CERTAIN IMPROVEMENTS IN THE CASTING OF IRON ROOPS FOR HOUSES, WAREHOUSES, AND OTHER BUILDINGS, AND IN COVERING THE SAME WITH SLATES
Year: 1809

page_text: CRAGG'S SPECIFICATION.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, JOHN
CRAGG, of Liverpool, in the County Palatine of Lancaster, send greeting.
WHEREAS His most Excellent Majesty King George the Third did, by His
Letters Patent under the Great Seal of the United Kingdom of Great Britain
and Ireland, bearing date at Westminster, the Twenty-first day of November,
in the fiftieth year of His reign, give and grant unto me, the said John Cragg,
my exors, admors, and assigns, His especial licence, full power, sole privilege
and authority, that I, the said John Cragg, my exors, admiors, and assigns,
during the term of years therein mentioned, should and lawfully might make,
use, exercise, and vend, within England, Wales, and the Town of Berwick-upon-
Tweed, my Invention of "CERTAIN IMPROVEMENTS IN THE CASTING OF IRON ROOPS
FOR HOUSES, WAREHOUSES, AND OTHER BUILDINGS, AND IN COVERING THE SAME WITH
SLATES;" in which said Letters Patent there is contained a proviso, obliging me,
the said John Cragg, by an instrument in writing, under my hand and seal,
to cause a particular description of the nature of my said Invention, and in
what manner the same is to be performed, to be inrolled in His Majesty's
High Court of Chancery within two calendar months after the date of the
said recited Letters Patent, as in and by the same, relation being thereunto
had, may more fully and at large appear.
NOW KNOW YE, that in compliance with the said proviso, I, tho said
John Cragg, do hereby declare that my said Invention, and the manner in
which it is to be performed, are described as follows:-
I make and cast iron rafters with a shelf or shoulder at the side, of the
breadth of one or one and a half inches on each side, upon which the slate rests
between two rafters (the rafters being first primed with paint), bedded in

page_text: cement or putty; upon the said shelves or shoulders of the rafters at the sides
and the bottom end of the slate, resting upon a flat cross bar of cast iron of the
breadth of two inches or upwards, which is made with a groove to slide along
the edge of the shoulders or shelf of the rafter to the exact length the slate
requires. The slate is there bedded in cement or putty, and pointed carefully,
lapping over half of the said cross bar, and the top of the next slate lapping
on the other half of the cross bar, bedded in the same manner, and thero
making a joint to be secured, and pointed by white lead or cement. In the
shelf or shoulder of the rafter I do make, in the casting, or afterwards drill, a
small hole or holes, and when the slate is exactly fitted to its place, I do also
drill or cut a hole or holes through the slate, and drive a lead peg or iron
nail or screw, through putty, into the holes in the slate and rafter, and clench
or revit the said peg or nail on the under sido to the iron rafter or the screw
by a nut, which prevents the slate from moving. I do also make two holes in
cach flat cross bar, into which a lead peg, or otherwise, may be driven through
the bottom of each slate and the top of the next, whereever it may be deemed
requisite, for the better securing of the joint. I do also cast upon the back or
top of each rafter, and which in the roof rises above the slate, a ridge or flange
which projects over the side joints of the slates, and forming a groove with tho
shoulder of the rafter, assists in securing the joint, by protecting the putty or
cement from the weather. I do also make and cast, in that part of the roof
which is usually called the ridge piece, or pole, or first piece, upon the top or
back thereof, rising above the ends of the slate and covering the ends also of
the rafters (which are bolted and screwed to the ridge piece), a ridge which
projects two or three inches over the top of the slate and the ends of the
rafters, and the same being well secured and pointed with putty and cement,
makes any ridge cover of lead, stone, tile, or other materials unnecessary, and
gives a particular neat appearance to the roof, whilst it, at the same time,
adds strength to the ridge, pole, or piece. In the said ridge piece I do make
and cast, or afterwards drill, at the proper distances which the breadth of the
slate requires, two holes, through which screw bolts (by which the flange at the
top of each rafter is fastened) are driven. A flange may also be cast at
the other or bottom end of the rafter, to rest upon the wall, or otherwise, as
the design of the roof may require. In roofs upon buildings, where flatness
and elegance of appearance is less an object, the sliding or flat cross bar may
be spared and omitted, and the sides of the slates (which in this as well as the
aforesaid other design should be of the largest size of sawed Bangor or
Westmoreland or other slates, and of equal width and paralel lines (equal
lengths not being material), bedded in lime or mortar upon the shelves or

page_text: shoulders of the rafters, and the bottom of one slate lapping over the top of
the next slate an inch and half or two inches, being thero secured in the
lapping with putty or cement, and the upper sides of the slate (under the
small ridge of the rafter) pointed with putty, as before described; or, the
ridge of the rafter may be omitted, and the slate, meeting over the shelf, bedded
in putty or cement, and secured in the same manner upon the cross bar, as
before described, screwed by lead nails or iron screws countersunk in tho slate,
and secured by putty or cement about and over the head of the nail or screw,
and rivetted underneath the iron rafter, as before described. The slato should
be strong and large, and sawed for cut in lines exactly parrellel. In each of
these methods of roofing my castings of ridge picce and rafters and covering
with slate may be accommodated and adopted to almost every design of
building, and being framed of materials durable and not combustible, and
much less liable to contraction and expansion by effects of the weather, than
wood, and also, from the simplicity of its construction, may be more easily
kept in repair than a roof upon a frame of timber. It will be necessary
occasionally to paint the iron to prevent rust or corrosion, and also to refresh
the putty or joints with a coat of paint, but as the occasion will not be
frequent, much less trouble or expence will be incurred than in the repairs of
a common roof.
And in order that my said Invention and improvements in the casting of
iron roofs, and covering them with slates, may be moro fully understood, I
have hereunto annexed certain sketches or Drawings, from which it will
nevertheless be necessary to deviate, as more or less span or extent of roof,
and more or less strength, may be consequently required.
No. 1. the ridge piece.

page_text: My cast-iron rafters may be used along with principals or beans of wood,
the iron rafters resting thereon, bolted and secured to the ridge piece of iron,
to avoid the injury consequent upon the contraction and expansion of timber
by change of weather or climate. When the principals and beams are of
iron, I do make and cast upon the back or top side of the principal a shelf
or shoulder and flange, a ridge similar to that upon the rafter, and it thereby
answers also as a rafter. I prefer iron, not only for economy and durability,
but because the frame may be removed without loss or injury of the materials,
or exported to the colonics or beyond the seas where labour is dear, ready
formed and only requiring to be there put together, and the iron for a roof,
as described, being suitable for ballast, both in weight and form, for the ship
which conveys it. And, lastly, I do declare that the forms, dimensions,
relative magnitudes, and other particulars relating to roofs, required to carry
my improvements into effect, are capable of great variations, and will require
to be modified according to the purposes to be answered, and the local and
under circumstances under which the work is to be performed; but that the
said forms and other particulars may, from the description and explanation
I have given, bo determined with facility by any person of ordinary skill and
fit to be entrusted with the execution thereof.
In witness whereof, I, the said John Cragg, have hereunto set my hand
and seal, this Twentieth day of January, in the year of our Lord One
1 dnd ton

page_text: Projection lower part of the ridge
pole upon whichy Flange at the
and of y Rafler rests.
The sides to which ye said, Flange
is secured to y" Ridge Post by screw
bolts thro' two Rafters, which are
opposite to each other.