Logistics of building a basement garage?

[Erin]

Okay, so the acreage we're looking at has a great building spot up against the northern hill.  Protection on the north, exposure on the south, perfect orientation to have a south-facing walkout basement, with garage on one side or the other.

How is something like that engineered, though?  Since you're essentially leaving a couple of really big holes in your basement walls.
Is there a beam across the tops of the bays?  Wooden?  Steel?  Do you have to have some sort of support in the center if you want a two-car? 

I'm just having trouble picturing this, but I know people do it! 

thanks for any thoughts. 

--Erin

[glenn kangiser]

The engineers will make it easy for you -- all you do is provide the money.

It can be steel - wood, concrete and rebar.  Concrete, wood and steel posts -- wood and wood posts.  Tons of ways to do it depending on your desires and the limitations of the materials the engineer or architect are working with.  Generally the walls will be some sort of concrete construction.  There are some ways to do pressure treated wood but it is not common -especially with engineered jobs.

You would take your house plan to an engineer and tell him you wnat to put that house over a basement with doors approx. in these locations - then he would review that -- tell you what you can or can't do structurally -- adjust it to the best compromise between what you want and what he can do then stamp and approve the works and charge you a fee. 

Inspectors will then see to it that you have built according to his specs.  You will have to request all basement changes through him and likely pay more fees for the extra work.

Hope that explains a bit of it.

[Erin]

Inspectors?  Approvals? 

The only thing my county inspects in new construction is the septic system.   

And so far as the engineer goes, I want to have as much designed as possible so that s/he can more or less say, yes, this will not fall down on you while you sleep.  And charge me the minimal amount necessary. 

[glenn kangiser]

Sounds good.  Ask around for a decent fair priced engineer -- you would be dealing direct with them then.  Prices can vary a lot just for the engineer, as well as cost of method of construction.  Find a good one and make your desires as to methods and costs known to them.

[MikeT]

Let me just chime in on finding and working with engineers.  I would go with who has been doing a lot of work in a given area and who has a portfolio that you can look at.  I am fortunate in that I live in an urban area and there is no shortage of well qualified engineers.  They typically work closely with architects and often on big projects their work is part of the architect's overall bid.  So if you talk to architects, they often know who is good to work with and designs good structures. 

mt

[TheWire]

An option instead of an engineer would be to use data provided by engineered wood companies.

I did this with a set of bedrooms over a garage.  It was a 26' x 26' garage.  I used a double 2x12 microlam beam over each 9' wide garage door and 16" deep I Joists to span the entire 26'.  Its very solid.

Factors in sizing the headers over the doors would be how many stories does it need to support, how wide is the house, is the wall with the garage doors a gable wall or will the headers also need to support the roof.  The literature from the microlam companies often cover all these scenarios.

Jerry

[Erin]

The literature from the microlam companies often cover all these scenarios.

Thanks, Jerry!  That's kind of what I'm after.  We aren't using an architect and I'm considering consulting an engineer as the absolute last, possible step so I want as much planned out well before then. 

also, i ran across this link: http://www.byoh.com/basementwalkout.htm
Which shows how a walkout basement can be created.  The part that in the hill is a regular, concrete basement.  The part that's exposed is framed. (which makes perfect sense now that I see it)

[MikeT]

How much hillside are you going to have behind that concrete wall?  In my case, I was retaining 13' of hillside in a wet climate.  My basement's back wall is also a retaining wall, but it was most certainly engineered.  My engineer calculated the pressure of the soil on the back wall and based on the type of soil, designed specifications for the back, side and front walls to resist that pressure.  When I get into the office today, I will include a set of the specs he designed for me.  I am all for doing as much as you can yourself, but if you are trying to build into a slope, you have other elements in play.....

mt

[MikeT]

I cannot locate my specs for my main retaining wall, but I have
included the specs for a smaller secondary wall that is upslope from my
main basement wall.   It will, I hope, give you a sense of the type of
calculations and specifications that go into a retaining wall.  I happen
to think the stakes are high and the investment in a professional to
figure out the appropriate design standards is important.   I also included a few other pictures to provide some context....

mt

IMG]https://i257.photobucket.com/albums/hh222/teskeym/Retainingwall1.jpg[/IMG]




Here is a picture of the main wall after pouring and forms removed..


And here is a shot of where we are today...

[glenn kangiser]

Thanks for taking time to post that , Mike.

I have seen a non-engineered wall -- built pretty decent including drainage,  by one of my customers, get pushed about 30 feet --big footing and all - into the corner of a garage.  I jackhammered it out and removed the landslide.

[MikeT]

You are most welcome, Glenn.  I had a geo tech engineer (required) who did a soils study.  It was on their specs that the structural engineer designed the foundation.  Actually, on my foundation, the walls (all of them) and the floor are intentionally tied together to resist sliding (getting pushed downhill) as well as the pressures of soil creep upslope. 

A neighbor who just got a permit yesterday ended up using my soils engineer and another structural engineer because the local folks were too minimalist in terms of specs.  The original guys gave a cheaper price, but they were not nearly as thorough and thoughtful at mitigating the hazards of building on a slope. 

I am fortunate that my foundation rests on basalt.  Many of the other foundations around here are resting on sand. 

Nuf said....