Framed Buildings and Roofs
the close of the 11th century, the rebuilding of the Saxon churches had
begun at Canterbury, Gloucester, St. Albans, Ely, Durham and Lindisfarne.
An additional 20 new sites running from Battle to Tynemouth had also been
colonised by monks. Throughout the 12th century this continued at an increasing
rate and by the mid 13th century another three hundred convents, financed
by land grants and endowments, were constructing abbeys or priories, and
other ancillary buildings.
these edifices were in their final form, invariably constructed of stone,
they took years to complete. It was therefore the job of carpenters to
construct temporary chapels, accommodation and storage facilities for
the founding communities during interim periods. These highly skilled
and important craftsmen also arranged the scaffold for the masons as work
on the walls progressed and constructed the complex, load bearing formwork.
Upon these, the arches and vaults could be assembled before finally raising
the framework to support the building's protective covering. Durham Cathedral
Priory Church is a good example of the length of construction for a project.
It was completed in 1133 after 40 years' work. Its cloisters, chapter-house,
dormitories, kitchen cellars and reception buildings were added later.
growth of religious communities was mirrored in the development of new
construction techniques. Master carpenters began to develop specialised
jointing techniques and explore the mechanics of structures. By the mid
14th century, they were able to produce structures like the internal scaffold
frame for Salisbury Cathedral spire and the octagon and lantern which
float above the crossing of Ely Cathedral. The culmination of this craftsmanship
occurred in 1400 with the completion of Master Hugh Harland's 'hammerbeam'
roof to the Great Hall at Westminster. Here, he transcended the limitations
of timber lengths to create the largest clear-span roof in the world and
a work of outstanding beauty.
building, which didn't have the backing of Church and State, was slow
to absorb and react to these developments. Instead, it tended to be predominantly
influenced by tradition and local custom. 'Cruck-framing', where
the roof is carried by paired curved timbers from ground level to ridge,
found predominantly in the Midlands, Mid Wales, the North and West of
Britain, may represent the survival well into the 16th century of timber
framing techniques from a pre-Norman, possibly Celtic, culture. Box framing,
on the other hand, seems to have developed predominantly in the South
and East of England. The introduction of the 'cill beam', a horizontal
wooden base into which timber posts were tenoned to overcome problems
associated with earth fast wall members, was attributable to the Saxons.
The'sans-purlin' roof of the medieval hall was simple. Uniformly sized
rafter couples, joined by a collar, were held vertical by steep hips at
each end, with intervening rafter spaces maintained solely by the thatch
or tile battens.
roofs were given the additional support of 'scissor' or 'passing
braces'. After 1350 use of a central purlin braced to crown posts
mounted on the tie beams became widespread in the southeast and continued
in use for the next 200 years.
sectioned principal rafters, jointed into the tie beam to form a truss
which could carry side purlins, came into general use towards the end
of the 15th century. These took the form of butt purlins tenoned into
the side of the principals or clasped purlins held between a deep collar
and the principal's inner face. In areas with a cruck tradition, these
principals tended to be heavy, carrying trenched purlins in notches on
their outer faces and ridge beams at the truss apex.
dissolution of the monasteries in the 16th century precipitated a change
in building layout from the open hall to houses more suited to occupation
by a priest or member of the emerging merchant class. These incorporated
smoke bays or brick chimneys through framed floors at storey height, with
glazed casements gradually replacing the open 'wind eye' or 'wind
hole'. In line with this development, the open hearth was slowly eliminated
from the halls by the introduction of the chimney allowing the hall to
be modified by the insertion of a floor.
of the monastic woodlands also had its effects as the increase in available
timber promoted a period of conspicuous consumption in such practices
as close studding, ornamental panelling, heavy mouldings and decorative
carving. As domestic oak stocks dwindled during the 17th century rising
prices led to the importation of Baltic softwood as well as oak billets
to supply the continuing demand for cleft oak panel interiors.
Great Fire of London in 1666 gave added impetus to the fashion for brick
construction favoured by the new architects for its greater design flexibility,
and marked the beginning of a decline in the timber frame tradition.
end tenon with diminished haunch. First use thought to be at King's
College Chapel, Cambridge, 1510-1512, where it was found on side purlins
began to look to Europe for inspiration and introduced from Italy the
'stressed' truss in which a 'king-post' is suspended from
the top of the principals, picking up the dead load weight of the tie
beam at its base. This, in combination with the great lengths available
in the imported softwoods, gave the ability to bridge wide spans with
roofs of low pitch. The king-post and its variant, the 'queen-post'
truss, was much used during the 18th century with the addition of iron
straps and tension bolts. The circulation of manuals giving construction
details, the mechanisation of timber conversion and the sourcing of new
softwood supplies from North America brought about the 'laminated'
truss. These foreshadowed the mechanical trusses of the 19th century as
solutions were sought for the roofs of industrialised England.
Gothic had the tendency to be an applied visual effect; ornate hammerbeam
forms being suspended from more conventional roof structures or held together
by iron ties. Exteriors on the other hand, were decorated with elaborate
fake half-timbering. Though carpenters remained responsible for the framing
of floors and roofs, the traditional framing of timber buildings had been
largely relegated to agricultural purposes.
problems encountered in timber framed structures fall into three main
categories: insect attack, fungal decay and mechanical damage.
a building is able to rack or twist, placing individual members under
excessive loads, then mechanical failure is likely to occur. This can
the frame is inadequately braced
foundations have moved
a cill beam has deteriorated bracing
resulting forces of compression, tension and torsion, will eventually
lead to mechanical damage when the timbers can no longer absorb them through
deflection or crush. Failure may occur in the form of shear, joint failure;
plate or post fracture; rafter spread or ultimate collapse.
often than not such events are initiated by alterations or 'improvements'
which have involved severing structural members to accommodate inserted
floors, communicating doors, additional windows or relocated stairways.
Internally, the removal of partition walls or, the installation of services
in trenches cut through floor joists, may have severely reduced the structural
frame, while beam ends encased in masonry walls can decay, allowing the
beam to descend along with the floor joists.
timber repairs are put in hand, a drawn and measured survey of the building
should be prepared, showing:
the timber type, condition and dimensions
surface finish or treatment
position, nature of construction and assembly marks
details of mouldings or decorative features
the exact location of any damage or distortion.
timber frames and roofs are designed to stand alone as a unit, it is our
opinion that the repair should be aimed at restoring that unity. Carpentry
solutions may therefore be preferred to alternative approaches - although
this will often entail a degree of replacement. Under these circumstances,
'green' or unseasoned timber may be used when the dimensions required
exceed 4 - 5 inches. (Dry stock is difficult to obtain and prohibitively
costly for most applications.)
lap joint designed to resist withdrawal, Coggeshall Abbey Barn, 1120-1147 (Hewett)
considering the replacement of such elements as shaped door heads, deep
mouldings, large boards and panels or wide braces, dry stable material
is essential. This is because subsequent shrinkage will cause distortion
and possible damage to adjacent fabric.
indication of conversion methods used in producing original members may
be obtained by examination of the cross-section. Heart/sapwood orientation
is important when considering the weathering of exposed timbers, whilst
conversion methods dictate to a large degree, the surface finish, and
at times, the final form.
the individual trying to minimise the visual impact of a repair, the material
which is to be permanently bonded to the original must be closely matched
in type, moisture content, surface, sectional grain pattern and colour.
This can easily be sourced from reclaimed material.
glues used in bonding should be boil and waterproof (commonly two-part
epoxy resins). Whilst this may also serve as a grout for bedding or to
fill fissures up to 10mm, suppliers should be consulted regarding suitability
for filling larger voids.
metal work is to be embedded in timber, as in flitch-plate repairs to
fracture, stainless steel should be used for both plate and fixing pins
or bolts. They should be set in a grout of resin and the entry point masked
by the insertion of a timber fillet. Surface applied plates, straps or
bands, may be of mild steel but adequate protection must be provided by
the application of rust inhibiting coatings or paint, particularly, on
- JR Armstrong,
Traditional Buildings Accessible to the Public, EP Publishing
Ltd, Wakefield, Yorks, 1979
- John and Nicola Ashurst,
Practical Building Conservation Vol 5, Gower
Technical Press, Aldershot, Hants, 1979
- RW Brunskill, Timber Building in England, Gollancz, London, 1985
- R Harris,
Discovering Timber Framed Buildings, Shire Publications,
- David and Barbara Martin,
Domestic Building in the Eastern High Weald
1300-1750, Hastings Area Archaeological Papers, Robertsbridge,
English Historic Carpentry, Phillimore and Co, Chichester,
- David Yeomans, The Architect and the Carpenter, RIBA Publications, Riba
Heinz Gallery, London, 1992
article is reproduced from The Building Conservation Directory, 1993
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