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Community and Q&A

Converting a 1830 house to a superinsulated house

Larry Broderick | Posted in General Questions on

I am diving into the insulation in my 1830 farm house, 1500 sq. ft., which is located in upstate NY. I am looking to retro the house into a tightly insulated house that will ultimately heat off of electric heat or heat pump minisplits. I just had a 10 kw Solar system to create the electricity for the heat. The solar system was designed to cover 110% of our projected electrical consumption with a minisplit system running. My goal is an 1830 superinsulated house.

Currently the house is very original and we are living in it. Most work will be done by myself, in the least obtrusive way to daily living. The frame is 8×6 post and beam with a slate roof. Any insulation that is present is not installed properly and is inadequate at best. Most windows are original with a few that were replaced in the early 1900’s. Most have triple track storms and the rest have old fashion storms. The roof is a beautiful slate roof that I have resurrected. The foundation is dry laid stone that has been parged with cement. It is mostly crawl space with a small root cellar.

Currently I am heating with a Woodmaster 4400 Outdoor wood boiler. I have an oil furnace as back up and a wood cook stove in the kitchen. The OWB and Oil furnace feed hot water radiators on one zone. The OWB heats the old drafty place up quite well.

The only insulating that I have done so far has been temporary. I dug a 2 foot trench around the foundation and laid in 4” Polyiso up to the 2nd row of clap boards. I then created a skirt with EPDM roofing rubber that was flashed under the clapboards and then went into the trench. I then back filled the trench with gravel. This sealed the dried laid foundation enough to keep the living room carpet from floating when the wind blows.

I am planning on turning my attention to the attics this winter. There are two attics, one is 21ft x 24ft and is over the second floor section of the house. This will be used for storage. The other is 18ft x 18ft and is over the first floor part of the building. This will be turned into a play room for the kids. I have a large amount of 4 inch poly ISO board. My plan is to place 4 inches of Polyiso in the rafter bays flush with the 4×6 rafters. This will provide a 2 inch air gap at the roof sheathing. I will then place another 4 inches of polyiso over the rafters as a thermal break. I will tape and seal the polyiso. I will do this on the gable walls as well. The attic that is getting finished as a play room will have sheetrock hung over the polyiso.

In the spring I will remove the old clapboards and sheathing from the outside and place 4 inches of Polyiso in the stud cavities and then apply a 2 inch polyiso skin over the studs and post and beams to create a thermal break. Then I will apply sheathing and new clapboards. How does all this sound? Will this be a good tight envelope? What should I modify/change?

In 2018, I am going to lift the house and do a complete dig out of the basement and put in new 9 foot foundation with insulated concrete forms with radiant heat in the slab.

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  1. Steve Knapp CZ 3A Georgia | | #1

    Larry. You may have already read through the site. If not, it contains quite a few articles on deep energy retrofits. You might want to start here:

    Also be sure to check out the links in the sidebar.

    You may want to consider posting a series of specific questions. I'm curious if your roof has soffit or ridge vents?

  2. Larry Broderick | | #2

    The roof is slate so there are no soffit vents and no ridge vent. Slates breath very well by design. I plan to add a ridge vent and open the soffits up when I do the insulation in the attics to keep the air moving. I have read a ton but the more the merrier. My situation doesnt usually fit well into most retrofits as I am on a very strict budget (single income family) and will do most of the work myself.

    The article you posted is very similar to my idea. I will have thicker insulation but thinner thermal break.

  3. GBA Editor
    Martin Holladay | | #3

    Polyiso insulation is not rated for burial or below-grade use in contact with the soil, so you chose the wrong type of rigid foam for burial. (It absorbs water.) When you install your new foundation, you can fix that error (and throw away the water-logged polyiso). For more information on this topic, see Choosing Rigid Foam.

    Your plan to remove the existing sheathing does not account for the need for wall bracing (racking resistance). It will be best if your new sheathing is in direct contact with the wall framing, and is well fastened. If you have any doubts on this issue, talk to an engineer.

  4. Larry Broderick | | #4

    I am aware that polyiso cant be in contact with soil but it was what I had on hand when we moved in. It is temporary and is doing its job thus far. I do plan to throw it all away or add it to the chicken coop when I do the foundation.

    I did consider the wall bracing with the removal of the sheathing. My conclusion was that stick built and balloon built construction relies on the sheathing for bracing. I believe post and beam does not. Each post is braced in multiple places with diagonal braces. I could be wrong with this as I am a weekend warrior. I look at old barns often and most of the time they do not have sheathing. I will look into it deeper. Thank you for your oversight!

  5. Larry Broderick | | #5

    Heres a photo of the house to give perspective and a photo of the quick foundation insulation project.

  6. Bob Irving | | #6

    Most post and beam frames are self bracing, but that assumes that the frame, including all braces and pegs, has not been compromised in the last 186 years. There is also a possibility that it's an early form of stick framing where large timbers are used in construction, but there are no braces. Either way, sheathing the walls with taped plywood is a good idea. I've substantially upgraded my old house and we're now using mini splits; the house has never been as comfortable.

  7. Larry Broderick | | #7

    The house is original and the joints are in excellent shape. They are all braced and all mortise and tenons are intact and pegged appropriately. I like the idea of sheathing but i feel like i will loose efficiency if i sheath then add a second layer of insulation and then sheath again. The walls will get thick and it will be twice as much plywood.

    Bob, How did you insulate? How big is your house and Mini Split system? My worry is that old houses are filled with small rooms which are the achilles heel of mini splits. I like to see how others have retroed them in to old houses, especially when they are pleased with the results.

  8. Bob Irving | | #8

    seems to be an old thread, but I'd recommend 4" of polyiso on the outside of your walls and the stud bays, if they are open, use Rockwool batts. I see no reason to remove sheathing. You do not want to sandwich wood studs or sheathing between two layers of impermeable material. Strap over the polysio for a rain screen, and attach your siding to that. A layer of sheathing there serves no purpose, but the strapping will allow the siding to breathe.

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