Update 12/5/15 - the foundation issue has been fixed for all lots in the 12/4/15 patch.
Sims cannot route up lowest foundation setting (one notch up from ground level) without stairs in certain areas on specific lots. It was confirmed by SimGuruHouts (via Twitter) that it is intended for sims to be able to route up these low level foundations without stairs. Lot specifics below:
Oasis Springs
- Arid Ridge - left side of lot does not route
- Granada Place - okay
- Sultry Springside - right and upper middle of lot does not route
- Rio Verde -entire lot does not route
- Yuma Heights - okay
- Affluista Mansion - all but bottom right portion of lot does not route
- Slipshod Mesquite - okay
- Sandtrap Flat - okay
- Nookstone - all but upper left portion of lot does not route
- Pebble Burrow - entire lot does not route
- Agave Abode - entire lot does not route
- Cacti Casa - left side of lot does not route
- Dusty Turf - left side of lot does not route
- Raffia Quinta - okay
- Vista Quarry - upper portion of lot does not route
- Springscape - entire lot does not route
- Rattlesnake Juice - entire lot does not route
- Burners & Builders - okay
- The Solar Flare - upper left side does not route
- The Futures Past - entire lot does not route
Magnolia Promenade:
- JF&S Clothiers - entire lot
- Paddywack's Emporium - entire lot
- Preeminent Domain - bottom 3/4 of lot
- The Roadstead - entire lot
Granite Falls:
- Green Getaway - upper 3/4 of lot
- Riverside Retreat - okay
- Forest Hideaway - bottom half and right side of lot
- Lakeside Retreat - okay
- Campground - entire lot
Willow Creek:
- Crick Cabana - entire lot does not route
- Streamlet Single - entire lot does not route
- Daisy Hovel - entire lot does not route
- Garden Essence - entire lot does not route
- Bargain Bend - lower left and lower right do not route
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Potters Splay - entire lot does not route
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Rindle Rose - entire lot does not route
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Pique Hearth - entire lot does not route
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Riverside Roost - okay
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Brook Bungalow - entire lot does not route
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Ophelia Villa - okay
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Hallow Slough - entire lot does not route
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Parkshore - entire lot does not route
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Umbrage Manor - entire lot does not route
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Cypress Terrace - entire lot does not route
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Oakenstead - okay
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Magnolia Blossom - entire lot does not route
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Willow Creek Archive - okay
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Movers & Shakers - okay
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The Blue Velvet - okay
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Municipal Muses - okay
Newcrest:
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Optimist's Outlook - entire lot
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Hillside Highlands - entire lot
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Civic Cliffs - upper 3/4 of lot
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Cookout Lookout - all but lower right
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Sandy Run - entire lot
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Tranquil Crescent - most of lot - bottom left, bottom right, and top right route
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Asphalt Abodes - all but right 3/4 upper
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Avarice Acres - upper 3/4 of lot
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Rippling Flats - entire lot
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Twin Oracle Point - entire lot
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Fern Park - lower half of lot plus a bit above on right
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Beech Byway - okay
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Oak Alcove - entire lot
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Comfy Cubby - right and upper middle
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Midtown Meadows - all of lot except a couple of small areas - top near left and bottom right
For images of lots, take a look at the Build Mode Feedback thread
here.