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Historic Preservation - Technical Procedures

Spectitle:
Replacing A Wood Window Sill

Procedure code:
0861004R

Source:
Hspg Prepared For Nps - Sero

Division:
Doors And Windows

Section:
Wood Windows

Last Modified:
02/24/2012

Details:
Replacing A Wood Window Sill



REPLACING A WOOD WINDOW SILL


PART 1---GENERAL

1.01 SUMMARY

    A.   This procedure includes guidance on replacing a severely
         deteriorated wood window sill.

    B.   To arrest deterioration, repair sill with epoxy
         consolidant (see 08610-06-R and 06300-01-R for guidance).
         If sill is beyond repair, it must be replaced (see
         procedure outlined below).

    C.   See 01100-07-S for general project guidelines to be
         reviewed along with this procedure.  These guidelines
         cover the following sections:

         1.   Safety Precautions

         2.   Historic Structures Precautions

         3.   Submittals

         4.   Quality Assurance

         5.   Delivery, Storage and Handling

         6.   Project/Site Conditions

         7.   Sequencing and Scheduling

         8.   General Protection (Surface and Surrounding)

         These guidelines should be reviewed prior to performing
         this procedure and should be followed, when applicable,
         along with recommendations from the Regional Historic
         Preservation Officer (RHPO).

1.02 SYSTEM DESCRIPTION

    A.   A wood window sill in good condition is free from decay
         and sloped away from the building to shed water.  The
         connection between sill and jamb is tight and well
         caulked.  The sub-sill should have a drip on the bottom
         that prevents water from entering the building under the
         window assembly.

1.03 DEFINITIONS

    A.   Window apron - A flat broad piece of finished lumber or
         trim placed directly under a window sill.

    B.   Window stool - A horizontal board on a window sill which
         forms a base on which the casing rests.


PART 2---PRODUCTS

2.01 MATERIALS

    A.   Lumber for new sill and subsill (match species, size and
         grain direction of original)

2.02 EQUIPMENT

    A.   Prybar

    B.   Wide blade putty knives

    C.   Back saw

    D.   Chisel

    E.   Hacksaw

    F.   Router

    G.   Caulk


PART 3---EXECUTION

3.01 ERECTION, INSTALLATION, APPLICATION

    A.   Remove stool and apron from interior of window.  Pry
         apron off and tap stool out from under jambs.

         1.   Insert the blade of a wide putty knife between the
              apron and the wall; carefully tap a prybar into the
              same gap, allowing the knife blade to protect the
              wall.
             
         2.   Using the wall as a fulcrum, work the apron away
              from the wall until a nail is visible, hold the gap
              open with a piece of blocking or another prybar.

         3.   Continue working at each nail location until the
              next nail is exposed.  When all of the nails have
              been exposed, the apron should easily lift off.

    C.   Attempt to tap sill out of place.  If this is not
         possible, measure sill thoroughly for replacement then
         saw or chisel sill out carefully.  Follow same directions
         to remove sub-sill, if required.

         NOTE:  The sill may be nailed at rail or under
         weatherstripping.
   
    D.   Remove exposed portions of nails that secured the dadoes.

    E.   If required, new sub-sill must be installed first.  Rout
         a drip to underside of sub-sill to prevent water from
         entering wall from under window.

    F.   Cut sill to match original and sand sill before
         installation.  Bevel ends slightly to ease installation.

    G.   Nail sill into casing from underneath.  Countersink nail
         and fill hole with putty and seal.  Seal edge of sill
         with caulk at jamb connection.

    H.   Prime and paint (see 06300-01-S, 06300-02-R and 09900-07-
         S for guidance on painting wood).

                             END OF SECTION