Heritage Restoration, Inc.

Roofing Primer

Roofing is another underrated trade.  It is one of the most backbreaking, dangerous and believe it or not, technically challenging.  I am not talking about slapping an asphalt roof over another, or using roofing from a tube, I am talking about roofing AND flashing.  There was a time in the trades when roofing and flashing were separate, and I think for good reason.  One of the top mistakes in every bad roofing project, and believe me we see many of them, is bad flashing.   So lets go through some basic principles of roofing.


Dos and Don’ts

  • Tar is for pits and flat roofs.  Same goes for Roofing in a tube.  It stays flexible for a time, but then gets brittle and breaks.  It is not a flashing.  It is a repair, not a fix, only to be redone in a few years.  When you slap it on a chimney it cannot be removed and traps moisture in and kills the brick.  Tar is for petroleum-based roofs, so use it sparingly. And use a mesh product with tar over cracks, same concept as drywall.
  • Metal expands and contracts, and some more than others.  When copper is used in long runs, there must be an expansion joint that is not soldered.  Copper is cost effective because it can last for 100 years…or 5 when it is done wrong.  Bad installs typically cannot be fixed.  Do your research and make sure installers are doing it right.
  • If you need a quick repair to a hole, missing shingle, or bad flashing, get an oversized compatible piece of metal and shove it underneath the roofing material.  Be sure it goes under any above seams.  And so it stays, you can cut the top edge of the metal on a diagonal so it stays.
  • A metal can react with another metal and rot, called a galvanic reaction.  You can look at a compatibility chart but the best choice is to stay true, copper with copper, aluminum with aluminum, etc.
  • Drip edge.  A drip edge can be a metal form, wood shingles, or really anything under a roof that allows the water to drip away from the building.  It is typically used on the eves to direct water into a gutter, not behind the gutter.  Each piece should be lapped by at least 2” over the other.  And it does not have to go up the gable, unless you are hiding a new plywood deck or something.
  • Overhang- Roofing materials should hang at least a 1” over the drip edge on the eves, and at least ¾” on the gable.  And it should be straight, so pick the furthest point out on a crooked building.


A bit about Slate:

Slate is a natural material that can have a tremendous life span, some lasting 150 years plus.  We just REPAIRED a 150 year-old Buckingham slate roof.  Some tricks to knowing if you have a good slate:

  • If less than 20% is damaged, fix it.
  • Flashing- Slate has mineral content, and those minerals eat certain metals.  Use copper only, it will eat tin or aluminum.  And if your flashing is shot, fix it, don’t tar it.
  • Fasteners- Nails can be a weak point in longevity.  Bronze or copper is best, although we have seen a well-laid roof with steel cut nails. The slating nails should be ¾” longer than the thickness of two slates.  With the existing slate 3/8” thick, the nail length should have been 1-1/2”.  Never over nail, leave the slate a bit loose.
  • Head lap- Head lap is the overlap on each course of slate by the second course above it. This overlap is critical in preventing the roof from leaking. Three inches is standard.  This roof had proper head lap.
  • Side laps: Lateral overlaps should be 3” minimum.  Incorrectly placed side laps allow water to direct water entry through the nail holes.  Many of the slate roof repairs had less than a 3” side lap.
  • Installing a new slate in an existing roof:  Remove the slate using a slate thief, or a hook bar that can grab the nail from underneath.  Cut it to proper width and length.  Slide into place.  Drill a hole in between the two upper slate’s vertical seam and fasten with a copper nail.  Cut a copper bib about 3” wide and about 4” longer than the exposure.  Slide bib to cover the nail.  Few existing slates were properly repaired.  They used tar to keep the slates in place, which does not allow the slate to expand a contract properly and allows them to prematurely fracture.




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