Cape Cod roofs, cold foundations and masonry walls can make an energy retrofit tricky. These Building America lessons show how to add insulation without creating new moisture problems.
Existing homes present a significant opportunity for energy savings—and a huge challenge—in part because of the diversity of existing housing stock and construction types. In addition, as you air seal and insulate a home, the HVAC and IAQ performance is affected, and needs to be addressed along with the energy savings.
A May 21, 2014, Building America session examined challenges that still matter when renovating older homes. To effectively retrofit homes, optimize energy performance, and assure occupant health and building durability, innovative and cost-effective strategies must be developed for existing homes. Examples suitable to a variety of climate zones, construction types and existing systems must be developed, tested, and documented. The session looked at four unique and challenging scenarios—high-performance enclosure retrofits for roofs of cold-climate story-and-a-half homes, high-performance wall retrofit for cold-climate occupied masonry structures, foundation insulation for existing homes in cold climates and pressure regain systems for existing air distribution systems.
Though there are myriads of unique construction situations in existing homes, Cape Cod-style (or story-and-a-half) houses and masonry walls both present challenges to high-performance retrofit of existing homes. The challenge is that “normal” retrofit strategies just don’t achieve high performance. Experts from Building America offered strategies for both the story-and-a-half and masonry walls that sidestep the typical limitations.
It may be effective to remove roof overhangs, then replace them after you have completed the air control layer. Why? Because this “chain saw” approach allows simple and direct connection of roof air control to wall air control.
This strategy allows for continuous insulation (it reduces thermal bridging) at roof-wall intersections, when the wall is also provided with continuous exterior insulation. In addition to creating a better end product, with an easier integration of roof thickness, there’s the opportunity to anticipate future wall retrofit or to coordinate with a concurrent wall retrofit using this strategy. There’s also the opportunity to establish/re-establish roof overhangs to improve water protection for walls and add aesthetic value. It can be difficult for a homeowner or contractor to absorb this concept, and therefore somewhat challenging to implement.
This is a planned roof retrofit, not a direction to cut structural framing without a design. The 2013 Mass Save Deep Energy Retrofit Builder Guide explains the connection details for its New England retrofit examples.
Adding insulation to a cold, wet foundation wall is a real challenge. Moisture impacts must be carefully assessed. Prospective robust, universal solutions can be expensive, and a quantitative-assessment approach to determine potential wetness of foundation walls can change with the season, the weather and/or new landscaping. These realities put additional research pressure on our approach to below-grade insulation for existing homes.
Insulating foundations in existing homes is critical to improving energy performance. Foundation heat loss can be significant in existing homes, and while below-grade temperature differences may be smaller, the surface area can be fairly large, and the above-grade portion can be large in older homes.
The bottom line is that energy performance, comfort and moisture performance can be improved by insulating foundations, but strategies are largely varied based on the situation in individual homes, and indoor air quality can suffer if proper solutions are not implemented.
Many older foundations lack waterproofing and/or capillary breaks. In cold climates, the top of the foundation is very cold in the winter, and the bottom of the foundation can be below the dew point in summer. Foundations get wet from all four sides by all four moisture transport mechanisms—bulk water, capillarity, diffusion and air flow. Where outward drying is limited, the foundation wall needs to dry inward; interior insulation must account for this drying potential. Building Science Corporation’s basement guidance emphasizes groundwater and rainwater control, airtight insulation and moisture-tolerant materials.
In 2014, Building America was exploring “excavationless” exterior foundation insulation strategies, seeking a cost-competitive upgrade with minimal impact to existing site/landscape features. A field-study dataset published in 2016 documented one Minneapolis home insulated using hydrovac excavation and liquid insulating foam. That is a useful research example, not evidence of widespread availability or long-term results for every foundation.
Cape Cod-style homes provide a unique challenge because their story-and-a-half configuration puts living space within roof framing.
One solution is to insulate on the outside, which provides an opportunity to add a lot of insulation and have better condensation control. This can include building a new roof—which means new flashing, and creates the opportunity to ensure robust water control. Simplified access can improve air-sealing performance. If you do go with the new roof approach, a high-performance, new roof assembly includes:
The Building America Solution Center’s roof-retrofit guide explains these details, including air-barrier continuity, condensation control and roof-load evaluation. Have the assembly designed for the house and local requirements.
In the National Grid Deep Energy Retrofit pilot project reported in the 2014 session and conducted by Building Science Corporation (BSC), this strategy, though not incidental in cost, provided best overall airtightness of those that implemented exterior roof insulation strategies. In that pilot comparison, next best in performance was a roof that had been spray foamed from the interior, followed by a roof with a vented attic. However, it is often very challenging to achieve effective air control with spray foam because the critical installation areas are often not readily accessible.
These figures are from a 2013 report on two Chicago masonry buildings, for exterior insulation and over-cladding—not roof insulation. They are historical dollars per square foot of gross treated wall area, not current estimates.
Two-Story-or-Less Costs: $14.43/sq. ft. (average of the three lowest bids); the final contract cost was $11.10/sq. ft.
Above Two Stories: $25.31/sq. ft. (average of the three lowest bids); the final contract cost was $23.65/sq. ft.
Construction materials cost considerably more today. The Bureau of Labor Statistics’ construction-materials Producer Price Index rose approximately 81% between the 2013 annual average and September 2026. That measures materials prices, rather than the full installed cost of a retrofit, which also includes labor, scaffolding, repairs and contractor markup. The Chicago figures remain useful historical benchmarks, but today’s projects need fresh local bids.
A newer masonry-specific comparison comes from an April 2023 New York City affordable-housing roadmap, which estimated R-15 exterior insulation and finish system over-cladding at approximately $10,000 per apartment for a representative brick-walled mid-rise. That estimate included materials, labor and markup; it was a planning estimate, not a completed-project price or a nationwide rate.
The report included cladding and related work, with building height and access affecting costs. For a project today, obtain itemized local bids that distinguish insulation, cladding, access, flashing and repairs.
Above-grade masonry can also be renovated for high performance effectively from the exterior, using layers of continuous, exterior rigid insulation. First, however, wood framing (vertical only, as horizontal risks holding water in the assembly and promoting damage) can be installed with exterior-grade masonry fasteners directly to the masonry. As always, flashing and drainage details are critically important, and the air control layer of the wall must connect to the air control layer of roof. The insulation can then be installed directly over the framing, to reduce thermal bridging. Furring strips can be attached to the framing first (if it’s irregular) with epoxy-coated wood screws, to provide a better base for insulation. Do not assume every wood member can be left untreated: specify durable materials, drainage and fasteners for the assembly’s moisture exposure and local requirements.
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Updated content: October 21, 2026.