# Walls that Can't Go To the Ceiling



## HooKooDooKu (Jan 7, 2008)

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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## Bob Mariani (Dec 1, 2008)

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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## HooKooDooKu (Jan 7, 2008)

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:
http://www.diychatroom.com/f19/basement-xps-batt-insulation-61855/ 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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## jlhaslip (Dec 31, 2009)

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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## wnabcptrNH (Jan 29, 2010)

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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## diykc (Dec 24, 2009)

HooKooDooKu said:


> 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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## wnabcptrNH (Jan 29, 2010)

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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## Bob Mariani (Dec 1, 2008)

wnabcptrNH said:


> 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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## bob22 (May 28, 2008)

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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## Bob Mariani (Dec 1, 2008)

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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## DIYHomeTheater (Mar 22, 2010)

Bob Mariani said:


> There is much more wrong with this job than it is right.
> 
> 1)pipe not sealed as it goes through top joist
> 
> ...


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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## HooKooDooKu (Jan 7, 2008)

DIYHomeTheater said:


> 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'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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## drtbk4ever (Dec 29, 2008)

Bob Mariani said:


> 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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## DIYHomeTheater (Mar 22, 2010)

HooKooDooKu said:


> 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.
> ...


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.


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## Bob Mariani (Dec 1, 2008)

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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## HooKooDooKu (Jan 7, 2008)

DIYHomeTheater said:


> 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.


Close.

The one thing I'm doing different is that I do NOT have a top plate for the short wall hanging from the ceiling. To improve strengh, the 2x4s should be nailed directly to the side of the floor joists. That way, the short hanging wall will resist twisting from the wall pushing against it.

I asked my local building inspector if this was fine for a non-load bearing wall and he had no problem with the way I described it.


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## DIYHomeTheater (Mar 22, 2010)

HooKooDooKu said:


> Close.
> 
> The one thing I'm doing different is that I do NOT have a top plate for the short wall hanging from the ceiling. To improve strengh, the 2x4s should be nailed directly to the side of the floor joists. That way, the short hanging wall will resist twisting from the wall pushing against it.
> 
> I asked my local building inspector if this was fine for a non-load bearing wall and he had no problem with the way I described it.


HooKooDooKu:
How did you handle fire blocking?
Thanks


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## HooKooDooKu (Jan 7, 2008)

DIYHomeTheater said:


> HooKooDooKu:
> How did you handle fire blocking?
> Thanks


Haven't gotten that far yet.

First question is where exactly does it need fire blocking? There isn't a vertical to horizontal transistion in a concealed space because the main wall has a top plate and the drywall will go up to there. 

Otherwise, my current plan calls for a drop ceiling, with the ceiling being about 2" below the horizontal parts of this soffit. So for me, it won't be a concealed space (beyond any fire blocking you are supposed to do above a drop ceiling).

And even if the plan was to cover the soffit with drywall, then the only fire blocking I can think that is needed is something every 10' of the run. For that, you can build up around HVAC (or what ever is inside the soffit) with 2x4s or 3/4" plywood, then use a fire block foam or caulk between the lumber and the "stuff" inside the soffit.

The only other place I can think you would need fire block is between the floor joist (there's your vertical to horizonal transistion), and again, 2x4 lumber between floor joist against the hanging 2x4s.


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## Bob Mariani (Dec 1, 2008)

> The only other place I can think you would need fire block is between the floor joist (there's your vertical to horizonal transistion), and again, 2x4 lumber between floor joist against the hanging 2x4s.


correct. the idea is to block any free air flow that a fire can use to rapidly spread.


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## DIYHomeTheater (Mar 22, 2010)

HooKooDooKu said:


> Haven't gotten that far yet.
> 
> First question is where exactly does it need fire blocking? There isn't a vertical to horizontal transistion in a concealed space because the main wall has a top plate and the drywall will go up to there.
> 
> ...


I asked the same question on a fire-blocking thread, and I received a response that basically implied that I needed to fire block at the top plate of the short wall. Thanks.


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## HooKooDooKu (Jan 7, 2008)

DIYHomeTheater said:


> I asked the same question on a fire-blocking thread, and I received a response that basically implied that I needed to fire block at the top plate of the short wall. Thanks.


Llike I showed... there is not top plate with my design. But the concept still holds, just block the floor joists. Guess it's time to pick up a few 2x8s on the way home today.


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## DIYHomeTheater (Mar 22, 2010)

HooKooDooKu said:


> Llike I showed... there is not top plate with my design. But the concept still holds, just block the floor joists. Guess it's time to pick up a few 2x8s on the way home today.


This is what I inferred from your earlier post that stated, "Framed a 2x4 wall against the basement wall. The top of the top plate for this wall was at a heigth...". So, I assumed that you _did _have a top plate for the short wall. By the way, my wall will be 21 feet long. Is that OK structurally?

I am trying to understand your arrangement. If you don't have a top plate on the short wall, then your 2" width of the short wall stud is supporting a 4" width of the soffit bottom framing member. That is not a perfect match. A top plate would have given greater contact area, right?

Also, I have TJI engineered I-beams for floor joists. Nailing soffit member directly to I-beams will present only a limited surface contact area because of the I-beam flange. Would a top plate in this situation not be beneficial?

A photo of your solution will be very helpful.

Thank you


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## HooKooDooKu (Jan 7, 2008)

DIYHomeTheater said:


> I am trying to understand your arrangement. If you don't have a top plate on the short wall, then your 2" width of the short wall stud is supporting a 4" width of the soffit bottom framing member. That is not a perfect match. A top plate would have given greater contact area, right?


Perhaps you've got the orientation of the 2x4 on the short wall wrong.

Keep in mind that the floor joists are perpendicular to the wall as shown in your original drawing. There is no top plate because the 2x4s of the short wall extend up into the floor joist space. The 4" face of the 2x4s are nailed to the face of the floor joists. While there isn't a top plate, there is a bottom plate. The top plate of the main wall connects to the bottom plate of the short wall with 2x4s laid flat.



As for your engineered wood, if its the classic I beam, then you can still do your 2x4 short wall just like I did, except that you will be limited to nailing at the top and bottom of the floor joist. But that's still good because that gives a long moment arm to resist the wall getting pushed sideways.



Now if your floor joist ran parallel to the wall, here's how I would frame it up.


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## DIYHomeTheater (Mar 22, 2010)

HooKooDooKu said:


> Perhaps you've got the orientation of the 2x4 on the short wall wrong.
> 
> Keep in mind that the floor joists are perpendicular to the wall as shown in your original drawing. There is no top plate because the 2x4s of the short wall extend up into the floor joist space. The 4" face of the 2x4s are nailed to the face of the floor joists. While there isn't a top plate, there is a bottom plate. The top plate of the main wall connects to the bottom plate of the short wall with 2x4s laid flat.
> 
> ...


HooKooDooKu:
Your pictures are so similar to mine that for a long time I thought that you hadn't changed a thing. But, on examining more closely, I realized that you had indeed changed them. Now it makes a lot more sense. Thank you for your input! Greatly appreciated!


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## HooKooDooKu (Jan 7, 2008)

DIYHomeTheater said:


> HooKooDooKu:
> Your pictures are so similar to mine that for a long time I thought that you hadn't changed a thing. But, on examining more closely, I realized that you had indeed changed them. Now it makes a lot more sense. Thank you for your input! Greatly appreciated!


Like I said, your first picture was oh so close to what I described. 

The only difference was that by attaching to the full height of the floor joist, the stud offers much more resistance to twisting from the push it's going to get from the main wall.

Now if the distance between the two walls was only about 6" and/or the short wall was only about 6" tall, then I would have just done it the way you showed. But my short wall is almost 2 feet away from the main wall, and is a little taller that 1 foot (from bottom of floor joist to bottom of short wall) that I wanted more resistance to the short wall.


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