Floor loading and joist sizing

[rozett]

OK, I'm sure someone on this board can help me. I've spent an hour on the web looking for joist loading information and all I can find is span tables.

Background: We have a barn that is well over 150 years old. The post and beam construction is raised above ground level. The north wall sits just about ground level, with the south wall about 5 feet above ground level (35 foot span). The barn was rehabilitated by the previous owner. Besides reskinning it, they removed all of the original floor boards and replaced them with 2x10's @ 16" OC topped with 3/4 ply. This results in joists of 11' 2" span hung from 2x12 rim joists with standard stamped hangers.

I've built two 11x13 stalls on one side of the barn, where we house our two horses (1000 & 1200 lbs). The floor always had noticeable deflection with the horses moving around their stalls. Well, after about four years, the floor joists have started splitting or broken completely. Obviously, the 2x10's aren't enough to support the load. I've looked for tables that provide loading info for various joist sizes, but all I can find is span tables for the standard residential loads of 30, 40, and 50 psf.

My thoughts are to replace the single 2x10's with a pair of sistered 2x8's with 2x4 blocking nailed below the joist hangers and to use 3/4 underlayment instead of regular 3/4 ply. I'm trying to find the loading specs for 2x8's vs 2x10's. I want to make sure that's going to be enough. I could sister 2x10's but wouldn't be able to block them.

So, there's got to be a contractor in this group.

 

[bugstruck]

I don't have time at the moment to think thru this. I'll try and get back to this later, but reducing joist depth and doubling up is not the answer.

 

[CurlyDave]

I've spent an hour on the web looking for joist loading information and all I can find is span tables.

I am not understanding why span tables are not good for what you want.

If I look here: http://www.southernpine.com/spantables.shtml and say that you need to design for 125 to 150 psf, I get some good choices.

I would personally go with 2x12 No.2 or better at 12" centers. But then I am an overkill kind of guy.

Doubled 2x8s are just not going to make it.

 

[Egon]

Have you considered a center wall for less span?

Is the 3/4 in. plywood heavy enough for horses?

As per Dave 2x12.

 

[MikePA]

My thoughts are to replace the single 2x10's with a pair of sistered 2x8's with 2x4 blocking nailed below the joist hangers and to use 3/4 underlayment instead of regular 3/4 ply. I'm trying to find the loading specs for 2x8's vs 2x10's. I want to make sure that's going to be enough. I could sister 2x10's but wouldn't be able to block them.

I am with the others, nothing less than 2" x 12" on 12" centers.

By way of reference, our hay loft is built almost like your current stalls.

Our hay loft is above the center aisle (12' wide) of our barn. 3/4" OSB, on top of 2" x 10" on 16" centers with bridging down the center. When full of hay, there's approximately 15,000 pounds (300 bales at 50 lbs each).

However, this load is a dead load, while yours is a live load and depending upon where the horses are standing, their entire weight may only be supported by one floor joist.

 

[rozett]

Thanks guys! I knew I would get some good feedback....

I am not understanding why span tables are not good for what you want.

Good question... first, because all of the tables I found were for residential loading. Obvioulsy, not what I need. Secondly, I have a degree in engineering (although not civil or architectural) and I want to see the numbers. That's in my nature. Also, none of the span tables provide any info for sistered joists. I had no clue what the change in loading is if I doubled the joists. But the link you provided has much of the info I was looking for. Thanks!!

Have you considered a center wall for less span?

Yes, unfortunately the stalls are on the uphill side of the barn. So I can't do the work from under the barn, I would need to tear out the existing floor/joists in order to access the ground to dig footings. So, I'm looking at at least a week to dig/pour/cure footings, pour/cure posts, backfill, build a 26' beam, and then rebuild the floor. The horses would be very unhappy about spending a week out in the pasture overnight. I know, who's in charge, me or them.... already had that discussion with the CFO.

Is the 3/4 in. plywood heavy enough for horses?

While I'd love to remake the original barn floor (full 2" hemlock planks cut on site), that's not practical. I do have standard rubber stall mats atop the ply. I think thats sufficient.

So, THANKS very much for the input. Looks like it will be 2x12's on 12's. I can do one stall a day and get the boys (well, they used to be boys ) back in for the evening.

 

[vmarc]

I would use all pressure treated and at least 2x for the floor.I find it amazing that the horses didn't go through the plywood.Horse urine is potent and will rot anything in short order.I'm a wussy,so for horses I would double up the joists and sandwich plywood between.I think you can get oversized joist hangers to fit..Check the whole thing for rot very often.On second thought it might be better to have an engineer who knows horses spec it out.It's frightening to me to have horses suspended on a wood floor.They can generate tremendous forces hopping around and landing on 1 or 2 hooves.

 

[bugstruck]

The recommendations for 2 x 12 @ 12" centers should work fine. However, you need to distribute the point load across them better than 3/4" plywood can do. If those horses are pushing 2 x 10's at 16" to failure it wouldn't be impossible to have a 2 x 12 fail too, even at 12" centers. The problem is they are putting 600 lbs or more directly over (1) joist at times and probably point loading near 1,500 lbs with impulse. If the decking won't span that load to the adjacent two joists, you could have another failure. Frankly, I'd rather have sistered 2 x 10's or 2 x 12's (later preferred) at 16" on center than single 2 x 12's at 12 if you are married to the 3/4" ply for load distribution. Another important method of load distrubution is blocking or bridging between the joists. Not where I prefer the initial load take-up to occur (prefer that as a secondary take-up point) with animals that size but it's rather better than nothing transferring the loads. Additional rows also limit deformation of the joists that can promote failure. That span is pretty short but I'd still have (2) minimum and (3) preferred rows of bridging if you are doing the 3/4" ply with 12" centers. Then I'd start to worry about degradation of the plywood over time and a hoof dropping thru. No doubt the 12" centers would be better protection against that. The simple solution is to do 2 x 12's at 12" OC and deck this with 2 x 6 decking. You could ply over that and screw it down if so preferred clean-up purposes. That plywood could be replaced if needed. All this is assumed for PT # 2 yellow pine.

I'm aware that 3/4" plywood has some spanning capability. It just isn't designed for this environment.

 

[rozett]

I would certainly prefer not to have them on a wood floor at all. I've even considered buying the cement block used to build retaining walls and building that around the perimeter of the two stalls and filling the space with crushed rock topped by the stall mats. But as the costs go over a grand, I start backing off.

As for the horse urine, there is 2" of pine shavings sitting atop the stall mats and it absorbs the vast majority of it. When I installed the 4'x6' mats, I drilled small holes through the ply in order to drain any urine that seeped through the seams between the mats. That has been pretty effective. Although the ply has deteriorated because of the urine, the joist failures have been structural failures, without any sign of deterioration from urine. I suspect what happened was that a section of ply rotted and deflected significantly. The 3/4" rubber stall mat prevented the horse from stepping through, but put lateral pressure on one of the joists causing it to fail. The rest of the joists have just cascaded into failure from overload. The breaks in the joists are free of any urine stains.

Bridging is another great idea (Thanks, bugstruck). There is no bridging at all in the current construction. If my failure hypothesis is correct, I suspect that bridging would have prevented the joist failures. The bridging will also provide better support for the seams between sheets of ply. That's not a problem in residential applications, but definitely a problem at these loads.

Again, THANKS for the advice. I knew I'd get some good input from you guys.

 

[bugstruck]

Bruce,
You understand the failure and the impetus very well. Armed with that and the comments here, you can work the solution. You also know to keep an eye on the plywood from time to time. Have at it and hurry up.... gotta keep the CFO happy . Don't we all know

 

[Egon]

Many years ago on the farm the only time a horse got to see the inside of a barn was when they were working. Most of the year was spent outside including the winter which could see -40F with no problem.

The plywood floor will eventually [ actually not that long ] become wet and lose its stength. If a horse puts its hoof through at the deep end there are really good chances of loosing a horse due to broken leg!

 

[MikePA]

Bruce, is there any way to get the horses on the ground floor? As others have mentioned, while going to 2x12 on 12" centers with the right flooring is an improvement on the existing situation, it's going to be an on-going maintenance issue that if it's forgotten, the horses could (would?) be hurt.

I've seen bank barns before, in fact the person I buy hay from has one. He keeps all his hay, tractors (2 ag tractors), hay wagons, etc. on the 'upper floor', but I've never seen a situation where animals are kept on the 'upper floor'. Of course, this doesn't mean it doesn't happen, perhaps others can chime in if they've seen this before.

 

[rozett]

Bruce, is there any way to get the horses on the ground floor?

No, there is really no ground floor. The barn is built into the hillside, with the north wall at ground level and the south wall about 5' above. I agree that it's not the best situation, but that's what I got. The stall mats have really been pivotal here. First, they hid the damage to the plywood until it because critical. But they have really prevented any injury by keeping the horse from stepping through the damage. I'm going to do a cost tradeoff between the PT plywood and 2x10 floor boards. In either case, the stall mats will be reintalled. The 2x10 floor boards may be prefereable because they'll allow better air circulation to dry the urine that seeps through the joints between mats.

Egon is right (again ) that in yesteryear, the horses would have been outside all the time. Our two definitely prefer to be outside all day long, but they have always spent the nights indoors. My wife's appy could easily deal with being outside with all those strange creatures at night. But my registered Quarter is a primadona. He gets very vocal about being brought in at night. His grandfather was 3 time world cutting champion. Obvioulsy, Peppe didn't inherite the right genes otherwise he'd still be in Texas.

 

[Egon]

With 2x10" wooden floor boards [ rough cut ] you would not need the mats.

 

[dmccarty]

Bruce,

How about composite decking. Yes I know its expensive.

But it sure beats have to rebuild over and over.

How about PT 2x12 with composite decking on top. I'm guessing that the composite would be better able to handle the pee and poo better than PT. And the composite would protect the PT 2x12s.

Later,
Dan

 

[MikePA]

Dan's post triggered a thought...What about engineered lumber (gluelam beams, wooden I beams, etc.) instead of the dimensional lumber for the underlying support structure?

 

[rozett]

What about engineered lumber (gluelam beams, wooden I beams, etc.) instead of the dimensional lumber for the underlying support structure?

I thought about that, but after crawling around under the barn, I am convinced that the joist failures were just a secondary failure. The primary failure was the plywood, which caused a lateral failure of one joist. With one joist out, the others have failed sequentially. The ply failure was caused by the horse urine, but aggrevated by the fact that the previous owner used 3/4 sheathing instead of 3/4 T&G subfloor and by the lack of any bridging. The lack of bridging meant that there was no lateral load support for the joists. So I will replace the joists with 2x12's 12" OC and bridging every 4 feet. I am still evaluating decking options..... PT subfloor, composite decking, and 2x10's. Unfortunately cost is an issue because I am covering almost 300 sq. ft. of floor.

These same two horses have been in these stalls for five years. If the primary failure was overloading the joists, I would expect that to have happened several years ago.

 

[dieselsmoke1]

Sure seems like some support near the center of the spans would help the situation. Would something as simple as some 4" solid blocks turned lengthways with the joists, laid flat on the ground and baited up to the bottom transfer most of the load and shock directly to the ground?

 

[rlk]

Bruce, interesting question you asked.

My response will be different from everyone else:

I would talk to a specialist in designing floor joists. Here is one web site where you can ask them questions about design loads, etc: http://www.trimjoist.com/spans.html A google search on engineered floor joists will give you more options.

The last time I put an addition onto my house, I had a similar question, as the addition was a sun room and I wanted ceramic tile. I called a similar floor joist company, and told them what I was doing, and asked for their recommendation.

They told me the size of engineered floor joists I needed. I upsized one increment, and doubled a couple of the floor joists to ensure there would be no bounce which could cause the tile and/or grout to crack.

My second recommendation is to talk to someone about the floor material. Some have said you should use 3/4 tongue and groove plywood or osb. If you go this route, be sure to seal the material with a good water sealer, I'm not talking about Thompsons, but a good sealer that you know will last.

To be sure you do not have a failure that could cause a horse to break a leg, I would use 2 layers of 3/4 tongue and groove material where each layer runs a different way. The material should be glued to the floor joists.

I know this will be more expensive, but if you do it this way, and thoroughly coat each layer with a good sealer, plus put a moisture barrier between the two layers, plus use 2 inches of wood shavings on top, you should not have to worry about the horses falling through the floor.

You only want to make this repair one time, and you want to be confident that your repair will be safe for the horses.

 

[MrJimi]

Here is a picture of my wooden I beams for my second floor, they are 16 inches tall and 3 and a half inches wide and 24 feet long and are designed to be spaced at 24 inches and I am putting them 16 inches on center, I am not sure what they will support but it is a huge amount

This is 2 on the end of my hoist, 108 pounds each

Jim