Replies

1. GBA Editor
   Martin Holladay | Aug 10, 2016 03:33pm | #1

   Rick,
   Q. "Does anything in my [attic air sealing and attic insulation] plans pose potential issues down the road?

   A. No.

   Q. "Referring to the overhang soffit: I'm thinking I need to build a dam here in order to keep the cellulose from spill over onto the soffits. If that's the case, should that barrier go all the way to the rafters, leaving only space for the baffles?"

   A. Yes. The dam extends from the exterior wall top plate to the underside of the ventilation baffles. For more information, see Site-Built Ventilation Baffles for Roofs.

   Q. "Since I'm removing the insulation, is it all right if a little time passes before the new insulation is installed ?"

   A. Yes.

   Q. "If I choose a ducted [heating and cooling system] and put [the] furnace in [the] basement, would it be all right to blow cellulose over the already insulated (and hopefully properly sealed) ductwork in the attic?"

   A. It would probably be all right, especially if the ducts were carefully insulated before the cellulose was installed. However, if you install uninsulated galvanized ducts under deep cellulose, it's possible to get condensation on the ducts during the summer. Insulated flex duct with R-8 or higher insulation (and obviously, with a plastic jacket) is less at risk of condensation. If you want to install galvanized ducts, the best way to install insulation on top of the ducts is to cover the ducts with closed-cell spray polyurethane foam.

2. Expert Member
   Dana Dorsett | Aug 10, 2016 03:50pm | #2

   You're making too much work for yourself.

   If you have R19 (likely)- R30 (if you're lucky) in the attic under the plywood, just leave it all in place. You can probably air seal the plywood decking more easily than what's that's below it, and as long as the new insulation is at least 40% of the total R, the existing plywood deck will have adequate dew point control. The plywood deck would be great support for going very high R if you wanted to, whereas 46 year old ceiling gypsum may not handle the additional weight well.

   It may even be possible to dense-pack cellulose over the existing insulation by drilling & blowing the plywood before air sealing it, which would tighten up any residual thermal by pass paths, but if the exising insulation is full-depth in the joists it's probably not worth bothering. A 2x10 joist full of lfiberglass batt is good for about R28-R30, but dense packing it with cellulose would bring it up into the R32-R33 range. If the ceiling gypsum is questionable for dense packing, a low density "2-hole method" fill may be worth it (and DIY-able) if the existing insulation is R19s in 2x8 or 2 x10 joists with a big air gap between the fluff and the plywood.

   At the eaves, build the insulation containment barrier roughly above the wall sheathing, and bring it all the way up to the roof deck's ventilation baffles.

   As for the HVAC upgrade, it's likely that this house can be heated with 3-tons or less of multi-split, and you can use floor units for the bigger open areas where wall-blobs would have aesthetic issues, and mini-duct cassettes in the backs or ceilings of closets to split the output between multiple low-load rooms. This would be far preferable to punching holes in your nicely air-sealed and insulated attic floor. Even at CT type electricity rates and this year's lower propane prices it'll be a lot cheaper to heat with mini-splits than with propane.

   Burying ducts in cellulose is a potential problem during the cooling season, since NE CT outdoor dew point averages are in the 60s most of the summer, and insulating over the ducts by more than an inch or two would lower the surface temp of the ducts to below 60F while the AC is running. That would cause moisture to accumulate in the cellulose along the ducts over course of the summer, which may reach problem levels. Deep moisture cycling of the cellulose would also cause the cellulose to settle substantially along those paths too.

   How is the foundation wall insulated below grade (if at all)? In 1970 it was common to have nothing insulating the foundation on a raised ranch, with a 2x4 / R13 studwall starting at the top of the foundation, even if there was 2+ feet of above grade exposure on the foundation. If that describes your house, some remediation is warranted.

   Many raised ranches have the upper floor cantilevered out from the lower level, often with no air dams and little or no insulation between the joists in the cantilevered section, which is often a huge air leak.

   If you have some mid-winter power bills and a May or September power bill for estimating baseline non-heating related power use it's possible to use your power use numbers between exact meter-reading dates to get a good handle on your real heat load on the as-is condition of the house (pre- upgrades.)

3. Expert Member
   Dana Dorsett | Aug 10, 2016 04:29pm | #3

   It should go without saying, but...

   ...before settling on any new heating system it pays to run a room-by-room Manual-J type heat load calculation on the "after upgrades" condition of the house, which will give you a means of making intelligent equipment choices. Most HVAC contractors in our area use some ridiculous rule of thumb- most commonly:

   "Lessee, 25 BTU/ft time 3000 feet of space gives ya 75,000 BTU/hr, so let's make it 100K just to be sure."

   Some contractors in southern New England even use 35 BTU/ft for anything built with 2x4s. These methods lead to RIDICULOUS oversizing factors, which leads to higher upfront cost and lower comfort (and with heat pumps & boilers, lower efficiency to boot.)

   The REAL heat load of a typical tightened up 1500' + 1500' raised ranch will come in at around 28-33,000 BTU/hr @ 0F, not more, assuming it has at least some foundation wall insulation, maybe as high as 40-45K with an uninsulated foundation (depends).

   And that's at 0F. Even coldest 99% outside design temps in CT are still in positive single digits, and in NE CT they're a bit north of +5F, which means your design heat load would be even a bit lower once its all tightened up.

   http://articles.extension.org/sites/default/files/7.%20Outdoor_Design_Conditions_508.pdf

   https://www.captiveaire.com/catalogcontent/fans/sup_mpu/doc/winter_summer_design_temps_us.pdf

   Using a power use heat load calculation on the "before" picture puts an upper bound on the whole-house load, but doesn't tell you what the room loads are. For a sketch of how to go about running those numbers, see:

   https://www.greenbuildingadvisor.com/blogs/dept/guest-blogs/out-old-new

4. 
   RickRock1202 | Aug 10, 2016 05:57pm | #4

   Thanks for the reply. The help is really appreciated! A few questions in response to your Answers…

   You're making too much work for yourself.
   >>>I don't mind the challenge if its worth it in the long run....but if i'm wasting my time and getting little return then it obviously doesn't make sense. I also forgot to mention that I have a whole house fan installed in the attic floor. Would that still be usable if I blew in cellulose.

   If you have R19 (likely)- R30 (if you're lucky) in the attic under the plywood, just leave it all in place.
   >>>Yes, I believe its R-19 (The ceiling joist are 2x8 on one half and only 2x6 on the the other half and those run the opposite direction.

   You can probably air seal the plywood decking more easily than what's that's below it, and as long as the new insulation is at least 40% of the total R, the existing plywood deck will have adequate dew point control. The plywood deck would be great support for going very high R if you wanted to, whereas 46 year old ceiling gypsum may not handle the additional weight well.
   >>>The plywood deck is not screwed down. What would involved in air sealing the deck? Also if I air sealed the deck would running batts in the opposite direction of the previous batts under the deck be an option as this would surely be easier?

   As for the HVAC upgrade, it's likely that this house can be heated with 3-tons or less of multi-split, and you can use floor units for the bigger open areas where wall-blobs would have aesthetic issues, and mini-duct cassettes in the backs or ceilings of closets to split the output between multiple low-load rooms.
   >>>one person mentioned installing a concealed duct minisplit and branching off into the 3 bedrooms . Although they mentioned that this would be placed in the attic. And small duct runs would have to again go into the attic. IF I did this I would then be able to use the same condenser and place a wall unit downstairs to heat/cool that whole half of the downstairs. I would then possibly add a second condenser on the opposite end of the house and place one wall unit up stairs for the large LR/DR/Kitchen area and one downstairs for the other half. If I went to this extent would you still recommend Mini-Split over Ducted Propane Furnace.

   How is the foundation wall insulated below grade (if at all)? In 1970 it was common to have nothing insulating the foundation on a raised ranch, with a 2x4 / R13 studwall starting at the top of the foundation, even if there was 2+ feet of above grade exposure on the foundation. If that describes your house, some remediation is warranted. Many raised ranches have the upper floor cantilevered out from the lower level, often with no air dams and little or no insulation between the joists in the cantilevered section, which is often a huge air leak.
   >>>the foundation is on the same exterior plain as the upstairs exterior. It is boxed out and into the room covered with sheetrock. It measures just under 4’ high and comes 10” into the room. I believe there is a small amount of insulation behind the foundation sheetrock but can’t say that I’m 100% confident in that answer.

   If you have some mid-winter power bills and a May or September power bill for estimating baseline non-heating related power use it's possible to use your power use numbers between exact meter-reading dates to get a good handle on your real heat load on the as-is condition of the house (pre- upgrades.

5. 
   charlie_sullivan | Aug 10, 2016 08:51pm | #5

   Another heating/cooling system option to consider might by a hydronic air-source heat pump, such as Chiltrix. it's sort of like a minisplit, except that the refrigerant is only in the outdoor unit and the heat or cold is delivered to the indoor units by water pipes. The advantage is that you can have more, smaller units indoors, so you can put on it each room that you want to supply without needing ducts at all. Dana can help you figure out how to do it with minisplits, and that will work, but you might get tired of trying to convince your HVAC contractor to do it that way.

   The downside of the hydronic approach is that it requires some design and installation expertise that might be hard to find. But I think you are far enough north that there are people around with experience .... except that the problem with that is that people with experience have experience with boiler based systems and they might assume they know how to do it and get it wrong. They might design in pumps and tanks you don't need (Chiltrix has a high efficiency pump built in) and they are used to plumbing without insulation, which you can get away with for hot water but is a disaster for chilled water.

   On the attic, I kind of like Dana's idea of leaving the plywood there. You might even get away with leaving it unscrewed, although I would think six quick screws on each would be worth it. Then tape each each seam with high quality tape. But the details at the eaves might be tricky--depends on exactly what you've got in terms of soffits and overhangs and roof pitch and how far the plywood deck goes to the eaves. Getting the deck air sealed but leaving open leaks at the edges won't do any good--it will just channel all the air leakage to where it can most effectively create ice dams. So I think you'd need to remove the deck and insulation from the last foot or so and put in blocking in each joist bay. That's still a lot of work, but I like the concept of having the plywood to support the weight of the insulation above.

   You could use bats above that, but it's a natural place to use blown-in cellulose, so why not go with cellulose? And batts are unlikely to work well at the eaves.