2 inch Rule Measured Vertically Above Concrete

[Glennman CBO]

2009 IRC, section 317.1 #5.

Has anyone required details on how this will be accomplished where they want to have their concrete porches/patios at the same elevation as their finished floors?

The way this reads, it does not appear to be enough to simply protect the wall or sheathing with a moisture impermeable barrier, or even to cover the wall framing with P.T. sheathing. The wall framing itself needs to be P.T.

We have been throwing this around for some time now. The only way we can see this happening is to have (2) P.T. bottom plates, P.T. sheathing, and something other than wood siding (unless naturally durable wood, etc) within the first 2 inches.

It seems odd that they can apparently pour the concrete against an impervious moisture barrier protecting a floor assembly such as at a rim (#7), but they still need 2" to the wall framing, sheathing, siding, 2" above the concrete slab.

Any thoughts?

 

[Yankee]

The section only covers what one would expect to find conventionally. If the intent is met (and it appears to be from what I can tell), go for it

 

[Uncle Bob]

"any thoughts?"

Yep,

First thought is; they changed 2006, R319 to 2009 R317.

Then they add " or less than 2 inches measured vertically from concrete step, porch slabs, patio slabs, and similar horizontal surfaces exposed to the weather."; without indicating a change or addition with a solid vertical line in the margin (not there in my book).

That aside; I think the wording of " having a clearance of less than 6" above the ground" was being used by some builders to insist that wood above concrete was a different than above ground; and, protected wood was not necessary; according to the wording in the code.

So, I am guessing that the 2" requirement above the concrete was a compromise; to protect the untreated wood above porches, patios, steps, etc..

Uncle Bob

 

[beach]

Use a channel drain tight to the wall, same height as the slab or floor and pour the porch against the channel drain. That leaves sort of an airgap and drain between the porch slab and sill plate. I did that at my own house nine years ago and it works perfectly..... I'm sure others may disagree!

 

[Glennman CBO]

The channel drain is actually a great idea. If it is at least 2" deep, it meets the wording of the code. The builders want to continue to have patios and porches w/ no height difference to the finish floor (as they have for years), but the new section does not allow for it unless they modify thier building methods.

Thanks beach (and others).

 

[peach]

OK.. part of the foundation shows. OR frame that area with PT lumber.

In areas that get snow, you are rarely going to see the stoop or deck at the same level as the finished floor inside (too much snow drifts against the door). See it more when someone wants column posts (with lick and stick stone) down to grade (or slab).

 

[beach]

The channel drains are about 3" deep, the narrow ones are about 1 1/2" wide. My interpretation says it meets code and it actually looks pretty good!

 

[Uncle Bob]

Sounds like a R104.10 Modification.

I believe the details of the action granting the modification should "be recorded and entered into the files of the Department of Building Safety".

Uncle Bob

 

[beach]

I don't think it needs a modification if it meets code....... there is minimum 2" vertical clearance from the bottom of the sill plate to the bottom of the channel drain, the code does not specify a hoizontal distance and, IMHO... it meets the intention of the code

 

[Uncle Bob]

Beach,

"there is minimum 2" vertical clearance from the bottom of the sill plate to the bottom of the channel drain"

If you used that reasoning; what prevents the builder from installing a channel drain below wood siding that is only 3" above the ground level? (requires 6" vertical above ground for untreated wood)

Using any of the following channel drains; they would meet your "intention of the code".

http://masco.net/web/index.php?option=com_content&task=view&id=150&Itemid=60#plasticdrain

All of these channel drains are more than 3" deep; which would meet the 6" requirement.

I can see where builders would use this; especially where only the rear side of the house is wood siding.

That is why I suggest the modification be specific to porches, decks, and steps; and be recorded and filed in the Department of Building Safety.

Uncle Bob

 

[beach]

If you used that reasoning; what prevents the builder from installing a channel drain below wood siding that is only 3" above the ground level? (requires 6" vertical above ground for untreated wood)

Most hardscapes experience more runoff than landscapes due to the lack of water absorption. [/size]]

The 2" requirement has been in the Cal code for a number of years, I have never had a contractor or homeowner want to install a channel drain in soil if that's what you're getting at. The quote is from your link, I don't think the channel drains are designed for soil installation. The intention is to keep water away from untreated wood in your example, and I think the drain would do just that, maybe even better than just a 6" clearance. Most building departments around here charge a fee for alternative methods, why charge people for something that meets the minimum code requirements?

I would think that water draining away from below the siding would be better than saturated soil sitting under it

 

[Uncle Bob]

I just see all sorts of problems with the drain channel. It is going to collect dirt and debris; and the end result will most likely be, the homeowner will get tired of keeping it clean and seeing bugs making a home in it; and they will fill it with concrete or some other product; and the intent of the code will be lost.

The code states; "measured vertically from concrete steps, porch slabs, patio slabs, and other horizontal surfaces esposed to weather".

The addition of the channel does not increase the vertical distance of the untreated wood above these horizontal surfaces.

I believe allowing the drain channel is a modification of the code requirement; and as such should be recorded and filed; in accordance with the code. Not doing so; makes the exception become a personal allowance by the Building Official.

When Architects and/or Engineers; draw up plans; all of the AHJ's ammendments and code modifications should be published for their use.

Most code changes require the builder to alter their plans in some way or another; and this is just one of those code changes.

Personally, I say just paint the wood with lead based paint.

Uncle Bob

 

[beach]

I have to respectfully disagree, the grating keeps large particles out and the rest drains with the water, I don't see any more bugs than usual. Strip drains are widely used for a number of drainage projects without the problems you describe, or the manufacturers would be out of business. It seems a little far-reaching to make your point.....

Again, this is widely used here for the past fifteen years or so and is an accepted method and in our opinion, meets the intent of the code.

Of course you can make your own interpretation......................... Like I said, I used it on my own home and I haven't any problems with bugs, dirt, debris, etc. and I haven't filled it with concrete or anything else and it's been over nine years. Just because it's new to you, doesn't mean it's wrong!

 

[Yankee]

I particularily like the idea, and I would make the grate at least 3' x 3' in order to wipe the snow off of my boots before entering my domicile : )

 

[beach]

That's a good idea, Yankee!!!!

 

[conarb]

This has always been a problem, even before accessibility. The way I handle it is to pour stem walls up where there are virtually level porches and patios, but have to be careful if there are too many because of getting adequate cross ventilation, sometimes having my tin man fabricates GSM boots to cast into the stem walls to get air circulation down there.

 

[beach]

I've seen that done, and air circulation can an issue, the strip drain is a lot easier and cleaner looking. French doors opening out onto the porch or patio was an issue along with accessibility when you have a thicker threshold......... ramped concrete looked like a wavy ocean when you have multiple openings!

 

[Francis Vineyard]

The way this reads, it does not appear to be enough to simply protect the wall or sheathing with a moisture impermeable barrier, or even to cover the wall framing with P.T. sheathing. The wall framing itself needs to be P.T.

I interpret this differently; it’s the framing on the exterior of the building; outside where exposed to the weather, and if it has a roof or similar covering to protect it from weather exposure it not need to be decay resistant wood or pressure treated.

R317.1(6) is the interior wall framing.

 

[Uncle Bob]

Beach,

Maybe this could eliminate the two inch requirement; and, the need for the mini-gutter; and it gets LEED points too.

"Drainscape™ - Pervious Concrete is also recognized by the U.S. Green Building Council’s Leadership in Energy and Environmental Design program for enabling integration of paving and drainage that allows for a smaller development footprint on land sites by reducing the amount of land needed to manage storm water."

http://www.perviousconcreteaz.com/

It's already being used for parking lots, driveways, and sidewalks.

This will probably be added to the IGCC code.

Uncle Bob

 

[jar546]

I interpret this differently; it’s the framing on the exterior of the building; outside where exposed to the weather, and if it has a roof or similar covering to protect it from weather exposure it not need to be decay resistant wood or pressure treated.R317.1(6) is the interior wall framing.

I do not agree if it is a slab being poured against the exterior wall because the framing is not "supporting" the slab.

 

[peach]

manufactured stone sucks up moisture like crazy.. the manufacturers tell you to keep it 6" above the ground and 2" above the concrete hardscapes.

there's a reason you need to look at the manufacturer's installation instructions before you approve.. as well as what the code says (which pretty much incorporates the manufacturer's installation instructions).