Looks like paying for the same thing twice?
Complicates your HVAC too. (If the plant is
in the basement)
What do you have against a Crawl?
Obviously you want a wood floor system.

 

I don't have HVAC concerns for this location, since it shares heating from the adjacent room of the (current) house, and will have a gas fireplace. Cooling is the old-fashioned way, windows & window A/C. (this matches the rest of the house).

I initially was thinking that the subfloor might add some insulation and "feel", as well as work better for the carpet. However I didn't really give much thought to just installing carpet over concrete. I know it's got to have the moisture barrier & proper padding...

Any thoughts?
BTW, thanks for the quick reply!
~Matt

 

I know it's got to have the moisture barrier & proper padding...

Any thoughts?
BTW, thanks for the quick reply!
~Matt

6mil visqueen under the slab
takes care of that. :thumbsup:

 

Oh, and a crawl needs access. I won't have it from the outside; though I could from the existing basement. However, since this portion of the existing house is brick walls with a stone foundation, I want to leave it alone as much as possible...

~Matt

 

Curious as to why you would not just pour a slab on grade? I mean if you want no basement/crawlspace then why use a wood flooring system?

 

To me carpet directly on top of concrete always felt colder than one put on wood. I'm basing this off no real experience or data other than walking around on carpet in a finished basement. I'm guessing the thermal break created by installing the sleepers and ply floor would make the floor more comfortable to walk on, and a little softer for the little ones.

I would concerned with termites building off a slab at grade level. Too easy for the little suckers to sneak in with no telltale mud tubes to clue you in until it is too late. Is there a reason you want to build at grade??

If you don't mind me asking what room are you expanding?? You said you had no heat/cooling concerns but an additional 384sqft could make the entire area pretty chilly in the winter, even with a gas fireplace.

Barry and can't sleep tonight.

 

Thanks for the questions guys!

Let me see if I can answer them. I've included the plot plan and 3D view of the proposed addition.

If you look at hte center of the plan, you'll see a 4 room square. This was an old salt box house, that was added onto in the 40's on the back (kitchen & bathroom), then in 1980 on the front (that's now my offices), and again in the back in 2004 (By me; more kitchen, laundry room, and second floor over back 1/2 of house).

The current living room will provide the entrance to the new living space. This room already has a heater that is too big for the space, making it one of the warmest rooms in the house usually. The heater we'd be using is currently in my master bedroom (that's the 2nd floor addition over the kitchen/bath/laundry). It's way too much for that space, and I'd like to back that down to a smaller heater.

There are 2 reasons I'd like to stay "up" with my addition as much as possible. Obviously, the cost is a factor, but the 2 concerns are first the stone foundation wall of the house, and second, the sewer plumbing under this area.

First, the walls. We put in a foundation last year that tied-into an old stone foundation. It was repointed on the inside, and looked great. When the city decided that they wanted a drainage system cut in around the entire old house, we discovered that the walls wern't all that great exposed... and my client ran out of money before she could get the walls repaired on the outside. I'd like to leave my walls along. They're doing a good job with their own space; I'll support the new stuff on new stuff.

Now, that drain line. This house was a total gut job when we bought it 5 years ago. I've buried a substancial amount of rock, brick, and debris in the yard, and have had the oppertunity to figure out a lot of what's under the surface. THe story goes that this was the (or close to the) neighborhood dump years ago, so there was more broken glass and old bricks than you could count. We spent weeks power raking, scraping, and clearing the yard!

I have done a bit of digging in this area. I know it's solid and compacted, but that it won't be fun to try and carve out a foll or 1/2 basement. Also, the current kitchen/bath/laundry are all basically at grade, although the kitchen is framed, and over dirt. (nothing I added on to, that is all over crete!).
The drain line for the kitchen runs toward the back yard, where it then turn around, runs under the corner of the house, and to the front of the property to hit the street. If memory serves, it's 10' + down at that point. Honestly, this line works, and I'd rather not try and dig it up, sice I can't get under my house to follow the rest of the line (I've tried) if I were to replace it.

So, My thought was to let sleeping dogs lie whenever possible, and build anything I can as properly as possible, and in the process, try and improve what is already here, if possible.

Oh, and the subfloor over the concrete- that was just to make it more comfortable to walk on...

OK, what other cans of worms have I now opened up?

~Matt

 

I would think a crawl space is the best method and also be the most affordable and giving you the most flexability for the space if you needed to run HVAC or any lines through that area. Once you slab that footing off and build directly on top you lose all access.

I am not sure if the crawl is option ?

just a thought

 

well, a crawl pushes my foundation wall lower, and I don't want to get too low with the stone walls I'm touching, or the old sewer line... and then I've got to frame a floor with 2x10's, instead of a sleeper system, so it's more $$.

And no need for HVAC access...

Although I do like the potential of extra storage space...

~Matt

 

well, a crawl pushes my foundation wall lower, and I don't want to get too low with the stone walls I'm touching, or the old sewer line... and then I've got to frame a floor with 2x10's, instead of a sleeper system, so it's more $$.

And no need for HVAC access...

Although I do like the potential of extra storage space...

~Matt

How come it brings down your foundation wall ? Is it the difference between the 4" slab and 2x10/sill plate ? What is difference between outside grade and inside floor height. I have seen alot of problems with slabs at grade in condo's with leaking and other problems

You still have the cost of the concrete slab

A few other ideas not sure if they are an option

Have you thought about SIP floor panels. We use them for sunroom floors built on a deck frame or block foundation wall It might work for either way

There also was an issue of Fine Home Building awhile back that went over a floor over concrete. It had 1" polystrene foam and 2 layers of 1/2 plywood over the concrete basement floor

 

Hey Bayn,

For the foundation walls, I was referring to the footer level. If there is a crawlspace, I've got to get below that level, so we'll be digging more.
Inside elevation is about 12" above outside elevation.

If I were to do a crawlspace, I'd want it to have at least a rat slab poured, which might be 2" thick... so the cost of 4" finished isn't much, especially sine it's work we can comfortably do. The time-frame is close, the cost of 6 yards of crete is less than $600 delivered. Depending on the height of your crawlspace, you're either digging out a lot of soil, or you're framing with PT, so those costs are variable.

I still like the simplicity of leaving the existing alone as much as possible. Footer @ 36", footer block to grade, pour a slab, frame the walls, and stick a roof on it. Nice and simple.

However, anyone who knows me, knows that I appreciate opposing ideas, and advice!
(So if you think I'm wacked, tell me!)

~Matt

PS, good reference in your tag line...

 

Hey Bayn,

For the foundation walls, I was referring to the footer level. If there is a crawlspace, I've got to get below that level, so we'll be digging more.
Inside elevation is about 12" above outside elevation.

If I were to do a crawlspace, I'd want it to have at least a rat slab poured, which might be 2" thick... so the cost of 4" finished isn't much, especially sine it's work we can comfortably do. The time-frame is close, the cost of 6 yards of crete is less than $600 delivered. Depending on the height of your crawlspace, you're either digging out a lot of soil, or you're framing with PT, so those costs are variable.

I still like the simplicity of leaving the existing alone as much as possible. Footer @ 36", footer block to grade, pour a slab, frame the walls, and stick a roof on it. Nice and simple.

However, anyone who knows me, knows that I appreciate opposing ideas, and advice!
(So if you think I'm wacked, tell me!)

~Matt

PS, good reference in your tag line...

Yeah I think cost for the excavating and the extra slab in the crawl would be more than your slab/footing combo idea
Sometimes if you are elevated a little more with your finish height there is not alot dirt to be moved. But in your scenario it would be a couple of feet to be removed for the crawl. I think as long as your slab is elevated off the ground level you will be golden. Here in Michigan i have seen alot of problems with condo's and not much of a difference between slab interior floor height and the exterior grade height

Thank you for the nice comments on the web site
Likewise, :notworthy I have learned alot from you and all the deck guys here

Good Luck with your addition!

 

BTW, AW- Beautiful decks in your website portfolio!

I can appreciate the mix of brick with composite decking...

~Matt

 

I wonder what DOW would have to say about using SIS instead of sleepers, PolySyrene and sheathing. I'd think it would be cheaper.

If your crete was nice and flat you could probably loose lay the SIS on the concrete w/o fasteners.

The SIS would also serve as a vapor barrier.

Just a thought.

 

SIS?


~Matt

 

SIS?


~Matt

Web site http://www.structuralsystems.com/sis.html

 

Sorry, I hate it when people do that too...

structural insulated sheathing

 

Thanks guys... I've been schooled.

~Matt

 

Matt, You need to dig a portion of the new addition at least 45 degrees to the depth of the existing basement. In order to not have unbalanced fill your addtion is going to require a stepped footing. If you were going out 8ft it would be pointless not to dig the whole thing. Your 16ft is more than certainly more but since you need to dig a part of it mind as well just do the crawl space.

 

Hey Tom,

Perhaps I'm missing something, so please bear with me as I mumble thru this...
I'm not understanding why there would be an issue of unbalanced fill? The ground will be 8" below the top of the foundation (this is the current elevation of grade). So the fill inside and outside of the addition walls will be at basically the same height. The footer block will be 8's, which are sufficient for this application & single story building...

The front and back walls are bearing, as well as the center points of the side walls (away from the house, and up against the house). At the center of the 24' run, where we'll be along side the house I will be digging down to the level of the main house's footer, and building a pier up to grade, so that the weight of the roof's ridge doesn't push down, and push in on the existing basement.

At the front of the house, where our new footer wall will be in line with the front of the house, I couldn't see anything pushing. However, I could see this being a concern at the back wall, where it appears that our new wall is in the center of the existing house. However, this is closely lined up with the back wall of the origional foundation, as the back 1/2 of the house is on slab & mystery methods of 100 years ago...

I guess what I'm saying is that everywhere where we could "push" in on the old foundation... we've either put a pier to cary the load straight down, or we're backed on the other side of the existing wall with a wall.

Thanks for your comments, and your advice- what am I missing here?
~Matt

 

Im not sure if Im missing something either. I dont know what your calling front and back ? It sounds like the front and back butting up to the existing and the center is just a floor support? If your new foundation butts up to an existing basement then the new foundation needs to be stepped. The adjoining earth where the new addition is going is considered disturbed. The earth has a force pushing in on the basement so if you build over it your adding more weight and force.

 

More Details

Tom,

Thanks for your patience and insight.

It's a quick sketch, but maybe it'll help clear things up.

The front, back, and single side walls of the addition are approx. 36" tall (block on crete).

There is a center support location of the left side (#3), against the existing house. This will serve to reinforce the existing foundation, and the new ceiling's ridge beam.

Are you suggesting that the footers (#1 and #2) must be stepped, or that there should be a footer along the entire outside of the old foundation, creating a step in the inside-of-addition, therefore prompting the idea of a crawlspace?

Let me know your thoughts,
~Matt

 

You're new foundation (1&2)
must "step down" to the level
of the existing foundation.
Generally one wouldn't want
to lay a slab over the old
back fill, so you would also
"step" the grade up from the
existing foundation until you're
out of the old back fill and replace
with gravel or stone.

 

Yea Matt--- Neo may have explained what I was saying better. It could be argued that backfill from eighty years is "disturbed" but there is still the lateral load issue.

 

gotcha. Thanks guys. I'll adjust the plans, and go from there!

~Matt

 

Matt,
I'm not one to go running to an
engineer for every little thing, but......
If you know a local one who
has at least one foot on the ground,
and keeps his head in a position where the
sun does shine,
you might run this detail past him.
That whole stone basement foundation
thing gives me the willys.
At the least you're gonna want to
brace the basement wall during back fill.

 

Thanks for the thoughts Neolitic.

We put together a bit of a foundation addition on a city property last winter that had many of these concerns. It was an old stone foundation, we added several block walls, most of them for at-grade slabs, some fully backfilled, some only on one side... stone walls were fallign apart... engineers and the archy were both involved, as well as the city extensivly.

We have a pretty good "feel" of what to expect- both with the project, as well as the city's inspectors.

I agree on the bracing concerns!! It's always worth it, "just in case".

Thanks for the continued feedback guys!
~Matt

 

oh, the other foundation never game along to completion (we were plannign to build the new house on it as well), due to the newbie investor's lack of funding.

It's still sitting, last I heard. I'd be interested in buying it if if her, but she'd have to take a +/- 40k loss to get out of it right now. She's still convinced she might be able to make or break even if she finishes it & sells... Many hours have been wasted talking that thru, for no result of work for my company!

Ah, well.
~Matt

 

If you are wanting to do the slab on grade, tieing in to an existing house with a basement.
My thoughts are this. Take 2 of the best ideas you end up with and go talk to your head building inspector and discuss best for your area & local codes.
You would have to put in a step footing to allow tie into your existing footing. bore holes needed for the rebar to tie into your existing footings, form footing to step up to needed footing depth for your area, 4feet, 2 feet, 1 foot, ect. pour footing, lay block to 1 foot above finished grade. (or do a mono pour, footing & slab at once).
Either or select from above.
Ground prep, do not skip tamping of soil under slab, to many problems result from this step being skipped. Use the 2 inch dow solid foam sheets for the footing walls & under your slab.
Install a perimeter drain.
Build & tie into your existing house.
Use a top quality carpet padding that is allowed for the carpet you select.
This will offer you the warmth & or comfort you want while keeping cost as a consideration.
The footing is key when having basements, crawl spaces, and slabs all connected.
Slabs on grade typically move with the soil as they should, but when having one part of your home with a basement and another part a slab, without the proper footing this will only lead to problems down the road.

You have a lot of good advice offered by others as well. Just keep in consideration any future wishes that you would have added plumbing, heating & air or at least pipes for chases prior to your pour. lol, cause it is so easy to do before that crete trucks comes backing up your drive.
Good luck & best wishes with your new project. :clap: