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149-155 DERBY STREET - WATER INFILRATION AND RELATED DAMAGE LTR Structures North U[NIH 60 Washington St,Suite 4.01 Salem,Massachusetts 01970-3517 P.O. Box 01971-8560 T 978.7E45.6817 1 P 978.745.6067 v�'r�..5tru+vktr'� -riUtiFt.cv�r 29 October 2021 Attn. Llyod Michaud, President 149 Derby St Condo Association 149 Derby Street Salem, MA 01970 Reference: 149-155 Derby Street Salem, Massachusetts Water infiltration & related damage due to roof drain outlet Dear Llyod: On Monday, October 4t', I met with you and other members of your condominium association to review the readily visible existing structural conditions of your basement space as well as the trench/gutter/alley between your building at 149 Derby Street and the adjacent 155 Derby Street just to the west.A follow-up visit was made on Wednesday, October 13''to view the basement space of 155 Derby Street. For the purposes of this report the front of the building along Derby Street faces north. General Description Your building is a four story multi-wythe brick structure that was originally built circa 1900. First floor framing generally spans east-west and is supported by the perimeter foundation walls and timber beams that span north-south. Timber beams are supported by a combination of the foundation walls and intermediate brick piers along their lengths. One exception is the front bay where the joists span north-south. There is a full basement throughout, and foundation walls consist of partially-mortared rubble stone masonry. Upper floors and roof were not observed and are covered by finishes; however, these levels are likely framed in a similar manner. Each floor has a deck at the rear of the building facing the parking lot that consists of wood framing with the exception of steel columns at the lowest level. Storage units are located in the basement along the west wall adjacent to the alley between 149& 155. The neighboring 155 Derby Street building is also four stories built circa 1900 with similar foundation conditions yet all wood framing above grade, including exterior walls and wood framed rear decks. Commercial retail space is located along Derby Street and residential units occupy the balance of the building. First floor framing that was visible in the basement generally spans east- west and a one-sided concrete pour was in progress during our second visit(this has been completed in some areas). It appears that the original rubble stone foundation wall was repointed, and this was verified by the contractor working for 155 Derby Street. There is a gap between the two buildings that varies in width and is generally 18"wide. Recently (in relation to the history of the original construction of the two buildings)the interior roof drain of 155 Derby was disconnected from the domestic sewer outlet(see Photo 1 on Page 1 of the Appendix)and redirected to the alley (see Photo 2 on Page 1 of the Appendix), though the exact date of this installation is unknown. According to the available photos and to descriptions that were provided about the exposure of this condition, the pipe was terminated in the alley with no connection to city storm sewer or drywells, but rather terminated directly to the alley with the open end of the pipe facing your building. There have been several reports of water infiltration in the storage units in your building. During our initial visit we had access to the storage units, however they had not yet been fully vacated. According to a recent account from unit owner Susanne May, most of the storage units have been cleaned out and now soil is visible on the basement floor, which may be a sign of soil transport as discussed below. Structures North 149-165 Derby Street 29 October 2021 Salem, MA Noted Conditions and Recommendations According to accounts by several unit owners, water infiltration along the west wall is common. The account relayed by Susanne May after the storage units were vacated indicated soil on the floor that appeared to have come through the wall as a result of soil transport, which is when natural agents move weathered soil deposits from one place to another In this case the agent is flowing water moving from the alley, likely due to the water that was funneled from the roof of 155 Derby and to the alley from the drain pipe. Due to the initial construction of walls of this type, any excavation alongside the wall may destabilize it. These walls are typically constructed with loose- laid stone with a thin layer of mortar on the inside face, if any, and soil that is compacted in the voids between the stones on the outside face. Therefore, the mere act of investigating this condition will inherently destabilize the wall, and hence any investigation should be avoided, and immediate repairs be performed as described below. The leaching soil may destabilize the foundation wall. We recommend the following actions be taken immediately in order to preserve the structural stability of both buildings and prevent future infiltration and soil transport. 1. In the shoe-term, water-management should be in place to divert water away from the alley. At the time of our initial visit, this was in place and will need to be maintained until the permanent repairs are complete. 2. Excavate the alley in order to repair the wall and replace the backfill with concrete or flowable rill(additionally fixing the drainage issue may be part of this process as discussed below). In order to avoid a collapse of either wall, we recommend the following procedure: a. Install temporary lateral bracing to resist the lateral pressure of the wet concrete while it cures. Please note that this will require vacating all storage units along the west wall. The partitions will also likely need to be removed as several are in poor condition due to water damage and the partitions may impede the work. b. Vacuum-excavate the soil between both buildings. This should be performed incrementally in order to maintain the stability provided by the existing soil yet to be excavated and extend to the bottom of the lowest footing elevation. Please note that this may require underpinning of 155 Derby Street as it appears to have a shallower basement, and hence the bottom of the wall at 149 Derby will likely be lower than that of 155. It is our understanding that scoping and or digging is underway to explore options for the outlet of the roof drain. This work must be done carefully and in a manner that does not disturb either wall,ideally a plan for the final destination of the pipe should be determined prior to further exploratory excavation. c. Place concrete or flowable Fill to replace the excavated soil. This should be done in both vertical lifts and segments along the length of the building in order to minimize the lateral pressure of the wet concrete while it cures. The height and length of each lift will need to be determined in the field by the contractor performing the work, and we recommend that the vertical lifts be in thirds of the height of the wall and performed in 4-to-6 foot horizontal sections. As there are potentially large voids in the soil below the sidewalk, concems with flowable fill have been raised. If concrete is used versus flowable fill, a peastone mix with a shrinkage-reducing admixture as well as a water-reducing admixture to assist the concrete flowing into the irregular surface of the stones. It is our understanding that the voids are being investigated and are beyond the scope of this report, and any such voids will need to be dammed-off or filled with gravel and a bond-break installed prior to the placement of any concrete or flowable fill in order to prevent the infill material from extending beyond any property lines to the north. d. Following the completion of the concrete placement, the interior surfaces of the wall should be repointed and locally repaired or rebuilt as required. While repointing may be performed prior to the concrete placement, we do not recommend this since any Page 2 of 4 Structures North 149-155 Derby Street 29 October 2021 Salem, MA damage that occurs during the concrete pour will require that the repointing be revisited after this process. Please note that the work described above should be performed before winter conditions. Currently the structures are at risk due to water infiltration, however winter conditions will add freeze-thaw risks. If this work is not done before the winter, measures should be taken to divert water from both the pipe and any surface or roof runoff, and the walls protected against any damage that may occur from freeze-thaw effects. 3. if allowable by the city, the drain pipe should be properly connected to the storm sewer through the alley prior to the installation of the final lift of concrete. If this is not allowable, the drain pipe will need to be diverted to a different connection point or drywells that will need to be installed in the parking lot of 155 Derby. Please note that this is beyond our area of expertise, and it is our understanding that a civil engineer is addressing these issues. In discussing this project with Susanne May and Building Inspector Tom St. Pierre, the possible presence of cisterns in the street was raised.As this is out of the footprint of the building it is beyond the scope of this report, however it should be investigated by the civil engineer who is addressing the drainage issues. 4. The top of the concrete pour between the buildings should be coated to prevent water infiltration and pitched to drain any water that falls into the alley by means of rainfall, melted snow, or overflow runoff from the roofs. In order to minimize any water penetration, a sealant joint between the top of the concrete and the curb should be considered. Please note that such a joint will need to be maintained and replaced periodically. 5. As the two buildings will be joined in perpetuity at these walls, an attomey should be consulted to generate an agreement between the two associations. Several other issues need to be addressed that are unrelated to the drainage and west foundation wall items addressed above, and include, but are not limited to the following: A. The steel columns that support the rear deck of 149 are severely deteriorated. These will need to be replaced with a more durable column with a thicker wall and more robust corrosion protection, such as hot-dipped galvanized(color-galvanized if desired for finish appearance) or a multi-step field-or shop-applied coating. B. Brick piers in the basement of 149 are in various states of deterioration, which is common in buildings of this age due to rising damp. These will need to be monitored and eventually replaced with a more durable vertical support, such as a standard steel pipe or tube section with welded cap and base plates. Bases of replacement column should be elevated slightly above the slab and coated with a protective marine-grade epoxy or cold-galvanizing coating to prevent future corrosion. The footing conditions should be verified during the pier replacement,however, these piers rarely have sufficient footings and replacement footings should also be budgeted for this project. Similar to what is described in#1 above, the partitions may impede the replacement of the piers and will likely need to be removed and reconstructed. C. The joints at the balance of the foundation walls are in various stages of deterioration. The foundation walls should be monitored for any changes in their condition. If any stones shift, or if the joints erode to a point where use of the basement space is hampered, a deep cut and pointing of the foundation wall should be considered. A cutting &pointing operation (sometimes also referred to as re pointing) involves removing the old, deteriorated mortar from the joints and replacing with a new, compatible mortar. A deep"cutting and pointing operation is recommended for stone construction such as this due to the thickness of the stone units and the likelihood that the original soil backfrll has settled andlor eroded and caused voids on the soil-side of the wall. A bonding agent should replace 113 of the mix water in order to improve the bond with the relatively low porosity of the granite. Page 3 of 4 Structures North 149-155 Derby Street 29 October 2021 Salem, MA D. Several embedded metal parts are corroded and rust jacking, causing damage to the exterior masonry, particularly at the rear wall along the south elevation. These elements will need to be removed and replaced with galvanized steel pieces and the surrounding masonry rebuilt. E. The sill in one of the windows on the east elevation is dislodged and the surrounding masonry damaged. The sill will need to be re-set and the surrounding masonry rebuilt. F. The roof of 155 Derby appears to be in contact with 149 at the northeast comer of 155/northwest comer of 149. This is particularly concerning since the front/north wall of 155 appears to have been heavily modified to create the storefront, resulting in a "soft story". A "soft story" is one that has substantially less lateral stiffness than the stories above. Buildings such 155 Derby rely on exterior walls to provide lateral stability and stiffness, and the exterior walls are required to have substantial amounts of continuous sheathing, either board or plywood, to achieve this. The length of continuous sheathing depends on the demands on the wall and how it is detailed. The north elevation of 155 Derby does not appear to have any solid sections of sheathing whatsoever. Therefore, the lateral stability in the east-west direction appears to be solely provided by the rear wall at the south elevation, and possibly unintentionally by interior partition walls. Due to the severe lateral translation of the northeast corner of 155 Derby, it does not appear that the lateral stability in the east- west direction is adequate.Additionally, 149 Derby has large openings in its north elevation with few segments of continuous solid masonry, which provides lateral stability and stiffness to these types of multi wythe brick masonry walls. On the north elevation of 149 Derby, it appears that the original openings have been infilled with wood framing in order to narrow the openings and accommodate smaller windows. While this modification does not reduce the lateral capacity of the wall, the wall likely does not have reserve capacity to support the demand of the neighboring building. This condition warrants further investigation and evaluation. A retrofit may be required, such as interior shearwalls or moment-resisting steel frames (also known as portal frames) at 155 Derby. Please note that any such intervention will likely impact the interior space of the retail unit at the first floor.At the 149 Derby north elevation, the existing openings that have been narrowed by wood framing may be replaced with solid masonry that is toothed-into the existing surrounding masonry to improve the lateral capacity of the wall. Please note that this type of work would require a mason who is well-versed in similar historic structures in order to match the new work with the existing to remain. Report Limitations This report is a summary of readily visible observations conducted during two separate visits to the property. No finishes were removed to expose hidden structure and no calculations have been performed to determine if the overall building complies with past or present building codes. This report is strictly limited to structural considerations noted. Other building systems were not reviewed, and they are beyond the scope of this report. We hope that the above information is helpful in determining your next steps. If we can be of further assistance, please do not hesitate to contact this office. Respectfully Yours, Greg N P.E. Structures North 149-155 Derby Street 29 October 2021 Salem, MA JW I .' W 1, ' P AL5 - l;Y Photo 1 Former roof drain connection points at domestic sewer at 155 Derby St �„ . Y Photo 2 Roof drain of 155 Derby St outlet towards alley (facing east/towards 149 Derby St) Appendix, Page 1