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  • Re-Roof Dead Load




    I. Purpose of Investigation: 2 of 3

    At the request of the Contractor, Thomas R. Price P.E., of Structural Solutions LLC, inspected the equipment repair building in Portage MI, in the attempt to determine the structural effects of installing a re-roof system over the existing roof, thereby increasing the gravity load that the structure must carry.

    II. Description of Building:

    The building is a single storey pre-engineered metal building. The main building dimen- sions are approximately 82 ft. x 142 ft. x 20 ft. eave. There are (2) lean-to additions: 36 ft. x 33 ft. and 24 ft. x 33 ft., both to be re-roofed. A 71 ft. x 26 ft. addition at one endwall and a higher eave addition at the opposite endwall, are not included in the areas planned for re-roofing.

    III. History:

    Our best information is that the main building was constructed in 1976. The facility is currently in operation as a truck maintenance building.

    Roof leak problems have created the need to repair the roof, and the re-roofing system described below is under consideration for this purpose.

    IV. Field Observations and Notes:

    The structural framing of the building appeared to be in generally good condition.

    Column mounted jib cranes were observed at two locations which did not appear to have been intended in the building design. These columns should be checked for adequacy to support the crane forces.

    A line of single channel endwall posts at the rear of the building have had their girts and wall panels removed, to accommodate a subsequent expansion. These members are likely overstressed under full roof load, and should be braced at the original girt elevations.

    V. Recommendations: 3 of 3

    MBC Sec. 3402.2 allows for increases in structural member forces of up to 5 percent, when making alterations or repairs to a structure.

    The proposed re-roofing system has a self weight of 1.25 psf. If the original building was designed for at least 25 psf gravity roof load, then the re-roofing materials can be installed, without any structural reinforcement necessary. Therefore, verification of original design loads is needed. Buildings in this area, and of this type, are and have been routinely designed for 30 psf or more snow load, and 3 psf dead load, so it is likely that the original design loads exceeded 25 psf. Verification is best made by reviewing the original building plans, or similar documentation.

    If original design documentation cannot be found, it may be possible to verify that at least 25 psf was used in design, by performing a structural survey, analysis and design check of a typical frame and roof purlin. Depending on the results, it may also be necessary to perform material tests on samples of the steel.

    MBC 3402.2 also calls for any structural elements which are found, in the course of altering or repairing, to be deficient, be reinforced, or otherwise made to meet current Code requirements. The jib crane columns and endwall columns described above, must be addressed, in order to meet this Code provision.


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Structural Solutions LLC
1200 Troon Ct. SE
Grand Rapids, MI 49546
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