Pocket Screw Strength/Excuse to buy new toys

[Durnik]

To all,

I have a large concrete floor crawlspace that's in desperate need of some shelving to store items (holiday decorations, paint, etc, etc). I'm thinking of using 2x4s with pocket screws for structural connection and then simple 1/2 plywood shelves. So:

Average height would be ~5 feet tall, 2.5 feet deep and 4 to 6 feet wide between vertical posts (undecided but would like more than 4' wide for storing containers but maybe 6' is a stretch)
Probably three shelves high (bottom, and two shelves above). Bottom shelve would not be resting on the floor due to a slope build into the floor leading to a drain.
Probably 1/2" plywood shelves laid over the 2x4s
Max weight per shelf would be <= 150 lbs spread over the length
The crawlspace is dry and I'm thinking I could get away with not using pressure treated and just put some rubber sheet below each support/vertical member to prevent wicking from the concrete. Does that sound ok or should I use pressure treated just because it's an unconditioned space.

I've seen bracket systems that seem to cost a bomb vs just cheap 2x4s and some plywood. I have also seen 1.5 inch wide "L" brackets that could be used under the horizontal pieces to provide extra support.

Would pocket screws work well to hold 2x4s together without having to use dados, brackets, etc, etc. This would give me one heck of a good excuse to purchase the new Kreg 5 system since it supports 2x4s (hence the ulterior motive)

Any advice?

 

[Barron]

I don't like pressure treated for anything, but that isn't what you asked. Not exactly sure how you are planning to construct the shelves. If you are just going to butt joint the rails, then no, I don't think pocket screws are enough. I Would use dados with pocket screws, that way it's strong enough and you get the new tool. Also, I would expect some sagging in the shelves unless you brace the undersides in some way. Lastly, you could also,use this as the excuse to get a Domino.

 

[SubGuy]

I hate to be the guy that says....I don't think you need that tool, but honestly, you would be fine just doing a butt joint with screws. Additionally, I would use treated for anything touching concrete in a crawlspace. What do you have in there now? Does it get moldy or mildew? That would be a consideration as well.

 

[Berta]

I hate to be the guy that says....I don't think you need that tool, but honestly, you would be fine just doing a butt joint with screws. Additionally, I would use treated for anything touching concrete in a crawlspace. What do you have in there now? Does it get moldy or mildew? That would be a consideration as well.

that would work fine

 

[Skymaster]

NO :}:} treated only way to go,sorry. between the moisture in the concrete and humidity untreated material is not going to last very long. As far as pocket screws YES YES YES BRING YOUR PARTS TO MY SHOP JUST bought the new Foreman WITH THE HD BIT SETUP FOR 1 1/2" and I wanna play

 

[Tarhead]

2 pieces of free advice:
Run the Sagulator calculations on your dimensions: http://www.woodbin.com/calcs/sagulator.htm This will give you an idea of the load you can store on the shelf.

If you are a relocated Yankee in the containment area (sorry, had to do it...noticed you are in Cary), you may not have dealt with crawlspaces or are used to dry basements. Concrete is a very good sponge. Water vapor can penetrate it very easily. Think twice about storing anything in a crawlspace without running a dehumidifier and a serious vapor barrier. Mold and mildew will be a problem. If you put untreated pine in direct contact with the concrete or dirt in a crawlspace plan to deal with rot and termites.

 

[ehpoole]

2 pieces of free advice:
Run the Sagulator calculations on your dimensions: http://www.woodbin.com/calcs/sagulator.htm This will give you an idea of the load you can store on the shelf.

If you are a relocated Yankee in the containment area (sorry, had to do it...noticed you are in Cary), you may not have dealt with crawlspaces or are used to dry basements. Concrete is a very good sponge. Water vapor can penetrate it very easily. Think twice about storing anything in a crawlspace without running a dehumidifier and a serious vapor barrier. Mold and mildew will be a problem. If you put untreated pine in direct contact with the concrete or dirt in a crawlspace plan to deal with rot and termites.

To expand on the above, it is generally Ok for the shelves to be untreated SYP (Southern Yellow Pine), provided you are not in an area with Formosan termites (such as Florida), but all vertical members for shelves should be exclusively pressure treated lumber with a 6" gap between the vertical member and the ground. If possible, an additional top gap between the vertical members and the wooden structure of your home is desirable, if achievable. The pressure treated lumber is undesirable to termites and will discourage them from tunneling through it to create a path to your home's wooden members. The gaps (at ground level, particularly) provide a termite inspector the opportunity to see if termites have created any tunnels between the ground and your shelving as termites can not survive extended direct exposure to up humidified air (hence their use of mud and wood tunnels). In areas with only subterranean termites, and no Formosan termites, untreated SYP is not especially palatable to them, though if desperate they can chew through such, which is why such can be used for the horizontal-only members (including 2x shelving). If in an area with Formosan termites then one should use pressure treated lumber exclusively. For reference, 2x10s and 2x12s make for great shelving members and can support heavy loads even over an 8ft span without excessive sag (3/4" lumber will sag considerably more over the same span).

However, I would suggest using butt joints as well for your shelves and to skip the pocket screws if these shelves will be used for any sort of heavy loads (I don't know precisely what your intentions are) as for such applications I prefer to use traditional #12 or even #14 wood screws (2-1/2" to 3" long if 2x construction) to support heavy loads. If the loads will be considerably lighter and these shelves of much lighter construction then the typically #8 pocket hole screws are acceptable. Two or three screws at each structural load bearing joint will give you good strength. Do not screw the horizontal shelving down as any sagging will pull heavily on your vertical members when the shelves sag under load, instead fasten a horizontal 2x at each end to create a ledge for the shelving to rest upon.

But do not forget to beef up your fastening of the vertical members your shelves attach to since they will not be in contact with the ground and your fasteners, and the surrounding structures, will have to bear 100% of the weight. The best place to attach the vertical members is directly to the crawlspace piers themselves using proper masonry screws (if piers are concrete block) with expanding plastic plastic inserts to securely support the vertical load.

Do monitor your crawlspace for awhile before building shelves to ensure the humidity is never excessive unless you pan to install a dehumidifier. You do not want your new shelving to mildew or your belongings to rot and rust away if the humidity is excessive. Humidity can be greatly reduced by covering all the bare exposed ground with plastic sheeting to seal in the moisture and keep much of it out of your crawlspace by reducing evaporation.

Good luck.

 

[JimD]

Five foot high crawl spaces seem terribly wasteful to me. We looked at a house with a workshop in a space like that when we moved here. It didn't work well due to the piers. It should have been a basement - but many southern builders don't know how to build a basement.

Even in a garage, I put pressure treated down to contact concrete. It is normally used in basement walls too. Crawl spaces may or may not be more likely to be moist than basements (they are typically vented unlike basements but were also not built for habitation so they may not have foundation drains). Pressure treated to contact masonary is a very good general rule, however.

I think everybody needs a pocket jig.

 

[Durnik]

To all,

thanks for all the comments and advice. Just some responses to the questions asked:

1) The crawlspace is actually ~7' tall at minimum. I just have flexible AC pipes running against the walls so I wanted to keep the shelves under them.
2) The crawlspace is dry as a bone and has a 4" concrete floor with gravel and vapor barrier underneath and a drain system below it (the floor is surrounded by a drain system that carries any water away from the house out into the yard where all the gutter drains feed). In addition, the concrete floor does have a slope into a corner drain so if any water (pipe burst or something else) will drain out of the crawlspace into the yard

Now, with all the great feedback and suggestions, I think I'll just go with good old pressure treated lumber and standard overlaps and screws to keep it together. I do have the crawlspace inspected and treated for termites once a year so (hopefully), that will never be an issue. However, as said, it can't hurt to be extra careful and prevent long term degradation due to humidity (and I'm still going to put something under the vertical posts to prevent wicking from the concrete floor).

Thanks all, I'll see if I can sneak the new toy in with the lumber purchase (not that she minds when I occasionally slip in a new tool every now and again)

 

[mkepke]

Funny I was thinking about doing the same thing in my garage.

PT 2×4 uprights dadoed for SPF 2×4 horizontals. Glue and screw. Rip som 3/4 OSB to width and flop onto the horizontals. A screw every so often to make everything rigid and you're done.

-Mark

 

[JimD]

The sagulator has several options including adding a lip at the front and/or back. It stiffens up the shelf significantly. OSB has kind of ugly edges - worse to me than plywood. putting a 1x2 on the edge would dress it up, minimize splinters, and reduce deflection. Could be applied with glue and pneumatic nails (another tool everybody should have is a pneumatic or cordless brad nailer (I have both)).