CARE OF YOUR OLD BARN
Tip #5 - Repair Structural Problems.
Structural problems in agricultural buildings can be a serious threat to their survival. Structural failure can rapidly lead to collapse of part or all of a building, particularly when the building is stressed by a heavy load of equipment, hay, snow, or even by high winds.
Wood frame agricultural buildings are relatively easily dated by the type of structure they have. Post-and-beam frames with heavy timbers and wooden pegged joinery generally date from the nineteenth century and perhaps earlier. Stud-frame construction with dimension lumber and roof trusses generally dates from the late-nineteenth and twentieth centuries. Sometimes farmers reused timbers or framed sections recycled from earlier barns in their new barns, confusing matters for the casual observer. Many barns are composed of two or more structures from different periods.
Before doing any structural repairs
make sure you gain a full understanding of what caused the problem.
You should then remedy the source of the problem first. Often you may need
a structural engineer or experienced timber framing contractor to accurately
assess conditions and develop repair options. Perhaps the most common problems
are decay of sill timbers, because soil, wet hay, or manure have built
up around the base of the building, and unrepaired roof leaks that lead
to decay in the roof structure or in the plate timber where rafters meet
the wall. Often if the foundation is affected by frost heaving, it places
unusual stress on the frame, twisting it and breaking and pulling apart
the joinery. Runoff or soil drainage problems may also keep some timbers
moist, leading to wood rot, insect damage, or fungus growth.
Check over the entire
frame of the barn, timber by timber, each year. Look for any structural
defects. Check sill timbers and their joints for decay or cracks indicating
stress. Look at support posts and footings in the basement to see that
they are sound and without long, deep splits. Are there any broken rafters
or is the ridge-beam broken or split? Have floor joists separated from
the timbers they rest on or are joined to? If you detect any of these problems
that indicate stresses on and movement of the structure, it is important
to determine whether the stress or movement is still occurring or if it
was an isolated incident or temporary condition some time ago. Overall,
evaluate where the structure has settled, where loads have concentrated,
and whether the floors and roof structures are weak.
Look for insect damage and fungus
growth in timbers that appear damp. Carpenter
ants make pencil-sized, entry/exit holes into the interior of the timber
leaving piles of coarse "sawdust" underneath. Exterminate the
ants' nests with insecticide as soon as they are detected. Wood boring
beetles make small tunnels in the wood dropping yellow powder below. They
do their damage more slowly than carpenter ants, but may require repeated
efforts to exterminate. Fungus growth may appear as a light or dark film
(powdery when dry) on timbers and may grow in cracks and joinery where
it is not visible. Probing with a sharp object for soft areas will reveal
whether wood is being damaged. Wood preservatives will stop fungus growth
and prevent further deterioration. If wood damaged by insects or fungus
can be isolated from ground or water contact, newly developed borate-based
treatments may be used both to exterminate pests and preserve the wood.
(Such treatments are much less toxic than most other insecticides and preservatives.)
Stabilizing and repairing structural damage usually involves hiring a contractor experienced in working on old buildings. Due to the risks, jacking and reinforcing a structure should be done by those with experience and proper tools. Local sawmills are usually the best source for custom-sawn timbers. Sometimes new steel cables or cross beams may prevent walls from splaying out and allow continued use of a barn. Often new wood may be "sistered" (joined) onto the side of deteriorated or broken timbers to reinforce them, avoiding replacement of structural members, such as sills, plates, or joists. Epoxy consolidants and fillers can sometimes be used to repair damaged wood that is not subject to structural stress.
© 1995 Vermont Division for Historic Preservation and Vermont Housing and Conservation Board. All rights reserved.
Forward to Barn Tip #6...
Back to the Table of Contents...