# Best practices for new insulation in 2x4 walls



## JWindmill (Jun 13, 2018)

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## Nealtw (Jun 22, 2017)

Do the walls extend above and below the floor with open holes? 
was the foam on the outside taped and sealed?
Are you in a warm or cold zone?


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## JWindmill (Jun 13, 2018)

Nealtw said:


> Do the walls extend above and below the floor with open holes?
> was the foam on the outside taped and sealed?
> Are you in a warm or cold zone?


I'm not clear on the first question... Below the bottom sill is a conditioned basement that will be fully insulated when it's finished. Above is unconditioned attic space that will be insulated above the ceiling.

I haven't exposed enough of the foam to know if it's taped and sealed, but where I can see it, I would say it's not on there with much care. It appears to be loosely covering the house.

I'm in Louisville, KY, so the annual range can be 0-100F


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## Nealtw (Jun 22, 2017)

I am in a different zone so I will leave the insulation for others to help you. 


This video shows what I was asking about, he shows open holes and they need to blocked when ever you have a wall open to make the house safer.


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## JWindmill (Jun 13, 2018)

I see what you mean. I have top and bottom sill plates in the walls, so it’s not like that. There are some gaps by the sill plates in various places that I can foam.


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## Nealtw (Jun 22, 2017)

JWindmill said:


> I see what you mean. I have top and bottom sill plates in the walls, so it’s not like that. There are some gaps by the sill plates in various places that I can foam.


I don't think your house is 100, maybe 70, 80 years.


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## JWindmill (Jun 13, 2018)

Nealtw said:


> JWindmill said:
> 
> 
> > I see what you mean. I have top and bottom sill plates in the walls, so it’s not like that. There are some gaps by the sill plates in various places that I can foam.
> ...


Maybe so. It’s listed as built in 1900, which around here means the city doesn’t know exactly but it’s believed to be at least that old. The basement was added in the 80s by a very determined home owner. It originally sat on a brick foundation.


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## Nealtw (Jun 22, 2017)

JWindmill said:


> Maybe so. It’s listed as built in 1900, which around here means the city doesn’t know exactly but it’s believed to be at least that old. The basement was added in the 80s by a very determined home owner. It originally sat on a brick foundation.


 I think platform framing came in middle 30s about.


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## NotYerUncleBob2 (Dec 29, 2017)

I don't have a ton of experience in vinyl siding, usually just tearing it off or telling people not to do it in the first place, but... From what I understand the "foam" you're talking about on the outside is fan fold which is really there to separate the vinyl from the original siding but is sold as having some insulating properties which are in reality negligible. 
If you want to get the most out of insulating this while sticking to a budget there are a couple approaches that I'd consider:
Rockwool instead of fiberglass. Fiberglass is a great air filter, but it's so hard to do a perfect install. Rockwool is fire retardant, deals with moisture better, and is less air permeable so it will cut down on drafts. Cost isn't much more than fiberglass. 
Bonfig wall. https://www.finehomebuilding.com/2014/11/26/breaking-the-thermal-bridge
This is basically thickening the walls using thin strips of foam and then strapping on each stud. A little bit of labor, but if you're DIY then that's not a big issue. You'll take your 2x4 wall and get close to a 2x6 thickness with this process.


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## JWindmill (Jun 13, 2018)

I did look into Rockwool, and I do think that might be a better option. I just need to find a place that sells it. I've never seen it at a big box store. I have heard that it will hold moisture and mold, so keeping water out is a must. I do plan on all new siding when the house is finished, so that will help. I already have interior walls framed and electrical run, so furring the walls from the inside would throw things off at this point. It would have been worthwhile from the beginning, from what I'm seeing. When I redo the siding, I'll at least have the opportunity to do a proper house wrap.


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## APA (Jul 13, 2018)

Go with R-13 fiberglass. If the house is not that valuable just get what is easy and get on with your life. You will get more value from good air sealing.


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## JWindmill (Jun 13, 2018)

APA said:


> Go with R-13 fiberglass. If the house is not that valuable just get what is easy and get on with your life. You will get more value from good air sealing.


I’m trying to determine the best way to air seal. I’d think to do it thoroughly, I’d have to foam or caulk between every sheathing board. If it’s worthwhile, I don’t mind taking the time. Or should I just wait until I replace the siding and do it from the outside.


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## Bud9051 (Nov 11, 2015)

I have tested a few homes with board siding and the infiltration into the walls greatly reduces the insulation value. While it is accessible now would be a good time. Caulking may be easier than can foam and brushing on duct mastic (it is messy) may be the most effective. Rubber gloves and throw away brushes, but you can picture frame every cavity and hit all horizontal seams. As mentioned, air sealing is a high priority.

They make an r-15 high density fiberglass. For mineral wool I have used Roxul and never heard the concern "that it will hold moisture and mold", in fact it comes without paper backing and is friction fit. Very dense so holds well and easy to cut and install. Also a bit higher in r-value.

Don't be concerned about vapor barriers as they have learned it is better to allow a wall to dry to one or both sides. 

Bud


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## APA (Jul 13, 2018)

I have never used the mastic, but foam and caulk can be tedious and time consuming with that many gaps. The foam has to be scraped away level with the boards after it expands and dries.


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## Bud9051 (Nov 11, 2015)

APA said:


> The foam has to be scraped away level with the boards after it expands and dries.


And that is one of the problems with foam, it has trouble getting into narrow cracks. The same putty knife attention to some caulking or Mastic pushes the material well into the cracks where it stays.

I've used mastic on ducts and it is very similar to the mastic used for flooring, how similar I don't know. Where ducts can be a challenge accessing all the way around I look at those walls and it looks easy. There would be no need to make it pretty, just push it into any gaps. Big gaps might need something more than just the mastic so some foam there could be useful

One of the misconceptions about using can foam is that is is providing some insulation value. The truth is, so little it would be difficult to measure. But the air sealing by whatever method is vary measurable.

Bud


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## NotYerUncleBob2 (Dec 29, 2017)

JWindmill said:


> I did look into Rockwool, and I do think that might be a better option. I just need to find a place that sells it. I've never seen it at a big box store.


I just needed a little bit of insulation last week and picked up some Rockwool from Lowes. It was cheaper than fiberglass in small quantities. 
The HO liked it so much they went out and bought some from Home Depot, but it was another brand and not as good as the Rockwool brand. 




JWindmill said:


> I have heard that it will hold moisture and mold, so keeping water out is a must.


Keeping water out is a must no matter what you're insulating with! Fiberglass won't do any better than rockwool.


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## JWindmill (Jun 13, 2018)

I can start trying mastic and foam in various places. Many of the gaps are plenty big enough for the foam can straw to fit in. I've never tried the mastic, but I'll get some and see if it would be a manageable job. If I spent some money, I could get the large spray foam kit from Lowe's which would probably be enough to do an inch or so on the 3 exterior walls I'm dealing with. It just might make R13 fiberglass too tight.

I looked into Rockwool, and apparently the other three Lowe's in my city carries it, just not the one closest to me. I'm leaning towards using that, although I do have plenty of electric and drywall blocking to contend with.


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## Bud9051 (Nov 11, 2015)

A fine tooth saw, bread knife, or some people use an electric knife to cut the mineral wool. Always make the width tight by 1/4" to 1/2", less for smaller gaps.

Bud


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## JWindmill (Jun 13, 2018)

Do I split Rockwool around electric the way I would fiberglass? Is it as sensitive to compression as fiberglass?


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## akjose (Jan 1, 2013)

JWindmill said:


> Do I split Rockwool around electric the way I would fiberglass? Is it as sensitive to compression as fiberglass?


Yes, you split it on the edge for the studs if if the wires run down the joist and split it horizontally if cables running left to right. It is essentially compressed fibers so compression shouldnt be an issue. It cuts nicely and is easy to handle. wear glasses if installing it in overhead areas.


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## alexjburkhardt (Jan 17, 2018)

Creating an air seal in every stud bay, at every horizontal joint between the sheathing boards would be a tremendous amount of work -- and hard to get perfect; though, if you're the labor, that's a big consideration. 

I'd just make sure you have a plan for the whole wall assembly, inside and out, before you button up he interior with drywall. You may be doing it in stages, as opposed to a complete inside/outside gut, but at least know you'll have access to both sides if not now, in the near future. 

If the exterior air barrier options aren't in the budget when you re-side (taped zip sheathing, taped rigid foam, etc.) then you might want to spend some quality time with canned foam and a caulk gun.


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