Wood Framing November 30, 2016 INTRODUCTION TO ARCHITECTURAL MATERIALS INSTRUCTOR: JOHN D CHILDS Wood Framing November 30, 2016

Timber or Braced Framing Medieval Tradition Carried into 19th Century INSTRUCTOR: JOHN D CHILDS INTRODUCTION TO ARCHITECTURAL MATERIALS Timber or Braced Framing Medieval Tradition Carried into 19th Century

Hewing with broad axe and adze Wood is hewn green Oak or pine

Secondary members (floor joists, common rafters) are sawn, either in a sawmill or with a pitsaw.

Timber Framing: Joints INSTRUCTOR: JOHN D CHILDS INTRODUCTION TO ARCHITECTURAL MATERIALS Timber Framing: Joints

Joints are cut and joined with axe, adze, chisel , slick, auger

Framing joinery must resist force in at least one of these directions: Compression Tension Shear

Strength in wood: Varies with direction and type of stress Tensile Strength Parallel to Grain: Strongest Compression Parallel to Grain

Compression Perpendicular to Grain Tension Perpendicular to Grain: Weakest

Bending Strength (Modulus of Elasticity, E) Breaking Strength (Modulus of Rupture, MR)

Mortise and Tenon joints hold main framing elements together Plain Open English Tying Joint Shouldered Housed Tusk

Lap joints attach crossing members Shouldered dovetail Dovetail Half lap Lap joints attach crossing members Dovetails attach members in tension Full lap Angled dovetail

Scarf joints attach framing members end-to-end

Pegs hold joints together Must be thick enough to resist shearing. Tight fit aids in this Must not be so thick that they diminish strength of joint

Timber Framing: Principle Elements INSTRUCTOR: JOHN D CHILDS INTRODUCTION TO ARCHITECTURAL MATERIALS Timber Framing: Principle Elements

Strength Considerations in Framing Compression Shear

Tension Crack at Mortise in Diagonal Grain Timber

If beam is long enough, dead weight (weight of beam) will exceed modulus of rupture. Truss structures solve problem of crossing increased spans.

Bents use trusses to add strength Trusses use diagonal members to add strength in all directions. Truss joints must be able to hold in tension as well as compression. Trusses add strength, allowing thinner members to be used. Trusses allow beams (girts, plates) to span greater distances. We will see later that trusses make it possible to build an entire house with 2 x 4 lumber

Raising Bents

Post Tension Brace Sill Post Knee Brace Girt

Joists Summer Beam Jackson House, Portsmouth, NH (Historic New England)

Tension Brace Rafter Purlin Jackson House, Portsmouth, NH (Historic New England) Pierce House, Dorchester, MA (Historic New England)

Interior Wall Coverings INSTRUCTOR: JOHN D CHILDS INTRODUCTION TO ARCHITECTURAL MATERIALS Interior Wall Coverings

Lath and Plaster Jackson House, Portsmouth, NH (Historic New England) Pierce House, Dorchester, MA (Historic New England) Lath and Plaster

Paneling Wainscot

Paneling mitigates effects of expansion and contraction of wood

Floors INSTRUCTOR: JOHN D CHILDS INTRODUCTION TO ARCHITECTURAL MATERIALS Floors

Wide pine boards Narrow oak boards Wide oak boards Tongue and groove joint

Parquet floors mitigate effects of expansion and contraction of many parallel boards

Stairs INSTRUCTOR: JOHN D CHILDS INTRODUCTION TO ARCHITECTURAL MATERIALS Stairs

17th C. 18th C. 19th C. 20th C.

Exterior Siding INSTRUCTOR: JOHN D CHILDS INTRODUCTION TO ARCHITECTURAL MATERIALS Exterior Siding

Clapboard: 17th & 18th C. – riven, 19th & 20th C. - sawn Board siding – sawn Shingles: 17th & 18th C. – riven, 19th & 20th C. riven or sawn

Nail History: Wrought nails Cut nails Wire nails

Log Cabins: Construction technique introduced by Swedish immigrants in the Delaware Valley in the 17th C. Does not appear in New York or New England until mid 18th C.

Balloon Frame Construction: Introduced in U.S. by G. W. Snow, Chicago, 1832

Uses dimensioned lumber (2x4’s) on 16” centers. Wall studs extend full height of building. 2nd floor joists rest on ledger nailed into mortises cut in studs

Balloon frames do not offer fire breaks between floors

Platform or Western Framing: 20th Century Platform frames offer fire breaks, and allow use of standard length lumber.

Truss Framing: 20th Century truss frames allow use of standard 2 x4 dimensioned lumber for all structural elements.