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Old 01-30-2010, 05:40 PM   #1
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Walls that Can't Go To the Ceiling


I'm about to finish in a basement. Along the cinderblock walls, I want to cover them with 1/2" polystyrene, and then build a 2x4 insulated wall.

However, For a long section of this wall, there is a 3" sewer pipe running a few inches under the floor joists and about 3" away from the wall.

Any suggestions on best practice on how to build a 2x4 stud wall under this pipe?

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Old 01-30-2010, 07:12 PM   #2
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Walls that Can't Go To the Ceiling


read more of the threads here on basement walls. 1/2" shows you have a lot to study before attempting this project. But for the pipe you build a soffit (box) around it. But this needs fire blocking, so read more on this also. Please use the search feature and then ask specific questions if you are still unclear on some issues.

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Old 01-31-2010, 12:43 AM   #3
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Walls that Can't Go To the Ceiling


Am I reading this wrong, or was I just insulted?


I have been reading up on how to do this sort of thing. As an example of where I'm getting my information includes this thread:
Basement XPS and Batt insulation? I've also read the Building Science web pages, and for areas closer to zone 3, they even include the following line:

Insulated sheathing with an R value ≥ 2.5 on a 2x4 framed wall

and that would be 1/2" xps, right?

So where I'm I going fundimentally wrong?




So let's back up a bit and give some more detail...

I live in the South (zone 3) and this is a cinder block wall that is partly above grade and partly below grade. As I understand it, because of the humidity we have here in the south, I've got to allow this wall to "breath", and in the above listed thread, it specifically talks about needing LESS THAN 1" xps (unfaced) to allow the wall to breath.

So my plan is to attach 1/2" unfaced XPS directly to the cinder block, then over the XPS, frame a 2x4 wall filled with unfaced insulation.


But now lets get back to my exact question... because my question still holds if I were using 2" xps as Building Science appears to suggest (for colder climates) and still need a 2x4 for electrical and hiding pipes.

Now as I understand it, one of the typical ways of framing a non-load bearing wall is to mount a pressure treated 2x4 plate to the concrete floor and nail a standard 2x4 to the underside of the floor joists. Then cut-to-fit 2x4 studs for between the two sets of 2x4s. This way, the wall is supported (from the stand point of tipping over) by attaching it to the floor joists above.

But my problem is that PART of the space I need to build this 2x4 wall (regardless of if the wall is directly against cinder block, on top of 1/2" xps, or 2" xps) is occupied by a 3" sewer pipe.

Now building a soffit, at least at first, doesn't seem like the right thing to do... at least not until I have something structural to tie the soffit to. But by problem is the pipe is in the way of buidling a structural wall.


Now as I ponder it some more... is the suggestion here that I build a soffit by attaching... oh lets say 2x3s... laid flat to the cinder block wall through the xps sheets, and then build the soffit with the floor joists the support on one side and the stud on the cinder block wall the support for the other side? Then use the soffit as the point to attach the upper 2x4 of the frame wall?
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Old 01-31-2010, 01:00 AM   #4
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Walls that Can't Go To the Ceiling


build the soffit first and then the 2 x 4 wall can join up to it.
add the fireblocking to the underside of the soffit before the 2 x 4 wall gets built.
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Old 01-31-2010, 08:59 AM   #5
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if you want the wall to have lateral strength why not tie it into the concrete wall? By this I mean tapcon a block onto the concrete wall and then have a black go from the 2x4 wall to the blocks you have attached to the wall. Then tied your soffit into this structurally sound wall.
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Old 01-31-2010, 09:29 AM   #6
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Originally Posted by HooKooDooKu View Post
I'm about to finish in a basement. Along the cinderblock walls, I want to cover them with 1/2" polystyrene, and then build a 2x4 insulated wall.

However, For a long section of this wall, there is a 3" sewer pipe running a few inches under the floor joists and about 3" away from the wall.

Any suggestions on best practice on how to build a 2x4 stud wall under this pipe?
HooKoo; here is the graphic answer to your question.


There are two ways to do this;

Build your frame wall attaching to the block wall with nailers between your studs (my approach) or as mentioned above, build your soffet first, nailing it to the block ball and then build your vertical wall to that. 6 of one, half dozen of another. I had to do this in several areas of my basement.

Either way, you get what you are after.
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Old 01-31-2010, 09:36 AM   #7
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FYI you typically do not want to have your studs in contact with the wall and also that picture offers no thermal break.
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Old 01-31-2010, 09:55 AM   #8
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FYI you typically do not want to have your studs in contact with the wall and also that picture offers no thermal break.
There is much more wrong with this job than it is right.

1)pipe not sealed as it goes through top joist

2) incorrect fire blocking

3) no condensation break at concrete wall

4) incorrect nailing of faced insulation

5) contact with concrete

6) fiber glass insulation in the joist space along the rim joists

7) no fire stop caulking for electrical wire top plate penetration (cannot see it but everything is wrong here, so it is an assumption)

8) most likely no sill insulation under sole plate.

Bottom line this picture posted most be to show all the things you can do wrong to assure yourself that the job will need to be redone each year.
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Old 01-31-2010, 01:09 PM   #9
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Walls that Can't Go To the Ceiling


Bob,
You wrote:
"fiber glass insulation in the joist space along the rim joists"
The builder installed it the same way in my home. Why is this an issue?
TIA,
Bob
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Old 01-31-2010, 01:25 PM   #10
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A lot of warm moist air flows into this area. This insulation is not suitable for moist conditions. You must use spray foam or sealed rigid foam for this area. And it is the most critical area in the home to seal properly.
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Old 03-22-2010, 02:55 PM   #11
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Originally Posted by Bob Mariani View Post
There is much more wrong with this job than it is right.

1)pipe not sealed as it goes through top joist

2) incorrect fire blocking

3) no condensation break at concrete wall

4) incorrect nailing of faced insulation

5) contact with concrete

6) fiber glass insulation in the joist space along the rim joists

7) no fire stop caulking for electrical wire top plate penetration (cannot see it but everything is wrong here, so it is an assumption)

8) most likely no sill insulation under sole plate.

Bottom line this picture posted most be to show all the things you can do wrong to assure yourself that the job will need to be redone each year.
Bob:

Thanks for the review of the above photo. My basement is a bit more extreme, although the general problem is basically the same. I have an unfinished basement with foil insulation nailed to the concrete foundation walls from slab to the top of the foundation wall along the entire basement perimeter. I would rather not remove this foil insulation anywhere. At the top of one of the walls, there is HVAC ducting (10"x12" approx) running below the floor joists, leaving no space to attach a top plate to the floor joists next to the foundation wall. The only way out for me is to build some sort of a bulkhead around the HVAC ducting and a low wall that does not quite reach up to the floor joists above, but terminates at a 'floating' top plate below the HVAC ducting at the bulkhead. I am not sure what a sound technique would be for doing that. Pictures/illustrations of how to do it correctly will be greatly appreciated!

I would also like to bear in mind the recommendations that you have made above in your review.

Thank you
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Old 03-22-2010, 03:31 PM   #12
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Originally Posted by DIYHomeTheater View Post
Bob:

Thanks for the review of the above photo. My basement is a bit more extreme, although the general problem is basically the same. I have an unfinished basement with foil insulation nailed to the concrete foundation walls from slab to the top of the foundation wall along the entire basement perimeter. I would rather not remove this foil insulation anywhere. At the top of one of the walls, there is HVAC ducting (10"x12" approx) running below the floor joists, leaving no space to attach a top plate to the floor joists next to the foundation wall. The only way out for me is to build some sort of a bulkhead around the HVAC ducting and a low wall that does not quite reach up to the floor joists above, but terminates at a 'floating' top plate below the HVAC ducting at the bulkhead. I am not sure what a sound technique would be for doing that. Pictures/illustrations of how to do it correctly will be greatly appreciated!

I would also like to bear in mind the recommendations that you have made above in your review.

Thank you
I'll have to take and post a picture of my results when I get to it... but here's what I did...

1. Attached 2x4s to the sides of the floor joists about 20" away from the wall.
2. Nailed and screwed a 2x4 along the underside of the hanging 2x4s.
3. Framed a 2x4 wall against the basement wall. The top of the top plate for this wall was at a heigth 1-1/2" lower than the bottom of the bottom plate on the underside of the hanging 2x4s.
4. Attached the wall to the hanging wall with 2x4. Nailed to the top of wall, nailed and screwed to the bottom of the hanging wall.
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Old 03-22-2010, 03:50 PM   #13
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Walls that Can't Go To the Ceiling


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Originally Posted by Bob Mariani View Post
A lot of warm moist air flows into this area. This insulation is not suitable for moist conditions. You must use spray foam or sealed rigid foam for this area. And it is the most critical area in the home to seal properly.
Hey Bob, This area is one of the leakiest areas in my home too. I have similar fiberglass insulation inthe joist bays. I was told to make sure my vapour barrier is sealed properly and completely and then all would be good. What is your opinion on that arrangement? (I should also say I live in Alberta where building codes where vapour barrier is on the inside of the insulation.)
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Old 03-22-2010, 04:05 PM   #14
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I'll have to take and post a picture of my results when I get to it... but here's what I did...

1. Attached 2x4s to the sides of the floor joists about 20" away from the wall.
2. Nailed and screwed a 2x4 along the underside of the hanging 2x4s.
3. Framed a 2x4 wall against the basement wall. The top of the top plate for this wall was at a heigth 1-1/2" lower than the bottom of the bottom plate on the underside of the hanging 2x4s.
4. Attached the wall to the hanging wall with 2x4. Nailed to the top of wall, nailed and screwed to the bottom of the hanging wall.
That's great! Do you know if this arrangement is code-compliant for non-bearing walls? Also, how did you handle fire-blocking in this arrangement?
I am attaching a picture that reflects my understanding of what you wrote.
Thank you very much.
Attached Thumbnails
Walls that Can't Go To the Ceiling-bulkhead-soffit.jpg  

Last edited by DIYHomeTheater; 03-22-2010 at 04:35 PM. Reason: Added my own picture
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Old 03-22-2010, 04:06 PM   #15
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in your area (cold climates) a vapor barrier on the warm side is required. However fiberglass insulation at the rim joists does not work well. Warm moist air in the summer will blow right past fiberglass and the moisture will collect in the insulation and lower the R-Value. You need to completely air seal the entire perimeter of the rim joist bay opening for it to work well. rigid foam board with all edges sealed with spray foam and then filled with Roxul will work (cheap way) or use the spray foam 4" thick. (best way)

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