House tucked in hillside --> lateral earth pressure resisted by roof trusses? 1

[TroyD]

This is a single story slab-on-grade, or patio home, tucked into a hillside. Typical 8 ft ceiling height. Gable end roof. No basement. Similar to a typical basement foundation, where the floor joists provide the lateral restraint against earth pressures, I assume the roof trusses (with blocking) can provide the same lateral restraint(?). The 2020 IRC R404.1 provides top of wall reactions for various soil types and wall heights. I assume I can start there, conservatively assume poor soils, and design blocking to distribute out to the adjacent trusses and to the perpendicular foundation walls. Full height soil along 20' wide endwall, and wrapping around one side of the dwelling, then tapering down at the garage.

Am I overlooking anything major? Any additional advice is appreciated.

 

[kissymoose]

Design the garage wall panels as vertical elements of the LFRS. Connections, sheathing, hold-downs, etc.

 

[ChorasDen]

You should be able to simply indicate the lateral thrust that the bottom chords on the truss will need to resist, and the truss designer should be able to incorporate these loads into the truss analysis software.

Edit: Just looked at your drawing, blocking will be needed on the side of the plan to resist the loads on the 20ft wall section.

 

[le99]

Unless necessary, I suggest designing the hillside wall as a cantilever retaining wall. Also, it looks like the opposite exterior wall has many openings that significantly reduce its rigidity to be considered a propped support without strengthening.

 

[Greenalleycat]

Something to consider would be what displacement of your timber-framed wall is actually required to mobilise that reaction
In principle though, yea I would use the ceiling as a prop for the top of my wall

 

[BAretired]

Am I overlooking anything major? Any additional advice is appreciated.

Whether the lateral force is taken by a floor or roof structure, it is not just the trusses which must be considered. In your case, the roof structure must be able to act as a diaphragm, a deep beam spanning horizontally, transferring the soil reaction to shear walls. Shear walls must be capable of delivering the lateral forces to the foundation and to the soil, without excessive movement. There have been cases where a residence has moved when the soil on one side has not been balanced by soil on the opposite side; the residence must be suitably anchored to the ground.

BA

 

[XR250]

I agree with le99 - design the walls as cantilevered retaining walls. You would be nuts to do it any differently. The structure is too long and narrow and the detailing would be ridiculously complicated and it would unlikely to be built properly. I have seen more than a few of these racked and bowed in my career.

 

[MotorCity]

Not sure how the house is situated on the hillside, but it would be prudent to have a geotechnical investigation to provide assurance that the hill and slope are stable, and the soil is decent to prevent the structure from sliding or tumbling down the hill.

 

[TroyD]

Thanks for the input. The mason who bid the foundation work had originally figured in some concrete "dead men" along the end wall to provide the resistance to overturning. I think I will approach this as a cantilever retaining wall, and possibly utilize several dead men too.