huangyhg

roof expansion joints
i am in the process of designing a warehouse structural that has tilt-up precast wall panels and a bar joist roof with steel beam lines. the building is about 160,000 sq.ft (approx. 350'x450').
i was wondering if anyone had any information or could direct me on how often or if i need an expansion joint in the roof. any guidance or information would be greatly appreciated. thanks
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roof expansion joints should coincide with structural joints. if there are no structural joints in the structure, then roof isolation joints should be installed so that you have no more than 200 feet in any direction that is not jointed. this guideline is for built-up roofing or hot-mopped modified bitumen roofs. for mechanically fastened or ballasted single-ply roof systems, that distance can be exceeded. for fully adhered single-ply systems, similar spacing would apply.
refer to the national roofing contractor's association for details on roof isolation joints. if the joint has to be placed such that it impedes drainage, you will have to get creative in the jointing process. i have designed "flat" isolation joints to accommodate drainage considerations.
which leads me to my next question... when is required to provide structural joints? is it better to use expansion joints versus structural joints.
joemarch...different systems and materials require different jointing. for instance, tilt-wall systems generally require no special joints, since they are jointed at each panel. the associated interior steel framing would require jointing based on the type of structure and its configuration. masonry requires jointing on different spacing than the structural steel would require.
joints are necessary when cumulative strains are such that the system would be inordinately stressed or damaging movement would occur. while you can compute this, there are some generally used guidelines such as the one for roofing materials at 200 feet center-to-center. joints in floors are required at much greater frequency because of the restraint conditions imposed on slabs on grade.
i would suggest you research and learn the differences between expansion, construction, isolation, and control joints. each has its purpose, configuration, and need.
ron, i would love to see the flat expansion joint that you came up with. ive got a similar situation now im struggling with, i have an existing sloped roof with 3" polyiso and bur and gravel, and the roof on my addition will simply continue along that same slope....so i need an expansion joint that wont hold water.
mcbarney....use a 36-inch wide piece of epdm across the joint, running longitudinally along the joint. place it "dry" and do not attach it. install the bur continuing over the epdm using the same ply lapping as in the rest of the roof. if you are tieing into an old roof, make sure your tie-in runs at least 36 inches above the edge of the epdm.
this "slip sheet" approach cuts the strain of the joint movement in half, and then attenuates the strain over an 18-inch wide section (1/2 on each side of the 36-inch sheet).
ron, thank you for your quick reply. i ran your suggestion by my boss and he says the epdm would not work well with the built up roofing, that it would cause swelling. i am far from being a roofing expert, what do you think about what he is saying?
will not cause swelling under hot mopped asphalt. he's right that certain petroleum solvents cause epdm to swell, but it works under hot asphalt.
ron, do you have any cad details and/or specs of this expansion joint that you could email to me? i like your idea, i just have to sell it to my boss.
mcbarney...i'll see what i can dig up. will need contact info.
ron, thanks, i appreciate your help. my email is

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