Defining a DER

What is a Deep Energy Retrofit?? A Non-Technical Explanation (by Liane; Laura’s more technical definition is below)

Say you are in your own home, and you notice you feel cold.   Do you go and turn on the heat?
A simple question, but of course there are a lot of variables, and here in New England, those variables depend on the season and the weather at the time.

There are always a few things that everyone does, automatically, without even thinking, before turning up the heat. You might close some windows, or make sure that they’re closed already. You will put on warmer clothes: if you are wearing shorts or a short sleeved shirt, you will put on pants and a long-sleeved shirt, for instance. You might add a sweater. Still cold? You might get serious about adding some more layers of clothes. Long johns and undershirts. Heavy socks. Still cold? Can we turn on the heat? Well, you could go farther still.  A hat. A scarf. A heavy wool shirt. A lap blanket. Another scarf.   Fingerless gloves.  Indoors? All those clothes? OK, that’s maybe going too far.  No one wants to be uncomfortable inside their home.

But what if we could put some of those extra layers on your HOUSE instead of on you? Then you could be warmer and comfortable indoors, and your house would be zipped up tight in a polyfill jacket, hat, scarf, and wool blanket. Or the architectural equivalent thereof. And with all those cozy layers on your house, you use a lot less heat and save energy!

That’s my understanding of what a Deep Energy Retrofit is.
It’s “deep” because you will be using less than HALF of the energy that you did before.
It’s “retrofit” because something previously constructed is being adapted for a new goal, employing new technology.

It’s all part of that latest in building science: to make sure the house is wrapped up tight – with no exposed gaps or leaks that let heat escape, and with lots of layers carefully configured to deal with all the extremes our climate offers.

I myself own several pairs of fingerless gloves. I anticipate using them a lot less in the future!

Check out the pictures of the foam arriving!!  That’s the “down coat” for my house!  Over the next six to eight weeks the skilled hands of the builders will be wrapping my house in it and zipping it up tight!  Stay tuned…


A Slightly More Technical Explanation (by Laura)

Technically speaking, one cannot really “manage what one doesn’t measure,” so the first thing we did was to measure the air leakage of the whole house.  We got a HERS Index rating of about 130—which is pretty high–the lower the number, the better…as in “net-zero”.  It translates to about 16.5 air-changes per hour.  That’s a drafty house.

The image above shows Nick from CSG doing the blower door test.  (Yes, he’s setting things up from the outside, rather than the inside because the house is a multifamily.)  He also measured the volume of the spaces and the number and type of windows.  We already know that the whole house is leaky, but it’s good to have a base-line before we begin the DER.  Here’s a link for more info about the Blower Door test.

Nick setting up the blower test

Structurally, Liane’s house has basically what is known as a “Balloon Frame”, where the studs go all the way up spanning floors vertically (as opposed to platform framing where studs start and stop at each floor).  Ben, our cellulose guy said that the structure should more correctly be called “bridge framing”—a hybridization of balloon-framing—where there’s lots of blocking, making it harder to get the cellulose in every cavity.

Typical balloon frame house

Balloon frame diagram

Below is Ben’s sketch of what the joists at the floor-ceiling assembly probably look like, and how he would spray-foam the rim joist areas where the house meets the foundation in the basement.  His other drawings were great too…

Proposed foam at basement rim joist

Ben's drawings showing--among other things--the stairwells, the roof pitch and the sizes of things

One reason that Liane is doing this Deep Energy Retrofit is because she really had to get the place re-sided and re-roofed anyway.  You could just look at the asphalt-on-homasote siding, and it would just fall away.  Also, a tree fell very close to Liane’s house during the heavy rains of March – grazing her roof and squashing the neighbor’s car.

Fallen tree

Squashing the neighbor's car

Hector stripping off the siding with ease

Also, a couple of very cute squirrels and probably their babies were living up in the roof.


So the time had really come to do something about Liane’s house.  If she had to re-side, then this would be the one window of time to do something about the thermal enclosure—for the next 30 years or so.  A Deep Energy Retrofit made a lot of sense.

Liane's house

Speaking of windows, another important aspect of the thermal enclosure is, of course, all the openings.  Liane’s windows weren’t that bad—mostly fairly decent replacement windows.  But we wanted “outies” (more on this later) and Serious Windows had seriously gotten our attention.  So Liane went “window shopping” at MaCleod and Moynihan in Watertown, MA.

Liane and Leslie, window shopping

Leslie Burrell was a sweetheart and gave us a great deal on the Serious 725 series, with an R-value of 7.  Serious even carries windows up to an R-value of 11!  (Most walls in the Boston area can’t make it to R-11.)

What will Liane do with the old windows?  Well maybe she can make a little green-house at the back of her house…

Future greenhouse?

Have more questions?
Check out the About Us section to contact us directly or go to the Resources page for links. Also, here is the Wiki we recently posted on DER’s From Wikipedia:
A process of super-insulating older properties, and making the appropriate mechanical upgrades, so that energy usage for heating and cooling is reduced very significantly, usually 50% to 95%. Beyond a green retrofit, a Deep Energy Retrofit (DER) focuses primarily on energy conservation–seriously addressing a building’s enclosure–literally on all sides. It combines strategies of energy conservation, air sealing, moisture management, controlled ventilation, and insulation so that dramatic energy savings are achieved alongside optimal building performance. Durability, good interior air quality and energy efficiencies are attained by sound building science practices. In a DER, filling a wall cavity with effective insulation also requires careful consideration of how that wall will dry if moisture does happen to get past its skin. Using very high R-value insulation systems on the exterior of the building enclosure is often one of the hallmarks of a DER. Where exactly the dew-point will fall in (or out) of those thickened walls–and in what climate zone–becomes crucial. Careful detailing, flashing and air sealing of windows and other building penetrations is also key to a successful DER. Systems thinking is required for these kinds of retrofits, where highly efficient windows are “tuned” to their orientation, and mechanical systems and heat recovery ventilation units are sized and integrated with how the walls, roof and basement are being air sealed, moisture-managed and insulated.

The performance of a Deep Energy Retrofit can be tested with building diagnostic tools such as a blower door test and an infrared camera. Rating systems in the U.S. such as the Home Energy Rating System, Home energy rating tests residential performance on a numerical scale. Savings can be documented through an energy analysis, or simply tracking one’s energy bills and consumption. The definitions of the term continue to be refined and debated. [1] While the cost-effectiveness of Deep Energy Retrofits is sometimes questioned,[2] the value of the method is being studied through numerous test cases [3] [4] [5], some of which have received support from energy utilities. [6] With the addition of energy generating abilities (such as solar panels), a Deep Energy Retrofitted house can be readily modified into a Zero Energy Home. Generally, the financials for a DER work better when another major renovation to the building enclosure becomes necessary–such as when the siding or roof needs to be replaced anyway. Usually, only Passive House standards can exceed the energy performance of a Deep Energy Retrofit. In cold climates where heating costs can be extreme, the DER method shows great promise for widespread viability.

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3 responses

6 07 2010
SeriousWindows User Blogs About Her Experiences | The Serious Materials Blog

[…] SeriousWindows into her home in Somerville, Massachusetts. The install was part of a large Deep Energy Retrofit project Liane is having done. This project will decrease her home’s energy usage to less than […]

14 11 2010
Jeff WIlson

Hello – I’m a host on HGTV and the diy networks, and I’m in the process of a Deep Energy Retrofit on my 1940s Cape Cod kit home. You can see more about the project at We’ve used the “curtain wall” process on our exterior walls & roof, added a small, super-insulated replacement garage addition, installed a 4kW solar array and an ERV. Last winter, even though the retrofit was only about 70% complete, our heating bills dropped by 2/3. We saw those savings despite the fact that we had the coldest winter in years AND we’d decided to turn the thermostat UP to 70F because we’d put so much time and energy into the retrofit. We’re now more comfortable, have more stable humidity, and have healthier indoor air quality – and we’re enjoying the aesthetic upgrades as well.

Future projects on our DER include adding an interior spray-foam curtain wall in the basement and installing two solar-thermal air heaters in the next few months.

Good work on your DER! Let’s spread the word to DER America!


8 12 2011
Energy Ratings

I love to build my own green house too.

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