PART THREE

Notes on Copper Roofing

   Copper possesses certain characteristics and physical properties which distinguish it from other metals used for roofing purposes. A thorough understanding of these is important. The greatest difference is in expansion and contraction. Copper has a higher coefficient of expansion than has iron and steel, and a lower one than has zinc and lead. This means that for a given temperature variation there will be more movement in copper than in iron and steel and less than in zinc and lead. For example, in a range of 200° F., the movement in a sheet 96 inches long is:

For Steel (Terneplate)......0.1171 Inches     (About 7/64ths)

For Iron...........................0.1325 Inches    (About 9/64ths)

For Copper.......................0.1824 Inches    (About 3/16ths)

For Lead...........................0.3053 Inches   (About 19/64ths)

For Zinc............................03322 Inches    (About 1/3rd)

   Another difference is in malleability or ductility. Copper is the most ductile of metals used for roofings. This property of ductility allows copper to adjust itself to stresses due to temperature variations. Soft (roofing temper) copper is used for roofings and flashings because it possesses to the fullest degree this valuable physical property.

  FUNDAMENTALS IN SHEET-COPPER ROOFING CONSTRUCTION

(There are a few fundamentals in applying sheet-copper roofing which cannot be over-emphasized. These are set forth in the ten rules listed below:)

RULE 1. Use 16-ounce soft (Roofing Temper) copper only.

(a) Do not use hard (Cornice Temper) copper except for cornice work.

(b) Do not use lighter than 16-ounce copper.

“SOFT" VERSUS “HARD" COPPER

   Soft copper will give the most satisfactory results. Hard (cornice temper) copper, though sometimes used for flashings and roofings, is not recommended. The soft sheet is, as can readily be understood, more easily workable, especially where bends, etc., are necessary.

THICKNESS OF COPPER SHEETS FOR ROOFS

   It is not fair to a good material to use too thin a sheet. As copper does not corrode, there is no question of durability in the thinner gages. Copper sheet weighing I pound per square foot, commonly known as 16-ounce copper, is considered the minimum standard sheet strong enough to withstand extraneous injury. Thinner sheets do not give the best results.

--------------------

RULE 2. Prepare the laying surface carefully and see that it is smooth and even.

(a) All copper sheets should be laid on rosin-sized paper or asbestos felt.

(b) Sheathing boards should be ship-lap, tongued-and-grooved, or splined.

(c) All nail heads should be set.

ROOFING BOARDS OR SHEATHING

   It is recommended that ship-lap or tongued-and-grooved roofing boards be used. All roof sheathing should be well laid with even joints and secured at all bearings with heavy nails well set. 

   Immediately after laying, the sheathing should be protected by covering it with paper as mentioned below. If possible the sheathing should be exposed to the weather at least 4 weeks before covering it with copper. The wood must be thoroughly dry and seasoned.

PAPER OVER SHEATHING

   Good practice requires either the ordinary building paper or a rosin-sized or asbestos paper weighing about 6 pounds per 100 square feet.

   On concrete roof slabs paper is not essential, provided the surface be made smooth and even as outlined on the following page.

- 21 -