Base of wall questions...

Saint in the City

Take a look at the attachment.  I'm looking at the base of exterior wall condition on yet another project.   

Anyway, i have two questions:

1).  See the condition marked "A".   If I were to run the 2" up to the top of the slab, how should the now wider than normal joint be handled?

2.  At "B"....  was looking to use the 4" wide tall portion of the foundation wall to provide water infiltration protection at the fin. flr. elevation...  however,  I am now wondering about condensation in the insulation area below the flashing.  Any thoughts on this?


Mar 14, 14 5:42 pm

45 the top of the insulation at A

Ever tried pouring concrete in a  3 1/2" wide space with #5 rebar? 

I wouldn't worry about condensation.  You will be using pressure treated sill plate below flashing, but do remember  pressure treated wood ...LOvES TO EAT ALUMINUM ! 

It is amazing what we will go thru for a thermal break....ya screw you structural guys.....and the guys in the field building..

Mar 14, 14 6:03 pm

Set the plate onto the outside portion of the wall. Slab rests on ledge with thermal break, insulate under slab. Ta-da!

Nice vinyl mold (eeewwww) detail.

Mar 14, 14 6:27 pm

the 4" concrete section extending up on the the outside of the stem wall is weird...

You are concerned about water hitting the building wall above f.f.? how do you know it is only going to go 4" or 6" above f.f. as drawn?  Where is this mini surge of water coming from?  is it standing water?

In that detail you will also need to provide a waterproof membrane minimum at the exterior face of the could also provide a vertical drain board and french drain to be safe.

just build a normal stem and wall base and push your f.f. up 4" or 6" or whatever.

Mar 14, 14 6:43 pm
Saint in the City

Granted, this is a weird one.  I should have mentioned there are some existing conditions /  factors pushing the exploration of it.  

Chigurh -- I think you are likely right about the membrane if they went this way.  I can't get on board with that area under the flashing.   

Miles -- commercial slab on grade, hence the vinyl.  Wait a second, isn't what you're describing the same detail you suggested/posted in my last thread?    Well played.  Seriously, I think with what you're suggesting I'd still end up with the weird 2" insulation like at "A" instead of the typical 1/2" joint because the cold-formed studs are bearing, and can't hang off the concrete ledge like in your detail.  

Snook -- 4" ledges are poured all the time -- that's the least of the problems with this detail!   But have you done the 45 degree insulation / slab pour?  I've seen the detail published but never constructed.

Mar 14, 14 8:33 pm

Ok, run the slab under the wall plate and insulate bottom of slab. Now the insulation is contiguous exterior to under slab (spec high psi foam if necesary for bearing), eliminating unsupported vinyl (eeewwww) mould.

In the previous detail you'd size the wall for full bearing.

Mar 14, 14 9:11 pm
Saint in the City

In the previous detail you'd size the wall for full bearing.   

In your previously posted detail, they cantilevered the wood plate -- that's how they covered the 2" insulation.  I can't do that with 6" load bearing metal studs -- not sure how feasible it's be to go with wide enough metal studs to allow the 2" overhang...

The high psi foam idea continues to be interesting.  Have you ever done it that way?  

Mar 14, 14 9:58 pm

With plate on slab you get full bearing. You can eliminate the ledge, too. Hold the wall in the insulation thickness for a cleaner exterior detail. Need extra long anchors.

Some of the rigid foams are 100 psi. I've looked at it but never had the need.

Mar 15, 14 10:23 am
Saint in the City

Miles  --  So, is one version of what you're saying:  taking the above detail and simply moving the slab to bear on the lower foundation wall ledge -- with insulation under it -- and stud wall fully on slab directly above...?

Because that sounds very intriguing, you magnificent bastard...   

The c.i. would actually be c.i.

The bearing on the 100 psi foam would definitely raise my engineers' eyebrows -- if they couldn't on board with that part, I'm wondering if I could substitute one of the R5 sill thermal breaks, which -- I think -- are about 1/2" think and have even higher compression than the 100psi.

Another consideration might be a potiental shear / cracking potential on the slab near the inside face of the stud wall...?

The slab would need to be poured out of the normal construction sequence as well.  





Mar 15, 14 2:18 pm

Eliminate the ledge, let the sheathing and exterior insulation lap over the foundation wall, covering the sub-slab insulation / thermal break.

What's the live load? Office, warehouse, D9 maintenance? Engineer the slab accordingly, provide interior piers with the same detail for bearing and point loads as required to assure consistent settling. Spec well-compacted sand on (tested) good undisturbed soil.

Normal construction sequence is what's necessary to build your design. You need two pours anyway, so what difference does it make when they are?

As far as sequence goes, your detail 'B' with sheathing and insulation between the concrete wall and the frame wall is not going to happen. You'd have to build it backwards - insulation, sheathing, then framing, or maybe slide the sheathing and insulation into a gap between the concrete and the studs? This detail is a very good reason to eliminate the ledge.

you magnificent bastard

I was hoping you'd catch on eventually.

Mar 15, 14 4:56 pm
Saint in the City

Oh, so close.

Office on industrial site.  

Existing soil is crap.  Newer fill down to ten feet, not compacted well.  Met with Geo and structural engineers.  Considered many solutions, and priced each.  If you deal with this situation a lot, you won't be surprised to learn that we are excavated all junk fill out down to native, and then will engineer upward in layers...  this allows us to then build conventionally.  So no piers or engineered slab.

I'll be sketching a bit more on this and then may post again.

Mar 15, 14 5:49 pm

I'm having a lot of difficulty in understanding the detail. Where are you located? In my neck of the woods, our frost depth is 4', and we don't provide a thermal break that large, ever. 1" should suffice, plus you could always insulate the perimeter of slab with rigid, go 1'-2'. Why would you want to deal with tack strips, or adhesives on rigid with flooring, or perhaps someday they expose the slab, and now they're stuck with poly iso? Are they forming that 4" stem as part of the foundation, or will it be another pour? How perfect do you expect the for m work to be, it would almost certainly be a bit wavy, right? Don't use a rigid material, spray in place foam, that way the sequencing issue is not n issue. Why batt? Spray the stud cavity. Kills two birds.

Mar 15, 14 9:19 pm

These details make zero sense to me, and there's a reason we're all confused about them. 

Is the stem necessary, or is it there b/c you think you need it to keep water out? Why are you moving your foundation insulation to the inside face?  Do you have any precedents for these?

Mar 16, 14 12:44 am

Inside face I've seen and done. The thing I don't like about outside face, it's the finish grade, and the water flowing down the wall wearing at the grade at the base of the wall. I've seen it happen before; a Perkins + Will designed addition to a school, and all around the perimeter of the building had the insulation poking up through the grade.

I really hate the stem.

Mar 16, 14 8:04 am
Saint in the City

Thanks for the comments....

I'm almost hearing some angst about the posted detail -- I appreciate all the comments --  it's definitely not a  final solution, it's a pause point to consider problems.  I'm trying to integrate some aesthetics demands, some energy efficiencies, and basic water management.

I'm trying to connect an unbroken path of insulation without putting insulation on the exterior for this building.

bowling -- outside face is not an uncommon precedent -- I had another thread about it.

Beta -- we've had stems poured with excellent aesthetic results -- but your input about spray foam is a much better idea.  The 2" thermal break --I hear you.  I was hoping to overhang the studs, but they are load bearing metal, so I'd have to go to even larger than 6" studs.  I'm trying to figure out what would provide a proper thermal break there without becoming  flooring attachment issue. 

Mar 16, 14 11:00 am

Outsolation is essentially default for any project I've ever worked on, where possible - I wasn't suggesting there's no precedent, quite the opposite.  My question is about why you'd outsolate the superstructure, but then bring the insulating plane to the inside face of foundation, rather than maintaining the same plane on the exterior of the building.  Just maintain that plane, wherever it is, and be done with it. 

Mar 16, 14 11:57 am
Saint in the City

Chigurh --  "You are concerned about water hitting the building wall above f.f.? how do you know it is only going to go 4" or 6" above f.f. as drawn?  Where is this mini surge of water coming from?  is it standing water?"

No mini surge, but I am always concerned about water at the wall-to-foundation wall juncture.  What's typically done is what you are essentially suggesting,  where you have maybe 4 to 6 inches of foundation wall exposed before the skin and wall begin -- and a caulk joint under the drip edge.   If that gap is maintained, then there is no problem.  Unfortunately that's not often the case -- maintenance workers regularly adjust grades, pile up ground cover, etc.    Caulk fails.  And, exterior doors often contribute a potential problem as grade is ramped up to fin floor. 

I just got through watching snow melting and pouring into one of our school additions along the type of joint you're recommending.    

Mar 16, 14 12:11 pm
Saint in the City

Bowling -- gotcha, my misunderstanding.  On my other thread about cover boards, we discussed the outsulation, which, I think is the thermally superior solution.  Unfortunately, I have yet to discover the cover board solution that seems aesthetically adequate.  What do you use for cover boards?

So, you do the outsulation regularly? -- I've never done it, and I think everyone posting on my other thread would be interested in your cover board solution.  Would you mind posting a detail reflecting how you go about it?  

Mar 16, 14 12:18 pm

Outsolation is required for many of our projects - For example, there's a requirement for a project I'm on right now that says minimum R30 effective walls, with no batt or cavity allowed. I work in the great white north where the temp in summer can reach 90+ and in winter -40.  I'll try to find an example of a detail but I'm at home today, we'll see.

This shows a better version of your stem wall approach:

Mar 16, 14 3:32 pm

I understand, but it still seems like an expensive and overly complicated detail when you can just raise the f.f. or the top of stem.  I would just raise the whole stem up (not the little notch as shown) and flash over the concrete edge.  Since the stem will be exposed, I wouldn't use a waterproof membrane as previously suggested, cause its going to be ugly as an alternative, call for xypex in the stem pour.  

Mar 16, 14 9:25 pm

There's no need for a stem as long as you're okay with covering the foundation with a finish material (and damp/waterproofing appropriately, which you should be doing anyway unless you have the budget for an admixture as chigurh brings up).

Mar 16, 14 10:37 pm

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