[OceanStateTunin]

Hey guys, I am trying to reduce my carbon footprint as much as possible and use my Mini Split A/C units with my Solar panels to heat/cool year round without having to use backup oil if possible. To do this I know I need to better insulate. I have a 1920s house with blown in Cellulous insulation currently. Windows were all replaced within past 5 years with Low-E. My original plan was to gut one floor at a time, spray foam and possibly double stud to eliminate thermal bridge then fill that with cellulous.

After some thought and running some numbers that project just keeps getting pushed further and further back. My wife hates our current walls (horse hair plaster with wall paper) and wants a new kitchen asap. So I got to thinking more practical ways for me to make her happy and make me happy with our R value of the walls. First thought was to put 2-4" of foam board on the outside of the house then just drywall over the inside to hide the horse hair. PROBLEM with this is I did the siding on the house not to long ago and would have to redo everything because now the house would be bigger and that is a huge project right there that I really do not know if I can tackle that this year.

Finally I THOUGHT I came up with a great idea as I have seen it before, 2" foam board over all my plaster then drywall over that, I would be adding an R10 to my wall, eliminating the thermal bridge of the studs and the wife would get the drywall she wants. I started pricing it out and liking what this option will cost me but then I started thinking of condensation and mold issues with having essentially a thermal barrier on an inside wall. Now I do not know much about this but I feel like this would be an easier way to create moisture in the walls then other insulation methods. Am I wrong? Will I have issues doing it this way? Suggestions? Recommendations?

 

[Windows on Wash]

Where is the home and what is the exterior finish. Foam board across the studs presents some issues that might create unintended condensation problems.

 

[Bud9051]

Hi OST and welcome to the forum.

The best way to begin this process is to evaluate where you are losing the most heat and the way to do that is with some heat loss calculations. Before your mini-split was installed they should have done a manual "J" calculation which would give you a room by room answer??

The foam followed by a double stud wall is expensive and the return is not that impressive beyond a basic thick wall. But we can show you how to do the saving calculation for each improvement.

Adding foam board over your plaster is possible, but requires all electrical boxes to be adjusted, new window, door, and baseboard trim, and some door swing issues resolved. And as Windows said, leaving the plaster in place may be a problem with moisture.

Your number one first step should be air sealing. It is the least expensive with the greatest return and should always be done before other improvements.

What's in your basement, any insulation, finished or unfinished?

Bud

 

[OceanStateTunin]

I am in Burrillville, Rhode Island (Ocean State)

I am a DIY'er and own a few houses (rentals), I currently have 9 mini splits I installed my self at different places but they are most just used for AC and cool weather heating so yes this 15RLS3H will be installed by me on my first floor. Currently during the summer I use a 8000 and 5000 btu window unit and it keeps it nice for us. First floor is 28x32.

I had requested a Manual J from a few contractors when I was getting Geothermal quotes ($32k+) And a few guys told me I needed a 3ton unit for my whole house (2 story) and one guy said a 4ton, No one seemed educated or willing to do an actual manual J. I attempted to do one a few years ago but the numbers I came up with made no sense. I would like to hopefully use the mini split full time but I will be keeping my Oil heat as backup but before using that I do have a Pellet stove I used to heat all last year and the year before (25-PAH) that is located on the other side of house where the mini split is going, I assume will only have to use that on the cooler days or at night. My pellet stoves output is "11,000*BTU/hr*–*25,000*BTU/hr" and it has a 120lb hopper so It can go for about 3 days at a time. I have never turned it up past the 1-1 setting (low). My goal for the mini split is to run it full time and if its getting cool I can run the pellet stove BUT I really want to try and stop using the oil and get some use out of my 5kw solar array (So the wife will let me add more ) Anyway no I do not have a official manual J BUT with my heating options I do not think that it is really necessary as I am keeping the pellet stove and oil boiler; for now.

My exterior walls of the house are vinyl sided, house was built in 1920 and has blown in cellulous. I did fan fold on 3 walls that I can remember, I can not remember if I did it on the first wall I sided as it took me a while to do, I'm sure I did but just question myself.

My basement is semi finished, it is studded and drywalled all around, only one side is painted, I had insulated YEARS ago with fiberglass bat insulation. I intend to gut this again at some point and go to foam board but it is on the bottom of the things to do as the wife needs her new kitchen. Basement is made of Field stone, little over 7 foot of head room, I cemented the floor a while ago. The oil boiler is down here and so is my heat pump water heater (I switch it to full electric mode come December) I do have a wood stove in the basement that I burn in when I am feeling ambitious, usually always have a few cords split and ready although this winter I only burned a few logs. I get a lot of free wood and own a log splitter So I usually keep at least 3 cords and give the rest to my neighbor but like I said I don't burn unless I am bored or if I just want to take the extra chill off and sit in front of it.

I have done my best with air sealing but I am sure I have a few leaks, I know my entrance doors leak a tiny bit as one is warped but that would be part of the new kitchen.

I never thought about door opening issues with going with thicker walls, I would have to address that with my new doors. Molding and stuff the wife wants to change to the more modern smaller, commercial style molding as she hates the big molding an older house like this has so that is not an issue.

 

[Bud9051]

Although the manual J is the most recognized it isn't entirely necessary to get a basic idea as to what doubling a wall r-value will save. The link below is a basic heat loss calculator where you can enter different r-values and see the improvement. I downloaded the programming to make it easier, Gary is very helpful.

Air sealing is far more than a few leaks you can see. The ones you can't see can add up to a small window being open 24/7. Another link below for air sealing.

https://www.energystar.gov/ia/partners/bldrs_lenders_raters/downloads/TBC_Guide_062507.pdf

http://www.builditsolar.com/References/Calculators/HeatLoss/HeatLoss.htm

Bud

 

[OceanStateTunin]

I either am very stupid or just put in the wrong numbers but I can not do a Manual J


Back onto my original question, I don't care if the unit will not supply enough heat as I have my other sources I use. Will Foam board on the inside of the house cause mold issues do to sweating and such or will it be fine?

 

[joecaption]

Mold issues aside there's lots of other possible issue's going on if that home was built that long ago.
Main one being possible balloon wall framing.
If so those walls are open from the basement to the attic unless someone has fire blocked them at some point.
If it was blown in insulation done years ago through holes made in the outside siding it long ago has settled under every window opening, lot of spaces where missed because they where working blind.
Most older homes had diagonal bracing in the outside corners and I've never once when pulling down the old plaster seen that area filled.
When those old windows where replaced did anyone remove the casing and fill the huge empty voids on the sides where the weights where with insulation?
The right way to have addressed the insulation and old wiring issues would have been before the new siding was installed.
That ship has sailed.
What I've done many times when working for at least 15 years on 100 plus year old is remove all that old plaster and lath, up date the wiring, add fire blocking, insulate, string the walls to see how flat they are, shim or sister if needed then drywall.
Doing it your suggested way would be far more expencive, effect all the outlets, and any window and door openings and you would never live long enough to see a pay back time.

 

[OceanStateTunin]

I did spray foam in the basement sill areas with those DIY kits last year.
I did remove all the weights from the windows when I did them and filled with foam (I scrap and wasn't loosing all that heavy iron!)
Wiring is all newer Romex but I have no problem ripping it out and rewiring, I do not like my outlet placement/lack of outlets.

I really do not want to pull down the old plaster, I have done that too many times in my rentals and it sucks so I am either going over everything that is there with 1/2" drywall to cover it. OR spending the $520 for 2" Foam board to go under my 1/2" drywall. (Only doing kitchen and bar room for now, it is $520 for the foam, obviously a bit more for some pine to build window casings out but the trim is all being replaced anyway. So adding the Foam will run me somewhere in the 600-800$ range ontop of my current project.

If I start pulling down plaster that will turn into a full gut/spray foam/new floors/bunch of other stuff and the project will have to be on hold for a while, was just hoping to be able to give my wife her new kitchen sooner then later and will hate to put up all the drywall kick myself later on for not adding insulation.

 

[OceanStateTunin]

Not trying to sound like I don't want your guys info, I do. I can either make this happen or were gonna have to wait another 3-5 years if I wanted to do a gut/spray foam. Wife has been asking for a new kitchen for a while now and for the mini split to be installed on this floor so now would be the time to do something. Thanks

 

[Gary in WA]

Welcome to the forums!

Yes, you can add unfaced R-10 to the inside over the plaster as it about .5 perms, close to same as asphalt coated kraft paper on batt insulation. This would work well as your Zone 5 requires a Class 2 vapor barrier, either Kraft (XPS foam also at 2"), or a SVR would work. Poly would also work but if there was high humidity in the room (esp. kitchen) you could have problems drying it out as the wood studs/board sheathing (higher than 32% MC) are now running much colder without the room's heat source- only relying on the seasonal changes.http://www2.dupont.com/Tyvek_Weathe...rior Insulation Building Science Bulletin.pdf

If you air seal the drywall (ADA; http://www.buildingscience.com/documents/information-sheets/air-barriers-airtight-drywall-approach/) and seal the foam; stagger the joints, caulk/tape the seams, caulk the top/bottoms; you will reduce/stop air/moisture exfiltration from the room to cavity. The cavity RH will be so much lower than the room RH, the wood will be able to store the small amount of incidental moisture (none from inside diffusion/air leaks) to dry later. Go for it, though you may want furring strips or really long drywall screws- 1/2" board, 5/8" plaster, 1/4" lath, 2" XPS, 3/4" into studs...

Gary

 

[OceanStateTunin]

Welcome to the forums!

Yes, you can add unfaced R-10 to the inside over the plaster as it about .5 perms, close to same as asphalt coated kraft paper on batt insulation. This would work well as your Zone 5 requires a Class 2 vapor barrier, either Kraft (XPS foam also at 2"), or a SVR would work. Poly would also work but if there was high humidity in the room (esp. kitchen) you could have problems drying it out as the wood studs/board sheathing (higher than 32% MC) are now running much colder without the room's heat source- only relying on the seasonal changes.http://www2.dupont.com/Tyvek_Weathe...rior Insulation Building Science Bulletin.pdf

If you air seal the drywall (ADA; http://www.buildingscience.com/documents/information-sheets/air-barriers-airtight-drywall-approach/) and seal the foam; stagger the joints, caulk/tape the seams, caulk the top/bottoms; you will reduce/stop air/moisture exfiltration from the room to cavity. The cavity RH will be so much lower than the room RH, the wood will be able to store the small amount of incidental moisture (none from inside diffusion/air leaks) to dry later. Go for it, though you may want furring strips or really long drywall screws- 1/2" board, 5/8" plaster, 1/4" lath, 2" XPS, 3/4" into studs...

Gary

That was exactly what I was hoping to get for an answer. So calk and tape all my foam seems including at the floor and ceiling, get 4" screws and I am good to go?

I will consider using furring strips, just wanted to make sure this idea would work.

Anyone else have anything good/bad to say about this plan?

Thanks!