Adding insulation can be good for your home, but you might be surprised to find that it does not always make as big of an impact as other types of efficiency-minded home improvement projects.

Regardless, 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 following frequently asked questions are intended to not only inform and inspire, but to demonstrate how you can properly insulate your older and historic home.

How do heat and air move through a building? Is the goal of insulating to completely seal things off?

Don't worry if it feels like you need a PhD in molecular biology to understand how heat and moisture affect your building; you're not alone.

Understanding how these things affect the performance of our building's insulation is complicated stuff. Your home, for example, is made up of many different components and systems, and it's essential to consider how a change to just one will impact all the others. Always keep this in mind:

  • Heat does not only escape through the roof and windows. To the contrary, warm air travels in all directions wherever there is a decrease in temperature, including through walls and the ground.
  • Warm air carries water vapor, so airflow carrying this moisture needs an escape or it can cause severe damage to your building's materials, especially its wood. Moisture is a homeowner's number one enemy. If you don't carefully choose your insulating materials and their compatibility with the rest of the structure, you may be creating places for that moisture to collect.

In short, buildings need to breathe. Homeowners must strike a careful balance between fully sealing their building and keeping it breathable. This probably seems confusing (here's that PhD thing again), which is why we highly recommend working with an expert who understands the characteristics of building materials and how they may rely on air movement to disperse moisture so that it does not become trapped. An absence of ventilation and/or improper insulation could result in dampness and mold.

I get that there's a balance between sealing your home and letting it breathe. So, how do I decide when I actually need to insulate?

For most older and historic homes and buildings, weatherization – and therefore insulation – is little more than a matter of responsible maintenance.

We recommend starting the process with these three steps:

  • Have an energy audit conducted by a qualified professional with experience in historic construction. The audit should include thermal imaging and a blower door test, and it should be done in the late fall, winter, or early spring when there is a significant temperature difference between the interior and exterior of your home.
  • Seal up your existing holes. This includes checking the dampers on fireplaces, weather stripping existing doors and windows, adding a baffle to all fans (including the ones in the bathroom), installing foam inserts at electrical receptacles, and plugging holes where cable TV and other utilities enter your home. There is also an operational component to this, such as making sure that storm sashes are lowered to their winter positions, and using shades and curtains to reduce solar gain in the summer.
  • Improve your existing systems. This includes having the furnace or boiler cleaned and serviced, as well as changing the air filters on the furnace or draining the rusty sludge from boilers. Make sure that distribution lines (ductwork or steam pipes) are wrapped with insulation so that the heat actually reaches the living areas. Also, make sure that registers and radiators are not blocked by curtains or furniture.

When all of these are done, then it makes sense to look at the payback period for new storm windows, improved insulation, new mechanical systems, and/or other projects.

Tell me more about the blower door test. What should I expect in arranging one for my own home as a part of a full energy audit?

Before making any changes to your home, you should first have an energy audit done to assess how it is performing and where the problems are.

An energy audit can be done by a number of professionals nationwide. The blower door test is done by mounting a high-powered fan to an exterior door frame, which then pulls the air out of your house. An air pressure gauge measures the difference in air pressure inside the house versus outside the house, determining the overall air tightness of the building. By understanding how air-tight your building may or may not be, you can then decide whether or not to proceed with adding or changing your insulation and to what degree.

I've done a home energy audit and the verdict is that I need to insulate. What are the right and wrong ways to tackle this project?

It's not just your windows! Air travels and escapes your home in all different directions, so let's take a look at three of the biggest problem areas.

Attic Insulation

Let's start by looking up and thinking about energy loss and how it might be escaping through your attic, which is where warm air (the air we want to keep inside during colder seasons) escapes. This is also the place that is, arguably, the easiest to insulate.

For starters, air might be coming and going through cracks from weather damage or small spaces and crevices around your cables, pipes, or light fixtures. Since attics are traditionally not living spaces, there are probably less historic materials to disrupt. This gives you the option of installing insulation on the floor or between the roof rafters. It is tricky, but as mentioned before, you must allow for ventilation while simultaneously trying to insulate against air leaks. Do not block or cover up existing vents. Additionally, if you insulate the attic floor, remember that the attic itself will then be cold. Therefore, if there are materials in the attic that might be susceptible to freezing or thawing (pipes are a big one), make sure they are also insulated.

When selecting the right insulating materials for an older or historic building, make sure that it has good thermal properties while allowing for the evaporation of moisture. It's possible to install insulation yourself, but you might want to hire a professional, especially when handling cellulose- or fiberglass-based products. Spray foam insulating is not recommended in historic buildings, as it can hinder air flow and lead to the rotting of timber frame members. We find that some expanding spray and other isocyanates work well to fill certain voids, but we do not favor their use as wall cavity insulation since the installation is not easily reversible and some people still have questions about the long-term health effects. We also support using more sustainable or natural materials, such as wood, plant fiber, or wool. Natural materials are especially recommended for attic insulation because they are so breathable.

Wall Insulation

Adding insulation in the walls of older and historic buildings is challenging for a number of reasons. This is because adding insulation here requires the disruption or removal of a great deal of material, and can therefore lead to the destruction of the historic details that make your older building so special. Additionally, older walls are very difficult to insulate because of the potential for moisture intrusion and problems with dampness or mold growth. We do not generally recommend wall insulation unless the project is a major rehabilitation, such as exterior cladding or if interior wall surfaces are being removed. For most buildings, it is difficult to ensure good coverage without major damage to the exterior cladding.

Solid masonry wall structures such as stone and brick (typical of older and historic buildings) are very difficult to add insulation within. 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.

Internal wall insulating measures are extremely complicated with historically-significant interiors. Interior spaces that have not-significant material or that have been altered over the course of the building's life clearly have more options with regards to adding insulation to internal walls. Owners of all other older or historic buildings, in particular those with historic interior detailing such as cornices and other structural and decorative details, should refrain from adding insulation to the interior side of their walls. The risk of losing valuable materials is too high, the potential energy savings are too low, and the potential damage to the wall through moisture intrusion is too great.

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.

Basements and Crawl Spaces Insulation

Like attics, basements and crawl spaces are traditionally not living spaces and are normally void of historically significant material. They therefore offer great opportunities for adding insulation to improve the performance in the rooms above, which helps since it is a space where a tremendous amount of heat is generally lost. They are also, however, the places where structural members live, as well as the infrastructure that makes your home run, such as wiring and pipes. In short, they are unheated/unconditioned service spaces. Basements and crawl spaces are also extremely wet and moist places, so great care must be taken to not speed up the rate of deterioration of the materials in these spaces.

Insulation can be added to basement walls in newer construction or in older homes with more sophisticated basement structures. Older and historic buildings, however, commonly have unfinished spaces beneath the ground floor with rugged walls and dirt, brick, or fieldstone foundations, making it difficult to insulate these walls. The recommended method of insulating in the basement or crawl space is to install the insulation on the basement ceiling or between the first floor joists. Note that the insulation's vapor barrier must be facing up, and that special anchors for moist areas should be used.