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# Floor slope

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 SteelPE (Structural) (OP) 22 Mar 10 12:25
 I am looking for a provision in a building code (IBC) that would indicate the minimum slope required for a garage floor.  Does such a provision exist?
 JAE (Structural) 22 Mar 10 13:00
 No minimum provision that I know of.  If you are trying to ensure that water drains, usually a 1/2% slope is sort of a civil engineer's minimum...they usually prefer 1% but "rain doesn't stand on a level surface" either.
 woodman88 (Structural) 22 Mar 10 13:42
 The minimum per IBC is in Section 406.1.3 "...The area of floor used for parking of automobiles or other vehicles shall be sloped to facilitate the movement of liquids to a drain or toward the main vehicle entry doorway....". The problem is that there is no easy definition (per the code) of what facilitate means in regard to slope. I will go along with JAE answer. Garth Dreger PEAZ Phoenix area
 SLTA (Structural) 22 Mar 10 13:45
 From the IRC, R309.4:  "The area of floor used for parking of automobiles or other vehicles shall be sloped to facilitate the movement of liquids to a drain or toward the main vehicle entry doorway."Agrees with what JAE said.
 SteelPE (Structural) (OP) 22 Mar 10 14:09
 Thanks guys, I had already found this provision but I was looking for an actual number.  The problem that I have is that there is no code provision that requires you to use the 0.5%.  If the architect or owner wants to use a different number, there are no requirements to dispute said number.
 BAretired (Structural) 22 Mar 10 14:29
 It is not a code requirement, but 1/8" per foot is a minimum slope that I have seen specified.  That would be close to 1.0%.  Anything flatter than that is liable to disappear if you have expansive clay underlying the slab. BA
 Ron (Structural) 22 Mar 10 14:51
 Agree with BA...1/8" per foot is minimum slope required to cause drainage.
 SteelPE (Structural) (OP) 22 Mar 10 15:01
 Thanks for the help guys.  However, I am looking for a code reference.  If there is no code reference (other than saying that it must pitch to a drain of the OH door) then that is an acceptable answer.  I just want to make sure there is no reference.
 steellion (Structural) 22 Mar 10 15:15
 SteelPE, it's not written in mandatory language, but ACI 362 recommends a minimum of 1.5% slope in any direction, with 2% being preferred for garages.
 Ron (Structural) 22 Mar 10 15:19
 SteelPE...I did a key word search through the 2006 IBC using several different key words (garage floor, floor slope, slope to drain, 1/8" per foot, 1/8" in 12") and came up dry on each.  As JAE originally noted...not in there!A 0.5% slope also as JAE noted, is pretty much the bare minimum (for pavements).  A 1/8" per foot is about 1% and will cause positive drainage; although not adequate for critical drainage such as a roof.It doesn't appear that you have a section to reference, just a general consensus that it should be in that 0.5 to 1 percent range at least.
 paddingtongreen (Structural) 22 Mar 10 21:13
 What is the required flatness of the floor surface. From that you can find the minimum practical to avoid puddles. Other than that, I agree on 1/8" in 12". Michael.Timing has a lot to do with the outcome of a rain dance.
 Ron (Structural) 22 Mar 10 21:43
 I don't know that anything greater than 1% is really workable.  For a typical 20' garage length, at 1% you have a 2-1/2" grade change.  A 2% slope would give a 5" grade change...likely not workable.  Would increase the cost of a typical 2000 square foot home by about $5000 for fill and compaction.  rowingengineer (Structural) 22 Mar 10 22:40  Ron,Your maths sounds off, because if you didn't grade the fill and just used extra concrete, you would get (20'x20'x (5/12)'/2 )*.333^3(6mx6mx.125m/2)= 3 cubyard (or 2.25cubm)which is about$2000 Max, probably more like $800 on a good day given. Someone please check my maths this whole feet to yard to inches thing has me in a spin. Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that they like it  Teguci (Structural) 23 Mar 10 9:59  Code says the floor has to be sloped (not designed but constructed). Given placed concrete tolerances, anything less than 1/8" per foot can come back to the architect when the contractor builds it dead flat or with occasional puddles. If the Architect wants higher construction tolerances he will need to note that and the owner will have to pay.  paddingtongreen (Structural) 23 Mar 10 10:11  Where I come from, the slope has to be shown on the drawing, and therefore, is part of the design. The Contractor won't slope the floor unless the drawing tells him to. Michael.Timing has a lot to do with the outcome of a rain dance.  Teguci (Structural) 23 Mar 10 10:44  To rephrase, if the drawings call for less than a 1/8" per foot slope without a specified higher construction tolerance, the resulting puddles, in my opinion, are owned by the Architect.  SteelPE (Structural) (OP) 23 Mar 10 12:00  In this particular instance the architect does not show anything on the drawings other that the floor must slope in this direction. The code has no direction on how much slope is to be provided. It seems like nobody wants to take responsibility for this number.  paddingtongreen (Structural) 23 Mar 10 12:09  As I said earlier, you must look at the flatness tolerance for the floor and slope it so that even the low points can slope toward the drain. Michael.Timing has a lot to do with the outcome of a rain dance.  BAretired (Structural) 23 Mar 10 13:18 #### Quote: The code has no direction on how much slope is to be provided. It seems like nobody wants to take responsibility for this number. The code has no direction on how far apart the floors should be either. Some decisions are left up to the designer. BA  Ron (Structural) 23 Mar 10 16:57  RE...you're right...left out a conversion factor. Mea Culpa  rowingengineer (Structural) 23 Mar 10 17:42  No problems Ron, had to make sure because I put a slope in all my garages, normally 1:200 (this way it can be converted to a room in the future if the need arises with minimal$). Don't know what that is in inches per foot, but I have never had a complaint about extra moneys.   Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that they like it
 BAretired (Structural) 23 Mar 10 18:02
 1:200 is very close to 1/16" per foot.    BA

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