OT - Need to make a curved deck rim joist
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  1. #1
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    Default OT - Need to make a curved deck rim joist

    Local building code seems to require heavy deck construction; 2x10, 16" o.c. PT joists; triple 2x10 PT beams, 4x6 PT posts on 12" dia. concrete pier, etc. Maximum cantilever of joists past beam about 18".

    Building a small (7' x 7') deck and wish to "bow" the side parallel to the house. Double 2x10 rim joist is called out. "Bow" is 6'-6" radius, adding 12" of depth at the midpoint. Being that the total maximum joist length is only 8', the rim joist is certainly not heavily loaded in any direction, and the required 4x4 rail posts can be attached to the joists rather than the rim.

    Looking for suggestions of material and method to create the bowed rim to satisfy the desired appearance, function, and building inspector. I'd prefer to use PT or equivalent weatherproof material, as decking will be Trex or similar synthetic.

    Current idea is to build a convex 1/2" or 3/4" thk. MDF form with the desired curvature on edge, spaced and stacked to a total thickness of 10".

    - What type and thickness of weather resistant, exterior grade plywood, OSB, etc. will easily deflect 12" over 7 feet? Something readily available from the local outlets, Dykes Lumber, etc.?

    - What type of glue?

    - Clamp with pairs of lengths of pipe and bolts? Cut pockets in the sides of the MDF form and use 2x4s on edge?

    - Suggested total thickness or number of layers?

    - Attachment of the glued up rim joist to the regular joists?

    Interior work space is limited, will current North Jersey outdoor temperatures inhibit proper glue curing?

    Thanks,
    Larry

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    If the inspector will agree that the curved rim joist is not structural, then just make it out of Trex. It is available in 3/4" thick planks and bends very easily. Let your joists run long over the structural beam, then layout the arc and trim each joist. Bend the Trex around the curve defined by the ends of the joists and fasten. You can get up to 12" nominal widths in Trex trim planks.

    http://www.trex.com/trim/default.aspx

    Dennis

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    Not sure if I understood correctly but I would definitely not use MDF in an exterior application.

    I just re-did a store front using Azek. The stuff is really great, I think it is PVC of some sort but it saws, planes, and nails just like wood. Won't rot, the bugs won't eat it, etc. You could bend a 3/4 piece around the radius you are talking about without a problem. Build up the interior structure with PT and cover with Azek trim boards.

    Alan

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    I did a 10 ft radius with 20 foot long cedar 1 x 10's screwed and glued together. Been 10 years now and still looks like new. It was a full 90 degree bend and the cedar wrapped around so that part of it was also flat to join up with the other facia boards.

    The fun part was the gutters!

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    Dennis - Trex would be fine IF I can dodge the structural requirement. The natural finish eliminates the need for anything else.

    Alan - I forgot about Azek. Great suff, I used it to replace exterior crown mouldings and rake boards on the 120 year old house. The blazing white color would need to be finished to match the deck. Or maybe not...

    The MDF was to build a temporary fixture to laminate a structural rim joist, rather than use the joist ends to define the shape. Maybe a lot of extra work?

    Motion - Cedar looks like Trex, or vice versa.

    The consensus seems to be to avoid laminating a structural piece. But what if that's what's REQUIRED? Material, glue, clamping?

    Thanks to all for the suggestions.

    Larry

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    Quote Originally Posted by ljgoldberg View Post
    Double 2x10 rim joist is called out.
    really? for the rim that's perpendicular to the joists? what exactly for? i would think that as long as a few of the joist bays are blocked above the beam you wouldn't need any rim at all unless the type of handrail used called for it as an attachment point. common sense IMO.

    wonder if you could get away with doing the "structural" rim in short 32" "facets" and then wrap it in trex or a 1x10 planed down enough easily take the bend? does it have to be pretty from underneath?



    dave

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    Hey Larry,

    If you were going to need a structural bowed beam, I would probably go with epoxy for the lamination. Construction adhesives are too flexible, PVA glue (Titebond III) would also work, but you don't have a lot of open time, and juggling multiple laminations that long would be a pain.

    Even if it's cold out, epoxy will cure, just slowly, which in this case is a good thing.

    The idea of an MDF form is perfect. Make sure you wax it well or wrap in plastic.

    1/2" laminations might be thin enough for that amount of bow. You'ld probably have to make the form a little tighter radius to allow for springback. the thinner the laminations the less springback you have to compensate for.

    Instead of bar clamps, think about using 2 or 3 strap clamps to pull along the entire face. Must faster and more even pressure. Another way is to make a mating MDF form (concave) that matches the curve of the convex one, minus the thickness of the beam. These would clamp together easily with bar clamps.

    Good luck,

    Burt

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    Default Success

    Eight layers of pressure treated 1/2'' plywood, Tite Bond III glue, and 14 3/4" pipe clamps later.

    Joist ends were cut on the appropriate bevel to the marked curve. Temporary cleats were nailed to the joists. Temporary brackets were nailed to the center and end joists to extend them outwards to provide a horizontal work surface.

    9 1/2" x 96" panels were ripped from the plywood, liberally rolled with glue, and temporarily rested on the brackets and held in place with rope. The center clamps were tightened against the cleat and a temporary 2x2 spreader on the outside of the beam. Everything proceeded so well we then did the clamp to the left, then one to the right, then the one to the left, and the last one to the left. Oops, forgot that we planned to do them symetrically from the center out.

    Eventually got them all pulled in clamped. Left to dry 48 hours. Setup an extended fence on the table saw, raised the blade to the max and cleaned up the two long edges. All joints were tight with the exception of the innermost ply near the center along the bottom only.

    2x10 blocking was installed behind the curved beam "just in case". The beam was then lag bolted to the joist ends. Trexx 4x4 posts were then carriage bolted to the beam.

    All in all a successful project. Thank you to all for the suggestions.

    Larry
    Attached Thumbnails Attached Thumbnails deck1.jpg   deck2.jpg   deck3.jpg  


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