# Rim Joist Sealing and Insulation



## velvetfoot (Dec 18, 2008)

For me I think I've settled on caulking and fitting multiple foam boards cut up with a table saw and covering the edge of the sill (which is sitting on foam) with fiberglass.
I figure for me it'll be least cost.
Would appreciate any tips on this method for those who have done it.
Like, when caulking, do you do the top and bottom joint only?  It would seem so since the joists just separate the bays.
I figure on caulking all around the outside of the outermost foam block.
I think BeGreen noted already that caulk in a tube can fit in those bays easier than a caulk gun.

Other methods I've read about:

-Spray foam contractor
    Cost, + it covers everything on the sill, like wires, right?

-Fiberglass, unfaced
     That's what my place has now, with no caulking.  Don't feel any draft, but I guess water vapor could condense on the rim joist if it got cold enough outside

-Fiberglass in plastic garbage bags


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## smokinj (Dec 18, 2008)

I used tiger foam all of mine, cost 800 bucks but the job was done in just a few hrs. and no way is anything getting through that stuff


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## d.n.f. (Dec 18, 2008)

smokinj said:
			
		

> I used tiger foam all of mine, cost 800 bucks but the job was done in just a few hrs. and no way is anything getting through that stuff



Do you have an approximate square footage for that job?
I just got a spray foam quote and was wondering what that Tiger Foam costs to do the comparo.


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## velvetfoot (Dec 23, 2008)

It was actually Rhonemas that suggested the caulk in a toothpaste tube:
https://www.hearth.com/econtent/index.php/forums/viewthread/3663/#37732

It's going slow.  I can appreciate a guy coming in and spraying it.


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## precaud (Dec 24, 2008)

velvet, just thought I'd pass this on. Just returned from Home Depot and they are now selling 2" Owens Corning Foamular 4'x8' extruded boards (R10) for $19.36 each. That is the same price as 2" expanded boards were last year. This is the first sign I've seen (besides at the pump) of a benefit from lower oil prices...


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## velvetfoot (Dec 25, 2008)

precaud, are you sure they are 4x8?  
I've only seen the 2x8 in the HDs around here.
For me the 2x8s can fit in the car, so I don't have to take the utility trailer.


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## precaud (Dec 25, 2008)

Yep, they were 4x8's. I was stunned because I had payed nearly as much for the equivalent 2x8 from Dow (at Lowes) six months ago. This is the first time the local HD has stocked the extruded. How do you fit 2x8's in a car?!?!


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## velvetfoot (Dec 25, 2008)

It's a hatch.  I can fit at least 10, maybe 12.
That's a smokin' deal.  I'll check it out next time I'm there.


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## precaud (Dec 25, 2008)

Ah yes, that would work in a hatch...
With no immediate need, I'm trying to decide if the price is a mistake or this is the 'new normal'.


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## billb3 (Dec 26, 2008)

I did my sister's raised ranch last Winter using foil covred solid foam.
Sealed all 4 sides with expanding foam. 
I covered the sealed edges of the cut foam with foil to discourage mice and weather breakdown of the foam.
She had air / wind / mice infiltration  problems.


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## velvetfoot (Dec 29, 2008)

Well, I'm proceding slowly.
It was really tough around the electrical panel.
The area behind the heat manifold will be tough too, but I'm keeping that for later just so I can have the illusion of progress.
The spray foam would have been great behind those tough areas.

I had some silicone caulk that was a month past its 'use by' date, and it wouldn't cure. 
Anyway, I switched to latex caulk.  I'm doing the wall with the multiple bays.
I have a 'system' now.  Using 4 layers of 2" foam on this wall.
Pre rip the boards to right height, cut 4 boards to the length of the bay using heavy duty box cutter knife..
Vacuum out the bay.  Caulk the 4 edges. 
Put in first piece.  Caulk the 4 edges.  Repeat 3 more times.

The toothpaste tube caulk dispenser gets hard to squeeze for my week hands and it's hard to control, so I've gone back to the gun, and schmeering the bottom innermost wood edges by hand, checking with inspection mirror.

It'd be so much faster with spray, but I'm gonna see this through.


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## precaud (Dec 29, 2008)

4 layers of 2" foam is SERIOUS insulation!


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## velvetfoot (Dec 29, 2008)

It matches up roughly with the foam on the wall.
In for a penny, in for a pound.


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## sinnian (Dec 29, 2008)

Don't seal your basement up too tight.  Remember your combustion  appliances (burner, gas dryer, etc) need air to work effectively.

Also, latex caulk will dry out and crack over time.  Why not do all of your rigid board work and then get a few cans of spray foam to seal the edges?

I had my rim joist sills spray foamed a few years ago, and you are right about being able to access wiring and plumbing.  Lucky for me I have no plans or illusions to ever finish off my basement.


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## velvetfoot (Dec 29, 2008)

I didn't know that about latex caulk.
It says 50 years on the tube, lol.
I was totally bummed by the non-curing silicone.
I've been cutting the foam blocks so they're pretty tight.
Some I even have to pound in with a rubber mallet and a board.
I really hate working with those foam cans, but am acquiring an inventory of stuff that I'll do at one time.


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## sinnian (Dec 29, 2008)

velvetfoot said:
			
		

> I didn't know that about latex caulk.
> It says 50 years on the tube, lol.



If you use the latex caulk on painted wood and then paint over the caulk it will last, otherwise the oil or whatever seeps into the wood and dries out ~ eventually.


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## Jackpine Savage (Jan 1, 2009)

I used 2" foamboard, left a 1/4" gap around the edges, and then filled in the gap with spray foam. It went pretty fast and I was happy with the result. I've learned to wear rubber gloves when I play with spray foam .


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## velvetfoot (Jan 14, 2009)

Well, I finished one side of the basement rim joist.
Pretty slow process.
I put the first piece on a side that is parallel to the joists, so there aren't all those bays.
I'm optimistic that side will go faster, but I'm still doing multiple layers and caulking.
Cutting, routing, etc, for wires and pipes also slows things.


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## d.n.f. (Jan 14, 2009)

That is what I was worried about in my situation (the time).  I have work, a million home projects, other stuff.  For me in this case I am going to pay someone to spray foam.  
Some jobs are worth doing, some jobs are enjoyable, and some jobs are worth paying someone for either due to my lack of expertise or in this case my time.

Do you notice a difference even with only part of it done?


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## velvetfoot (Jan 14, 2009)

No.  It was well insulated with fiberglass.  I feel like I am wasting my time.  But, I'm stubborn and will finish it.
The foam on the wall, on the other hand, is great-notice a big difference.


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## homebrewz (Jan 14, 2009)

Velvet, did I read in another thread that you also insulated your ceiling with fiberglass bats? If so, I'm wondering 
how it worked out for you and if you noticed a difference in the living space.


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## velvetfoot (Jan 14, 2009)

That's the way it came.
The basement is definately warmer with the foam on the walls.


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## velvetfoot (Jan 21, 2009)

Still going slow, but am finding frosty spots, so maybe it won't be a total waste.

Oh yeah, I found a new knife at Home Depot to cut the foam.
It's a Stanley Fat Max Extreme, I believe.
The locking blade wheel and wider and longer blade were improvements over the one I had been using.
Heavy though.


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## velvetfoot (Jan 22, 2009)

They don't let us root around at the transfer station, and neither did the last place I lived.  I could when I lived in NH but that was back in the '70's.


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## velvetfoot (Jan 27, 2009)

Almost half done.
Found a fair amount of ice this PM.
The fiberglass was unfaced.  
I guess it dries out at some point, but there was a pretty good chunk of ice in there.


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## mainstation (Jan 31, 2009)

We had our rim board and cellar walls professionally foamed , and man what a difference.  It has already paid for itself with this extra cold winter. 
My question is, 
Is it ok to put fibreglass insulation in your floor joists, my kitchen floor is always cold--it is farthest from the corn stove.   If yes can I put up vapour barrier also.?


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## velvetfoot (Feb 1, 2009)

I don't see why you can't put up insulation, but I don't think you would actually need a vapor barrier if your basement walls are insulated.
My house came with fiberglass insulated floors and I am insulating the basement walls to make the basement a little warmer.
The insulation that I have are thick batts with paper on the first floor side.  They are just wedged in there.
I'm not too crazy about the stuff hanging there, so I'm going to cover with something or other.

I'm not so sure how much it would help though since you already have foam on the basement walls.  I might help some but maybe not a super lot.


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## ihookem (Feb 11, 2009)

I just took out my fiberglass insulation between my rim joists and I won't ever do that again. My home is four years old and the wood id turning black and has frost between the joists and the fiberglass. I think spray foam is the only way to go because it sticks tight to the wood and plugs every hole and leak. I am getting spray foam this time. I have heard  a home looses a lot of heat this way. Foam sheets may be ok but might leave an air gap and leave room for a leak and a leak means frost. No reason you can't fiberglass your floor joists in your basement and vapor is better cause it keeps fiber particles in place .


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## velvetfoot (Feb 11, 2009)

I'm still at it.  I'm about a third done on the third wall which is one with a lot of bays.
I'm doing about one bay a night, but on this wall I'm doing five layers, covering the top of the concrete and meeting the wall foam.
I think I'm getting it pretty tight, caulking between each layer.
I've noticed a lot less condensation when it's warmer.  Today's bay didn't have much.

But man, this is so tedious.
I have plenty of detail work to do on the wall foam too.


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## velvetfoot (Feb 15, 2009)

I probably should have made more use of the Great Stuff.
I'm going to foam those spaces below.
Another void is pretty deep so I might try that straw trick.


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## j00fek (Feb 16, 2009)

velvetfoot, are you just sealing above the concrete walls? 

im still planning mine out and have 4ft of brick, then 5ft of concrete (which is 2in out from the brick above) i plan to cover the brick with the 4x8 sheets of rigid foam i got. then ill have a mainly flush wall after. thing im stuck at is getting the foam on the brick...(liquid nails...or drilling into the brick and using plastic anchors. 

ill try to get some pics tonight....


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## velvetfoot (Feb 17, 2009)

I started with the walls but then thought that I should do the rim joist area which is taking a long time.
I'm not sure about brick.  You have to make sure you're not getting any water in.
You have to cover the foam that I'm using with 1/2" of sheet rock (or something else of equal fire retarding capability).
Then you still have the concrete to insulate.
Maybe you could put another 2" of foam on the whole wall and put a stud wall in front of it and put insulation and sheet rock on that.
Then you wouldn't have to drill holes.
They seem to be saying to put a layer foam on the inside wall so water vapor doesn't condense on the concrete.

I was thinking a little about the cost of this method of rim joist insulation while I was cutting up the stuff yesterday.
I think it's pretty high.  The stuff isn't cheap.
I'd get a quote on a contractor spray job if I was considering this again.


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## d.n.f. (Feb 18, 2009)

Can't remember how you said you are cutting the foam but Fine Homebuilding just had a tip that you sharpen the edges of a putty knife or a 3 or 4" drywall knife (application tool).  Slices through like butter along a straight edge and no positively charged bits clinging to everything.


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## velvetfoot (Feb 18, 2009)

I've seen that tip about a sharpened putty knife but I've been using a snap-off knife by Stanley.


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## velvetfoot (Mar 13, 2009)

Well, I finished today.
I told you I was stubborn.
Now I move on to finishing the wall insulation.


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## precaud (Mar 13, 2009)

Good on ya, velvet. Perserverence furthers.


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## Cutter (Mar 13, 2009)

Howdy all.  I just got through reading this thread and I realize that it might be too late, but here are a few things to consider.
1. My favorite insulation tool is cheap and works on batts and ridgid foam. I take an old 12" Saw-zall blade with course teeth. Duct tape the tang end for a handle and then sharpen both top and bottom edges with a file or grinder. This gives you a knifes edge for cutting through thick batts and a saw for fine fitting of foam.
2. buy  4-6" length of tubbing the same size as the little tube that comes with cans of Great Stuff. Stick it on your can and then you have better dexterity in getting your foam where you need it. Of course you need to do all of your other work first. You can go through several cans of foam with the tube. Then throw it away.
3. You can use Great stuff as a glue to stick your foam board to just about anything. A little goes a long way. Small globs on the back, let it expand a little while and then press into place. You do have to go back to make sure that it hasn't expanded more and pushed your board away from sub-strate.
4. Be careful with vapor barriers. One is good and two are generally bad. If moisture happens to get in between barriors  resulting unseen rotting can have devestating effects. Both structural decay and groth of molds.
Brad


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