Half Basement

 
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Old 10-17-2017, 12:28 PM   #1
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Half Basement


I have a customer wanting a house built with a half basement under it due to how the lot lays. Every house I've built has just been footer with crawl space and a garage. I have an idea on how to do it based on talking to some fellow contractors in the area but want to get feedback and techniques from here as well. any help on how to dig the half basement and attach it to the footer for the other half of the house as well as keeping it a dry basement and meet codes would be great. I don't like doing things twice so i wanna learn all i can before hand!

Side note I specialize in framing and finish work and i can finish concrete pretty good. I've always poured my footers and driveways just never done a basement or half basement before. Any and all help would be appreciated!
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Old 10-17-2017, 04:21 PM   #2
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Re: Half Basement


might be time to entertain the services of an architect/engineer....or another professional that can walk you through this and meet all your local codes/ordinances.

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Old 10-17-2017, 10:23 PM   #3
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Re: Half Basement


That was another option I was considering thanks for the reply
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Old 10-18-2017, 12:42 AM   #4
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Re: Half Basement


I would sub out the walls/footer to a foundation company. And find one that can do 9 foot walls with brick pattern forms.
If you wanna finish the flat work, go for it.

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Old 10-20-2017, 03:41 AM   #5
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Re: Half Basement


Look at the last 10-20 homes built with a Half basement in your area, call the subs that poured the concrete/ laid the block for bids.

Tile to day light or a STORM sewer = no sump pump ever, saving $ till doomsday.

Consider using "formadrain" plastic form boards/tile system as a back up.

Key way in spread footing under basement exterior wall panels.

At least one egress window, and cross flow vent windows as needed.

DON'T allow HVAC and plumbing in valuable, future living spaces in basement. lazy tinners and plumbers will run duct work down below basement ceiling to save a few bucks, but destroy the future utility of the space. Consider using Wood I-beams or trusses to allow running ducts and plumbing in between floor levels.

Spend some time planning the stairway, Draw a section cut to scale to verify it will meet code clearances...

Insulated the basement with 2-3" of "blueboard" and damproof/waterproof.

Install filter fabric above & to sides of all washed rock around tiles for long term performance of drains.

DON'T backfill till floor diaphragm is installed and basement slab is poured....

10 mil poly vapour barrier under slab and crawl spaces +SOGs

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Old 10-20-2017, 04:44 AM   #6
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Re: Half Basement


Quote:
Originally Posted by Framer44 View Post
I have a customer wanting a house built with a half basement under it due to how the lot lays. Every house I've built has just been footer with crawl space and a garage. I have an idea on how to do it based on talking to some fellow contractors in the area but want to get feedback and techniques from here as well. any help on how to dig the half basement and attach it to the footer for the other half of the house as well as keeping it a dry basement and meet codes would be great. I don't like doing things twice so i wanna learn all i can before hand!

Side note I specialize in framing and finish work and i can finish concrete pretty good. I've always poured my footers and driveways just never done a basement or half basement before. Any and all help would be appreciated!
Same way you would build a house with a garage, the only difference you will bring your stem walls up and bring fill up high enough so when you pour a 4" concrete slab it would match your floor elevation of the main house. The last course of block on your stem wall would be a solid header block like in the image below, the ledge is what your slab will rest on and framing will go on top. You can add a few piers in the middle to support the slab, etc. I mean the architect will provide all the details as everything else goes and whoever is doing your slab will know how to prep everything.
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Old 10-20-2017, 05:57 AM   #7
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Re: Half Basement


If you are in termite country... you want the FFL ~18" above finished grade of the yard, an attached garage slab at FFL would provide access to the wood framing by termites etc... unobserved till too late.

the ~ 18 inches or so increase the light and air flow through the basement windows, adding further value to the basement space IMO.

Build the staircase between the house and garage, somewhat like a split foyer house plan, 2 or 3 risers up to FFL, 12-13 risers down to -9'-8" or -10' Basement Floor Level, the garage slab actually a few inches above yard grade for drainage.

For an elderly/handicapped customer a higher garage slab height would require special treatment for termite control.

Don't forget the the continuous drywall firewall between the garage and house sill plate to roof sheathing. And fire rated door of course.
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Old 10-20-2017, 07:39 AM   #8
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Re: Half Basement


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Originally Posted by Fouthgeneration View Post
If you are in termite country... you want the FFL ~18" above finished grade of the yard, an attached garage slab at FFL would provide access to the wood framing by termites etc... unobserved till too late.

the ~ 18 inches or so increase the light and air flow through the basement windows, adding further value to the basement space IMO.

Build the staircase between the house and garage, somewhat like a split foyer house plan, 2 or 3 risers up to FFL, 12-13 risers down to -9'-8" or -10' Basement Floor Level, the garage slab actually a few inches above yard grade for drainage.

For an elderly/handicapped customer a higher garage slab height would require special treatment for termite control.

Don't forget the the continuous drywall firewall between the garage and house sill plate to roof sheathing. And fire rated door of course.
If thermites are a concern, thermite shield should be used at the sill plate. Common practice and you don't need to be 18" above the grade.
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Old 10-20-2017, 05:07 PM   #9
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Re: Half Basement


Step footers with bulkheads. All basements we do are full basements, typicall 9'. Garage foundations are 4' unless we need to dig down deeper for solid ground.
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Old 10-21-2017, 11:27 AM   #10
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Re: Half Basement


I like greg24k detail except for the lack of a poly vapour barrier, are all the joints and opening sealed with the correct tape/product? And I'd install the vertical insulation on the OUTSIDE of the footings and walls to prevent a "cold" sill plate which rot over the years... Add a layer of foam or better in the Air conditioner country a layer of foil faced insulation so basement foam is plumb under the first floor sheathing More or less.

I'd recommend installing foam under and around the garage, if their is ever a chance it will be converted into a heated space or a living space.

I would avoid ever having a garage floor less then 7" lower then the FFL to reduce the flow of flammable/ toxic fumes into the home.

The exposed basement foam can be stuccoed, tinned, or sided. One can offset the sill plate( 2 x 6) over the footing up to 2 inches outward if needed.

And of course the living space is on crawl space.....

You can build stuff out of termite food in contact with damp ground, but expect to spend $ yearly to kill the bugs that do eat wood with over 12% moisture content... Are there many 100+ year old wood framed homes that are less then 18" from the ground in your county?

If you want a ground level first floor in termite land, build entirely out masonry ( and non-cellulose based insulation)
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Old 10-21-2017, 04:05 PM   #11
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Re: Half Basement


I didn't make this drawing I got it online just as an example.

Everything else, of course, it would be typical construction, 6mil plastic etc.

As garage floor elevation goes, min requirement is 4" drop below main floor level.

100+years they didn't have foam, termite shields, etc. and they haven't thought about lots of things and some houses are still built better than today
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Old 10-21-2017, 11:27 PM   #12
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Re: Half Basement


Thanks for all the insight it's very helpful!!!!

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