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 DESIGN DEBATE

http://www.zerowasteamerica.org/Images/j0115834.gif PREFERRED CONSTRUCTION DESIGN FOR CONCRETE FOUNDATIONS & HISTORIC STREET-

  1. A modified-aggregate stone foundation topped with sand, then pavers - no cement (see: Jessup Street Report: Condition Assessment And Recommendations by Milner + Carr Conservation, LLC, Philadelphia, PA (Oct 2010). Currently, the Streets Department is using 8-12 inches of concrete as a base. We have strongly urged them to use something similar to the Netherland's model (see below).
     

  2. SPACING, SMOOTHNESS, & ADA COMPLIANCE: The bricks and stones should be tightly set, and in some cases, stone pavers should be ground smooth in order to make walking and biking safe and easy, and to be compliant with The Americans With Disabilities Act (ADA). See NYC Historic Districts Council shares these concerns in a report  and NYT article: http://www.nytimes.com/2013/03/30/nyregion/time-is-past-for-many-of-citys-old-cobblestones.html?pagewanted=all&_r=1 or (doc)
     

  3. SIDEWALK GRADIENT (i.e, slope): The restoration of historic streets should include in the bid contract a requirement that all sidewalk gradients be in compliance with Street Department standard of 1/4 inch per foot, and if such is not the case, curbs should be reset to be in compliance with that standard.

The case FOR “modified aggregate and screening” &

AGAINST "concrete foundation & mortar":

FOR MODIFIED AGGREGATE FOUNDATION

AGAINST CONCRETE FOUNDATION

FOR REPAIRS:

FOR REPAIRS:


Easy removal & replacement: Pavers, aggregate, and screening can be easily removed and reset by hand or using light equipment, thereby protecting adjacent properties.

 


Difficult & Damaging: Concrete foundations make it extremely difficult to access underground utilities for repair or installation, plus jackhammers and other heavy equipment can cause damage by vibration to nearby underground utilities, adjacent buildings, and historic structures.
 


Reliable foundation: A modified-aggregate foundation allows for proper tamping-down to prevent subsidence, as much as possible.


Creates future problems: After excavation work is complete, concrete chunks usually get thrown back into plumbers ditches by contractors, which cannot be properly tamped down, thereby creating future subsidence problems.
 


Early Warning System: Pavers serve as a vital "early warning system" for subsidence issues, as they slowly begin to collapse into any hole developing under the street or sidewalk, due to leaks in plumbing or other causes, and thereby giving homeowners an opportunity to fix the problem before it becomes catastrophic.
 


Conceals problems: Concrete conceals any "subsidence" issues beneath the pavers until they become catastrophic


Pedestrian friendly: tightly-fitted pavers with minimal screening between them makes walking or biking a safer experience


Pedestrian unfriendly: mortar, of the required ¼ to ½ inch-span between pavers, can make walking or biking over pavers very difficult - as in reality it is often 1inch or more.
 


Great Esthetics: simply lifting up and resetting pavers, properly, will leave no evidence of a repair

 


Unsightly Esthetics:  concrete and mortar cannot be repaired without looking like a patch-work quilt, as the visual difference between old and new mortar will be obvious and unsightly
 

 FOR PERMEABILITY:

 FOR PERMEABILITY:


Good:

Allows for slow permeability which keeps streets drier and safer in icy conditions, although storm drains are still necessary for stormwater runoff.

It also protects pavers from water damage  & nearby properties.

And promotes a dryer environment which is better for mosquito control.


None: Prevents any road surface permeability for rainwater, thus increases storm water run-off and icy conditions in the winter.

Creates drainage problems for nearby properties: Creates a subsurface barrier that would trap rain water between the road and  adjacent buildings, resulting in wet basements.

Damages pavers: Creates a wet environment which is particularly harmful for wood and brick pavers, as well as stone. Camac Street, The Wood Street, between Walnut and Locust completely rotted away due to concrete foundation under a sand layer, as well as the type of wood.  Black locust, Osage Orange, or another water-tolerant species of tree should be used or at least experimented with. 

Increases Health & Safety concerns: Creates conditions that breed mosquitoes
 


http://www.zerowasteamerica.org/Images/j0115834.gif  RESTORATION REPORTS AND EXAMPLES:

MORE ON HISTORIC RESTORATIONS:

OTHER RESOURCES--

Small Streets
 Phil LaCombe, Director and Co-Founder
email: phil@smallstreets.org
web: http://smallstreets.org
mobile: 413.648.7445

Paul Daniel Marriott & Associates
 3140 Wisconsin Avenue, NW
Suite 804
Washington, DC 20016
info@historicroads.org
 http://www.historicroads.org