# Rigid foam rim joist - how does this look?



## cjaustin81 (Sep 4, 2014)

I'm working on insulating my rim joists w XPS foam cut 1/4"-1/2" short around the perimeter and then sealing it w great stuff. Does this look ok or am I using too much great stuff (can version)?

I put a bead on the lower rim section first then I seat the rigid foam, followed by making a picture frame w the great stuff. After a couple minutes of the foam expanding the piece of rigid foam will need to be pushed back against the rim joist. This causes some excess foam. How does this look?


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## Windows on Wash (Aug 30, 2011)

Looks just fine. As long as you're getting an excellent perimeter air seal, a little extra foam is no big deal.

You might find it a tad bit easier to just do it with a good caulking/sealant.


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## cjaustin81 (Sep 4, 2014)

Thanks, I wasn't sure if I should be using less spray foam or not. I tend to be a perfectionist.

It's getting a good seal. After I spray foam the perimeter, the rigid foam will pop out just a touch (after a couple minutes of expansion) and I'll push it back in 2-3 times so that it seals flush with the wood before it dries. 

I get about 5 rim joist pieces per 16oz can. I work on 5 at a time so that I can keep pushing them back and make sure they are nice and snug. When I do this some foam slightly oozes out and that's why I have a touch of excess. 

I'll try and use slightly less.

I plan on using the fireblock version of great stuff for the gas line entry, electrical box area, and around the heat ducts.


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## ProGreen (Oct 2, 2014)

I was wondering how your job went, cjaustin81! Now I know. Looks great. Where are you physically cutting your foam? Is this a full basement (can't recall) so you cut and can reach/step up? What depth XPS foam did you select? TIA.


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## cjaustin81 (Sep 4, 2014)

ProGreen said:


> I was wondering how your job went, cjaustin81! Now I know. Looks great. Where are you physically cutting your foam? Is this a full basement (can't recall) so you cut and can reach/step up? What depth XPS foam did you select? TIA.


Thanks! The job is going alright, I'm a perfectionist so sometimes I get discouraged when it's not perfect. It's good to know it looks decent though. 

As for the foam, I used 2" XPS (Owens Corning) and I ripped them to about 9" (height) using a table saw at my parents. I then used a snap-off blade utility knife (almost fully extended) to trim the sides (width) after I measured the openings of the joist and have been doing that in my basement. I left 1/4"-1/2" around so I had room to spray foam. I use a little 4 step ladder when working in the basement to reach the rim joist. The basement is currently unfinished.

The trick was to only spray foam a can (5 boards) at a time. This allowed me to push them back in place once the foam started to expand. If I had tried to spray foam more than 5 at once it would have been hard to keep pushing them back until the foam sets up.

I have about 45 rim joist boxes left to do (south wall) along with the side walls. The north wall is almost done as seen in the pictures but it's a slow process so I'm working on a little bit each night.

Once all is done I will cover the foam using blocks of Roxul as a fire barrier and added R-value.


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## ProGreen (Oct 2, 2014)

Thanks. Nothing wrong with being a perfectionist: I'm one too. You're doing a great job.


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## SeniorSitizen (Sep 10, 2012)

Nice job but I hope the interior rim surface doesn't ever drop below the 38 or 40 degree range.


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## cjaustin81 (Sep 4, 2014)

SeniorSitizen said:


> Nice job but I hope the interior rim surface doesn't ever drop below the 38 or 40 degree range.


Thanks. Are you referring to the backing of the XPS foam (where it meets the wood)? Why should I be worried about it getting below 38-40?


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## ProGreen (Oct 2, 2014)

cjaustin, do you have sill plates above the concrete foundation all the way around?


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## cjaustin81 (Sep 4, 2014)

ProGreen said:


> cjaustin, do you have sill plates above the concrete foundation all the way around?


I do have wooden sill plates all the way around that sit on top of the concrete slab. I can take a pic when I get home. 

The sill plate is exactly 2" deep (on the side I did) so when I put the XPS foam it filled the gap perfect.

Is this something to be concerned about? the DIY articles showed this sill plate as well. 

My setup looks similar to the picture below.


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## ProGreen (Oct 2, 2014)

As I understand it, as long as your rim joist (now insulated) doesn't sit directly on the concrete you should be good. So if the 2" sill plate has the rim joist directly on top, then there should be no problem. 
Problems can arrive when the rim joist lies directly on the masonry (concrete) itself, due to the hygrothermal behavior of moisture-sensitive wood. I have a crawl space with such a design, and have left it alone. But my other side has sill plates, rim joists and floor joists needing my attention.
Let's see what SeniorCitizen and WOW and other experts have to say. Remember, since it's fresh, no harm done: it can be removed if/where wood sits directly on concrete.


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## ProGreen (Oct 2, 2014)

No, that picture illustrates perfectly how the sill plate sits under the rim joist as well as the floor joist on the sill plate. No wood on concrete (no embedded beam on concrete). You're good as I understand it.


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## SeniorSitizen (Sep 10, 2012)

cjaustin81 said:


> Thanks. Are you referring to the backing of the XPS foam (where it meets the wood)? Why should I be worried about it getting below 38-40?


 I would be concerned about that area reaching dew point temperature since it is now not a part of the basement atmosphere with free air movement.


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## cjaustin81 (Sep 4, 2014)

It was my understanding by sealing it up and preventing air movement from the outside coming in, you prevent condensation from forming. While also insulating.

I had regular batts in before and the basement was very humid, I s tuly did a mold remediation last summer.


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## cjaustin81 (Sep 4, 2014)

I took a couple pics and have some questions.

This is the rim joist on the north wall (one I showed pics of). I noticed the builders put insulation on top of the concrete wall and below the rim sill, then they cemented over it.


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## cjaustin81 (Sep 4, 2014)

This is the south wall, which I haven't started on yet. I was going to do it like the north wall, but I was also going to xps foam the section I show below which is the concrete lip. Is this a good idea to do foam the rim joist and the cement lip?

The second pic shows how I would foam that lip.


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## Yodaman (Mar 9, 2015)

I can not answer the question of whether your rim joist will condensate or not. But for piece of mind take a few of your blocks and seal them with foam backer rod in liu of the greatstuff. Then when the urge strikes you take out the block and see whats going on back there. Looks good from here!


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## cjaustin81 (Sep 4, 2014)

This is what the sides of the basement look like. 

I got the idea of placing XPS at the top of the concrete wall to act as a draftstop from buildingscience.com > http://www.buildingscience.com/documents/information-sheets/basement-insulation/

Instead of just sealing the rim joist you can seal the top of the wall as shown in the blue of this picture:




























This is how I was planning on insulating it, and sealing it w great stuff



















What do you guys think?


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## cjaustin81 (Sep 4, 2014)

As I was looking around I noticed this area on my south wall rim joist. I can actually push up ever so slightly on the wood in the back-right corner










Angle from the ground










I went outside to see if any water could be getting in (directly above that joist) and saw this



















I imagine the outside gap in the corner of the patio caused this. I believe I need a foam backer strip, followed by re-caulking that hole outside. Does that sound right?

Now on to the big question, once I have it sealed up outside do I need to repair any of that wood or does it look ok? Only in that top-right corner there was a tiny crack in the wood which had some minor flex.


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## cjaustin81 (Sep 4, 2014)

pics of my basement


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## HDS (Jun 21, 2014)

You could always caulk the bottom and tops of the rim joists for added air stoppage. 

With as many as you have to do, a great stuff gun would be a good item to have. 

What's above the water damaged floor? Its the wood crumbly? If not, probably fine to leave alone.


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## cjaustin81 (Sep 4, 2014)

HDS said:


> You could always caulk the bottom and tops of the rim joists for added air stoppage.
> 
> With as many as you have to do, a great stuff gun would be a good item to have.
> 
> What's above the water damaged floor? Its the wood crumbly? If not, probably fine to leave alone.


The sliding patio door is above the damaged floor. 









That's the picture above. The wood isn't crumbly but it does have a very slight flex to it where the other wood is hard.

In your picture did you use caulk or foam? And was it from the gun?


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## Yodaman (Mar 9, 2015)

cj - I don't see anything from here that would make me want to tear out the rim joist. I would seal the hole from the out side with 100% silicone immediately. Watch the spot from the inside to make sure it dries. Do not cover it with the foam board until it is thoroughly dry.

The silicone is still only an temp fix. It will break apart next winter with the frost heave. 

A permanent fix should involve cutting the siding back away from the concrete. Flashing behind the step and under the siding.


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## cjaustin81 (Sep 4, 2014)

Yodaman said:


> cj - I don't see anything from here that would make me want to tear out the rim joist. I would seal the hole from the out side with 100% silicone immediately. Watch the spot from the inside to make sure it dries. Do not cover it with the foam board until it is thoroughly dry.
> 
> The silicone is still only an temp fix. It will break apart next winter with the frost heave.
> _*
> A permanent fix should involve cutting the siding back away from the concrete. Flashing behind the step and under the siding.*_


Thanks for the info. I'm actually just about to have my siding done in the next couple of weeks. Should I have the siding company put flashing all in that spot? 

I also have a wooden strip that's caulked right under the sliding door (on the concrete). I wonder if that could be causing it.

Any way to do a leak test?


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## cjaustin81 (Sep 4, 2014)

Should I put up flashing like this?










And along the sides of the steps as well. I found an article that talks about this issue > http://seattleareahomeinspector.com...lders-do-it-this-way---but-it-is-still-wrong-

Another article I found shows to put the flashing along the wood, in my case this would be the wood behind the back of the patio steps. I'm not sure if I will have access behind there. 










http://kwlandscaping.com/blog/build...-need-flashing-when-building-a-deck-or-patio/


I want to fix this since I'm having siding done in a couple weeks and I will have access behind there. What approach looks best?


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## Yodaman (Mar 9, 2015)

cjaustin81 said:


> Should I put up flashing like this?
> 
> 
> 
> ...



The flash system in the top photo only works when the steps are attached to the house. Yours are are not and most likely float up and down with the ground freeze each year. This system would likely fail for you.

The lower design is more appropriate for you. Creating a complete water plane from the siding down below the rim joists. With this system any water that ran between the step and the house would still stay out of house.

Since you are residing, if you want new steps too, now would be a good time. Your current steps are too close to the house. New steps could be installed after the new siding is in place far enough away that no 
additional flashing is needed. The siding just runs like normal right behind the steps.


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## cjaustin81 (Sep 4, 2014)

Yodaman said:


> The flash system in the top photo only works when the steps are attached to the house. Yours are are not and most likely float up and down with the ground freeze each year. This system would likely fail for you.
> 
> _*The lower design is more appropriate for you. Creating a complete water plane from the siding down below the rim joists. With this system any water that ran between the step and the house would still stay out of house.*_
> 
> ...


To do the lower design, I need to make sure I have enough space where the patio meets the house to attach a piece of flashing to the house. Do you think I will have enough room without destroying the concrete steps?

I'm doing the siding, roof, and gutters now so I don't think I will have anymore money to remove the steps. I would like to avoid that for the time being if possible but I do need to get this issue fixed. The step is at the height of the sliding door, how would you be able to move the steps farther away from the house? (don't you need it to be right next to the door)


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## Gary in WA (Mar 11, 2009)

IMO, just lay a saw on its side (guide-edge on filler material) to cut the existing siding, slipping some metal flashing behind the WRB, to gain the code-required 2" clearance to walkway concrete; http://publicecodes.cyberregs.com/icod/irc/2009/icod_irc_2009_3_sec017.htm?bu2=undefined

Check with local AHJ. 

Definitely air seal the wood joist before the foam board-* post #8; *http://www.diychatroom.com/f103/insulating-rim-joist-caulk-spray-foam-around-edges-168849/

Use "gap-n-hole" canned foam as it is closed-cell------- not open-cell; as is "window/door" foam. Use foil-faced foam board to stop any interior-air supplied condensation on the rim joist, last para.; http://www.buildingfoundation.umn.edu/RimJoist/rimjoistphenom.htm

You won't have condensation there if foam is thick enough for location., but it also depends on how much interior insulation you add in front of the board to reduce its warming potential;


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## Gary in WA (Mar 11, 2009)

"I would be concerned about that area reaching dew point temperature since it is now not a part of the basement atmosphere with free air movement."------ The wood rim doesn't rely on the interior air to warm it as the foam is covering it and is now the (new) "condensing surface of interest";http://www.buildingscience.com/documents/insights/bsi-049-confusion-about-diffusion

Forgot to include my last link above showing how adding fibrous (rock wool) will lower the condensation temperature at the foamboard,* Fig. 4; *http://www.buildingscience.com/docu...ld-weather-condensation-using-insulation/view

How much cavity fill were you planning on?

Gary


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## cjaustin81 (Sep 4, 2014)

Gary in WA said:


> IMO, just lay a saw on its side (guide-edge on filler material) to cut the existing siding, slipping some metal flashing behind the WRB, to gain the code-required 2" clearance to walkway concrete; http://publicecodes.cyberregs.com/icod/irc/2009/icod_irc_2009_3_sec017.htm?bu2=undefined
> 
> Check with local AHJ.
> 
> ...


I didn't caulk before I put the foam up, I just used Great Stuff Gap-N-Hole to seal the perimeter and make it air tight. Any hole were filled with Great Stuff and then shaved off with a knife before adding more foam. 

I was going to use a latex with silicone caulk before I put the foam up but was concerned with mold that would form on the caulk eventually. I have a lot left to do so I could still caulk it. Any specific type of caulk you recommend? 

I used 2" un-foil faced XPS foam, which provides a vapor barrier. I plan on adding a good thickness of Roxul wool in front as well.


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## cjaustin81 (Sep 4, 2014)

Gary, any tricks to get less foam when using great stuff around the perimeter? Do you just use a very small amount? 

It seems to ooze out when I push the foam back in place when it expands.

Is it better to add more or less roxul in front of the foam? I was planning on using it to act as a fire barrier. And also added R value.


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## Yodaman (Mar 9, 2015)

hold the foam in place with a couple cap nails or screws, or adhesive and spray after it drys


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## cjaustin81 (Sep 4, 2014)

Gary in WA said:


> "I would be concerned about that area reaching dew point temperature since it is now not a part of the basement atmosphere with free air movement."------ The wood rim doesn't rely on the interior air to warm it as the foam is covering it and is now the (new) "condensing surface of interest";http://www.buildingscience.com/documents/insights/bsi-049-confusion-about-diffusion
> 
> Forgot to include my last link above showing how adding fibrous (rock wool) will lower the condensation temperature at the foamboard,* Fig. 4; *http://www.buildingscience.com/docu...ld-weather-condensation-using-insulation/view
> 
> ...


Gary, I looked at the link you provided and excuse me if I'm not understanding this correctly but it showed a 'hybrid' insulation approach in figure 4 that looks like they were referring to exterior insulation being used in combination with interior insulation. Isn't my application all interior?

The Roxul I bought is 3.5" thick comfortbatt, which has the 15-minute fire barrier rating. I was planning on cutting that the size of the rim and friction fitting it in front of the XPS. 

I was a bit confused as to how adding more insulation would create more condensation (by lowering the dew point). Could you explain that?


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## cjaustin81 (Sep 4, 2014)

After doing some reading here's the reality of the situation:

1) XPS foam without foil facing is vapor semi-permeable & so is the Roxul. So any condensation or water could in theory be removed through evaporation where fiberglass batts will just let the water sit. 

2) Code required in my zone for basements is 15/19, in my case I'm using the 2nd number for the cavity. This means I have to add more R-value any way you slice it since I only have R10 with the XPS. 

3) Code also requires a fire barrier.

With these 3 things being said I have to increase my R-value anyways and add a fire barrier. It would appear to me that Roxul in 3.5" would fit the bill and it's vapor permeable as well. 

The only part that confuses me is why would the Roxul lower the warming potential of the XPS foam if I were to put Roxul in front of it? Is it because the foam won't full absorb the room temperature of the basement having the Roxul in front?


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## Gary in WA (Mar 11, 2009)

Read the two last paragraphs below Fig.4. The added insulation (going from a 3-1/2" insulation to 5-1/2" insulation) lowered the example dew point 5*F- in FIG.4.

To arrive at the dew-point of the insulation board (not the rim-it is not the first condensing surface anymore), you need to deduct the R-value of any insulation in front of it. 

Look at Fig.2 in that link, for Chicago even... pretend you don,t have any sheathing and the inside face of the foamboard is the condensing surface now. See the dew-point graph.... see Fig. 4- study it and search the insulation R-values -at bottom of drawings) in both pictures---- R-12 in the 3-1/2" wall, R-19 for the 2x6 wall--- added only R-7 which drops the DP temp by about 7*F because the warm room air cannot warm the foam because of the added fibrous (Roxul) in front of it. ONLY 2" dropped it 7*F------ so don't add more than 3-1/2" of Roxul in front of the foam. Yes, cover with drywall for an ignition barrier, or whatever local AHJ requires. "Is it because the foam won't full absorb the room temperature of the basement having the Roxul in front? "-------- yes.

Depends on local Inspector if the rim area is your floor (R-30 required), your basement wall (R-10/13 required) or (in fact) your above-grade house wood-frame wall (R-20 required); http://energycode.pnl.gov/EnergyCodeReqs/index.jsp?state=Illinois You meet the two, add more foamboard rather than more fibrous Roxul; lowering the DP--- if they call it a "floor". I need to update insulation values I sited, sorry.

Gary
PS. look at post #18- see the rim, see the two red dots at the foam/rim interface and one red dot at bottom of interface- that is your air/vapor barrier bead of adhesive/caulk/sealant to stop outside air from condensing on backside of rim joist under the foam.


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## cjaustin81 (Sep 4, 2014)

Gary, The part I'm struggling with in your example is that the examples are referring to EXTERIOR (R-10) insulation in combination with INTERIOR (R-12 and R-19) insulation being used.

My application is 2 types of INTERIOR insulation, therefore those calculations he's using don't apply in my situation (for example > *Table 1:* Ratio of exterior-interior insulation to control air leakage condensation)

I can however see that placing insulation in front of insulation could drop the dew points just slightly.

I reason I want to add 3.5" R-15 Roxul is to act as a firebarrier and because in the 2012 IECC climate 5 indicates you need a minimum of R-19 (cavity filled). I could put up two layers of the R-10 but then I wouldn't have a fire barrier. I'm avoiding putting up drywall just in front of the rim joists because that will eventually get taken down when I redo the basement.


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## Gary in WA (Mar 11, 2009)

cjaustin81 said:


> Gary, The part I'm struggling with in your example is that the examples are referring to EXTERIOR (R-10) insulation in combination with INTERIOR (R-12 and R-19) insulation being used.--------------The cold side of the foam is same in both cases. The dew-point is at the ply rather than your cavity insulation; same because both have a foamboard, both have cavity insulation on warm side in front of it. IGNORE exterior/interior, they are the same except ply is around R-1.
> 
> My application is 2 types of INTERIOR insulation, therefore those calculations he's using don't apply in my situation (for example > *Table 1:* Ratio of exterior-interior insulation to control air leakage condensation)----------- same table pertains.
> 
> ...


------------------ verify with Inspector the insulation R-value required. My point was; you will meet code for a wood wall (above grade), a basement, but not a floor. Depends on which energy rating local Inspector requires.

Gary


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