Introduction to Minimal Excavation Foundations
What is a minimal excavation foundation? A construction technique that minimizes disturbance of the natural soil profile within the footprint of the structure
Common Foundation Types perimeter / continuous / stem wall pilings post and beam slab on grade
Perimeter / Continuous / Stem Wall Typically constructed of reinforced concrete, masonry, or pressure treated lumber Construction may require extensive grading with heavy equipment
Pilings Elevated stilt pilings are commonly used in areas prone to flooding Deep soil bore pilings are commonly used to support multistory high rise structures Typically costly due to structural engineering
Post and Pier Constructed of masonry, reinforced concrete, or lumber posts connected to girders Posts are anchored to a concrete pier block or pad
Slab on Grade Constructed of reinforced concrete and perimeter footings Requires grading and / or filling to create a level foundation surface
How do minimal excavation foundations work? Structural loads are transferred from a beam through a pin, pile, or post system, which preserves the natural drainage patterns of the soil underneath the structure
Where can minimal excavation foundations be used? boardwalks foot bridges decks ground-mounted solar panels houses observation platforms pavilions sheds
Types Custom designed systems combine conventional piling and concrete components Proprietary systems are pre-engineered, pre-fabricated, and assembled on site
Economic Benefits Reduces consultant costs for preparing grading and drainage plans Reduces excavation costs for constructing a continuous foundation Controls cost of heavy machinery on sites that are not easily accessible Reduces cost to transport fill and / or concrete to the building site Reduces costs to transport excavated waste fill off site Eliminates costs of constructing trenches or drywells
Environmental Benefits Minimizes soil compaction and site disturbance from heavy equipment and machinery Preserves rainwater infiltration and subsoil water flows Allows rainwater to flow more naturally at shallow soil subsurface level
Social Benefits Potentially useful for emergency housing construction due to ease of installation of preengineered proprietary systems
Design Soils must be analyzed by a licensed geotechnical engineer Structure must be designed by a licensed architect or engineer Pre-engineered systems for smaller projects likes decks or boardwalks may not require additional engineering Selection of an appropriate foundation system is dependent upon many factors: soil and groundwater conditions slope type of structure
Construction Grade site by blading or surface terracing using light tracked equipment Drive piles using a machine mounted, frame mounted, or hand-held automatic hammer Install connection component (pre-cast or poured-in-place) Install plastic vapor barrier in crawlspace
Costs Costs are variable and dependent on Soil type Size and complexity of structure Structural load
Challenges Building code barriers City of Seattle Department of Planning and Development issued a code interpretation to allow small diameter pipe pile construction in May 2009 City of Bellevue Utilities Department s January 2012 Storm and Surface Water and Engineering Standards encourages minimal excavation foundations Architectural fees and structural engineering costs may be prohibitive
Case Study: Sol Duc Cabin, Olympic Peninsula 350 square feet fishing cabin on stilts to accommodate occasional river flooding Most of the structure was pre-fabricated off-site to reduce construction waste and site disturbance Architect:: Olson Kundig
Case Study: Berkshire Boardwalk, Stockbridge MA 2700 feet long boardwalk along the edge of a 50 acre wetland on a residential property Assembled by hand to limit construction disturbance Design included a nine-month review process with biologists, permit specialists, contractors, and conservation commissioners to ensure wetland protection Landscape Architect: Reed Hilderbrand
Case Study: Mercer Slough Environmental Education Center, Bellevue WA Sited with minimal landscape disturbance, with buildings elevated on a sloping site Cantilevered buildings are supported by steel framing anchored to concrete caps and helical piles Site includes classroom and multipurpose buildings, a visitor center, and lab Architect / Landscape Architect: Jones + Jones
Mercer Slough Environmental Education Center Site Plan Illustrating Rainwater Flows
Case Study: Loblolly House, Taylor Island MD Prefabricated 2220 square foot single family residence located on a barrier island Sited between a loblolly pine forest and a shoreline meadow Constructed on timber piles to minimize ground disturbance Architect: Kieran Timberlake
Case Study: Clearwater Commons, Bothell WA Residential co-housing community House foundations are constructed with patented Diamond Pier Pin Foundations Concrete pods are anchored by steel pins that hold them in place Developer: Infiniti Real Estate & Development
Professional Resources Built Green of Jefferson County Federal Highway Administration Wetland Trails Design and Construction Northwest Ecobuilding Guild Peninsula College Green Construction and Remodeling program WSU Extension LID Technical Workshop Series
References City of Bellevue. Storm and Surface Water Engineering Standards. Bellevue, WA: January 2012. City of Seattle. Director s Rule 10-2009. Seattle, WA: Department of Planning and Development, 18 May 2009. Clearwater Commons. http://clearwatercommons.com/ Hinman, Curtis. Low Impact Development: Technical Guidance Manual for Puget Sound. Olympia: Puget Sound Action Team, January 2005. Hopper, Leonard J. Landscape Architectural Graphic Standards: Student Edition. 2 nd Ed. Hoboken, New Jersey: John Wiley & Sons, Inc., 2007. Jones + Jones Architects and Landscape Architects. http://www.jonesandjones.com/ Kieran Timberlake Architects. http://www.kierantimberlake.com/ Northwest EcoBuilding Guild. http://www.ecobuilding.org/ Olson Kundig Architects. http://www.olsonkundigarchitects.com/
Image Credits Slide 1, left to right: http://www.pinfoundations.com/ http://www.asla.org/2011awards/351.html http://www.olsonkundigarchitects.com/projects/1909/sol-duc-cabin http://media.treehugger.com/assets/images/2011/10/matalicrasset1.jpg http://www.djc.com/stories/images/20081010/mercerslough_big.jpg Slide 2: http://www.jetsongreen.com/images/old/6a00d8341c67ce53ef010536e9df2b970c-500wi.jpg Slide 3, left to right: http://www.libertynaturepreserve.com/user/cimage/6-28-6-29-09-003small.jpg http://www.ecoboot.nl/artikelen/weblogfloatingcommunitiesgraphics/tiescambodiahouseonstilts640x447.jpg http://4.bp.blogspot.com/_eo8kdjhdwti/svynf1-6czi/aaaaaaaaez0/k-j-tixx11g/s400/crawlspace_new_floorbeam.jpg http://www.esogrepair.com/images/slab_foundation_repair.jpg Slide 4, left to right: http://www.asilverweb.com/img/house-foundation2.jpg http://blog.buildllc.com/wp-content/uploads/2012/01/build-llc-foundation-vent.jpg http://www.eisenhourhomeimprovements.com/pb/wp_45224b20/images/img29195461f83c46f701.jpg http://nbbd.com/npr/preservation/oliverscamp/stemwall0004.jpg Slide 5, left to right: http://thisfacade.com/wp-content/uploads/2011/01/house-on-stilts4s.jpg http://densitykatrina.files.wordpress.com/2009/03/house-on-stilts.jpg?w=460 http://www.nottingham.edu.my/engineering/research/images-multimedia/matmechstru/geomechanics/pilefoundation.jpg Slide 6, left to right: http://www.frontierbasementsystems.com/core/images/foundation-repair/foundation-problems/sagging-crawl-space/crawl-space-post-shimming-lg.jpg http://inhabitat.com/wp-content/blogs.dir/1/files/2010/05/holyoke-cabin.jpg http://www.backwoodsconstruction.com/mediac/450_0/media/img_0605.jpg http://www.countryplans.com/images/lemay-3.jpg Slide 7, left to right: http://upload.wikimedia.org/wikipedia/en/thumb/1/10/raft-slab.jpg/220px-raft-slab.jpg http://www.dropyourenergybill.com/wp-content/uploads/2010/10/tmp883d.tmp_tcm10-267609.jpg http://upload.wikimedia.org/wikipedia/en/1/10/raft-slab.jpg http://www.esogrepair.com/images/slab_foundation_repair.jpg
Image Credits Slide 8: http://www.cusa-dds.net/seed/?tag=foundation Slide 9, left to right: http://www.asla.org/2011awards/351.html http://sonsdevelopment.com/images/products_pin2.jpg http://www.freewatt.co.uk/images/page/16_9369c53872.jpg http://lakeshorepreserve.wisc.edu/photo-gallery/1918marsh/lg/class%20of%201918%20marsh%20observation%20platform,%20cronon,%20dsc_0196_800.jpg Slide 10: http://www.buildinggreen.com/cgi-bin/scale.cgi?width=200&src=/productimages/1627_diamondpier.jpg Slide 11: http://www.flickr.com/photos/tracy_olson/61056391/sizes/l/ Slide 12: http://media.dwell.com/images/480*384/a-lot-to-love-house-exterior-from-hillside.jpg Slide 13: http://graphics8.nytimes.com/images/2008/04/13/us/13trailers.600.jpg Slide 14: http://cdn.freshome.com/wp-content/uploads/2010/10/architect_drawing-e1287585143184.jpg Slide 15, left to right: http://netdrive.bobcat.com/attachments/mediawidget-landscape_rake.jpg http://www.djc.com/stories/images/20010712/pin2.jpg http://www.capitalcleanspace.com/core/images/home/vapor-barrier-system-lg.jpg Slide 16: http://www.flickr.com/photos/tracy_olson/61056391/sizes/l/ Slide 17: http://www.archithings.net/wp-content/uploads/2010/08/tyler-engle-raised-house-plan-budget-588x399.jpg Slide 18: http://www.olsonkundigarchitects.com/projects/1909/sol-duc-cabin Slide 19: http://www.asla.org/2011awards/351.html Slide 20, left to right: http://www.djc.com/news/en/11205540.html http://www.seattlepi.com/ae/article/on-architecture-mercer-slough-center-treads-1298476.php#photo-719119 http://www.flickr.com/photos/premiersips/5219476512/in/photostream/ Slide 21: http://www.flickr.com/photos/premiersips/5219476016/sizes/l/in/set-72157625500929970/ Slide 22: http://www.kierantimberlake.com/featured_projects/loblolly_4.html Slide 23, left to right: http://clearwatercommons.com/houseplans.php http://www.ecobuilding.org/green-building/project-spotlights/clearwater-commons http://clearwatercommons.com/gallery.php?gallery=houses Slide 24: http://2aem.files.wordpress.com/2009/07/oska-rollinghuts1.jpg
Acknowledgements This project has been funded wholly or in part by the United States Environmental Protection Agency under assistance agreement PO-00J08601 to Jefferson County Department of Community Development. The contents of this document do not necessarily reflect the views and policies of the Environmental Protection Agency, nor does mention of trade names or commercial products constitute endorsement or recommendation for use.