# rim joist sealing/insulation



## Out2pasteur (Sep 18, 2011)

I’m in Massachusetts in a 1958’s ranch with a basement that is dry, but semi-finished poorly (no insulation, some shoddy work). I am starting to demo it to finish the basement properly, and starting with sealing and insulating the Rim joists. 

For the outside end of the floor joists, at the rim, concrete appears to have been dumped inside of the rim between the joists. This photo shows the end of a joist bay after removal of a board that was tacked on. 










Is this something that is/was common? 

What are best practices for sealing and insulating the joists? 
I’m thinking of putting a cut 2inch thick xps board at end of joist bay and caulking/foaming around edges. 

Thanks for any insight you may have.


----------



## Gary Evans (Jan 27, 2014)

In many areas that's a common practice to bury part of the floor structure in concrete.

I've seen a lot of homes where the top of the concrete foundation either has the floor joist buried in it or they place a wood "ladder" for attaching the joist to.... in the top of the form before it was poured. 
This is a little different......the joist is sitting directly on top of the foundation with no gasket and then they filled up the end with concrete.
Is this cantilevered ?..........Can you show a picture of the outside.........it looks like someone built this in a very odd way.

Either way.......this is a bad idea and usually leads to premature rotting and makes it easier for pests to enter the structure of the home. 
Keeping the wood sealed from the weather on the outside and at least 6" away from the ground is your best bet to avoid those problems. 

I would use 3" thick xps board and yes, use the xps foam in a can for sealing
Good way of insulating between the joist.


----------



## Out2pasteur (Sep 18, 2011)

Gary, 
Your reply is much appreciated. Here is a picture of the outside. 










Also, here is another picture of a bay that shows another view. The joists are not sitting directly on the foundation. There is another wood beam they rest on that sits on the foundation. That beam is hard to see in the first photo, as its front is covered by plaster on metal lathe (just like the ceiling that was removed in that room). I can rip that plaster front section out to expose that beam if it'll help clear up what is going on.


----------



## Gary Evans (Jan 27, 2014)

That looks good.
Clean up the underside of that overhang........shop vac will work good and take a few cans of xps non expanding foam and seal off the gap under the overhang.

And insulate between the joist like your planning.

And you should be fine.


----------



## hsnopi (Jan 24, 2014)

I am in the same boat but in Maryland. I used leftover 1" XPS and used the foam to seal it in. I've only finished one quarter of the basement but I swear I already feel the difference. Definitely worth it.


----------



## Windows on Wash (Aug 30, 2011)

Sealing up the ribbons can really tighten up the home in total.


----------



## Gary in WA (Mar 11, 2009)

I encourage FB/canned foam at the rims. Your case has concrete fire-stopping so any water intrusion can only dry to the outside---if fb inside--- and wood joists would stay wet a very long time (seasonal) as concrete is a water reservoir (think sponge). This is why codes require a minimum 1/2" air space on sides/top of wood beams in concrete saddle- to limit capillary wicking and surround air to help dry it. With the concrete wall outside wet, the moisture can easily wick to the wood joists with new FB on both sides, giving ideal conditions for rot if the joists transmit a little heat.....

Gary


----------



## Gary Evans (Jan 27, 2014)

I'm not so sure that code requires 1/2" clearance for the end of beams in a concrete saddle.......I agree with the reason your doing it Gary but this is what I do.

Where I am it does require that the end of those beams be protected against moisture from concrete but what we do is either wrap the end of the beam in poly or waterproof it.
I make the beam pocket wider than the beam, waterproof the end of the beam, install it and shim the beam securely in the pocket with treated plywood shims.

Locking the beam in place so it can't move in the pocket is structurally better.


----------



## Gary in WA (Mar 11, 2009)

*#4;* http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_3_par228.htm?bu2=undefined

No plywood here (in US), it compresses; http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_6_par173.htm

Using a rim/header/band joist is required even without the concrete fire-blocking; http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_5_par023.htm


Gary
PS. I just think sealing one of two drying sides is risky- only because the concrete is there ( a 5 minute demo will tell if a rim joist present or not) and mulch holds water at the concrete (porous) wall---- I hope I'm wrong and he may never have a problem; http://www.buildingscience.com/docu...nvestigating-and-diagnosing-moisture-problems


----------



## Out2pasteur (Sep 18, 2011)

Thanks all. 
I'm taking the consensus as
1) getting canned foam and sealing the outside junction--once it warms up
2) putting 1-2" foam board at the end of all the joist bays and sealing with canned foam.

Gary from WA: thanks for the Building Science link. Interesting stuff about moisture movement.
I think I understand your concern about wicking to the wood and not drying, as it was built. 
I'll have to be vigilant about the gutter maintenance and keeping moisture away from the foundation as much as possible.

But I didn't get what the "5 minute demo" would tell me about the rim joist. 
Should I knock the cement out of one of the bays to inspect what is behind?


----------

