If you have a Cape-Cod style home and you are wondering if you can air seal and insulate effectively - the answer is yes, however not without a good plan.
Houses with Cape-Cod style framing stem from being built in the 1940's and 1950's when the cost of heating was dirt cheap and insulation was an afterthought.
If you live in this style home, chances are very good that it has not been properly addressed due to the complexities of the way it was built.
Take a look at this recent Cape-Cod insulation project and what steps were taken to seal and insulate. This one is located in the friendly residential Southland Hills community of about 200 homes in the heart of Towson, Maryland. The homes in the neighborhood were built in the 1940s.
The Comprehensive Energy Audit
Bonus Room House!
When I pull up to a home as an energy auditor I have my radar on: What style home is it? What is the footprint of the home? What condition is the home in? Is the heating and cooling gas or electric? These are some of the take-off points to begin a great home energy audit.
One thing at this house stood out to me when I arrived.
I window at the top of a wall within the side gable usually means the house has a "bonus room". Another, more well known way to describe the style of home is Cape-Cod style.
If you have a Cape-Cod style house then you know it really means the bonus room is really just an extra dose of difficulty.
The small attic behind the wall at the bottom of the sloped ceiling is usually hard to reach and a source for discomfort and dust due to old/worn insulation, poorly sealed hatches and general basic neglect (nobody's judging ya!).
Panel that leads to attic space behind bonus room wall. The attic area behind the bonus room wall.
I find these attics in older homes throughout Baltimore County and if you take a drive through this Southland Hills neighborhood, it is easy to see that many of the 200 homes built in the development are all of similar Cape-Cod style.
How to Make Insulation Decisions in a Cape-Cod
Finding a Good Air Sealing & Insulation Treatment Approach
The best approach to take in a house that is a Cape-Cod configuration is to see what the house has to offer as a starting point. What I mean by that is to figure out what areas of the space can be easily accessed.
Collar Attic Plan
Treatment to the top flat portion of the attic (called the collar attic) should be evaluated for treatment including sealing and adding insulation. If space permits air sealing and insulation should be installed.
Look at these similarly constructed homes with varying amounts of space above the top flat ceiling. The lines indicate the approximate ceiling location.
Example Home with only 20" of space Home Where Audit was Conducted has 36" of space to work
In the two different configurations, literally the difference between 16" makes the difference between being able to work in the space or not.
The good news for this home in the Southland Hills neighborhood is that it had sufficient space for a human to work.
Check out some of the details...
The ceiling measures 7' across. A hatch that was cut for HVAC in the collar attic.
A pop up inside the space reveals not much room to move, but a good opportunity
to make improvements, nonetheless.
At the end of the day a air sealing and adding insulation to the collar attic was feasible and recommended to the homeowner. Each Cape-Cod collar attic should be independently evaluated for feasibility.
Sloped Attic Approach
Sloped ceiling portions of a Cape-Cod attic should be evaluated both visually and with thermal imaging. One possible deterrent for homeowners to treat a Cape-Cod attic is that finished sloped ceilings can be costly to re-insulate.
But don't over-think or try to over-do the job. With a few subtle installation techniques, the R-value in the sloped cavity can be increased in some cases and treating areas that are more practical to reach will only improve overall leakage of the ceiling bays.
The solution for this home was to seal the cavity bays from below and from above and leave the existing insulation to keep the project within a budget.
Knee Wall Areas
Another challenge to getting measurable results when air sealing a Cape-Cod style home is getting to all of the small spaces between the roof and the knee wall.
In many cases access will need to be made in several locations, so knowing this and prioritizing improvements is critically important.
As an example, don't re-paint the upstairs bonus room if you are considering insulation or if you are finding this article because you are not comfortable in the space and want to find solutions.
Energy auditing, home performance and the BPI guidelines all work towards finding areas around preexisting homes to treat where the return on investment is positive over time.
In some instances, costs will outweigh value, but when it comes to treating these inaccessible spaces that have older insulation - the gains in energy savings and comfort can really pay off if a little finishing work is required after the project is done adds a little to the overall cost.
Every situation should be evaluated on a case by case basis and a home energy audit is precisely a way to figure all of this out.
Notice how the front dormer windows create multiple areas that need to be treated, making it a bit more difficult.
Check out how we create access to an attic area that is not currently accessible.
Final Plan: Sealing and Insulating in the Best Locations for this House
The stack effect drives the air change conveyor belt inside your home quite a bit in the heating season. This is due to leakage in the basement and in the attic.
During an energy audit I am literally "on the hunt" for places that air can infiltrate (come into your conditioned space) and exfiltrate (your conditioned air goes out). Sealing up these two places in cost effective ways is the name of the game!
So, after careful review and consultation between myself and the homeowner, we decided on the following work scope:
Foundation -- Air Sealing / Insulation
Air seal any penetrations at the accessible rim joist in the basement with two-part spray foam (~60 linear ft) which will also insulate the area to R-19.
Attic -- Air Sealing / Insulation
Cut access in three wall locations to gain access to upper floor attic. Reinstall the drywall with removable panel for future access if needed.
Treat three existing attic access areas by adding insulation to each and weatherstripping. (2 wall, 1 ceiling)
Add 5-7” of open cell spray foam to the accessible sloped roof surfaces of the kneewall attic areas (~392 sq ft).
Blow 10” of loose fill cellulose to the flat collar attic using the existing ceiling hatch in the closet (~154 sq ft).
Basement Rim & Band Joist - Every Home Should Get this Treatment by the Way
If you are not sure what the rim and band joist are in your basement and if it is accessible for treatment - you are about to find out!
First, put yourself in the unfinished part of your basement. Usually it is a utility room with HVAC, water heater and maybe washer/dryer.
Identify your foundation wall at the top and you have found your rim and band joist.
Take a look at how the electrical "main" is coming through the rim joist in the basement of this Towson, Maryland home performance home. This is happening in a lot of homes.
Look at the size of that hole. And this is the point - it is a hole going directly to the outside which means this:
Summer: humidity infiltration Winter: cold air infiltration
Just look at those spider webs. The spiders like to make their traps where air is moving. It is instinctual. So if you see a spider web, air is flowing.
Now get your full frame of reference by watching this short video clip that shows where the electrical main and gas line enter into the rim joist from the outside which appears "invisible", but it is not.
Results - A Look at the Final Project and the Test-Out Numbers
Rim and Band Joist Treatment - Closed Cell Spray Foam
Watch the spray foam team treat a portion of the rim and band joist in this up close and personal clip.
Knee Wall Attic Treatment Before / After
Blower Door Results
Many factors drive the overall reduction in leakage that each home is schedule to achieve during a home performance project through the BGE program. I make this very clear to my customers that for every house I am believe we can get 30% reduction and don't there is a home that I am convinced we can only achieve the minimum required to meet the program standards (10%) - only to exceed that by a lot.
As a result of many audits and challenging situations when I was wrong, the partnership I formed with this customer went a long way. We both agreed that 20% reduction was a good target and that due to other factors that were not reported here, we will do everything we can to nail the work scope and see where it takes us.
Ultimately, this home performance project achieved an 11% reduction in leakage.
Initial Blower Door Test In CFM: 3775 Cubic Feet Per Minute at Negative Pressure -50 Pascals
Final Test Out Number: 3255 Cubic Feet Per Minute at negative pressure -50 Pascals