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Community and Q&A

Improve efficiency and comfort of this room?

alawishy | Posted in Energy Efficiency and Durability on

Please see the 2 attached pictures of a room that I would like to improve the efficiency of. The room is between the garage and the main house. I don’t like coming in from the January cold only to be greeted by a cold room. I dislike paying the oil man even more that.

The house was built in 1986 and I am in zone 5 (seacoast NH). Right now, the 2 half walls are gone, the wood frame half of the floor is stripped down to the joists and has 3.5 inches of cut n’ cobble polyiso between the joists. I tried to create an air barrier below the polyiso using plywood, caulk, and tape between each joist. I also spray foamed around the semi-loose fit polyiso at each layer. This part of the floor is located over the ground and has only about 6 inches of clearance. There is a poly vapor barrier in place to limit vapor migration into the construction above. The original floor framing used ground contact rated pressure treated lumber that appears to still be in great shape.

The tile half of the floor sits about 5.25 inches above the wooden step down floor. The tile sits directly on an uninsulated slab. The main house has a full basement. I think half of this room shares the garage slab.

The wooden construction half was added later. At the end of this project, besides improved efficiency, I would like to have one level floor. Not too particular about the kind of finished flooring (whatever will work), more particular about not wanting a cold slab floor or the step down.

The walls are 2×4 with R13 batts. I already brought the cathedral ceiling up to code minimum. The room is currently on its own zone (oil heat). You can see 2 of the base boards in the picture. There is also a sort of kick space register out of view that is heated off the same zone. Now that you have the lay of the land, here are my main questions:

1) The uninsulated slab floor seems to be the biggest hurdle. The window for insuating underneath the slab has long since closed. Perhaps I could insulate around the perimeter by digging, but there are obstacles such as the existing paved driveway and a deck that sits too close to the ground to work underneath it. Putting insulation and sub-flooring on top is probably doable, but I have 2 doors to contend with then. The single door leading to the garage, which is in one of the pics, and a double french door leading to the front deck, which is not pictured. It seems both doors would have to raised to accomplish much as there is at most 2 inches to work with and probably less. There is also the possibility of radiant heating the floor, but I don’t know anything about the options, cost, or effectiveness for my situation. Do you agree that it will be hard to make the room comfortable as long as this uninsulated slab takes up half the floor? What would be a reasonable approach to the problem?

2) The wood framed half of the floor has at least 5.25 inches of vertical space remaining in which to add additional insulation (to get to the level of the slab). It could be more depending on where the height of slab floor ends up (question #1). What would be a reasonable approach to building up this floor while also adding additional R-value? Build another floor frame on top and perpendicular to the original? Or, forget the joists and just lay down more foam board with a sub-floor on top of the foam and timber screws through to the original joists? Something else? Also, would any of this require pressure treated lumber? Worried about the earthen crawl space underneath as well as any new wood construction that would contact (or come close to) the slab. The old plywood sub-floor is gone now, but my recollection is that it might have been pressure treated.

3) What is a reasonable way to increase the R in the 2×4 walls? I’d really like to do this from the inside even though I have read enough on this site to know that applying foam sheets on the outside is ‘better’. I was thinking of perhaps a Mooney wall approach in order to get a thicker wall, but I will not pay a contract outfit to dense pack the cellulose, so i would probably use Roxul for center cavity R, I would first seal all the bays with acoustic sealant, tape, or caulk, then add a sheet of some sort of rigid foam over the whole thing before the drywall to serve as a thermal break. However, I would certainly like to hear of a better plan, even one that calls for exterior rigid foam, assuming that you can convince me that this is a retrofit that is just as easy to accomplish for a DIYer. I would have to remove the cedar lap siding (can this be done without ruining all of it? — doubtful), and my windows and doors would no longer be in the correct spot according to the new wall thickness, right? Wouldn’t they have to be physically moved ‘outwards’ to sit flush with the new wall that might now be located 3 or 4 more inches to the exterior ?

4) What is a reasonable way to create one level floor given that the floor is built with half slab and half wood frame construction? Preferably one that doesn’t call for the cement truck.

Thank you for you input and thank you for this site. It is great.

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  1. alawishy | | #1

    Sorry, I don't see the attachments. Second try...

  2. GBA Editor
    Martin Holladay | | #2

    You have lots of questions. There is no way I can answer them all at once.

    Before providing advice, I have a question for you: If this area is heated by a hydronic heating system, and if the area has its own zone, why do you think it is cold? Is it cold because you don't want to turn up the thermostat? Or is it cold because, even when the thermostat is set to 78 degrees, the existing baseboard units and fan-coil unit can't keep up?

    Here's my advice: the only way to achieve your goals is to demolish the existing concrete slab in this area.

  3. user-2890856 | | #3

    Could you add a picture from the room with the skylight looking back to the area under the second floor ? Would be good to see the whole situation .

  4. Expert Member
    Dana Dorsett | | #4

    If you're not going to jackhammer out the slab, you may be able to insulate above the tile floor with 2-3" of foam above the existing tile, with a new subfloor above the foam, provided you don't run into headroom issues at the doorways, and can accommodate it in a code-compliant fashion at the stairs, etc.

    Framing over the existing wood floor to raise it to the level of whatever you do for the slab/tile floor works, provided that you have sufficient headroom at the low-edge of the cathedralized ceiling. The new framing doesn't have to be a fully thermally bridging full dept joist- 2x4 joists with supporting posts to keep the spans within a code-legal floor-loading spec would be fine. Blown rock wool or blown fiberglass would give you a decent thermally broken R-value for the framed floor at much lower cost than stacked foam. Blown cellulose could work too, but could be an issue if you're in the habit of upending the punch bowl during your wild parties, since it would hang onto the moisture much longer than rock wool or fiberglass- potentially long enough to get a mold colony going.

    With all-new floor all at the same level and at least R10 under it on the slab section, you can gain a lot of comfort (and some efficiency) using a Roth Panel ( )or WarmBoard ( )radiant floor solution. With the existing fin-tube baseboard convectors in the overly-tall room you're probably getting quite a bit of temperature stratification. With a radiant floor solution much of that stratification goes away, and the average radiant temperature of the room is higher, even if the average air temperature isn't. Warm feet & cool head provides more comfort than the converse. It's not cheap (and nowhere near cost effective on the very modest-if-any fuel use savings), but it's going to improve comfort considerably on a 2x4 framed house on the edge of Zone 5/6.

    If the windows are 1980s vintage clear-glass double panes, tight fitting low-E storm windows will improve both comfort & efficiency, at much lower cost than a replacement window.

    Blower door testing with IR imaging to find & fix the air leaks & thin spots in the insulation is probably going to be worth it. It's unlikely that stripping cedar siding that is still in good shape to do major improvements on the walls would be cost-effective in any reasonable time frame, but simply re-commissioning the wall bringing it up to it's designed specification can be (and may even be subsidized.) A few insulation blowing holes in the siding isn't tough to repair after fixing any gaps or compressions in the original insulation.

    If you're fully gutting walls, caulking the framing to the sheathing, and glueing 1.5"thick strips of polyiso to the stud edges, then damp spraying the now 5.5" deep cavity with celluose (or perfectly installing R23 rock wool batts), and detailing a layer of MemBrain or Intello Plus as an air barrier for the interior-side vapor retarder under the gypsum provides a better thermal break than a Mooney Wall solution, beats code-min performance (since the ~25% framing fraction is now R13, instead of ~R6.5 for a 2x6), and has far better moisture resilience than a kraft-facer or interior polyethylene vapor barrier treatment of the interior.

    If the boiler doesn't already have heat purging controls, a retrofit economizer such as the Intellicon 3250 HW+ will deliver on fuel savings (with no effect on comfort) and "worth it" even at this year's reduced oil pricing. Almost all oil boilers in New England are 2-4x oversized for their peak loads, which reduces the as-used AFUE efficiency. The greater the oversizing factor, the bigger the efficiency hit. This is due to excessive standby & distribution losses, and all too often, short-cycling ignition losses. Heat purging economizers reduce those losses by parking the boiler at a lower temp between burns, and purging the residual boiler heat into the zone before firing up the boiler on a new call for heat. And by fully purging the boiler to it's low-limit it maximizes the burn times, reducing the number of burn cycles when serving a zone that can't take the full boiler output. This can be a DIY retrofit of a ~$120-200 part, for those with electrician skills, provided you can follow the control documentation schematic of the boiler. (Many new boilers already come outfitted with smarter controls.)

    From an operating cost point of view the better-class cold climate ductless mini-splits are cheaper to heat with than 85% efficiency oil, even at 25 cents/kwh & $3/gallon oil. (And at a NH mix of power generators it would be substantially lower-carb than an oil burner too.) While that won't be nearly as cushy as a radiant floor heating solution, they improve the summertime sticky-days comfort by quite a bit, at extremely high cooling efficiency.

    A load calculation of that room would be necessary to spec either a mini-split or radiant floor solution. At the moment it looks like you have 12-14' of baseboard heating that space, which means the design heat load is under 10,000 BTU/hr even now (assuming it actually keeps up), and it's going to be even lower after upgrades. If the design heat load much under 7000 BTU/hr after upgrades, even the smallest mini-splits would be sub-optimally oversized for the loads.

  5. alawishy | | #5

    Martin and Dana. Thank you for the advice. I have a follow up question about raising the sunken floor. The floor is currently stripped to the studs along with the rigid foam that I cobbled into each stud bay. I was planning on building a new 2x4 16OC floor perpendicular to the original floor and then laying a subfloor and finished floor to match the height of finished slab side floor. Dan tells me that I don't need a fully framed 2x4 floor as this adds unnecessary thermal bridging. I agree, but this might still be the easiest way for me to build it seeing as I am not a professional builder. I think this plan works, at least in theory. However, upon closer inspection, I can now see that the original floor joists and ledger board are pretty far out of level from front to back and from side to side. Right now, if my new floor was to sit flush on the high spot of the old floor framing (which happens to be in one corner where the outside (rim?) stud and ledger board meet), the opposite corners would need about an inch of shimming material to bridge the gap between new 2x4 stud and old 2x8 stud. Given these conditions, will shimming at all of the old/new perpendicular joist intersections even result in a stable floor (aside from the huge PITA factor). What shimming material(s) work over such a large gap? Do I have to worry about shrinkage if I was to use wood shims of some type (plywood, ripped 1x, etc)? Is there a better way forward given how far out of level the old floor is? By better, I mean maybe more rational, but not at many times the cost?
    Also, you may not believe this, but it looks like they framed in this addition by incorporating what used to be the outside wall of the garage. So, what was once detailed as an exterior facing wall surface of the garage is now the inside wall surface of the addition. They covered the OSB exterior sheathing with drywall and left the kraft facing of the insulation on the garage side instead flipping it to the 'new warm side'. There is no poly in the 2x4 wall, just the fiberglass. They then built a floor, 2 new walls, and a roof to finish off the addition. From what I can see through the fairly small hole I cut through the drywall and OSB, their is no mold or rot in the wall, but it seems wise to address this now that I have half the room torn up anyways, no? Or, is this really not as big of a deal as I am thinking, even if unprofessional?

    Thanks again for your advice.

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