Flooring in my shop attic question

  • Advertise with us

« back to Designing Woodworking Projects forum

Forum topic by brantley posted 01-21-2011 10:31 PM 1840 views 0 times favorited 14 replies Add to Favorites Watch
View brantley's profile


185 posts in 2681 days

01-21-2011 10:31 PM

Topic tags/keywords: question flooring attic

Ive got a 20 ft x 30ft shop at my house thats 5 years old. The structure is made of cinder blocks. The main area in the shop is 20ft by 20ft with a small room in the back. Right now there is no flooring on the rafters and i would like to put some there to utilize for storage. The rafters are 2ft apart and are made of 2×8’s i believe. My question is, without seeing it, do you think iw ould be able to put some sort of flooring up there and be able to walk on it? Or would i be better off putting the flooring up there, climbing up the ladder and putting boxes up there and not walking on it? Thanks

updated with pics




14 replies so far

View IrreverentJack's profile


724 posts in 2267 days

#1 posted 01-21-2011 11:06 PM

Brantley, The guys that know “loads” will want more info. Rafters support the roof, joists are horizontal. List joist size, span and headroom, maybe roof pitch. A diagram might help. By “rafters” did you mean trusses? -Jack

View chrisstef's profile


15491 posts in 2431 days

#2 posted 01-21-2011 11:40 PM

Talking with our new construction guy here the maximum span for a 2×8 @ 24” OC is 11’6”. So without a center beam below the existing joists to pick up the load it may not be a great idea.

-- "there aren’t many hand tools as awe-inspiring as the #8 jointer. I mean, it just reeks of cast iron heft and hubris" - Smitty

View brantley's profile


185 posts in 2681 days

#3 posted 01-21-2011 11:44 PM

irreverent jack sorry i was unclear. Im not too experienced when it comes to this stuff. The wood thats horizantal to the walls are 2ft apart. There are 2×4’s that attach to these wood pieces that run vertical and attack to the frame under the roof,which i tried to illustrate in my crude drawing. There is about 3 1/2 feet between each vertical piece. I have also attached a picture of the outside of the shop that can give you the idea of the pitch of the roof. Its the only picture i had on this computer currently



View brantley's profile


185 posts in 2681 days

#4 posted 01-21-2011 11:46 PM

Chrisstef , what if i put some more 2×8 joists between the existing joists so they would be 12” OC?

View Gregn's profile


1642 posts in 2408 days

#5 posted 01-22-2011 12:18 AM

If I’m understanding you correctly, you will either need a load bearing wall or a load bearing beam down below to support and carry the weight of the floor and items you would be storing up there.

-- I don't make mistakes, I have great learning lessons, Greg

View crank49's profile


3979 posts in 2395 days

#6 posted 01-22-2011 03:18 AM

There are ways to make this work without columns, but you will have to talk to an engineer. The problem is most engineers won’t make a recommendation for free, and they can’t make a cheap one due to liability issues. I design buildings and industrial processing structural steel all the time, but I’m not a PE (professional engineer) so I do the work, take it to someone who is a certified PE, he looks it over, puts his “PE Stamp” on it and charges me a minimum of $600. That’s just the way it works. If a structure falls and hurts someone, guess who is going to loose a major piece of their ass; the engineer who’s name is on the drawing.

I just had a similar job, in my kitchen. It is a 21ft X 22ft space with a load bearing wall through it. I wanted to remove the wall so I went into the attic and built a truss, along the length of the room, parallel to, and under the peak of the roof. My truss is sitting on top of the ceiling joists. It is 24 ft long and 16” high. The web of the truss is two layers of 3/4” OSB with staggered joints and glued together with structural adheasive and screws. The top and bottom flanges (chords) are 2 X 6s and 2×4s. I ran a 2×4 along the bottom edge of the truss web on both sides. Glued and screwed. Then set a 2×6 on the top surface of the ceiling joist and stood the web up on edge on top of it. Glued and screwed. Then did the same thing on the top of the truss. Finally I tied the truss to each ceiling joist with hurricane clips and added diagonal braces to keep it from flipping over (lateral bracing). I think this truss will carry a 4ft snow load plus the weight of the roof and ceiling plus whatever junk I store in the attic. About 40,000 lbs.

I absolutely do not recommend you do what I did, but an engineer might recommend a solution that works for you.

-- Michael: Hillary has a long list of accomplishments, though most DAs would refer to them as felonies.

View canadianchips's profile


2310 posts in 2421 days

#7 posted 01-23-2011 02:43 PM

You said you building is made from cinder blocks:
1. How is the original joists attached to the walls ?
2. Are they sitting on top of cinder block or attached to the blocks ?
When calculating what you are going to store up there ALWAYS figure on worst case scenario. You really don’t want this floor falling down .
I looked at my “span load chart” Spruce,pine,fir 2” x 8” on 24” o.c. allow for 11’6” span. When you go to 12” o.c. it increase to 14’11”.
It is difficult to offer suggestion without seeing pictures of the inside of the building.

-- "My mission in life - make everyone smile !"

View Sailor's profile


543 posts in 2689 days

#8 posted 01-23-2011 03:51 PM

This is what I would do, it should work no problem but you sacrifice a bit of storage space.

It sounds like you do not have trusses, because there aren’t many trusses that have a 2×8 bottom chord on them unless they are attic trusses, tray ceilings, scissor trusses, or +80’ers ect. ect. ect.

Basically you have your 2×8 ceiling joists that are spanning 20’ when they should only span 11’6”. So you need a beam or a wall or something running across your ceiling suporting each ceiling joist. Instead of building a beam under the joists that would take up you headroom in the shop below, build a beam on top of the joists and run plywood on each side of it. I wish I knew exactly what size beam you needed to span that 20’ but I am not sure about that. But, build the beam to rest it’s load on the block walls then tie each ceiling joist into it with a 2×4 nailed onto the side of each ceiling joist and then nailed to the beam.

I think this will solve your problem.

-- Dothan, Alabama Check out my woodworking blog! Also my Youtube Channel's Facebook page

View Sailor's profile


543 posts in 2689 days

#9 posted 01-23-2011 04:00 PM

After reading crank’s post a slower the second time I realize that basically he built a beam on the top of his ceiling joists, but just in the form of a floor truss which is basically a beam. Like he said, you probably don’t want to build one of these.

A problem you may have though is actually getting the beam into the attic, unless you built in shorter sections and actually did the building in the attic. If you did this you would want to stagger your joints at least 4’ apart I would think.

You should have not problem getting up there and walking on the ceiling joists now. I would put up a few sheets of plywood where I knew the joist wasn’t going to be before I started building for two reasons.
1. to give you something to stand on
2. so that you can go ahead and nail the joists on their correct 32” centers on the plywood which probably needs to be done because the boards are not going to be perfectly straight and the spacing will be off somewhere that needs to be corrected

-- Dothan, Alabama Check out my woodworking blog! Also my Youtube Channel's Facebook page

View IrreverentJack's profile


724 posts in 2267 days

#10 posted 01-23-2011 06:45 PM

Garages are often built to minimum standards, without much of a safety margin. You need to be careful adding any unanticipated loads. Before you install a ceiling or a floor make sure it will be safe. Talk to the/a builder about it.
You’ll need to decide what you want to put up there. Empty boxes and Christmas decorations are probably okay. If you want to dry 4000 bft of hardwood, store a few outboard motors and your brother in laws spare race engine, even Sailor’s hanging beam might not help. Good luck. -Jack

View KnotWright's profile


252 posts in 2912 days

#11 posted 01-23-2011 07:14 PM

After looking at the photo and the drawing, it looks like you have very simple trusses. Its not the normal to have the bracing running completely vertical (90 degree angle) from the bottom cord. Normally when the bracing runs completely vertical these are the end wall trusses and the reason for this is to make attaching the siiding easier.

You can do a “google” search on trusses and find a lot of pictures of trusses.

If in fact you do have trusses framing your roof you should not alter them without contacting an engineer because you can do more harm than good if you aren’t careful.

I’m lucky enough to have a couple of truss builders in the Austin area that I can call and ask questions, you might check your area and see if you have someone near by. Most of the time they are happy to answer your questions.

If you load up the bottom cord with a plywood floor and then store too many items you can get at the least a sagging ceiling and roof, and worse case truss failure. So just make sure you get good information before you decide on what you want to to.

-- James

View brantley's profile


185 posts in 2681 days

#12 posted 01-24-2011 04:56 PM

updated with pictures of the inside.

View IrreverentJack's profile


724 posts in 2267 days

#13 posted 01-24-2011 06:43 PM

Brantley, You don’t have much of a snow load in Georgia and your roof does have a good pitch, but I wouldn’t put any more weight up there. -Jack

View Nomad62's profile


726 posts in 2382 days

#14 posted 01-25-2011 07:55 PM

Your question reads to me as if you are only concerned about walking around once you have put some flooring down; you would probably be ok, but then you need to worry about the weight of the flooring, whatever you store, and then your weight of walking around on it. I know from experience (as well as most everyone else, I’m sure) that a horizontal surface, such as the the flooring you want to install, is little more than a crap magnet and will be the place to go when you have that special piece of something that you just cannot throw out. And you will have more and more of those. So, in the end, it will not be strong enough. I would strongly suggest that if you need to do something of this sort, and do not do the engineer thing (like most people don’t), then at least put a pair (or 3) of posts under a beam that runs down the center of the garage for added support.

-- Power tools put us ahead of the monkeys

Have your say...

You must be signed in to reply.

DISCLAIMER: Any posts on LJ are posted by individuals acting in their own right and do not necessarily reflect the views of LJ. LJ will not be held liable for the actions of any user.

Latest Projects | Latest Blog Entries | Latest Forum Topics