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Energy Efficieny upgrades for historic buildings

gbauser-20428 | Posted in Energy Efficiency and Durability on

I have a project that entails the rehabbing of over fifty small historic buildings for energy efficiency and comfort upgrades. Because these buildings are part of a National Historic Landmark, we are very limited to how we effect the exterior of the structure including window changes. My plan is to start with insulation upgrades to the attics and crawl spaces. Funds are limited as this is part of a non-profit organization so I want to be sure to spend the money wisely. I’d appreciate any input as to getting the most bang for the buck while respecting the historic preservation aspect of the project.

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  1. GBA Editor
    Martin Holladay | | #1

    You didn't mention where you are located. Your climate will affect your project specifications.

    In general, though, I would recommend:
    1. Air sealing the top-floor ceiling from the attic side.

    2. Installing a thick layer of cellulose insulation on the attic floor.

    3. Air sealing the crawl space, especially around the rim joist area. All crawl space vents should be sealed.

    4. Installing a poly vapor barrier on the crawl space floor.

    5. Installing spray foam insulation or rigid foam insulation on the crawl space walls. This insulation may need to be protected with a layer of moisture-resistant drywall, depending on the local code.

    6. In some cases, it may be necessary to condition the crawl space (for example, with a forced-air register). However, recommendations differ depending on climate and the peculiarities of your buildings. Consult a home-performance expert concerning the need for crawl space conditioning.

  2. gbauser-20428 | | #2

    Thanks for the feedback. I agree with all your recommendations but have a couple of wrinkles to throw into the conversation. The majority of these buildings, which were originall built in the early 1900's as summer cottages, were mostly built on pier foundations and subsequently had framed skirting walls installed which form the crawl space walls. This means there is no tight connection at grade level. Also, they have had some insulation added over the years to both these framed in fill walls and the attics. We have begun the upgrade process by installing loose fill cellulose blown in the attics over the existing batts. Calculating the existing R value of the fiberglass and the cellulose topping, we are averaging about an R50 (theoretically). My concern is that if we are not pulling back the fiberglass throughout the attics to perform proper air sealing (no small task, keep in mind there are sixty of these buildings)are we wasting time and money? The same problem applies to the crawl space walls. Unfortunately, most of the cottages have been fitted with forced air furnaces and ductwork that are located in the crawl space so air sealing and insulating the floor system leaves the mechanicals "out in the cold". I am considering foaming the rims and installing a vapor barrier over the soil and up the wall, and draped fiberglass blanket over whats existing. It seems starting from scratch is the best answer but I'm concerned about the cost and environmental impact of removing and disposing of all that fiberglass.
    By the way, the project is located in Boulder, Colorado so we are a heating dominated climate.
    Any additional feedback is appreciated.

  3. GBA Editor
    Martin Holladay | | #3

    As I'm sure you know, there are at least two ways to do most jobs: the cheap way and the right way. Sometimes a builder has to explain to the client that cutting corners isn't acceptable.

    I don't think it makes any sense to locate a furnace and ductwork outside of the thermal envelope of a building in Boulder, Colorado. That means that someone must come up with a different location for these furnaces.

    There are lots of choices, none of them cheap:

    * Jack up the buildings and install concrete crawl space foundations under them. Insulate the crawl space walls, bringing the furnaces into the thermal envelope of the building.

    * Build a mechanical room addition on the back of each building. Relocate the ductwork.

    * Install spray foam under the roof sheathing to create conditioned attics. Install the furnaces in the attics.

    By the way, it makes absolutely no sense to install attic insulation BEFORE air sealing the attic floor. Don't put the cart before the horse. Air sealing is more important than insulation, in any case. No insulation contractor worth his or her salt should be up there with a cellulose hose unless the air barrier has first been checked!

  4. [email protected] | | #4


    I have been thinking about your attic insulation. I believe that the correct answer is all about what density of cellulose you are able to achieve. If it is a loose fill, I think you will not be sufficiently effecting air movement to make it a good choice. If however, you can really fill the space, and you can achieve a density that starts to slow the air down appreciably, then go for it. But, before you do, we should talk a bit about attic ventilation. What is the current venting like?

    - Ron Flax

  5. Aaron Lubeck GC | | #5

    Jeff -

    Working on old inefficient homes, we do a lot of balancing acts between the historic preservation and sustainable building movements. If your homes are restricted by historic guidelines then your windows, siding and streetscape are all untouchable. I would note, you can (and should) rehabilitate historic windows. Re-glaze, caulk, weatherstrip, and add a storm window and they'll offer the same R-Value as the most commonly specified cheaper replacements. As for insulation, in order of importance: Attic, Crawl/Basement, then Walls.

    I concur with Martin, You can insulate till the prairie dogs come home. If you don't air seal, it's all for naught.

    I’m glad you’re doing this work. Greening our old building stock is the elephant in the room we have to eventually address. Architect Carl Elefante notes that there’s no mathematical way to achieve a zero energy building stock without fixing our old buildings. It’s impossible to BUILD our way to a green future, we have to conserve and preserve our way to it instead.

    Hope it helps,

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