CHAP. XII.
Of Coverings of ſtrait Lines; of the Beams and Rafters, and of the uniting
the Ribs.
the Ribs.
Of Coverings, ſome are to the open Air,
and ſome are within; ſome conſiſt of
ſtrait Lines, others of curve, and ſome of both:
We may add, not improperly, that ſome are
of Wood, and ſome of Stone. We will firſt,
according to our Cuſtom, mention one Obſer
vation which relates in general to all Sorts of
Coverings; which is this: That all manner of
Roofs, or Coverings have their Ribs, Nerves,
Finiſhings, and Shells, or Cruſts, juſt the ſame
as the Wall: Which will appear from the
Conſideration of the Thing itſelf. To begin
with thoſe of Wood, and conſiſting of ſtrait
Lines; it is neceſſary for ſupporting the Cover
to lay very ſtrong Beams acroſs from one Wall
to the other; which, as we took Notice be
fore, are Columns laid tranſverſe: Theſe
Beams therefore, are a Sort of Ribs; and if
it were not for the Expences, who would not
wiſh to have the whole Building conſiſt, if we
may uſe the Expreſſion, of nothing but Ribs
and ſolid Work; that is to ſay, of continued
Columns and Beams cloſe compacted? but we
here conſult Oeconomy, and ſuppoſe every
Thing to be ſuperfluous, that without Pre
judice to the Strength of the Work, may be
poſſibly retrenched; and for this Reaſon, we
leave Spaces between the Beams. Between
theſe we lay the Croſs-beams, Rafters, and the
like; which may not at all improperly be
reckoned the Ligatures: To theſe we fit and
joyn Boards and Planks of greater Breadth,
which there is no Reaſon why we ſhould not
call theFiniſhing; and in the ſame Way of think
ing, the Pavement and Tiling is the Outward
Shell, and the Ceiling, or Roof, which is over
our Head the Inward. If this be granted, let
us conſider whether there is any Thing ne
ceſſary to be obſerved with Relation to any of
theſe Parts, that having duly examined it, we
may the more eaſily underſtand what belongs
to Coverings of Stone. We will ſpeak of them
therefore as briefly as poſſible: Firſt, taking
Notice of one Thing not foreign to our Pur
poſe. There is a very vicious Practice among
our modern Architects; which is, that in
order to make their Ceilings, they leave great
Holes in the very Ribs of the Building to let
the Heads of the Beams into after the Wall is
finiſhed; which not only weakens the Struc
ture, but alſo makes it more expoſed to Fire;
becauſe by theſe Holes the Flames find a
Paſſage from one Apartment to another. For
which Reaſon, I like the Method uſed among
the Ancients, of ſetting in the Wall ſtrong
Tables of Stone called Corbels, upon which
they laid the Heads of their Beams. If you
would bind the Wall, and the Beams together,
you have Braſs Cramps, and Braces, and
Catches or Notches in the Corbel itſelf, which
will ſerve for that Purpoſe. The Beams ought
to be perfectly ſound and clear; and eſpeci
ally about the Middle of its Length it ought
to be free from the leaſt Defect, placing your
Ear at one End of it while the other is ſtruck,
if the Sound come to you dead, and flat, it is
a Sign of ſome private Infirmity. Beams that
have Knots in them are abſolutely to be re
jected, eſpecially if there are many, or if they
are crouded together in a Cluſter. The Side
of the Timber that lies neareſt the Heart,
muſt be planed, and laid uppermoſt in the
Building; but the Part that is to lie under
moſt, muſt be planed very ſuperficially, only
the Bark, nay, and of that hardly any, or as
little as poſſible. Which-ſoever Side has a
Defect that runs croſſways of the Beam, lay
uppermoſt; if there is a Crak longways, ne
v̊er venture it of the Side, but lay it either
uppermoſt, or rather undermoſt. If you hap
pen to have Occaſion to bore a Hole in it, or
any Opening, never meddle with the Middle
of its length, nor its lower Superficies. If, as in
Churches, the Beams are to be laid in Couples;
leave a Space of ſome Inches between them,
that they may have Room to exhale, and not
be ſpoyled by heating one another: And it
will not be amiſs to lay the two Beams of the
ſame Couple different Ways, that both their
Heads may not lie upon the ſame Pillow;
but where one has its Head, the other may
have its Foot: For by this Means the Strength
of the one's Foot will aſſiſt the Weakneſs
of the other's Head; and ſo vice verſa. The
and ſome are within; ſome conſiſt of
ſtrait Lines, others of curve, and ſome of both:
We may add, not improperly, that ſome are
of Wood, and ſome of Stone. We will firſt,
according to our Cuſtom, mention one Obſer
vation which relates in general to all Sorts of
Coverings; which is this: That all manner of
Roofs, or Coverings have their Ribs, Nerves,
Finiſhings, and Shells, or Cruſts, juſt the ſame
as the Wall: Which will appear from the
Conſideration of the Thing itſelf. To begin
with thoſe of Wood, and conſiſting of ſtrait
Lines; it is neceſſary for ſupporting the Cover
to lay very ſtrong Beams acroſs from one Wall
to the other; which, as we took Notice be
fore, are Columns laid tranſverſe: Theſe
Beams therefore, are a Sort of Ribs; and if
it were not for the Expences, who would not
wiſh to have the whole Building conſiſt, if we
may uſe the Expreſſion, of nothing but Ribs
and ſolid Work; that is to ſay, of continued
Columns and Beams cloſe compacted? but we
here conſult Oeconomy, and ſuppoſe every
Thing to be ſuperfluous, that without Pre
judice to the Strength of the Work, may be
poſſibly retrenched; and for this Reaſon, we
leave Spaces between the Beams. Between
theſe we lay the Croſs-beams, Rafters, and the
like; which may not at all improperly be
reckoned the Ligatures: To theſe we fit and
joyn Boards and Planks of greater Breadth,
which there is no Reaſon why we ſhould not
call theFiniſhing; and in the ſame Way of think
ing, the Pavement and Tiling is the Outward
Shell, and the Ceiling, or Roof, which is over
our Head the Inward. If this be granted, let
us conſider whether there is any Thing ne
ceſſary to be obſerved with Relation to any of
theſe Parts, that having duly examined it, we
may the more eaſily underſtand what belongs
to Coverings of Stone. We will ſpeak of them
therefore as briefly as poſſible: Firſt, taking
Notice of one Thing not foreign to our Pur
poſe. There is a very vicious Practice among
our modern Architects; which is, that in
order to make their Ceilings, they leave great
Holes in the very Ribs of the Building to let
the Heads of the Beams into after the Wall is
finiſhed; which not only weakens the Struc
ture, but alſo makes it more expoſed to Fire;
becauſe by theſe Holes the Flames find a
Paſſage from one Apartment to another. For
which Reaſon, I like the Method uſed among
the Ancients, of ſetting in the Wall ſtrong
Tables of Stone called Corbels, upon which
they laid the Heads of their Beams. If you
would bind the Wall, and the Beams together,
you have Braſs Cramps, and Braces, and
Catches or Notches in the Corbel itſelf, which
will ſerve for that Purpoſe. The Beams ought
to be perfectly ſound and clear; and eſpeci
ally about the Middle of its Length it ought
to be free from the leaſt Defect, placing your
Ear at one End of it while the other is ſtruck,
if the Sound come to you dead, and flat, it is
a Sign of ſome private Infirmity. Beams that
have Knots in them are abſolutely to be re
jected, eſpecially if there are many, or if they
are crouded together in a Cluſter. The Side
of the Timber that lies neareſt the Heart,
muſt be planed, and laid uppermoſt in the
Building; but the Part that is to lie under
moſt, muſt be planed very ſuperficially, only
the Bark, nay, and of that hardly any, or as
little as poſſible. Which-ſoever Side has a
Defect that runs croſſways of the Beam, lay
uppermoſt; if there is a Crak longways, ne
v̊er venture it of the Side, but lay it either
uppermoſt, or rather undermoſt. If you hap
pen to have Occaſion to bore a Hole in it, or
any Opening, never meddle with the Middle
of its length, nor its lower Superficies. If, as in
Churches, the Beams are to be laid in Couples;
leave a Space of ſome Inches between them,
that they may have Room to exhale, and not
be ſpoyled by heating one another: And it
will not be amiſs to lay the two Beams of the
ſame Couple different Ways, that both their
Heads may not lie upon the ſame Pillow;
but where one has its Head, the other may
have its Foot: For by this Means the Strength
of the one's Foot will aſſiſt the Weakneſs
of the other's Head; and ſo vice verſa. The