Walkout Basement Question 1

[jmme]

I have a question about building a house on a slope. The site slopes from north (high) to south (low). The north wall will be fully buried and the east and west walls will be fully buried on the northern side and taper to no bury on the southern side. The south wall will be fully exposed. Can a concrete foundation wall be built for the north, east and west sides and then just a typical wood wall for the south side? Thanks.

 

[SixDegrees]

I'm sure you can do that. My house is built into a hillside like that. You still need to take the downhill side down below frost line and as deep as the local building codes specify. and be sure to build a really good drainage system on the uphill side. If you're worried about out of balance earth pressures against the house (if it's narrow) you can always add a key or rib on the underside of the basement slab. Hillside houses are great!

 

[MiketheEngineer]

Done all the time. Ususally have a 2x6 wall for insulation - with the southern exposure - you will get a lot of heat gain.

 

[TDAA]

That is exactly like my house - one story built into the slope. I wish we had 2x6 walls though, more for heat retention than stopping heat gain.

Use the sun wisely. We have somewhat larger overhangs that shade the house in the summer (along with the trees), but let in direct sunlight in the winter, warming an interior brick wall. This keeps us cool in the summer, but warms the house to about 85 in the winter when the sun is out (most of the time in Colorado). When the furnace would go out, the min. temps would go down to about 60-65.

 

[oldestguy]

If in cold country add insulation around and under the slab. Makes it much more usable. Use closed cell stuff.

 

[darthsoilsguy2]

2 bucks says jmme follows up with wondering if the north wall has to have a cantilever footing.

 

[jmme]

Thanks for all the replies.

darthsoilsguy2, why would a cantilever footing be needed for the north wall? The north, east and west walls will be concrete walls with footings.

 

[darthsoilsguy2]

i guess i owe somebody $2 Hah!! It's just poking fun at a topic that has been discussed pretty extensively on this site. It's worth checking out the threads with a search of the old topics though.

 

[IceNine]

jmme:
If the north wall is long between return walls and supporting a large amount of backfill, the wood floor diaphragm may not be strong enough to support the top of the concrete wall, and you'll be better off designing the wall as a cantilever. As darth suggested, search the site for previous discussions.

 

[oldestguy]

Wood floors are, in effect, a deep beam laid, on its side, Very strong. By adding some "scabs" under the floor joists, providing horizontal resistance (at the top of the foundation)to moving in, and by securing the floor system to the end walls with plenty of anchor bolts, you should be in good shape. Remember also where there is weight on the wall, as at the supports of the floor joists and roof trusses, that also helps to keep the foundation wall in place. Where there is little structure weight on the foundation, as at those walls parallel to the floor joists and roof trusses, you don't have much resistance to the foundation moving in due to that weight effect.

 

[jmme]

oldestguy, so if I understand you correctly you are saying I should run my floor joists in a north-south direction so they bear on the north wall. My trusses will be in the east-west direction.

 

[ToadJones]

Along these lines, I never backfilled the houses I built until I couldn't stand it anymore. I at least made sure the shingles were on ...MORE WEIGHT!

 

[darthsoilsguy2]

jmme - when i designed walk-out foundations, i got the reaction loads at the top by beefing up the bridging between the 1st three or rows of joists (its been a while) that ran parallel to the wall. As well as having the appropriate Simpson Strong-tie connections to the sill plate and beefed up sill plate anchorage to wall. (Belt and suspenders - one layer of plywood ceiling nailed to the joists and bridging and butting the sill plate). Even if you ran joist north to south into the hill, you would want to give those exterior joists on the east and west sides a little help since the soil doesn't drop to grade immediately.

drinking and posting

 

[oldestguy]

Darthsoils guy got it right. I'd only run floor joists across the shortest dimension, probably from north to south, as I'd guess your case. The bracing of the east and west walls at the tops with the doubled up bridging. That can be just the same lumber size as our floor joists, with staggering for the nailing thru the joists. Belt and suspenders would be some actual scabs against the tops of the wall inside edge, in addition to anchor bolts.

One neat addition, if you can is return the full height of wall at the south at the corners, maybe 24" into the low backfill area. That is very helpful in bracing that end wall. Running the down hill wall along at 4 feet above grade also helps brace those end walls. Of course no such wall at doors. You can put your siding over those low height walls by securing wood strips in the concrete as nailers. Taper the sides of these some for anchoring into the concrete. They get nailed inside the forms at what ever spacing you wish for siding studs. You don't need real secure nailing to the forms or you have trouble removing forms.

Again,don't backfill until you have the foundation braced as in the final case, maybe after the roof is on at least. Too many a wall has been shoved in by early back filling.

I have even gone so far as to wet down the walls for a week or more after stripping forms to keep hardening of the concrete going.

 

[InDepth]

Its better just to design it as a cantilever wall and avoid soil loading on the lateral system. On top of it you can then eliminate several internal shear walls and other diaphragm issues. If you are in seismic country you'd have to deal with the soil sesimic load as well. Based on the C shape, your building will have a torsional irregularity. From a long term persepective, seperate the building design from the retaining wall so you can effectively modify the structure much easier in the future.

 

[jmme]

Thanks for all the replies. You have provided me with some great information.

 

[rittz]

We do that all the time with a preserved wood foundation . The distance between the finsh grade and the bottom of the footing must be 5 ft min depending on the code. The grade line likely slopes either uniformly from high side to walkout side or some varying slope. The footing is stepped to maintain the min depth. Max riser 2 ft min run 2 ft. In each step.