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Tightening up a 1949 mid-century modern

I just bought a really cool 1949 mid-century modern 2200 s.f. split-level home in the Chicago area (Zone 5) and will be doing a bit of work to it. The work to the exterior consists of all new siding - cement fiberboard and cedar siding set over the existing sheathing as a rain screen on 1x4 furring strips. I will be adding 1 1/4” extruded poly where the cement fiberboard is going, and for aesthetic reasons, adding 2” extruded poly where the cedar siding is going. I will cover the sheathing with the a WRB. New orientation specific Integrity Low E windows will be set as ‘outies’.

I haven’t been able to verify what the existing insulation is (I don’t close on the property until June 20) - I will check this right aware. I believe the walls are 2x4’s and I am betting there is 2” thick fiberglass insulation with either a kraft face covering or a petroleum coated kraft face of some sort. If that is the case, I think I would be creating a double vapor barrier. Should I use expanded poly instead of extruded? I have read through many of the GBA articles and haven’t seen this come up.

Because the house will be significantly tightened up, I will be doing a few things to the mechanical system. The home is an open split level plan, meaning the air flows easily from the 2nd floor to the main level and across to the lower level. The mechanical system is a gravity flow - the furnace is in the lower level in a room that is all angled wood louvers on one side, and basically all of the supply air flows down to the lower level. There are no supplies in the lower level. This was apparently not uncommon in the late ’40’s.

I am adding a new sealed combustion/direct vent water heater and at this time keeping the existing gas fired furnace but connecting the outside combustion air supply. I will add an Air Cycler system to bring in fresh air. The exhaust hood in the kitchen is variable to a maximum of 300 cfm. The bathroom exhausts are in the 60 to 110 cdm range. What I would like to do is interconnect the Air Cycler to the kitchen exhaust so the fresh air is being supplied into the home in a more balanced way when the exhaust hood kicks in.

Any input would be great.

Asked by Nathan Kipnis
Posted Thu, 05/01/2014 - 11:28
Edited Fri, 05/02/2014 - 06:53

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5 Answers

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1.
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The most important item in an MCM home is the attic or roof insulation. "Foam over" is the best way to handle it.

Answered by Kevin Dickson, MSME
Posted Thu, 05/01/2014 - 13:50

2.
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Thanks Kevin. I am considering foaming over or encasing the roof rafters with 8" of open cell foam, sealed with a vapor resistant paint. The attic is currently not insulated, and (shockingly) there is hardly any storage in the house. Even though the attic is small (3'6" tall, 10' usable wide and about 40' long) it is important storage space. I will either put in vents at opposite ends of the attic to help condition it, or, as noted in a previous GBA article, install a supply and return in the attic with a smoke detector disconnect to the furnace.

Answered by Nathan Kipnis
Posted Thu, 05/01/2014 - 14:27

3.
Helpful? 0

Nathan,
Q. "I believe the walls are 2x4s and I am betting there is 2-inch-thick fiberglass insulation with either a kraft face covering or a petroleum coated kraft face of some sort. If that is the case, I think I would be creating a double vapor barrier."

A. No, you wouldn't. Kraft facing is only a vapor retarder, not a vapor barrier. If you add at least R-5 of exterior rigid foam to a 2x4 wall in your climate zone, you'll be fine; the kraft paper won't cause any problems.

Q. "Should I use expanded polystyrene (EPS) instead of extruded (XPS)?"

A. Yes, if you care about the environment. To learn why polyiso and EPS are preferable to XPS from an environmental standpoint, see How to Install Rigid Foam Sheathing.

Q. "What I would like to do is interconnect the Air Cycler to the kitchen exhaust so the fresh air is being supplied into the home in a more balanced way when the exhaust hood kicks in."

A. Considering the age of your house, and the leakiness of the building envelope, I believe that you are overthinking this. It's tricky enough to properly program an Air Cycler and to commission the system so that you aren't overventilating or underventilating. Trying to come up with relays and programming systems to integrate a range hood fan is an approach that is ripe for screw-ups. After all, there are many cases to consider: (a) Range hood fan off, furnace running, no need for ventilation. (b) Range hood fan on, furnace running, no need for ventilation. (c) Range hood fan off, furnace not running, no need for ventilation. (d) Range hood fan on, furnace not running, no need for ventilation. (e) Range hood fan off, furnace running, house needs ventilation.... and so on. (I'm not done yet.) With these three variables, there are 27 modes of operation.

Answered by Martin Holladay, GBA Advisor
Posted Fri, 05/02/2014 - 07:10
Edited Fri, 05/02/2014 - 07:12.

4.
Helpful? 0

Martin, thank you for your answers. I do believe that I will be getting the home very tight. New exterior insulation boards around the entire house, new Integrity low E windows, and foaming the roof. The floor are above the garage is being insulated as the wall be between the house.

Anyway, I think the only condition I am interested in for the Air Cycler is 'on' when the kitchen exhaust is on. I understand it is not optimal, but I think the 300 cdm draw in this smaller, tighter home might be an issue. I did speak to someone at Air Cycler, and they said this is getting to be a common request and that they are working on providing a product for it.

Answered by Nathan Kipnis
Posted Fri, 05/02/2014 - 08:42

5.
Helpful? 1

Nathan,
If you have talked to the people at Air Cycler, and they can provide a solution that works, you are all set.

Answered by Martin Holladay, GBA Advisor
Posted Fri, 05/02/2014 - 08:55

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