Garage- doubling up on joists

[BigguyZ]

I have no idea what the lumber rating is, or what was said when the plans were submitted, because I just bought the house 3 months ago.

It looks like normal 2x8 lumber to me. I walked up on the "2nd floor" (it's currently ply wooded), and there was a definite level of spring in the "floor". But it seems to me that it was meant to be some kind of usable space. The roof peaks about 7 feet above the second floor in the middle, and there is a full-size window in that space as well.

It just seems that it's a lof of space to waste. And the ceiling definitely seems sturdy enough for at least drywall and some storage up there... There definitely seems to have been storage up there in the past.

I'm just wondering about reinforcing what's already there by laminating two additional 2x8's butted up against eachother. Wouldn't that add strength? Or would that only help if I used a single 2x8 to span the entire length?

[woodturner]

I'm just wondering about reinforcing what's already there by laminating two additional 2x8's butted up against eachother. Wouldn't that add strength? Or would that only help if I used a single 2x8 to span the entire length?

Another option is to retrofit steel flitch plates - same idea, but steel plates that are engineered and designed for this purpose. They will provide a LOT more stiffness than a 2x8.

[BigguyZ]

Another option is to retrofit steel flitch plates - same idea, but steel plates that are engineered and designed for this purpose. They will provide a LOT more stiffness than a 2x8.

I'm open to options. However, I am on a budget- both financially and time-wise. The garage is my future wood shop, and I need to get moved into it ASAP, as I have to get to pen turning for a show. How are the steel plates installed? Is this something I can do myself (a big factor)? And how much more $$ is it?

Thanks,
Travis

[woodturner]

How are the steel plates installed? Is this something I can do myself (a big factor)?

They are "sistered" to the existing joists, in the same way one might sister another wood member. The plates are nailed to the side of the joist. It's really just a steel joist (but much thinner, of course) with holes to nail to the wood.

Cost will vary with location, but often it's less expensive than wood. Should be able to DIY, assuming some carpentry skill.

[pelligrini]

I'm open to options. However, I am on a budget- both financially and time-wise. The garage is my future wood shop, and I need to get moved into it ASAP, as I have to get to pen turning for a show. How are the steel plates installed? Is this something I can do myself (a big factor)? And how much more $$ is it?

Thanks,
Travis

You might call a good local lumber yard for options and pricing. They might have some other solutions too. Most decent yards will have an engineer on staff to help with designs.

Do you even have room to get a full length 2x8 joist into place next to your existing ones? I was trying to figure out how I would maneuver one in a 14 1/2" space and get it over the top plates and the small clearance of the rafters and roof decking. I suppose it wouldn't be too bad if one end had a lot of room, like the attic being open to the rest of the house.

I don't think butting two shorter 2x8s fastened to the sides of your existing joists would help all that much. Maybe some sort of plate connector at the joint might work. This is getting into engineering territory, of which I defer to the professionals.

[woodturner]

This is getting into engineering territory, of which I defer to the professionals.

As a practical matter, none of us can give professional engineering advice over the internet. In most states (including mine), professional practice laws prohibit doing engineering work on a building that we have not personally inspected.

Even as an engineer, I share the reluctance to spend the money when I need engineering that is outside my field of expertise. Every time I "save that money", it ends up costing more and results in a less suitable solution.

I recommend paying the $350 to $500 to hire the engineer and get a solution that is optimal for the OPs situation. You will be money ahead in the long run.

[mleichtle]

Ok, I've worked in design at a lumber yard for 8 years, both stick frame design, and designing trusses. but its been 5 years and I haven't kept up. but I disagree with most of you. the dead load is the joists its self, drywall, inulation and flooring above. What does a 12"x 12" peic of plywood and drywall weigh? Well under 5 lbs. and live load is items being stored and you walking around. WRONG WRONG WRONG. It takes more household items than you think to add up to that much weight, 10 Psf. same with dead load. According the linked code, SPF #2 will span 22' 4" @ 16 o.c. alone. I recomend talking to your code inspector and a designer at the lumber yard, Actually the sales person at lumberyard should be knowledgeable enough to tell you if you need to do anything, the guy at contractor desk at HD should know too, but I wouldn't count on it. If your buying a permit or lumber it may not cost anything. It might feel a little springy, but its not a living space, so comfort isn't a priority.

My 2x6, 16" o.c. garage joists span 22', hold drywall, insulation, avg storage above, and wood ladders hung below, don't forget the garage door and opener. and after 40+ years this house has been alive, there isn't even a crack in the drywall. in this part of the country snow tires used to be household items around the time this house was built. My dads garage is about the same, and he had an old V8 engine block in his attic for years. I think your fine as is. Check with the building inspecter just to be sure.

For engineered trusses you might fined a small stamp with a maker and order number to track down some drawings. there is still a live load calculated into them. they had to consider the builders and there tools climbing around to build it. Most likely storage loads are built in also, cause you never know what the home owner is going to do later.

[woodturner]

According the linked code, SPF #2 will span 22' 4" @ 16 o.c. alone.

Which table are you reading?

live load is items being stored and you walking around, mechanicals like furnace, wiring and the like.

Sorry, that is not correct. Mechanicals like the furnace, wiring, etc. are dead load, not live load. Live load is, by definition, load that changes. It's mostly people, but for residential buildings, it includes people, bookshelves, stored items, etc. Anything "permanently" attached to the building is dead load.
http://www.businessdictionary.com/de...live-load.html

If the building is designed for dead load only, NOTHING can be "legally" stored there.

Your example of a vastly under-engineered building surviving merely demonstrates that there is a safety margin in the code tables. It doesn't meet code and is not safe.

If it's just your shop and you never sell it, maybe that is OK. If you ever sell it, though, you open yourself to huge liability. There is a guy serving jail time in this area for under-engineering a deck. He built a deck on his house about 17 years ago, house had been sold three or four times before the deck collaped and caused a death. The authorities traced it back to him and he was charged with negligent homicide. Rather a rare and unusual situation, but should give one pause when working on a home they may one day sell.

With respect, these are examples of why, in the US, a stamp is required by a Professional Engineer certifying the structural design was approved by an engineer or architect. It is not legal for a designer to do structural design unless the design is checked and stamped by a P.E.

[iceman61]

According the linked code, SPF #2 will span 22' 4" @ 16 o.c. alone.

according to what Im seeing on the online calculator, the recommended span for 2x6 SPF is only 11 ft. 9 in. You have to bump it up to a 2x12 to span more than 19 ft.

http://www.awc.org/calculators/span/...orizontal+Span

[pelligrini]

That's a handy calculator.

The loads and deflection you've got in there is a lot higher than what the OP is probably needing.

[mleichtle]

Thanks for correcting me Woodturner, I was wrong. I was looking at the PDF that Pelligrini posted. It states, second from the bottom in the 16" o.c. table 2x8 col. 22' 4". It also states right on top, (which like a dummy I didn't see) "Without Storage"

So what are they thinking the 10 psf live load is for? When I was working Wisconsin didn't use the IRC, I believe we are now, and that was considered storage.

[woodturner]

So what are they thinking the 10 psf live load is for?

The 10 psf live load allows for a workman to work in the attic.

10 psf is a light load. A 200 lb person standing would be about 200 psf. However, the load ratings in the table are for distributed load. So if that workman is crawling around on a 4x8 sheet of plywood, he is generating a 6.25 psf load, with the rating.