Cape Cod Style Houses

by Erik North on November 16, 2011

Cape Cod Style House


OK, I’m re-using the photos from last week’s post. Heck, it’s my house. Why not.

I wrote last week about the difficulties with heating Capes. Cape Cod style houses are enormously popular throughout the country and particularly in their region of origin, New England. The style has been around for centuries but leapt into popularity after World War II. Young Baby Boomers looking for inexpensive starter homes found Capes to be ideal. Cape Cods are common subjects for audits, with some notorious (but relatively easy to fix) Achilles’ heels.

Cape Cod Style Houses – The Boring Wiki Style Definition

Cape Cods are a very popular housing style dating back to the 17th century. They are characterized by steep pitched roofs, half-height knee walls and full gable end walls. Older construction often locate the chimney centrally while newer variants move it to one of the gable ends.

Like I alluded to earlier, Capes have grown enormously in popularity because of their compact, affordable design. One irony (and we’ll get to this!) is that the difficulty of air sealing the second floor knee walls make the design challenging one when ocean breezes on the actual Cape Cod whip through the building.

Cape Cod Style Houses – Advantages

The advantages of the Cape Cod come from its compact design. There’s a Latin phrase “multim in parvo” used to describe pugs. It means “A lot in a little” which is an apt description for Cape Cods. There’s a lot of living packed into a small footprint. The layout can accommodate up to four bedrooms and with a dormer can easily accommodate bathrooms on both floors.

Their footprint makes Capes appealing for infill construction (small lots split off other lots in the city). For the budget conscious first time home buyer, Cape Cods are a great choice.

Cape Cod Style Houses – Disadvantages with Insulation

Capes have some real challenges keeping warm (check out this article for a summary). The vast bulk of Cape Cod style houses in the US were built between 1925 – 1960 (from the Great Depression through the Baby Boom). What else happened during that time? Not insulation that for sure. Many Capes predate the modern conception of insulation.

Cape Cods often have no insulation, very old versions of insulation (my Cape had “Kimsul”, an odd cellulose and kraft paper deal and one of the oldest commercially available insulations in the US) or a half-assed retrofit job. Start with the assumption that older Capes need their insulation improved and then start figuring out how.

Cape Cod Style Houses – Disadvantages with Air Leakage

Air sealing … oh, boy. The second floor knee walls in Cape Cods leak air like crazy. The knee walls are framed on top of the floor joists, connected to the roof rafters. Here’s a diagram of an attic knee wall in a Cape Cod style house:


Warm air flows from under the knee wall, roof deck and out the attic’s vents. Often the knee walls have built in bookshelves, closets and drawers which leak air like crazy.

When retrofitting a Cape’s attic, a great deal of attention should be paid to air sealing. If the soffits are vented, the air flow needs a clean, uninterrupted path from the soffit to the peak. If the soffts are unvented, consider insulating with an unvented design (with all that entails).

A Cape Conclusion

Cape Cods are a justifiably popular housing choice. They’re a great affordable pick for a first time buyer or small family. However the insulation and air sealing often needs detailed work.

{ 6 comments… read them below or add one }

Eric December 12, 2011 at 3:35 am

Excellent article Erik. I live in Mass and own a cape. Here is my challenge. I had major ice damns last winter and one leaked. I hired a handyman to change out some old damp insulation and treat mold (which there was none).

The roof has a ridge and gable vent. It also has a vent at the edge of the roof that runs the entire length of the roof near the sofits. Before the project, the old 1960s wool insulation ran from the sofit right up to the tiny attic. Now the insulation was removed from the knee walls down to the sofits and vertical and horizontal insulation was put in.

It was much more tolerable this summer up there. My worry is now in the winter. We have knee wall drawers. They are not wrapped in plywood but they are wrapped in faced insulation. The paper face faces the warm side. The problem is that it’s not completely sealed and it’s wet between the insulation. How should I insulate this? Also, the roof nails have condensation build up on them. The roof is fairly new to my knowledge. Do you think I have other issues to be concerned with?


Erik North December 12, 2011 at 8:01 am


I grew up in Mass so I know how the winters can get.

Capes are a challenge, no doubt about it.

First off, there are many different approaches all of which can be made to work. The important thing is stopping the loss of conditioned air from your house. The warm air escapes through the top of your house, warming and melting the snow at the roof peak. The vented soffits make a perfect cold edge for the water to refreeze and form ice dams.

You’ve opted to insulate along the horizontal/vertical flats, meaning you need to air seal those flats.

With built-ins, I usually build an xps foam board box around the framing. Tape the seams to form an air tight seal. Seal all electrical outlets, foam block air seal against the soffit vents (assuming you have some form of styrofoam or similar venting), against the top of the knee wall and under the knee wall base between the floor joists. *whew*

The end result should be continuous air flow from the soffits to the attic peak without the cold air getting in the house. And a continuous air and thermal barrier running from the soffits to the base of the kneewall to the top of the kneewall.

If you have access to the attic space over the second floor and there is a centrally located chimney, make sure it is sealed around the framing in the attic flat.

As an aside, you don’t need a gable vent and a ridge vent. Ridge vents perform better so you could have the gables vents closed.

In my house, I opted for an unvented approach. I installed 2″ polyiso foam board against the rafters then dense packed cellulose behind it.

Good luck



emad May 2, 2012 at 3:18 pm

I have question. I just insulated my cape between the rafters with r 21 and went over that with foil backing foam board and sealed it with great stuf
f sealant. This was done in knee wall area and I have no vents in my soffits but have a ridge vent and gable vents at both ends. I used vent baffled and I have plumbing in the knee walls. Wa
s this a good approach to insulate?? I’m nervous about roof problems. I could not afford spray foam. Thanks


Erik North May 3, 2012 at 4:13 am

Thanks for the comment,

That is very close to the insulation approach I used in my house (netted cellulose instead of fiberglass).

You didn’t specify but I’m assuming you’re in a colder climate from the description.

Here’s my posted on unvented attics

The key for an unvented attic is a continual air barrier aka your foil faced insulation. If you can arrange it, have a blower door test conducted to examine any flaws in the attic air barrier.

Also, the purpose of a vented roof is controlling the roof deck temperature year-round. Air should flow cleanly from soffit to peak. if you don’t have vented soffits, the ridge and gable vents are really just letting out heat. And having both a ridge and gable vent is redundant.


emad May 4, 2012 at 1:46 am

thank you for your reply to my question about my insulation job I did on my cape. I live in New York on Long Island. The ridge vents and gable vents where there already when I purchased the house last June. Im not sure if I want to close them. This past winter it was comfortable up there but we had a mild winter. I heat my house with a pellet stove and the heat rises up there with no problem. I try not to use my oil for heat. But in the summer it does get hot up there ,you notice the difference from the downstairs. My other house I used to have was a one level small ranch so I was not too familiar with a cape style house.
The cape house was built in 1950 and had the original insulation of what was left of it on the slopes of the roof rafters also. The builders back then insulated the slope with no sofit vents.
I have another question I forgot to ask .t
he rest of the slope I continued with the R21 with the kraft paper backing and covered that with sheetrock and primed and painted it. Should I have used vapor barrier paint they have out there for the slope with the sheetrock or that is not needed??
thanks again the information from your site is so very helpful.


emad May 4, 2012 at 1:56 am

I forgot to mention my cape has a shed dormer in the middle of the roof which is a bathroom so the plumbing is in the knee wall and the other knee wall has the baseboard heating plumbing located in there with built in shelving units so it is hard to vent. just forgot to mention that.


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