SardonicSmile's 20x30' 1/2 Cottage Home (with costs)

[SardonicSmile]

Septic yet?

Yep, septic has been done - check page 1 of this thread for pics.

[SardonicSmile]

Alright, the footings are done and we should be getting it poured tomorrow. Had to get it inspected twice because there was a soft spot. Incoming pictures!


I do have a few questions.. for reference, i'm pouring a 4" slab with a 3 block stem-wall. The top block will be L shaped to accommodate a 4" slab.  I will be back-filling with #57 gravel up to the bottom of the L block.

---What is the best way to secure my walls to the concrete? Let anchors dry in the concrete?  Will be using 6" walls. I have also heard of people using high-powered nails?

---What do I need to do to keep out moisture under the slab? Visquine sheeting on top of the gravel? Does plumbing go over or under the sheeting?

---I'm planning on having rebar sticking up from the foundation every four feet. Does this seem good enough? I'll obviously concrete fill the stem wall blocks that have rebar in them.

[devildog]

I dont have answers for any questions.sorry about that. But are you saying your going to fill 2.5 blocks high with rock? Id be afraid of settling(eventually) and a chance of alot of cracks.The way we normally do stem wall foundations is to backfill with dirt,pack it down and cover with thick plastic. I think it would be hard to pack that deep of rock. maybe a 4" layer. Maybe Im wrong,but Ive never seen it done that way
Darrell

[diyfrank]

I'm not entirely clear what you have going on here. "The top block will be L shaped to accommodate a 4" slab"

Generally you fill the inside up to grade. The top 4" usually gets sand or gravel for cap break.

The plumbing is installed and backfilled. Any thicken footings you may have are dug and 6 or 10 mil plastic on top.

[SardonicSmile]

I dont have answers for any questions.sorry about that. But are you saying your going to fill 2.5 blocks high with rock? Id be afraid of settling(eventually) and a chance of alot of cracks.The way we normally do stem wall foundations is to backfill with dirt,pack it down and cover with thick plastic. I think it would be hard to pack that deep of rock. maybe a 4" layer. Maybe Im wrong,but Ive never seen it done that way
Darrell

The concrete foundation will be lower than ground level, so the first wall block will be underground. Also, I may be doing only two blocks. Just depends on how it looks after we pour it. I agree, it would probably settle if I had 3 blocks above ground level. I'm just trying to get the foundation about 6" off the ground.

[SardonicSmile]

Here's a rough drawing of the top L-block. The foundation is backfilled up to the arrow, and then there is 4" remaining for a concrete slab. It's very common around here.

I'm not entirely clear what you have going on here. "The top block will be L shaped to accommodate a 4" slab"

Generally you fill the inside up to grade. The top 4" usually gets sand or gravel for cap break.

The plumbing is installed and backfilled. Any thicken footings you may have are dug and 6 or 10 mil plastic on top.

Anyway, here's an image of the foundation.

[diyfrank]

I see, pictures make sense.
You didn't mention insulation. Do they insulation the walls before backfilling? Where I am It's required.

[cbc58]

why do a foundation if you are building on a slab?  just curious.

[SardonicSmile]

why do a foundation if you are building on a slab?  just curious.

Well, the concrete foundation is required, and I just want to raise the house up a little. I'm building on a fairly flat area and water can become a problem on 4" slabs. Just want to be on the safe side. My uncle has a 4" slab in his garage and he has had flooding during heavy rains. My inspector advised that I do it also.

[cbc58]

i am north of you (nc) and they build on 4" slabs here all the time.... sc must be different or the soils must be different.  had you considered going up 3 more courses on the blocks/concrete and have a crawlspace with no slab..?  i look forward to seeing this system and your progress and how you do the pipes/plumbing with the slab/foundation combo.  

[SardonicSmile]

i am north of you (nc) and they build on 4" slabs here all the time.... sc must be different or the soils must be different.  had you considered going up 3 more courses on the blocks/concrete and have a crawlspace with no slab..?  i look forward to seeing this system and your progress and how you do the pipes/plumbing with the slab/foundation combo.  

The way my house is going to sit, I'll have to build up dirt all around the house to create a slope.. so it needs to be higher than 4 inches.

[SardonicSmile]

I see, pictures make sense.
You didn't mention insulation. Do they insulation the walls before backfilling? Where I am It's required.

No requirements for insulation this far south. We don't even have a frost line : )

[John Raabe]

I would also suggest getting higher is better. Almost all houses over 100 years old are sitting up high off the ground. Ground height just seems to creep up over time and many slab on grade houses are "sunk" after a few decades.

You might consider a thickened edge slab as that could be done in one pour, however if your block wall will be relatively high doing it separately will be better. The slab and foundation wall can be tied together with rebar in the block cores wired to the rebar or mesh in the slab. You will still want to place foundation bolts in the cores so they tie the foundation wall and sill plate together. Your code will have size and spacing requirements for these.

Around here we insulate slabs with a couple of inches of foam. They are usually "floated" inside the foundation walls and there is no need to notch the block wall as the slab can sit inside the standard wall.

If you are in dry soil just the crushed rock under the slab may be enough for moisture control. If you want a better barrier put down 6 mil poly or 4 mil cross-laminated poly followed by 2" of sand and then pour the slab.

[SardonicSmile]

I would also suggest getting higher is better. Almost all houses over 100 years old are sitting up high off the ground. Ground height just seems to creep up over time and many slab on grade houses are "sunk" after a few decades.

You might consider a thickened edge slab as that could be done in one pour, however if your block wall will be relatively high doing it separately will be better. The slab and foundation wall can be tied together with rebar in the block cores wired to the rebar or mesh in the slab. You will still want to place foundation bolts in the cores so they tie the foundation wall and sill plate together. Your code will have size and spacing requirements for these.

Around here we insulate slabs with a couple of inches of foam. They are usually "floated" inside the foundation walls and there is no need to notch the block wall as the slab can sit inside the standard wall.

If you are in dry soil just the crushed rock under the slab may be enough for moisture control. If you want a better barrier put down 6 mil poly or 4 mil cross-laminated poly followed by 2" of sand and then pour the slab.

We were only going to use rebar sticking up from the foundation into the first block on the stem wall (and fill it). I'm not familiar with any of the other ideas you gave.. Are they really necessary? There are no rebar code requirements pertaining to the house I'm building. I thought there would be, but I asked the inspector myself. We will be using wire mesh in the slab.

We can't do what you're suggesting with the foundation bolts (putting foundation bolts in the stem wall) because we are using those L blocks on top. Instead, we will have shorter 8" foundation bolts stuck in the actual slab.

[cbc58]

i'm just curious cause i've never seen it done that way.  if you build on the foundation walls... (the peremiter wall that you are putting in)...what's the slab for?... you don't lay any joists on the slab do you?

[SardonicSmile]

i'm just curious cause i've never seen it done that way.  if you build on the foundation walls... (the peremiter wall that you are putting in)...what's the slab for?... you don't lay any joists on the slab do you?

A slab is cheaper than a crawlspace foundation if you're not putting wood or flooring over it. I'm using the concrete with no "flooring". Just area rugs in some places.

It may not seem like it at first glance but..

Slab: $1500 for concrete, $700 for block, $100 for mesh and plastic.

Crawlspace with traditional flooring: something like $800 for wood, and then thousands for flooring.

[archimedes]

I think you're better off with a crawl space too.  For many reasons.  Not the least of which is the plumbing.  And a slab will probably end up costing more than you think and require additional help. 

[MountainDon]

I am a tad confused.   

I guess I don't understand the low block wall around the perimeter if the concrete slab is going to be the actual home floor. The block section would be more difficult to insulate than a stick built, floor to ceiling, wall.



Our homes slab foundation was poured as a monolith with the perimeter being about 12 inches wide and 18 inches deep into the ground. The infield was no less than 4 inches. The rebar in the perimeter footing is wired to vertical rebar in the footing trench and that is wired to the steel wire mesh in the slab. The minimum grade to slab top distance was about 6 inches. The land slopes slightly to one side and the front street. It took lots on concrete and good form work but after 25 years there is no apparent settling or cracking anywhere.

Unfortunately this was built in the 80's and back then there was not much perimeter insulating done on the slab. Today's homes around here have floors that are notably warmer in the winter. Heat transfer inwards in the summer is also an issue that good foundation insulation will take care of.  I would check into the best practices for concrete slabs in whatever part of the country you are in. Building science (Google is your pal) would have information on this I'm sure. No time for me to check that out right now.

[SardonicSmile]

I am a tad confused.   

I guess I don't understand the low block wall around the perimeter if the concrete slab is going to be the actual home floor. The block section would be more difficult to insulate than a stick built, floor to ceiling, wall.

So your point is that by raising the slab above ground level, It's going to be tougher to insulate? Sorry if I'm having a hard time understanding things right now, not getting enough sleep lately!

What keeps the water out if I were to have a regular 4" slab?

[ScottA]

Rasied slabs are very common around here. Usually they are 3 blocks high and filled with crushed limestone. The plumbing is installed in the fill. I see them all the time. The issue is termites and water. By raising the slab you solve both problems.

[MountainDon]

Okay, I said I was confused. I had a picture in my mind of the slab down near ground level and the perimeter 2 or 3 block high wall extending above that. That was my puzzle.

Now if I understand correctly the idea is to dig a perimeter foundation, lay in a footing and build a perimeter wall on that. Then lay a slab at the level of the top of the blocks.  That makes sense now.  That's sort of the same thing as pouring a monolith as we have, only a little higher out of the ground.

You're still going to have heat loss/gain through the slab. That's where looking up the techniques for properly insulating the slab and block wall comes in.

[SardonicSmile]

Okay, I said I was confused. I had a picture in my mind of the slab down near ground level and the perimeter 2 or 3 block high wall extending above that. That was my puzzle.

Now if I understand correctly the idea is to dig a perimeter foundation, lay in a footing and build a perimeter wall on that. Then lay a slab at the level of the top of the blocks.  That makes sense now.  That's sort of the same thing as pouring a monolith as we have, only a little higher out of the ground.

You're still going to have heat loss/gain through the slab. That's where looking up the techniques for properly insulating the slab and block wall comes in.

Yep, you got it right. But since the weather is pretty mild around here, I don't think I'll do a whole lot in the way of insulation.

By the way.. we got the foundation poured. Looks great, perfectly level because we added a little more water than usual. We have rebar hooks sticking up every 3-4 feet, about 5 inches high. This is not code either, but it was simple so why not?

Cost Update

Backhoe to dig footings: $200
8 yards of concrete for footings: $720

[archimedes]

So you're going to lay a short block wall around the perimeter, fill those blocks (with rock?) and then pour a slab on top, correct?  How many rows of block? 

[ScottA]

Normally with a raised slab 2" foam board is placed inside the block before the fill is added to help insulate the floor.

[SardonicSmile]

Normally with a raised slab 2" foam board is placed inside the block before the fill is added to help insulate the floor.

Actually, I may do this.. because it would also help with expanding/contracting concrete.

So you're going to lay a short block wall around the perimeter, fill those blocks (with rock?) and then pour a slab on top, correct?  How many rows of block?  

Yes, the slab will be level with the top block. See earlier in the thread to see the "L block" i'm using. I will most likely be using two blocks and then the L block.