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oldpops
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# Posted: 1 Mar 2024 05:20pm
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Hello all - new to the website. Searched some posts but not sure if what I need. I need to build a 16' x 20' storage shed, in which I will store some woodworking tools along with other household stuff. We live in southern California so there is no snow load, frost line, or ugly weather. Just occasional rain. It's been nearly 40 years since I built an outdoor shed. Anyway, I was thinking about using concrete blocks and pressure treated wood 9for the foundation and floor. Anyone here have any advice or suggestions on how to lay out the blocks, and how best to frame the the floor? (what spacing of the concrete blocks, what size wood, and what their spacing should be?)?etc.) Any help, advice, layout and framing suggestions are welcome!
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gcrank1
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# Posted: 1 Mar 2024 07:06pm
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Welcome!
Have you considered a diy pole building?
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spencerin
Member
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# Posted: 1 Mar 2024 10:46pm
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Or buying a pre-built 16' x 20' shed and having it delivered? All you'd have to worry about is site/foundation prep.
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paulz
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# Posted: 2 Mar 2024 08:41am - Edited by: paulz
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I'm at the north end of the state but same environmental conditions. My structure is only 12x20 (9x6 bathroom later added) so I only ran two rows of girders (4x8) on concrete blocks 4' apart. You probably need 3 rows but I have no real construction knowledge, others here do. I got a screaming deal on 2x8s so that is my floor joists, on 1' centers. This was over a decade ago and so far so good, we pretty much live there. Wood stove is the only real dead weight, as I recall I stuck another block under that.
Good luck on the project.
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Brettny
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# Posted: 2 Mar 2024 09:10am
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It's just a storage shed and your frost line is prob 8in at the most. I would just put it on a compacted gravel pad at the most.
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909
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# Posted: 2 Mar 2024 09:34am
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Beautiful photo Paulz. I agree, I'd also use 3 rows to span 16' . I used compacted gravel, pads, and PT 2 x 10's @ 16" OC.
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paulz
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# Posted: 2 Mar 2024 12:55pm - Edited by: paulz
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Thanks 909. Just watched your new video too. Very nice job, you're obviously one of those construction knowledgeable people I was referring to. My place was more of a "I'll just build a fort, like up in the hills when I was a kid". Closest I ever came to a construction job was as a laborer wielding a shovel.
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oldpops
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# Posted: 2 Mar 2024 01:54pm
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Thanks everyone! I may buy a kit and build it here with my son (he wants me to build it 4 feet longer 16'x24'), but either way I want to make sure that I do the footing & base frame correct! I've seen some videos on YouTube where they use concrete cap stones as the base (2' thick X 8" inches wide, X 16" inches long, but then they still dig a hole in the ground so I don't know how that's any better than compacted gravel. Is 3/4 inch gravel good?
Anyway, what would you folks here suggest? How many concrete piers and how far apart? How many 20' girders? Should I build the actual floor frame out of 2x8 or 2x10 floor joists? And is spacing the floor joists out 16" inches apart OK? I'm planning on 3/4' plywood for the floor - is that smart? I built a lot of interior walls with my dad (as a kid) so I can frame the walls OK, but I'm not to sure on the footing.
Sorry for all the questions, just want to get this right!
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oldpops
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# Posted: 3 Mar 2024 01:21pm
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Anyone still here?
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spencerin
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# Posted: 3 Mar 2024 08:45pm - Edited by: spencerin
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So, are you using pavers on gravel for the piers? Or, actual concrete piers, like sonotubes? It's not clear in your last post.
IMO -
Girders? 3
Floor joists? Minimum 2x6s, if 16" OC
3/4" plywood would make a solid, firm subfloor, yes
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oldpops
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# Posted: 4 Mar 2024 02:28pm
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I'm sorry - new to this. I was thinking of either putting a concrete pier/deck block on 3 or 4 inches of 3/4 gravel. I was also toying with putting down the 3 to 4 inches of gravel, then putting down cap blocks (2"x8"x16), then putting the concrete piers/deck blocks - but my son wondered if that might cause possible shifting in the future. Let me know what you folks think.
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gcrank1
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# Posted: 4 Mar 2024 02:58pm
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Use crushed 3/4 gravel, it will lock together into a good base (rounded off 'river rock' won't). Compact well.
Since you have no frost to heave put down the blocks on the gravel (I like repurposing concrete silo staves if you can get them; they have a bigger footprint. My 'new' batch is $2 @  )
You are ok with your proposed blocks at 4' apart, I think (but I'm no engineer), my 10x16 pre-built spec'ed those. You might check online what pre-built structure companies are saying as a 'blocking schedule' for whatever your size turns out to be, then add a few more.
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spencerin
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# Posted: 4 Mar 2024 08:19pm
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I'd put down the 3/4" gravel and then make the piers out of stacked 4" x 8" x 16" solid concrete block. Although you might not have to worry about frost heave, I'd still grade the ground beneath the shed first so water doesn't collect underneath - you don't want the weight of the shed on soft ground. Also, make sure you leave enough room underneath the shed for ventilation (18" min). Shifting shouldn't be an issue if done right, and even if it does happen, it's easy to jack up a shed and re-level it with shingles as shims.
The spacing of the piers is dependent upon the strength of the girders. For example, I've seen 2 2 x 10s screwed together span 8' and support one-storey load-bearing walls fine. Do you know yet the size of the girders?
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909
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# Posted: 5 Mar 2024 09:53am - Edited by: 909
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Trex Designer
Click the link above.
Scroll down and click "Design Your Deck Online".
It's the Green box on the left.
Once it loads, click on dimensions on the left side.
Add in your dimensions.
16 x 20 = 12 pads.
16 x 24 = 15 pads.
This will give you a rough idea of how to build your base . It's not a replacement for a structual engineer , but it can be a helpful tool. Keep in mind you'll be using 3/4 plywood , while the website assumes you're using 5/4 PT deck boards. Also pay attention to the bracing, connecting hardware, ect.
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gcrank1
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# Posted: 5 Mar 2024 10:30am
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Link doesn't seem to work unless one logs in?
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paulz
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# Posted: 5 Mar 2024 10:44am - Edited by: paulz
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“Problem occurred” here too.
The Net sure has evolved from a time when I could surf around uninhibited to now, can’t even read the news without signing up. That and ads, ads, ads… understandable I suppose, but a bummer.
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909
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# Posted: 5 Mar 2024 11:45am - Edited by: 909
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Thanks. I fixed the link. That page takes a long time to load and is heavy on resources. When you enter 16 X 24 this is what it produces.
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oldpops
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# Posted: 5 Mar 2024 11:47am
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Thanks everybody!!! My next question will be about building rafters with Gussets. I've seen a few videos where they build their rafters with gussets by making a jig on the plywood floor. Unfortunately, I haven't found much info on what dimensions to use (for a 16' wide shed span). Anyone here know? My plan was to have 2 foot spacing, but length & height, is where I'm drawing a blank (I wasn't good in math after they started putting alphabet letters next to the numbers either - lol)
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oldpops
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# Posted: 5 Mar 2024 11:49am
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Maybe '909' has a link to a place that can help me figure out the dimensions to building a rafter/gusset combo for my shed (That would be GREAT!)!
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gcrank1
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# Posted: 5 Mar 2024 02:46pm
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I had considered that 5 'piers' per side for my future
12x28' but have pretty much decided to go with 7 per side of silo block.
With as many as I have available I could even do a complete run under each side.
BTW, if you use any concrete product under wood it is a good idea to put a piece of asphalt shingle between the 'Crete and wood.
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spencerin
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# Posted: 6 Mar 2024 12:59pm - Edited by: spencerin
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oldpops, it's more or less up to you as to the pitch of the roof, especially since you stated there's no snow where you are. Are you doing a metal, or shingle, roof?
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oldpops
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# Posted: 8 Mar 2024 11:07am
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Probably just an asphalt shingle or asphalt roll. I'm thinking of a 3/12 or 4/12 pitch/slope. Because the top cords for this width of shed (18' feet) will be close to 10 feet each, I'm wondering if plywood gussets would be enough, or if I should use a king stud gable design?
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ICC
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# Posted: 8 Mar 2024 03:06pm - Edited by: ICC
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Quoting: oldpops My next question will be about building rafters with Gussets.
That had me thinking you intend to build a gambrel roof, sometimes called a barn roof. Those have two pitches.
Then, I got confused by this.... Quoting: oldpops I'm thinking of a 3/12 or 4/12 pitch/slope.
So, I feel I need some clarification on just what style of roof you are planning; gambrel or gable?
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Quoting: oldpops use a king stud gable design
I think you might mean a "king post", a component of a roof king truss. Is that what you mean?
If you mean a king post, are you aware that the purpose of the king post is to suspend the weight of the cross bean or rafter tie from the ridge. Perhaps you know that; I mention it only because I have met a number of folks who believe the king post is supporting the ridge and transfers weight to the beam. I want to be sure we are on the correct and same page.
FWIW, and because I have a handy illustration, here's something about king studs.
A "king stud" is found in a wall at each end of a header beam. A king stud looks just like a regular full-height wall stud but may not be on the walls 16" or 24" centers. The king stud is adjacent to the jack or trimer stud which is under the end of the header beam. There may be more than one jack/trimmer stud needed depending on the load on the header beam.
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ICC
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# Posted: 8 Mar 2024 03:10pm - Edited by: ICC
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Note that in a king post truss the king post is in tension and so is the rafter tie. The rafter tie keeps the tops of the walls from spreading outwards. It can also hold up the ceiling is one is used. In a king post truss design the rafter tie, or crossbeam can even be two pieces with a butt joint in the center directly under the king post. Proper connecting plates and fasteners must be used.
Probably more than you want to know link
IMO, a 16 ft wide building requires rafter ties unless the roof structure is designed with a ridge BEAM instead of a ridge BOARD.
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oldpops
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# Posted: 9 Mar 2024 09:40am
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I was thinking of using a rafter with gussets similar to the attached illustration. If I don't have too much of a rise, will this work/be strong enough?
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oldpops
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# Posted: 9 Mar 2024 09:42am
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Oh, don't pay attention to the measurements or the dimensions called out on the attached picture, I was just trying to find any illustration on the internet to show what I am thinking about. Do you folks think this design would this be good enough? or should I use a ridge beam design?
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oldpops
Member
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# Posted: 9 Mar 2024 09:51am
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P.S. I probably using the wrong names/terminology when describing the type of roof support system I want
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spencerin
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# Posted: 9 Mar 2024 04:54pm - Edited by: spencerin
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I don't know why you couldn't do a 3/12 or 4/12 roof pitch with gussets. But, you'd definitely need appropriately spaced rafter ties, too, like suggested.....
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oldpops
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# Posted: 10 Mar 2024 09:32am
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Thanks, I think that's going to be the plan: a 3/12 or 4/12 with gussets and roof ties.
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ICC
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# Posted: 10 Mar 2024 11:15am
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Since it is a shed and not a habitable building you can probably get away with using site-built roof triangles, as pictured. I can't call them a truss as there are no internal struts to restrain all loads internally.
Question. What size of 2x material is planned for the rafter and the rafter tie components?
Looking at the rafter tie (horizontal component) a 2x4 could be used in a shed if there is no ceiling to be attached and nothing will be stored on top of the rafter ties. If a ceiling or attic floor is considered that member should more likely be a 2x8 on a 16 foot span and no center supports.
Looking at the rafter itself, a 2x4 is marginal for 10 PSF DL and 20 PSF LL with rafters on 24" centers. (DL = dead load, the materials that make the roof. LL=live load; wind, rain, people working on the roof, snow) 2x6 would be stronger, or use 16" OC rafters. There is no snow load but winds and rain load can add up. The 20 PSF LL is the standard that is used for calculations even when there is no snow at all.
Is this in a seismic zone?
Another question. I've seen people use common deck screws to fasten the gusset plates to the 2x members. Those deck screws are not structurally rated. They can and do snap/break under shear loads that they will be subject to in this manner. Nails are much better. I'd use 6d common nails with about 14-15 into both the rafter and the rafter tie with a 4:12 pitch. Common nails, not box or sinker.
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Quoting: oldpops If I don't have too much of a rise, will this work/be strong enough?
Actually the shallower the rise the greater the forces on the two lower gussets.
The two rafters try to push the tops of the walls outwards. The rafter tie restrains those forces. As we make the roof pitch steeper the rafters produce less horizontal outwards force. So from a standpoint of strength of the lower gusset connection, a 4:12 pitch is better than a 3:12 pitch.
On a 16 ft wide building with 24" OC rafters, the rafter thrust with a 4:12 roof is about 25% less than with 3:12 pitch. That is not a linear relationship; the reduction is less for increases in pitch, but the thrust is reduced with higher and higher pitches. A 4:12 pitch is nicer to work on than a 6:12 though, IMO. And a 3:12 is the minimum pitch for shingles. It is always better to stay away from the minimum end of anything.
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If you build a rafter triangle like this you will not be able to use the H-1 hurricane ties to connect the rafter or rafter tie to the wall top plate. You can use the H2.5A tie although if you use all 2x4 materials. These ties resist uplift and lateral loads from wind better than toe nailing to the top plate.
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