I want to add a second floor to my garage, which is made of cinder
block 21 x 22 feet. I am very new at woodwork and my English is pretty
poor. So please be patient with me. I need some input about my design
for the second floor, which will be used as storage, not a living
space. The garage is by itself, completely separated from the house.
I am planning to have an engineered center beam that span 21 feet and
will support all the 2x8" 11' joints 16" oc. The second floor
will be 8' at the center and 6' on each side with 2x6" 12'
rafters 16"oc. These rafters will be supported at the center by a
4x8 solid ridge that spans 21 feet. The framing will be made of 2x4
16"oc. One of my concerns is about lateral support for the side
1. Is the entire wall of the first floor cinder block?
2. By "framing," do you mean the exterior walls of the second floor?
If so, that's a traditional construction method.
3. I'm afraid I got a little lost on 'lateral support for the side
frame.' I think your concern is keeping the exterior walls from bowing
out when the rafters are put on top of the walls. With only 2 feet of
fall in 11 feet, I would have similar concerns. I would rethink a roof
pitch that shallow, particularly if you are going to use an asphalt
shingle roof system. If not, collar ties will be a must.
Additionally, I think a 4x8 ridge is a bit of overkill, but that's just
4. Why only 6-foot walls? The cost of raising your ceiling 2 feet
should be minimal, and it's better to have it and not need it than the
other way around.
5. Why a clear span beam on the first floor? By putting one post in
the middle, you could use a doubled 2x10 and still have more strength
than you need. That would save you a bit of money.
I hope I didn't muddy the waters too much :)
1.- Only the first floor is cinder block. The second floor is what I
want to build.
2.- By framinng I meant exterior framing. Not sure that we want to
divide the space inside.
3.- By lateral support I meant exactly that. Bowing out. (new word
The idea is that the 4x8 ridge will sit on 4x4 post on both end to
support the weight, in order not to "bow out"
4.- The city inspector (where I got the permit) told me that it can not
be taller than 18 feet and that is why I am thinking on 8 feet in the
center and 6 feet on the side.
5.- You are right we could have a middle support. My concern was that
my wife or son could hit the post.
I want to thank everybody specially Todd.
I checked with the building inspector and got not permission to build
a second floor, so I am just going to change the roof. It is quite
old, more than 50 years old metal roof and I am planning to build a
A-Type with shingle and about 9/12 pitch to have some attic space. In
this way it is pretty simple and I should be able to do it by myself.
Thanks again to everybody.
Your design sounds unnecessarily complicated to me.
I would forget about all the beams, and simply span the 21 feet with 2x12's
at 16" OC, and use 2x6 rafters at 16" OC. Nail the rafters to a 2x8 ridge
board at the peak.
This arrangement would give you a clear span inside the garage, without the
point loads you would have with a large beam. And, the floor joists will
also serve as collar ties to keep the rafters from spreading the supporting
We used this exact structure on our garage which is 24'x28', and it works
very well, despite a free-span of 23'. It's too great of a span for a
living space, but it works great for light storage.
You would actually have better results with a 21' garage (should result in
a 20' span or less?). If you needed more support, you could switch to 12"
OC spacing, or use engineered wood I-Joists.
It's also much easier to lift 21 foot 2x12's into place than it would be to
lift a 21' engineered beam.
Good luck with your project!
Yes, that is probably a very good idea. I do not know why I did
think about. I guess because the way the garage is right now and
because I have not seen in the hardware store anything longer that 16
feet. I will check tomorrow in a lumber store for 21 feet joist.
However, I do not understand how the floor joist will server as
collar ties because I planning to have 6 feet walls on the side for the
Thanks a lot.
We bought lots of 24 foot 2x12's for our garage and house. Not everyone
carries those lengths, but they shouldn't be too difficult to locate.
If you choose wood I-joists, those can usually be ordered in lengths of 40'
Basically the rafters and floor joist form a triangle. The rafters are
attached at the top, and nailed to the floor joists at the bottom. This
keeps the bottom of the rafters from spreading outward, as the floor joists
are holding them in place. Essentially the floor joist "is" the collar
tie. It's a very strong structure.
Maybe I'm missing something about your requirements... Are you building 6'
walls on "top" of the cinder blocks, and then building the roof on top of
Let's see if I understand this...
You currently have cinder block walls.
The 2nd floor will be built on top of that (You can use the 2x12's @ 16"
OC) for that.
You will be building 6' high walls on top of the 2nd floor deck.
You then want a roof on top of that, but want 8' of headroom in the middle?
If that's the case, you have a couple of options:
1. Scissor Trusses. Quick to install, lightweight, and strong. And, the
truss company will take care of all the engineering for you. But, if you
have to work alone, it could be difficult installing roof trusses.
2. Conventional rafters/collar ties. You can usually move the collar tie up
off the top plates about 1/3 of the total height. In other words, if your
roof rises 6' higher than the walls at the peak, you could raise the collar
ties about 2'. That would give you the 8' headroom you seek.
I originally assumed the roof was being built right on top of the cinder
block walls, with the 2nd floor being framed within the attic space (That's
how we built our garage). If that's the case, you could use the plan I
detailed earlier. You could also check into "attic trusses" which provide
similar space, but I found that stick framing provided a bit more room and
cost a bit less.
My shop is above my two-car garage. I went with the Beam and 2x8's as
suggested by Claudio. The only difference was that I used steel. YMMV, but
my 12"x25' steel beam cost around $260 and about the same for the guy with a
crane to deliver and drop it into place. The cost of the beam was offset by
being able to use 2x8s to frame the floor. I would have otherwise needed a
nominal 14" floor joist to span the whole garage. The bonus was that I got a
free 6" of headroom upstairs bu virtue of the thinner floor.
It sounds as though elevation limiting factor. A beam approach can buy some
extra head room.
By the way, it's a very solid floor.
The beam sat in pockets in the wall. The load of the beam (and what it
carried) was supported by 5 2x6's ganged together to form a post. The floor
structure simply sat on top of the beam. The 2x8 floor joists had an overlap
and were nailed together over the beam. A couple of holes should be drilled
through the top plate of the beam so that a lag screw can be inserted to
lock the beam to the floor structure.
My beam weighed in at about 600 lbs whickhwas not really as much as I
expected. It turned out that I had to make adjustments in its placement.
With a little creativity and leverage, it was not all that hard to
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