Renovation - Spray foam or Batt Insulation! Advice please! (1 Viewer)

[nolaswede]

We are in the middle of a renovation! Adding to our house and making some major renovations. Overall e have been happy with our contractor and we seem to be on schedule.

Situation - Our contractor, recommends spray foam in the addict and in the walls in the new addition. Which is about half of our house, and we already have regular batt insulation in the rest of the house. We have talked to others(including contractors) and we seem to get many different answers. My dad wants rock wool insulation, but that’s crazy expensive!

Question - Is it better to only have spray foam in the addict or in our new addition as well? The house is about 70 years old and in pretty good shape. Can ventilation be a problem? Our A/C bill is usually pretty cheap.

Please advice! I know we have a lot of knowledgeable contractors on the forum!

Thanks in advance!

 

[dtc]

It can be a complicated question, but my short answer is that it's not worth the money if you're not doing the whole house. The benefit is that it seals the house from air infiltration. If you're not going to seal the whole thing you're paying too much for the R Value than necessary.

If you have areas where you can't get good batt or blown coverage then it can be worth it to do parts - knee walls and restricted spaces.

The only place I've used it on my own house rennovation is on the man-cave / wine cellar which is on the lower floor of an elevated house, but that's simply because I get it cheap and I am going to be conditioning that space to below 60 degrees using a completely isolated unit.

 

[brandon8283]

Our contractor, recommends spray foam in the addict

TWSS

 

[nolaswede]

TWSS

Haha...oops

 

[nolaswede]

It can be a complicated question, but my short answer is that it's not worth the money if you're not doing the whole house. The benefit is that it seals the house from air infiltration. If you're not going to seal the whole thing you're paying too much for the R Value than necessary.

If you have areas where you can't get good batt or blown coverage then it can be worth it to do parts - knee walls and restricted spaces.

The only place I've used it on my own house rennovation is on the man-cave / wine cellar which is on the lower floor of an elevated house, but that's simply because I get it cheap and I am going to be conditioning that space to below 60 degrees using a completely isolated unit.

Thanks for the detailed reply! Was hoping you would see this!

Our contract has spray foam quoted, and it seems like he prefers to do spray foam. I’m not sure we will save any $ by going regular insulation. If so, any drawbacks by going with spray foam?

 

[dtc]

Thanks for the detailed reply! Was hoping you would see this!

Our contract has spray foam quoted, and it seems like he prefers to do spray foam. I’m not sure we will save any $ by going regular insulation. If so, any drawbacks by going with spray foam?

Foam is more money so if he's pricing the job based on a percentage of the cost, then he benefits by you spending 10k instead of 5, but that's probably not the whole answer.

Foam is better if it's done right, but imho only if the whole house is done.

Insulation is measured in R value which is essentially the measure of how long it takes heat to migrate through a certain space. Foam, rockwool, air, fiberglass and chopped paper all have different values. Where foam is better is that it stops air from passing through little cracks and crevices, but it costs at least twice as much per R value so if you're paying 10k to get r30 in your attic space instead of 5k you're paying too much.

It has some other benefits and drawbacks, as well. In the attic, you would typically spray the underside of the roof deck thereby making your attic semi-conditioned space. Your attic is cooler and neater because the heat is kept out, but you have to cool that space and circulate air or you'll end up with possible moisture issues. If the roof leaks, you can't find it as easily. When it leaks, the R value of the foam decreases. When you have a roof replacement it will compromised the foam. Voids and crevices decrease the effectiveness, but that's the installer and contractor's job to avoid.

The sprayed area would be less drafty, but basic construction quality would eliminate draftiness in new construction/addition anyway.

How big an addition are you talking and is there going to be a separate ac?

In most cases, I would hazard to suggest you'd be better off using batt or blown insulation for an addition and spending the savings vs foam on a high seer AC system.

 

[nolaswede]

We will have 2 different A/C systems. One upstairs in the attic, and one brand new downstairs. The addition is about 1/3 of the house(total 2500sqft with the addition).

The addition is facing west and will get a lot of sun/heat in the summer months. Want to make sure that the systems don’t have to work too hard and that spray foam makes sense to have both in attic and in the walls of the new addition.

The price will not be cheaper if we go regular insulation. So trying to see if there is any reason not to go with spray.

Rock wool would be too expensive in our opinion and we wouldn’t be doing it in the entire house anyway!

Thanks!

 

[dtc]

We will have 2 different A/C systems. One upstairs in the attic, and one brand new downstairs. The addition is about 1/3 of the house(total 2500sqft with the addition).

The addition is facing west and will get a lot of sun/heat in the summer months. Want to make sure that the systems don’t have to work too hard and that spray foam makes sense to have both in attic and in the walls of the new addition.

The price will not be cheaper if we go regular insulation. So trying to see if there is any reason not to go with spray.

Rock wool would be too expensive in our opinion and we wouldn’t be doing it in the entire house anyway!

Thanks!

It doesn't matter how hard the ACs work. I mean they're either on or off unless you have variable speed fans and compressors which is what I'd suggest. Still, the AC is most efficient when it's running and the longer it runs the better so the variable speeds running at low capacity for long intervals is the most efficient.

It makes no sense to me that it wouldn't be cheaper to do batts vs foam so make the builder spend his money and install the foam which is obviously what he likes. Sounds like he's done the math for AC size based on foam and it won't make you any savings to skip it so let him do what he's planning.

 

[Goatman Saint]

If that wall is going to be catching the heat, then the higher R value of the sprayed in foam would let you come out ahead because that wall will not heat up as much as fiberglass batts. Since the cost is even, go with the foam if that’s what he recommends as it will also quiet down that portion of the house as foam is about the best damper of sound out there.

 

[nolaswede]

It doesn't matter how hard the ACs work. I mean they're either on or off unless you have variable speed fans and compressors which is what I'd suggest. Still, the AC is most efficient when it's running and the longer it runs the better so the variable speeds running at low capacity for long intervals is the most efficient.

It makes no sense to me that it wouldn't be cheaper to do batts vs foam so make the builder spend his money and install the foam which is obviously what he likes. Sounds like he's done the math for AC size based on foam and it won't make you any savings to skip it so let him do what he's planning.

Last question! If we decided to spray the attic, would the old batt insulation upstairs need to be removed? I have read that at a few places!

 

[dtc]

If that wall is going to be catching the heat, then the higher R value of the sprayed in foam would let you come out ahead because that wall will not heat up as much as fiberglass batts. Since the cost is even, go with the foam if that’s what he recommends as it will also quiet down that portion of the house as foam is about the best damper of sound out there.

R value is R value. Why would he put more R in with foam than batts?

 

[dtc]

Last question! If we decided to spray the attic, would the old batt insulation upstairs need to be removed? I have read that at a few places!

The batts between the bottom truss chords should come out. There's no need for it and you'll need to condition the attic slightly. Leaving the old dusty stuff in a conditioned space will have the dust and crap from the old insulation in your inside air.

 

[nolaswede]

The batts between the bottom truss chords should come out. There's no need for it and you'll need to condition the attic slightly. Leaving the old dusty stuff in a conditioned space will have the dust and crap from the old insulation in your inside air.

Makes sense to remove it! And no issue to add spray to an older house? Built in 1949. Thinking if there is a roof leak, will it be tougher to see a leak and add moisture to it?

A lot of new shingles were added a few weeks ago. We haven’t had any issues with the roof and we are happy with him so far, but feel like he recommends spray just cause that is what he does.

 

[Goatman Saint]

R value is R value. Why would he put more R in with foam than batts?

He said it’s a wall that has the sun hitting it in the afternoon. If he has a standard 2x4 wall with fiberglass it’s only giving him an R value of slightly over 6. If he has 3 inches of foam applied it’s almost an R value of 20. That’s a huge difference on a wall the sun beats down on. That part will be noticeably warmer due to that. Also, if he’s not upsizing his A/C unit, there is that to think of also and a foam insulated room costs very little in additional AC. There really is no substitute for foam, and certainly if the price is the same. It will be 3x the insulation R value per inch, and the quietness is very different in a foam house.

 

[Wisco Steve]

I am way up north in Wisco, my last 2 houses were purchased new...1 with 2x4 construction and base R11 (built in 2006) and the most recent built 2 years ago with 2x6 and sprayed green foam...both full walk out ranches around 3000 sq ft. The difference in energy savings with the foam is remarkable.