# Adding insulation to finished walls, foam or blow in?



## sosnpk

I am taking on the task of insulating our 1946 house. I am in the process of removing the wallpaper in the dining room and figured since I am going to be filling in holes to prepare the wall I might as well look into insulation. The room has one exterior wall, 2 interior and one facing the unheated garage. Should all walls be insulated? What is the recommended type of insulation for behind these plaster walls, foam or blow in insulation? Any tips for install?


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## inspectorD

My opinion of insulating older homes is ... It needs to be done correctly!!  Check out www.Buildingscience.com for lots of info.
First make sure the house is in good shape , no leaks on the outside siding or roof that can leak into the walls. When a house has no insulation and it leaks even a small amount, it has the ability to dry out because there is no insulation or vapor barrier to trap moisture.When you insulate, now you changed the dynamics of the building and this can lead to rot or mold problems in the future.
Another thing to do is to install fans in your bathrooms and kitchen. You need to evacuate any moisture you put into the home so you dont get the insulation wet from the inside.This happens because you cannot install a good vapor barrier on your interior wall unless you remove the plaster or paint with a certain type of paint.
Finally, I would go with the blown in and check to see if you have Balloon framed construction, I think you may due to the age of your home.Go into the basement along the foundation wall/ceiling area and if you can see a cavity that goes up into the wall above the floor then you will need to insulate that area with regular fiberglass first. If you dont ,the blown in insulation will just fill the basement as they fill the walls.

Always consult a professional at least to get their advise , then you will have a chance of doing it correct because every case is diferrent.

 Hope I left you with a warm feeling!! 

InspectorD


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## zander

I could be wrong but.
A newer house comes with tyvek or some sort of barrier to wind/infiltration on the out side of the house.
A older house is probably not as tight as a new one because they used tar paper that has deteriorated over the years.  Also the sheathing(if that is what it is) could be 1by12s with 1/4 inch or better gaps under your siding.  So the wind can freely blow into the wall cavity.
Now, if you inslulate with fiber glass or blown in stuff then the wind will still blow into the wall cavity-mabey a little slower though.  Also your house is probably not built out of two by six lumber so your still going to have a thinner wall less insulated then what a new built house should have-not that builders don't put up lots of houses with 2by4 walls and call them well insulated(they are lying or uninformed).

I would go with the foam because it will create a vapor barier that keeps both the wind from blowing into yer wall cavities and the moisture in the house from getting into the wall.  It will also expand some to fill gaps unlike blown in insulation which can leave gaps.  It also has a higher R-value than blown in insulation.

Do the garage wall.  You could do it from the garage side.  Do the exterior walls.  The interior walls arn't going to make much difference as far energy use in the whole house goes unless you have some zone control on your furnace that would allow you to only heat chosen areas.  May do something for noise though and make the house feel more solid.

Like the inspector said you could creat a moisture problem.  But it should not come from inside the house if you inuslate well as it will be condensing on the windows first.


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## inspectorD

Well zander... your on the right track,but...
As you said, "new homes" have a material like tyvek or tar paper on the outside . The real purpose of this stuff is to repel water in rain storms, the air barrier is a farce, marketing at its best!!It may slow down the air but it still comes on through.

Now we get to the old home part where things DO leak as I said earlier, It needs to be done correctly in an older home to keep out water, Otherwise it defeats the purpose of insulating if you rot the house away.The exterior clading is the most important part of this senario.

Now about foam insulation, this stuff is a sponge when it is wet. No kidding I have installed it on 3 jobs. (20 years in remodeling historic homes from 1648 on up)
The last job we had with foam had a leak from a chimney flashing area and we found it 2 years later when the chimney sweep stepped through the roof.The insulation was saturated!! The roof had decayed so bad we had to replace the missing rafter area surrounding the chimney.The kicker was the no rain in 2 months.

I am a big fan of foam in new houses because you control how the inside stays dry. I am not a fan in remodel projects as you can see.
Also with the blown in it does dry out after time if it gets wet.

Again check the web site I mentioned earlier and any links. There is a lot of misinformation out ther and this may help sort some of it out for everybody.As a remodeler and a home inspector I get to see the failures of the trades. I would hate to see some of my earlier attempts at remodeling myself.

Always learning, 
Brian


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## zander

Thanks for the information.
Makes sense to me.
Foam is not used to much in this area of the country, but i understand it is getting more common.
I take it the stuff that they put in existing walls is different from the stuff that they put up in new construction when the walls are open.
I shall look for your links.
At some point im going to pull the drywall out of a couple rooms in my house.
I know the siding and windows are very rain tight as i did them myself.
I am thinking about getting foam sprayed in if finances allow so i have been interested in the subject for some time.


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## PaPaDan

My home is mid 1800s. Some years ago I decided to insulate and started to use the foam. The first wall started bulging in and cracking the plaster and laths. I had to use the blow in. After about 5 years I checked the attic and the blow in had settled about 18" down into the wals so i just topped it off from the attic. I put Tyvek and vinyl siding on the year before and have had no problems.


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## fmt9110

My home is a ranch style home and built in 1975.  The home feels colder compared to the outside.  Five years ago replaced furnace with a high energy heat pump.  I'm going to add insulation in the attic but need recommendations on insulating the walls, especially the north wall.  Recommendation on how and type of insulation.

Thank


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## nealtw

You have 2x4 studs, to do this right I would remove drywall add a few inches to the studs. This would allow thicker insulation and insulation at the header where you have none now, replace the vapour barrier and re-drywall. When you add to the attic make sure you don't plug the airflow from the soffet vents.


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## CallMeVilla

My call would be blown-in because foam, if over applied, will expand and blow out the walls.  You won't know there is a problem until it is too late.  Blown-in just fills the cavity to the top and you stop.

You only have to do two walls:  exterior and garage.

BTW, the trick with blown-in has to be fire blocks.  If you have them, then you will have to locate them and fil 1/2 the cavity to the block, then fill the upper cavity.  Since your walls are going to be messed up anyway, cutting fill holes is no big deal to patch and then repaint.


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