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Help needed... building a small deck
Old 03-09-2009, 10:35 PM   #1
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Help needed... building a small deck

Hi,

I am in the process of setting up a small container garden (for fruits and vegetables) on my back patio. The containers I will be using are self-watering containers and they must be level to work as intended. The problem is, my patio is not level (it's slightly sloped for drainage).

So I was thinking about building a small, level deck which would be sitting directly on top of the patio slab. The deck would be very low, probably no more than just a few inches off the slab. I would like the deck to be about 8' x 8'. The deck has to be able to support a load of about 700lbs.

I am used to building furniture but not structural things like a deck, so I need some advice from the experts.

I wanted to use pressure treated lumber (I do not want to either paint or stain the deck). I would use 2x8s for the frame, 4x4s for the (short) legs and 1x6s for the actually decking. Does that sound reasonable?

The frame would be built as shown on picture 1. I was thinking about using butt joints to join the 2x8s (using 3-4 wood screws per joint). It that OK or should I reinforce the joints using other types of fasteners? Other question: how much space should I leave between the joists? 16, 18, 24"? Also, should I use cross-braces between the joists?

For the decking itself, what space should I leave between adjacent 1x6s? 1/4", 1/2"?

And finally, should I secure the deck to the slab? I was thinking that, since it's gonna be sitting very low to the ground, it wouldn't be necessary to anchor it...
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Old 03-09-2009, 10:48 PM   #2
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Given use of PT and a sloped concrete slab: Likely that you have a common 1/4"/foot slope - if so maybe just cut your floor joists at that same slope (removing a 2" x 8' wedge from each one). Done that way you do away with the need for legs and the step up will be just about the perfect 7" rise for a common step at the high part of your deck (assuming 2x6 decking). No need for cross braces then and you could do 2'OC joists. fewer critters /stuff getting lost under the deck. 1/4" gaps should do.
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Old 03-09-2009, 11:07 PM   #3
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Given use of PT and a sloped concrete slab: Likely that you have a common 1/4"/foot slope - if so maybe just cut your floor joists at that same slope (removing a 2" x 8' wedge from each one). Done that way you do away with the need for legs and the step up will be just about the perfect 7" rise for a common step at the high part of your deck (assuming 2x6 decking). No need for cross braces then and you could do 2'OC joists. fewer critters /stuff getting lost under the deck. 1/4" gaps should do.
Thanks for the idea. The reason I wanted to use the legs in the first place:

1) I have a downspout coming out on the slab upstream from the deck. So I want the water to be able to drain downward freely under the deck. If I set the joists directly on the slab, I am afraid that it's going to disrupt the flow of water. Plus, as I water the planters, I want the excess water to drip though the decking and flow freely downslope.

2) The slab is sloped at an angle under the deck (45 degree angle relative to the direction of the joists), so the high part of the slab would be under one corner of the deck and the low part under the opposite corner. Cutting the joists at the right angle would probably take me all summer (and the slab is quite uneven)!
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Old 03-09-2009, 11:14 PM   #4
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OP. For such a small deck, I would also skip the 4x4 legs as previously mentioned.

Instead of cutting the joists as previously suggested, I would place small pieces of concrete (brick, etc) under each joist to level the deck.

You could even put pieces of pressure treated wood under the joists to level the deck.

The less cutting the better. Also use screws when attaching your deck to the joists. If you ever need to replace a board, much easier than nails.

Lumber comes in standard sizes, (lengths). Build to a "standard". Less sawing and waste.
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Old 03-09-2009, 11:23 PM   #5
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OP. Just read your post. I would attach a "plastic drain" pipe to run under the deck. It should fit, if you are using 2 x 8. I seem to remember the drain pipes are 5-6 inches in diameter. (you need to visit your local store and measure).

Also, you might need braces. But you can easily test. Before you screw you decking, place the boards on top of the 2x8 and walk around.

If it seems secure, go ahead and screw. If not, add braces and put the joists closer together.

I still would avoid using the 4x4 posts if possible. Laying the deck on the concrete patio is much more stable and much easier to construct.
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Old 03-09-2009, 11:31 PM   #6
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I would use pressure treated 2 x 8's for the frame. Support it on a pressure treated horizontal 4x4 on each end, then level the 4x4 with shim blocks cut from pressure treated lumber every 2'- they won't disrupt the flow of water. Fasten your rim joists to the 4x4's with toenailed screws , and then use joist hangers to tie everyting together- they are cheap, and will really help tie things together. The deck is only 8 x8 - splurge and use a synthetic decking material like Evergrain or Trex. It will hold up better to the weather and the watering, and be much easier on your feet. They both come in 16' lengths, (actually 192.5") so your waste will be neglible. I would go 16" OC for the joists- it is only 2 more boards, and will be a lot stronger. Fasten one end to the house, no need to anchor it to the slab; (I'd squirt some constuction adhesive under the shims to keep them from shifting) the weight of the planters will hold it down just fine.

Sounds like fun.
Post photos of the completed job!
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Old 03-09-2009, 11:40 PM   #7
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Wolf, good suggestions. Thanks.

As you mentioned, I want to limit the amount of sawing and use as much stock lumber as I can. That's why I picked the 8' x 8' size for the deck.

I was also planning on using screws to attach the deck to the joists.

I'm going to measure the slope tomorrow to see if setting the deck directly on the slab is possible without using the 4x4s.
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Old 03-09-2009, 11:50 PM   #8
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I would use pressure treated 2 x 8's for the frame. Support it on a pressure treated horizontal 4x4 on each end, then level the 4x4 with shim blocks cut from pressure treated lumber every 2'- they won't disrupt the flow of water. Fasten your rim joists to the 4x4's with toenailed screws , and then use joist hangers to tie everyting together- they are cheap, and will really help tie things together. The deck is only 8 x8 - splurge and use a synthetic decking material like Evergrain or Trex. It will hold up better to the weather and the watering, and be much easier on your feet. They both come in 16' lengths, (actually 192.5") so your waste will be neglible. I would go 16" OC for the joists- it is only 2 more boards, and will be a lot stronger. Fasten one end to the house, no need to anchor it to the slab; (I'd squirt some constuction adhesive under the shims to keep them from shifting) the weight of the planters will hold it down just fine.

Sounds like fun.
Post photos of the completed job!
Thanks a bunch. Lots of great ideas. I like your suggestion to use shims to keep the deck level. I also have to check out the synthetic decking material, sounds interesting.

I'll post some pictures on this thread when I am done building the deck and setting up the planters! My goal is to be done by mid-April, just in time for planting season...
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Old 03-10-2009, 01:26 PM   #9
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Quote:
Originally Posted by FIREdreamer View Post
Hi,

I am in the process of setting up a small container garden (for fruits and vegetables) on my back patio.

I wanted to use pressure treated lumber (I do not want to either paint or stain the deck).
Sorry, I don't quite follow you and may misunderstand ... but it doesn't
seem like such a good idea to use treated lumber in close proximity to
your edibles. Another option is products like Trex (there is another big
thread around talking about these various engineered lumber products).
Of course, Trex is only for decking proper, it has little structural strength ...
maybe some of the other products do.
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Old 03-10-2009, 01:58 PM   #10
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Quote:
Originally Posted by Westernskies View Post
Fasten your rim joists to the 4x4's with toenailed screws , and then use joist hangers to tie everyting together- they are cheap, and will really help tie things together.

The deck is only 8 x8 - splurge and use a synthetic decking material like Evergrain or Trex. It will hold up better to the weather and the watering, and be much easier on your feet.

I would go 16" OC for the joists-
I agree with all that, especially joist hangers, or corner brackets, Toe-nailing is for the pros, or at least people better than I am at it.

except:

Quote:
Fasten one end to the house,
Oh, checked your profile and you live in Alabama - no frost there I take it. Generally, if you attach something to the house, it needs to be on a foundation. Up North, frost will heave the deck and it will tear away at your house. But you can still have shifting from moisture changes in the soil. I'd be wary about that. I've done some things where I "hang" the small deck or step from the house, so it can move up/down freely- you can get away with that depending on what it is you are trying to do.


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Old 03-10-2009, 02:21 PM   #11
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Yeah, I wouldn't attach to the house either. I have a pier-and-beam and it floats on a sea of clay.

Use composite decking. As Rusty wrote, you don't want PT wood next to your bare feet or food.
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Old 03-10-2009, 04:51 PM   #12
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Thanks everyone,

The food will be completely insulated from the PT lumber, so I am not concerned about food safety issues (or should I?). The planters, which will be resting on the top of the deck, are made of safe plastic and at no time will the food/potting mix be in contact with the decking. I knew that I should avoid using PT lumber for edging edible in-ground gardens, but is there a similar concern with planters? And I don't go outside bare feet... We had our roof redone in 2007 and every once in a while I find yet another one of those pesky roof nails laying around, waiting to empale something. So I am super careful.

Of course, If I could have my way, I would make the deck out of redwood or cedar, but I think that my wife would balk at the expense...

The deck will be several feet away from the house and I won't be able to attach it to the house anyways. Since it's hard to describe it, I drew a few diagrams to illustrate the current situation. The "downspout" I was talking about earlier is in fact the hydraulic relief for the retention wall. The higher patio is about 12" higher than the lower patio and the deck will provide an intermediate step to go from one to the other (right now we have just one huge step).
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Old 03-10-2009, 05:30 PM   #13
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i like Westernskies idea better than mine, though given your drawing i would probably run the floor joists parallel to the retaining wall and put the 4x4s at right angles and several inches in from the L edge to give a toe kick area. Glue the shims to the 4x4, i'd let it float free on the patio surface. Corner metal is cool, i'd just nail through the perimeter board into the ends of the joists but hangers could be used, just more difficult to work with.
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Old 03-10-2009, 10:28 PM   #14
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Toe-nailing is for the pros, or at least people better than I am at it.
Use 3" galvanized deck screws, predrill with a 1/8" drill bit and they will go in just fine. If you predrill, the joists won't walk when you tighten the screws.

If I were building this, I'd put the whole frame together with 3" deck screws; you could eliminate the joist hangers if you screwed the joists to the rims. If you don't have one, get a 99cent driver bit for your drill, it will go together fast, especially on the decking. I'd use screws there, too, you can use 2" screws for 1x decking.

Calmloki's idea of leaving a 3" toe kick is a good one. It would also make the deck look like it was floating, and you wouldn't see the shims between the deck and the patio if you trim them off flush with the 4x4 girders.

Ideally you want a step of no more than 7.5"-8" above the patio. with a 4x4 frame, 2x8 joists, and 1x decking you will be at 11.5" -12" plus shims- should work out good with one step between the deck and the patio.
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Old 03-11-2009, 04:44 AM   #15
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A new forum on home improvement might be able to help or maybe you can help them. My Home Forums - Powered by vBulletin
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Old 03-20-2009, 07:29 PM   #16
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So, after a couple of days of hard work, I am ready to show you the fruits of my labor.

I ended up building the frame out of pressure treated 2x8s and shimming it until it was perfectly level. I built the decking out of 1x6 cedar planks for food safety. As a finishing touch, I cladded the frame with 1x6 cedar planks (to hide the greenish pressure treated lumber), cutting the planks on an angle so that they would follow the slope of the slab. I left a 1/4" gap between the slab and the cladding for drainage.

The cedar smells great after basking in the sun for a while!

Thanks again for all your suggestions!
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Old 03-21-2009, 04:55 PM   #17
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Great job! Thanks for posting the photo.
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