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HomeMy WebLinkAboutDRB140257_DRB140257 Roof Pre-Design Rpt_1404248520.pdf 14828 West 6th Avenue □ Unit B8 □ Golden, CO 80401 Phone: 303/233-1092 □ Fax: 303/233-2205 ROOF AUDIT & PRE-DESIGN REPORT REPAIR/REPLACE ROOFING BUILDINGS 1 & 2 VAIL RACQUET CLUB VAIL, COLORADO MAY 23, 2014 14828 West 6th Avenue □ Unit B8 □ Golden, CO 80401 Phone: 303/233-1092 □ Fax: 303/233-2205 May 23, 2014 Mr. Steve Loftus Director of Facilities & Grounds Vail Racquet Club 4695 Racquet Club Drive Vail, CO 81657 re: Roof Audit/Pre-Design Report Replace Roofing – Vail Racquet Club Buildings 1 & 2 Executive Summary: Existing Conditions The roofing systems that cover Buildings 1 and 2 at the Vail Racquet Club are located on two levels. The roofing has a plan total area of 11,000 sf. The decking that the roof sits on has a slope of 3/12. This results in a slope factor of 1.03 to raise the surface area total to 11,330 sf. The wood plank deck has an insulated asphalt Built-Up Roof (BUR) over it. This BUR system was installed 32 years ago. The system has now shed much of its scoria (lava rock) surfacing and the felts are exposed. These exposed areas have been deteriorated by UV light and the roof is now in need of replacement. Design Concerns As with any mountain roofs, harsh winter conditions can lead to icing on even cold roof assemblies. This is due to differential melting of the snow on sunny but freezing days. The facilities team understands how ice accumulates on the building and will be addressing that concern. The skylight curbs are low and we would recommend raising them with a 2x6 collar. Other concerns will be covered in more detail in the body of the report. Proposed New Roof The existing insulated asphalt BUR system will be removed to the surface of the wood decking. A new vapor retarder ply will be set on the wood deck. This ply of felt will then be covered with two layers of isocyanurate foam insulation totaling 4.5” in thickness (R-25). The foam will be covered with a layer of ½” thick CDX plywood. An ice and water guard felt will be set on the new plywood sheathing. This layer of felt will then be covered with asphalt dimensional shingles. Schedule The estimated cost of construction for the new roofing system will be supplied in a separate letter report. It is assumed that a typical crew will be able to demolish and reroof an 800 sf area per day. This results in a roofing time period of about 3 weeks. With another week for sheet metal trim installation. May 23, 2014 Roof Audit/Pre-Design Report Replace Roofing – Vail Racquet Club Bldgs. 1 & 2 Page - 2 I. Background: Our firm has been contracted to provide roofing audit and pre-design services on this project. The roofing replacement work is to take place on all of the roof areas shown on the Drawings. This document comprises the pre-design phase submittal for the project. The objective of the report is to provide information indicating that the pertinent code, energy and insurance requirements will be addressed with the new roof system. Along with this information we will also be presenting a new roofing option to the Owner for review. II. Site Visit: A. General While at the site, as-built information was gathered during the roof inspection. This work included coring the existing roof system in order to determine its construction. Photos have also been included that were taken during the site visits. B. Existing Roof System Description The attached roof plan shows how the roof is laid out. The wood plank decking on this building is 1.5” thick and nominal 5.5” wide. The planks are joined along their lengths with a single tongue and groove. This planking has a single layer of 3” thick isocyanurate foam (R-17) over it at the interior space areas. Where the decking bridges over exterior space, the insulation was switched to two layers of 1.5” thick perlite insulation. This lower thermal value (R-8.2) insulation is also half the cost of the foam insulation. Along with the insulation that covers the wood deck, there are also 3” high buried sleepers. We did not find them when we cored the roof, but they are required for BUR systems set on decks with more than 2/12 slope. These wood nailers are used to nail the felts off to. Otherwise the roof membrane would slowly slip down the deck slope. The insulation and nailers are covered with an asphalt BUR system. The roof was constructed with Type IV asphalt. This was also done to help keep the roof from slipping. The surface of the roof was flooded with hot asphalt and then red scoria was broadcast into the asphalt while it was still fluid. It should be noted that as much as 30% of the scoria surface has broken free from the roof surface. This aggregate is very soft and dusty. As a result it doesn’t lock into the asphalt flood coat very well. C. Asbestos The current Federal regulations require that the Owner test for the presence of asbestos roofing products when a roof is removed and replaced. There are exceptions to this testing requirement. If a knowledgeable party can determine the roofs are too new to be suspect or are of the type that would not contain asbestos reinforcing fibers, the testing may be waived. In this instance the roof was installed right around the 1981 ban on asbestos related roofing products. We have taken a membrane sample and it is being tested for the presence of asbestos reinforcing felts. We will issue a separate letter report covering the testing results. May 23, 2014 Roof Audit/Pre-Design Report Replace Roofing – Vail Racquet Club Bldgs. 1 & 2 Page - 3 III. Design Considerations: In preparing a roof replacement design, several considerations must be taken into account during the preparation of the construction documents. Some items are mandated by code, while others are tied in with insurance requirements. This portion of the report covers the basic design criteria that we review prior to the development of the construction documents. A. Roof Deck When roof systems reach the end of their service lives, leakage can occur. This water can damage the substrate roof decking. On this project, there are wood plank roof decks. This type of decking is not easily damaged by roof leaks. The facility’s staff has also done a good job maintaining these old roof areas and therefore extensive long-term leakage has been avoided. At this time we do not anticipate the need for any deck repair or replacement. B. Vapor Retarder Moist air can condense on cold surfaces in the winter time and create problems with mold or building component deterioration. Because of our dry climate, if the interior air is not humidity conditioned and the occupancy load is low, this condensation concern does not play a big role in the roof design. At this facility, some visitors and owners do humidify their units. The facilities group has no control over how much humidity is placed in the units during the course of someone’s stay. As a result it would be prudent to include a vapor retarder in the new construction. C. Insulation The proposed insulation system increases the thermal value of the roof assembly by a factor of about R-8. It is my understanding that the Facilities Department at Vail Racquet Club and the Vail Building Department have been in discussion over roof R-Value and that this would be in an acceptable range. A heating energy savings payback calculation was generated for the proposed R-25 insulation system. The attached calculation indicates that the payback period for the new insulation comes to 5 years. It should be noted that this is a very simplistic calculation that does not take into account air infiltration and other factors. Therefore, the payback periods and energy savings will vary from those actually experienced. The calculation was performed to provide information on the basic performance of the insulation systems. The calculation only takes into account the insulation over interior spaces. D. Wind Resistance When a roof system is replaced, one must make sure that the new roof is able to withstand the uplift forces exerted by the wind. Factory Mutual (FM) has developed a simple calculation that determines the fastening or ballasting requirements for a roof system. This calculation was performed for the roof areas in this project. The results are seen on the table that follows. The upper roof height was used for the calculation as it will experience the greatest uplift forces. May 23, 2014 Roof Audit/Pre-Design Report Replace Roofing – Vail Racquet Club Bldgs. 1 & 2 Page - 4 ITEM UPPER ROOF Design Wind Speed 90 mph Roof Elevation 32’ Parapet Height 0' Multipliers (Perimeter/Corner) 1.23/1.96/2.67 Perimeter Width 6’ FM Approval Rating 1-60 Field Uplift Pressure -21 psf Perimeter Uplift Pressure -32 psf Corner Uplift Pressure -45 psf A separate wind uplift analysis was performed using ASCE 7-05. This calculation can be found attached to the report. Here, the field of the roof uplift comes to -12.3 psf. The results vary slightly between the two calculations. Both the FM & ASCE 7 calculations indicate that an FM 1-60 rated roof would be sufficient. E. Fire Resistance The roofs on this building must also meet fire resistance criteria. The surface of the roof must be able to meet UL Class A requirements. The insulation used in the system must meet FM 4450 Class I approval. If the insulation meets this approval criteria a thermal barrier will not be required between the foam insulation and the wood deck. This thermal barrier would consist of a layer of 5/8” Type X gypsum board. F. Drainage 1. Roof Valley Slope: While the roof gables slope at the rate of 3/12, the two valleys where gable sections meet have no slope built into them. This situation will be remedied with the installation of tapered insulation crickets in the valley areas. The shingle roofing will be held back 2’ up the slope from the cricket valleys. The valleys will be constructed with either 90 mil EPDM roofing or modified bitumen roofing. 2. Gutters: When the roofing system is replaced, new gutter should be installed. The current gutters will have to be removed when the sheet metal gravel guard/fascia is replaced. G. Structural Considerations: The current roof weighs about 6 psf at the perlite insulation areas. The new proposed shingle roofing system will have a unit weight of ~8 psf. Therefore, there will be a structural gain of 2 psf with the installation of a new plywood deck and shingle system. We recommend that a check be made of the original design to ascertain whether the system can carry the small amount of additional weight. H. Specific Design Concerns 1. Skylight Curbs: The asphalt BUR flashings at the skylight are inherently waterproof. Some of these flashings are only 4” to 6” above the existing roof. The new roof will be 2” higher and some of these flashings will be too low to properly flash. May 23, 2014 Roof Audit/Pre-Design Report Replace Roofing – Vail Racquet Club Bldgs. 1 & 2 Page - 5 Recommendation: We would recommend raising the low skylight curbs with a rough timber 2x6 collar that has an interior surface finished to match the wood curb that is to be extended. 2. Siding at North Wall of Lower Roof: The base flashing and cricket in this area will need to tie into a wall that has wood siding on it. The current flashing will lose 2” of height. Also it would be best to tie the new flashing into the underlayment behind the wood sheathing. Recommendation: The facility’s group will remove and replace this siding as part of the construction process so that a proper flashing can be installed. 3. Heat Cable on Roof: There are a couple of runs of heat cable on the current roof. Recommendation: The facility’s group will lift and reset and heat cable that is encountered. IV. Discussion and Recommendations: The Facilities Management group at Vail Racquet Club would like to change this roofing system over from an asphalt BUR system to high quality dimensional shingle roofing. The scoria is difficult at best to keep in place on high slope asphalt BUR systems. One a new insulated deck is constructed it would much easier and more economical to maintain the new roofing. The insulation system would not be lost every time the roofing is replaced. The proposed new roof system description follows: A. Asphalt Dimensional Shingle Roofing SYSTEM WEIGHT: 8 PSF Adhered SERVICE LIFE: 20 Years 1. Remove the existing insulated asphalt BUR system down to the surface of the wood plank decking. Any insulation sleepers encountered will be removed. Remove flashings and sheet metal trim as required to install new roofing. 2. Install a new 2x4 nailer on top of the two existing perimeter nailers. 3. Cover the interior roof deck areas with a vapor retarder ply of peel and stick modified bitumen felt. 4. Set 4.5” of roof insulation board over the new wood deck. Use perlite insulation over the deck areas that cover exterior space. Use isocyanurate foam insulation over interior space areas. 5. Cover the insulation with ½” thick CDX plywood sheathing. 6. Install tapered insulation crickets in the valleys. Cover with 90 mil EPDM or modified bitumen roof systems. Bring sheets 3’ up roof slope. 7. Cover the sloped deck areas with an ice and water guard modified bitumen sheet. 8. Cover the underlayment sheet with Certainteed Presidential Series dimensional shingles. The “Aged Bark” color closely matches the typical scoria color. May 23, 2014 Roof Audit/Pre-Design Report Replace Roofing – Vail Racquet Club Bldgs. 1 & 2 Page - 6 9. Sheet metal flashings and counterflashing will be installed. Shingle roofs are designed to be installed on 3/12 sloped roof decks. The mountain climate in Vail results in harsh winter conditions. While an asphalt BUR when installed properly is waterproof, shingle roofs rely on a series of components to result in a watertight roof. It is recommended that the facility’s group choose a knowledgeable installer and monitor the installation. The proper construction of the valley flashings will be key to the long term performance of the new roof system. Reported By: Ronald D. Scott, P.E. attachments RDS/\\moe\survey\vail racquet club\vail racquest club roof pre-design rpt.docx