# Type 1 hood clearances



## JKJeremy

I need to install a type 1 hood in a project. it is located on the rear wall of the structure mounted to the ceiling joists and rear wall. i see section 507.9 of the mechanical code that has an exception for clearances provided that the hood is mounted to sheet metal on gypsum on NONCOMBUSTIBLE structure that extends 18 inches in all directions from the hood.  We have changed the wall studs to metal to accomodate this requirement and extended the height of the walls so that the wood ceiling joists are 18" above the top of the hood. However today the hood manufacturer informs me that they can manufacture a hood that is labeled as a zero clearance to combustibles. that being the case can i go back to using wood studs and drop my roof bearing back down 18". we would still place 5/8" type x gyp. on the walls and bottom of joists with a sheet metal panel on the walls extending beyond the hood 18" on the sides. any help at all would be appreciated as we would really like to use wood framing everywhere.


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## fatboy

Welcome to the forum JKJeremy!

Before you make any plan changes, i would ask for the actual listing on the "zero clearance" hood and check it out, and make sure the AHJ will accept it. I was just at a training a couple weeks ago where the instructor, who is very knowledgable in the IMC, stated categorically that there are no zero cleaance hoods.

EDIT: Having said that, I googled and did find an immediate hit, and claim of zero clearance. I would still proceed cautiously and make sure the AHJ will accept the listing.

Again, Welcome.


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## JKJeremy

The company manufacturing the hood is a big company that supplies probably half the hoods in the state, so I trust in his ability to provide a listed zero clearance hood. I do have a call into the AHJ to ask the question but figured i would see what i could find on here. My questions is really if a zero clearance hood is provided does this negate the requirement for noncombustible structure.


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## kilitact

If its UL listed and tested and installed in accordance with the listing, then I would say your good to go.


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## steveray

304.2 Conflicts.

Where conflicts between this code and the conditions of listing or the manufacturer's installation instructions occur, the provisions of this code shall apply.

Exception: Where a code provision is less restrictive than the conditions of the listing of the equipment or appliance or the manufacturer's installation instructions, the conditions of the listing and the manufacturer's installation instructions shall apply.

507.9 Clearances for Type I hood.

A Type I hood shall be installed with a clearance to combustibles of not less than 18 inches (457 mm).

Exception: Clearance shall not be required from gypsum wallboard attached to noncombustible structures provided that a smooth, cleanable, nonabsorbent and noncombustible material is installed between the hood and the gypsum wallboard over an area extending not less than 18 inches (457 mm) in all directions from the hood.


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## Gregg Harris

_ 0_ clearance hoods are designed with insulated air cavity


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## cda

do you want to post the manufacture's web site???

''''''  Clearance to Combustibles: Standard built in 3" rear standoff to meet NFPA 96 requirements, when installed in a wall application."""""""


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## cda

nfpa 96

2011 edition

Chapter 4 General Requirements

4.2* Clearance.

4.2.1    Where enclosures are not required, hoods, grease removal devices, exhaust fans, and ducts shall have a clearance of at least 457 mm (18 in.) to combustible material, 76 mm (3 in.) to limited-combustible material, and 0 mm (0 in.) to noncombustible material.

4.2.2    Where a hood, duct, or grease removal device is listed for clearances less than those required in 4.2.1, the listing requirements shall be permitted.

4.2.3 Clearance Reduction.

4.2.3.1    Where a clearance reduction system consisting of 0.33 mm (0.013 in.) (28 gauge) sheet metal spaced out 25 mm (1 in.) on noncombustible spacers is provided, there shall be a minimum of 229 mm (9 in.) clearance to combustible material.

4.2.3.2    Where a clearance reduction system consisting of 0.69 mm (0.027 in.) (22 gauge) sheet metal on 25 mm (1 in.) mineral wool batts or ceramic fiber blanket reinforced with wire mesh or equivalent spaced 25 mm (1 in.) on noncombustible spacers is provided, there shall be a minimum of 76 mm (3 in.) clearance to combustible material.

4.2.3.3    Zero clearance to limited-combustible materials shall be permitted where protected by metal lath and plaster, ceramic tile, quarry tile, other noncombustible materials or assembly of noncombustible materials, or materials and products that are listed for the purpose of reducing clearance.


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## klarenbeek

The IMC does not have an exception for a zero clearance hood. If you look at 507.1, certain sections are ignored if the hood is listed. 507.9 for clearance to combustibles is NOT one of them.


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## cda

2003 imc  think this is the correct section::

later version may have different wording

SEC TION 507

COMMERCIAL KITCHEN HOODS

507.1 General. Commercial kitchen exhaust hoods shall com -

ply with the requirements of this section. Hoods shall be Type I

or Type II and shall be de signed to capture and con fine cooking

vapors and residues.

Exceptions:

1. Factory-built commercial exhaust hoods which are

tested in accordance with UL 710, listed, labeled and

installed in accordance with Sec tion 304.1 shall not

be required to comply with Sec tions 507.4, 507.7,

507.11, 507.12, 507.13, 507.14 and 507.15.

507.9 Clearances for Type I hood. A Type I hood shall be installed with a clearance to combustibles of not less than 18

inches (457 mm)

Exception: Clearance shall not be required from gypsum

wallboard attached to noncombustible structures provided

that a smooth, cleanable, nonabsorbent and noncombustible

material is in stalled be tween the hood and the gypsum wallboard

over an area extending not less than 18 inches (457

mm) in all directions from the hood.


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## kilitact

Section 105 of the mechanical code provides for alternative methods and allowable/acceptable testing.


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## fatboy

As I said when I ate crow in my first reply, I would at least look at the listing for the unit. Then sort it out, hence my reply to get on board with the AHJ.


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## rgrace

When I encountered this proposed installation, I had a dozen questions. I will not go through all of them, but I will cover a few points. The testing that was used for this "listing" (or engineering judgment is more the appropriate language) was from UL 710, Sections 30, 32, 33, 34, and 35. The temperature test itself used a 67,500 BTU/hr gas griddle. One of my first questions to this was "What if I install this hood above a solid fuel burning cooking appliance?" (there is nothing that says that I cannot). I did not receive an answer to that question. The standard itself does not include testing for clearances to combustibles. An engineer (or someone instructing the engineer) selected specific tests from UL 710, and equated these tests as a method of equivalence for testing hoods for clearance to combustibles. As stated by several others in this thread, the IMC does not provide for reduced clearances to combustibles for hoods, other than what is found in Table 308.6. As an AHJ, I would not consider approving a code modification request for such clearances based on the information that has already been provided to me through designers and the manufacturer. I have seen this design proposed many times on plans, and I have informed the designers that this type of installation does not meet code requirements.


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## cda

rgrace said:
			
		

> When I encountered this proposed installation, I had a dozen questions. I will not go through all of them, but I will cover a few points. The testing that was used for this "listing" (or engineering judgment is more the appropriate language) was from UL 710, Sections 30, 32, 33, 34, and 35. The temperature test itself used a 67,500 BTU/hr gas griddle. One of my first questions to this was "What if I install this hood above a solid fuel burning cooking appliance?" (there is nothing that says that I cannot). I did not receive an answer to that question. The standard itself does not include testing for clearances to combustibles. An engineer (or someone instructing the engineer) selected specific tests from UL 710, and equated these tests as a method of equivalence for testing hoods for clearance to combustibles. As stated by several others in this thread, the IMC does not provide for reduced clearances to combustibles for hoods, other than what is found in Table 308.6. As an AHJ, I would not consider approving a code modification request for such clearances based on the information that has already been provided to me through designers and the manufacturer. I have seen this design proposed many times on plans, and I have informed the designers that this type of installation does not meet code requirements.


507.9 exception??? 2003 IMC


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## klarenbeek

cda said:
			
		

> 507.9 exception??? 2003 IMC


That exception would only apply to the drywall itself, which is considered a combustible by the IMC.  The framing behind the drywall still needs to be noncombustible.  The exception itself even states that.


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## klarenbeek

One option would be to look at the clearance reduction methods in IMC section 308. Section 308.1 specifically allows their use for kitchen exhaust equipment.


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## rgrace

cda said:
			
		

> 507.9 exception??? 2003 IMC


Is there a question hidden in there somewhere. What does the exception to 507.9 have to do with anything I just said?


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## kilitact

Clearance Reduction Methods

Clearance reduction methods have been evaluated and

tested and are listed by UL (Underwriters Laboratory).

The method of test was derived from the UL 710 test

standard.

The hood may be installed with zero clearance to

combustible materials if constructed in the following

manner.

1. One inch (2.54 cm) thick layer of insulation of Owens

Corning® Type 475, Johns Manville Type 475, IIG®

MinWool-1200® Flexible Batt, or Knauf Insulation

Type EI 475.

2. Insulation must be held securely in place. Pins that

are welded or secured with an adhesive may be used.

3. A backsplash panel must be attached to the wall

(insulated or uninsulated).

To comply with the UL listing, the cooking appliances

must be as follows:

• Maximum surface temperature is 700°F (371°C)

• Appliances are located at least 3 in. (7.62 cm) from

the rear wall

• Appliances are at least 40 in. (101.6 cm) below the

bottom front edge of the hood


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## rgrace

Interesting kilitact. I have seen that information somewhere; the manufacturer's brochure or installation instructions .....

IMC 301.4 Listed and labeled. Appliances regulated by this code shall be listed and labeled for the application in which they are installed and used. Nowhere in the scope of UL 710 does it state that the hood is tested for clearance to combustibles, someone simply decided to take certain parts of 710 and use those tests in a different mannor from which they were designed. There are people that think UL 710 is the all-encompassing standard for all grease exhaust systems. This is simply not so. There are pollution control units out there that are being tested to "parts" of the UL 710 standard as well, and claiming code compliance. These units are installed inline with the grease duct system, and have nothing to do with hood capture or containment what-so-ever. Appliance manufacturers of clothes dryer booster fans were having their product tested to UL standards that had nothing to do with the application in which they were installed and used, and marketing their products as "Clothes Dryer Booster Fans". It will not be until the 2015 IMC that the new standard for these booster fans will be recognized. It is a slippery slope that we traverse when we start approving products based solely upon an engineering judgment, and forfeit a consensus process specifically designed to ensure product safety.


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## kilitact

If UL doesn’t meet the requirements of section 105.3.2, as an approved testing agency, how do you approve alternate methods, or do you?


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## mtlogcabin

This is from the 2009 ICC "Commercial Kitchen Hood Application Guide

It is a little confusing but I think it agrees with what rgrace is saying " A UL 710 listing does equate to a reduced clearance installation" we must verify what the manufacture limits are with regards to the specific installation.

cda's post ''''''  Clearance to Combustibles: Standard built in 3" rear standoff to meet NFPA 96 requirements, when installed in a wall application.""""""" is usually what we see in the design

 While the normal operating temperatures within a Type I hood are relatively low, combustible materials exposed to elevated temperatures over long periods can eventually become susceptible to ignition from commercial cooking activities. Accordingly, the IMC requires a minimum clearance of 18 inches (457 mm) from the hood to the combustible material. Section 308 of the IMC provides methods of reducing the required clearance, and there are hoods on the market that have been tested and listed for reduced or even "zero" clearance. Installers must strictly adhere to the manufacturer's installation instructions and listings in order to achieve the reduced clearance. 



It should be noted that IMC Section 507.9 is not one of the sections listed in IMC Section 507.1 that can be exempted for listed hoods tested in accordance with UL 710. The clearances from a listed hood to combustibles would need to comply with the exception to IMC Section 507.9 or the reduced clearance requirements of IMC Section 308. The initial clearance to combustibles in IMC Table 308.6 must be 18 inches (457 mm) prior to employing the reduction method. 

The exception to IMC Section 507.9 allows gypsum board to be considered non-combustible for hood installations when attached to noncombustible structural elements. The IMC considers gypsum board to be combustible, while the IBC con-siders it to be noncombustible. The difference is that the IBC intends for gypsum board to resist a single fire event. In IMC applications, the gypsum board can be exposed to elevated temperatures on a regular basis, which will cause the gyp-sum board to deteriorate to the point that it can collapse during a fire event. Even though the gypsum board may not actually burn, it can fail to provide resistance to the spread of fire. 

Hoods can be installed with no clearance from walls constructed of gypsum 

board attached to metal studs if there is a layer of smooth, nonabsorbent and noncombustible material installed between the hood and the gypsum board. Stainless steel or ceramic tiles are typically used because of the ease of cleaning the grease deposits that inevitably accumulate on all surfaces near a commercial cooking appliance. This exception cannot be applied to grease ducts.


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## mtlogcabin

http://www.greenheck.com/media/pdf/otherinfo/ZeroClearance_other.pdf

It seems the manufacturer is incorporating NFPA 96 4.2.3.2 in the design and construction of their "zero" clearance hoods. In reality they are providing a 3 inch reduction system


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## rgrace

kilitact said:
			
		

> If UL doesn’t meet the requirements of section 105.3.2, as an approved testing agency, how do you approve alternate methods, or do you?


UL is an approved testing agency, 105.3.2 is not in question. The standard to which a product is tested is in question. Using my example of a clothes dryer booster fan; if I said that they were listed and labeled to UL 507 and UL 705, would I then be permitted to use it as an exhaust means for lint and moisture from a clothes dryer? UL 507 is an electric fan standard, and UL 705 is a power ventilator standard. These standards do not cover the use of these fans to convey lint and moisture, which is why the UL 705 standard was revised through a consensus process to include such application. We cannot simply just pick and choose elements from a standard to test a product to (such as happened with clearances to combustibles for hoods), and say that the product is now capable of doing whatever we wish it to do. I personally would not approve such a risky application, even through a modification process, not having vetted it through a thorough consensus process. I do not believe that taking certain elements from a closely related UL standard and testing a product to only those elements, and claim compliance, meets the spirit and functional intent of the code.

Additional comment where NFPA 96 has been recently referenced ... Unfortunately, NFPA 96 is not referenced in the 2009 IMC, and the only section that references this in the 2012 IMC is the exception to 507.2. One has to ask themselves why this is so. Why has there not been more approved code changes referencing, in part or in whole, this standard? On a positive side, any AHJ certainly has the opportunity to consider this standard's contents when presented with a code modification request.


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## kilitact

rgrace said:
			
		

> UL is an approved testing agency, 105.3.2 is not in question. The standard to which a product is tested is in question. Using my example of a clothes dryer booster fan; if I said that they were listed and labeled to UL 507 and UL 705, would I then be permitted to use it as an exhaust means for lint and moisture from a clothes dryer? UL 507 is an electric fan standard, and UL 705 is a power ventilator standard. These standards do not cover the use of these fans to convey lint and moisture, which is why the UL 705 standard was revised through a consensus process to include such application. We cannot simply just pick and choose elements from a standard to test a product to (such as happened with clearances to combustibles for hoods), and say that the product is now capable of doing whatever we wish it to do. I personally would not approve such a risky application, even through a modification process, not having vetted it through a thorough consensus process. I do not believe that taking certain elements from a closely related UL standard and testing a product to only those elements, and claim compliance, meets the spirit and functional intent of the code.Additional comment where NFPA 96 has been recently referenced ... Unfortunately, NFPA 96 is not referenced in the 2009 IMC, and the only section that references this in the 2012 IMC is the exception to 507.2. One has to ask themselves why this is so. Why has there not been more approved code changes referencing, in part or in whole, this standard? On a positive side, any AHJ certainly has the opportunity to consider this standard's contents when presented with a code modification request.


If UL tested to an appropiate standard for reduced clearence to combustibles, you would still want the product to be approved with a consensus? A concensus process somtimes approves items by whoever shouts the loudest, has the most money kisses the most ... etc. If its tested and listed (with the appriopate standard) by an approved agency, the code allows approval.


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## rgrace

~sigh~ one of the problems with text discussions is that often times one does not recieve what is being transmitted ~sigh~


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## kilitact

rgrace said:
			
		

> ~sigh~ one of the problems with text discussions is that often times one does not recieve what is being transmitted ~sigh~


Yes, even with face to face discussions this happens.


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## mtlogcabin

> Additional comment where NFPA 96 has been recently referenced ... Unfortunately, NFPA 96 is not referenced in the 2009 IMC


True but it is usually listed as part of the manufacturers installation instructions.

I have fought the "it meets NFPA 96" many times over the years and the only time I allow an installer to go there is if it is part of the installation instructions

It works both ways because in my area everybody wants to put a wood stove in a garage. However the manufactures installation says to follow NFPA 211. Section 12.2.4 says Solid fuel burning appliances shall not be installed in any garage.


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## fireguy

The listed hoods I have seen have a 3" spacer built on the hood at the top and at the back. The spacer and the insulation are included in the hood package.  In the past, at least 10 years ago, the 3" spacer was installed on the wall or the hood by the installer. I also supplied the insulation.   Now the spacer is built at the factory, and hood mfr supplies the insulation.

Go here for a picture of a hood with spacer built-in to the hood. ND-2 Series Hood


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