31 PRESERVATION 

BRIEFS 

Mothballing Historic Buildings 

Sharon C. Park, AlA 

U.S. Department of the Interior 

National Park Service 

Cultural Resources 

Heritage Preservation Services 

When all means of finding a productive use for a historic 

building have been exhausted or when funds are not 

currently available to put a deteriorating structure into a 

useable condition, it may be necessary to close up the 

building temporarily to protect it from the weather as well 

as to secure it from vandalism. This process, known as 

mothballing, can be a necessary and effective means of 

protecting the building while planning the property's future, 

or raising money for a preservation, rehabilitation or 

restoration project. If a vacant property has been declared 

unsafe by building officials, stabilization and mothballing 

may be the only way to protect it from demolition. 

This Preservation Brief focuses on the steps needed to "deactivate" a property for an extended period of time. The 

project team will usually consist of an architect, historian, 

preservation specialist, sometimes a structural engineer, and 

a contractor. Mothballing should not be done without 

careful planning to ensure that needed physical repairs are 

made prior to securing the building. The steps discussed in 

this Brief can protect buildings for periods of up to ten years; 

long-term success will also depend on continued, although 

somewhat limited, monitoring and maintenance. For all but 

the simplest projects, hiring a team of preservation 

specialists is recommended to assess the specific needs of the 

structure and to develop an effective mothballing program. 

A vacant historic building cannot survive indefinitely in a 

boarded-up condition, and so even marginal interim uses 

where there is regular activity and monitoring, such as a 

caretaker residence or non-flammable storage, are generally 

preferable to mothballing. In a few limited cases when the 

vacant building is in good condition and in a location where 

it can be watched and checked regularly, closing and locking 

the door, setting heat levels at just 

above freezing, and securing the 

windows may provide sufficient 

protection for a period of a few years. 

But if long-term mothballing is the 

only remaining option, it must be 

done properly (see fig. 1 & 2). This 

will require stabilization of the 

exterior, properly designed security 

protection, generally some form of 

interior ventilation - either through 

mechanical or natural air exchange 

systems - and continued maintenance 

and surveillance monitoring. 

Figure 1. Proper mothballing treatment: This building has been successfully mothballed for 10 years 

because the roof and walls were repaired and structurally stabilized, ventilation louvers were added, and 

the property is maintained. Photo: Charles E. Fisher, NPS. 

Comprehensive mothballing 

programs are generally expensive and 

may cost 10% or more of a modest 

rehabilitation budget. However, the 

money spent on well-planned 

protective measures will seem small 

when amortized over the life of the 

resource. Regardless of the location 

and condition of the property or the 

funding available, the following 9 

steps are involved in properly 

mothballing a building: 

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to be structurally unsound until the 

condition of the structure can be fully 

assessed (see fig. 3). If pigeon or bat 

droppings, friable asbestos or other 

health hazards are present, precautions 

must be taken to wear the appropriate 

safety equipment when first inspecting 

the building. Consideration should be 

given to hiring a firm specializing in 

hazardous waste removal if these 

highly toxic elements are found in the 

building. 

Figure 2. Improper treatment: Boarding up without adequate ventilation, lack of maintenance, and 

neglect of this property have accelerated deterioration. Photo; NPS file. 

Documenting and recording the 

building. Documenting a building's 

history is important because evidence 

of its true age and architectural 

significance may not be readily 

evident. The owner should check with 

the State Historic Preservation Office 

or local preservation commission for 

assistance in researching the building. 

If the building has never been 

researched for listing in the National 

Register of Historic Places or other 

historic registers, then, at a minimum, 

Documentation 

1. Document the architectural and historical significance of 

the building. 

2. Prepare a condition assessment of the building. 

Stabilization 

3. Structurally stabilize the building, based on a 

professional condition assessment. 

4. Exterminate or control pests, including termites and 

rodents. 

5. Protect the exterior from moisture penetration. 

Mothballing 

6. Secure the building and its component features to 

reduce vandalism or break-ins. 

7. Provide adequate ventilation to the interior. 

8. Secure or modify utilities and mechanical systems. 

9. Develop and implement a maintenance and 

monitoring plan for protection. 

These steps will be discussed in sequence below. 

Documentation and stabilization are critical components 

of the process and should not be skipped over. 

Mothballing measures should not result in permanent 

damage, and so each treatment should be weighed in 

terms of its reversibility and its overall benefit. 

Documentation 

Documenting the historical significance and physical 

condition of the property will provide information 

necessary for setting priorities and allocating funds. 

The project team should be cautious when first entering 

the structure if it has been vacant or is deteriorated. It 

may be advisable to shore temporarily areas appearing 

the following should be determined: 

• The overall historical significance of 

the property and dates of construction; 

• the chronology of alterations or additions and their 

approximate dates; and, 

• types of building materials, construction techniques, and 

any unusual detailing or regional variations of 

craftsmanship. 

Old photographs can be helpful in identifying early or 

original features that might be hidden under modern 

materials. On a walk-through, the architect, historian, or 

preservation specialist should identify the architecturally 

significant elements of the building, both inside and out 

(see fig.4). 

Figure 3. Buildings seriously damaged by storms or deterioration may need to be 

braced before architectural evaluations can be made. Jethro Coffin House. Photo: 

John Milner Architects. 
Figure 4. Documenting the bUl1ding's history, preparing schematic 

plans, and assessing the condition of the building wl1/ provide necessary 

information on which to set priorities for stabilization and repair prior to 

securing the building. Photo: Frederick Lindstrom, HABS. 

By understanding the history of the resource, significant 

elements, even though deteriorated, may be spared the 

trash pile. For that reason alone, any materials removed 

from the building or site as part of the stabilization effort 

should be carefully scrutinized and, if appearing historic, 

should be photographed, tagged with a number, 

inventioried, and safely stored, preferably in the building, 

for later retrieval (see fig. 5). 

A site plan and schematic building floor plans can be used 

to note important information for use when the building is 

eventually preserved, restored, or rehabilitated. Each room 

should be given a number and notations added to the plans 

regarding the removal of important features to storage or 

recording physical treatments undertaken as part of the 

stabilization or repair. 

Because a mothballing project may extend over a long 

period of time, with many different people involved, clear 

records should be kept and a building file established. 

Copies of all important data, plans, photographs, and lists 

of consultants or contractors who have worked on the 

property should be added to the file as the job progresses. 

Figure 5. Loose or detached elements should be identified, tagged and stored, preferably on site. Photo: NPS files. 

Recording all actions taken on the building will be helpful 

in the future. 

The project coordinator should keep the building file 

updated and give duplicate copies to the owner. A list of 

emergency numbers, including the number of the key 

holder, should be kept at the entrance to the building or on 

a security gate, in a transparent vinyl sleeve. 

Preparing a condition assessment of the building. A 

condition assessment can provide the owner with an 

accurate overview of the current condition of the property. 

If the building is deteriorated or if there are Significant 

interior architectural elements that will need special 

protection during the mothballing years, undertaking a 

condition assessment is highly recommended, but it need 

not be exhaustive. 

A modified condition assessment, prepared by an architect 

or preservation specialist, and in some case a structural 

engineer, will help set priorities for repairs necessary to 

stabilize the property for both the short and long-term. It 

will evaluate the age and condition of the following major 

elements: foundations; structural systems; exterior 

materials; roofs and gutters; exterior porches and steps; 

interior finishes; staircases; plumbing, electrical, mechanical 

systems; special features such as chimneys; and site 

drainage. 

To record existing conditions of the building and site, it 

will be necessary to clean debris from the building and to 

remove unwanted or overgrown vegetation to expose 

foundations. The interior should be emptied of its 

furnishing (unless provisions are made for mothballing 

these as well), all debris removed, and the interior swept 

with a broom. Building materials too deteriorated to repair, 

or which have come detached, such as moldings, balusters, 

and decorative plaster, and which can be used to guide later 

preservation work, should be tagged, labeled and saved. 

Photographs or a videotape of the exterior and all interior 

spaces of the resource will provide an invaluable record of 

lias is" conditions. If a Videotape is made, oral commentary 

can be provided on the significance of each space and 

architectural feature. If 35mm photographic prints or slides 

are made, they should be numbered, dated, and 

appropriately identified. Photographs should be crossreferenced with the room numbers on the schematic plans. 

A systematic method for photographing should be 

developed; for example, photograph each wall in a room 

and then take a corner shot to get floor and ceiling portions 

in the picture. Photograph any unusual details as well as 

examples of each window and door type. 

For historic buildings, the great advantage of a condition 

assessment is that architectural features, both on the 

exterior as well as the interior, can be rated on a scale of 

their importance to the integrity and significance of the 

building. Those features of the highest priority should 

receive preference when repairs or protection measures are 

outlined as part of the mothballing process. Potential 

problems with protecting these features should be 

identified so that appropriate interim solutions can be 

selected. For example, if a building has always been heated 

and if murals, decorative plaster walls, or examples of 

patterned wall paper are identified as highly significant, 

then special care should be taken to regulate the interior 

climate and to monitor it adequately during the 

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mothballing years. This might require retaining electrical 

service to provide minimal heat in winter, fan exhaust in 

summer, and humidity controls for the interior. 

Stabilization 

Stabilization as part of a mothballing project involves 

correcting deficiencies to slow down the deterioration of the 

building while it is vacant. Weakened structural members 

that might fail altogether in the forthcoming years must be 

braced or reinforced; insects and other pests removed and 

discouraged from returning; and the building protected 

from moisture damage both by weatherizing the exterior 

envelope and by handling water run-off on the site. Even if 

a modified use or caretaker services can eventually be 

found for the building, the following steps should be 

addressed. 

Structurally stabilizing the building. While bracing may 

have been required to make the building temporarily safe 

for inspection, the condition assessment may reveal areas of 

hidden structural damage. Roofs, foundations, walls, 

interior framing, porches and dormers all have structural 

components that may need added reinforcement. 

Structural stabilization by a qualified contractor should be 

done under the direction of a structural engineer or a 

preservation specialist to ensure that the added weight of 

the reinforcement can be sustained by the building and that 

the new members do not harm historic finishes (see fig. 6). 

Any major vertical post added during the stabilization 

should be properly supported and, if necessary, taken to the 

ground and underpinned. 

Fi$,ure 6. Interior bracing which will last the duration of the mothballing 

WIll protect weakened structural members. Jethro Coffin House. Photo: 

John Milner Architects. 

If the building is in a northern climate, then the roof 

framing must be able to hold substantial snow loads. 

Bracing the roof at the ridge and mid-points should be 

considered if sagging is apparent. Likewise, interior 

framing around stair openings or under long ceiling spans 

should be investigated. Underpinning or bracing structural 

piers weakened by poor drainage patterns may be a good 

precaution as well. Damage caused by insects, moisture, or 

from other causes should be repaired or reinforced and, if 

possible, the source of the damage removed. If features 

such as porches and dormers are so severely deteriorated 

that they must be removed, they should be documented, 

photographed, and portions salvaged for storage prior to 

removal. 

If the building is in a southern or humid climate and 

termites or other insects are a particular problem, the 

foundation and floor framing should be inspected to ensure 

that there are no major structural weaknesses. This can 

usually be done by observation from the crawl space or 

basement. For those structures where this is not possible, it 

may be advisable to lift selective floor boards to expose the 

floor framing. If there is evidence of pest damage, 

particularly termites, active colonies should be treated and 

the structural members reinforced or replaced, if necessary. 

Controlling pests. Pests can be numerous and include 

squirrels, raccoons, bats, mice, rats, snakes, termites, moths, 

beetles, ants, bees and wasps, pigeons, and other birds. 

Termites, beetles, and carpenter ants destroy wood. Mice, 

too, gnaw wood as well as plaster, insulation, and electrical 

wires. Pigeon and bat droppings not only damage wood 

finishes but create a serious and sometimes deadly health 

hazard. 

If the property is infested with animals or insects, it is 

important to get them out and to seal off their access to the 

building. If necessary, exterminate and remove any nests or 

hatching colonies. Chimney flues may be closed off with 

exterior grade plywood caps, properly ventilated, or 

protected with framed wire screens. Existing vents, grills, 

and louvers in attics and crawl spaces should be screened 

with bug mesh or heavy duty wire, depending on the type 

of pest being controlled. It may be advantageous to have 

damp or infected wood treated with insecticides (as 

permitted by each state) or preservatives, such as borate, to 

slow the rate of deterioration during the time that the 

building is not in use. 

Securing the exterior envelope from moisture penetration. 

It is important to protect the exterior envelope from 

moisture penetration before securing the building. Leaks 

from deteriorated or damaged roofing, from around 

windows and doors, or through deteriorated materials, as 

well as ground moisture from improper site run-off or 

rising damp at foundations, can cause long-term damage to 

interior finishes and structural systems. Any serious 

deficiencies on the exterior, identified in the condition 

assessment, should be addressed. 

To the greatest extent possible, these weatherization efforts 

should not harm historic materials. The project budget may 

not allow deteriorated features to be fully repaired or 

replaced in-kind. Non-historic or modem materials may be 

used to cover historic surfaces temporarily, but these 

treatments should not destroy valuable evidence necessary 

for future preservation work. Temporary modifications 

should be as visually compatible as possible with the 

historic building. 

Roofs are often the most vulnerable elements on the 

building exterior and yet in some ways they are the easiest 

element to stabilize for the long term, if done correctly. 

"Quick fix" solutions, such as tar patches on slate roofs, 

should be avoided as they will generally fail within a year 

or so and may accelerate damage by trapping moisture. 

They are difficult to undo later when more permanent 

repairs are undertaken. Use of a tarpaulin over a leaking 

roof should be thought of only as a very temporary 
Figure 7. Non-historic materials are appropriate for mothballing projects when they are used to protect 

historic evidence remaining for future preservation. This lightweight aluminum channel frame and 

roofing covers the historic wooden shingle roof. Galvanized mesh panels secure the window openings 

from intrusion by raccoons and other unwanted guests. Photo: Williamsport Preservation Training 

Center, NPS. 

Figure 8. Appropriate mortar mixes should be 

used when masonry repairs are undertaken. In 

this case, a soft lime based moriar is used as an infill between the brick and wooden elements. 

When full repairs are made during the 

restoration phase, this soft moriar can easily be 

removed and missing bricks replaced. 

emergency repair because it is often blown off by the wind 

in a subsequent storm. 

If the existing historic roof needs moderate repairs to make 

it last an additional ten years, then these repairs should be 

undertaken as a first priority. Replacing cracked or missing 

shingles and tiles, securing loose flashing, and reanchoring 

gutters and downspouts can often be done by a local 

roofing contractor. If the roof is in poor condition, but the 

historic materials and configuration are important, a new 

temporary roof, such as a lightweight aluminum channel 

system over the eXisting, might be considered (see fig. 7). If 

the roofing is so deteriorated that it must be replaced and a 

lightweight aluminum system is not affordable, various 

inexpensive options might be considered. These include 

covering the existing deteriorated roof with galvanized 

corrugated metal roofing panels, or 90 lb. rolled roofing, or 

a rubberized membrane (refer back to cover photo). These 

alternatives should leave as much of the historic sheathing 

and roofing in place as evidence for later preservation 

treatments. 

For masonry repairs, appropriate preservation approaches 

are essential. For example, if repointing deteriorated brick 

chimneys or walls is necessary to prevent serious moisture 

penetration while the building is mothballed, the mortar 

should match the historic mortar in composition, color, and 

tooling. The use of hard portland cement mortars or vaporimpermeable waterproof coatings are not appropriate 

solutions as they can cause extensive damage and are not 

reversible treatments (see fig. 8). 

For wood siding that is deteriorated, repairs necessary to 

keep out moisture should be made; repainting is generally 

warranted. Cracks around windows and doors can be 

beneficial in prOViding ventilation to the interior and so 

should only be caulked if needed to keep out bugs and 

moisture. For very deteriorated wall surfaces on wooden 

frame structures, it may be necessary to sheathe in plywood 

panels, but care should be taken to minimize installation 

damage by planning the location of the nailing or screw 

patterns or by installing panels over a frame of battens (see 

fig. 9). Generally, however, it is better to repair deteriorated 

features than to cover them over. 

Foundation damage may occur if water does not drain 

away from the building. Run-off from gutters and downspouts should be directed far away from the foundation 

wall by using long flexible extender pipes equal in length to 

twice the depth of the basement or crawl space. If underground drains are susceptible to clogging, it is recommended that the downspouts be disconnected from the drain 

boot and attached to flexible piping. If gutters and downspouts are in bad condition, replace them with inexpensive 

aluminum units. 

Figure 9. Severely deteriorated wooden siding on a farm building has been 

covered over with painted plywood panels as a temporary measure to 

eliminate moisture penetration to the interior. Foundation vents and loose 

floor boards allow air to circulate inside. 

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If there are no significant landscape or exposed archeological elements around the foundation, consideration 

should be given to regrading the site if there is a documented drainage problem (see fig. 10). If building up the 

grade, use a fiber mesh membrane to separate the new soil 

from the old and slope the new soil 6 to 8 feet (200 cm-266 

cm) away from the foundation making sure not to cover up 

the dampcourse layer or come into contact with skirting 

boards. To keep vegetation under control, put down a layer 

of 6 mil black polyethylene sheeting or fiber mesh matting 

covered with a 2"-4" (5-10 cm.) of washed gravel. If the 

building suffers a serious rising damp problem, it may be 

advisable to eliminate the plastic sheeting to avoid trapping 

ground moisture against foundations. 

Figure 10. Regrading around the Booker Tenement at Colonial Williamsburg has protected the masonary foundation wall from excessive damp. 

This building has been successfully mothballed for over 10 years. Note the 

attic and basement vents, the temporary stairs, and the informative sign 

interpreting the history of this building. 

Mothballing 

The actual mothballing effort involves controlling the longterm deterioration of the building while it is unoccupied as 

well as finding methods to protect it from sudden loss by 

fire or vandalism. This requires securing the building from 

unwanted entry, prOViding adequate ventilation to the 

interior, and shutting down or modifying existing utilities. 

Once the building is de-activated or secured, the long-term 

success will depend on periodic maintenance and 

surveillance monitoring. 

Securing the building from vandals, break-ins, and 

natural disasters. Securing the building from sudden loss 

is a critical aspect of mothballing. Because historic 

buildings are irreplaceable, it is vital that vulnerable entry 

points are sealed. If the building is located where fire and 

security service is available then it is highly recommeded 

that some form of monitoring or alarm devices be used. 

To protect decorative features, such as mantels, lighting 

fixtures, copper downspouts, iron roof cresting, or stained 

glass windows from theft or vandalism, it may be advisable 

to temporarily remove them to a more secure location if 

they cannot be adequately protected within the structure. 

Mothballed buildings are usually boarded up, particularly 

on the first floor and basement, to protect fragile glass 

windows from breaking and to reinforce entry points (see 

fig. 11). Infill materials for closing door and window 

openings include plywood, corrugated panels, metal grates, 

chain fencing, metal grills, and cinder or cement blocks (see 

fig. 12). The method of installation should not result in the 

destruction of the opening and all associated sash, doors, 

and frames should be protected or stored for future reuse. 

Figure 11. Urban buildin.$.s often need additional protection from 

unwanted entry and graffiti. This commercial building uses painted 

plywood panels to cover expansive glass storefronts and chain link fencing 

is applied on top of the panels. The upper windows on the street sides have 

been covered and painted to resemble 19th century sash. Photo: Thomas 

Jester, NPS. 

Generally exterior doors are reinforced and provided with 

strong locks, but if weak historic doors would be damaged 

or disfigured by adding reinforcement or new locks, they 

may be removed temporarily and replaced with secure 

modem doors (see fig. 13). Alternatively, security gates in a 

new metal frame can be installed within existing door 

openings, much like a storm door, leaving the historic door 

in place. If plywood panels are installed over door 

openings, they should be screwed in place, as opposed to 

nailed, to avoid crowbar damage each time the panel is 

removed. This also reduces pounding vibrations from 

hammers and eliminates new nail holes each time the panel 

is replaced. 

For windows, the most common security feature is the 

closure of the openings; this may be achieved with wooden 

or pre-formed panels or, as needed, with metal sheets or 

concrete blocks. Plywood panels, properly installed to 

protect wooden frames and properly ventilated, are the 

preferred treatment from a preservation standpoint. 

There are a number of ways to set insert plywood panels 

into windows openings to avoid damage to frame and sash 

(see fig. 14). One common method is to bring the upper 

and lower sash of a double hung unit to the mid-point of 

the opening and then to install pre-cut plywood panels 

using long carriage bolts anchored into horizontal wooden 

bracing, or strong backs, on the inside face of the window. 

Another means is to build new wooden blocking frames set 

into deeply recessed openings, for example in an industrial 

mill or warehouse, and then to affix the plywood panel to 
the blocking frame. If sash must be removed prior to 

installing panels, they should be labeled and stored safely 

within the building. 

Plywood panels are usually 1/2"-3/4" (1.25-1.875 cm.) 

thick and made of exterior grade stock, such as COX, or 

Figure 12. First floor openings have been filled with cinderblocks and 

doors, window sash and frames have been removed for safe keeping. Note 

the security light over the windows and the use of a security metal door 

with heavy duty locks. Photo: H. Ward Jandl, NPS . 

.. 

Figure 13. Ifhistoric doors would be damaged by adding extra locks, they 

should be removed and stored and new security doors added. At this 

lighthouse, the historic door has been replaced with a new door (seen both 

inside and outside) with an inset vent and new deadbolt locks. The heavy 

historic hinges have not been damaged. Photo: Williamsport Preservation 

Training Center, NPS. 

marine grade plywood. They should be painted to protect 

them from delamination and to provide a neater 

appearance. These panels may be painted to resemble . 

operable windows or treated decoratively (see fig. 15). With 

extra attention to detail, the plywood panels can be 

Figure 14. A: Plan detail showing plywood security panel anchored with 

carriage bolts through to the inside horizontal bracing, or strong backs. 

B: Plan detail showing section of plywood window panel attached to a new pressure treated wood frame set within the masonry opening. Ventilation should be included whenever possible or necessary. 

Figure 15. Painting trompe l'oeil scenes on plywood panels is a neighborhood friendly device. In addition, the small sign at the bottom left comer gives information for contacting the organization responsible for 

the care of the mothballed building. Photo: Lee H. Nelson, F AlA. 

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trimmed out with muntin strips to give a shadow line 

simulating multi-lite windows. This level of detail is a good 

indication that the building is protected and valued by the 

owner and the community. 

If the building has shutters, simply close the shutters and 

secure them from the interior (see fig. 16). If the building 

had shutters historically, but they are missing, it may be 

appropriate to install new shutters, even in a modem 

material, and secure them in the closed position. Louvered 

shutters will help with interior ventilation if the sash are 

propped open behind the shutters. 

Figure 16. Historic louvered shutters make excellent security closures 

with passive ventilation. 

There is some benefit from keeping windows unboarded if 

security is not a problem. The building will appear to be 

occupied, and the natural air leakage around the windows 

will assist in ventilating the interior. The presence of 

natural light will also help when periodic inspections are 

made. Rigid polycarbonate clear storm glazing panels may 

be placed on the window exterior to protect against glass 

breakage. Because the sun's ultraviolet rays can cause 

fading of floor finishes and wall surfaces, filtering pull 

shades or inexpensive curtains may be options for reducing 

this type of deterioration for significant interiors. Some 

acrylic sheeting comes with built-in ultraviolet filters. 

Securing the building from catastrophic destruction from 

fire, lightning, or arson will require additional security 

devices. Lightning rods properly grounded should be a 

first consideration if the building is in an area susceptible to 

lightning storms. A high security fence should also be 

installed if the property cannot be monitored closely. These 

interventions do not require a power source for operation. 

Since many buildings will not maintain electrical power, 

there are some devices available using battery packs, such 

as intrusion alarms, security lighting, and smoke detectors 

which through audible hom alarms can alert nearby 

neighbors. These battery packs must be replaced every 3 

months to 2 years, depending on type and usage. In 

combination with a cellular phone, they can also provide 

some level of direct communication with police and fire 

departments. 

If at all possible, new temporary electric service should be 

provided to the building (see fig. 17). Generally a telephone 

Figure 17. Security systems are very important for mothballed buildings 

if they are located where fire and security services are available. A 

temporary electric service with battery back-up has been installed in this bul1ding. Intrusion alarms and ionization smoke/fire detectors are wired 

directly to the nearby security service. 

line is needed as well. A hard wired security system for 

intrusion and a combination rate-of-rise and smoke detector 

can send an immediate signal for help directly to the fire 

department and security service. Depending on whether or 

not heat will be maintained in the building, the security 

system should be designed accordingly. Some systems 

cannot work below 32°P (OOe). Exterior lighting set on a 

timer, photo electric sensor, or a motion/infra-red detection 

device provides additional security. 

Providing adequate ventilation to the interior. Once the 

exterior has been made weathertight and secure, it is 

essential to provide adequate air exchange throughout the 

building. Without adequate air exchange, humidity may 

rise to unsafe levels, and mold, rot, and insect infestation 

are likely to thrive (see fig. 18). The needs of each historic 

resource must be individually evaluated because there are 

so many variables that affect the performance of each 

interior space once the building has been secured. A 

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Figure 18. Heavy duty wooden slated louvers were custom fabricated to 

replace the deteriomted lower sash. The upper sash were rebuilt to retain 

the historic appearance and to allow light into this vacant historic 

building. Refer back to Fig. 1 for a view of the building. Photo: Charles E. 

Fisher, NPS. Drawing by Thomas Vitanza. 
mechanical engineer or a specialist in interior climates 

should be consulted, particularly for buildings with intact 

and significant interiors. In some circumstances, providing 

heat during the winter, even at a minimal 45° F (7°C), and 

utilizing forced-fan ventilation in summer will be 

recommended and will require retaining electrical service. 

For masonry buildings it is often helpful to keep the 

interior temperature above the spring dew point to avoid 

damaging condensation. In most buildings it is the need 

for summer ventilation that outweighs the winter 

requirements. 

Many old buildings are inherently leaky due to loose-fitting 

windows and floorboards and the lack of insulation. The 

level of air exchange needed for each building, however, 

will vary according to geographic location, the building's 

construction, and its general size and configuration. 

There are four critical climate zones when looking at the 

type and amount of interior ventilation needed for a closed 

up building: hot and dry (southwestern states); cold and 

damp (Pacific northwest and northeastern states); 

temperate and humid (Mid-Atlantic states, coastal areas); 

and hot and humid (southern states and the tropics). (See 

fig. 19 for a chart outlining guidance on ventilation.) 

Once closed up, a building interior will still be affected by 

the temperature and humidity of the exterior. Without 

proper ventilation, moisture from condensation may occur 

and cause damage by wetting plaster, peeling paint, 

staining woodwork, warping floors, and in some cases even 

causing freeze thaw damage to plaster. If moist conditions 

persist in a property, structural damage can result from rot 

or returning insects attracted to moist conditions. Poorly 

mothballed masonry buildings, particularly in damp and 

humid zones have been so damaged on the interior with 

just one year of unventilated closure that none of the 

interior finishes were salvageable when the buildings were 

rehabilitated. 

The absolute minimum air exchange for most mothballed 

buildings consists of one to four air exchanges every hour; 

one or two air exchanges per hour in winter and often twice 

that amount in summer. Even this minimal exchange may 

foster mold and mildew in damp climates, and so 

monitoring the property during the stabilization period and 

after the building has been secured will provide useful 

information on the effectiveness of the ventilation solution. 

There is no exact science for how much ventilation should 

be provided for each building. There are, however, some 

general rules of thumb. Buildings, such as adobe 

structures, located in hot and arid climates may need no 

additional ventilation if they have been well weatherized 

and no moisture is penetrating the interior. Also frame 

buildings with natural cracks and fissures for air infiltration 

may have a natural air exchange rate of 3 or 4 per hour, and 

so in arid as well as temperate climates may need no 

additional ventilation once secured. The most difficult 

VENTILATION GUIDANCE CHART 

CLIMATE AIR EXCHANGES VENTILA nON 

Temperature Winter air Summer air Frame Buildings Masonry Buildings Masonry Buildings 

and exchange exchange passive louvering passive louvering fan combination 

Humidity per hour per hour 

% of openings % of openings one fan + 

louvered louvered % louvered 

winter summer winter summer summer 

hot and dry less than 1 less than 1 N/A N/A N/A N/A N/A 

Southwestern 

areas 

cold and damp 1 2-3 5% 10% 10% 30% 20% 

Northeastern & 

Pacific northwestern 

areas 

temperate/humid 2 3-4 10% 20% 20% 40% 30% 

Mid-Atlantic & 

coastal areas 

hot and humid 3 4 20% 30% 40% 80% 40% 

Southern states & or more or more or more 

tropical areas 

Figure 19. This is a general guide for the amount of louvering which might be expected for a medium size residential structure with an average amount of 

windows, attic, and crawl space ventilation. There is currently research being done on effective air exchanges, but each project should be evaluated 

individually. It will be noticed from the chart that summer louvering requirements can be reduced with the use of an exhaust fan. Masonry buildings need 

more ventilation than frame buidings. Chart prepared by Sharon C. Park, AlA and Ernest A. Conrad, PE. 

9 
10 

buildings to adequately ventilate without resorting to 

extensive louvering and/ or mechanical exhaust fan systems 

are masonry buildings in humid climates. Even with 

basement and attic vent grills, a masonry building many 

not have more than one air exchange an hour. This is 

generally unacceptable for summer conditions. For these 

buildings, almost every window opening will need to be 

fitted out with some type of passive, louvered ventilation. 

Depending on the size, plan configuration, and ceiling 

heights of a building, it is often necessary to have louvered 

opening equivalent to 5%-10% of the square footage of each 

floor. For example, in a humid climate, a typicaI20'x30' 

(6.1m x 9.1m) brick residence with 600 sq. ft.(55.5 sq.m) of 

floor space and a typical number of windows, may need 30-

60 sq. ft.(2.75sq.m-5.5 sq. m) of louvered openings per floor. 

With each window measuring 3'x5'(.9m x 1.5 m) or 15 sq. ft. 

(1.3 sq.m), the equivalent of 2 to 4 windows per floor may 

need full window louvers. 

Small pre-formed louvers set into a plywood panel or small 

slit-type registers at the base of inset panels generally 

cannot provide enough ventilation in most moist climates to 

offset condensation, but this approach is certainly better 

than no louvers at all. Louvers should be located to give 

cross ventilation, interior doors should be fixed ajar at least 

4" (IOcm) to allow air to circulate, and hatches to the attic 

should be left open. 

Monitoring devices which can record internal temperature 

and humidity levels can be invaluable in determining if the 

internal climate is remaining stable. These units can be 

powered by portable battery packs or can be wired into 

electric service with data downloaded into laptop 

computers periodically (see fig. 20). This can also give longterm information throughout the mothballing years. If it is 

determined that there are inadequate air exchanges to keep 

interior moisture levels under control, additional passive 

ventilation can be increased, or, if there is electric service, 

mechanical exhaust fans can be installed. One fan in a 

small to medium sized building can reduce the amount of 

louvering substantially. 

Figure 20. Portable monitors used to record temperature and humidity 

conditions in historic buildings during mothballing can help identify 

ventilation needs. This data can be downloaded directly into a lap top 

computer on site. These monitors are especially helpful over the long term 

for buildings with significant historic interiors or which are remaining 

furnished. If interiors are remaining damp or humid, additional 

ventilation should be added or the source of moisture controlled. 

If electric fans are used, study the environmental conditions 

of each property and determine if the fans should be 

controlled by thermostats or automatic timers. 

Humidistats, designed for enclosed climate control systems, 

generally are difficult to adapt for open mothballing 

conditions. How the system will draw in or exhaust air is 

also important. It may be determined that it is best to bring 

dry air in from the attic or upper levels and force it out 

through lower basement windows (see fig. 21). If the 

basement is damp, it may be best to zone it from the rest of 

the building and exhaust its air separately. Additionally, 

less humid day air is preferred over damper night air, and 

this can be controlled with a timer switch mounted to the 

fan. 

The type of ventilation should not undermine the security 

of the building. The most secure installations use custommade grills well anchored to the window frame, often set in 

plywood security panels. Some vents are formed using 

heavy millwork louvers set into existing window openings 

(refer back to fig.18). For buildings where security is not a 

primary issue, where the interior is modest, and where 

there has been no heat for a long time, it may be possible to 

use lightweight galvanized metal grills in the window 

openings (refer back to fig.7). A cost effective grill can be 

made from the expanded metal mesh lath used by 

plasterers and installed so that the mesh fins shed rainwater 

to the exterior. 

Securing mechanical systems and utilities. At the outset, 

it is important to determine which utilities and services, 

such as electrical or telephone lines, are kept and which are 

cut off. As long as these services will not constitute a fire 

Figure 21. This electric thermostat/humidistat mounted in the attic vent controls a modified ducted air/fan system. The unit uses temporary 

exposed sheet metal ducts to pull air through the building and exhaust it 

out of the basement. For over ten years this fan system in combination 

with 18" x 18" preformed louvers in selective windows has kept the 

interior dry and With good air exchanges. 
hazard, it is advisable to retain those which will help 

protect the property. Since the electrical needs will be 

limited in a vacant building, it is best to install a new 

temporary electric line and panel (100 amp) so that all the 

wiring is new and exposed. This will be much safer for the 

building, and allows easy access for reading the meter (see 

fig. 22). 

Most heating systems are shut down in long term 

mothballing. For furnaces fueled by oil, there are two 

choices for dealing with the tank. Either it must be filled to 

the top with oil to eliminate condensation or it should be 

drained. If it remains empty for more than a year, it will 

likely rust and not be reusable. Most tanks are drained if a 

newer type of system is envisioned when the building is 

put back into service. Gas systems with open flames should 

be turned off unless there is regular maintenance and 

frequent surveillance of the property. Gas line,s are shut off 

by the utility company_ 

If a hot water radiator system is retained for low levels of 

heat, it generally must be modified to be a self-contained 

system and the water supply is capped at the meter. This 

Figure 22. All systems except temporary electric have been shut off at this 

residence which has been mothballed over 20 years. An electric meter and 

100 amp panel box have been set on a plywood panel at the front of the 

building. It is used for interior lightinS and various alarm systems. The 

building, however, is showing signs ot moisture problems with effIourescent stains on the masonry indicating the need for gutter maintenance 

and additional ventz1ation for the interior. The vegetation on the walls, 

although picturesque, traps moisture and is damaging to the masonry. Photo: H. Ward Jandl, NPS. 

recirculating system protects the property from extensive 

damage from burst pipes. Water is replaced with a 

water / glycol mix and the reserve tank must also be filled 

with this mixture. This keeps the modified system from 

freezing, if there is a power failure. If water service is cut 

off, pipes should be drained. Sewerage systems will require 

special care as sewer gas is explosive. Either the traps must 

be filled with glycol or the sewer line should be capped off 

at the building line. 

Developing a maintenance and monitoring plan. While 

every effort may have been made to stabilize the property 

and to slow the deterioration of materials, natural disasters, 

storms, undetected leaks, and unwanted intrusion can still 

occur. A regular schedule for surveillance, maintenance, 

and monitoring should be established: (See fig. 23 for 

maintenance chart). 

MAINTENANCE CHART 

~iodic 

U regular drive by surveillance 

o check attic during stonns if possible 

monthly walk arounds 

o check entrances 

o check window panes for breakage 

o mowing as required 

o check for graffiti or vandalism 

enter every 3 months to air out 

o check for musty air 

o check for moisture damage 

o check battery packs and monitoring 

equipment 

o check light bulbs 

o check for evidence of pest intrusion 

every 6 months; spring and fall 

o site clean-up; pruning and trimming 

o gutter and downspout check 

o check crawlspace for pests 

o clean out storm drains 

every 12 months 

o maintenance contract inspections 

for equipment/utilities 

o check roof for loose or missing shingles 

o termite and pest inspection/treatment 

o exterior materials spot repair and touch up 

painting 

o remove bird droppings or other stains from 

exterior 

o check and update building file 

Figure 23. Maintenance Chart. Many of the tasks on the maintenance 

chart can be done by volunteer help or service contracts. Regular visits to 

the site wm help detect intrusion, storm damage, or poor water drainage. 

11 
hazard, it is advisable to retain those which will help 

protect the property. Since the electrical needs will be 

limited in a vacant building, it is best to install a new 

temporary electric line and panel (100 amp) so that all the 

wiring is new and exposed. This will be much safer for the 

building, and allows easy access for reading the meter (see 

fig. 22). 

Most heating systems are shut down in long term 

mothballing. For furnaces fueled by oil, there are two 

choices for dealing with the tank. Either it must be filled to 

the top with oil to eliminate condensation or it should be 

drained. If it remains empty for more than a year, it will 

likely rust and not be reusable. Most tanks are drained if a 

newer type of system is envisioned when the building is 

put back into service. Gas systems with open flames should 

be turned off unless there is regular maintenance and 

frequent surveillance of the property. Gas line,s are shut off 

by the utility company_ 

If a hot water radiator system is retained for low levels of 

heat, it generally must be modified to be a self-contained 

system and the water supply is capped at the meter. This 

Figure 22. All systems except temporary electric have been shut off at this 

residence which has been mothballed over 20 years. An electric meter and 

100 amp panel box have been set on a plywood panel at the front of the 

building. It is used for interior lightinS and various alarm systems. The 

building, however, is showing signs ot moisture problems with effIourescent stains on the masonry indicating the need for gutter maintenance 

and additional ventz1ation for the interior. The vegetation on the walls, 

although picturesque, traps moisture and is damaging to the masonry. Photo: H. Ward Jandl, NPS. 

recirculating system protects the property from extensive 

damage from burst pipes. Water is replaced with a 

water / glycol mix and the reserve tank must also be filled 

with this mixture. This keeps the modified system from 

freezing, if there is a power failure. If water service is cut 

off, pipes should be drained. Sewerage systems will require 

special care as sewer gas is explosive. Either the traps must 

be filled with glycol or the sewer line should be capped off 

at the building line. 

Developing a maintenance and monitoring plan. While 

every effort may have been made to stabilize the property 

and to slow the deterioration of materials, natural disasters, 

storms, undetected leaks, and unwanted intrusion can still 

occur. A regular schedule for surveillance, maintenance, 

and monitoring should be established: (See fig. 23 for 

maintenance chart). 

MAINTENANCE CHART 

~iodic 

U regular drive by surveillance 

o check attic during stonns if possible 

monthly walk arounds 

o check entrances 

o check window panes for breakage 

o mowing as required 

o check for graffiti or vandalism 

enter every 3 months to air out 

o check for musty air 

o check for moisture damage 

o check battery packs and monitoring 

equipment 

o check light bulbs 

o check for evidence of pest intrusion 

every 6 months; spring and fall 

o site clean-up; pruning and trimming 

o gutter and downspout check 

o check crawlspace for pests 

o clean out storm drains 

every 12 months 

o maintenance contract inspections 

for equipment/utilities 

o check roof for loose or missing shingles 

o termite and pest inspection/treatment 

o exterior materials spot repair and touch up 

painting 

o remove bird droppings or other stains from 

exterior 

o check and update building file 

Figure 23. Maintenance Chart. Many of the tasks on the maintenance 

chart can be done by volunteer help or service contracts. Regular visits to 

the site wm help detect intrusion, storm damage, or poor water drainage. 

11 
MOTHBALLING CHECKLIST 

Mothballing Checklist 

In reviewing mothballing plans, the following checklist may help to 

ensure that work items are not inadvertently omitted. 

Moisture 

• Is the roof watertight? 

• Do the gutters retain their proper pitch and are they clean? 

• Are downspout joints intact? 

• Are drains unobstructed? 

• Are windows and doors and their frames in good condition? 

• Are masonry walls in good condition to seal out moisture? 

• Is wood siding in good condition? 

• Is site properly graded for water run-off? 

• Is vegetation cleared from around the building foundation to avoid 

trapping moisture? 

Pests 

• Have nests/pests been removed from the building's interior and 

eaves? 

• Are adequate screens in place to guard against pests? 

• Has the building been inspected and treated for termites, carpenter 

ants, and rodents? 

• If toxic droppings from bats and pigeons are present, has a special 

company been brought in for its disposal? 

Housekeeping 

• Have the following been removed from the interior: trash, hazardous 

materials such as inflammable liquids, poisons, and paints and 

canned goods that could freeze and burst? 

• Is the interior broom-clean? 

• Have furnishings been removed to a safe location? 

• If furnishings are remaining in the building, are they properly 

protected from dust, pests, ultraviolet light, and other potentially 

harmful problems? 

• Have significant architectural elements that have become detached 

from the building been labeled and stored in a safe place? 

• Is there a building file? 

Security 

• Have fire and police departments been notified that the building will 

be mothballed? 

• Are smoke and fire detectors in working order? 

• Are the exterior doors and windows securely fastened? 

• Are plans in place to monitor the building on a regular basis? 

• Are the keys to the building in a secure but accessible location? 

• Are the grounds being kept from becoming overgrown? 

Utilities 

• Have utility companies disconnected/shut off or fully inspected 

water, gas, and electric lines? 

• If the building will not remain heated, have water pipes been drained 

and glycol added? 

• If the electricity is to be left on, is the wiring in safe condition? 

Ventilation 

• Have steps been taken to ensure proper ventilation of the building? 

• Have interior doors been left open for ventilation purposes? 

• Has the secured building been checked within the last 3 months for 

interior dampness or excessive humidity? 

Yes No Date of action or comment. 

Figure 26 .. MOTHBALL CHECKLIST. This checklist will give the building owner or manager a handy reference guide to items that should be addressed when 

mothballing a historic building. Prepared by H. Ward Jandl, NPS. 
MOTHBALLING CHECKLIST 

Mothballing Checklist 

In reviewing mothballing plans, the following checklist may help to 

ensure that work items are not inadvertently omitted. 

Moisture 

• Is the roof watertight? 

• Do the gutters retain their proper pitch and are they clean? 

• Are downspout joints intact? 

• Are drains unobstructed? 

• Are windows and doors and their frames in good condition? 

• Are masonry walls in good condition to seal out moisture? 

• Is wood siding in good condition? 

• Is site properly graded for water run-off? 

• Is vegetation cleared from around the building foundation to avoid 

trapping moisture? 

Pests 

• Have nests/pests been removed from the building's interior and 

eaves? 

• Are adequate screens in place to guard against pests? 

• Has the building been inspected and treated for termites, carpenter 

ants, and rodents? 

• If toxic droppings from bats and pigeons are present, has a special 

company been brought in for its disposal? 

Housekeeping 

• Have the following been removed from the interior: trash, hazardous 

materials such as inflammable liquids, poisons, and paints and 

canned goods that could freeze and burst? 

• Is the interior broom-clean? 

• Have furnishings been removed to a safe location? 

• If furnishings are remaining in the building, are they properly 

protected from dust, pests, ultraviolet light, and other potentially 

harmful problems? 

• Have significant architectural elements that have become detached 

from the building been labeled and stored in a safe place? 

• Is there a building file? 

Security 

• Have fire and police departments been notified that the building will 

be mothballed? 

• Are smoke and fire detectors in working order? 

• Are the exterior doors and windows securely fastened? 

• Are plans in place to monitor the building on a regular basis? 

• Are the keys to the building in a secure but accessible location? 

• Are the grounds being kept from becoming overgrown? 

Utilities 

• Have utility companies disconnected/shut off or fully inspected 

water, gas, and electric lines? 

• If the building will not remain heated, have water pipes been drained 

and glycol added? 

• If the electricity is to be left on, is the wiring in safe condition? 

Ventilation 

• Have steps been taken to ensure proper ventilation of the building? 

• Have interior doors been left open for ventilation purposes? 

• Has the secured building been checked within the last 3 months for 

interior dampness or excessive humidity? 

Yes No Date of action or comment. 

Figure 26 .. MOTHBALL CHECKLIST. This checklist will give the building owner or manager a handy reference guide to items that should be addressed whe

mothballing a historic building. Prepared by H. Ward Jandl, NPS.