1 4 over 4 feet will drain but slowly much over that and front to rear on a 28 to 30 foot garage is becomes noticeable.
Minimum slope for garage floor.
Garagetips 101 offers at a nominal price a set of single car garage plans 12 x 24 consisting of 6 sheets of drawings on 11 x 17 sheet sizes with details that show how the floor slope in the type 1 garage foundation is accomplished.
At this point the garage slab is 3 8 below the main house floor.
This will add cost but if you will have a lot of snow and ice melting off the cars you might want to put a couple of drains in the middle of each bay.
1 4 a foot is a lot.
On a 20 deep garage concrete sloping toward the big door that would be 5 and 6 on a 24 deep garage.
In the winter the runoff from whatever snow is on it just pools on the floor in the garage.
I mean you can add an additional layer of material to the garage floor and slope garage floor from high to low.
Then the garage slab slopes to the big garage door maybe 2 5.
Entry to the house from the garage is at the back of the house.
Here is the citation from the international residential code irc.
We could find no reference to recommended slopes when trench drains are used in a floor.
The building code requires that a garage floor be sloped towards the door but does not specify a minimum slope.
It is usually 1 8 to 1 4 per foot.
Of course we don t have to deal with heavy snow etc.
They are available in pdf format and can be used for own project of building a garage.
The recommended slope for flat roofs is usually 1 1 8 inch per foot or 2 1 4 inch per foot according to the professional handbook of building construction published by john wiley sons new york.
Fyi having a wash machine in the garage is probably more or less exclusive to the deep south.