IRC Grading Requirement

Question

IRC Grading Requirement

OSUCivlEng (Civil/Environmental)

(OP)

11 Jul 22 19:11

I am building a new covered patio (roof supported by 6x6 posts) and am concerned about the slope of the concrete slab, or rather the lack of it. I put a 4 foot level on many places on the slab and it's essentially dead on level. I am under the 2015 IRC and section R401.3 states "Impervious surfaces within 10 feet of the building foundation shall be sloped a minimum of 2 percent away from the building". The building inspector does not inspect slabs in my municipality so I'm getting no help there.

When the concrete contractor came out he claimed to not know what the code says and also say it doesn't matter because the patio is covered. I've always done it like this, blah, blah, blah. I talked to another home builder and he said he always uses 1/4" per foot (i.e. 2%) for porches, patios, driveways and even garage floors. I live in Oklahoma and we regularly receive torrential downpours with 70 mph winds, so water will blow up on the patio as it faces south. I checked my front porch and it's 1/4" per foot or very close. Obviously the contractor is not going to admit he did anything wrong.

Regardless, the code does not differentiate between impervious surfaces covered by roofs, but no walls. Anyone ever ran into this before? Thanks

EireChch (Geotechnical) · Answer 1 · 2022-07-12 05:04:13

If you didnt specify a small slope then the contractor wasnt required to build one. I dont think you are going to be able to hold a contractor to IRC 2015.

A 2% slope would be what I would want too but I dont think you can make the contractor re-do for the simple fact that you didnt say put a 2% slope on it.

(Edit- I would have a different opinion if it was the driveway to your house. But a covered patio, I think you would have needed to specify. Thats based on my interactions with builders in my own area. It is very monkey see monkey do, no initiative.)

OSUCivlEng (Civil/Environmental) · Answer 2 · 2022-07-12 15:26:57

The 2015 IRC is the adopted building code for the city I live in. If you have to regurgitate the code all over the plans, then what is the point of the code? The contractor is responsible to know the building code they are working under. I don't think the electrician, framer or HVAC installer can get out of a building code violation identified by the building inspector because the plans didn't say verbatim what the code said.

I agree with you that a lot of builders are lazy and set in their ways. They have a "I've always done it this way, so that's the right way" attitude.

TerryScan (Civil/Environmental) · Answer 3 · 2022-07-13 14:03:24

I agree that contractors SHOULD be following the building code regardless of plan.

The slab should have been sloped regardless of roof. It is not uncommon to have wind with rain/snow. There will be water on the slab that will not drain.

MotorCity (Structural) · Answer 4 · 2022-07-14 20:22:29

The contractors build what you tell them. They are not responsible for knowing the code, thats the job of the design professional and AHJ. The drawings need to comply with the code. Did the contractor have drawings that specified the required slope?

If the building inspector does not inspect slabs, then you become the "inspector". Did you tell the contractor how to slope the slab? Did you watch the contractor or ask about it during construction?

dik (Structural) · Answer 5 · 2022-07-14 20:39:58

Is there a roof over it? Might be the roof provides the slope? ponder

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

EireChch (Geotechnical) · Answer 6 · 2022-07-15 05:08:08

Im kinda somehwere between Motorcity and Terryscan.

A good reputable contractor that does regular concreting for drives etc should not the min slope. At the same time, contractors are often "I only did what you told me to do, and you didnt tell me to put a slope on it".

At the same time if its only open on one front and has a roof, I wouldnt be overly worried. It needs to be wind blown rain, blowing towards your open thats going to throw some rain it there.

Is it enough to make the contractor re do the concrete, IMO, no.

phamENG (Structural) · Answer 7 · 2022-07-18 18:15:00

If this were some reference in ACI 360...I'd say it's on you. But it's from the IRC. I disagree with MotorCity that "they are not responsible for knowing the code." The IRC was written so buildings could be built without a design professional. Many house plans have nothing but dimensions on them...and in some localities even that may be optional. But when the inspector comes out, the footing had better be the right size, the rebar in the right place, the joist size correct, the right number of nails where they need to be, etc. The prescriptive building code - whether the IRC exactly as published or as modified by the state/locality/jurisdiction - should be well known to every contractor at least to the extent that it impacts and governs the minimum requirements of their work.

Is there a warranty period for the work? If so, make sure you inform of this in writing and observe it during the warranty period. If it doesn't perform, force them to fix it. If it's not a problem, then it's not a problem. No warranty? Get them to give you one or have them re-do it if you're sufficiently concerned. But the question there is, is it worth going to court over it to fight a lien claim when you withhold payment?

SwinnyGG (Mechanical) · Answer 8 · 2022-07-18 19:10:10

Drumroll...

Did you pull a permit for this (or did the contractor) because if so, you have a path to force them to fix it.

The contractor 'not knowing what the code says' means nothing; ignorance of the code does not grant permission to violate it. If it did, every contractor in the world would claim to not know how to read and we'd just build whatever we wanted. Not so.

EireChch (Geotechnical) · Answer 9 · 2022-07-19 06:02:08

I think PhamEng has put forwards a very good approach to dealing with it

OSUCivlEng (Civil/Environmental) · Answer 10 · 2022-07-20 18:11:05

I think phamENG's solution is the best. I also appreciate the explanation of the International Residential Code (IRC). The work does include a warranty.

phamENG (Structural) · Answer 11 · 2022-07-20 22:27:18

Thanks - every once in a while I have a good idea. Might be worth it to have them agree (in writing, of course) to what will constitute a warranty claim. Just water ponding? Water ponding over X% of the slab? That sort of thing. Otherwise, they'll reject the warranty claim out of hand if you call them in 3 months.

OSUCivlEng (Civil/Environmental) · Answer 12 · 2022-09-29 18:13:36

The contractor came around and decided to replace the slab at his expense.

phamENG (Structural) · Answer 13 · 2022-09-29 19:19:44

Outstanding. What triggered the change of heart?

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