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Community and Q&A

Remodel in southern NH

chiefsilverback | Posted in Energy Efficiency and Durability on

Having started down this path in RI a couple of years ago and pulled the plug we’re now about to purchase a 1600 sq/ft gambrel style home in southern NH and do some remodelling.

It’s a 1986 construction, 2×6 exterior walls (presumably with batt insulation), original wood framed double pane windows, vinyl siding, oil fired baseboard heat, no A/C, electric hot water. I’m planning a phased remodel, starting with re-doing the kitchen and half bath on the 1st floor as soon as we get the keys.

The oil boiler is a 2 year old, 86% efficient unit so I have no intention of touching that. Electric water heater is getting a bit long in the tooth so I will likely look to replace that with a 50 gallon Geospring and benefit from any rebates/credits that are available.

I don’t have any numbers for heating costs, and any that might be available would be from an elderly couple who used to live in the property and therefore might be significantly higher than an average family? We will add a wood burning stove which will be located on the 1st floor with the stove pipe exposed to the room and exiting through the west facing wall towards the ceiling in order to maximise the heat generated.

On the 1st floor I want to add a window on the west facing wall to bring light into the new kitchen, replace the existing french style patio door with a slider and then replace and simultaneously relocate 3 windows on the north facing wall overlooking the back yard. I just got a quote for Intus windows and they seem pretty reasonable given the performance numbers, although I might have to forego my plan to add a door from a newly created mudroom to the back yard given the Intus quote of over $3000!

A couple of questions I have for right now:

1. Would it be worth taking down the dry wall on the exterior walls where I’m remodelling to replace the insulation, or would I be better served looking to apply a layer of rigid foam to the exterior at some point in the future?

2. The french door on the north wall that I want to replace with a slider opens into a three season room that is glazed on all sides (3′ south facing, 12′ west facing, 16′ north facing, 12′ east facing) and has actually been quite warm when we’ve viewed the property over the last couple of weeks. To that end my assumption is that I don’t need to worry quite as much about the performance numbers for the slider because it is already sheltered from any direct wind, doesn’t receive any direct sunlight, and benefits from solar gain due to the south and westerly glazing. Am I making the proverbial “ass of u and me” with my thinking?

Any thoughts on those two items would be greatly appreciated.



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  1. Expert Member
    Dana Dorsett | | #1

    It's worth at least some IR imaging of the walls during blower door pressurization/depressurization before committing to rip out the wallboard and start over. That will give you a sense of how well the existing insulation was installed and is holding up over time. If you are planning to re-side, in most cases you'll get a lot more bang/buck out of insulating sheathing than re-doing the cavity insulation. If there are gaps in the cavity insulation it can often be spot-insulated with blown fiber drilling from the exterior, and for a lot less money than a full-gut rehab & replace from the interior.

    When installing the insulating sheathing, if it's going to be foam make sure that it's a sufficient amount for dew point control at the sheathing layer. If there is a pre-existing polyethlene vapor barrier it's advisable to give yourself a LOT of margin over the IRC prescriptives- R5 for climate zone 5, R7.5 for zone 6, depending on which side of the line you're located, or use rigid rock wool, to ensure adequate drying capacity toward the exterior. If you're not sure if you're zone 5 or zone 6, find your county on this map:

    The greenest rigid foam out there is reclaimed/reused foam, and there are multiple vendors in our region selling at a fraction of retail-new.

    If the wall cavities are leaking scads of air under blower door testing it may be worth dense-packing over the crummy R19s from the exterior even before re-siding as a tightening measure.

    Don't neglect the basement, especially if that's where the oversized oil-fired beast is located (and it IS oversized, guaranteed!), even if you never plan to finish the space. With an air tight and insulated foundation the standby & distribution losses accrue to the heat load of the house. In most cases the basement will idle along in the 50s prior to insulating, but rise to the mid-60s after insulating, and even with the higher basement temperature the basement losses will be cut by something like 90% or more. This is another place where you can save a ton of money by using reclaimed roofing foam. Insulating & air sealing the basement typically cuts 10-25% off the oil bill.

  2. chiefsilverback | | #2

    Thanks Dana. We're in Hillsborough country so zone 5.

    What are the rules for insulating a basement if you're not finishing it? Can I just glue up rigid foam, and maybe hit the rim cavities with a DIY spray foam kit, or would I also have to put up dry wall as a fire barrier?

  3. GBA Editor
    Martin Holladay | | #3

    Dana gave you good advice on the wall insulation and basement insulation.

    It's a very bad idea to try to vent a wood stove horizontally through an exterior wall. That method guarantees that your flue will be cold (and subject to creosote accumulation) and difficult to clean. Instead, run your metal chimney straight up through the roof.

    To my mind, replacing French doors with sliding doors is backwards. Usually we recommend that homeowners replace sliders with French doors, because sliders have bad weatherstripping and lots of air leakage problems.

    -- Martin Holladay

  4. chiefsilverback | | #4

    Thanks Martin. The current french door is the original wood frame from 86/87. Per my first post, my logic regarding the slider was that it's already somewhat protected from the weather by the 3 season room. The existing door is still in good shape so it might be better to refresh the weather strips etc... and leave it as is.

    With regards to the stove pipe, it's a 2 story house, so to take the pipe through the roof would require taking it through one of the bedrooms. I actually quite like this idea as it would serve as a heat source for the second floor, but I would worry about it over heating that space and making one of the rooms unusable?

  5. Expert Member
    Dana Dorsett | | #5

    If you used fire rated polyiso (Dow Thermax) you might not have to install a thermal barrier against ignition, but in terms of total cost it's probably going to be cheaper to install 2-3" of reclaimed roofing polyiso held in place with 1x4 furring through-screwed to the foundation, hanging the half-inch wallboard on the furring, or trapped to the wall with a 2x4 studwall.

    It takes 3" of polyiso to hit IRC code minimum performance, but if you use a studwall you can go with as little as 1" of polyiso + R13s (unfaced or kraft faced, but not foil) in the framing to hit the same thermal performance at low mold risk. But reclaimed foam is often cheaper than batts (!). (I did 3" polyiso + furring in my own house.)

    The band joist & foundation sill needs at least 2" of closed cell polyurethane, so you're probably looking at 1000 board-feet of foam or more. DIY kits are usually more expensive than having a pro do it once you're over 600 board-feet, and the quality of the installation is usually better, since they have the precision temperature control & mixing on the chemicals that you just can't get with a DIY kit, and much higher quality spray guns. The spray foam should be continuous from the subfloor down to & over the top of your wall-foam, so put up the wall foam first.

    With polyiso you need to keep the bottom edge off the slab or it can wick ground moisture. If you take the studwall approach, cut strips of 1-2" EPS to lay on the floor extending from the foundation wall to under the bottom plate of the studwall as a capillary & thermal break for the wood, otherwise the cool bottom side of the bottom plate will take on moisture during the summer.

  6. GBA Editor
    Martin Holladay | | #6

    If you run the chimney vertically, you won't be using stovepipe. You'll be using a metal chimney; most brands are double stainless-steel pipe with insulation between the two pipes. (Most brands of stovepipe are single-wall steel pipe.)

    Because this is an insulated metal chimney, there is no reason to believe that the chimney will cause overheating in your upstairs bedroom. But you can box in the chimney if you want, installing mineral wool insulation between the chimney and the box, as long as you maintain any clearances required by the chimney manufacturer.

    -- Martin Holladay

  7. chiefsilverback | | #7

    With regards to insulating the basement, what about the floor, is it necessary to insulate or do I only need to worry about the walls?

  8. GBA Editor
    Martin Holladay | | #8

    Insulating your basement slab is not required by code, but it's a good idea -- especially if you intend to convert the basement to finished space.

    For instructions on insulating an existing basement slab, see Fixing a Wet Basement. Scroll down until you find the paragraphs under the subhead that reads, "Insulating an existing basement slab."

    -- Martin Holladay

  9. Expert Member
    Dana Dorsett | | #9

    In southern NH the subsoil temps are about 50F, and the summertime outdoor dew points (and ventilation air dew points) average north of 65F. With an uninsulated slab, anything resting mold susceptible on the slab that has any significant insulating characteristics (such as a cardboard box full of stored goods, or a rug, or a wood subfloor) will be at high risk of developing mold. But with as little as R4 on the floor (an inch of EPS) mitigates that risk almost completely, but long term even R8 (2" of EPS) is rational on heating energy savings alone, and mitigates it even further.

    The other way to mitigate the problem it is to run a room dehumidifier to keep the dew point of the basement air bounded in summer, but that can easily to burn through 300-500kwh/year, sometimes more. At 18.5 cents /kwh (the NH state average) 500 kwh that's about $90/year that you wouldn't have to spend if the slab is insulated.

    Insulating the slab is part of the equation for avoiding a basement that SMELLS like a basement. At reclaimed foam pricing 2" of reclaimed EPS or reclaimed XPS would come in between 25-50 cents per square foot, about the same as only 3/4" of crummy Type-I R2.9 EPS at box store pricing.

  10. chiefsilverback | | #10

    Thanks Martin. I don't have plans to finish the basement, so this would purely be for improving the efficiency of the envelope. The basement was retrofitted with a 'dry basement system' a few years ago, I think using the WaterGuard drain system, so I'm wondering if that would impact the insulation design for the basement?

    The WaterGuard drain includes a channel to allow and seepage through the walls to run down into the drain. Would I need some kind of dimple mat on the walls before I put up my first layer of foam?

  11. GBA Editor
    Martin Holladay | | #11

    The WaterGuard system appears to be a type of interior French drain (see photo below). With that type of French drain, it is a good idea to install some type of dimple drainage mat between the concrete wall and the rigid foam.

    -- Martin Holladay


  12. user-228058 | | #12

    With your oil heating system and a perimeter slab drainage , make sure you have a sound oil tank. A failure of the tank would put the heating oil right in the ground. ( assuming you have a basement tank here)

  13. charlie_sullivan | | #13

    If you haven't already done one, I recommend a radon test, as that drainage system might also provide a good entry path for radon.

  14. chiefsilverback | | #14

    Thanks for the responses Martin, Scott and Charlie.

    Scott - The tank is located on a crushed stone 'drip pan'. I will have to take a look at it more closely when we close, I'm not sure if it was installed as part of the dry basement system and is designed to hold 250 gallons of oil in the event of a total tank failure? From memory the interior french drain goes around the tank, rather than behind it. That said it might be worthwhile investment to have a new tank installed and not have to worry about it for a couple of decades!

    Charlie - we had radon tested as part of the home inspection and the concentration is 0.8 pCi/l.

  15. Expert Member
    Dana Dorsett | | #15

    Radon decay emissions of 0.8 pCi/l is about the same level the OUTDOOR air in many parts of New England- not sure I'd trust that data point on an indoor air reading in the Granite State. (Maybe out in the garage with the garage door open?)

  16. chiefsilverback | | #16

    Hi Dana - That was the average over a 77 hour test in the basement with a Radalink monitor that was last calibrated 12/29/16. The readings range from 0.2 to 1.8 pCi/l.

    It also tells me over the same period that the basement averaged 56.7F and 36% RH, with highs of 59/44 and lows of 55/30.

  17. chiefsilverback | | #17

    I'm trying to workout which blower to pair with the downdraft range hood I'm installing. The options are 280, 600, 800 or 1100 CFM, with the ability to vary the blower power. I'm inclined to think the 600CFM unit would be powerful enough, especially as I do most of my 'smelly' cooking outside on the grills.

    The 800 CFM unit is $150 more than the 600CFM, and the 1100CFM another $70 on top of that, so is it worth having the extra power available (make up air to be addressed as building envelope is tightened), or is 600CFM more than enough for a residential kitchen?

  18. user-2310254 | | #18

    The ASHRAE guideline is 15 cfm per 100 square feet of occupied space. See Martin's article for additional details:

  19. chiefsilverback | | #19

    Hi Steve,

    Thanks for the link, I recall reading through many of those a couple of years ago. Correct me if I'm wrong, but the 15cfm/100sqft is the limit before you need to be concerned by backdrafting and makeup air isn't it?

    The house we're buying is ~1600sq ft and we'll likely add another ~400 over the next 2 years. So we're somewhere between 240 and 300 cfm before makeup air becomes a concern. In his post Martin recommends between 150 and 250 for the exhaust hood, so the 600cfm blower would give me plenty of 'extra capacity', and I can just set the control back to 1/3-1/2 for regular use.

    I was thinking about a makeup air solution that would see the exhaust duct enclosed by the intake duct (think an 8" duct inside a 12 or 14"). I think I might have read about a similar concept for a dryer vent on this site? I wonder if it would have any meaningful benefit?

  20. Expert Member
    Dana Dorsett | | #20

    A 3 day "radon" test is really worthless, and wouldn't be accurate to even one significant digit, independent of the number of digits displayed, no matter how recently it was calculated.

    For such a short test period it's basically a "Yup, there's some flux of alpha particle emissions happening here, at least right now", but may not even get the order of magnitude correct relative to average emissions over the course of a year.

    If it had been integrating and averaging the radiation rate continuously since 12/29/16 (the calibration date) until the past week the number would be more meaningful.

  21. chiefsilverback | | #21

    Dana - would you recommend a 90+ day test then? Unfortunately when you're buying a home the 'industry standard' for radon testing is the three day test as recommended by the EPA.

  22. Expert Member
    Dana Dorsett | | #22

    If a 3 day test showed 50 pCi/l it might be meaningful, though not accurate. When indicating low single digits it's pretty meaningless- it's in the noise. The EPA residential radon testing protocol (= industry standard) is really pretty crappy, and would be laughed out of the room (or not so-laughing: thrown out of a COURT room) if used in an OSHA compliance environment. It was designed to be cheap (and it is).

    There are a few easy ways to "beat the test" with that type of detector (none of which I'll go into here, since I don't want to encourage house sellers to commit that fraud), but when the numbers are 0.2 to 1.8 pCi/l, (the same range as outdoor air,) it shouldn't be accepted at face value, especially in a state with so much radioactive granite for bedrock. Most homes in southern NH will test between 2-4pCi/l indoors prior to any mitigation, according to this map, which would make yours a real outlier, if validated:

  23. chiefsilverback | | #23

    We closed on the property last week and we've demo'd the old kitchen, and here's the existing batt insulation. I'm moving the location of windows, so obviously I'll re-insulate as required, but do I need to replace the bulk of it, especially as my plan is to do an exterior layer of rigid foam at some point?

    On the subject of the exterior, it turns out we've got vinyl siding over the original wood. What are the recommendations for preparing the new window openings given that scenario? Remove the vinyl, cut back the wood, prepare as normal and then replace both layers?

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