IIIB exterior walls

[barlovian]

Is foam insulation permitted in the cores of cmu at exterior walls in Type IIIb construction? Or, is combustible insulation only permitted as part of an interior or exterior finish? (Ref 2006 IBC 602.3, 2603.5)

 

[EPrice]

Re: IIIB exterior walls

I believe the answer is in 2603.5. and depends on how the insulation did under the tests listed there.

Edit to add: I don't see anything there that would limit it to exterior or interior finish. I think it could be in the cores if it meets the conditions listed.

 

[Plans Approver]

Re: IIIB exterior walls

Is foam insulation permitted in the cores of cmu at exterior walls in Type IIIb construction? Or, is combustible insulation only permitted as part of an interior or exterior finish? (Ref 2006 IBC 602.3, 2603.5)

CMU should fulfill the requirements of a thermal barrier. Maintaining the 2 hour rating depends. If it is a UL marked cmu (haven't seen one in years) then look at the listing. If it is common cmu then 721.3.2 & Table 721.3.2 should provide some guidance.

 

[TJacobs]

Re: IIIB exterior walls

What EPrice said, plus check 719.2 if loadbearing exterior wall.

 

[barlovian]

Re: IIIB exterior walls

I see that foam plastic insulation is allowed in Type II construction; 603.1 item 3 makes that quite clear. I don't see a section similar to 603.1 for Type III construction to provide exceptions to the requirement that IIIb exterior walls be non-combustible. (Code text follows)

602.2 Types I and II. Type I and II construction are those types

of construction in which the building elements listed in Table

601 are of noncombustible materials, except as permitted in

Section 603 and elsewhere in this code.

602.3 Type III. Type III construction is that type of construction

in which the exterior walls are of noncombustible materials

and the interior building elements are of any material

permitted by this code. Fire-retardant-treated wood framing

complying with Section 2303.2 shall be permitted within exterior

wall assemblies of a 2-hour rating or less.

 

[RLGA]

Re: IIIB exterior walls

See 2603.4.1.1, 2006 IBC.

 

[EPrice]

Re: IIIB exterior walls

I don't see a section similar to 603.1 for Type III construction to provide exceptions to the requirement that IIIb exterior walls be non-combustible.

Yes, it would make things more clear if there were some language in Chapter 6 that gave us the exceptions for type III as it does for types I and II, but 2603.5 if very specific in stating that it covers exterior walls of buildings of type III along with the others. 2603.5 is more specific than Chapter 6 (it deals specifically with foam insulation in exterior walls), so in accordance with the last sentence of 102.1 I think 2603.5 trumps the more general requirements in Chapter 6.