Admittedly, a completely non-Firebird topic, but I thought I'd run it by the knowledgebase here- we're building a house with a basement, here in Silicon Valley. (a relatively new concept for the west coast, but, given the cost of land, the only way to get more space is to go up or down - or both) We have a choice between doing the basement foundation with cinder blocks or solid cement. We are leaning toward cinder blocks because of the significant cost savings. But we are not sure if we are compromising quality or longevity. Our soil sample showed no water tables under the land, but we're worried that cinder blocks could shift or crack over time (particularly with our little earthquake problem here), and ultimately lead to leaks that would make us regret going for the lower cost. I know there are quite a few basements to the east of us, and that many FGFers work in the building industry... Any advice or comments would be greatly appreciated.
Are you sure you want a basement in quake country? I would have to agree with Jim. A solid concrete wall with re-bar would hold up better given you're on shaky ground. Expense would be the last of the worries since the rest of the house sits atop these walls.
Well, it won't be hollow cinder blocks- they'll be filled with cement and a bunch of rebar, so it's all up to code, which is pretty stringent here. Most modern single family homes will survive the "big one" when it comes. However, point taken- even if the blocks are up to code, why not take the extra strength. Not to sound cheap, but, while I don't have a quote on the solid foundation yet, I've heard guesstimates that it could cost over $30k more.
Well, it won't be hollow cinder blocks- they'll be filled with cement and a bunch of rebar, so it's all up to code, which is pretty stringent here. Most modern single family homes will survive the "big one" when it comes. However, point taken- even if the blocks are up to code, why not take the extra strength. Not to sound cheap, but, while I don't have a quote on the solid foundation yet, I've heard guesstimates that it could cost over $30k more.
WOW That's a crazy price difference. Unless the square footage is super big..... I've seen quite a few poured walls being used around here and they can't be that much more or they simply wouldn't do it.
When I did a house in Kirkland (Seattle area, also quake area), we were told by the engineer to go solid concrete walls (but its also on a steep slope, 2 story one side ,three on opposite), they were 10" thk with rebers...a conc. blk wall "might" also hold up, BUT I`d say to check with a local structural engineer...
we build these also in Austin area ,Texas, also with solid concrete , no quake zone ,but slopes...
I forgot to mention our third option- foam block forms: also like cinder blocks, but made of foam, so after you stack them and fill them with cement and rebar, the foam acts as additional insulation. Apparantly this has really caught on on the East coast. I saw this being used for a new house in a very pricey neighborhood here.
Its a flat lot, dry soil, far enough from the bay that ocean water is not a factor. But, close enough to the fault lines that we will be shaken, if not stirred.
maybe for a flat lot its ok with blocks...esp since your engineer blessed both...in Sweden we do basically only the block version ,or did when I lived there.... frost line is at 6'+_ so they dig basement down to that...footoers ,then a 4 " slab over it...8' conc blk walls, with 'leave outs for windows, water proofing on outside , a french drain outside the footer, crushed rock abv drain ,then back fill....stripping with 2x 2 or 2x4 or 2x6s on iside for insulation to fit (dep on thkness you want ,R factor)and ease of running electrical...the styrofoam block walls have a problem with that ,unless you strip that too, which you would with solid concrete...
your conc blocks would be hollow ,right? with rebars ,then filled w concrete?
if structural engineer blessed both ,I`d go with the $30,000 less version ,you can spend that on furnishings oR another F/B!
I forgot to mention our third option- foam block forms: also like cinder blocks, but made of foam, so after you stack them and fill them with cement and rebar, the foam acts as additional insulation. Apparantly this has really caught on on the East coast. I saw this being used for a new house in a very pricey neighborhood here.
I`ve seen that in pics from the east coast too...if you have a builder with experience in doing it ,its ok, but dont pay for someone to get experience and get his knowledge on YOUR house!
sell the place and move to the country where you can build a larger house for 1/4 the price.the taxes in ca are horrible and real estate prices are too there,like south florida.
400 plus- will the tar be flexible enough to keep water out if the cinder blocks shift or crack? ( I don't expect a lot of water to be around tho- and no snow or frost. BTW, what you described is exactly what the plans call for....
Tommy- any reason for concrete- is it really worthh the extra $30k?
Terry- yeah, that day will probably happen eventually, but not yet.... I still haven't found a place out in the country where I can find decent sushi...... (kidding)
Concrete. I've been involved for the past few years working in a house in Occidental with a full poured basement. On a rock, in the redwoods, in quake zone. I'd be happy to put you in touch with them to learn why they went with concrete.
Vikki 1969 Goldenrod Yellow / black 400 convertible numbers matching
Concrete. I've been involved for the past few years working in a house in Occidental with a full poured basement. On a rock, in the redwoods, in quake zone. I'd be happy to put you in touch with them to learn why they went with concrete.
I did my basement 10 years ago with the foam block walls and am very pleased with the result. Assembling the foam blocks for my basement was like building with Lego and was done in well under a day and that was my first time. Rebar is easy to install during the assembly. The foam also helps slow the curing time of the concrete, giving the wall more strength than with plywood forms. It was especially important for my basement as we poured the walls in February! The foam kept the walls warm as they cured. My basement is cool in summer, warm in winter.
Putting in the electrical is very easy as well, just use a utility knife to cut a slot in the foam for the wire and box, stuff in the wire, use the quick foam to seal it in, then drywall directly over top, no strapping needed or drilling holes through studs and feeding wire.
Make sure you figure in the labour saved to get to a finished wall, no strapping of 2x4s for the drywall (the drywall screws go directly into plastic tabs), no extra insulation inside or out, and I used a sheet "tar" product around the outside for waterproofing that sticks directly to the foam. No water problems whatsoever! It ended up being about the same price as standard concrete walls for me because I decided on 9 foot ceilings for my basement. Obviously prices will vary!
If you decide to do this, PM me and I'll give you a more detailed description and pictures of the process and what to look for in foam blocks.
The block will not shift if the bar is pour into the footer and extended into the core holes. Grouted solid.If your footings slide your poured wall will slide. Yes the tar is flexible enough. But then again Im a bricklayer and have laid a few basements. Still 30k is a lot of money left on the table. .02
I wouldnt tell Banshee (just him for instance, not specifically ,just as a comparison) anything about engine building, but being an architect that works in Texas, Colorado, California (lake Tahoe) and Seattle area....I think I know some about construction....of course my experience is only 40 years or so...
water proofing can be done several ways ,no matter which type of construction you use...and I`d say go with conc. blocks if your structural engineer blesses it...but make sure any structure is water proofed! all concrete will contain moisture...keep it and mildew out... please listen to your structural enginer, thats his job and if he`s registered in California he sure knows earthquake structures!
The wing wall in the garage area is for sheltered stairs that go directly from the garage down to the basement. I did it this way because eventually exterior stair well drains get clogged with leaves and heavy rain floods the basement. Our neighbors had five inches of rain in their basement in 1993 during Hurricane Emily because they had an outside stair well. Exterior stair wells also turn green with mold.
I put a drain tile system around the exterior of the footers and also around the interior of the footers. They gravity drain to daylight.
This house has the driest basement of any house I've ever owned. Concrete is the way to go.
I still say , listen to the structural engineer , this is his baby....I wouldnt ask my fellow architects about building an engine...I`d listen to an engine builder for that...if the engineer is California refgistered (which he obviously is if he works there), he`s taken test on the quake structures as part of his registration ,and VERY PROBABLY done a few structures before...not just a few.....
if he says blocks will work ,they do...they will work like a conc wall since they are reinforced,..and if any cracking occurs , it will be cracking along the joints (not always), rather than irregular cracking...its not the concrete that holds the wall up, its the reinforcing...
just like freeways and house slabs around Houston ,where we have very expansive (and then shrinking) soil, no concrete holds up to that, maybe 25 yrs,but after "bending" back and forth for 20-30 yrs it cracks....but the reinforcing holds it together...
my std comment to home owners here is : there are two kinds of concrete slabs , the ones that are cracked and the ones that will crack!
That's why I love this site!! I told my wife- let me ask the FGFers- any group of people who can argue passionately for 8 pages about original tires are going to have a lot of opinions about this. I still haven't decided, but this info does help, so thanks to all (but no need to stop- keep it coming!!) I am particularly interested in the reasons why the concrete advocates are advocating it- is it more for structural strength or for waterproofing?
Bjorn, thanks very much for your input, and rest assured, experience does count! I will weigh all input based on that, and I greatly appreciate your experience and advice.
I have to admit, just from a layman's perspective, I've rarely seen concrete that didn't have some kind of crack somewhere, so perhaps my worries about cracking are moot, if both structures are prone to it, and the earthquakes are bound to come eventually. Sounds like I just have to be sure the exterior tar is done properly. I should reiterate that the ground here is very dry, with no snow, so I don't think the surrounding earth is going to get saturated with moisture. In terms of structural strength- yes, the architect, structural engineer, and builder have all blessed the cinder block design, and the city is just about to issue the building permit. And yes, the codes in California are very strict- I believe every new structure has to be designed to withstand, if I recall, an 8.0 or greater quake. Just some additional questions- should the rebar be forged or cast, and should I use 4 bolt mains when I attach the framing? ;-)
good , you`re taking it all in... re cracking , yes you`ll see spiderweb size cracks esp in dryer climates ,they actually come very early ,those are shrinkage cracks and are of no importance....you usually get those in dryer climates when you cant keep it moist enough during curing...thise are the size you could barely slip a dollar bill in..."real cracks" are 1/8 " or larger...
moisture proofing ,you`ll need anyway ,even if its dry...b/c once in awhile you`ll get rains etc, and it wont all evaporate..and re rebar, those will be specified also in the structural engineers drawings/details/notes...every quake anchor , every nail pattern etc is decrsibed...not to worry, and you have inspectors making sure the drawings are being folloed...
I started doing foundations 30 yrs ago, both block and poured. Poured a floor today. There is no comparison between block and poured. I am going to pour a foundation next month for my new home.........
Go with concrete. It's faster than block. I had mine poured here in the northast 24 yards for my footings and 120 yards for my walls. They were done in 2 days vs. keeping tabs on a crew of masons to show and finish the job on time. Also, walls are more true when poured.
Think about it, concrete is solid and has no seams/joints as it is poured all at the same time. Block, ok so you have a seam/crack every 10" in height and one every 18" in length. So concrete MIGHT crack some day, block will have cracks from day one. Go with concrete, tar the outside and use Dry-Loc on the inside and you will never be sorry. Go with block and you will one day wish you had gone with poured concrete. All of this is based on my contracting experience, homeowner experience and what I have seen over the years. So all in all this is JMO. Good luck!
Rick and 6Bigbird: thanks very much for the input and pic, but, why is it better?
I was actually forced into the decision to pour my basement walls. My original plans called for 12" block with wire enforcement strips set in the joints every few courses. I had six foot of "unbalance fill" and the longest span was around 19-20 foot before a corner offered extra strength.
I had a contract with a newish builder for time, materials and 15% markup on subcontracted work. I explained to the contractor that all elevations related to the existing rough driveway existing at that end of the house. He decided that elevation numbers on the site drawing mattered most, despite specific discussion only three days earlier. I don't know exactly how he decided where 490 foot above sea leval was without the ocean nearby. We didn't have GPS in our trucks back then. I left for work after meeting with them at 7AM, thinking the job was finally started.
I drove up during lunch time to see the roof of the loader below final grade .
That vertical board is an eight foot long 2x4 standing on end placed for sighting excavation depth. Keep in mind, the plans called for the first floor to be 18" to 24" above final grade with an eight foot basement.
I was really ticked off. And the contractor was not on site for this very critical part of the build. You can't tell the excavator to "put it back" because you can't build on fill dirt. I instructed the excavator to bring the bottom of the hole true and level and don't remove any extra material in the process. The heck of it is, he had questioned the contractor about the foundation depth early that morning and he had spent the last two hours grinding up his loader treads and bucket fighting rock. He was ticked off too, because he was tearing up his equipment, not making progress and he was loosing money while destroying his gear. If there hadn't been fractured rock, he might have continued digging to China. He thought he had to go two more feet!
The next week, the footers were completed. Except it took more like three weeks. Now we were getting into really nasty weather for setting block. When the footers were finally complete, I instructed the contractor to have four inches of stone brought inside the foundation perimeter and leveled out with a bobcat. I didn't want to pay for labor to wheel barrow 1800 square feet by 4" thick of gravel base into the basement. Meanwhile, I looked into building codes. My basement walls now had to be ten foot tall just to get the house elevation correct relative to final grade. Otherwise my front door would be at grade and my garage floor would be two foot below grade! Golly, I don't think this contractor had a clue.
Anyone ever see a foundation this deep? Maybe at the world trade center. That is a full size loader, not a bobcat in the background. I don't know what these guys thought they were building.
I visited the job just after Christmas 93 and there was no gravels in the basement, despite my specific instructions just the week before. I had told the builder under no uncetain terms that no block foundation construction was to begin until the gravels were delivered and leveled out by the bobcat. When I got there at 7AM on December 26th, there was numerous skids of block dropped in the hole and the block truck was still offloading. Over Christmas break, I had studied the building codes because I was skeptical about nearly nine foot of fill against 12" block. I learned that with tis much unapposed fill, block required pillasters with full concrete core fill and rebar. It would require a civil engineer's certification and stamp that the design was adequate. I paid the block vendor $200 to remove the block he had delivered from the hole and to cancel the order. I also paid several hundred more to the clueless mason who was already delivering materials and scaffolding to the job to rrect a block foundation wall that would fail inspection. And I paid for a $200 pile of masonry sand that vanished completely into the weather.
It was all money well spent. I fired the contractor and paided his subcontractors to go away. When it came to making him go away without a lawsuit, I noticed that his handwriting filled out all the invoice for the footer construction. He had a bad habit of going over certain letters two or three times and it really stood out. I showed this to the excavator, so the air-tight nature of my observation would get back to him. This was to be 15% time and markup on subcontracted work. He claimed this was subcontracted work, but he completed the invoice in his own hand writing. It turned out, as my excavator later explained, the footer guy could pour concrete, but he actualy couldn't read or write. He couldn't fill out his own invoice. So we told the builder if he wished to contest the contract cancellation, his handwriting on these illegally presented invoices might become a sticky topic.
I took over the project myself and I had the foundation poured in concrete. Concrete didn't require pillasters, engineering design study or certification. I back filled this foundation with absolutely no wall bracing in February. We just pushed eight plus foot of dirt back against these unbraced walls. Block couldn't do that without risk of cracking or even toppling. Around here, they erect sturdy wood braces and they push the dirt in ever so carefully. Actually, around here, they rarely use block foundation anymore at all. The major builders move the same form set up and down the street from house to house. Poured concrete foundation got my project out of deep trouble, (pun intended) because this was now February and each freeze/thaw cycle was causing dirt to cave into the hole.
There is one concrete foundation wall in the house. The concrete foundation vendor didn't understand the drawings, so he didn't build out the front porch support. I guess few had vision from looking at a front elevation with the front porch above final grade. I laid up that block myself because it was safer than having him come back. He had dragged mud up and down the street. The original builder called for footer inspection four or five times for the inspector to look at only one more length of forms installed. Inspectors were crawling up my butt, so I didn't want any more "noisy" constuction going on.
Here's my wife mixing mud for the missing wall. Yeah, she puts up with a lot from me and her most recent challenge is her participation the Firebird debacle.
Every home I have been in that had concrete block wall had a musty damp smell and higher humidity. Each had cracks running along mortar joints lengthwise and vertically. My friend who built around the same time has cracks fifteen foot long. He reinforced the wall, filled block cores, built pillasters and it still failed. Houses move season to season. My house probably rises 1/8" or 1/4" at the center between winter and summer.
This concrete foundation, after many years has two hairline cracks that don't leak. The only leak we ever had was where the plumber failed lay the well pipe penetration in a gravel bed for drainage. We fixed that ourselves after much digging and laying the drainage gravel. The basement is very dry and there is no musty odor. The basement can be finished space and it wouldn't be cold, damp or moldy because of dampness instrusion.
Why is concrete better? Because is is stronger, more damp-proof, easier to close on schedule and it can be filled against promptly without fuss. Why is it worse? It conducts heat in or out of the home rapidly, so it has to be insulated either inside or outside. I recommend doing both and I wish I had layered styrofoam on the outside the walls, but I was running over budget for some reason. It costs a bit more to pour concrete, but when you consider it makes finsishable space for expansion, it is well worth the small increment in price. I think the price difference fifteen years ago on this job was around $3-4K and that is because the thickness had to be increased due to the height.
Think about it, concrete is solid and has no seams/joints as it is poured all at the same time. Block, ok so you have a seam/crack every 10" in height and one every 18" in length. So concrete MIGHT crack some day, block will have cracks from day one. Go with concrete, tar the outside and use Dry-Loc on the inside and you will never be sorry. Go with block and you will one day wish you had gone with poured concrete. All of this is based on my contracting experience, homeowner experience and what I have seen over the years. So all in all this is JMO. Good luck!
In all fairness, both types are good , both can be bad, it all depends on the engineering of ea, and site conditions and most of all the laborers doing it...in my 40 yrs experience , I`ve seen both good and bad results of both...
apples to apples, they can have the same results, so if labor or anything else gives a $30k difference...I`d use that variation to my advantage....
either case should be moisture proofed ,,even in dry ground
The crew that did mine was very quick and fast they had new equipment and brand new 9 ft forms. They pour about 200-250 foundations a year. My walls were very true, the framers were amazed at how true they were. Ask around on who has the best reputation. Ask the concrete plants in your area who they reccommend. The one thing to think about out in California is ask about vibrating the conrete in the forms to ensure no air pockets.
The crew that did mine was very quick and fast they had new equipment and brand new 9 ft forms. They pour about 200-250 foundations a year. My walls were very true, the framers were amazed at how true they were. Ask around on who has the best reputation. Ask the concrete plants in your area who they reccommend. The one thing to think about out in California is ask about vibrating the conrete in the forms to ensure no air pockets.
vibrate is always recommended ,but not too much then you get it 'watery'....too loose
I will be an Owner/Builder, but I am using a contractor for the demolition, excavation, and basement/foundations. Well, I have some news - I just talked to the contractor, and he said the cost of concrete vs blocks would be anywhere from $0-$5,000 extra, depending on how much rebar is required. So, it looks like the estimate of $20-$30k was way overblown, although from trusted sources. So I talked to the architect again. He says both are equal in his opinion, so why spend $5k if you don't have to. He said there is no advantage when the "big one" hits. However, he said he will talk to the strucural engineer and get his opinion. So for now, I will wait for the final bid, and the structural engineers input, and decide from there. If its no extra cost I think I'll go with concrete. Thanks to everyone for your input, particularly 68Bigbird for that detailed response and Vikki for your referrals . Man!! Somebody tell me it gets easier after this- this should ba a piece of cake, right....?...?....
LOL, it's just the tip of the iceberg. I'm a MI licensed general contractor too. The general contractor role would not be so bad except for...insurance, contracts, subcontractors showing up, loss on supplies, major screwups, minor screwups, weather, over budget, over time, scheduling conflicts, inspectors, what you thought you contracted for (visualized as code plus, top quality) and what your subs think you contracted for (minimum cost and effort possible)...and oh yeah, cash flow.
Last edited by Yellowbird; 08/02/0711:50 PM.
Vikki 1969 Goldenrod Yellow / black 400 convertible numbers matching
I will be an Owner/Builder, but I am using a contractor for the demolition, excavation, and basement/foundations.
So I talked to the architect again. He says both are equal in his opinion, so why spend $5k if you don't have to. He said there is no advantage when the "big one" hits.
A recession is the best time for an "owner builder". But you need to be very careful to not loose money to bankrupt suppliers or contractors. I was one of the last few to receive my kitchen appliances and cabinets when there was $10,000 in jeopardy. My friend at work a month later was sweating bullets. Those following him lost their 2/3 deposit.
Meanwhile, there were some really decent contractors who didn't normally frame houses (they framed six to eight unit townhomes) who came out and did an awesome job framing my home because they were hungry. They were a family operation and they cranked out quality work and kept the work site tidy.
The trouble is that later, only 1/4 of those quoting work were capable of doing the job. It's sometimes difficult to tell the difference between a salesperson and capable contractors. Visiting work in progress is a very important step. I visited homes that wood flooring contractors gave as references. The home owner was astonished at my visit because they had never authorized their project as an example. Soon they were leading me through their home pointing to defects in sanding. I visited work in progress where half the second story of the house was standing on two studs and the job appeared abandoned. There were inch diameter rust rings surrounded all the framing nails. Their complete home had a couple inch bow in the rear wall. Another under construction lacked ties at the trusses and it was spreading apart because nothing tied the top of the second floor walls together.
We are now in a major housing recession. The broader recession will hit us next year. Folks in the auto industry are already feeling the pain as are the builders. You need to be very sure your subcontractors are solvent and will complete their work... at least that they complete work they are paid for. You also need to be absolutely certain that these contractors pay for materials they have delivered because if they leave materials unpaid, there will be a lien against your home. That's the hard facts and you need to be very careful. You are better off paying for time and providing the materials. Then you can send folks packing if they don't perform and at least know the materials are paid up.
I sort of agree with your architect. I think they are both equal because they will both will collapse in the big shake. I wouldn't build with a basement in South Florida and I wouldn't build a basement in earthquake zone either. Both pose design issues that are best case senario to civil engineers. The problem is that California property costs so much, so if you want some space, you have to build multiple levels. That is at odds with having a basement. If I required a basement, I would pour eight inch concrete and keep as much as possible above the ground.
I almost think you would be better off with a wooden foundation below grade because flexible strength is what allows structures to survive the shake. You're also faced with what the inspectors are used to seeing, and that will make a big difference for smooth sailing on your project. If they see something out of the ordinary, the get worried about their scope and their knowledge. That means if they have never seen a wooden foundation or styrofoam block that's filled with pumped concrete, you're in for a battle regardless of the suitability. Both are most satisfactory methods, btw. They (inspectors) start citing codes they don't really understand and start asserting the authority that they have to disrupt your progress. A p/o'ed inspector can cost you tens of thousands without reason or consequence to him. Tread really carefully here. Always ask in advance what he wants to see. Here, the inspector wanted to see purple primer on plastic pipe. He wanted visible view of the perimeter drains too. The excavator was ticked off because the sides of the hole had covered the pipe. When I told him I would come out and dig it up, he returned to dig it up and pass inspection that had turned into an arguement.
I had inspectors here demand doubled joists because there was a pipe penetration running through the center inch of a 2x12 mid span. That part of the joist was not relevant to strength. He had no clue about where holes effected joist strength and where they didn't. His notion was also not supported by code. It was easier to add a double the 2x12 than to argue because if you start a debate, that sets the tone for everything that follows.
Installing that worthless double 2x12 will fall on your own list as general contractor, because the carpenters followed code. That means it's a new contract or an add-on. It won't interest them so it's going to cost a lot. This will be harder than you think. We nearly crushed an aluminum ladder putting this 18 footer in when it fell. Now it's on your list, so pay up or do it yourself. That fell on my own list as general contractor and my brother helped put the redundent and useless joist in. It was much easier and cheaper than launching a debate with the inspector, but it didn't benefit the home in any way.
As general contractor, I hope you have come to understand there are tons of "punch list" items that only fall on your own list. You won't be able to contract out these short list items because the cost will be too high with general contractors for numerous small items. There is no way to estimate and bid this long list of small but numerous items. I think Vikki knows what I'm talking about here. I think she's been down this road. You'll need decent tools, knowledge that surpasses your subcontractors, time and the patience to get through this. I've been through this... and it was worth it the first time through as a life experience. I wouldn't do it again unless I was very set on what I wanted for a home.
I also took courses in brick laying, carpentry and construction. That followed rehab of an older home where I learned a lot by trial and error. My wife and I also snooped around various construction projects for a year, sometimes visiting every weekend as construction progressed.
The carpenters were amazed when they asked what to do about a header for the garage windows where there was no space for code headers above the windows. I told them to put it inside the band board. They knew this was acceptable to code, but the didn't know I grasped the concept. That single demand change the relationship from "geek" building a home" to someone who knew his stuff. The same thing happened when the brick layers saw me do a respectable job laying up block across the porch. Really, this experience helped me to understand leading vs following too. If you can't do every task, you'll have a hard time leading the project.
I wouldn't do it again. Every penney you think you saved.. you earned. If this is your dream home and you're particular, get up to speed on every process. If not, move on and buy something completed.
Build to suit is not a bargain. It's all about getting exactly what you want.
sort of agree with your architect. I think they are both equal because they will both will collapse in the big shake. I wouldn't build with a basement in South Florida and I wouldn't build a basement in earthquake zone either. Both pose design issues that are best case senario to civil engineers. The problem is that California property costs so much, so if you want some space, you have to build multiple levels. That is at odds with having a basement. If I required a basement, I would pour eight inch concrete and keep as much as possible above the ground.
I totally agree, but You probably knew that before...as far as the 8" concrete , I`d go 10" though..(thickness)
re the question for being your own GC, you`ll save money BUT you`ll (as most owner/GC`s) will spend lots more time than a GC you hire...because of the experience in scheduling things...in my estimate ,you`ll spend at least 50-75% extra time for that...
my friend who moved to Seattle and I designed 2 houses for up there (he did his first owner/GC job as my neighbor here in Houston) is taking A LOT of of extra time...of course he can afford it, retired after selling a businness, but one extra thing is ,as an owner you also tend to think more about items to install, change your mind on finishes etc ,and delay the job...a GC is just going to follow the drwgs and finish schedule and or your list...you will, possibly with 'help' from the wife, keep thinking and changing...thats just my experience with some of my owner/GC`s, even guys that started out to be GC`s themselves for other customers ,or spec homes...you put a lot more of yourself into it ,(and if its a spec, you shouldnt build it as yours, its for sale, not your case, but its just how "people" will do)
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