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HomeMy WebLinkAboutExhibit 2_Anne Thayer Email_20170823_v1From: Anne Thayer Sent: Thursday, August 24, 2017 9:23 AM To: Alex Morganroth Cc: Terrence J. Flatley Subject: RE: Routine Vegetation Management Permit - 4108 NE 22nd Pl. Hi Alex, The following is a general statement regarding retaining trees for hardscape repairs, followed by some links. There are certainly more links available online. Once pavement is installed over a tree's roots, the tree loses some of its ability to get water and air, since most pavement is nonporous and will seal the roots away from the aeration and rainfall the tree needs. In addition, the tree roots are liable to push up the pavement as they grow, resulting in damage to driveway. The roots may also cause a tripping hazard as they push through the pavement. Once the tree becomes less healthy, it may blow over in a windstorm, or the tree may simply die from its inability to get water and air. If you can get by just cutting one or two roots, neatly cutting them with a hand saw helps them heal properly. It is recommended that buttress roots not be cut closer to the trunk than a distance equal to three times the trunk diameter (DBH). If they need to be severed closer than 1.5 times trunk diameter, tree removal should be considered since it is very likely that tree stability will be affected at this distance, depending on tree species and condition. When reinstalling the pavement next to a root cut tree, allow space for callus and trunk diameter growth. Installation of a root barrier or root excluding base (foam board or washed gravel) should also be considered under the new pavement to avoid reoccurrence of the problem.. Cutting multiple roots of the tree is not an option, since the health of the tree will likely decline and the tree may become structurally unstable. Pavers offer a beautiful option in place of concrete or tar paving since they do not show cracks from roots invading the pavement. Pavers allow water and nutrients to reach the roots. If the roots continue to grow, it's easy to lift the pavers and regrade the area. Another option includes the use of permeable paving, also known as permeable concrete. Permeable paving offers an effective way to allow water and air to seep into the ground around the roots of your tree. Another advantage to permeable paving includes its ability to collect rainwater while reducing stormwater runoff and erosion. Replacing concrete with interlocking paver blocks or rubber pavers. This alternative will not slow pavement lifting, but will allow for a smoother transition and the removal of blocks that have lifted too high. Pavers are installed by removing the concrete and base materials above the roots and removing the soil between the roots if needed using a supersonic air excavation tool, installing a new sub-base of coarse sand or pea gravel, leveling and compacting the sub-base slightly above the existing roots, install a geotextile fabric (e.g. Typar 3341) on top of the base, then installing and compacting a coarse sand base layer, and finally installing the pavers. Paver joints should not be mortared. Here are a few links to alternatives for hardscape repair around tree roots: Rubber is an alternative product to concrete or asphalt. http://hort.ifas.ufl.edu/woody/rubber.shtml www.rubbersidewalks.com/ Porous pavement allows air and nutrients to get to the tree roots Use of Geotextile products http://www.typargeotextiles.com/paved.html Polymer as a repair for areas in driveway http://www.pavement-repair-products.com/fastpatch-dpr-asphalt-repair-c-34.html Using reinforcements in concrete reduces heaving from roots and weather related heaving http://hort.ifas.ufl.edu/woody/reinforced-concrete.shtml Expansion joints and ramping over roots https://www.portlandoregon.gov/transportation/article/443054 This is a must have for maintaining our Urban Forest: Tree Protection on Construction & Development Sites (OSU) http://ir.library.oregonstate.edu/xmlui/bitstream/handle/1957/13729/EM8994.pdf?sequence=5 Please feel free to contact me if I can be of further assistance at 425-430-6698. Anne Thayer Contract Arborist Inspector Davey Resource Group for City of Renton From: Alex Morganroth Sent: Wednesday, August 23, 2017 4:22 PM To: Anne Thayer Subject: RE: Routine Vegetation Management Permit - 4108 NE 22nd Pl. Great, thanks Anne! Alex Alex Morganroth, Associate Planner City of Renton | CED | Planning Division 1055 S Grady Way | 6th Floor | Renton, WA 98057 (425) 430-7219 | amorganroth@rentonwa.gov From: Anne Thayer Sent: Wednesday, August 23, 2017 4:17 PM To: Alex Morganroth <AMorganroth@Rentonwa.gov> Subject: RE: Routine Vegetation Management Permit - 4108 NE 22nd Pl. Alex, I will get a list together for you first thing tomorrow morning.