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HomeMy WebLinkAboutFile Documents.1007 E Durant Ave.0078.2019 (2).ARBK Studio M Engineers, LLC May 6, 2019 Re: 1007 East Durant Ave., Aspen Colorado Hot Tub Patio Surface To Whom It May Concern: My office was contacted by Mike Kuhn, acting general contractor, and asked to inspect the framing conditions discovered during a partial intrusive investigation into a roof leak discovered on a 2nd level hot tub platform located over a parking area at the address above. Apparently water was noticed in the light fixture at some point in the past. After further investigation it was found that spot locations in a waterproof (bitchuthane ) membrane deck had failed, creating a structural framing deterioration issue in spot locations. The purpose of my involvement was to identify how much concrete topping can be safely reinstalled on the renovated deck system, and if any deck framing members (wall or ceiling) needed to be improved, abandoned or replaced so they can safely support the anticipated design loads typical of this type of occupancy and use. Project Description: The hot tub deck is located on the South side (back) of 1007 East Durant. The deck is located one story above ground level, over several parking spots. The deck surface had been removed at the time of my inspection. A layer of pre existing bitchuthane was visible (see photo below). The contactor reported that at least 5 inches of concrete topping were removed, which was noted as being different than the plans the contractor had located for the original build, which indicated a concrete topping thickness of 1. ½ inches. It should be noted that the framing conditions discovered in the field were completely different than the framing conditions shown on the out dated set of prints used for the original construction. Photo NO. 1 05/08/2019 05/13/2019 justinh 1007 East Durant Page Two Observations: During the contractor’s investigation into the water leak, several deck support joists, rim board, parapet wall, and deck plywood were noted as having areas of moisture deterioration. Deterioration amounts varied from minor stains to complete degradation (no structural integrity). Deterioration was most severe in areas where the privacy fence post supports extended through the deck. The membrane did not extend to the top of the concrete surface, but rather stopped short. The moisture was able to penetrate through these points and saturated the framing below, causing fairly extensive deterioration (see photos). Photo NO. 2 Photo NO. 3 Rim Deterioration Joist Deterioration 05/08/2019 05/13/2019 justinh 1007 East Durant Page Three Photo NO. 4 Photo NO. 5 Complete deterioration Of the Rim Board Joist End Deterioration 05/08/2019 05/13/2019 justinh 1007 East Durant Page Four Framing conditions: The 432 sq. foot deck (approx) is framed with a 14 inch BCI 650 joist product (2. 5/16” flange) at a spacing of 12 inches on center. BCI 650’s are an I Joist product made by Boise Cascade that has since been replaced by a product known as a BCI 6500. A double joist was situated below the north south oriented parapet walls. A double 14 inch LVL was situated at the exterior edges (West and East) of the deck system. The members supported an 18” cantilever roof overhang. The roof is a 5:12 over-framed system that covers the 95 ft area (approx) located on the east and west sides of the 2nd level deck. The deck is geometrically characterized by a T-shape (long ‘vertical’ narrow section on the south) configuration. Joists over the long span slope approximately ¼ inch per foot. Joists in the short span condition have a built up plywood taper system directing moisture towards the long slope area. The joists are single span and are supported by a W10x30 steel beam with wood nailer plate located where the deck widens from 11’-10” to 23’-2”. An 88”x88”x36” spa (Jacuzzi Model) with an estimated weight of just under 3,500 lbs will be situated over the deck in the north east corner. The joist span in this area is 9’-2”. Joists in this area are well within the load specifications given by the manufacturer, even with the fully filled spa and 4 inches of concrete topping. It should be noted that the connection of the joists to the house was not visible at the time of my inspection and cannot be commented on during this report. Recommendations: The observable areas of decay I could see during my inspection were inspected, probed and photographed. Probing occurred with a pen knife. It is my understanding that additional decay in the plywood decking and the parapet walls was discovered after my inspection, once portions of these elements were removed. For this reason, the contractor will need to be on the look out for newly discovered areas of decay that remain hidden until floor sheathing (or any construction components) is removed. Decay in joists in leaky floor or roof systems typically begin at the area of water intrusion, which is usually on the top surface. This surface is commonly hidden from view until the floor sheathing is removed. If there is any question at to the integrity of a member, my office should be called and a diagnosis can be reached through a phone directed field probing exercise in combination with some photographic correspondence. At the time of this report, the members noticed during my inspection that are in need of being companioned and abandoned are identified in the attached drawing labeled 3.A which is attached to this report. 05/08/2019 05/13/2019 justinh 1007 East Durant Page Five Replace, Repair or Abandon: The ceiling joists of the car port (i.e. the hot tub deck floor system) are difficult to remove without causing unintended secondary damage to the floor sheathing to which they are fastened. I would recommend that the members with substantial decay (to the point where they need to be companioned) be abandoned (remain in place), with extremely decayed segments cut out in an effort to prevent future micro-bacterial growth or further decay to new members. Unsupported member ends should be avoided by screwing member ends to full length, new companion members. The weight of abandoned members is negligible. New members need to be adequately fastened from above (through the sheathing) with an 8d nail at a spacing of no more than 12 inches on center. In situations were the members are completely destroyed (parapet wall segments and rim board) I would recommend complete replacement. In areas with surface staining (no fiber deterioration), the members can remain. Analysis: The existing framing was analyzed assuming 100% non decayed members under a 4 inch thick cast in place concrete topping over drain mat over hot tar membrane over insulation over ¾” untreated (or treated) plywood. If treated plywood is used, fasteners need to comply with the faster manufacturers recommendations for treated material. Snow loads used in design were 75 psf (roof snow load). Drifting effects were considered for the portions of deck adjacent parapet walls and 2nd story-to-roof walls near the hot tub area. Drift loads range from 20 psf to an additional 75 psf. Drifting patterns are trapezoidal (taper to zero) in accordance with the ASCE 7-10 Chapter 7 Figure 7-8. Deflection limits were set to the values shown in the IRC 2015 Table R301.7. It should be noted that the floor joist limitations in this table are the same as they were in 2001, during the original build of 1007 East Durant, i.e. span /360. This means the long span joists would be expected to deflect 5/8 inches before they would reach 100% capacity in deflection. With the full design loads required by the City of Aspen, it was noted that a majority of the wood framed joists are required to perform at near full capacity in order for the system to support the floor assembly described above. The limiting design criteria was deflection (the degree to which a structural element is displaced under load). Bending capacities were noted as being generally around 80% capacity. For this reason, it is important that any decay extent in members intended to remain and perform be limited to staining of external surfaces only. The fiber decay of any web or flange of any joist would without a doubt lead to an overstress situation in deflection. 05/08/2019 05/13/2019 justinh 1007 East Durant Page Six Deflection failure would be characterized by floor performance such as deflection, bounce, and superficial cracking of the concrete in areas not characterized by control joints. Deflection failure is not typically associated with system collapse (i.e. life safety issues), although in extreme situations it can redirect drainage, cause ponding and accelerate waterproofing failures. Slab Characteristics: The original specification on the 1007 East Durant plans showing 1. ½” topping thickness was most likely abandoned because thin toppings in this mountain climate tend to rapidly disintegrate. I would recommend a 4 inch (uniform) cast in place slab thickness. The specification is attached to this report. Particular attention should be made in regards to the control joints. The joints are important in regards to controlling the cracking caused by curing and thermal movements. Cracking of the slab is unavoidable (but not unmanageable), because of the geometrically changing nature of cured concrete (moisture leaving, slab shrinking), in combination with a host of other factors. Minor cracking in the slab is considered normal. Per the nationally recognized code standard for concrete construction, the ACI 302.1R, even with the best slab designs and proper construction, it is unrealistic to expect completely crack-free and curl-free slab results. ACI Section 3.2.5 specifies that random cracking should be expected in slab construction; a reasonable level being as much as 3% of the slab panel. A panel is defined as the region between control joints. Recommended control joints are shown on the attached sketch labeled sheet S2.0. The slab cracking can be caused by one or more of the following: • Too much water or water added during construction • To high of a cement content in the concrete mix • Accelerated curing as a result of hot and/or dry weather during curing • Concrete mix design • Improper location of reinforcement in the slab depth (lower than upper 3rd of slab depth) • surface friction on the slab bottom (‘gripping’ slab base during curing) • slab thickness (to thin) • shrinkage restraints (pouring tight to foundation walls) • location of contraction and control joints (spaced to far or improperly cut) • structure deflection • moisture intrusion followed by a freeze-spall effect Based on ACI 302.1R section 3.2.5 every effort should be made to avoid pouring slabs tight to any other element of structure. According to the ACI, restraint, from any source, whether internal or external, will increase the potential for random cracking. It should be noted here that the slab will be a radiant slab (heated). 05/08/2019 05/13/2019 justinh 1007 East Durant Page Seven LIMITATIONS: • The areas that I observed were readily accessible using conventional means of access and observation. Likewise, framing and structural system deficiencies that were hidden behind finishes or obstructed from readily available points of visible access may exist, and would similarly invalidate the conclusions in this report. Such anomalies should be reported as they are discovered. • Unless indicated otherwise, my comments or lack thereof, do not indicate an approval of existing structural systems or an indicator of future structural movement or lack thereof. • No warranty is either implied or expressed. • The foam insulation specification for the material below the cast in place 4 inch thick radiant concrete slab is beyond my area of expertise and scope. It is considered a non structural component. • The foam needs to be protected from water intrusion, saturation and absorption throughout the life of the structure. • The 4 inch thick radiant concrete slab is not considered a water proof element. The slab will crack. Cracks will not be water proof. Moisture is fully anticipated to penetrate the slab, travel to the membrane and be redirected through controlled and well thought out and controlled paths that direct the moisture away from susceptible systems (i.e. wood framing etc). • The following services are beyond scope architecture, site plans, energy studies, building component assembly descriptions, land surveying, civil, geotechnical, electrical, mechanical, heating ventilating and air conditioning plumbing, site grading, or acoustical engineering, architectural issues including, but not limited to, site location, access, egress, zoning conformance, stairs, guardrails, water-proofing, insulation, architectural plans, elevations, sections, and schedules. This concludes this report. Please contact my office with any questions or comments. Sincerely, Michael J. Baca, PE NCEES Principal, Studio M Engineers LLC Enclosures: Sheet 1A,2A,3A,4A 05/08/2019 05/13/2019 justinh 05/08/2019 05/13/2019 justinh 05/08/2019 05/13/2019 justinh 05/08/2019SEE NOTES #1 PLANS05/13/2019justinhThis sheet hasbeen updated,see additionalinformation/clarification 05/08/2019SEE NOTES #1 PLANS05/13/2019justinhThis sheet hasbeen updated,see additionalinformation/clarification