What Are Structural Home Repairs
Structural Timber Repairs
Robin Russell
 | |
| Final tightening of side-planted timbers which were |
Timber has been used in building structures for centuries, whether for roofs, flooring beams and joists, posts and lintels for windows and doors, or for complete timber framed buildings, including load-bearing walls and screen partitions.
The apply and class of the timber elements and signs of how they were shaped are useful in dating celebrated buildings because the type of joints, framework design and tool applied science changed over the centuries. Whether or non they are visible, timbers are intrinsic to the historic and archaeological interest of the building.
Structural timbers may deteriorate as a result of decay, over-loading, or as a result of poor design and alterations carried out in the by.
A common trouble is decay brought about past moisture, oft owing to a leak, poor maintenance or condensation. This allows fungi (dry rot for example) or wood-boring insects (such equally woodworm and deathwatch beetle) to colonise the timber and past their activity reduce its strength.
Over-loaded structural members fail by cracking, bending or crushing. The over-loading may arise either every bit a consequence of weakening post-obit decay, or considering they were designed poorly or frugally, or considering they were meant to take a different prepare of loads than they are currently begetting. For instance, a roof structure designed for thatch or slate may not exist capable of supporting the weight of heavy tiles.
REPAIR OPTIONS
Repairing failed structural timbers is, of class, non a new practice. For centuries repairs have been fashioned using carpentry methods or with blacksmith-made splints, brackets and ties, and these ancient repairs certainly add character and help tell the story of the building.
In more recent times we accept likewise utilised modernistic materials such as steel, epoxy resins, carbon fibre rods and wire rope to reinforce structures. Building repairs can as well be effected by completely replacing timbers with new timber or, where used appropriately and sympathetically, materials such as steel or reinforced concrete. It may too be possible to reduce the loads through the pattern of secondary structures and in-fills such every bit brick panels, or packing-upward nether partly decayed timbers.
The relative merits of each grade of repair largely depend on the situation. Although there is no right or wrong method, there is always a solution that is almost appropriate to the circumstances presented by the edifice. The art is to identify it.
When dealing with historic structures, the principles which come into play are:
- Structural integrity – ensure the structural members are capable of taking the loads they may have to bear
- Minimal intervention – retain the maximum amount of historic timber and minimise alteration or introduction of new elements. Consider the impact of the repair process on the component and the structure, including access problems, the viability of moving the timbers for repair, and the extent of harm which might be washed to other building elements in executing the repair
- Reversibility – try to ensure that alterations and additions can be undone without harm to the fabric
- Like for like – where possible, use the same materials and techniques equally previously used.
- Honesty – make the solution honest simply aesthetically and architecturally elegant and either keen or invisible: there is no justifiable reason why modern repairs should not add graphic symbol and appeal in the same way as the historic ones
- Documentation – record the fabric before intervention and certificate the intervention itself so that futurity conservation piece of work is well informed.
In choosing the right approach and repair mechanism you lot must accept all the evidence into account, including the type of failure that has been observed and, past deduction, the reason for it. Things to look for might include the source of actress loading, or the reason why a beam end is getting moisture. So, for example, you lot might look at a cracked upper floor beam in a befouled where the crack at the terminate of the beam is in an area of severe insect attack. In this case yous would demand to consider the presence of moisture in the wall in which the timber is embedded, and whether there is a leak in the roof, an alluvion gutter or another source. You lot will also need to consider whether the upper floor is existence asked to take specially loftier or increased loads. Perchance a huge amount of hay or straw is sometimes stored in the barn, or maybe there is a repair mail service mounted onto the beam which is transferring additional load, mayhap following a alter in the roof roofing and the subsequent deflection of the roof.
Another cistron for consideration is the impact of any particular repair. If the timber were removed, how much damage or loss of fabric would occur around information technology?
Oft these observations, decisions and design solutions are the realm of specific professional consultants, such as structural engineers or building surveyors. Plainly when dealing with celebrated textile, it becomes absolutely essential to choose the right specialist, that is: i who is well-versed in devising sympathetic solutions with minimal intervention, and who is used to working with historic structure methods and materials.
However, it has to exist said that if you have the right contractor doing the work, this also helps profoundly. A specialist conservation contractor who is familiar with executing such repairs can work nearly finer with the engineer and may well exist able to requite guidance on what options are achievable.
The wrong team volition invariably result in a impuissant and/or expensive solution or the excessive loss of celebrated fabric.
LIKE-FOR-Similar REPAIRS
Sometimes the simplest repair is a straightforward replacement of the whole timber, like for like: for example a completely rotten lintel or exposed verge rafter. At times, replacement provides the opportunity to fit a stronger or more than substantial piece of timber or to slightly adapt the design to foreclose future failure.
Even so, as a thing of principle it is important to endeavour to retain equally much celebrated fabric every bit possible, then the best solution is usually to repair rather than replace components. A common technique is to scarf-in a new piece of timber to the old, like for like. The new section can be continued by a lightning bolt joint (pegged or bolted) or, if in pinch, a V-shaped splice. Scarfed joints are particularly useful in cases where one section of the timber has rotted out, such as the foot of a postal service or jamb, or the ends of a rafter, truss or axle which have been affected by damp. They provide a nice neat repair, in keeping with the grapheme of the original, but crave a reasonably high level of carpentry skill if they are to be done well.
REINFORCEMENT OPTIONS AND SUPPLEMENTARY STRUCTURES
Information technology's often possible and preferable to leave historic timber in place and either take or help take the strain with an alternative structural member. For instance, the spreading of a roof truss may be restrained by adding a 2d collar, or a rafter may be doubled upwardly with a new timber either shut by or attached to the original. In some cases the right roof repair solution is a new framework built around or over the sometime. This is sound conservation exercise because information technology saves the original fabric and is more often than not reversible, although information technology tin look a fiddling impuissant if it is on show.
 | |
| Typical solutions where a axle stop has decayed |
Where beams or joists are not deep enough for their loading, the upshot is excessive bending, bouncing floors, and maybe even cracks. 1 option is to increment the effective depth by fixing additional timber to the peak of the component to increment its stiffness. If the depth of a beam only needs to be increased marginally, one very peachy solution is to firmly attach the floorboard material to the top of the beam. Nevertheless, fixing the residuum of the floorboards around information technology tin can be a head-scratcher.
When the ends of beams or joists are decayed, or in cases where either the beam or its back up has moved, leaving too little bearing, it is essential to increase the junction between the two. Extending the terminate of the timber can exist washed with side-planting or splicing-in only the alternatives are many and varied. The bearing tin be extended by introducing steel or timber bolted under the beam; by forming a whole box section steel shoe fastened into the beam; by calculation a timber, steel or masonry post under the cease of the beam, down to the basis; or by creating a timber or steel corbel on the wall beneath the end of the timber. Similarly, a beam pulling out of an adjacent beam tin can exist picked upward with a fabricated strap like a joist hanger.
Another identify for simple splints similar these is where overloaded purlins have split. Side-planted steel sections or timbers bolted beyond the failure and attached to audio timber often work well.
STEEL AND RESIN OPTIONS
Where beams are in need of a petty more help, flitch plates can be inserted along part or the whole length of the beam. This method involves cutting a slot into the timber and making the beam a composite of steel and timber. The plate may besides take a T-shape either the right mode up (top of the beam) or upside down (underside of the beam). From an applied science viewpoint, the steel section is best allow into the underside of the beam and stock-still upside downwards, then the broad part of the T is positioned to carry the greatest tensile forces. From a applied viewpoint, these are difficult repairs to carry out in situ, requiring overhead cutting of the slot by multiple drillings or chain-morticer or chain-saw cut. The hazard assessment alone takes some serious thought.
Despite its higher cost, stainless steel is highly suitable for this kind of repair: it offers higher force for its size than plain steel, and it withstands corrosion in oak beams. (Even in aboriginal timbers, the tannic acid present will corrode many metals.)
The downside to using any steel is that the parts which show may not exist as aesthetically pleasing as with other solutions. However, with a chip of forethought elegant solutions are possible (albeit at a slight actress cost), such as recessing nuts and commodities heads and plugging the holes with timber, or just rounding the ends of brackets. Adding a simple blacksmith-style decoration tin make the repair much more elegant, while keeping the repair 'honest' and its history clear. Where the ends of fastenings are on prove, square plates can be neatly welded to the ends of threaded bar or bolt-heads and rebated into the surface of the timber.
Another method of strengthening timbers in a like manner is to let in steel confined or carbon fibre rods. These are normally fixed with an epoxy resin. The letting-in can involve cutting slots or drilling holes lengthwise from the stop of the timber or diagonally across cracks.
When the timber to be repaired is historically significant, a partial replacement is vital. To preserve the character of the original timber, one option is to remove the confront every bit a veneer for subsequently reapplication over a newly inserted slice. Where there is limited access or hazard of damage to the surrounding plaster, information technology is possible to care for a axle which has been eaten away to within an inch of its life by building up a laminated resin and timber beam in situ. The face can and then exist consolidated with resin poured into the beetle flight holes before being reattached to the axle. Such solutions tend to be very satisfying, but patently complex, expensive and unnecessary for most repairs.
A combination of replacing rotten or failed timber with new timber and strengthening with resin bonded steel or carbon fibre rods can be adopted to expert effect in many situations. Some companies volition even supply pre-shaped repair pieces with the rods already bonded in place, ready to fix to the prepared cease of a failed timber.
Resins offering a variety of advantages: minimal loss of textile, versatility, gap-filling and the opportunity to carry out certain repairs which are incommunicable by other methods. However, they are not specially reversible and tin can be decumbent to failure in humid environments.
SPREADING ROOF STRUCTURES
Turning our attention to roof structures, spreading out of the A-frame is oftentimes indicative of inadequate ties or decay at eaves level. Inserting additional, oft lower collars (necktie beams) between the trusses or rafters, assists profoundly in reducing roof-spread, and this consequently restrains the outward thrust on walls. Timber is ordinarily used but an culling is steel wires bolted in a substantial, but sensible style to the timber and tensioned.
Improved rigidity tin can also exist achieved by securely bolting a gusset fabricated of ply to a nearby truss or rafter and to a ceiling joist below. This strengthens the joint and triangulates the roof. The technique is particularly useful in roof spaces where the collars are necessarily high for headroom. It is an effective solution but shouldn't really be on prove.
Where the junction of trusses and collars take weakened or slipped, a unproblematic steel Y-shaped plate bolted in place can stabilise the structure.
Stainless or other wire ropes can also be employed to withstand lateral motility such as where all the rafters are 'racking' – that is to say the apex of the roof has shifted sideways at correct angles to the line of the trusses. In that example tensioned wires fixed diagonally beyond the rafters can add together some triangulation, which volition prevent farther movement. Timber or solid steel straps can exist used in a similar way, but it is often a neater and more than easily installed solution to utilise wires. However, the strength of the wire in tension must be able to withstand the loads involved in service or they volition simply stretch and become ineffective.
Clearly, there are many possibilities for repair. The right solution is the 1 which works for the building (and ideally for the client as well). Probably the conservation principle to which yous should give well-nigh emphasis is minimising the extent of intervention. Each technique and each material has pros and cons, but we generally find that the minimal intervention arroyo will lead to a cost-effective solution which saves surrounding historic fabric. If this means the repair is visible, well at least it's honest and with a spark of creativity can be made tidy and aesthetically pleasing.
~~~
Acknowledgement
Working on timber repair solutions with Patrick Stow & Associates over the years has inspired me greatly, for which I'd similar to thank him.
The Building Conservation Directory, 2013
Author
ROBIN RUSSELL BEng(Hons) is managing director of Corbel Conservation
Ltd. He has over 25 years of management experience and believes that his house of ontractors tin provide the best historic building repairs by ensuring that his managers fully understand the engineering options and the conservation approach.
Further information
RELATED ARTICLES
Structural
Timber-framed buildings
RELATED PRODUCTS AND SERVICES
Structural engineers
Structural repair and stabilisation
Timber frame builders
Timber suppliers
Timber testing, structural
Site Map
Source: https://buildingconservation.com/articles/structural-timber-repairs/structural-timber-repairs.htm
Posted by: woodsidetowery.blogspot.com
0 Response to "What Are Structural Home Repairs"
Post a Comment