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I would like to use the attic space above my 2-car garage for storage of items around the house and garage, and if possible, utilize some of the space as a small work area. The previous owners left the space with some randomly placed pieces of particle board and other flat wood (including an old door!) over the joists to aid with walking around up there. I want to put down some consistent thickness plywood or good quality particle (fiber) board as flooring.

But first, I need to make sure that what I have is strong enough, and if not, get some good ideas on how to strengthen it adequately. I would like to get some expert advice regarding this.

I have included a set of photos that have text in them to help explain my situation and my questions. Thinking that strengthening is a good idea, I included some ideas I have for that, explained in the photos. I would like to know if my proposal is adequate to strengthen the floor sufficiently.

Please review what I've shown and explained and give me your feedback. It would be greatly appreciated!

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After posting my questions and original photos, Chileab Construction gave me some great feedback and asked some good questions. Based on what I've learned I am proposing to add a steel H-beam across the span of my attic space in order to strengthen/stiffen the floor. Chileab asked about the load bearing points for the beam, so I took some additional pictures and created a couple of sketches (first sketch without the beam; second sketch with the proposed beam added) to help show this. I am looking forward to what Chileab Construction thinks about this idea (and others who might want to comment).

One end of roof truss (support point) Other end of roof truss (support point) Sketch of the support structure (as is now) Sketch of the support structure with proposed steel beam and end support blocks added

I read David French's question and I would like to answer him here. David asked how I attached the joists to the underside of the steel beam. What I did was use pieces of heavy gauge steel L-brackets that I bought at a local home improvement store (Menards). I used two L-brackets per joist, one at each side of the steel beam. It's been over 3 years now since I worked on this, but I believe I remember that I used 3/8" carriage bolts to attach each L-bracket to the joist (two carriage bolts per L-bracket). I used a washer under each nut, between the nut and the L-bracket. I believe I used locking nuts. For attaching the top of each L-bracket to the bottom flange of the steel H-beam I decided to create a "sandwich" type of joint using strips of fairly heavy weld steel "straps" (I think 1/8" thick), that I also bought at the home improvement store, along with a stack of thick washers. I used a heavy high grade steel 1/2" bolt to run through each L-bracket, the washer stack, and the steel strap. The result was a joint formed by clamping the edge of the beam flange between the steel strap and the L-bracket, with the stack of washers there to symmetrically load the bolt (distribute the clamp load across the washers and the beam flange edge, and not allow the edge of the beam flange to try to slip out). This is kind of hard to explain, so I will include some pictures that I took back at the time to hopefully help you see what I'm talking about. Something to note is that I had to grind off a good amount of each washer so that I could keep the 1/2" bolt close to the edge of the beam flange for best strength of the joint. (Each stack of washers thickness equaled the thickness of the beam flange.)

view of one side of the beam showing the L-brackets, bolts, steel straps

More views: enter image description here enter image description here enter image description here

  • That's odd that they framed the floors with 2x10s but that attic with 2x6s. Anything to save a few pennies, I guess. – DA01 Dec 15 '14 at 2:27
  • Al, I realize this is an old post, but what did you use to hang the 2x6's to the H-beam? Also, did you put a gusset in that triangle? – David French Apr 14 '18 at 2:53
  • Hi David, thank you for your questions. Those are good questions. I hope I answered your first question by editing my post and adding some text and pictures to help answer your question on how I hung the 2x6's from the beam. Your second question asked if I added a gusset in the triangle. No, I did not. I've been wanting to add to this post anyway to kind of show folks where this project went. It actually went well. I now have a solid floor in my attic above the garage :-). – Al Schuppe Apr 15 '18 at 17:30
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You have 2x6 joists 16" o.c. and lets assume #2 fir- the MAXIMUM spam (where they are supported underneath - bearing the weight) for a 20 lb dead load is 9'10" and for 10 lb dead load: 13' 2"
You show 11' +- in photo but it is unclear if there is support at that point. you can check span table at: https://www.awc.org/pdf/codes-standards/publications/wfcm/AWC-WFCM2018-ViewOnly-1711.pdf

There is some interesting framing in that attic: The 2x4 at the peak of the triangle which is set on top of the ceiling joists is very odd, in my opinion. It is transferring a load from the roof to the ceiling, and unless there is a wall underneath: you probobly have a bow in the ceiling at that point below.

Soooo: minimal storage, depending upon support at the 11' 3/4" point - Once you put a floor downs there even with the intentions of keeping it light up there - people forget in time.. . . .

As to the beefing up the joists with 2x8s that is an option - but the total span is more important. Is the entire width unsupported? and if so what is that total span?

  • Construction: Thank you for your comments. They are very helpful, as is the table that you provided via the link. Regarding your questions on total span and support, the total span of the 2x8 double bottom chord is 22' 4-1/2" and there is no support underneath. Below all that you see in the photos is a 2-car garage that is fully open (no poles or pillars in it). Crazy idea: What if I installed a solid steel I-beam running the full span (22’ 4½”) in parallel with, and bolted to, the 2x8 bottom chord? As for I-beam size, maybe 4x6 inches? That would certainly be stiff and strong. – Al Schuppe Dec 15 '14 at 4:04
  • Beam: Remember that there is a point load beneath the beam which has to be carried down to the foundation - and at that point must be sufficient to carry half of the total load at that one point. If you could include an overall idea of the layout of joists in total it would help - even rough sketch. – Chileab Construction Dec 16 '14 at 4:10
  • Chileab Construction: Thank you again! Please see additional text, photos, and sketches that I added to help show more of a 'total picture' of what I am proposing. – Al Schuppe Dec 18 '14 at 12:56
  • Nice drawings. Note that the item you labeled "roof truss" is not a truss. It actually reduces the load carrying capacity of that double 2x8. I take it that the room is 22x22 - or there about? The points under that center 2x8 'beam' are not over windows or doors correct? That center beam will have to be calculated out for the load - something I would normally farm out to an accredited engineer. Although there are some good internet sites to walk you through it. – Chileab Construction Dec 19 '14 at 9:15
  • Chileab Construction: Thanks. Yes, the total attic room would be about 22' x 22'. Correct, there are no windows or doors under the center 'beam'. (I don't know if the builder doubled or tripled up on the garage wall vertical studs under the center 'beam'. I would think the compressive load bearing ability of vertical studs would be pretty high.) I did actually use the internet to size the steel beam (using tables and load carrying specs). I settled on using what they call W10x22 H-beam, 23' 3" long. It weighs 22lbs/ft, so I'm getting a bunch of guys to get it up to the house. – Al Schuppe Dec 20 '14 at 14:40

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