# Garage Rim Joist Confusion



## doublejz (Apr 17, 2010)

Ok, so my two car garage is under my master bath and bedroom. Its been cold as crap up there. I landed up pulling the ceiling down in the garage due to a plumbing issue and decided to insulate the "rim joists" now since the ceiling is open.

However, the end of the "rim joists" actually hang out past the garage about 2.5' due to how they constructed the bed & bath. Here are some pictures to help show what I'm talking about.














































Every time the wind blows hard outside I can actually see the dust and cobwebs blow as seen here...

http://www.youtube.com/watch?v=3vozTyQTVzc

What I'm thinking about doing is getting some great stuff spray foam and putting 2" XPS on the bottom where the 3/8" plywood is (where the soffit is underneath) and at the end. Then I'll fill the rest in with faced fiberglass rolls.

My thinking here is that the 2" XPS will do its job as an air and moisture barrier on all the wood that share with the outside. Then the fiberglass will help with the floor in the master bed and bath without having to worry about mold.

Am I correct with this or is there a better way (other then getting the whole rim joist spray foamed)?

TIA


----------



## joecaption (Nov 30, 2011)

I'd also be more worryed about the way that deck is attached to the house.


----------



## doublejz (Apr 17, 2010)

joecaption said:


> I'd also be more worryed about the way that deck is attached to the house.


Not really worried about that portion of it. Nobody uses it over there and the rest of it is actually supported underneath. Believe it or not, the chain doesn't get tight unless you jump on that corner of the deck either.


----------



## Gary in WA (Mar 11, 2009)

What you have planned will help magnitudes, but lack uncoupling the joists themselves from the air/ground temps, Fig.7; http://www.buildingscience.com/documents/insights/bsi-009-new-light-in-crawlspaces/

Gary


----------



## doublejz (Apr 17, 2010)

So another words is to do it right I should spray foam the opening and the bottom of the floors?


----------



## gregzoll (Dec 25, 2006)

doublejz said:


> Not really worried about that portion of it. Nobody uses it over there and the rest of it is actually supported underneath. Believe it or not, the chain doesn't get tight unless you jump on that corner of the deck either.


Are you in correct in stating that you have a chain, which is secured with what appears to be 2" Eye bolts, not rated at the kind of stress that is being placed on them.

Was the Deck pre-existing to the structure, or added by someone later on.

I am surprised that your local code enforcement office has not seen that, and ticketed you for an unsafe deck.

As for the original question, you are going to have to still allow the soffits to breath, otherwise, you will have to take those off, when you insulate, and use Spray foam to fill in any gaps, along that 2 1/2 foot span.

Plus you need to remove and properly install that deck, before it comes crashing down, and someone either gets injured or killed.


----------



## joecaption (Nov 30, 2011)

You may be under the impression where trying to avoid your question, change the subject, whatever, but trust me that deck should be addressed first.
No way was that a permitted deck, if it was the inspector should be fired, any home inspector that did not show up with a white cane and a seeing eye dog should have seen that and red flagged it.


----------



## doublejz (Apr 17, 2010)

It will be coming off the house in the spring/summer. It was on the house when I bought it about 5 years ago and it was added (put sliding doors in the bedroom and added on that small ****ty section of deck) on about 5 years before that. The house was inspected at the time of purchase and was also sold once before I bought it which was also inspected (had to add a radon mitigation system).

Anyway back to my question as I would like to get the ceiling back up by the weekend. The soffit has me a little confused as to why its even there as its under the bath and bedroom floor.

From top down it goes like this.

bedroom floor
joists
3/8 ply
soffit

Is the soffit really doing anything or was it just a quick/easy way to finish the job?

I would like to spray right over the 3/8" ply or lay XPS on it. Since its wood there and not the soffit, it shouldn't hurt anything right? If its "breathing" then it would have to breathe between the ply and soffit already, yes?

Oh if it matters, its all solid soffit not vented.


----------



## gregzoll (Dec 25, 2006)

You cannot have that Soffit there, if you are using Spray Foam for that living space. You are going to have to wait for it to warm up, and start carefully taking down all soffit on that side of the house, to see how bad the insulation is.

As for the deck, you right now need to nail a couple of 2x4's across the outside, to keep anyone from walking out on the deck, and also remove the stairs leading up to it, since it is not considered safe.

When it warms up, attack the deck first, by removing it, then you can have it out of your way, while you work on insulating the rooms that are getting outside air under them, through the Soffit area.

Your best bet is to use a couple of layers of 2" XPS, with 5/8" Drywall as a fire barrier on the inside, and 5/8" or 3/4" External grade Plywood to protect the XPS from the Weather.

The way you are looking at this problem, is that you still want the Sofft, and want the floors insulated also, but still want outside air to get in there, which is not what you want.


----------



## daveplot (Apr 29, 2011)

Here is a site that has a good graphic for insulating a cantilever, near the bottom.
http://www.finehomebuilding.com/des...art-details/how-to-insulate-a-cold-floor.aspx

As to the deck, a Professional Engineer is the correct person to determine if the deck is safe or not. A deck attached to a cantilever can be done correctly.


----------



## doublejz (Apr 17, 2010)

gregzoll said:


> You cannot have that Soffit there, if you are using Spray Foam for that living space. You are going to have to wait for it to warm up, and start carefully taking down all soffit on that side of the house, to see how bad the insulation is.


Not sure what insulation you're talking about here. Currently there isn't any insulation around the soffit or garage ceiling. It's just 3/8" plywood, soffit joist, soffit, fascia board, fascia. From inside the garage ceiling you cannot see nor access the soffit like you can in an attic.


----------



## Gary in WA (Mar 11, 2009)

doublejz said:


> So another words is to do it right I should spray foam the opening and the bottom of the floors?


No, add foil-faced foam board to the bottom of the joists, then ply, cement board, Hardie soffit board, etc. to cover. 

*Figure 7 *shows my concerns of decoupling, as I stated you did not read..... in Post #4.

The floor soffit does *not *"need to breathe". It is similar to a wall but on its side.

Gary

PS. Notice the text under figure7 also = "used under rooms over garages" with fire code drywall, check locally.


----------



## doublejz (Apr 17, 2010)

Gary in WA said:


> No, add foil-faced foam board to the bottom of the joists, then ply, cement board, Hardie soffit board, etc. to cover.
> 
> *Figure 7 *shows my concerns of decoupling, as I stated you did not read..... in Post #4.
> 
> ...


Sorry missed that part. I was reading your post while driving. I saw the reference to figure 5 and spray foam and started looking at 8a,b,c, etc. So looking at figure 7. What's the easiest way to get the air cavity above the fiberglass insulation? Also, since the foamboard has foil should I go with an unfaced fiberglass insulation to prevent having 2 vapor barriers?


----------



## Gary in WA (Mar 11, 2009)

Please don't read while driving..... R-30 is code OR R-19 min. OR enough to fill the cavity, footnote "g"; http://energycode.pnl.gov/EnergyCodeReqs/index.jsp?state=Pennsylvania

If you want the space above; http://www.buildingscience.com/documents/insights/bsi-064-bobby-darin-thermal-performance Just add enough to meet code.

No need for faced as the exterior glue in the plywood is lower perms than the facing paper.

Gary


----------



## Msradell (Sep 1, 2011)

I'm not sure why everybody is trying to make this much more complicated than it needs to be. Obviously decoupling the stringers so they don't transmit the cold would be the ideal situation but in this case I'm not sure how valuable that approach would be. The rest of your house probably has many other installation problems that would provide a greater benefit. It was my home I would fill that cavity with spray foam as well as spraying the floor under the bedroom with at least 6 inches of closed cell foam. We did that for our over garage master bathroom a couple of years ago in it may be significant difference!


----------



## gregzoll (Dec 25, 2006)

Msradell said:


> I'm not sure why everybody is trying to make this much more complicated than it needs to be. Obviously decoupling the stringers so they don't transmit the cold would be the ideal situation but in this case I'm not sure how valuable that approach would be. The rest of your house probably has many other installation problems that would provide a greater benefit. It was my home I would fill that cavity with spray foam as well as spraying the floor under the bedroom with at least 6 inches of closed cell foam. We did that for our over garage master bathroom a couple of years ago in it may be significant difference!


Overkill filling in that 2 1/2 for cavity with Spray foam, along with decoupling.

No one is making this more complicated than it is. Well, the OP driving and answering to forum posts on his smartphone, although the reading Gary's information, makes it harder for the OPto understand what is being stated.


----------



## doublejz (Apr 17, 2010)

Gary in WA said:


> Please don't read while driving..... R-30 is code OR R-19 min. OR enough to fill the cavity, footnote "g"; http://energycode.pnl.gov/EnergyCodeReqs/index.jsp?state=Pennsylvania
> 
> If you want the space above; http://www.buildingscience.com/documents/insights/bsi-064-bobby-darin-thermal-performance Just add enough to meet code.
> 
> ...












So looking at the diagram above, does the rigid foam still need to be 2" thick on the bottom of the joists? Just thinking about the already low ceiling height.


----------



## Gary in WA (Mar 11, 2009)

Per your location using the coldest 3 months average temp of 29*F, using R-10 (2"XPS) the cavity is safe to 38%RH in the room above. With R-7.5, the dew-point in cavity is 35%RH room air moisture. Depends on the temps in the garage compared to outside, if garage is always warmer due to less wind, furnace removes excess RH, room used only occasionally, etc. , you could get by with the lesser thickness. I didn't even run the numbers for less FB because of your location. http://www.google.com/url?sa=t&rct=...ptCRFxe_jer0-7l3cR8cm4g&bvm=bv.58187178,d.cGU

Gary
PS. you could always add some XPS between the joists and use PIC on the joists in only 1/2" thickness, depends on local products...


----------



## doublejz (Apr 17, 2010)

Gary in WA said:


> Per your location using the coldest 3 months average temp of 29*F, using R-10 (2"XPS) the cavity is safe to 38%RH in the room above. With R-7.5, the dew-point in cavity is 35%RH room air moisture. Depends on the temps in the garage compared to outside, if garage is always warmer due to less wind, furnace removes excess RH, room used only occasionally, etc. , you could get by with the lesser thickness. I didn't even run the numbers for less FB because of your location. http://www.google.com/url?sa=t&rct=...ptCRFxe_jer0-7l3cR8cm4g&bvm=bv.58187178,d.cGU
> 
> Gary
> PS. you could always add some XPS between the joists and use PIC on the joists in only 1/2" thickness, depends on local products...


Well I just bought a small 30k BTU wall mount heater for the garage. Not to keep it up to a desired room temp but to at least take the chill off. I may have to put the XPS between the joists and then just re-drywall it due to my garage door/ceiling clearance.


----------



## Gary in WA (Mar 11, 2009)

Ouch, well- anything with FB is an improvement....

Gary


----------

