Insulating a Basement Wall

Home Performance Considerations for Expanding Living Spaces in Northern Virginia Homes. Important Steps for creating a finished basement.

Home Performance is a philosophy and science based on the premise that homes should be constructed to be safe, healthy, comfortable, durable and efficient.  This article will address some issues to consider when expanding your living space in homes in Northern Virginia.

Creating extra living space in Northern Virginia is expensive.  Two strategies that are often used to create additional space at somewhat lower costs include finishing a basement or in some cases finishing an attic space.  These options take advantage of the existing structure by converting what is often underutilized space (read storage space) into conditioned spaces that meet a higher level use including recreational space, entertainment space, additional bedrooms or office space.  The cost advantage of these solutions derives from the starting point of having existing walls, floors and ceilings at the commencement of the project.  The new space does not require extensive excavation, framing, roofing or other expensive and disruptive construction steps required of an expanded foot print for your home.

When creating a living space in a basement, care must be taken to address Water Intrusion, Vapor Intrusion, Insulation and Air Sealing details in addition to good aesthetic design, or you may end up with a good looking nightmare rather than a comfortable living space. 

Gus Handegard, a Canadian Building Scientist famously quoted that, “The three biggest problems for a house are: Water, Water and Water.”  Uncontrolled water in the house in the form of bulk intrusion (leaks), vapor intrusion and condensation is the basis for most problems with the health of a house, the durability of a house and in some cases the safety of the house.  Imagine a freshly completed basement that has a flood after a large rain storm, or a persistent “Musty Smell” encountered while you watch the big game on your newly completed home theater.  These results of improper planning would lead to long term discomfort in the finished basement.

In a recent article entitled, “Build a Risk-Free Finished Basement” in Fine Home Building, Steve Baczek outlines his approach to rating the conditions that are appropriate for your basement space.  His categories are:

1.      Low Risk: Those basements located in high, well drained areas that have no evidence of water infiltration from the walls or the slab.  He cautions that even these basements require careful detailing as weather and site conditions are changing all the time, and what is dry today, could flood tomorrow.  One example we see in the field of these changes are the impacts of clogged gutters that overflow and can create low spots in the grade near the foundation.  This simple maintenance item can cause formerly dry basements to flood over time.  Down spouts not routed to exhaust 10 feet from the foundation are another example of this.

2.       Moderate Risk: Those basements that experience seasonal challenges.  The clay soils in northern Virginia can move and shrink when dry, providing pathways for water to find a way into your foundation.  Summer pop-up storms in our area can also provide challenges during the rainy season.  Evidence of these issues can often be found by finding staining or “Efflorescence” or mineral streaks on the basement walls or slab.  Moderate Risk properties are at risk 6 months of the year or less.

3.       High Risk: Basements that face a daily challenge of moisture infiltration.  These basements can still be finished, but require a water management system that has several layers of back-up systems.

When planning your basement conversion, make sure that you start with a review of your site conditions and your houses existing water management systems.  A few dollars allocated to the installation of systems outside the house will ensure that the interior work provides you and subsequent owners of the house with a comfortable, safe and durable space.  The importance of this step increases as you move from Low Risk to High Risk, but it is an important step in all basement remodeling projects.  Comfenergy’s Home Performance Evaluators can help you with this review.

Site considerations include:

1.       Making sure that the grade of your lawn is pitched away from your home at least ¼” per foot (5” every 20 feet).  Home builders in Northern Virginia often do not pay enough attention to this detail, and even if they do, the grade gets morphed into something different as landscapers and others come in subsequent to final inspection to install specialty house upgrades.

2.       If required, consider installing a “Curtin Drain” or “French Drain”, a perforated pipe buried in gravel to catch run-off from hills pitched toward your home.

3.       Gutters and Down Spouts should be functional, and lead to some sort of channeling to get the water away from your house.  Often, this means buried 4” PVC drain tiles with pop-ups to exhaust the water onto your yard.

4.       Consider using Ground Gutters if your house is buried in the trees like many of the more mature neighborhoods in Northern Virginia, and it is impossible for you to keep your gutters clear of debris.

5.       Basement Window Sills should be at least 4” above grade to prevent water from getting into the window well.  The base of the window well should have substantial (1 foot or more) of crushed gravel so that they drain well. 

Next, evaluate the construction of your foundation walls.  While many homes in Northern Virginia are Poured Concrete Walls (the most resistant to water infiltration), some homes still have foundations made of concrete block, brick or stone.  All mortared together and providing numerous opportunities for water to get in.  Each of these construction types have various levels of quality that were built or cast into the final product.  They are all also influenced by the quality of work done on the day that your home was put together.  Irrespective of the construction type and quality, if water is present on the outside of the foundation, it will want to get into the home in bulk, or in Vapor form.  All masonry is essentially like a hard sponge, and moisture wants to travel through it in bulk (leak), or in vapor (capillarity).

Moisture control is the most important step in preparation for finishing your basement space.  The first step in moisture control is making sure that you have measured your risks and addressed any present or potential bulk water infiltration issues.  For Low and Moderate Risk basements, you may be able to get away with creating a drainage plane or vapor barrier on the walls by installing a continuous layer of material that has a low water permeability.  This can include: use of a continuous layer of foam board on the walls sealed with tape, or a continuous coat of closed cell spray foam.  These products will stop capillarity from pulling moisture through the walls.

Where bulk water infiltration is a concern, you will want to establish a drainage curtain that will direct bulk water to a sub-slab perimeter drain, and then onto a sump pump for evacuation.  These drainage curtains take many forms, but all are impervious to water and act like the shingles on your roof to drain material down to the perimeter drain.  At Comfenergy, we install “Smart Pipe” perimeter drains, or in some cases work with dedicated subcontractors to provide a complete system.  Sump pumps often come with redundancies.  Comfenergy sells a “Triple Safe” sump pump that has a primary pump, secondary pump and a battery back-up pump for the ultimate in redundant systems. 

Once this drainage curtain has been established you will want to insulate with the same materials just mentioned, either foam board taped and sealed together or closed cell foam.  This will again provide an inorganic, mold resistant product that will keep your basement dry as well as providing good thermal protection to resist condensation.  We use SilverGlo foam panels or 2 pound density closed cell spray foam at Comfenergy.  If studs are not already in place and the basement allows for it we install Basement to Beautiful Panels that integrate steel studs into SilverGlo panels in order to not only insulate but also created a framed wall to facilitate installation of sheet goods like drywall or inorganic basement panels.

As a final step in controlling moisture in the basement, it is important to air seal the rim joist when installing your insulation system on the walls.  Studies have shown that up to 30% of all uncontrolled air flow into your home leaks in through the rim joist, the area sitting on top of your foundation wall that ties together all of your floor joists for the floor above.  This air carries in contaminants like pollen, dust and moisture from the outside of your home.  You want to stop this uncontrolled air flow so that these unwanted visitors do not migrate into your new space.  Sealing your Rim Joist will not only make your basement room more comfortable, durable and healthy, it will do the same for the rooms above.  Closed Cell Spray Foam is the material of choice to achieve this goal, but other approaches are available to those who do not want to introduce Spray Foam into their home.

Creating comfort through proper insulation and air sealing:  Having addressed the most important construction details in you basement, preventing moisture intrusion, you are now tasked with creating an environment that will feel comfortable.  If you have followed the steps indicated previously in this article you are already there.  Sealing the Rim Joist with spray foam, spraying closed cell foam on the walls or the use of foam board all serve to provide thermal protection as well.  Your goal is to achieve a wall system that is insulated to about ½ of what the walls on above grade floors are.

Why half the level of insulation?  Code requirements spell this out, but the rational is that the soil temperature on the other side of your basement wall remains pretty constant at the mean temperature for your area.  In Northern Virginia, this means that just a few feet below grade the solid temperature remains at 55 degrees F year round.  So, while your walls one floor up are laboring to keep you warm on a 20 degree winter day (a 50 degree gradient from outside to inside temperatures), or a 95 degree summer day (a 25 degree gradient from outside to inside temperatures), the walls in your basement are consistently having to deal with less of a gradient (around 15 degrees).

You will never see the White or Reflective “Insulation Blanket”, product most new home builders install on basement walls recommended as the means of insulating your walls.  These materials allow for air flow between the blanket and the foundation wall, do nothing to prevent water infiltration, often harbor rodents (that’s right Mice love that stuff), and generally does not suite your purposes for creating a warn environment.  Why is it installed? Because it is cheap.

Fitting out your basement space:  Drywall is the most prevalent sheet good we see on walls, but recent advances have developed inorganic basement panels for use in those basements that may be prone to flooding.  These panels when used in conjunction with the insulating materials mentioned previously and steel studs, create a construction detail with no components that support mold growth.  For High Risk basements, this is a must consider option.  They are attractive, never require paint and easy to install as a wainscoting or full height panel.  Your consultant from Comfenergy can help you work through the details of what these panels look like and how they work.

Mechanical considerations in fitting out a basement include making sure that your HVAC system can handle the load from the additional space you have now created.  Comfenergy can help you get in touch with a qualified HVAC contractor, or just call the company that currently services you HVAC system.  Add a cold air return to recycle the air in your basement in order to make sure that the relative humidity in your new space does not spike due to “settling”.  Your home is constantly exchanging air with the outside.  During the “muggy” summer days in Northern Virginia that means that you are bringing in air that has high temperature and high humidity levels as you open doors and through the natural leakage process.  As this outside air cools (by you running the A/C system), some of it settles into the basement where the temperatures are going to be the coolest in your house.  For each degree that this humid air drops in temperature, the relative humidity goes up 2 points.  It is not that hard to create a scenario where you can reach the dew point in your new basement space.  To combat this, add the cold air return so that the basement air is being recycled in the air handler of your HVAC system and consider adding Whole House Humidification systems like the Sanidry System offered by Comfenergy.  Running a whole house dehumidifier often reduces the load on your current HVAC system, reducing it’s run time and increasing your comfort throughout the home.

Building a finished basement in Northern Virginia is a great way to add livable space to your home.  It is often way more cost effective than building an addition and increasing your home’s foot print.  Building Science needs to be considered to make sure that you maximize your Home Performance in these new spaces, or you may end up with a room that has issues that are expensive to repair.  Comfenergy can help you evaluate the risks associated with finishing your basement including: your site and exterior water management systems, your foundation construction and interior water management system requirements, your air sealing and insulation requirements and your mechanical air conditioning requirements.  We are systems thinkers that incorporate all of these things into the designs we create for what you do not see in your home, but what you feel in your home.  Call us today.