KEEP
IT
SIMPLE:
FOUNDATIONS
FOR
ADDITIONS
by Stephen Coyle
Connect new to
old — without forms,,
footings,or frost
*Soil Bearing Values
Allowable
Material bearing
(tons/sq.ft.)
Massive crystalline bed rocks,(granite,gneiss,trap rock,etc.)in sound condition 1 00
Foliated rocks (bedded limestones;schist,slate)sound condition 40
Sedimentary rocks (hard shales,siltstones,sandstones,soft limestones),sound 15
condition
Hard pan;gravel,sands,exceptionally compacted 10
Gravel,sand-gravel mixtures;compact 6
Gravel,loose;coarse sand,compact 4
Coarse sand,loose;sand-gravel mixtures,loose;fine sand,compact;coarse sand,3
wet,confined
Fine sand,loose;fine sand,wet,confined 2
Stiff clay 4
Medium stiff clay 2
Soft clay 1
*Values are for general reference only.Consult engineers and local codes for
allowable values
To design a foundation,you must first determine the soil's bearing capacity at the footing level.
When underlying soils have been previously disturbed,contain expanding clays,or are filled
with organic debris such as stumps and peats you must excavate down to undisturbed or