Insulating rim joist

Reply

  #1  
Old 11-01-16, 05:41 PM
X
Member
Thread Starter
Join Date: Dec 2011
Location: Usa
Posts: 236
Received 0 Votes on 0 Posts
Insulating rim joist

I have been working on swapping out the fiberglass insulation that was in my rim joist to 2" foam with silicone sealing the edges. Easy enough for the most part. However, I am at a loss on how to insulate the rim joist that runs long ways on the house. On the one side of my basement there is only about 1/2" of an opening between the current floor joist and the concrete wall, that is the only access to the rim joist on this side. The other side of the basement has more room, but is still going to be tight to get it all sealed up once the foam is in. So any ideas on how to get these insulated properly?
 
Sponsored Links
  #2  
Old 11-01-16, 06:45 PM
XSleeper's Avatar
Group Moderator
Join Date: Dec 2004
Location: USA
Posts: 26,230
Received 723 Votes on 669 Posts
You could either have it professionally spray foamed or blow it full of cellulose.
 
  #3  
Old 11-01-16, 06:46 PM
J
Member
Join Date: Jan 2011
Location: USA
Posts: 4,835
Received 79 Votes on 74 Posts
Got a picture?
No way should you be using silicone, need to be using low expanding spray foam to fill the gaps.
Silicone can eat out the foam.
 
  #4  
Old 11-02-16, 05:25 AM
B
Member
Join Date: Oct 2008
Location: New England
Posts: 10,523
Received 37 Votes on 34 Posts
If these are 2x10's or larger you could remove an inch at an angle and the floor would not know the difference. If you were concerned about the reduction then a sister along the modification would restore the full strength.

Bud
 
  #5  
Old 11-02-16, 10:03 AM
X
Member
Thread Starter
Join Date: Dec 2011
Location: Usa
Posts: 236
Received 0 Votes on 0 Posts
Thanks for the replies. X if I filled it with cellulose wouldn't I still have the issue of air infiltrating and possible mold/rot issues?

Joe im not sure what you mean, everything I have read said to use 2" closed cell ridgid foam and seal around the edges with spray foam or silicone.

Bud that seems like a plausible idea for about half of it, the other half of the beam has all the wires from the panel box stapled to it.

Im thinking the only way im going to be able to do that side is to fill the cavity with spray foam.
 
  #6  
Old 11-02-16, 02:07 PM
XSleeper's Avatar
Group Moderator
Join Date: Dec 2004
Location: USA
Posts: 26,230
Received 723 Votes on 669 Posts
The only way it will get moldy is if it gets wet. It won't get wet if you don't have a leak. If it gets wet behind your foam, I guarantee it would mold too, since it can't dry out. You are limited in what you can do in a tight space.. no magic wand. Millions of houses have cellulose in attics and walls and you don't hear horror stories about mold in the cellulose.

Prior to spray foam, the rims in many houses got blown in with cellulose, and all those houses are just fine.
 
  #7  
Old 11-02-16, 03:09 PM
X
Member
Thread Starter
Join Date: Dec 2011
Location: Usa
Posts: 236
Received 0 Votes on 0 Posts
I guess i'm just concerned about all that I read that if the warm moist are from inside the basement reaches the cold rim joist it will condensate, then develop mold or rot, this is why they say fiberglass batts on the rim joist are a no no.

However there has been fiberglass there for at least 6 years and so far I haven't seen any sign of a moisture issue behind them as I pull them out.

I'm not sure If I would even be able to get cellulose up in there because of how limited the opening is. It seem like the only option would be to just fill it with expanding foam, because I don't even think I would be able to direct the foam where it needs to go with such a small opening. I'll get a picture of what I'm working with.

I guess I'm just really paranoid about getting mold behind it, from what I read it seems like if you have the slightest air leak, it will develop condensation.
 
  #8  
Old 11-02-16, 03:26 PM
X
Member
Thread Starter
Join Date: Dec 2011
Location: Usa
Posts: 236
Received 0 Votes on 0 Posts
Name:  20161102_171216.jpg
Views: 187
Size:  37.9 KBName:  20161102_171400.jpg
Views: 180
Size:  33.8 KB

Here are the pictures. The one has a much bigger opening, if I took the foam down off the walls, I can fit 2" foam up in there with no problem, but I wouldn't be able to seal the edges.

As you can see in the other picture though, that the joist closer to the panel box, there is only a 1/2" opening. However beside that joist, its only about 4" over to the rim joist, so maybe just fill that whole void with expanding foam?
 
  #9  
Old 11-02-16, 04:12 PM
B
Member
Join Date: Oct 2008
Location: New England
Posts: 10,523
Received 37 Votes on 34 Posts
Expanding foam has limits on how thick each application can be and how long you need to wait until you add another coat.

Another type of insulation is mineral wool. I'm familiar with Roxul and it is very dense. If you stuffed those cavities full of Roxul there would be very little air getting in.

For the joist that leaves only 1/2" I would still be taking a saw to it, at least a 45 cut off of the bottom to get you up over an inch.

Let's assume you get something in there that isn't perfect but has little risk if causing moisture related problems. What's the penalty, a little extra heat loss? The difference between filling those spaces with foam and filling them with fiberglass in minimal. The biggest benefit comes from air sealing the rim joist to the foundation.Create enough space so you can get your hand in there and tube caulk or rope caulk and seal the foundation to wood seam. Then fill it with as dense an insulation as you can. As you said, the fiberglass that was there hadn't created a problem.

Bud
 
  #10  
Old 11-02-16, 04:24 PM
XSleeper's Avatar
Group Moderator
Join Date: Dec 2004
Location: USA
Posts: 26,230
Received 723 Votes on 669 Posts
To fill it with cellulose you would rent the blower/hose... then you could cover the 1/2" gap with a 2x2 that is nailed to the joist and the top plate, then drill a 1" hole at a 45 degree angle through the 2x2 every 4ft or so, then blow it full.

Too much information on the Internet is definitely a problem.
 
  #11  
Old 11-02-16, 04:35 PM
X
Member
Thread Starter
Join Date: Dec 2011
Location: Usa
Posts: 236
Received 0 Votes on 0 Posts
Bud are you referring to sealing the sill plate to the concrete foundation? I know that wasn't done, and the previous owner already has foam board over it, so I would have to cut some of the foam board down to access the sill plate.

Cutting some of the joist away is an option, but I would be very close to all the wires from the panel and that would make me a little uncomfortable, blowing in some cellulose in that section might be the safest bed. For the other side I'll seal the sill plate then stuff roxul up in there nice and tight, and I think that should do it.

This section isn't too crucial since it's in the unfinished area and I can access it any time. Im going to have to cut some drywall out of the finished parts to access the joist on the opposite side of the basement, he didn't even bother with any insulation over there.
 
  #12  
Old 11-02-16, 04:45 PM
X
Member
Thread Starter
Join Date: Dec 2011
Location: Usa
Posts: 236
Received 0 Votes on 0 Posts
I was down taking a look at it. I have no issue accessing where the sill plate comes in contact with the masonry block, and that would be very easy to seal up. What I would have trouble reaching would be where the rim joist comes in contact with the sill plate and the sub floor, I assume those areas should be sealed up well too?
 
  #13  
Old 11-02-16, 05:28 PM
B
Member
Join Date: Oct 2008
Location: New England
Posts: 10,523
Received 37 Votes on 34 Posts
The sheathing on the outside stops at the foundation so less likely to leak above that point. It is the irregularities of the foundation and the less than stellar effort by the builders that makes the concrete to wood seam a frequent leaky spot. The rest, if you can, but the wood to concrete s most important.

On a cold day with the kitchen and bath fans running you can often feel the cold air coming in. Your hand is a good test instrument.

Bud
 
  #14  
Old 11-02-16, 06:01 PM
X
Member
Thread Starter
Join Date: Dec 2011
Location: Usa
Posts: 236
Received 0 Votes on 0 Posts
Then that's not a problem at all to seal up. In the finished section I'll just have to remove about an inch of foam board off the top to access the sill plate
 
  #15  
Old 11-05-16, 11:55 AM
X
Member
Thread Starter
Join Date: Dec 2011
Location: Usa
Posts: 236
Received 0 Votes on 0 Posts
Since I'm cutting away the insulation that is covering the sill plate to silcone the gap shut, should I replace the insulation over the sill plate or is it thick enough with wood to not effect anything?
 
  #16  
Old 11-05-16, 12:59 PM
B
Member
Join Date: Oct 2008
Location: New England
Posts: 10,523
Received 37 Votes on 34 Posts
While you are there I would recommend re-installing the foam board, it is actually protecting the wood.

Bud
 
  #17  
Old 11-06-16, 10:49 AM
X
Member
Thread Starter
Join Date: Dec 2011
Location: Usa
Posts: 236
Received 0 Votes on 0 Posts
Bud, due to the tight working area, my cuts were very crooked, and is making it impossible to put a small piece of foam board against it. What about just using great stuff to spray above the foam?
 
  #18  
Old 11-06-16, 11:07 AM
B
Member
Join Date: Oct 2008
Location: New England
Posts: 10,523
Received 37 Votes on 34 Posts
Works for me. In a small area anything will do.

Bud
 
Reply
Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: