Technical Procedures Disclaimer
Prior to inclusion in GSA’s library of procedures, documents are reviewed by one or more qualified preservation specialists for general consistency with the Secretary of Interior Standards for rehabilitating historic buildings as understood at the time the procedure is added to the library. All specifications require project-specific editing and professional judgement regarding the applicability of a procedure to a particular building, project or location. References to products and suppliers are to serve as a general guideline and do not constitute a federal endorsement or determination that a product or method is the best or most current alternative, remains available, or is compliant with current environmental regulations and safety standards. The library of procedures is intended to serve as a resource, not a substitute, for specification development by a qualified preservation professional.
We’ve reviewed these procedures for general consistency with federal standards for rehabilitating historic buildings and provide them only as a reference. Specifications should only be applied under the guidance of a qualified preservation professional who can assess the applicability of a procedure to a particular building, project or location. References to products and suppliers serve as general guidelines and do not constitute a federal endorsement nor a determination that a product or method is the best alternative or compliant with current environmental regulations and safety standards.
- This procedure describes three alternatives for preventing icedams on slate tile roofs.
- Ice-damming can occur on roof eaves when ice and snow back up along gutters.
- Ice can build up at the eaves from the intermittent melting of snow. As the snow above melts and runs down the roof, it eventually reaches the cold roof eaves where it may refreeze creating a "dam" and enabling additional snow to accumulate.
- Accumulated water may then seep behind roof shingles causing damaged to interior building components such as insulation, plaster and framing members.
- See 01100-07-S for general project guidelines to be reviewed along with this procedure. These guidelines cover the following sections:
- Safety Precautions
- Historic Structures Precautions
- Quality Assurance
- Delivery, Storage and Handling
- Project/Site Conditions
- Sequencing and Scheduling
- 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).
- Roofing Underlayment Options
- Shingle or metal leak barrier
- Snow Guards
NOTE: Chemical products are sometimes sold under a common name. This usually means that the substance is not as pure as the same chemical sold under its chemical name. The grade of purity of common name substances, however, is usually adequate for stain removal work, and these products should be purchased when available, as they tend to be less expensive. Common names are indicated below by an asterisk (*).
- For Metal Ice Edge:
- Galvanized Steel: Available in 4 ft. x 8 ft. sheets that permit a 3 ft. exposure of the metal with a 1 ft. overlap of shingles. For more steeply pitched roofs, less exposure is needed and 3 ft. x 8 ft. sheets should be adequate.
- Metal primer and paint for exterior use
- Mineral Spirits:
- A petroleum distillate that is used especially as a paint or varnish thinner.
- Other chemical or common names include Benzine* (not Benzene); Naphtha*; Petroleum spirits*; Solvent naphtha*.
- Potential Hazards: TOXIC AND FLAMMABLE.
- Safety Precautions:
- ) AVOID REPEATED OR PROLONGED SKIN CONTACT.
- ) ALWAYS wear rubber gloves when handling mineral spirits.
- ) If any chemical is splashed onto the skin, wash immediately with soap and water.
- Available from construction specialties distributor, hardware store, paint store, or printer's supply distributor.
- For Ice & Water Shield:
- A waterproofing sheet made of flexible, rubberized asphalt laminated to a polyethylene film.
- Used as an underlayment along the edges of wood shingle, slate, tile, cedar shake or metal roofs.
3.01 ERECTION, INSTALLATION, APPLICATION
- Method 1 - Ensure There is Adequate Insulation and Ventilation in the Attic.
- Method 2 - Install a Metal Ice Edge: A metal edge absorbs heat faster than shingles and, thus, tends to shed ice from its slick surface during thaw.
NOTE: GALVANIZED STEEL IS PREFERRED OVER ALUMINUM. IT IS NEARLY AS INEXPENSIVE, MORE DURABLE AND DOES NOT EXPAND AND CONTRACT AS MUCH. HOWEVER, IT MUST BE PAINTED.
- Paint the galvanized steel.
- Wash the metal with a solvent such as paint thinner or mineral spirits to remove any dirt or oil.
- Etch it with a zinc primer and apply two coats of exterior paint.
- Firmly bed the metal in roofing cement and join in sections with a crimped standing seam.
NOTE: It is preferable to cut the sheets in half, providing seams every 4 feet, though it is possible to join the full 8 foot length sections. HAVING MORE JOINTS GIVES GREATER ALLOWANCE FOR EXPANSION AND CONTRACTION.
- Paint the galvanized steel.
- Method 3 - Install an Ice & Water Shield (in combination with a snowguard):NOTE: THE BEST TIME TO INSTALL THIS SYSTEM IS DURING A REROOFING JOB.
- Apply to a smooth and continuous sheathing.
- The space under the membrane should be well vented, as the shield acts as a vapor barrier.
- If the shield is not installed during a reroofing job, the lower 3 feet of the exposed roof will need to be removed.