The Difficulties in Heating Cape Cod Style Houses

by Erik North on November 12, 2011

Cape Cod Style House


One of the great ironies in construction (I bet you didn’t even know there was ironic construction) is that Cape Cod style houses perform pretty poorly on Cape Cod. The year-round sea breeze wash (wind wash even) right through the Cape building frame, making them chilly and uncomfortable in the winter months.

How did Cape Cod style houses which performs not so great in the winter become popular in New England? Maybe the name was a marketing scheme? And how can we address the air leakage and heat loss issues to make Capes more comfortable?

About Cape Cod Style Houses

The second floor framing in Cape Cod style houses packs a lot of living into a compact space. In as little as a 600 square foot footprint, one can fit a 4-bedroom, 2 bath 1100 square foot home. For the price and availability, Capes can be quite a deal. However that same framing, which makes great use of space, also leaks conditioned air like crazy. If some half-assed attempt to ventilate has been made, odds are very good the second floor will be frigid come January.

Cape Cods – Heating Distribution

The heating distribution is the first area of concern. Most heating system and insulation issues with Capes stem from having been built in the cheap-oil era. Insulation was an after-thought circa 1950 and heating was dirt cheap. It’s the rare Cape which has had these shortcomings fully addressed since its construction.

Sometimes the second floor isn’t piped for heat at all. On other occasions, the hot water pipes are run through the walls. When the baseboard units are on the opposite side of the house, hot water pipes are often run through the knee wall space outside the attic insulation. All of these are exciting ways to lose heat (or in the case of the unheated second floor, not gain enough).

Each problem has its own solution. If the second floor isn’t heated, have the heating baseboard/ducting installed. No amount of fans/wishful thinking will move enough heat in Cape Cod style houses from the first floor to make it comfortable.

If the hot water pipes for the second floor baseboards run through the exterior walls, well, you have a more challenging problem. If the exterior walls are uninsulated, dense pack them with cellulose which will also insulate the pipes.

If the walls are insulated, try to determine whether the pipes run inside the insulation (I know…not easy. I use a fiber optic boroscope and infrared camera to look inside the wall cavity). If not, you’ll need to reinsulate that cavity and put some thermal resistance between the pipe and outside sheathing.

Here’s a diagram of an attic knee wall in a Cape Cod style house.

Air Leakage in Attic Knee Wall

Image: DOE's Office of Energy Efficiency and Renewable Energy

Cape Cod style houses are often insulated at the vertical wall and joist flats in the knee walls. If the hot water pipes for the second floor heating are run through the knee walls, they’ll be outside the thermal envelope.

Cape Cods – Air Sealing

Insulation and air sealing are just as problematic. The knee wall framing usually has built-in bookshelves, drawers and closets. The knee wall sits on top of the first floor joists, meaning interior air is flowing from under the knee wall. Finally, the tops of the knee walls are usually not sealed. Much more conditioned air than you’d like flows up the wall slopes and out the attic cap.

There are three possible approaches to insulating and air sealing a Cape. One can adopt an unvented approach and seal the whole thing (and you’d better have moisture under control).

You can insulate the roof deck and vent the attic. This vented approach is challenging in Cape Cod style houses as the ventilation needs a clear path from soffit to peak, the eaves need to be sealed to prevent unwanted unconditioned air wind washing (I’m looking at you ocean winds) and the tops of the knee walls sealed around the vents.

Finally, they can be insulated at the horizontal and vertical flats. In this case, the tops and bottoms of the knee walls need to be air sealed.

Cape Cod style homes date back a couple hundred years. They’ve been optimized for space but were not developed with energy efficiency in mind. Cape Cod style houses can be warm and efficient if these issues are kept in the fore front.

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