Thread: Stair stringers for fire escape

Hi All,
I am looking for an answer to something that may be simple, but I can't find any documentation for.

What is the building code pertaining to exterior wooden stairs and stringers? I have been given a set of engineered drawings for exterior fire stairs. The drawings indicate a double 2x12 stringer, which means 3 double stringers, as opposed to 3 single stringers. This is the first I've heard of this, and no one I've talked to seems to have solid answer. The only theory I have heard for it so far is that it is required to provide a longer burn time in the event of fire.

The stairs are for individual units in an 6 unit apartment complex. I am building 6 sets of these stairs, each set of stairs being the only point of egress for daily and fire egress from a single unit.

I am questioning the drawings as I have found other discrepancies in some of the other drawings this individual has provided us, and he will not answer questions as he was fired by the previous contractor.

The specs include 40" wide treads (two 2x6), and a stringer length of ~14'.

Any help with this would be greatly appreciated.

Cheers
Tom Richard
Richard Property Maintenance

The best way, and perhaps the only way to question an engineer is with another engineer.

Check with the building department. A engineers specs would most certainly meet the building departments requirements or exceed them.

Check with the fire department - they are the ones who typically have the final say on anything fire related, and in many (most?) locations if there is a conflict between the building code and the fire code, the building official and fire chief/inspector/plans examiner will meet and work it out, and usually (but not always) the fire code wins as it is typically slightly more restrictive than the building code, so meeting the fire code also meets the building code, whereas meeting the building code does not meet the fire code.

I would agree that he probably drew it up that way to provide for a longer burn time for the wood components. A lot of extra work and materials.
When I was a contractor I looked into using wood stairs for this type of situation a few times. It was never work it to meet the requirements. Always worked out easier and cost comparable to have a steel guy fabricate and install a steel staircase.
A copy notes ...
- Run the numbers on what the guy drew and then get some numbers on a steel stair case; see if you can make some gravy on it
- Don't build anything based on drawings done by a guy who got fired
- Take the drawings to the appropriate building dept and have them see if they would sign of on that type of construction and give you a Permit
- See what Code the municipality is under and review egress and fire resistive sections to see if what once drawn looks feasible or not
- You could also look into fire protective coatings that could be applied to the wood to provide sufficient fire rating, this would cut down on material cost and fabrication time; I've seen other people wrap wood in various fire resistive materials to get sufficient rating
There's probably more than one way to get this done

Originally Posted by Tom richard

........
The drawings indicate a double 2x12 stringer, which means 3 double stringers, as opposed to 3 single stringers. .......

....each set of stairs being the only point of egress for daily and fire egress from a single unit. .....
The specs include 40" wide treads (two 2x6), and a stringer length of ~14'. .......

Beefing up the stringers sounds reasonable for a 14 ft run considering the fact that it is the the only point of egress. Doubled today as opposed to cracked tomorrow.

The proper thing to do is build them to the engineer's specs. Unless another engineer is hired and provides different specs.

Thanks everyone for the feedback! All of it is sound advice.

I am definitely a "more is better" kind of guy when it comes to construction, and don't have a problem making these stairs with double stringers, but of course my client doesn't want to just throw away money. (I'm sure most, if not all, contractors have been in this position before!)

The only issue with the engineering side of it is that it costs about $1000 here for an engineer to review and provide recommendations/changes to existing drawings, which we have already done a couple of times now. So even to just go ahead and double the stringers still wouldn't cost me as much as getting a revision.

We are currently trying to get an answer from the city as to what the requirement is.

And interestingly enough, I was in the fire service for about 8 years, spending the last few years as the training officer. Although building codes were not my primary focus in this role, safety was. I never did come across anything like this back then either.

Originally Posted by Tom richard

Thanks everyone for the feedback! All of it is sound advice.

I am definitely a "more is better" kind of guy when it comes to construction, and don't have a problem making these stairs with double stringers, but of course my client doesn't want to just throw away money. .........

Liability concerns ($$$$$$) will get their attention. Pose the question of 2 to 4 people at 230 Lb each on the stairs carrying furniture and appliances, bouncing as they go, and the single stringers. Or how about 4 firemen completely turned out with tanks and hoses running up the stairs. A lot of force on the stringers. Penny wise pound foolish ??????? The bucks will stop with the owner if there is a problem.

I would not be surprised if they required fire protection for the wood, or at least fire retardant treated wood (I am surprised they did not) ... however, the fire retardant treatment may not be permitted to be exposed to the weather (just pondering a ponderable) and protecting the wood could be a problem.

One set of exterior wood stairs I inspected a couple of days ago which was being rebuilt could best be described as 'heavy timber construction' - the stringers were 4x and the treads were 4x - this was on an older apartment complex where various stairs were being repaired.

You might consider using 4x instead of 2x lumber - that makes a difference in fire resistance and burning time.

My recommendation would be steel stairs over wood. The positive of the steel stairs is that they do not burn, the negative of steel stairs is that when they reach their softening temperature - they collapse suddenly without warning, unlike wood which typically moans and groans and gets weak before collapsing.

I entirely agree with you Garry that liability should be at the forefront, and which it is in this project. As with every comment on this thread so far, the common theme is stronger the better, which is great to hear. My only problem is it's hard to justify extra costs in a project without providing some solid documentation to prove it's necessary. My client owns and manages multiple buildings and has never come across a set of stairs with double stringers.

I know everyone is saying to go with the engineer, or building inspector, or fire marshal, but I haven't gotten a straight answer from any of those groups. As I mentioned earlier, the engineer's drawings are questionable at best, and revisions are expensive. The town building inspector is also the town fire chief, and while a great guy to deal with, he admits he is still learning the job and usually ends up asking the provincial fire marshal for answers, especially concerning this issue. Unfortunately, it has taken up to a month to hear back from the fire marshal's office to review drawings in the past.

It's not that I am trying to prove anyone wrong, but really just wondering where the engineer got his information from. And I know this is a great group for being able to send someone in the right direction!

Originally Posted by Tom richard

I entirely agree with you Garry that liability should be at the forefront, and which it is in this project. As with every comment on this thread so far, the common theme is stronger the better, which is great to hear. My only problem is it's hard to justify extra costs in a project without providing some solid documentation to prove it's necessary. My client owns and manages multiple buildings and has never come across a set of stairs with double stringers.

I know everyone is saying to go with the engineer, or building inspector, or fire marshal, but I haven't gotten a straight answer from any of those groups. As I mentioned earlier, the engineer's drawings are questionable at best, and revisions are expensive. The town building inspector is also the town fire chief, and while a great guy to deal with, he admits he is still learning the job and usually ends up asking the provincial fire marshal for answers, especially concerning this issue. Unfortunately, it has taken up to a month to hear back from the fire marshal's office to review drawings in the past.

It's not that I am trying to prove anyone wrong, but really just wondering where the engineer got his information from. And I know this is a great group for being able to send someone in the right direction!

I think that you have gotten as much free advice as is available here - it is now up to the owner to do one or more of the following:
- pony up for another engineer
- pony up for the cost of the stairs are designed and approved
- be will to sit on their investment until the cows come home waiting for the fire marshal to let them or you know what they will approve other than the stairs as designed

It now comes down to "cost", i.e., "money" ... what the owner wants is no longer relevant - other than how much, or how little, the owner wants to spend or save constructing the stairs as specified, get another engineer, or wait ... and wait ... and wait ... for a decision from the fire marshal.

It's the owner's money, provide the above options and let the owner select one.

Yep. Agreed Jerry. Right now I have a feeling it will be build as currently designed. Thanks

Don't know about Canada but the double stringers and 2x treads may be explained in the I-code Chapter 16 for commercial apartments (more than 3 dwelling units); the exterior stairs or fire escapes would be constructed with a minimum uniform live load of 100 psf. instead of the 40 psf. in single family homes.

The 40 inch wide tread doesn't fit with the I-codes to meet the minimum width of 44 or 36 inches between the handrails required on both sides.

Stairs are normally protected from fire exposure with separation (fire barrier) walls. It's pointless to construct fire-resistant rate stairs not to be confused with fire-retardant (non-combustible) construction.

Hope input this is helpful.

Originally Posted by Francis Vineyard

The 40 inch wide tread doesn't fit with the I-codes to meet the minimum width of 44 or 36 inches between the handrails required on both sides.

Sort of, but not necessarily. Check out handrails and projections allowed at and below handrail height.

It may be a carry over from the 1997 UBC Section 605.4.2 for interior stairs in Type IV (Heavy Timber) construction, which required that stair stringers be at least 3" in thickness. Your local code may have been amended to include this for both interior and exterior stairs.

You did not mention if these were “solid” or “cut” stringers (we can assume the middle stringer is “cut”).
The permitted “horizontal” span of a 2x12 “cut” stringer (pine) is not that much: about 6-7 feet (depending on the source).

You may not even be able to get away with doubled-up stringers.

You may need intermediate supports (posts) half-way down the stringer; or an intermediate platform.

You may not need an engineer; you should certainly refer to the local codes.

Originally Posted by Gerry Schmitz

You did not mention if these were “solid” or “cut” stringers (we can assume the middle stringer is “cut”).
The permitted “horizontal” span of a 2x12 “cut” stringer (pine) is not that much: about 6-7 feet (depending on the source).

You may not even be able to get away with doubled-up stringers.

You may need intermediate supports (posts) half-way down the stringer; or an intermediate platform.

You may not need an engineer; you should certainly refer to the local codes.

I also believe the stair stringers have to be 12 inch o.c.

The horizontal run (span) of an ~14 foot long stringer which provides for an 11 inch tread depth with a 7 inch riser height would be ~9 feet.