Hey, gang..

We (OK, builder) installed Roxul Acoustical Firebatt as fireblocking for the 1'' decoupled walls along my foundation.

Problem is - they installed about 2 FEET vertically, instead of a few inches.

Does this recouple my wall (defeating the purpose of building it out an inch to begin with), or are we OK here?

Should they go back and shrink this down?

First pic below is our room. 2nd pic below is a Roxul fireblock pic I pulled from AVS as to what I thought it "should" look like..

Thanks..

http://jstolzen.smugmug.com/photos/172802133-M.jpg

http://jstolzen.smugmug.com/photos/172801379-M.jpg

You really need to check with the local building inspectors and determine their expectation. If possible you should be onsite for the close in inspection and you can ask them.

Our local code interpretation would require additional regular (fiberglass) insulation filling up all the way to the floor in addition to what you have pictured assuming that's an exterior foundation wall.

Also from looking at the picture it looks like the top of the wall sits tight to the ceiling joists. If so, I'd be worried a bit more about that. How are you planning on having the drywall attached? RSIC clips and channel? If you are just banging up the drywall to the studs the amount of decoupling going between the roxul and the foundation may be a moot point.

If you were serious about decoupling the walls they would sit 1/2 lower than the joists and would have been connected with something like:

http://www.pac-intl.com/pics/PAC_Decoupled.gif

Sorry for beating up on you.

Thanks, Big..

The walls are indeed decoupled with RSIC DC04s, hanging the top plate away from the joists..picture's just a bit misleading.

We plan to fill each cavity with Roxul AFB (Acoustcial Fire Batt) as our insulation. That was supposed to be done today, but the guys "called in sick" (hmmm..Saturday..'sick' alrighty..ie: didn't want to work Saturday!)

The Roxul that's there today is for fireblock ONLY, which was approved by my building inspector already. (I got his approval on the concept ahead of time, by pointing out where in the Code it says you can use Insulation for vertical draft/firestop). The builder was supposed to put 3 inches or so along the top plate only, jammed between the plate and the wall to hold it in place. Worker guy got carried away and put a foot and a half - two feet vertically.

I was worried about ANYTHING between the top plate or the studs and the wall, as it's decoupled 1'' from the foundation. But, I read on some threads earlier that Insulation is an "OK" compromise where fireblock/draftstop is required, and a heck of a lot better than wood "recoupling" the wall.

What I'm wondering about is if the Roxul that's shown in the pic, jammed between the top plate and the wall, is too much recoupling. (Additional Roxul will fill each cavity, but will be put in as normal insulation, and we won't have to worry about any recoupling there)..

Thanks for the help!

- J

Here's a pic of how I have the top plate decoupled..

http://jstolzen.smugmug.com/photos/172810302-M.jpg

Now that I see the details just leave it. There is still the wall sized gap between the roxul and drywall which gets filled in with the other insulation.

I have no scientific evidence to back this up, but I wouldn't worry about it. Even using the DV04's, I think the wall-to-joist construction is going to be more rigid than the compressed Roxul.

jstolzen:

Some places float (decouple) floors by having them over fiberglass/rockwool. You've already got your walls coupled a bit with the RSIC anyway.

Having insulation in the wall will reduce flame spread to 'acceptable' levels. There's a NRC study about that.
But it won't prevent fire vapor (smoke) spread.

There's probably some things wrong with this diagram (such as that top plate needs to be lowered a bit so that the far wall (not shown) can have a similar rockwool/drywall above it), but it is a design that handles both fire (required) and decoupling (optional).
http://www.bobgolds.com/Soundproofing/BasementRSIC_rod.gif
Obviously it's a little late for you to look at, but the reason I'm posting it for you is the comment in the diagram about compressing the rockwool.
Also, you need to make sure that the rockwool is permenantly there -- that it won't vibrate and slip down and out later on. Even your inspector might give a tug on it, and if it moves he may want you to stuff more in or put in something mechanical every few feet to hold it in place.

Thanks, BasementBob..

The Roxul that we used is 3'', and the gap is 1''..so, it is compressed pretty tightly in there and I wouldn't expect it to go anywhere..

Building inspector already passed it, so I think we're good on that (whew - this was one of my biggest concerns..my city is VERY fussy about fireblock/draftstop..seems to be the #1 thing that they care about..everything else has been MUCHO easier..)