Retrofit 'Green' : Insulation

"When insulating, it is critically important to consider the uniqueness of your building, the characteristics of its materials, the climate in which it resides, and the specific building methods that were used in its construction. Always keep in mind that improperly adding insulation to a building has the potential to wreak havoc on its overall performance. You can (perhaps unknowingly) do irreparable damage to priceless historic features by adding insulation where it is not needed, inappropriate, or ineffective. Many older and historic homes were not designed with insulation, so it requires great care to select compatible insulating systems and materials. Older buildings, or those built before modern HVAC systems existed, were actually built to deal with the movement of air naturally through special design features. If your building was constructed before 1950, you need to give careful consideration before upgrading insulation. All systems – new and old – need to work in harmony. " - The National Trust for Historic Preservation

As mentioned earlier, the building envelope is designed to protect occupants from the elements. The envelope consists of the structural elements, sheathing, siding, fenestration, plaster, and trim. All of these components transfer heat, and their resistance to heat tranfer is measured by R-Value. Materials with high R values resist the amount of heat loss and gain.

Infrared Thermal Imaging

Infrared cameras can actually document heat loss and gain in the building envelope. Because the goal of installing insulation is to reduce the heat transfer, including infrared thermal imaging in an energy assessment can be especially helpful when considering where to add this insulation. You may be surprised by what you find! The infrared thermal assessment should be conducted when the indoor and outdoor temperature differences are most drastic.

"The walls of a house are typically where occupants feel air flow, so the natural reaction is to fill it. Windows suffer the same finger pointing. The industry created the least-effective solutions of fill and replace, with the reasoning that the most cost-effective solution is the best." - Robert Cagnetta, Heritage Restoration, Inc.
Before installing insulation, remember: The most effective and responsible building efficiency solution is to seal air leaks.

Selecting the right insulating materials!

Or none at all... Solid brick or stone wall structures common in historic structures are very difficult to add insulation. "Before HVAC systems existed and natural ventilation was required, these solid masonry walls were constructed because of their thickness and high thermal mass. They are conductors of heat, and you might have noticed that they sometimes feel cold to the touch. Masonry walls are traditionally not good insulators (confusing, we know). What this means is that the stone and brick have a tremendous natural ability to store and slowly release energy or heat. If you add insulation to this system, the exterior wall will be colder than it was previously, slowing the process of evaporation of wetness on the surface, and thus causing it to stay damp. This dampness will mean the breakdown of materials and possibly frost, which can lead to corrosion of internal members and spalling of stone and mortars. This can be utterly catastrophic to a wall and the multitude of components in and around it.

Although the above image is new construction, the walls are packed with dense cellulose, a great choice for insulating historic buildings, as it is reversible, unlike spray foam! The ceiling reveals the first floor joists packed with recycled denim from the Dungaree Plant! Recycling and removable, a great choice!


Insulation in Historic Homes!

How do I decide if I need to insulate?


Like masonry walls, timber framed walls are also difficult to insulate without altering their appearance or creating a potentially damaging situation. Depending on the original construction method and the extent to which the walls have deteriorated and/or need maintenance/replacement, infill insulation could be installed within a timber frame wall. But again, this is for walls that have irreparable damage or prior renovations or alterations." - The National Trust for Historic Preservation

Not recommended: Irreversible Insulation

Spray foam insulating is not recommended in historic buildings, as it is not reversible and can lead to drastic changes in air flow that can damage historic building fabric.

Recommended: Reversible Insulation

Sustainable or natural materials, such as cellulose, wood, plant fiber, or wool are "breathable" amd recommended for historic bulidings, specifically in attics.

"Weatherization can enhance comfort and keep a building healthy. Once the air seal is complete, the attic is the next place to start, then basements, and then walls. Too many buildings have their walls completed first, where airflow and moisture infiltration continues to cause significant reductions in efficiency and potential serious rot and mold damage." - Robert Cagnetta, Heritage Restoration, Inc.

Not recommended: Wall Insulation

Wall insulation tends to be difficult in historic buildings, especially when significant historic materials exist on the exterior or interior walls, or both! Given Charleston's climate, the energy and cost savings of adding wall insulation do not outweigh the difficulties of installation and potential for damage. In fact, once insulation is in place, the potential for future damage only increases. Historic walls are known for their 'breathability.' When insulation is added, the wall is permanantly altered, and the insulation itself is particularly suspectible to condensation, caused by the differences in temperature outdoors and indoors. The thermal mass value of materials determines condensation. Where stone can maintain a relatively constant temperature, despite weather fluctuations, wood has a lower thermal mass and is prone to changes in temperature. Before assuming all of your side walls require insulation, take note that ceilings and floors tend to cause much more air loss than walls!

Recommended: Attic, basement, & crawl space Insulation

Attics and basements (and of course, crawl spaces) are not traditionally living spaces, thus they tend to have less historic materials and serve as the the easiest (and most effective) places to insulate in historic homes!

Attics can often be a major source of energy inefficiency, as rising heat escapes through the attic and roof. Adding insulation is an effective device for lessening this air loss and minimizing cooling and heating loads. Insulation in the attic helps maintain warm air to reduce heating loads in colder months. Properly installed insulation can also help reduce the cooling loads in warmer months.

The most common mistake in the installation of attic insulation is incorrect placement. Before installing the insulation, it is important to investigate the notoriously leaky points in old houses! Insulation can not help any house, if cracks and drafts are allowing air to escape. Pay attention to the weathertightness of eaves, the point at which the rafters meet the walls. Also check the sill plate, the point where the frame meets the foundation. Depending on the size of the gap, the joint may have to be sealed with wood and caulked, or use caulk and expanding foam where possible. Also before installing insulation, beware of structural members, wiring and pipes!

Installing insulation along roof rafters!

The addition of insulation along the roof rafters can resolve the loss of rising warm air escaping from the roof. However, it is important to note that insulation in an unheated attic requires ventilation to prevent the insulation from attaining moisture from condensation. As soon as insulation gets wet, it reduces its ability to hold heat. Thus, when installing insulation directly against the udnerside of roof rafter, it is important not to shut off necessary ventilation to the roofing materials. Natural materials, such as wood, plant fiber, or wool, are especially recommended for attic insulation because they are so breathable.

Insulating an attic requires a balance - ventilation must be maintained! Do not cover existing windows or vents. Historic buildings specifically include design features to accomodate rising hot air. Cupolas, vents and other windows in the attic are meant to be opened during warmer months to allow that hot air to escape!

Installing insulation along attic floor!

Insulating the attic floor, or along the ceiling of the room directly below is another effective option in historic homes. However, keep in mind that addition of this type of insulation will make your attic cold. Thus, any pipes present in the attic will need to be individually insulated.

In unheated attics, it is best practice to install insulation between the floor joists with the vapor barrier down.

Basements & crawl spaces insulation!

Crawlspaces and unheated basements are common in Charleston. And lots of heat tends to be lost in these spaces. The first floor of the house should be inspected for gaps, to prevent potential air leaks and loss.

The floor should be inspected for gaps. These gaps can be filled from the underside with felt strips. After these gaps are sealed, insulation should be installed against the underside of the flooring or underlayment between the joists with the vapor barrier up. and insulation can be added on the basement ceiling or between the first floor joists.