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Community and Q&A

Best use of funds after home energy assessment

William Hedberg | Posted in Energy Efficiency and Durability on

My home qualified for a utility rebate of $4000 that I want to take advantage of. I’ve attached the pdf with the table illustrating the proposed  improvement and consequent energy savings from the NH HPwES program.  Some info on the house… located in zone 5, right on the border of zone 6, plaster walls, steam boiler that is one year old. We have loose vermiculite in the attic that is currently covered by the subfloor planks.  We are going to professionally abate the vermiculite when our current tenant moves out, which will be no sooner than June 2020 as she just renewed the lease.  There is some loose cellulose insulation in the walls but it has settled and there’s still approx 80% walls that are not insulated.  Half the house is over dirt basement, half over dirt crawlspace.

Water is well managed around the house. I’ve done a lot of work air sealing. I’m currently finishing up encapsulating the crawlspace and basement. We have 80% new windows, and what’s left of the original windows all have newer storms over them.  

One concern I have is cracking the plaster from dense packing the walls. 

My second concern is the “estimated” annual energy savings for each proposed improvement for insulating the basement and crawlspace walls seems dis-proportionally low. 

Essentially we want to max out our rebate and that’s it.  The prices through the program seem inflated a bit. I’m looking for advice on where to spend this money (about $8000 total job cost). This calculates to either (1) dense packing the walls or (2) using CC to insulate the underside of the roof sheathing in the attic

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  1. Expert Member
    Dana Dorsett | | #1

    Hopefully when the windows were replaced the window flashing details were verified or updated?

    Clearly air sealing is a necessary pre-cursor to insulating, and worth every penny.

    Insulating the wall cavities always has good bang/buck. Any competent cellulose installer would be able to assess the likelihood of blow-out or cracking. Wood lath is pretty strong compared to wallboard, so it's mostly a matter of how many of the nails have rusted completely through. If the walls don't have lots of cracks or bowing/bulging sections now, it'll probably do fine at 3.2lbs, which is sufficient for preventing settling for most zone 5 locations.

    At 17-21 cents per R per square foot insulating the underside of the roof deck with closed cell foam is always expensive and low payback (even with and all closed cell foam solution). You might just wait until the Vermiculite remediation is complete, then air seal and insulate at the attic floor at a small fraction of the cost.

    Unless you're fully heating the basement the return on investment on basement walls is pretty low, especially if it involves insulating the foundation with closed cell foam at 17-21 cents per R per square foot. What methods are you using to encapsulate the basement? How many square feet of above-grade exposure is there on the foundation walls?

    If the basement walls are poured concrete or CMU (and not fieldstone or rubble) it's probably possible to DIY-insulate the walls at a fraction of the $3.5K quote for the 3" of ccSPF. The 336' of "uneven surface" described in the quote makes me think it's a rubble foundation. A few pictures might inspire alternative methods. At the very least the band joist and foundation sill should get 1-2" of closed cell foam to seal and partially insulate with sufficient R value for dew point control on R15 rock wool or something.

    1. William Hedberg | | #3

      The house was built in 1879 and sits atop a rubble foundation. The sills are 6x6 rough timbers and the first floor studs are framed off the sill. Quite impressive how level the foundation is after all these years. There's even a granite column in the basement which has not sunk. The "new windows" are replacement windows that were installed long before I purchased the house. They are made by Paradigm and were manufactured in 2006. I did pull the interior stops. The jambs have previously been cut open to access the weight, and the weight pocket contains some loose fill in it along with the weight. Should I suck out as much of the cellulose in the pocket, remove the weight, and fill with foam?

      There was some serious termite damage to the floor framing in the living room. With the boiler sitting bellow and a sea of steam pipes running beneath I chose to pull up the two layers of subfloor to repair from above. I felt complete removal of the joists would rob the house of some of it's character and dishonor the men that built it so I decided to sister up 2x8 to the old rough 3x6s (24OC) and dropped a new joists between the originals. To fit the 2x8 joists I set them flush with the top of the first layer of original subfloor then laid 3/4 Advantech for the subfloor. I'm doing this to the whole first floor (2/3 complete).

      I suppose I should have asked some questions before I came up with the idea to keep the plaster bc it's in such good condition, and that encapsulating the basement and crawlspace was the best choice. So far in the crawlspace I've laid 10 mil poly over the floor of half. Now the rubble foundation is much more irregular on the interior than in the basement. My plan for the walls was to secure strips of the poly to the wall with XMAS tree fasteners then seal it to the stone with polyurethane adhesive sealant. Lap the wall poly under the floor poly and tape that seam. Tape/seal around support posts and all other penetrations. Now the crawlspace under the kitchen will be the most complex to seal as there's some giant boulders in the middle of the space of which the old chimney was built off of and the second girder is shored off of. The biggest one is only partially uncovered and could easily be bigger than a car. There are a few smaller ones between the size of an oven and trash can. The perimeter is dirt. I'll get some pictures of that space soon. I was planning to continue this encapsulation method into the basement. Like Dana noted the sills will not be air sealed by my encapsulation methods. I will note there is mortar stuffed tight against the bottom of the sill.

      The basement has a 2" slab poured where the stairs come down up to the boiler and electric HW tank, approx 10x10. Should I chip this up so I can get the poly to run under this area? I've been considering to then repour the basement, mainly to protect the poly from the inevitable foot traffic to service the boiler or electric panels.
      I've added a few pictures, will add more in the near future. Also I will be closing off the two vents/windows in the basement.

  2. Trevor Lambert | | #2

    Did you test for and confirm asbestos in the vermiculite? If not, thehe's no point in remediation and it would be a colossal waste of money.

    1. William Hedberg | | #4

      Sending sample to Zonolite, but am anticipating it to come back positive

  3. William Hedberg | | #5

    One fun fact (though unrelated to green building) is Emma Borden, sister of Lizzie Borden, used to live at my house

  4. Expert Member
    Dana Dorsett | | #6

    If you're going to pour a new slab you can put sheet polyethylene over the rat slab and pour over it rather than breaking it up .

    With a non-structural slab floor it's still possible to build a non-structural 2 x 4 on top of it an inch or two away from the rubble foundation and install enough closed cell foam to meet the exterior side stud edges, and put batts in the stud bays.

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