Recommended: Using hardware that is hot-dip galvanized or stainless steel to avoid rust or rapid deterioration. Replacing historic materials with in-kind contemporary materials when necessary (i.e. wood siding should be replaced with wood siding)

Not Recommended: Using untreated steel elements or inappropriate replacement material.

The choice of materials for repairs and retrofits has a major influence on the strength, appearance, and durability of a house. A few extra dollars spent on quality materials pays off in the long run.

Hardware, such as nails, screws, bolts, and tie rods should be either hot-dip galvanized or made of stainless steel. Introduction of untreated steel elements should be avoided as these are highly prone to rust and more rapid deterioration. Ordinary zinc electroplating, a common coating on hardware, is different from hot-dip galvanizing and is not durable enough for historic homes in Louisiana, especially those located on the coast.

Likewise, anchors embedded in masonry or existing concrete should be hot-dip galvanized or stainless steel. On the coast, a best practice is to use stainless steel rebar or stainless wire mesh for reinforcement in concrete footings and slabs. Such reinforcement is expensive, but will never corrode. Costs can be offset somewhat by placing it closer to the surface than normal and using the bare minimum reinforcement.

For off-the-shelf wood fasteners, buy hardware that uses the manufacturers’ highest level of corrosion protection. For custom steel fabrications, hot-dip galvanizing is preferable and should be done after all cutting, drilling, and welding is complete to avoid gaps in corrosion protection. Series 5000 aluminum is a good choice for corrosion resistant fabrications.

Historic lumber compared with
modern lumber is:

  • Stronger and more durable
  • Hold nails better
  • Longer lengths
  • Straighter grain
  • Fewer knots

Wood should always be either preservative-treated southern pine or the heartwood of a naturally durable species. Non-durable wood species such as white pine, poplar, fir, or untreated southern pine should only be used in locations where they are protected from moisture and humidity and should not be placed in contact with the ground.

According to Secretary of Interior Standard’s priority should be given to retaining historic materials. If materials are damaged or deteriorated it is better to repair than to replace. When replacement is the only option it should be done by in-kind materials that have the same characteristics and material properties. By using in-kind materials for replacement over time the materials will age and act similarly to the environment.

This historic cypress rafter has a new cypress piece sistered in to replace damaged material. The darker wood is the historic material that was retained. Image Credit: NPS|Sarah Marie Jackson.

This historic cypress rafter has a new cypress piece sistered in to replace damaged material. The darker wood is the historic material that was retained. Image Credit: NPS|Sarah Marie Jackson.

References

Coastal Building Materials: Home Builder’s Guide to Coastal Construction, FEMA

Additional Resources

Preservation Brief 16: The Use of Substitute Materials on Historic Building Exteriors, H. Ward Jandl

Technical Bulletin 2, Flood Damage-Resistant Materials Requirements, FEMA

Technical Bulletin 8-96: Corrosion Protection for Metal Connectors in Coastal Areas, National Flood Insurance Program


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National Center for Preservation Technology and Training
645 University Parkway
Natchitoches, LA 71457

Email: ncptt[at]nps.gov
Phone: (318) 356-7444
Fax: (318) 356-9119