# Rim joist insulation



## NE78FJ40 (Feb 7, 2010)

My house is 6 years old and located in Nebraska. In the basement, in the rim joist area, the builder installed batt insulation with the faced side toward the outside or against the wood. I was going to install some more insulation in the area but this is what I found. I remove some pieces that the builder had installed and found the wood and the vapor barrier was damp on the lower horizontal and outer vertical surfaces. What can I use to insulate this area to avoid moisture showing up again? XPS? If XPS then where should it be installed? The pictures I have attached show the area I'm dealing with. The pictures with the insulation installed is how the builder put it in.

Thanks, Mark


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## Bob Mariani (Dec 1, 2008)

batt insulation is this area is incorrect. Best to use spray foam. It will create a complete air barrier while still allowing moisture to travel freely in both directions as needed. Rigid foam is another acceptable approach but must be done very tightly with all seams sealed with spray foam. remove the old batt insulation first.


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## Chemist1961 (Dec 13, 2008)

*Rim Joist*

Bob, Not to question your wisdom, or hijack the post but I was of the impression (2lb) spray foam creates an air tight vapor barrier, until I read your comments about moisture traveling both directions.
I am in a zone colder or as cold as Mark and debating about spray foam, versus rigid HD foam on my inside basement walls and some rim joist around my slab porch with cold room below. Can you proivide more details on foam?


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## ccarlisle (Jul 2, 2008)

There are 2 types of foam, one with almost perfect sealing ability and one with less...open versus closed cell foam. Also one expands alot more than the other.


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## Chemist1961 (Dec 13, 2008)

Morning CC , Yes 2lb as referenced versus 1/2 lb. Thats what I 'm trying to get Bob to expand on...pardon the pun


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## ccarlisle (Jul 2, 2008)

hey chemist!....are you in fact a 'chemist'? Love the stuff.


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## ferris13 (Sep 25, 2009)

> In the basement, in the rim joist area, the builder installed batt insulation with the faced side toward the outside or against the wood.
> 
> Thanks, Mark


Paper/vapor barrier should have been on the warm side. It was installed incorrectly which caused the moisture.Alos in your first pic. The batt insulation is laying horizontal and should have been vertical. In any case, closed cell spray foam is best. I am also about to do this in my home. I think I am going use the 2" extruded polystyrene, caulk and spray foam to seal gaps.


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## NE78FJ40 (Feb 7, 2010)

When you say "spray foam" are you talking about the kind of spray foam you spray in and it expands to competely fill in the area? Is this something I could buy at a home improvement center? If so, what do I need to ask for?

If I go the rigid board way, once I place the rigid against the outer surfaces on the inside of the rim joist, do I still need to install batt insulation to fill the rest of the area? Some of my rim joist areas are about 2 feet deep. Do I put the rigid board on the outer vertical and lower horizontal areas? Like creating an L shape inside the area.


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## Chemist1961 (Dec 13, 2008)

Mark,
Smoke from foam can be toxic so our codes here require that it be covered with fire proofing such as drywall. I insulated the rim to R33.
In my case I sealed the sole plate top and bottom at concrete then the rim joist, each joist bay top bottom and sides and came out 8" from the wall with a foam gun with needle tip, the around all windows, then tucked R33 batts into the bays, rather than fully foam. 
Cost for 1000 square ft basement, approx 160 ft of rim was about $130 in R22 batts plus a couple of cartridges for my foam gun. My energy auditor rated my sealing work as superior to ANY of 300+ homes he has tested, foam sprayed or otherwise and he was blown away by the air loss blower door test results. My change in air loss was substantial after doing the rim and under my baseboards that I have surpassed new building code He said if I continue I may need to consider an HRV...0ver 50 % reduction in air change.. House is far less drafty, 35 years old
I have yet to do any exterior work or insulate the basement walls.

However, I chose to increase by R22 in addition to my old batts properly cut ant tucked because I have aluminium wiring and want to have future access. 

I am still interested in Bob`s experience and comments about foam in all areas , rim joist or other. Bob is a pro and he uses this stuff...

CC, I`m not a Chemist just my nickname, I use a lot of homeopathics and herbal remedies and recommend them to friends so I got tagged with a nickname...


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## mferguson0414 (Jan 6, 2009)

chemist- is there any way you can provide pictures of what your process was? I cannot mentally see what coming out 8" did for your joist area. I am a visual type of guy, pictures would be greatly appreciated.


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## joncampbell (Feb 7, 2010)

*rim joist is difficult problem*

I haven't seen a good solution published yet for this problem, I'm attempting to find one for my own basement, and will share when I do.

The problem is this: if you seal it (from water vapor going through, that is), you run the risk of water collecting on one side or the other, and the growth of mold growing on wood, dirt, etc.

Vapor barriers in basements in general are very dangerous mold problems.

My first cut is to use Tyvek to seal against air intrusion, then EPS. Once you've stopped air, the seal around the EPS doesn't need to be perfect. The Tyvek will allow the end of the bays (rim joist) to breath water vapor in either direction.

Jonathan


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## Bob Mariani (Dec 1, 2008)

Chemist1961 said:


> Bob, Not to question your wisdom, or hijack the post but I was of the impression (2lb) spray foam creates an air tight vapor barrier, until I read your comments about moisture traveling both directions.
> I am in a zone colder or as cold as Mark and debating about spray foam, versus rigid HD foam on my inside basement walls and some rim joist around my slab porch with cold room below. Can you provide more details on foam?


moisture travels in many ways not only with air movement. We need to control air and moisture in different ways. A basement wall needs to dry to the inside below grade and to the outside above grade. The rigid foam still allows moisture to escape from the moisture in the concrete or block foundation into the void between the insulation and the wall.

The foam board is used warm the exterior wall enough to prevent condensation. The perm value is not 0 and as such does not prevent water moving by diffusion but does stop water movement by capillary action. This is why it is needed below the sill plate also.


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## Bob Mariani (Dec 1, 2008)

joncampbell said:


> I haven't seen a good solution published yet for this problem, I'm attempting to find one for my own basement, and will share when I do.
> 
> The problem is this: if you seal it (from water vapor going through, that is), you run the risk of water collecting on one side or the other, and the growth of mold growing on wood, dirt, etc.
> 
> ...


there is no need for tyvek on the basement wall. No air movement to block. But you are not blocking moisture traveling through the wall cavity to escape to the exterior. Then the water will condense on a cold wall. this is why you need at least 2" foam on the wall in colder climates.


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## mferguson0414 (Jan 6, 2009)

Does a can of Great Stuff have enough pressure to "spray" out if somehow a smaller tip were placed onto the nozzle? I have been looking into the spray foam, found 100bf on ebay for a decent price but even that decent price is a whole lot more than some rigid foam and some caulk. There are a couple joist that at a later time I would love to access to be able to replace/run new wire and the spray foam might make that a problem. Well I'm starting to ramble..sorry.


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## Bob Mariani (Dec 1, 2008)

another way to approach this is the "hybrid" method. Use a can of spray foam (hilti no great stuff) to seal all edges along the outside and top. Then use Roxul insulation batts. This is not effected by moisture.


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## mferguson0414 (Jan 6, 2009)

Where do you get Roxul insulation in the states? What is the price of Hilti, and why do you recommend that product?


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## mferguson0414 (Jan 6, 2009)

I found a local provider of Roxul, very close actually. I cannot find online pricing as of now. I think I will start doing my basement ceiling with this product because it looks like I will be able to take it down if need be for wiring or other future problems. I just want to keep all the heat I can on the first floor. Right now with insulating my ducting in the basement, I would say that the basement is probably low-mid 50's in temp and the first floor is 65.


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## joncampbell (Feb 7, 2010)

*I didn't mean Tyvek on basement wall...*

I'm going to use Tyvek on the joist ends just above the foundation wall, at the house sill, areas typically not sealed very well. In my home, you can feel the air moving through them.

Yes, there is a big problem with cold basement walls in summer and winter. But concrete in general can also transmit water in both directions, so using a vapor seal is not a good idea. Nor is most wallboard or fiberglass insulation. But that is another story...

Jonathan


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## NE78FJ40 (Feb 7, 2010)

I've decided to use 2" extruded polystyrene. Does anyone know of a brand and/or type of caulk to use when you seal the gaps. The people at the home centers didn't know what would work with the extruded polystyrene.


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## Wildie (Jul 23, 2008)

mferguson0414 said:


> I found a local provider of Roxul, very close actually. I cannot find online pricing as of now. I think I will start doing my basement ceiling with this product because it looks like I will be able to take it down if need be for wiring or other future problems. I just want to keep all the heat I can on the first floor. Right now with insulating my ducting in the basement, I would say that the basement is probably low-mid 50's in temp and the first floor is 65.


 I've been using Roxul for years, with good result! it doesn't 'wick' like fibre glass!
If you float a chunk in a bucket of water, it floats for a long time, whereas fibre glass will sink over-night!
It also forms a fire barrier. For this reason, I insulated my entire attached garage with it.


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## VelvetFoot (Mar 9, 2009)

I don't know whether or not it was the right thing to do, but I put in multiple layers of 2" XPS with silicon latex caulk. It got pretty tedious at times:


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## Gary in WA (Mar 11, 2009)

Nice work! Just as pretty as the picture: http://www.rd.com/57548/article57548.html

Figure #2: http://www.buildingscience.com/documents/information-sheets/5-thermal-control/basement-insulation

Don't use EPS, it will hold the water.

Be safe, Gary


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## VelvetFoot (Mar 9, 2009)

They weren't all that hard:


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## NE78FJ40 (Feb 7, 2010)

Just to make sure I understand the abbreviations. 

What does EPS and XPS stand for?


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## gma2rjc (Nov 21, 2008)

Velvetfoot, are you going to put anything in the space under the joist and between the two pieces of EPS to seal it off ?


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## Chemist1961 (Dec 13, 2008)

VF has pretty much done what I did directly to my rim joist but I also came out about 8 inches from the wall on the underside of the floorboards and even at the contact point where the joist hangs on the sill . I did the entire sill plate at the concrete and windows as Bob mentions. In addition I knotched my R22 Roxul to overlap the sill plate until I determine what I waill use to finish my walls.
Then I added R22 Roxul and topped it off with the original R10 pink.
The advantage for me was future access to my aluminium wiring.
EPS and XPS are brands names for different types of foam board. There is both open breathable and closed cell-airtight which is why I am after more info from Bob.
ANY foam has the potential for Toxic fumes in a fire and our code requires it to be covered with a fire resistant board such as drywall. 
I am still debating between options for the wall given our HUGE swing in temperatures and high humidity here between the Great Lakes.

Photos at:http://picasaweb.google.com/mopcop/Desktop#


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## Chemist1961 (Dec 13, 2008)

*Roxul*

Roxul is a Canadian product :thumbup:and can be found at some US home building centers in major centers near the border. As Wildie noted , it has been around for years, nice to work with if you go that route...not itchy, doesn't sag or wick, cuts clean and staright with a bread knife or serrated rock wool cutter,


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## gma2rjc (Nov 21, 2008)

Chemist, you said Roxul doesn't sag. So when I put it up in the ceiling of my mom's basement, I won't need to put straps underneath it to hold it in? It's an old, damp farmhouse basement and will never be drywalled.

Thanks for all the useful information you've given about Roxul! It sure is helpful.

Barb


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## Bob Mariani (Dec 1, 2008)

With overhead installation I would recommend using the spring insulation rods to prevent gravity eventually taking over. Roxul does not sag is often referring to in wall cavity settling that is an issue with other types of batt insulation.


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## gma2rjc (Nov 21, 2008)

Thank you.

Barb


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## VelvetFoot (Mar 9, 2009)

Yes, I filled that gap. Sometimes with caulked in foam and sometimes with canned foam. That can foam is messy.


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## Chemist1961 (Dec 13, 2008)

*Messy Foam*

I lucked out on a NEW foam cartridge gun at the Habitat Re-Store for $20 and a case of foam later on for $5 a cartridge. Having a dial control on the cartridge gun makes this job a snap and if you use it much it 's a quick payback for the foam you save, you never have a dried up half can to throw out...there are also extension guns with long barrels and disposable extension straw tips .
If you have just a bit to foam, latex is much nicer to clean up after, especially for under your baseboards with carpet rolled back, just in case you get a drip of foam.
Bob what are your thoughts on open cell foam or closed on the wall as a thermal break with or without an air gap and then a layer of R 13 Roxul between studs?


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## gma2rjc (Nov 21, 2008)

> That can foam is messy.


Thanks. Yes, it's very messy stuff, but well worth the trouble.


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## VelvetFoot (Mar 9, 2009)

I don't think I said it earlier, but if I had it to do over again I'd hire a foam guy.


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## Chemist1961 (Dec 13, 2008)

For the most part mine was a breeze and revealed a few issues behind ducting that a foam guy might have sprayed over. I think its good to know your house especially with my wiring, regradless of who does the final work, but thats why we're all here


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## Bob Mariani (Dec 1, 2008)

Open cell allows enough air flow to not need a space. But closed cell has more R-Value/inch and is better for use in the basement walls. I use open cell for cathedral ceilings where getting sufficient venting is tougher to do. To use the hybrid method (foam edges and batt or rigid) use the closed cell type. When using either type of spray foam the space is not needed.


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## mferguson0414 (Jan 6, 2009)

I understand what you were talking about now Chemist when you said you came out about 8" from the rim. Thank you for the pictures!!


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## NE78FJ40 (Feb 7, 2010)

Is Great Stuff expanding foam compatible with XPS?


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## Bob Mariani (Dec 1, 2008)

yes it is. For rim joists use expanding foam, not the non-expanding or low expanding types which are used for windows and doors. The high expansion is good to get all the nooks and crannies filled.


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## HeloOne (Feb 25, 2010)

HeloOne said:


> Thanks, Bob, for the reply.
> 
> Since i won't be using duct tape to hold these drywall boxes together, what kind of tape is recommended to keep them sturdy and square?
> 
> -HeloOne



Bob, 

Any thoughts on what I could use to keep the drywall boxes together?

Thanks!


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