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  1. #1
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    Default Insulating a 100 yr. old house

    I am a new but old DIY'er, my question is, can a person add a new 2x4" wall on the inside exterior wall to insulate and run new (upgrade) wiring for outlets and lights. What do I need to do to do this project or what problems could this cause, it would be going over an old plaster and lathe system that doesn't have much insulation. By the way, I live in South Dakota...

  2. #2
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    Default Re: Insulating a 100 yr. old house

    Yes you can build a wall inside. Be aware that there will be gaps in the envelope such as where intersecting walls meet.

    Jack
    Be sure you live your life, because you are a long time dead.-Scottish Proverb

  3. #3
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    Default Re: Insulating a 100 yr. old house

    I would not recommend it, there is a danger of trapping moisture between the walls. I would tear out the lath and plaster and look at what you have. You may want to run new wiring in the old wall and replace any old insulation with new, put in a proper vapor barrier and then sheetrock.

    If you want more insulation, you can fur out the existing studs to use 6" insulation or you could build a 2x4 wall frame next to the old wall, but with the new studs offset from the old. Use two layers of R-11 unfaced, then vapor barrier, then sheetrock.

    You could also use unfaced new fiberglass in the old wall, then 1-2" closed cell foam panels, taped at the seams as you vapor barrier, then sheet rock to this with long screws. Both the double wall and the foam panel system break the heat conduction path between the interior and exterior walls. The heat conduction paths are the studs that have much lower R value than the insulation and make up about 10% of the walls.

  4. #4
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    Default Re: Insulating a 100 yr. old house

    Quote Originally Posted by thisoldfool View Post
    I am a new but old DIY'er, my question is, can a person add a new 2x4" wall on the inside exterior wall to insulate and run new (upgrade) wiring for outlets and lights. What do I need to do to do this project or what problems could this cause, it would be going over an old plaster and lathe system that doesn't have much insulation. By the way, I live in South Dakota...
    Yes, you can --- it's a fairly common method --- just keep in mind you will loose some space and any doors or windows on these walls will need the jams extended.
    I would suggest ( with the proper adesive ) glue extruded rigid foam ( at least 3/4 inch -- one inch would be better ) to all the plaster wall surfaces first. With foam in a can seal all the joints at the ceiling , floor and intersecting walls --- use a housewrap tape to seal the butt seams betweem foam sheets.
    Then put up the new framing so the backs of the studs ( 2X3 or 2x4 ) are up against the foam -- run your electrical ( have that inspected ) -- fill the joist bays with unfaced batt insulation -- cover with drywall.
    Depending on your local building department they may or may not require a vapour barrier ne appied over the batt insulation --- this will depend if they recognize the extruded foam is a vapour barrier and the drying can take place into the room.
    "" an ounce of perception -- a pound of obscure "
    - Rush

  5. #5
    Join Date
    May 2011
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    Default Re: Insulating a 100 yr. old house

    Don't ruin all that wonderful original plaster. DO some math first. IF the payback exceeds 1o years, is it really worth it. Drywall isn't superior, it's just cheaper and easy to work with. Its' doesn't absorb sound well either. IF you live on a street a drywall house won't be nearly as quiet as a plaster home.

    Start by insulating the attic really well, then seal up air leaks. Once you've done that, then look at cutting holes from either the outside sheathing or inside near the ceiling and filling the cavity with insulation.


    IF you heating bills in winter are $1000. Figure that about 30% of the heat loss is through wall cavities (not infiltration, studs, roof, windows or floor) So we're only working with $300. Now if you went from the current R4 that the paster, sheathing and air gap provide, and upgrade to R12, you've saved $200.

    SO IMO you better not spend more than $2000 making the upgrades. That's a 10 year simple payback.
    1925 Two-Story Stucco Beaux Arts Neoclassical

  6. #6
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    Default Re: Insulating a 100 yr. old house

    Quote Originally Posted by motoguy128 View Post
    Don't ruin all that wonderful original plaster. DO some math first. IF the payback exceeds 1o years, is it really worth it. Drywall isn't superior, it's just cheaper and easy to work with. Its' doesn't absorb sound well either. IF you live on a street a drywall house won't be nearly as quiet as a plaster home.

    Start by insulating the attic really well, then seal up air leaks. Once you've done that, then look at cutting holes from either the outside sheathing or inside near the ceiling and filling the cavity with insulation.


    IF you heating bills in winter are $1000. Figure that about 30% of the heat loss is through wall cavities (not infiltration, studs, roof, windows or floor) So we're only working with $300. Now if you went from the current R4 that the paster, sheathing and air gap provide, and upgrade to R12, you've saved $200.

    SO IMO you better not spend more than $2000 making the upgrades. That's a 10 year simple payback.
    What about the daily comfort level ? Isn't being warm and cozy also worth something ? There's also added value with insulating the home when it comes time for resale.
    Keep in mind the OP also mentioned doing rewire which would be easier doing the way he wants.

    Btw -- old plaster walls aren't always wonderful.
    "" an ounce of perception -- a pound of obscure "
    - Rush

  7. #7
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    Default Re: Insulating a 100 yr. old house

    very true about plaster walls not always being wonderful..if the plaster is sound its great as it can take a pile of abuse... but if it is starting to fail you cant patch it it will continue to crumble and fall off the wall.


    for soundproofing you can use 5/8 type x drywall, or sound board, its a type of drywall that has a thin layer of fibreglass in the middle, its rated at having 11 x more sound dampening than a sheet of regular 1/2 drywall.. only thing is its special order
    fire up the saw and make some dust

  8. #8
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    Default Re: Insulating a 100 yr. old house

    Hi a real concern is the potential of creating a dew point inside of the wall cavity( referring to the idea of installing foam inside of the walls may not be such a great idea) instead of outside of it. When super-insulating walls one must remember condensation issues so consider getting on the web pages for green building as some real smart folks there to also assist you.
    I sm renovating a 107 year old grand home and do a double wall and using cellulose in the cavity. Another ida would be to add 2" of XPS foam to the outside of the walls and then residing. The Foam is $$$
    Another benefit of the double stud wall is to stop heat transfer from the wood studs to the outside. Thermo image cameras show how cold each stud is in any single stud wall. seperating the two walls with an inch or better two stops this heat sink action.
    Any an all of my comments are just my opinion and not to be confused with facts.

  9. #9
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    Default Re: Insulating a 100 yr. old house

    Quote Originally Posted by Timothy Miller View Post
    Hi a real concern is the potential of creating a dew point inside of the wall cavity( referring to the idea of installing foam inside of the walls may not be such a great idea) instead of outside of it. When super-insulating walls one must remember condensation issues so consider getting on the web pages for green building as some real smart folks there to also assist you.
    I sm renovating a 107 year old grand home and do a double wall and using cellulose in the cavity. Another ida would be to add 2" of XPS foam to the outside of the walls and then residing. The Foam is $$$
    Another benefit of the double stud wall is to stop heat transfer from the wood studs to the outside. Thermo image cameras show how cold each stud is in any single stud wall. seperating the two walls with an inch or better two stops this heat sink action.
    Installing the rigid foam continously along the interor side of the wall raises the wall's tememperature which raises the dew point --- which reduces the possiblity of condensation.
    This method also reduces thermal bridging that you a talking about.
    It's similar to installing the rigid foam onto the exterior surface of the wall though not as expensive when you consider having to reside the exterior of the home.
    Last edited by canuk; 11-23-2011 at 06:00 PM.
    "" an ounce of perception -- a pound of obscure "
    - Rush

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