2nd floor joists - are my 2x8x16s going to be strong enough?

I am building a shop/shed/barn all in one. it is going to have a Gambrel roof and a 2nd floor for storage. The plans I purchased said to use 2x6 for my 16 foot joist span. But I wanted to build it a little hardier so I bought 2x8x16.

I have been at this for over 3 years and have learned a lot. I have used 1/2x12"plywood for the gussets instead of 7/16x6"osb. 2x12x16 instead of 2x6x16 for the floor joist/bands. Used Cap blocks with 4"rock and gravel as base and black plastic over rock.
Everything is 16"OC instead of 24"OC.
Plans did not mention wall sheathing, I added 7/16 osb then Tyvek before my smart sideing.

But now i"m at the point of adding 2nd floor and I am thinking I need to upgrade to a 2x10x16 instead of the 2x8x16 that I already purchased. I bought the materials years ago so I can't exchange them but I don't want the floor to buckel or fall either. I thought that if the plans said to use 2x6x16 and I went to a 2x8x16 that I should be good, I'm not sure, after I looked into it.

What can I do?
Bite the bullet and buy the 2x10x16?
Double every other 2x8x16?
Use Blocking?
or a Multiple of each?

I am going to be storing some hay, house goods, seasonal items, furniture, a lot of things but nothing more than 30lbs per sq foot I think.

This is a warning to every one out there. You may think that "if I buy some plans and follow them then I'll be within code and if there is no code then i will be ok since its on a plan". NO not allways the case. Not all plans are done by certified architectural, engineering and technical designers.

Thank you. pictures to follow when camera/phone is fixed

P.S.  I just found out that my house wrap is wet as we unrolled it. Can we still use it some way?

Hi Lloyd, welcome to permies.

Let me start by saying I am not a builder, or an engineer. I'll offer some free advice, which may be worth the price: nothing. :) I used to remodel houses, and I'm currently building a house, so I've dipped my toes in residential building. I myself would not span 16 feet with a 2x8. I have 2x12 floor joists in my new home, set at 16" on center, some spanning 14 feet, some 16 feet (the total span is 30 feet, with the 14 & 16 foot 2x12's attached to a beam going down the middle of the house). The engineer who drew the plans for my home originally had 2x10's for the floor joists, but I changed them to 2x12's because I want a rigid floor with minimal sag/flex, and I like to over engineer things to make them stronger. It's my opinion that code minimums are just that, a minimum, and I personally like to go a little above and beyond codes. I just went to the codes site to look at the residential building codes floor joist table, and while I was unable to copy the link to the image, I was able to take a screen shot of the top of the chart. You'll see that not only does the dimensional size of the lumber matter, but different species of wood have different load capacities. The following chart in its entirety can be found at https://codes.iccsafe.org/public/document/IRC2018/chapter-5-floors

Hope this helps!

There are many tables of span specs available, for both dimensional lumber and manufactured pieces.  Worth looking at 3 or 4 to get a feeling for what you're looking at and how they agree - or not. But it's not rocket science. Many of the specs are tied to the amount of sag allowed and acceptable, so you need a thought there. Then read various contractors  forums about "springy" floors to help flesh out your opinions.

Don't ever design to the lowest spec that will hold your average load. Maxing out specs leads to risky situations in many "edge" cases.  It's done only in special situations where somebody has thought a lot and decided the trade off is worth it.

Get smart about load. What happens when you DROP a large load, eg. a large hay bale? Buying and storing material for future work can add a lot of weight to one spot - eg. a few hundred sheets of gypsum board. OTOH, it also helps to have a realistic take on your actual use which may allow some serious savings. For example, in a barn, loft, etc., you may not care if the floor bounces and squeaks a little while still being well w/in it's load range.

I don't see how sistering  makes much sense because you still need to buy another load of lumber. Spend the needed to get the more appropriate material and keep install costs in the same ball park. Repurpose the other.

I assume you want big open space beneath, but one of the ways to deal w/loading problems is added support. So give those options some thought, if not as plan A, just to have looked at it with a level head before facing it in a dark alley, sorta speak.

I was a plumber and now I'm down to just remodeling/repairing 100 yr-old houses (for some 40 years). Presently cutting the legs off a big old garage and adding stem walls and new top plates courtesy of termites.


BTBT - BeenThereBrokenThat. <g>

Rufus

Yea, I've seen those span charts but not knowing the stiffness and the class wood lowes sent me makes them useless. I was just looking for some honest experienced labors voice/opinion on the matter. Thank you. Depending on what I use for the sub flooring, and don't put any cannons in the center of the floor without adding some walls down below or some type of support the floor shouldn't collapse but will have some bounce for the kiddies(joking).

Thank you.

Anyone have any comments on the house wrap being wet?
Could I still use it?
I can't be the 1st person to have wet Tyvek.

I'd have no concerns about the tyvek being wet.

On the joists, what is the other length? If its 16ft x 16ft you could run a center beam (double 2x12 with plywood core) then run the 2x8s at a 8ft span.

I am renovating a 1922 Foursquare house that had 2x5 stringers spaced 24 inches on center, spanning 18 feet, and can say that it took (2) 20 ton jacks, and a 8x8 beam across the center to get the 2 inch sag out of the floor. How the second floor did not collapse into the first floor is beyond me.

I would go with 2x10's, but maybe 12 inches on center and not 16 inches on center.

Lloyd Carter wrote:Yea, I've seen those span charts but not knowing the stiffness and the class wood lowes sent me makes them useless...

Hey Lloyd the lumber that Lowes sent you ought to have a stamp on each piece. It might say S-P-F and No. 2. S-P-F stands for Spruce, Pine, Fir, and the No. 2 being the grade. It could say SYP, Southern Yellow Pine, and it might also have KD on it, Kiln Dried, or even MC 15, meaning Moisture Content 15%. A lot of the type of lumber found in stores or yards is based on geographic location, whatever grows regionally, instead of trucking in lumber from across the country.

It's a 16 foot x 30 foot Gambrel style.
I bought the lumber 4yrs ago just before the prices sky rocketed. A 2x4x8 was $1.49, the 2x12x16 PT were $15.24 all the markings are either worn off, faded, or covered up by something. Amazing how prices jumped. I figured buy it in bulk get a better price. thats fine for most things but it took me a long time to find time to work on it.

also was going to ask about thoose nails that have the plastic cups, should they be used, do they have a particular job besides keeping the wrap from blowing off or are staples just fine?

Wet Tyvek is not a problem at all. Pretty much every house built outside of the desert gets wet during construction. The purpose of house wrap is to stop new moisture from getting in. The construction moisture will breathe through the interior walls over time — that's why we only put house wrap on the outside.

The nails or staples with the plastic disks are there to increase the surface area holding down the Tyvek, preventing a tear.

thank you all

If siding is going on quick,  staples will work. If its gonna be slow, use the plastic headed nails  prob ok to use them just on the edges where wind can get under it.

Just thought I'd add a note about "span tables"  The figures in those tables aren't just for safety, they are also designed to make a floor that feels "solid", no shaking when you walk on it.  Plus they are also designed for a specific "dead load" (stuff that doesn't move) as well as "live" load (stuff that does move, like people.

If the storage area is mostly just for storage, you're not planning on storing really heavy stuff, and you don't mind the floor vibrating a bit when you walk on it, you can safely get away with using those 2x8s.  On the other hand, if you have to have the finish building inspected at any point, then the inspector might give you some grief so in that case it would probably be worth the extra cost for using 2x10s

Lloyd Carter wrote:It's a 16 foot x 30 foot Gambrel style.
I bought the lumber 4yrs ago just before the prices sky rocketed. A 2x4x8 was $1.49, the 2x12x16 PT were $15.24 all the markings are either worn off, faded, or covered up by something. Amazing how prices jumped. I figured buy it in bulk get a better price. thats fine for most things but it took me a long time to find time to work on it.

All the hurricanes and the destruction they caused have driven the price up on construction materials. Thankfully for us that log this has been a great asset as well. Last year I was selling Spruce Logs for a mere $265 per thousand board feet, and now I am getting $425 per thousand board feet and the sawmills say they cannot get enough.