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slabless slab

I reread a bit more of GBA article and author - the builder - said he'd never had a code issue, on several such builds. No interior load bearing walls (plenum trusses to ease air handling) and floor easily supports 40 psf live load. I'm leaning toward thinking this complies prescriptivly with the IRC.
 
I hope the insulation is closed cell, Open cell foam has a high probability of absorbing groundwater
 
bill1952 said:
I reread a bit more of GBA article and author - the builder - said he'd never had a code issue, on several such builds. No interior load bearing walls (plenum trusses to ease air handling) and floor easily supports 40 psf live load. I'm leaning toward thinking this complies prescriptivly with the IRC.
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How? "Prescriptively" means the code "prescribes" it. This system isn't addressed at all in the IRC, or the IBC. IMHO it can't comply "prescriptively." The building official has the authority to accept such a system on his/her own iniative, if he/she is willing to assume the risk.

R104.9 Approved materials and equipment. Materials,
equipment and devices approved by the building official shall
be constructed and installed in accordance with such approval.
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The Commentary, however, reminds us that we should not exercise this authority lightly:

The code is a compilation of criteria with which materials,
equipment, devices and systems must comply to
be suitable for a particular application. The building
official has a duty to evaluate such materials, equipment,
devices and systems for code compliance and,
when compliance is determined, approve the same for
use. The materials, equipment, devices and systems
must be constructed and installed in compliance with,
and all conditions and limitations considered as a
basis for, that approval. For example, the manufacturer’s
instructions and recommendations are to be followed
if the approval of the material was based even in
part on those instructions and recommendations.
The approval authority given the building official is a
significant responsibility and is a key to code compliance.
The approval process is first technical and then
administrative and must be approached as such. For
example, if data to determine code compliance are
required, such data should be in the form of test
reports or engineering analysis and not simply taken
from a sales brochure.
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If it does not meet one of the provisions explicitly allowed it is not prescriptively allowed. Then it may be acceptable if it satisfies provisions of the IBC.

With regards Section R104.9 the building official must, not optional, decide if it meets the criteria and if it does the building official is required to accept it.

What is the risk that the building official would accept? I understand that if the building official acts in accordance with his authority, which includes code compliance. he has governmental immunity. What risk does a building official have if he has governmental immunity.
 
Thus when a building official expresses concern about his liability I assume that the individual either does not know what he is talking about or that the individual is admitting that he is acting outside his authority..
 
Yankee Chronicler said:
How? "Prescriptively" means the code "prescribes" it. This system isn't addressed at all in the IRC, or the IBC. IMHO it can't comply "prescriptively." The building official has the authority to accept such a system on his/her own iniative, if he/she is willing to assume the risk.



The Commentary, however, reminds us that we should not exercise this authority lightly:
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It's a slab on ground floor. I can't find anyplace in the 2028 IRC that specifies what that slab is. Not defined and Merriam Webster says: a thick plate or slice (as of stone, wood, or bread). It supports the required loads of chapter 3. It meets or exceeds the insulation requirements. Foam is used on grade and required by IRC. Maybe not suitable where termites of any nationality are an issue but the subject is in northern Minnesota and I'm in northern NY. Termites not an issue. Moisture protection is addressed. Wood floors on ground are even addressed in the IRC.

So where in the IRC is this slab floor not allowed?
 
Mark K said:
What is the risk that the building official would accept? I understand that if the building official acts in accordance with his authority, which includes code compliance. he has governmental immunity. What risk does a building official have if he has governmental immunity.
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Personally, he is indemnified. His employer (the county or the municipality) is not indemnified and can be sued.

I've been there and done that. I was sued as the plan reviewer, the chief building official was sued, the mayor was sued, the ZEO was sued, and I think a couple of other officials were sued. The suit was NOT dismissed because of sovereign immunity or qualified immunity. Even though each of the officials were defended by the attorney provided by the town's insurer, the case went through all the steps and was ultimately heard in court. If we had lost, the town (through its insurer) would have paid the judgment.

At trial, we prevailed. All the issues had been well-documented throughout the process, so the plaintiff had no luck trying to argue that we acted arbitrarily and capriciously, and that we had denied his permit only for political reasons.

Even though I am personally indemnified, I would prefer not to open up my employer to being sued. It can still happen, but Ill do my best to head it off at the pass.
 
I've worked through permitting two of these composite wood-SoG floors. My understanding is that they are quite common in Europe, particularly in the northern regions where thermal performance is an important design element.

While the IRC does not spell out exactly how to construct these floors, the principles of construction are direct enough that I fully believe that these floors can be permitted under the IRC. We already, predominantly through the energy codes, require foam under concrete slabs. Placed WSP directly on top of this foam, the sheathing has no span and is continuously supported. Using T&G floor sheathing, double layered, the floor is rigid and joints are supported. From a risk standpoint, I think we all see termite/pests as a risk - although, that is location specific and readily mitigated. Risk of collapse or structural failure is less than that with a wood framed floor.

And beyond what I have noted, keep in mind that the IRC already includes PPT Wood Floors on Ground (2021 IRC Sec. 504).

Section R504 Pressure Preservative-Treated Wood Floors (On Ground)

R504.1 General
Pressure preservative-treated wood basement floors and floors on ground shall be designed to withstand axial forces and bending moments resulting from lateral soil pressures at the base of the exterior walls and floor live and dead loads. Floor framing shall be designed to meet joist deflection requirements in accordance with Section R301.
R504.1.1 Unbalanced Soil Loads
Unless special provision is made to resist sliding caused by unbalanced lateral soil loads, wood basement floors shall be limited to applications where the differential depth of fill on opposite exterior foundation walls is 2 feet (610 mm) or less.

R504.1.2 Construction
Joists in wood basement floors shall bear tightly against the narrow face of studs in the foundation wall or directly against a band joist that bears on the studs. Plywood subfloor shall be continuous over lapped joists or over butt joints between in-line joists. Sufficient blocking shall be provided between joists to transfer lateral forces at the base of the end walls into the floor system.

R504.1.3 Uplift and Buckling
Where required, resistance to uplift or restraint against buckling shall be provided by interior bearing walls or properly designed stub walls anchored in the supporting soil below.

R504.2 Site Preparation
The area within the foundation walls shall have all vegetation, topsoil and foreign material removed, and any fill material that is added shall be free of vegetation and foreign material. The fill shall be compacted to ensure uniform support of the pressure preservative-treated wood floor sleepers.

R504.2.1 Base
A minimum 4-inch-thick (102 mm) granular base of gravel having a maximum size of 3/4 inch (19.1 mm) or crushed stone having a maximum size of 1/2 inch (12.7 mm) shall be placed over the compacted earth.

R504.2.2 Moisture Barrier
Polyethylene sheeting of minimum 6-mil (0.15 mm) thickness shall be placed over the granular base. Joints shall be lapped 6 inches (152 mm) and left unsealed. The polyethylene membrane shall be placed over the pressure preservative-treated wood sleepers and shall not extend beneath the footing plates of the exterior walls.

R504.3 Materials
Framing materials, including sleepers, joists, blocking and plywood subflooring, shall be pressure-preservative treated and dried after treatment in accordance with AWPA U1 (Commodity Specification A, Special Requirement 4.2), and shall bear the label of an accredited agency.
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RichInKY said:
I don't know about all of this... I mean what is the POINT? To me, I would venture to guess this is a lot more costly than having a concrete slab?
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I was told that it was fairly reasonable on cost compared to a traditional concrete SoG. Time to construct was much faster; can put the slab down and frame walls same day, no concrete curing. And then there is the energy efficiency (R-20 continuous is what I saw).
 
This method is increasingly popular with those concerned about carbon intensity of building materials.
 
classicT said:
I've worked through permitting two of these composite wood-SoG floors. My understanding is that they are quite common in Europe, particularly in the northern regions where thermal performance is an important design element.

While the IRC does not spell out exactly how to construct these floors, the principles of construction are direct enough that I fully believe that these floors can be permitted under the IRC. We already, predominantly through the energy codes, require foam under concrete slabs. Placed WSP directly on top of this foam, the sheathing has no span and is continuously supported. Using T&G floor sheathing, double layered, the floor is rigid and joints are supported. From a risk standpoint, I think we all see termite/pests as a risk - although, that is location specific and readily mitigated. Risk of collapse or structural failure is less than that with a wood framed floor.

And beyond what I have noted, keep in mind that the IRC already includes PPT Wood Floors on Ground (2021 IRC Sec. 504).
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Thanks for this post. Kind of what I was thinking.
 
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