# Fire Separation Distance for Decks



## Glenn (May 28, 2014)

I've always had to teach this subject based on hypothetical judgement, as the IRC does not provide clear guidance about fire separation distance for decks.  For the first time in ten years in my jurisdiction, I'm faced with a proposed side-yard deck in a new development where the planning/zoning division will allow a deck over 30" to be built right to the property line.  Usually the setback is 5 feet, so I have never had to face this question other than hypothetically.

I know what the IRC says, but not what my code peers have done in real world application.

How do you handle FSD for decks?

Ground level...we're dealing with burning brands landing on the deck.  This is a very different dynamic than an upper deck that will experience fire similar to a roof projection.  Decks need their own provisions in the IRC, but they aren't there...yet...

What if the neighbor builds a deck in the same spot and they are essentially touching?  I've dealt with plenty of fires that started at the BBQ and spread to the home, so it seems a real possibility that a deck could contribute to fire spread.  "hypothetically" I've wondered about a large common deck off the back of a townhome and how/if it would be regulated for FSD.

Thanks in advance for your professional opinions and experiences.  I hope this sparks some conversation.  There was work out of San Diego in the 2015 IRC process to create specific language for deck FSD.  It was all disapproved (I spoke against), but it goes to show it is a subject that needs (and will) get addressed some day.


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## jar546 (May 28, 2014)

We are usually brought into this whenever someone goes for a zoning variance and we let them know about the FSD requirement.  That usually ends the variance quest right there.  We enforce it because that is how it reads, therefore it is real world.  We recently had a new home burn to the ground when one of those clay fire pots fell over.  The wind was just right and the house was gone in minutes.


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## Glenn (May 28, 2014)

Yes, we've had over a dozen fires from BBQ's, firepits and even a short-circuited boom-box.  There is a real issue, do doubt.  However, the IRC only speaks of "walls" and "projections".  Neither of those provisions really work well for decks.  What good is it to protect a "projection" (deck) with one hour underneath when the whole surface of the deck is where the fire origin or spreading may occur.  That method also eliminates your conventional type of deck (gapped deck boards).  The IUWIC has provisions for protecting conventional-type decks, but how do you start enforcing that code for FSD.  Perhaps as an "alternative" to one-hour underneath?

So what do you tell them when you let them know about FSD requirements.  What are your requirements?


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## Glenn (May 28, 2014)

Discussed in staff meeting today.  It was decided that when called out, we would not have an adopted code to support FSD requirements for decks.  The IRC is clear, "wall" or "projections".  Truely a deck is neither.  We are bound to our adopted code, and interpretations thereof.

This is a big hole in the IRC.  I would still love your comments and experiences on this issue, as I will likely be involved in crafting provisions to propose for the 2018 IRC.  We can't just rely on planning/zoning codes to cover this topic for us.

Thank you.


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## Francis Vineyard (May 28, 2014)

There's another debate about decks and balconies on the lot line but project from walls that are parallel to the FSD are not required to be protected.

Also an IRC committee replied to a code change proposal about requiring fire-resistance on the underside of a carport that projected into the FSD would-be ridiculous.

2009 VIRGINIA CONSTRUCTION CODE (Part I of the Virginia Uniform Statewide Building Code) – Effective March 1, 2011

Add Exception 6 to Section R302.1 to read: 6. Decks and open porches.


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## georgia plans exam (May 28, 2014)

At least for townhouses I think the question is answered in Section R302.2.1 (2012) where the rating is only required for a wall extension through and separating attached *enclosed* accessory structures. GPE


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## Chad Pasquini (May 28, 2014)

We have a project for a 2nd unit and the new entrance is at the side yard 5 feet from property line (garage conversion), they proposed a ramp as it is for their mother, we required the ramp to be constructed out of concrete due to location, but we are in California.


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## Francis Vineyard (May 29, 2014)

Additional reference search fire separation of decks interpretation No. 17-04 issued 12-29-05

How about free standing decks are they exempt?


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## Glenn (May 29, 2014)

Francis Vineyard said:
			
		

> How about free standing decks are they exempt?


That is one of the problems with using "projections" as a way to regulate decks.  The project I am faced with has a brick exterior, so the deck is being built free standing.  The presence of a beam as opposed to a ledger has no effect on how well the deck spreads fire.  Therefore if that makes a difference in one's interpretation, then I think they are well off target...

Oh decks... such a strange beast when it%2


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## zigmark (May 30, 2014)

If you felt the addition of a deck without separation from a property line created an unsafe condition you would have every right to not issue a permit IRC R102.7.1.  Given the experience and history with deck fires is this a stretch?  We may not all agree about the language needed to deal with this issue but we can certainly see the need.  I understand your reluctance to regulate something you feel is outside the scope of your adopted codes however if you truly feel this creates a potential life safety issue and ignore it the consequences are potentially much greater.

ZIG


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## BSSTG (Jun 1, 2014)

Greetings,

Just had a similar situation. Wheelchair ramp across the building line made of combustibles. I told them no and they got a variance. To follow, now the next door neighbor is complaining about the ramp up to the fence on the property line. Oh well. I would treat a deck the same.

BSSTG


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## Glenn (Jun 25, 2014)

The collective decision is that we had no provision to address this.  "one hour on the underside" if we had called it a projection, just didn't seem to make sense.


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## Pcinspector1 (Jun 25, 2014)

Glenn,

Is this a deck being build over a utility easement?

pc1


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## north star (Jun 25, 2014)

*( + )*



In lieu of there not being any specific language directly addressing FSD's,

you might consider using Section R104.11 [ from the `12 IRC  ]:

"*Alternative materials, design and methods of construction and equipment:*

The provisions of this code are not intended to prevent the  installation of any

material or to prohibit any design or method of  construction not specifically

prescribed by this code, provided that any  such alternative has been approved. 

An alternative material, design or method of construction shall be approved 

where the building official  finds that the proposed design is satisfactory and

complies with the  intent of the provisions of this code, and that the material,

method or  work offered is, for the purpose intended, at least the equivalent

of  that prescribed in this code...........Compliance with the specific  performance

-based provisions of the International Codes in lieu of  specific requirements

of this code shall also be permitted as an  alternate.*"*



Also, the BO can craft policy or policies to address the flammable &

combustible nature;  as well as, the FSD's of the decks and their locations

[  RE: Section R104.1,  `12 IRC  ].

The trick is to have an accurate review of an accurate Scope of Work

from the contractor, ...B E F O R E  anything is constructed.    

*( + )*


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## jar546 (Jun 26, 2014)

Glenn said:
			
		

> The collective decision is that we had no provision to address this.  "one hour on the underside" if we had called it a projection, just didn't seem to make sense.


I wonder what the POCO has to say about the electrical meter base and it's new location now that there is a deck in front of it, lowering the height?

Now that those windows are part of a walkway, are they being changed to safety glazing?


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## mtlogcabin (Jun 26, 2014)

It might be a stretch but here goes

2009 IRC

EXTERIOR WALL. An above-grade wall that defines the exterior boundaries of a building.......

BUILDING. Building shall mean any one- and two-family dwelling or portion thereof, including townhouses , that is used, or designed or intended to be used for human habitation, for living, sleeping, cooking or eating purposes, or any combination thereof, and shall include accessory structures thereto.

Is a deck an accessory structure to a SFR?

Do the support post define the exterior wall line?

The space between the supporting post are the just "openings" within the wall?

Table R302.1 1-hour if less than 5 feet

Unlimited openings in the "wall" 5 ft.

Do the support post on a carport define the "exterior wall" line? Why would a deck be any different?

EXTERIOR WALL. An above-grade wall that defines the exterior boundaries of a building.............Includes between-floor spandrels, peripheral edges of floors,

In reality is a deck just an exterior floor?


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## Pcinspector1 (Jun 26, 2014)

Glenn,

The reason I asked if the deck in the picture is over a utility easement, we have a 7.5 utility easement on both sides of a property line in most new subdivisions. The POCO could request a fence be removed if in an easement. If this is just a normal SE or other utility to a residential structure it would be allowed to go beneath the deck.

Zoning here would not allow that deck to be build if it is beyond the 8' PL setback here. So sometimes the building code should be enforced after the zoning code IMHO.

pc1


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## Glenn (Jun 27, 2014)

You guys are so cute...trying to catch me missing a deck violation...   



			
				Pcinspector1 said:
			
		

> Glenn,Is this a deck being build over a utility easement?
> 
> pc1


Nope.  Planning division looks at that.  They approved it.



			
				north star said:
			
		

> *( + )*
> 
> In lieu of there not being any specific language directly addressing FSD's,
> 
> ...


I love 104.11, but I can't really say this is an issue of an alternative being proposed.  We considered a policy about this, but the decision was to wait until our official amendments and adoption of the 2015.  I'm pretty confident we will address it with an amendment...but in what manner?  This is why I hope this discussion turns into a technical one about fire behavior on decks.



			
				jar546 said:
			
		

> I wonder what the POCO has to say about the electrical meter base and it's new location now that there is a deck in front of it, lowering the height?Now that those windows are part of a walkway, are they being changed to safety glazing?


I should have known this would happen if I post a picture in front of you hawks! ha, ha!

Our utility has no specifications for how "low" a meter base can be.  All we lean on with that is our "anticipated snow accumulation" of 12 inches, suggesting that panels should be at least above the anticipated snow level.  The windows do not meet all four requirements for safety glazing required at walkways, so it's not required.  I've been looking at safety glazing by decks since I wrote an article on the subject back in 2007.  http://www.deckmagazine.com/Images/STRUCTURE_tcm122-1378437.pdf



			
				mtlogcabin said:
			
		

> It might be a stretch but here goes2009 IRC
> 
> EXTERIOR WALL. An above-grade wall that defines the exterior boundaries of a building.......
> 
> ...


I've looked at this interpretation before, (calling the area between the posts an "opening" in an exterior wall), but again...it just feels like a stretch, and like that's not really what those provisions were intended for.  This is why I believe the IRC should really address decks specifically.  The reason this particular deck would be different from a carport is because of how low to the ground it is, but that's a really good comparison to consider.



			
				Pcinspector1 said:
			
		

> Glenn,The reason I asked if the deck in the picture is over a utility easement, we have a 7.5 utility easement on both sides of a property line in most new subdivisions. The POCO could request a fence be removed if in an easement. If this is just a normal SE or other utility to a residential structure it would be allowed to go beneath the deck.
> 
> Zoning here would not allow that deck to be build if it is beyond the 8' PL setback here. So sometimes the building code should be enforced after the zoning code IMHO.
> 
> pc1


Yeah...normally our planning division has a 5 foot setback, so I've never faced this issue.  This particular neighborhood finished it's build-out about a year ago, so only now are we starting to get deck submittals.  This is the first time I've not been able to "blame planning", and we have to address it.  Zero side setback.

Good stuff, guys, I do love the responses!  However, my division made the call to let this happen, so it's happened.  I'd like to learn more about this issue and how to craft good code to address it in the future (our 2015 amendments, or a 2018 proposal to the hearings).  Is there a way to distinguish between when the hazard is fire from above or fire from below.  What if the deck was literally sitting on the ground?  What if it was second story?  non-combustible material?  There is obviously a significant difference between the nature of fire spread between various decks.


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## fiddler (Jul 16, 2014)

INTERNATIONAL RESIDENTIAL CODE

CHAPTER 3

BUILDING PLANNING

SECTION R302.1

IRC Interpretation No. 17-04

2003 Edition

Issued: 12-29-05

R302.1 Exterior w alls. Exterior walls with a fire separation distance less than 3 feet (914 mm) shall have not less than a one-hour

fire-resistive rating with exposure from both sides. P rojections shall not extend to a point closer than 2 feet (610 mm) from the line

used to determine the fire separation distance.

Exception: Detached garages accessory to a dwelling located within 2 feet of a lot line shall be permitted to have roof eave

projections not exceed ing 4 inches.

Projections extending into the fire separation distance shall have not less than one-hour fire-resistive construction on the underside.

The above provisions shall not apply to walls which are perpendicular to the line used to determine the fire separation distance.

Exception: Tool and storage sheds, playhouses and similar structures exempted from permits by R105.2 are not req uired to

provide wall protection based on location on the lot. Projections beyond the exterior wall shall not extend over the lot line.

! ! ! ! ! ! ! ! ! !

Q: Do the requirements in Section R302.1 for projections apply to exterior balconies and decks as defined in Section

R202?

A: Yes. Exterior balconies and decks that are attached to the building but not under roof are considered projections.

Exterior balconies, decks and porches that are attached and under roof are considered to be a part of the primary building

structure. Section 302.1 regulates projections into the fire separation distance. Projections can not extend more than 12

inches (305 mm) into this area. In addition, projections that do extend into an area where walls are required to be of onehour

fire-resistive construction must be protected on the underside with one-hour fire-resistive construction.

______________________________________________________________________________________________


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## Sifu (Jun 9, 2020)

Glenn, has there been any updates or further analysis of this topic?


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## Glenn (Jun 9, 2020)

Sifu said:


> Glenn, has there been any updates or further analysis of this topic?


Cool to see an old topic dug up, but it's still a new subject.  Or not a subject...yet?

I have not heard of anyone tackling this yet, but it is on my to-do list.  I represent the North American Deck and Railing Association in an awesome, informal coalition of parties interested in deck codes.  I do plan to work on this subject for 2024 IRC, but have not yet.

So... there is hope.  But I have no guidance as of yet.


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## Sifu (Jun 10, 2020)

I have a situation exactly like the one in your OP.  I didn't find the code language satisfying either, and came up with the same conundrum as you and figured I would check here to see if it had been discussed, not surprisingly it had been.  I was leaning in the "projections" direction but couldn't quite come up with how I could tell somebody they could build the deck....but protect it from the bottom.   Now I see the interpretation and have a little more confidence in the conclusion but I still can't quite bring myself to tell them that.  In searching for that opinion I found it may have been superseded at some point so I tried to find the interpretation for myself in order to have a firm base to bring this up as a policy decision for the CBO but am not able to access any of the technical opinions on the ICC website.  (I noticed this several days ago and it is still not working).  That interpretation isn't listed in my book of ICC code interpretations from 2009 so I want to make sure it is still valid (can they become invalid?).


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## Sifu (Jun 10, 2020)

Also, in taking the code section verbatim, it reads "_construction,_ projections, openings and penetrations".  Even if projections is a stretch, "_construction_" would include decks, though how that is then applied to the tables is still a mystery.


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## Glenn (Jun 10, 2020)

Sifu said:


> Also, in taking the code section verbatim, it reads "_construction,_ projections, openings and penetrations".  Even if projections is a stretch, "_construction_" would include decks, though how that is then applied to the tables is still a mystery.



As you read about projections, take note the relationship to attic ventilation openings in the two footnotes to Table R302.1.  They are basically exceptions to rating the underside if there is no ventilation openings.  Now apply that to decks...

Think about that.  That is what tells me decks aren't at all meant to apply to the projections provisions.  Also look at how foundation vents are in the exception to R302.1.  That's because they are low to the ground.  Burning brands and hot gasses go upwards and under projections, but only if there are openings into the attic do we require protection.  So decks low to the ground are very different than these projections, but in the same proximity of foundation vents which are allowed.

These are all just clues that make it even more confusing.  Decks need their own provisions so desperately, because their height above grade changes things.  Trying to fit them to anything we currently have for FSD is like a square peg in round hole.  Only a hammer makes it fit.

Please report back how it goes in your jurisdiction.


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## Paul Sweet (Jun 10, 2020)

Several years ago I worked for an architect who designed McMansions along the SC coast.  The decks had to be 10 ft. or more above ground to get above the FEMA flood line.  They also had to be supported separately from the house, and were separated from the house by an inch or two, probably for seismic reasons if I remember properly.  I don't recall having to fire rate any of them, although the localities they were built in had very strict zoning which probably kept them out of the fire separation distance.

There's a lot of difference between a 200 SF or so deck a couple feet off the ground and these huge platforms, so one size won't fit all.


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## Sifu (Jun 10, 2020)

I agree with everything you point out Glen.  In searching for more information I came across an ICC forum thread that hinted that ICC was now giving information contrary to the projection interpretation but I haven't been able to confirm it or find out what that information might be.  This is the first time I have encountered a property line separation question for a deck, but I have had townhouse issues.  In at least one former jurisdiction we required rated wall construction between the decks.  I can't remember if we had any minimum extents such as height but I do remember requiring the separation.  I suppose a similar method could be used if one absolutely had to have the deck that close to the property line.


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## Rick18071 (Jun 10, 2020)

So Glen there are no definition of a deck in the IRC.

So when is it a deck, or a covered deck, or a porch, or a balcony. or just a large landing?


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## Glenn (Jun 10, 2020)

Rick18071 said:


> So Glen there are no definition of a deck in the IRC.
> 
> So when is it a deck, or a covered deck, or a porch, or a balcony. or just a large landing?


Funny.  That's also on my to-do list for 2024.  You forgot "elevated walking surface", "patio", "paved surfaces" (for cladding clearances).  This terminology is a huge mess.

There was a definition of deck and balcony up until the 2009 IRC.


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## Sifu (Jun 11, 2020)

_That's also on my to-do list for 2024._ 

You are a busy man...but we're better for it so thanks.


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## Rick18071 (Jun 11, 2020)

I always question does a simple wood stairway landing landing or a wood porch that is barely off the ground need to build with the deck requirements with tension devices.


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## classicT (Jun 11, 2020)

Rick18071 said:


> I always question does a simple wood stairway landing landing or a wood porch that is barely off the ground need to build with the deck requirements with tension devices.


Oooohh.... I want to see Glenn's response to this question. He may just leave you wondering if you ever need tension ties.


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## Rick18071 (Jun 11, 2020)

If someone builds a roof over a deck does it now become a Category 1 Sunroom per 2015 IRC 301.2.1.1.1 and it will need stamped plans? In the past I have asked questions about sunrooms on this forum (just search sunrooms) from this section and the AAMA/NPEA/NSA 2100 but only got crickets. Doesn't anyone else comply to this?


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## tmurray (Jun 11, 2020)

The code here requires any platforms built closer then 4' to the property line to be non-combustible.


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## Glenn (Jun 11, 2020)

Rick18071 said:


> I always question does a simple wood stairway landing landing or a wood porch that is barely off the ground need to build with the deck requirements with tension devices.



I've done a lot of research into this connection detail in the code and the research others have done on the subject.  I put this video together before the 2015 IRC in an attempt to remove the provisions.  I was not successful.  I have a lot to say about this subject, but if you have not seen this video, please watch it first.


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## Rick18071 (Jun 12, 2020)

Thanks but i saw it and it's very interesting. But without a definition of a deck I don't know if a wood Category 1 Sunroom floor, landing, covered deck, porch, etc. can or is is required to be built as the IRC requires for a deck..


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