Insulation question.

skyhighZJ

skyhighZJ

Gov retirement < needs to live
Joined
May 31, 2012
Location
Aberdeen, NC.
The house I live in here in Louisiana was built in the early 40’s. It was moved from the original location to where it is now. When they moved it, instead of setting it on a foundation, it is set on pillars. The land slopes under the house so at the northwest corner there is about a foot between the hoist and ground and at the opposite corner about 3.5 feet. Under the house the joist and subfloor is completely exposed with no form of insulation. I’m not looking to blow the family fortune but I’m tired of my feet being frozen in the colder months. I’d like to fit foam board in between the joist to help out a bit. I’m looking at 1” thick single sided foil face polystyrene as the cheapest by R value. Should the foil go against the sub floor or towards the open air?
 
Thermax is what I sell that you are describing and man that is some expensive stuff. In commercial applications It would be foil side to the exterior. So in your case, down towards the ground.
You would benefit more from regular insulation between the joist, a good 15mil or thicker vapor barrier that is turned up the sides of the exterior block/brick with a good 3” R10 or greater insulation on those exterior walls before turning the VB up. In short a sealed crawl space. But that is money. But it will take money and a lot of time to cut and place rigid insulation on the bottom as well.

My house is only 13 years old and insulated well. It’s actually quite warm under my house (I was under there last week) but I have lots of tile and hardwood and it just stays cold to the feet no matter what.
 
Foil reflects back radiant heat, so it should face the floor if you're trying to keep heat in. But, the foil won't work without an air gap; the foil just thermally conducts into the floor if it is in direct contact.

If you're trying to keep out heat in the summer, the foil would face the ground.

I'd spend your money on proper insulation instead on an inch of EPS or XPS foam. The best you'll do is about R-5 for an inch of styrene-based foam, and that assumes a lot about air sealing the foam to the joists.
I know the stuff you're looking at is super cheap, but it's also very little actual insulation performance. You're going to spend a HUGE amount of time cutting foam to fit between all of those joist cavities, so not really doing yourself any favors by installing a product that doesn't give you much performance benefit for your time.

You could do mineral wool ($$$) or fiberglass batts, or fasten foam or osb to the bottom of the joists and then fill the joist cavities with blown-in loose fill.

Because it's open under the house (no crawlspace walls, etc), wind-washing will reduce the performance of any exposed insulation that doesn't have some type of air barrier over it.
 
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There are some knock offs like @Fabrik8 mentioned. Not worth your time/money at all.
Thermax is R7.5 per 1” and is poly-isoanurate and $35+ a sheet.

I had the fortune of selling 2 entire truck loads a couple months ago!
 
77GreenMachine said:
There are some knock offs like @Fabrik8 mentioned. Not worth your time/money at all.
Thermax is R7.5 per 1” and is poly-isoanurate and $35+ a sheet.

I had the fortune of selling 2 entire truck loads a couple months ago!
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It's not a knock-off, it's just a different kind of foam that is cheaper than polyiso. There's 3 really common foam types, EPS, XPS, and polyiso. There's also urethane foams, but not as common in sheet form for building I don't think.

My point is, there is more than one sheet foam product on the market. ;)

I'll agree though, polyiso is the only sheet foam worth using as far as I'm concerned. The hippie part of me really doesn't like the blowing agents used in the polystyrene foams (EPS and XPS), and they just don't insulate as well as the polyiso.
 
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Well shit, there goes that plan lol. Thanks for the input guys. The sheets were used from a old warehouse or something so they were only a couple bucks a sheet but I agree that the cutting part of the project didn’t seem enjoyable at all. The house is skirted from the bottom of the siding to ground level so I know that helps some but was just looking for another alternative. And there is no existing vapor barrier on the house. I just put in some windows this past week and the exterior of the house is: 2x4 stud wall, tar paper (not consistent in all locations) 6” pine lap siding, 1” polystyrene foam (foil closest to the house) and vinyl siding on top. This was all existing when we moved in. Just to clarify I rent I do not own. This is an old family farm and we have an allotment to spend each month that goes towards credit on our rent. If it’s a bigger project then we don’t pay rent. If I don’t do anything for the month our rent is $500. If that makes sense.
 
skyhighZJ said:
Well shit, there goes that plan lol. Thanks for the input guys. The sheets were used from a old warehouse or something so they were only a couple bucks a sheet but I agree that the cutting part of the project didn’t seem enjoyable at all. The house is skirted from the bottom of the siding to ground level so I know that helps some but was just looking for another alternative. And there is no existing vapor barrier on the house. I just put in some windows this past week and the exterior of the house is: 2x4 stud wall, tar paper (not consistent in all locations) 6” pine lap siding, 1” polystyrene foam (foil closest to the house) and vinyl siding on top. This was all existing when we moved in. Just to clarify I rent I do not own. This is an old family farm and we have an allotment to spend each month that goes towards credit on our rent. If it’s a bigger project then we don’t pay rent. If I don’t do anything for the month our rent is $500. If that makes sense.
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If it is built on piers with no continuous foundation wall,

Is there ductwork for the first floor in the crawlspace?

If no ductwork in crawlspace,

The best will be to spray foam the floor and floor joists.

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Next would be rigid foam board with joints taped and sealed on the bottom of the joists. Foil facing downward 2” polyiso would be great for this.

Could also use two layers of 1” with all joints taped and staggered.

And you could fill lower portion of cavity with fiberglass during insulation leaving Air space at the floor.

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If it is built like this with open piers, the crawlspace vapor barrier is not necessary, especially when the vapor barrier (foil faced poly iso) is placed on the bottom of the floor system.

Check out this link. BSI-009: New Light In Crawlspaces

If there is ductwork in the crawlspace, that changes everything.
 
I would certainly address the no vapor barrier in the very near future. Go with something white, you’ll be glad you did working under there in the future.
 
skyhighZJ said:
The house I live in here in Louisiana was built in the early 40’s. It was moved from the original location to where it is now. When they moved it, instead of setting it on a foundation, it is set on pillars. The land slopes under the house so at the northwest corner there is about a foot between the hoist and ground and at the opposite corner about 3.5 feet. Under the house the joist and subfloor is completely exposed with no form of insulation. I’m not looking to blow the family fortune but I’m tired of my feet being frozen in the colder months. I’d like to fit foam board in between the joist to help out a bit. I’m looking at 1” thick single sided foil face polystyrene as the cheapest by R value. Should the foil go against the sub floor or towards the open air?
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I live in an old house with no underfloorinsulation and only blueboard insulation behind the vinyl too. The only difference is that I have a crawlspace and not just pillars. I too got tired of cold floors. My energy bills aren't too crazy though, max $200 in summer and $140 in winter) I looked into insulatingunder the floor and the cost/benefit ratio just didn't work. We're building in the spring so I should only have to hear my wife bitch about cold floors this last winter though!
 
77GreenMachine said:
I would certainly address the no vapor barrier in the very near future. Go with something white, you’ll be glad you did working under there in the future.
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He doesn't have a crawl space, so a vapor barrier on the dirt isn't necessary. He does need an air barrier on the underside of the elevated floors, which Mac's details cover.
 
It looks like you're in the Climate Zone 3 area of Louisiana, so it appears that code specifies R-19 for floor insulation (2012 IECC?). I'm assuming you need to meet code, as the house doesn't belong to you and you're getting some financial gain from doing the improvement work?

How big is the house BTW?
 
Fabrik8 said:
It looks like you're in the Climate Zone 3 area of Louisiana, so it appears that code specifies R-19 for floor insulation (2012 IECC?). I'm assuming you need to meet code, as the house doesn't belong to you and you're getting some financial gain from doing the improvement work?

How big is the house BTW?
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Not sure about the code as things around here are definitely done on the good ole boy system. As far as home improvements like adding insulation I’m not sure but I would by no means want to wind up in trouble over the situation. House is about 1300 sq ft one one floor.

To add, there is no hvac in the house. A couple wall mounted radiant heaters (propane) and 2 large window mount a/c units. Hvac is a project I’m not getting into at all. That is their issue to pay for/deal with. Only thing under the house is a cold water feed from the pump house that goes up into the floor joist and runs to the water heater, washer, kitchen sink, bathroom sink and tub and obviously the hot water lines that follow suit from the water heater and the drains for the sinks/tub.
 
If it was my house, I'd do a minimum of R-23 mineral wool batts, which satisfies code and is a lot nicer to deal with and install than fiberglass batts (my opinion). It's less than $1 per square foot for R-23 Roxul (for 2x6 stud wall) in the quantity you need.
The Johns Manville mineral wool is okay too and about the same price but I definitely prefer the Roxul for ease of use.
I don't think I'll ever deal with fiberglass again if I can help it.

But as simple as that plumbing sounds, I'd still consider closing off the joists with full sheets of foam and then doing loose blow in. Might be some cost parity if you're doing the sheets yourself and just hiring out the blow-in install, but that'd just what I've heard.
 
skyhighZJ said:
Not sure about the code as things around here are definitely done on the good ole boy system. As far as home improvements like adding insulation I’m not sure but I would by no means want to wind up in trouble over the situation. House is about 1300 sq ft one one floor.

To add, there is no hvac in the house. A couple wall mounted radiant heaters (propane) and 2 large window mount a/c units. Hvac is a project I’m not getting into at all. That is their issue to pay for/deal with. Only thing under the house is a cold water feed from the pump house that goes up into the floor joist and runs to the water heater, washer, kitchen sink, bathroom sink and tub and obviously the hot water lines that follow suit from the water heater and the drains for the sinks/tub.
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In that case I would do r13 bats stapled to the bottom of the floor joists, so the Air space is between sub floor and insulation, then cover that with r13 2” foil faced polyiso. Foil facing down towards the ground. Screw it to floor joists and tape all joints and tape over the screw holes.

I have no idea the price difference between the mineral wool bs fiberglass batts, but I would do the cheapest per ft and r value. There isn’t enough temperature differential most of the year in your climate to necessitate spending any more than you can.

Minimum would be 2” foil faced poly iso taped and sealed on the bottom of the joists. The air sealing will do the biggest improvement. Adding insulation above that is just a plus.

You can also do two layers of that foil faced 1” you said was available. Just stagger and tape all the joints in both layers.
 
Generally you won’t get in trouble for not meeting the code as it’s not a new build, and you aren’t making any changes that require a permit and inspection. If you were planning to sell the house then it would be a good idea to bring it up to code for the sake of pleasing the buyer and home inspector.

They can’t make you bring a house built in 1960 up to meet the current building code

It’s a good idea to use the code as a guide on what minimum to shoot for however, anytime you are changing anything.
 
If you don't own the house, I wouldn't do shit.
 
^^^^ what he said.


And... stuffing insulation between the joists with an open pier foundation just says "mice habitat" to me....

Sent from my SM-G930V using Tapatalk
 
kaiser715 said:
^^^^ what he said.


And... stuffing insulation between the joists with an open pier foundation just says "mice habitat" to me....

Sent from my SM-G930V using Tapatalk
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So it doesn’t really “cost” me anything cause as long as I don’t go over my rent per month (500) I don’t come out of pocket cause they deduct my materials from the rent.

The rodent issue is the thing I’m worried about. We haven’t had any issues to this point even with the cold and them trying to find a winter hideout but I’m not trying to build them a fawking Hilton with a big OPEN sign either that’s why I have benn trying to figure out the foam vs batt type of insulation.
 
The foil faced poly iso should keep the rodents out. Only use fiberglass/wool batts in addition to foam board across the bottom of the joists, not either or.

You are looking at maybe 40-50 sheets depending on House. Not sure what you can get or how many sheets of the 1” you can get cheap.

If I just guess and don’t shop, 50 sheets at $30 per sheet for 2”, that’s 3 months rent.

If using two layers of 1”, that’s 100 sheets at $14 per sheet.
 
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I’m not an engineer, I’m not in the insulation business. I’m just trying to solve moisture problems in an environment that has high humidity conditions almost half of the year. IMO using fiberglass in the floor above a crawl space has a couple of challenges. First, installation has to be perfect to achieve worthy R- values. Any voids around pipes, wires, ducts, and wood blocking allows air movement which degrades the insulation performance. Most of our building insulation works by trapping air. So a single void can destroy the insulation potential in that area. Compressing fiberglass also reduces R-value by replacing trapped air with the insulation material. Closed cell insulation( foam board ) works better but still has to be installed with out voids.
Moisture in the air has special relationship with open cell insulation materials including fiberglass, mineral fiber, and cellulose. When we trap air to provide resistance to transferring temperature the air needs to be as dry as possible. Why? Dry air resists temperature transfer but as the moisture level increases it loses it ability to resist and when the insulation becomes wet the insulation becomes a conductor of temperature. So on a humid day our fiberglass is not doing very well. Raise the moisture level only 1 1/2 percent and the R- value can drop 36 percent. Closed cell then can work better with out regard to humidity.
Since moisture can affect R-values in many insulation products moisture barriers should be able to help. Then we start to think about where should the moisture barriers installed. One problem of convential moisture barriers is they work in either direction unlike a check valve or a diode. They can trap moisture in a building or prevent it from entering. This about crawl space insulation so do we use a moisture barrier to keep our insulation dry so it will work better? Maybe put on the ground to keep the moisture out of the crawl space ? Does the vapor barrier on fiberglass batt insulation go up or down when installing in the floor above a crawl space? Our humidities drop during cold weather so the insulation will be drier during the winter when need it the most. Insulation is used when there is undesirable temperature difference. You want your floor about 70 degrees and your crawl space is 30 or 40 degrees? Throw some insulation in the floor. In the summer it’s cool in the crawl space, pull the insulation out to help the A/C oops it’s not working because of high humidity.
Serveral years ago I was inspecting a crawl space in the summer. It had a moderate moisture problem with moisture high enough in wood joists to support mold growth. What was interesting was about half of the floor had the insulation vapor barrier ( some kind of coated kraft paper) installed up and the other half down. I was a kid in a candy store with a moisture meter. Pulling down insulation batts I was checking moisture everywhere possible. I was going to answer the age old question of which way to install fiberglass insulation in a crawl space. Conclusion, it didn’t make a difference . I see many crawl spaces with mold on exposed floor joists below the insulation and brand new clean wood above the insulation. So the insulation is stopping the moisture either by preventing transfer or absorbing it.
In a vented crawl space the cheapest way to insulate is batts in the floor. Install carefully around obstructions and in corners. Cut to fit odd sized spaces.
Moisture problems are another discussion and some solutions could change the insulation needs and applications.
 
Wait so the key to this whole situation is, it really dosnt cost you anything, bc you trade the materials cost for rent.
So as ling as your landlord agrees, I'd think you'd be best to do tbe most appropriate thing possible even if it's expensive - bc it costs you nothing but time.

It sounds to me the BEST move is spray-pn closed cell foam. That solves all sealant and moisture problems, isn't attractive to animals and can cover all the gaps, joists, etc.
And the labor isn't bad, although generally people contract that.

Only hitch is its pricy, so you'd have to get the landlord on board. Maybe you can convince him it will save $$ in the long run on utilities (although in reality it will be a long payoff time)
 
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