Splicing loft floor joists

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Forum topic by WoodZenStudent posted 05-27-2021 01:23 AM 741 views 0 times favorited 38 replies Add to Favorites Watch
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22 posts in 122 days

05-27-2021 01:23 AM

I’m adding a 15’x15’ loft over one side of my shop. I’m using 2×8x15 wood joists. However, the pieces are too long to put into place as a whole piece. I was thinking about cutting them down and splicing them back together once in place. Roof is already on so there is no way to do it the easy way.

Here’s my plan:

  • Cut the wood into two pieces
  • Put the two pieces together in place and splice them using 1/2” plywood, glued and screwed (both sides)

Would it matter if all were cut in the center or should I stagger the cuts of each board? How long should the splice be? The span is 15’.

Any better ideas?

The loft will be used mainly for storage (scraps of lumber, holiday stuff, etc.). There is no crossbeam running down the center.

38 replies so far

View Ocelot's profile


3238 posts in 3794 days

#1 posted 05-27-2021 01:26 AM

Pictures would help a lot.

-- I intended to be a woodworker, but turned into a tool and lumber collector.

View Ocelot's profile


3238 posts in 3794 days

#2 posted 05-27-2021 01:28 AM

You might consider a scarf joint.

-- I intended to be a woodworker, but turned into a tool and lumber collector.

View WoodZenStudent's profile


22 posts in 122 days

#3 posted 05-27-2021 01:43 AM

Hopefully, you can see the pics. I plan to put it over the garage door.!Ark3-0_Xv9Qdhq1_m57YpsfBAVKXmA

View corelz125's profile


3264 posts in 2132 days

#4 posted 05-27-2021 02:05 AM

Its empty in the pics. You can’t get them at full length or can’t get them to the shop at full length? Definitely stagger them if you do cut them.

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22 posts in 122 days

#5 posted 05-27-2021 02:26 AM

I can get them in full lengths. Just just won’t fit into the space needed as one solid piece.

The picture is loading upside down? It looks normal on my laptop.

View CWWoodworking's profile


2021 posts in 1335 days

#6 posted 05-27-2021 02:57 AM

Put a ledger board underneath the ends and leave them whole. I would use bigger than 2×8

I would not cut them under any circumstance

View CaptainKlutz's profile


4659 posts in 2650 days

#7 posted 05-27-2021 04:25 AM

+1 Would not cut them under any circumstance

Splice load bearing joists are supposed to be supported under the splice area per IRC. There are approved methods for repairing a damaged joist. These require addition of sister joist(s), adhesives, and fasteners. Need to consult a structural engineer or your local building inspector for methods approved locally. Splicing joist usually means putting up 3 boards instead of 1. With current lumber costs, would try hard to avoid splices.

+1 Double check size of lumber .vs. weight loading capacity.
Typical 2×8 length limit used as load bearing floor joist 16” OC is ~10-12ft for SYP. SPF framing lumber is shorter. Might want to look at IRC (building code) chapter 5, Floor Joist spans table.

+1 Add a ledger board,
and use face mount joist hanger’s.

Have you tried to fit a 15ft board in that space yet?
Appears the garage door and track are above the header plate on walls.
Where are you going to attach the loft joist, half way up the roof framing? Then can not use ledger plate and hangers. Plus, Will roof joist anchor point support the weight? Due you have hurricane, coastal wind, or snow loads to accomidate on roof/walls, that subtracts from possible loft weight loading?

Don’t shoot the messenger.
Am sure there a many redneck ways to slap loft floor up there that might work for awhile,
until it comes crashing down on top of your vehicle or tools parked in garage. :(

Be safe, not sorry.

-- If it wasn't for bad luck, I wouldn't have no luck at all, Doom, despair, agony on me… - Albert King - Born Under a Bad Sign released 1967

View therealSteveN's profile


8193 posts in 1730 days

#8 posted 05-27-2021 04:52 AM

Best case scenario is you must put the loft on the back half of the building. As Capn K pointed out your door is going to be in the way of doing anything up front.

Now you are saying you are building a 15×15 loft, then you say a 15” 2×8 won’t fit? So what is the actual measurement side to side on the top of your top plate? Whatever that is is where you will set the joists. Actually all of this should have been done before you put the roof on, A lot easier, and probably to a better end.

I also am wondering where you got info that on a 15’ span a 2×8 was sufficient to bear weight of a loft, much less put anything on the loft floor? You could use a 2×8 if you were working on 10” placement, but if this is to be looked at for code, you should be looking at 2×10. Back the width to 10 or even 12’ you might be ok, at 15 2×8 is light. I am talking side to side width, the measurement I asked for.

-- Think safe, be safe

View Madmark2's profile


2957 posts in 1744 days

#9 posted 05-27-2021 05:42 AM

Plywood won’t work. Splice plates are usually 1/4 or better cold rolled steel 24” long and full width. Agree 15’ unsupported is too long for 2×8’s.

You should have saved the cost of the 16’s and just bought 8’s if you have to cut them.

What are you going to support this with? You can’t splice a cantilever (well YOU can but I won’t walk on it!)

-- The hump with the stump and the pump!

View tvrgeek's profile


2068 posts in 2805 days

#10 posted 05-27-2021 11:28 AM

Read the “Captain’s” post carefully.

Now, you don’t say what this loft is to be used for. Do you intend to use it as work space, as in walk in it? Or is it to be just ab open shelf you set a ladder against and store a few light items? Empty boxes, x-mas ornaments etc. The following is the assumption you want to use the space.

If you were in an agricultural zoned space and no building codes, I might double sister with a 10 foot 2×8, but I am sure that would net meet code. Remember code is MINIMUM. Anyone who does not like trampolines for floors goes one size larger.

I do not see how you think you are going to get a minimum 8 foot garage ceiling below a loft floor. That door does not look like an oversize 8 footer, so I am guessing, correct me if I am wrong, but your walls are only 7 foot.

Look at code for the stairs. There are minimum head-rooms. Stairs that meet code can take up a lot more space than you expect, especially when a sloped wall or ceiling is in the way.

Remember, all lumber is not the same. The junk sold at the local stores in not the same strength as what it used for pre-fab roof trusses. Again, the code will tell you max span for various options.

In other words, an open loft “shelf” makes sense for light storage in a garage. I do not think anything else would be wise in the building as I see in the picture.

View tomsteve's profile


1175 posts in 2375 days

#11 posted 05-27-2021 12:33 PM

2 by 8 shouldnt span 15 feet. in the pics in the link it appears there are 2 in place already. those are collar ties. their purpose and load are different than floor joists. they are intended to keep the walls from bowing out so have no load on them on them.
rule of thumb i was taught quite some time ago:
2 by 6= 6’ span
2 by 8= 8’ span
2 by 10= 10’ span
2 by 12=12’ span

ive added loft space to a structure with a gambrel roof. we were able to get the floor joists in with full bearing on the walls. tricky but doable

itvrgeek brought up a good point about about quality/species of lumber used between framing and trusses. typically the bottom cord will be yellow pine. the top cord and webs are syp BUT that syp isnt the same as big box junk. it will have tighter growth rings.

if you were to use yellow pine, youd still want 2 by 10 for floor joists

View higtron's profile


279 posts in 3833 days

#12 posted 05-27-2021 05:22 PM

Nail or screw a ledger at the height of your loft joists, cut your joists to the length between the ledgers and use joist hangers (Simpson hangers) to attached to the ledgers just like you would build a deck.

-- A friend will help you move, a good friend will help you move a body

View Knockonit's profile


890 posts in 1358 days

#13 posted 05-27-2021 05:35 PM

no header on overhead door, could be an issue, what is loft used for, perhaps divide in two, beam in middle, hang joists on beam side to side then joist short way, one can splice a beam if done correctly, or build a flitch beam to carry load. if spaning the 15 ft, diaghram block it, on joints of plywood, will help with load.
good luck, give it a whole lotta thought of use and design
rj in az

-- Living the dream

View CWWoodworking's profile


2021 posts in 1335 days

#14 posted 05-27-2021 08:47 PM

You could run an LVL in the front and it would be a lot less bouncy and is only 30$ more than a 2×12.

View Knockonit's profile


890 posts in 1358 days

#15 posted 05-27-2021 08:54 PM

12’’ lvl are running around 14.00 a foot

-- Living the dream

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