Residential Guardrail 9

[dik]

Does anyone have a typical residential guardrail detail? I'm looking for something with 2x2 @ 5.5" o/c x 42" high pickets with a top 2x6 rail. The pickets are secured to a 2x? trimmer secured to deck joists. Anyone have something similar they might share? Residential stuff is not really my forte.

thanks, Dik

 

[SlideRuleEra]

Dik - Is this the type you need? Just spaced 2x2 pickets, each fastened with screws to a joist or a 2x spacer sistered to a joist. Either a 2x4 or 2x6 rail on the inside top of the pickets. Adding a second 2x4 or 2x6, on the flat, above the rail (shown below) gives a nice shelf for cups. Cut the bottom of each picket at a 45 degree angle for looks. (Same with the top of each picket if a flat shelf is not used.) A fairly popular style in our area.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[Ron]

OK...all you juniors...this is an example of SRE practicing what he preaches! Did similar for my younger son's play platform when he was young (he's a 25 year old magazine editor now....doesn't want anything to do with engineering!!)

dik...the key is going to be attachment of the top rail...the rest is almost superfluous (did I spell that right?).

 

[dik]

SRE: That's exactly the guard I'm looking for; anyone have a sketch of same.

Ron: Spelling's good... and, I don't blame your son...

I would have thought the bottom connection of the pickets would have been the problem...screws in withdrawal and securing the trimming member to the deck joists... Top rail 2x4 secured to the pickets with a 2x6 running on top... easy connection

Dik

 

[XR250]

Hmm, don't think that meets the out-of-plane guardrail requirements of the IRC.

 

[dik]

ZR250: 'out of plane'?

Dik

 

[jayrod12]

Dik, I'm pretty sure Part 9 requires 4x4 posts at 4 ft maximum spacing.

 

[dhengr]

Dik:
See if you can find (Google or otherwise) a copy of the AFPA, “Design for Code Acceptance #6, Prescriptive Residential Wood Deck Construction Guide.” It is based on the ICC International Residential Code (IRC). Various localities (AHJ’s) have minor variations on this Guide. Top of handrails or guardrails should be from 36" to 42" above the deck. Min. loads perpendicular to the railings are 50lbs./ft. or a concentrated load of 200 or 250lbs., anyplace on/along the handrail, at the handrail height, and in, out or down. And, 50lbs. on a one sq. ft. area anyplace on the balusters. The 50lbs./ft. of length and the 200lbs. concentrated, generally lead to 4x4 posts every 4' o/c. The baluster or post canti. connection is almost always the critical connection detail, as (200lbs.)(at 36 to 42" rail ht.) is a fairly substantial canti. moment on the 4x4, and reacted by a couple bolts, only one in tension, with about 4-5" spacing, at the rim joist. You should worry about ripping/rolling the rim joist right off the ends of the fl. jsts, with only 2 or 3 - 16d end nails into each fl. jst.; or rolling the last/exterior edge joist out from under the decking. There are several good details, blocking and pieces of hardware to make these post connections more robust. They don’t like you notching the bot. of the 4x4 posts because this weakens them too much, but I usually do notch .375 or .5"; this bearing on the joists takes the vert. loads and the through bolts only have to deal with the canti. reaction. No opening in the guardrail system can pass a 4" dia. ball.

 

[dik]

Jayrod: Thanks, but, I could find no reference in part 9 to using posts at 4'. Also, the City of Winnipeg has a deck guide that makes no reference to it, and on the cover, they show a deck with 2x2 (?) pickets and no posts. Can you provide a citation? I'll also check with the City. I'm not very familiar with Part 9 and wood framed construction.

dhengr: I'll check that publication out. Loading is prescribed and can be distributed over 3 pickets. I'll also check with the City for requirements.

My only involvement is only to verify that the screw piles are adequate to support 6000 lbs and the load doesn't exceed this. The guard, the attachment to the house, and the deck design is outside the scope. Construction of the deck consists of 2x8@24 joists, spanning 10' c/c and the guard attaches to this. As an engineer, I want to know where the gremlins are lurking.

It would be easy, but, the proposed construction is 'out of kilter' It's a mix of screw piles and bearing on concrete.

The screw piles were installed (not anywhere enough) and sleeved through a 2' thick slab on grade so no slab adload. There is no easy way around the 2' thick slab to introduce new screw piles. Intermediate supports bear on the slab and the tributary load on the piles is OK. It's a mess, and, I'm involved because the homeowner is a good client. Why a 2' thick slab, I have no idea.

The only positive thing is that there is nothing life threatening about the proposed construction.

Dik

 

[dik]

dhengr: Picked up a copy of the publication and it has posts @ 6' o/c and no reference to pickets by themselves. Will check further.

Dik

 

[dik]

Something like the attached...

Dik

 

[bridgebuster]

dik -I found this in my files; maybe it will be of some help.

 

[Ron]

dik...my little brain was thinking top rail anchored between two stationary walls or columns. That condition makes the rest of the rail/picket system minor by comparison.

The case that SRE illustrated relies on rotation resistance at the posts as well as the shear resistance of the intersecting sections perpendicular to the other sections. As an example, the long section on the left of SRE's photo would try to pull away from its wall connection for the top rail and rotate each of the pickets at their connections if the load were placed on the intersecting center section. Since the right section has no wall attachment at the top rail, it would be subject to rotation about the post connection adjacent to the steps.

Each picket would be subject to the relatively small distribution of a 50 lbf load placed on any 1 square foot area of the pickets....not a big deal if you put a couple of screws in each picket at the rim board.

 

[dik]

Thanks, BB

Dik

 

[Ron]

dik...just looked at your sketch. That is typical of rails I've done in the past. Usually mine are done in steel attached to the wood, but have done wood also. The posts take the primary load (I usually space them at 48" oc)....you can use a bottom rail to terminate the pickets or let them die into the platform or rim board with relatively light attachment.

 

[dik]

Thanks Ron... I was thinking that the top rail could be secured against the portions of pickets at right angles and put a post in at a stair location if there is one. I'll have to wait until tomorrow when I get a chance to talk to a building inspector to see what is permissible. Again, it seems to be a simple problem in an area I'm not used to. I put together a sketch to use in an SMath program, just to see if it's do-able.

Dik

 

[dik]

Each picket would be subject to the relatively small distribution of a 50 lbf load placed on any 1 square foot area of the pickets....not a big deal if you put a couple of screws in each picket at the rim board.

Steel is a more comfortable medium... I was thinking about distributing the loads to 3 or 4 of the pickets since the top rail is stiff enough to transfer the loading.

Dik

 

[bridgebuster]

you're welcome dik

 

[dhengr]

Dik:
Yes, the AFPA #6 Guide shows a max. post spacing of 6' because the canti. post connection is so difficult to make work. My comment was..., given the 200lb. concentrated load reqr’mt. anyplace on the guardrail, right at a post for example, is equal to 50lbs./ft. times 4', so posts are typically spaced at 4', either load condition causes a 200lb. load at the top of the posts. 6' spacing will cause 300lbs. at the top of a post, not an easier canti. connection to make for the avg. deck builder. The 200lbs. is not unreasonable when you consider a couple drunk linemen showing off for the girls, out on a deck. And, they can produce a sizeable lateral load at deck level when they start swaying or dancing in unison. 40lbs./sq.ft. is maybe not enough out within a couple feet of the railing where people are invariable congregated when decks fail, and they may have moved there quickly to see a couple deer in the yard, or some such, thus a lateral load away from the house. Deck bldg. is a bitch if done right, and is not really a simple DIY’er. weekend project.

2x8 jsts. at 24" o/c on a 10' span is really stretching the deck fl. framing and many of the newer decking materials, which perform much better on 16" jst. centers. 40lbs./sq.ft. LL is not normally a bad overall deck loading. Except, for people, plus snow and ice and snow drifting off the bldg. roof. With the right wind, a 6" snow fall will product 18-24" of snow on my deck. Then, in no time, they ask if they can put a hot tub on the deck.

As for your latest handrail detail..., with the 2x6 & 2x4 railing, I would allow the loads to distrib. to more than three balusters; but, assuming only 3, you have (200lbs.)(36" + 1.5" + 1" or maybe 42 + 2.5") on 3 balusters and 3 screws with only 1.25 - 1.5" penetration into the rim jst. This all happens at a deck jst. end with 6 or so 1.25" 16d nails from the jst. hanger in withdrawal (never intended in the hanger design), and maybe a few nails from the edge deck board. You will roll the rim jst. right off the end of the deck jst., thus the more elaborate details for the posts at the canti. connection.

As for your foundation, a 2' thk. slab? If the slab is stable, I’d found a whole house on a 2' slab, that’s a mat found. Then you say you’ve got a few ill spaced and located screw piles. Did they core the slab to place the screw piles? I’d roughen that cored hole, and dig an inverted bell under the slab and onto the screw pile, and fill that bell and core with conc. Then, just assume that 2' thk. slab distributes a few 2-3kip post loads to the soil. What is the soil, unless it is wet mud the IRC will give you 1 or 1.5k/sq. ft. just for being soil.

 

[dik]

dhengr:

I haven't looked at the attachment yet; I'll do that as I write the SMath program. Haven't even run a quick thumbnail calculation. First 'kick at the cat' I'll be using 3" #14 screws... and go from there.

He has a 'real' contractor.

Agree about the loading adjacent to the guardrail.

Agree about the joists... actually ran it through Woodworks and it worked. Woodworks is one of the best wood programs going. My original thoughts in earlier eMails that I assumed the joists were 2x10@16... common. You cannot add an enclosure (roof or whatever in future) with 2x8s. I'll talk to the client and building inspector tomorrow.

As far as distribution of loads, I'll see what is needed and go from there... The top rail is pretty stiff.

As far as the 2' thick pad? I dunno... it was cast after the screwpiles were installed and sleeved to prevent bonding. Soil is med-firm highly plastic clay and should be capable of 2 ksf to 2.5 ksf without issue. I'm not concerned, except, with the letter I'll provide (screwpiles only) I'll note the unconventional construction where the deck is supported on screwpiles and a concrete slab below for some of the support. I'll also note that in the event there is any movement, it will not occur catastrophically and there will be ample time to remedy... there's a similar issue with a small retaining wall 2' high, with 1' frost protection... can move but not catastrophically... won't use those words in letter.

Dik