After waiting for four weeks, I finally got some drawings back from the foundation engineer – with all sorts of problems that even I can recognize.
What does “(4)-2 x 14 stringer beam” mean? Four 2×14’s?
After specifically telling them I expected 2×6 cripple walls, I end up with 10′ tall 12″ thick cement walls. We will be discussing that one in the morning.
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Replies
It does not make sense to me either - The span is just over 8' and this is a one story house. The spacing is variable between around 9' in one case to about 16' in another. They appear to be lined up with the above walls that I thought were non-load bearing.
The garage slab is a 4" slab with #4 rebar on 12" centers. That seems like a lot of steel.
seems like overkill to me but that is what you pay him for doing.
Some of the joist spans are close to 16' which seems fairly long to me, and I do expect a stick built roof. So maybe that makes more sense that I first thought.However, I have reservations about this design due to other things that I see.The worst problem is the 18" and 12" thick grade beam walls that are 9 foot tall in some places around the crawl space. My calculations show that to be about 35 extra yards of cement and a whole lot of steel where I was expecting to see 2x6 cripple walls.
Paul,
Perhaps the engineers expected backfill along those walls.
Sounds that way to me anyway .
>> The garage slab is a 4" slab with #4 rebar on 12" centers. <<
Is this slab suspended or being installed on a large depth of fill dirt? Like maybe 4 or 5'? Is the rebar 12" OC both ways? - ie: in a grid pattern?
(4) 2 x 14 does mean a 4 member built up beam.
Bet he shows a stick built roof, load bearing path down to the beam.
Unless for some reason he has floor joists running with very long spans.
Other than that he/she is just being an engineer...;-)
Edited 3/26/2007 10:04 pm by dovetail97128
I think a stringer beam is simply a girder that goes the long way down the middle of a structure. So, say a building is 26'x40' with a 40' "stringer beam" down the center. I'I'm not so sure though that this is a common term in residential construction.
re >> "(4)-2 x 14 stringer beam" mean? Four 2x14's << That is exactly what it sounds like: four 2x14s - they sell those at Lowes don't they? ;-) Normally if you needed something 14" tall it would be LVLs...
Regarding the 12" think concrete foundation wall, maybe there is some reason that the foundation can't be stepped (I think that is what you want to do) but normally the 12" thick concrete would only be required for a wall with a lot of unbalanced fill against it - like maybe 6' or 8'. It is true that 10' tall foundation wall is pretty tall and a bit out of the ordinary.
Are you sure this guy is a residential PE?
PS - do me a little favor and call it concrete. Cement is a white or gray powder that is used for making things like concrete and mortar.
Edited 3/26/2007 10:24 pm ET by Matt
The garage slab is on a lot of fill dirt, with piers going down to rock on the perimeter and one in the middle.The concrete walls do not have any unbalanced fill at all. I explained in the beginning that I was expecting 2x6 cripple walls, and he seemed to understand what I was saying at the time.The drawings show some of the piers under the grade beams as 18" in diameter and some as 12". Going down to rock, I would have expected the 12" to be more than sufficient - and that was what I was expecting.
It sounds like the garage slab is basically suspended. You didn't answer my Q if the rebar was both ways... It's a little hard to place rebar both ways in a 4" slab. Anyway though, since the slab is basically suspended, the 12" OC sounds a little heavy but not unbelievable. OTOH, we can't see your plans from here, so, for example, we don't know how large the slab is.
When you say grade beams - do you mean in the garage floor or what?
again, not being able to see the plans is a big disadvantage so whatever we say here is just speculation. Is this a full basenent - I assume it is...
Bottom line, If you think some of the stuff is overkill, see if you can talk it out with him and maybe negotiate for something that would use less material. If he feels it is not a good idea, you have no choices other than going with what he says, or getting another engineer.
BTW - normally you - the builder - would make a decision for engineered roof trusses or not before having the floor system and the rest of the house engineered. Is the roof all cut up or fairly simple? A truss salesmen can usually help you with this decision - granted he is gonna want to sell you something - but you gotta read between the lines a little, and maybe also do a takeoff of how it would be stick framed for price comparison. A seasoned builder can usually make that call after a 5 minute look at the basic house design. Then you know (and the engineer knows) if there are going to be load points going down through the house or if they are just gonna be on the perimeter based on the fact that you said it was a one story house.. This makes a big difference with regard to the way the first floor system is designed.
Edited 3/26/2007 11:26 pm ET by Matt
Fairly simple roof, big rectangle with a big front and back porch tacked on = hip roofRebar is 12" on center both ways. 22' x 33' garage slab, 24" x 12" stiffeners on roughly an 8x10 grid. I expected a 6" thick slab and less steel.grade beams are under the exerior walls of the house. They are 18" thick and 24" tall with a 12" thick concrete wall with brick exterior going from there to the bottom of the floor joists. House is on tall crawl space 5' to almost 10'. A full basement is not in the budget.There is unbalanced fill on the side of the crawl space next to the garage and I expected to see 5' high cement wall there. Just not all the rest of the way around the crawl space.Is there a more cost effective answer than 4 2x14's? Or is a LVL even more expensive?
Edited 3/26/2007 11:41 pm ET by paul42
>>Fairly simple roof, big rectangle with a big front and back porch tacked on = hip roof <<
Sound like a good candidate for a trussed roof unless you definitely want a walkup attic, and even that you could have with trusses - the attic just wouldn't be "huge". The usage of trusses is somewhat regional though. For custom homes, it is about 50/50 here in NC.
>>Rebar is 12" on center both ways. 22' x 33' garage slab, 24" x 12" stiffeners on roughly an 8x10 grid. I expected a 6" thick slab and less steel. << We would call those "stiffeners" grade beams.
Sounds like a conservative engineering job. The guy is just trying to CYA (CHA). I can tell you that there is a pretty good chance it won't fail - again not having any drawings.
>> grade beams are under the exerior walls of the house. They are 18" thick and 24" tall with a 12" thick concrete wall with brick exterior going from there to the bottom of the floor joists. House is on tall crawl space 5' to almost 10'. A full basement is not in the budget. <<
Are you saying 12" of concrete PLUS 4" of brick???? !!!!!!! or is it 8" concrete + 4" of brick?. Is it a brick veneer house all the way up to the roof eaves?
I think you are using the term grade beam differently that I would use it. To me a grade beam is a beam going through somewhere other than the edge a slab - ie in the middle of the slab. The beams are formed by digging a trench, adding rebar, and then pouring the "beams" at the same time the slab is poured - it's a monolithic pour. The grade beams being in the dirt and their purpose to bridge unstable soil or fill. When you say >> grade beams are under the exterior walls of the house. << we would call those strip footers. Or is the soil so unstable that you are actually building beams at grade between piers that are sunk into the soil below the beams until they hit something hard like rock or very firm soil?
Again, it is hard for me to understand this without the plans, seeing the site, etc, but why is the low side of the crawl 5' tall? Is there actually 5' of height drop in the width or length of the garage? Either way, we would probably build this crawl space foundation out of brick and block and yes - it would be stepped using pony walls.
>> There is unbalanced fill on the side of the crawl space next to the garage and I expected to see 5' high cement wall there. Just not all the rest of the way around the crawl space. << OK, that makes sense, and again, we would probably do a stepped foundation using framed pony walls. No doubt thought that the foundation wall between the house and garage would need to be either concrete or block.
>> Is there a more cost effective answer than 4 2x14's? Or is a LVL even more expensive? << I've never seen a 2x14, much less priced one. When I said "They sell those at Lowes, right?" it was a joke. Maybe they are readily available where you live - here it would be strictly special order. When you are building a house you never do special order unless it definitely required. Did you ask for the piers for the interior beam to be rather far apart? Above you made reference to 8' and 16' spans (I think it was) but you didn't say if those were girder spans between the piers or joist spans between between an interior girder and the exterior walls. The only compelling reason to need a four ply 14" beam is if the interior piers were rather far apart, like maybe 12', 14' or maybe 16'. Normally piers would be spaced at roughly 8' intervals and an interior beam would be 3 2x10s or maybe 3 10" LVLs. Is the soil so bad that you can only get a hard spot every 14 or 16'?
Lastly, looking at the title for your thread "pier and beam foundation question" That pretty much of insinuates a pier and curtain foundation, however then you talk about 12" thick concrete walls, which sounds more like a standard foundation with strip footers, masonry or concrete walls, on top of the strip footers, some interior piers with one or more interior beams (girders) to make the joist spans something more reasonable like < 14' and probably some pilasters where the interior beam(s) tie to the foundation and maybe a few pilasters along long walls to add rigidity. Maybe we are having a communication problem based on regional differences in use of terminology, but I suspect that that is not the problem.
I'm not gonna answer any more of your Qs until you draw and post a simple drawing of what the foundation layout looks like with a few dimensions and rough elevations on it. I could do it in 10 minutes if I knew the layout with M/S paint. It doesn't have to be to scale as long as it has a few dimensions on it. It just took me a half hour to think through and type this. This is a 2 way street. Further, I'm surprised I haven't already gotten reamed by other forum members for answering Qs based on such sketchy information as it is.
edited for spelling...
Edited 3/27/2007 2:31 am ET by Matt
Can someone please reply to me on this thread so it will be cleared out of my "New Message To Me" queue? Aparently one of the above deleted messages was to me. Thanks.
Hi Matt
Paul,
In your engineer's defense and for your edification, Texas is divided up into multiple regions depending on soil type. The insurance companies have developed these maps to define minimum standards for foundation type based on soil types. If you as a builder or engineer build or design anything less your warranty or liability insurance company will not cover the structure.
Based on your descriptions, you are building on some clay soil. Your engineer may or may not be overengineering, you can always get another opinion, but I think you will find that any engineer who has had a defective foundation claim against them will always overengineer. Some of these Texas clays can be awful. We are finishing a house with 36" beams on nearly 8' centers with a 5" slab. The 1100sf slab had 8 tons of steel and 110 yds of concrete. I sure hope it does not go anywhere.
Best of luck
Bruce
I kept thinking that there was something big this guy was leaving out - like bad soil problems...
BTW - >> The 1100sf slab had 8 tons of steel and 110 yds of concrete. I sure hope it does not go anywhere. << If it goes anywhere it will probably be DOWN - but I bet it will stay in one piece :-) So much for the floating slab concept :-)
It's suprising how many folks tend to forget the soil type issue when it comes to slabs around here. My favorite remark was a homebuyer having his house build by one the big tract companies. The day after the pour, an 1/8 crack went diagonally corner to corner across the slab. The superintendents remark was "no problem, that why we use post tension, it just pulls both sides back together again".
According to the soil test, the soil is a minor problem.
The foundation engineer and I are still working out the details and I should have some new drawings to look at later today. Until I get those, there is not much point in agonizing over it.
I think we are getting closer to what I originally expected, the major thing being cripple walls instead of 12" thick cement walls. I'm still not sure where that last came from.
The 2x14's are gone - What they get replaced with is still up in the air.
One more question for the experts. I want what some on this forum have called a "rat slab" on the floor of the crawl space. Keeping the cost down is important, so cracks will be expected and tolerated. No structural strength necessary, just something to keep the crawl space dry and mostly dust free.
In my mind, that means they scrape off the grass, put down a plastic vapor barrier, and pour a couple of inches of cheap concrete on that. In reality, what should I be asking for when I go out for bids?
The grade has about a 1 in 10 slope.
Let us know what the foundation design ends up being. I'm still pretty amazed at the size of the footers. For us, 24" wide and 10" thick would be normal for that situation. OTOH I think that (reading between the lines) your house is requiring a grade beam foundation because the non-uniform support that is being provided by the combination of rock and soil. So, it's not so much that the soil is bad, but more that the load bearing capacity (LBC) of the rock that will be supporting part of the foundation is so much different from the soil LBC that will be under other parts.
Several posts back you said >> The garage slab is on a lot of fill dirt, with piers going down to rock on the perimeter and one in the middle. << Is this the way the house foundation is to be constructed too - piers down to rock below the foundation?
Just out of curiosity, has there been some exploratory excavation (drilling?) performed or other method used to somehow identify the depth of the rock in various locations of the house footprint on the lot?
BTW - what did the eng say when you questioned him about the 2x14s other than 'OK, we won't use them'...
You might want to read through this web page: http://www.raisedfloorliving.com/footings.shtml . It has some good info on different types of foundations including terminology.
Edited 3/30/2007 7:36 am ET by Matt