I'd get that fg out of the sill area. It will inevitably become moist and cause a problem. Replace it with spf, xps or eps.

Are you thinking it will become moist because of the framing I am doing? So far its been there 20 years and I do not think its been moist? I also thought XPS really should not go there since there is no simple way to encapsulate it? (fire saftey code etc)

Worthy,

...had a few people look at the pics....they think there is not fireblock code for basements inPA and sealing off this area could be bad for a few reasons including if I ever needed to fish a wire or cable AND there should be some breathing room. They reccomended to move the wall out to the edge of the joist. This would leave about an inch of space for everything to breath, fish a wire etc.

What does building science say about having 1.5" of XPS then a 1" space then my wall with kraft backed (all I found so far--unless I pull thepaper off) insulation. I do not believe the space is necesary by any means but I can it hurt anything...ie downsides to this...your opinion please...

The fg is dry because it's open to the basement and can dry in during summer and out during the winter. Once you seal it behind drywall, conditions will change.

The rims are a very leaky place and the fiberglass doesn't do anything to seal the space from exterior airflow. Once separated from the rest of the basement, it will be an attractive environment for mould growth--condensation in the winter and dampness in the summer from both water vapour and minor water leakage. (So much so that at least one insurance company reportedly won't cover builders from damage claims if they use fg on the sills.) As you can see from this thread at JLC, detail-minded builders favour other methods. Infill builders in my area generally spray the rims. But you can also use foam board and sealant, as illustrated in the link below. For the fireblocking issue, you can put fireblocking in front of each board or use foil faced boards. (In my jurisdiction, the inspector only needed to be assured that the basement ceiling is drywalled.)

The fg is up to Code generally, so you're probably not required to do anything.

Here is a link that might be useful: How to Insulate Rim Joists

Pennsylvania has adopted the International Building Code. The International Building Code has fireblocking requirements. (Activate "See Here" link) Ergo fireblocking is required. Your municipality may interpret it differently than others, so it's best to consult with them if this is being inspected.

The space between the drywall and the XPS doesn't cause any problems, though in your climate R 7.5 is way below the recommended R value of the US Department of Energy.

Thanks worthy. FYI on the wall I will have the R7.5 plus the R13 fg I am stapling between the studs in the wall to be built an inch from the XPS.

Re: Joists. I read the links. Very interesting indeed. If I were building a new home I would want the foam sprayed in. That is simply not cost effective for me on my 20 year old home.

Cutting all those pieces of XPS and then drywalling in front would apear to be a real PITA. What holds the XPS in place? What holds the drywall to the XPS. Also, in my case it hard to even get in there, much les get the pieces in place and somehow seal it up for a nice tight fit. Likely, it would end up only marginally better when done and would only have an R Value of 7.5 unless you thru more fg in front of it....again, if affordable, sprayed foam would be the way to go.

Also, re that Thermax foild backed stuff, I thought somewhere on Building Science I saw stuff against foil against concrete..I would think the same applied to foil against wood?

I think, in my case, the best I can do is pull the fg out and caulk everything as best as possible, again it will not be perfect because I can bearly get in there; much less see; and put the unfaced fg back. Not the BEST nor most modern solution but one that should leave me better than what I had and likely not violate any codes.

Not capping the 1.5" of xps may violate some fireblock code but doing so seals the area which I think we determined was a bad move...the lesser of 2 evils is to leave it uncapped. I am unsure framing needs inspected in PA. I do not plan on looking for trouble either. My intent has been to be safe as possible and it sounds like having the breathing room for the fg is far more a safety issue than a 2 X 4 cap over the XPS.

My hope is that 1 inch of space will be enough to allow the fg up there to breath and not start to mold. Do you think it will be?

When there is an air space between the XPS and the fg, you can't add the two together to come up with a nominal R value. Just fill it all with fg.

Where the joists run parallel to the wall, there's nothing effective but foam. Where you have access, friction fitting foam board, followed by expanding foam or caulking works fine. The fire blocking drywall on top is only if it is required in that manner by your municipality. Foil-covered foam board, intead, is usually acceptable.

Thermax is used against concrete in at least one of the Building America model structures--Suwannee River Administration Building; and it is mentioned in other Building Science prepared factsheets, so I'm not sure where you saw a negative reference.

The fg likely meets Code, but if it were my house I'd take it out. It's not sealing air leaks, its insulation value is close to nil and damp, it provides a home for mould. The mold feeds on the things in the fiberglass.

I'm not totally positive, but 1" might not be enough to ensure that condensation does not occur in a cold climate. You might need 2" up against the rim joist if it's cold enough. That's just what I think I remember I've read. :)

I did notice that there was frost on the exposed concrete as well when I took out the fiberglass. I have no idea if this is a factor.

Building Science Research Report-0202 "Basement Insulation Systems" evaluates different basement insulation systems in a climate similar to Minnesota. At page 8, it concludes, in part, that 3.5" of XPS performs best. "However, walls with 0.75 inches of extruded polystyrene and 3.5 inches of fiberglass batt insulation in the cavity would perform well as long as interior humidity was controlled below 50 percent during the summer."

Incidentally, with regard to rim joists, Building Science's "Designs that Work in a Cold Climate: Chicago Profile", says:

# Rim joist insulation - Fiberglass cavity insulation at the rim joist is only acceptable if the exterior sheathing is cavity-warming rigid foam insulation that extends down over the entire rim joist. If non-insulating exterior sheathing is used at the rim joist then one of the following insulation details must be used at the rim joist to manage condensation potential:

* Spray foam insulation in the rim joist cavity
* Fully air-sealed rigid insulation
* Inset rim joist with rigid insulation between the exterior sheathing and the rim joist

I wonder how much an inch will deminsih it? I want to leave a gap at the top to let the fg in the joist breath. Imagine pic #2 with a 2 X 4 but now about an inch from the XPS creating breathing space for the fg. I thought the 1" vertical gap, ALL THE WAY down the wall would help. Again, its beyond my ability / cost to foam the sill area...best I can do is caulk it up as best I can and put back fg. I see no other options...now you got me worried using the kraft backed stuff...I realize it adds nothing to the eqaution when the framing is butted up against the XPS...hopfully it is not hurting anything with an inch of space...I could pull the paper off or slit it....

One thought, I can goop up the seams and somewhat effectively seal the sill area (almost working blindly, and sticking a mirror up there). Can I then put the fg back. man if I leave a space it should be able to breath. Its winter now and I have yet to come across any 'wet' areas or spots....hope sealing does not make things worse...

Why couldn't you put a pipe say 3/4" should be plenty or 2 pipes either rigid or that blue plastic flex in that area and put a piece of twine in it. If you ever want or need to add a circuit or wires for anything else you can pop open a place in that corner and add a T or just run your cable from there. You are really not that worried about the conduit aspect as having a cavity to run wires/cables so in this case I would try to use pipe with a smooth interior CPVC for example rather than the blue flex if possible.

You guys really motivate me.

I went down and finished caulking everything and then I saw all the 2' cutoffs of XPS I had kept over in the corner so I grabbed one, cut it down and tried to get it up in there. It went in but not willingly! I have not caulked it in place yet. It was a pain but on the the other hand, I'd only have 5 more to do but that task is daunting....

I have two choices before framing:

1) If I can get this XPS vertically in place for the 12' joist area span(not horizontally on the underside of the floor just on the side wall!), if I caulk it in place, if I put my my fg back up against the floor and then back against the XPS - covering it AND if I build my wall out and inch or so and push my R13 insulation in the wall cavity back up against the XPS so I don't loose any of its value.....Have I created a mold safe environment up there? Remember the joist area is sealed off sans the inch of space I left...but which is filled with R13...the nice thing is I could pop my ceiling tile (once up), push down the wall's R13 bat and fish a wire thru if I needed. Again, am I mold safe? Oy yeah, does the underside of the floor above act as a fireblock for the top of the XPS in this area?

Or I could....
2) Just put the fg back in there now that I caulked it up, build my wall out an inch, R13 against the XPS in the wall cavity only up as high as the dropped ceiling will be. Now I have an inch of space to allow fishing a wire to the cavity and more importantly allowing the cavity to BREATH above the dropped ceiling...WILL THAT BE ENOUGH BREATHING SPACE TO PREVENT MOLD. This obviusly is the FAR EASIER solution, allbeit not most effecteive for heat loss / gain but no worse than where I saterted. If I am mold safe I'd like to go this way.

Wheeew, So time to end this thread, Which do I go with?

Fiberglass is not living. It doesn't need to breathe! To add to the R value of the wall though, it has to be tight to, in this case, the XPS.

Seal up the sill space as best you can and leave the fg out. The reason you haven't seen water is that with the space open, the area dries by evaporation to the interior in summer, to the exterior in winter. If you want to still stuff some insulation up there, use either XPS or EPS and you throw some tape over the seams. It doesn't have to be pretty. Just sealed.

does the underside of the floor above act as a fireblock for the top of the XPS in this area? I'd contend that it does.

Good idea on the conduit! (Though it would be easier to just figure out what you need and do it before you board.)

I meant if the space could 'breath' nothing would condense in the fg...it would be much the same as it had been for 20 years...no mold.

If I put the XPS in there why not shove the fg back in against it for added r value. I'd also think you'd want the bat against the underside of the floor too! It should be mold safe once the XPS is in place on the ouside of the sill....isn't that the purpose of the XPS...keep moisture out.

To me no fg at all means lower Rvalue. XPS means less mositure infiltration. A combo sounds best, no?

I think you are trying to tell me to double up the XPS, forgo the fg and let the area be sealed up....Oh sure now I need to cut and wedge another 6 of these. (ha ha ha!)

Worthy,

I have also been contemplating what to do in the rim joist area, currently it is stuffed with fg (and spiders and ....). I have a bunch of EPS foam from the previous basement finish that I could re-use. What R value is recommended it that area? I couldn't find this specific information on the DOE site you referenced. I have the thickness of a 2x4 on one wall so with EPS I could achieve ~R13.
I also found that dover projects link very interesting. I looked at HD yesterday but could not find the DOW Thermax Heavy Duty, only TUFF-R. Know who sells that stuff? I would prefer to use that if I can find it since it is rated for exposed installation (no thermal barrier). Or a combination of the the EPS and Thermax (since I have the EPS) to fill up the 3.5 inch space.

-Tom

If I put the XPS in there why not shove the fg back in against it for added r value.

Sorry, maybe I got mixed up in your details.

As long as the rims are sealed with caulking or foam and there is at least 3/4" xps (or equivalent) on first, fiberglass up against the board type insulation adds to R value. It's really no different from what is recommended on the wall.

the purpose of the XPS...keep moisture out.
It does so by raising the temperature of the condensing surface, so moisture doesn't condense on the wood.

_________________
The rim insulation should match the R level of the upstairs walls. The Dover link has some good pics and careful workmanship. I can't help you on suppliers. If the Big Boxes don't have what you're looking for, try a building supplier or even contact Dow.

bottom line, if get the XPS in there I can put my fg back in against and need not worry about mold if that area ends up pretty much sealed up....right..

____________
maybe I'll have a picture later....I am gonna give it a try!

right.. Probably. But if you're reusing the fg that's already jammed in there, be aware that its R factor is greatly degraded. FG works because it creates a circuitous route for air movement and heat transfer. Once fg has been distorted and compressed, that mechanism is short circuited. If you presented a wall with fg that looks like that in your rim joist areas, the inspector wouldn't pass it.

It only looks like that because I have pulled it in and out 5 times!!!

Ok, right or wrong I added the xps to the area--2 layers. The first layer fit nice and snug but I did foam here and there. I had enough scrap to do a second layer; though it was a half inch too short. Waste not want not...I added the layer and foamed the top. I'll need to trim the foam neat of course and caulk here and there. I admit it no longer feels drafty there. Pic # 1.

I see no need to put any fg against the XPS up in there. I believe I have an R15 with the 2 layers of xps whereas I only had and R13 before. The question is, do I put a bat of fg up against the underside of the floor, or just leave it go?

If you say its not necesary then I assume I can build my wall right up against the XPS. There will be a very small opening to the joist area. (Pic #2--looking up at what could be an example of the plate). Alternativly I can still build and inch or so away to let some air circulation in there; maybe safer if the fg bat is to be put there. (Pic #3, again looking up at an example of could be the top plate)

What do you think....either way t will soon have a wall in front of it so let me know if it looks like I did something wrong before I frame!

The rim looks fine to me as is! There's no need to trim the foam. It doesn't show and it doesn't interfere with anything.

btw, the R 13 fg you had in there before was a fraction of the stated R factor.

(We should note that you may not meet local fireblocking requirements vertically or horizontally. But we've been over this before. Strips of 1/2" drywall attached to the top of the vertical sheets would satisfy the horizontal separation requirement.)

yea, I guess I'd need to throw some drwall in the joist area...guess i w ould need to trim the foam if I did that.

The drywall would go on top of the vertically installed sheets.

I am framing in front of the 2 X 2 X 8 XPS and of course drywalling over that. Technically the joist area likley should have drywall glued over the XPS as well...I think thats what you are talking about....wether worth doing or not I am not sure....

I'm only suggesting details that might be required in case of inspection.

It looks good! I would recommend you build the wall as close as possible to the XPS. You will most likely have gaps between the framing and the XPS along the wall due to the concrete walls not being straight.

-Tom

likely will not be inspected but if it ever were and they somehow saw in there, it would be a pain to fix at that point. If I scrounge up some drywall, maybe I'll just glue it up...so...new real need for some new bats up against the floor right?

Not for any reason I can see.

I decided to my scraps of scraps, pop out the insulation, put a single layer of XPS in and put back the fg....alittle tougher since I need to cut a 14.5" x 9" piece for between each joist. I have the material so what the heck...

So you can see why this is not a viable method where you're paying somebody x dollars an hour to do it.

YES. However it is sort of theroputic in a way. I am down there alone, the tv on, all the trouble of the upstairs world gone away....

I may just cover that sill XPS w/drywall too...HD had scraps there were pretty much giving away..I may just pick them up and stick 'em up there what the heck I came this far...I can not do any major work down there for a while (new heatpump being installed)...I need an excuse to stay down there!