some sort of method to control humidity (dehumidifier) and if it is a dirt floor then want to look at installing (minimum) 6mil VB and running it 6-10" up the wall (on the warm side of the rigid insulation then tuct tape all the seams - that way any moisture that builds behind the rigid foam will stay under the VB.

I did both with mine. Foam board insulation first with an adhesive, then Great Stuff around the perimeter of the foam board, then fiberglass.

Having the crawl conditioned and fully insulated is a best practice

If he caulked each rim joist area then add fiberglass insulation may not have condensation that causes it to stick or turn to meldew.

I did this in my basement about 13 years ago when I moved in my house in 2009. I just went and checked and I’ve got ZERO moisture, mold, or discoloration happening. It’s not a problem for everyone so I’m leaving mine alone.

Roxul is perfect for those rim joists. Fast easy tight and effective.

whats up where the foundation meets the ground ? looked like the plastic is a foot from the blue board...is that finished?

My basement is not finished and never will be, did put rock wool around the rim joists. And it make's a big difference in my heating bill

Don't know if I solved the problem or made it worse as I've since moved from the house, in Ohio but when i moved in there was batted insulation at the rim joists, I removed it and placed each batt into a heavy plastic bag ,sealed it and replaced them. No loose insulation to shed, no dampness in the insulation and cleanly removable for inspection. Never saw (over 15 yrs.) wetness, insects or mold. Perhaps just lucky, perhaps a solution?

I’d like to add, after watching YOUR video and listening to you explain why you do certain things certain ways, I’d let you work on my house anytime!

If moisture developed, and eventually rot, with the fiberglass batt why wouln't it with what is being proposed?

I live in Quebec. It gets very cold. My house has had this type of insulation since 1970. No issues.

After putting the blue board would I then put the rest with insulation. This will be under the house on a pier bean?

Softwood lumber already has molds on them when they come to the lumberyard. Even if you sprayfoam it the moisture is going to activate the biologicals.

I've read just about every comment listed for this video. I've determined that there is NO WAY of learning how to do this correctly by watching these videos. People in the comments have listed about 2 dozen different ways that they think it should be done. You would think mankind would've more fully evolved on this topic by now. It can't possibly be this controversial! Oh well, I'll do it my own way.

VAPOR BARRIER & TUCK TAPE One quick question...is the ground covered with a vapor barrier of some sort? Moisture and Argon gas will build up if the ground is not covered with some sort of vapor barrier. There is a 10 mil. heavy poly that is used under slabs, which can be used for this application. This will help to alleviate any ground moisture problems. Now if each rim joist gap is sealed with vapor barrier and tuck tape, or accoustic caulk / sealant, using fiberglass insulation is just fine. Any moisture within that crawl space will be stopped. But if you constantly have moisture coming up from the soil, the joists could eventually rot too. Vapor sealing the entire crawl space is what needs to happen.

Won't condensation still build up at the median of temperature transfer. Won't there still ne that issue. And if it's sealed onto the joists than how will you inspect it once a year for the same problem. Does it solve that mold issue

air flow is good, that is not your problem. your problem is that you do not have vapor barrier on the inside of your insulation like you do everywhere else in the house, the air moves right through as warm, moist, air and then condensates into actual moisture once it leaves the zone of the heated house inside of the insulation. you should cut a piece of poly for every joist spacing and acoustical seal it into place. I seriously cant believe you are an inspector. Styro is a good idea but I would still do batt insulation first so that the wood can breath instead of placing styro foam directly to the wood, that will lock moisture up against the wood with no way to escape.

Cut/place properly whoever placed those shouldn’t be touching homes

This is exactly what I did when I finished my own basement last year, replaced all the fiberglass batt with glued-in rigidboard and sprayfoam sealer. What a difference it made. Basement is warm and dry, heat bill is way less than what it was. Just wanted to reaffirm what this gent is saying.

Just came across this & really like it. What would be better for this application, open or closed cell spray foam & for regular stud bays?

Do u have a video on fixing the problem

I've just seen 2"x10" or 2"x12" cutoffs plugged into the space. I'd like to see the rim joists a 40 year old house that has been sealed wit foam before I would do that to my house.

Is that a dirt floor?

Its not just the air transfer its the temperature difference causing condensation. Partially conditioned crawlspace with dehumidifier and blueboard, no fiberglass hydroscopic mold grower, use rock wool it breathes and is not hydroscopic and wont grow mold. Radiant barrier helps also. My crawlspace is at 65 degrees and 30 percent humidity. In house its 68 and 37 respectively.

Surely ventilate the crawl space to outside and insulate under the floor, with no ventilation from the house interior to crawl space. That way you will avoid warm moist air coming into contact with the cold rim joist.

I have the pink fiber glass insulation just like this. Better to just remove it and have nothing until I can purchase the hard foam board?

What about using Rockwool insulation there?

what about for brick homes what should i use? rockwool?

Thanks.

I prefer air infiltration a little for my wood coal stove in basement keeps me from drilling holes through wall for added air

Only thing missing was the vapor barrier. Facing the heated side of room? comment please

Glad I saw this before. I need to re-insulate my cantilever floors in my house. I was going to use bat insulation.

Where are the vents under the house to circulate air within the crawl space?

Looks identical to my crawlspace. The guy who built my house extended the floor joists directly out over the rim joist and build a deck on top of those. We had flooding horribly earlier this year so we had to remove the decks to.install proper perimeter drainage. We almost removed the front deck with the Excavator, could you imagine how bad that would have been if so...would have ripped my whole house down.. now I'm trying to square off those floor joists along the front and install a proper ledger, huge gaps and wet insulation was stuffed in between the joists just like in this video. It's been a complete nightmare. I'm about 1/4 of the way done. Perimeter drainage is in, backfilled etc but now it's making everything right. Or as rigjt as I can anyways Some people just shouldn't build houses! Total pain in the a@@!

What about Rockwool?

Putting plastic on the ground helps as well

I presume you haven't yet gotten to the part where a fire barrier must be on top (inside) of the foam blue board and how you do that.

The question is where the damp come from. Is it from the outside or from inside. In general I think it is a problem when the inspector likes or dislikes solutions. They are either accordingly to code, or not.

Would have liked to see what he recommended actually shown.

Good video

Thanks

I too have been building for a while. Never seen mildew or mold cause by air transfer, if everything else is done within tolerances. The foam is great, but it’s highly flammable. Spray foam is even better. It makes a solid flex free glued together building. However, if you need or want to modify things, it’s a nightmare. Very easy to cut romex with any tool. So, R-19 in a 2x6 wall with type X 5/8 drywall, is my choice for applications.

What about in a dry basement environment?

Thats scary to know that can cause that much damage on a new home that fast

Here is short, more drastic video of what can happen to fiberglass batt insulation in crawlspaces: kzfaq.info/get/bejne/fJ-mgZiDx8fXYnU.html

Would Killz and then flex insulation work?

I’m hoping n praying that my place is safe. When constructed sopposedly floor trusses set in an inch n foam placed at the rim perimeter n tyvec over. 🤞🤞

In this instance nothing you have spoken to will eliminate the rim joist being a condensation point and thus in need of a way drying after condensation. I'm not sure I know how to deal with it. Joseph Lstiburek does, though.

Why is the floor not insulated anyway? Especially in an area of the country that has a tendency to get harsh winters.

TY

Very good tip. 👍👍

Looks like a dirt floor in there so it would be important to direct the downspout water over 10 feet from the foundation, make all the difference in how dry your crawl space is.

Interesting. Wouldn't the blue board trap the moisture on the inside of the rim joist even worse though?

I'm a building inspector. I write people up on this all the time: lack of vapour barrier. Best way is to scab foam into the space.

This is a classic vapor barrier scenario, not a fiberglass specific issue. Lower cost solution is to use faced fiberglass cut to size, with the facing stapled and tucked as with any fiberglass install. The facing on fiberglass is generally around 1 perm. EPS offers nothing, you'd have to use XPS specifically (blue board as mentioned, Foamular, etc)

Missed the mark. The major issue is a lack of a vapor barrier. If this crawl space is not heated/conditioned air, then we should be seeing vents in addition to good insulation and vapor barrier. This space has insulation on the foundation, so maybe it is heated. In this case, the vapor barrier belongs on the outside of the rim joist.

I have a three year old house that has black mold because of this exact problem.

Another option if you want the extra insulation is install the rigid foam to the rim joist and spray foam/tuct tape seams then install your bat insulation on top of that.

I removed my insulation and the rim board was covered with ice. Removed it and has been dry ever since.

I'm a professional installer and they don't sit right because they are too big and using a Kraft is better than an unfaced.. smaller squares fit beautifully and the paper on the bat helps tremendously..those "sandwiched" piece's belong as a blocker for a baffle on the roof..

curious to what the impact is on this type of insulation on termite inspections? I encapsulated my crawlspace and have two inch foam boards against the cinder blocks. my termite inspector wants to see more wood to verify no termite infestation. just curious, I've seen other videos advocating spray foam adjacent to the joists.

Makes perfect sense, im about to finish my basement and the builder used bats, ima change that right now, thanks