Foam Board on an Inside Wall?

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Shawnshawn

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Hoping someone could help me. I don't want my house to be featured on a 'Don't Reno Like This' TV show :)

I have an 1860 home. Heating bills are insane. The wall, currently, is as such (inside to outside):
- Lathe & Plaster (painted w occasional wallpaper)
- Nothing - 4" cavity
- Barn board
- Black felt
- Wood siding, painted

I really don't want to demo the existing interior walls.
What I'd like to do is attach rigid foam board (2 - 4") to the interior existing plaster walls and cover with drywall. I'd probably use fresh framing/studs as I'd like fresh wiring, and it adds strength / good for cabinets, etc. Although *I could* just screw right through the drywall&foam to the old studs, with long screws, and skip the framing.

So my question is - If the interior foam board becomes my vapour barrier, does this pose a problem? Is there an issue taking what is currently an interior lathe plaster wall (painted, occasionally w wallpaper) and suddenly making it part of the "exterior" as it would be on the cold side of the foam board?

Any insight is GREATLY appreciated.
Kind Regards
Shawn

Ps should I use two or four inches of foam?
 
Do you know if the lath is wood lath or button board or gypsum lath?

If it is either of the last two, you could drill a 2-1/2 hole near the top of the wall and just below each fire block and blow insulation into the cavity.

Cabinet do not long survive being hung off of 6" screws.
 
Welcome to the site.
Your house will be balloon framed. The studs will full height of the house with floor joist nailed to the studs, so instead of adding strength with any new wall you would be adding dead weight to the floor.
In many of these house there is space between the studs from the basement or crawlspace to the attic. they should be blocked where possible as they are a fire hazard and stopping that air flow is like adding some heat loss value
If the interior is in good shape removing siding and some boards on the outside to insulate should also be considered.

Although covering the inside would be away of covering old lead paint and nothing would be hurt by making a new vapour barrier.
 
Thank you for the replies!
Snoonyb: Fairly certain it is wood lath. There seem to be random horizontal pieces, I don't have the confidence that blow-in will fill the cavity completely; also worried about it getting damp and/or settling.
True about your cabinet comment, thank you.

NealTW: Blocking airflow: valid, thank you. I do like the bonus of covering lead paint. I just didn't know if putting a vapour barrier on the inside of room would degrade everthing that is now exterior of it.

Follow up question, regarding "removing siding from outside". Do I have to remove the siding? I'm trying to limit demo-work. In a few spots, I'd like to put the rigid board there, directly over the siding, with strapping, and then do vinyl siding. As the siding is beveled, there would be little triangles of space behind the rigid foam. Is this acceptable? Do I need a house wrap over the existing siding?

Proof_1283 Oct. 24 09.42.jpg
 
You could have showed us a picture of broken or rotted siding. With that picture my mind says no.
Old houses had doors and windows that allow rain water and condensation in all over the place, what saved them was the airflow that allowed them to dry out afterward. With foam on the outside you really should re install windows and doors with an equally modern method. And you will have to do a lot of mill work around doors and windows for the extra thickness..
 
Having lived in many houses around the age of yours and with quite similar construction to yours and been involved in paying the heating bills, I have thought about all these options many times. Every option has a cost related to it and a payback period thru energy savings. Then you have the practical problems with doing any of these. Lastly you have the long term problems changes might cause.

Your biggest bang for the buck will be windows and doors and heat loss thru the attic. Your next best improvement will be a better efficiency heat source.

If your siding is caulked well and has layer of plank sheathing below it and then lath and plaster with somewhat dead air between I wouldn’t be in a big hurry to frame out all the walls making smaller rooms and deep set in windows etc. if the plaster is bad in a room and you rip it off it is a mess but can be done and remove the lath fill the walls with insulation and then a layer or two of drywall. do any new wiring when you have it open. There is no easy way to get around it. if you want to frame out and add foam panels and then spray foam the cracks and do the whole house that way I think it would work.

You say your heating bills are insane I would start with trying to figure out where the heat is leaving the house. Do some infrared photos as a start.
 
note, The windows & doors are nearly all replaced. Siding is well caulked

NealT: So it sounds like you're saying, re: Exterior: foam&vinyl will stop airflow and harm the underlying wood siding, as it can no longer dry out. So if I want to do foam/vinyl, I should remove the siding and go to the barnboard? Should I use housewrap at that point?

bud: re: Interior: My concern with tearing down the lath/plaster, is how to install a vapour barrier. If I put fibreglass/roxul in, there's no vapour barrier and I wonder if these 'soft' insulations could get damp. Best option is closed cell spray foam, but its very expensive. Budget alternate, I could fill the bays with 4" foam board it and seal the edge with Great Stuff, but then, I start thinking, could I have done that inside the room without doing the demo. I'm not concerned about losing 4" in the room, they are sizeable. I'm looking at all possibilities. If having the lath/plaster on the cold side of the foam is of no consequence, I may do that, but which insulation route is best?

Thanks for all help on this.
 
note, The windows & doors are nearly all replaced. Siding is well caulked

NealT: So it sounds like you're saying, re: Exterior: foam&vinyl will stop airflow and harm the underlying wood siding, as it can no longer dry out. So if I want to do foam/vinyl, I should remove the siding and go to the barnboard? Should I use housewrap at that point?

bud: re: Interior: My concern with tearing down the lath/plaster, is how to install a vapour barrier. If I put fibreglass/roxul in, there's no vapour barrier and I wonder if these 'soft' insulations could get damp. Best option is closed cell spray foam, but its very expensive. Budget alternate, I could fill the bays with 4" foam board it and seal the edge with Great Stuff, but then, I start thinking, could I have done that inside the room without doing the demo. I'm not concerned about losing 4" in the room, they are sizeable. I'm looking at all possibilities. If having the lath/plaster on the cold side of the foam is of no consequence, I may do that, but which insulation route is best?

Thanks for all help on this.

The photo shows FG behind 6 mil poly the attic is pumped in after the drywall is up

New windows does not mean best practice installation
[ame]https://www.youtube.com/watch?v=t2VOrk1MuWY[/ame]

56.jpg
 
So if you are happy with the windows and doors, the siding is good, the plaster is good enough as is, this might be the answer. Everything here can be rented.
Keep in mind plaster is more like concrete and does not support mold and paint is a vapour barrier.
With this method you could inspect or replace wiring, inspect cavities from the inside catching and making repairs from inside or outside a needed.
Repair the plaster after or just add poly sheeting and new drywall.
[ame]https://www.youtube.com/watch?v=vc8xSQs4l3w[/ame]
 
Thank you for the helpful videos. I've always been hesitant to use blown-in insulation, since I read this website: http://bobyapp.com/blog/2009/06/myths-about-insulating-old-house-walls

His viewpoint is that without a vapour barrier, the blown-in stuff will get damp and cause problems. But if I use vapour-barrier paint, I may be alright? Your video showed them filling from the inside; wondering if I could do it from the outside. Sorry - I just re-read your response - you would put poly sheeting over the existing wall when complete, and then drywall over that. Sorry I need this spoon fed to me - the idea is to keep interior moisture from hitting the insulation, correct? Exterior moisture isn't the concern, because the insulation will dry to the outside, through the barnboard and siding. Wondering if anyone has had the problems that Bob Yapp describes with the wet blown-in stuff?
 
The key is to keep the warm wet air in the house from getting in the insulation.

There is a chart that shows the vapour resistance for paint, but you have lots of holes.

If you were doing wiring to or really going after vapour you wrap the outlet and switch boxes too.

They sell boxes covers for this and then you caulk the holes.

[ame]https://www.youtube.com/watch?v=_eT0wI7ElbU[/ame]
 
Thank you for the help. BobYapps's website turned-me off blow-in insulation, but I've come around; I believe if I create a vapour barrier on the inside as you've said, to stop interior moist air from hitting the blow-in, and don't add anything exterior of the blow-in so it can 'breathe' - I should be in good shape.

For my exterior project - same approach. Sounds like rigid foam & vapour barrier is the way to go for new construction, but not a good approach for my 160 year old house; my wood construction needs to breath to survive. Frankly, I should retain the approach that's been used for the 16 decades previous, house looks not bad :)

So I'll be doing this: blow-in [cellulose], packed as tight as possible, with interior vapour barrier on the warm side of the blow-in (I'm still leaning towards 2" foam board & drywall)... this is my approach now. Or, if I skip the foam, I could put up 6mmPoly sheeting on the inside walls & use a thinner drywall, although I like the idea of having nice open structure for fresh re-wiring.

Welcome to opinions.
 
So I'll be doing this: blow-in [cellulose], packed as tight as possible, with interior vapour barrier on the warm side of the blow-in (I'm still leaning towards 2" foam board & drywall)... this is my approach now. Or, if I skip the foam, I could put up 6mmPoly sheeting on the inside walls & use a thinner drywall, although I like the idea of having nice open structure for fresh re-wiring.

Welcome to opinions.

At that age you may need to rethink the project, because unless it has been rewired, you have Knob & Tube electrical wiring and you cannot encase that with insulation.

https://en.wikipedia.org/wiki/Knob-and-tube_wiring

You can find this out by a trip into the attic, opening a switch or recepticle box.
 
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Even if wiring isn't knob and tube, check for un grounded wire, this would be the time to fix all that.

In new construction up here all outside walls are 2x6 we make sure every bay has holes to the outside for venting, fibreglass insulation then vapour barrier
 

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