# Insulate and encapsulate crawl space - best practices



## Bud9051 (Nov 11, 2015)

I prefer the encapsulation approach because, as you stated once you use the spray foam you are locked in. Another negative is that even with the floors insulated with foam they are difficult to heat, the warm air above gets pushed to the ceiling leaving drafts on the floor. The encapsulation approach results in a warm crawlspace and warm floors.

But first, where are you in terms of climate region? 

Water intrusion is a concern as the floor will need to be covered with the plastic. If the posts are above the dirt floor getting the plastic around the base is not a big issue.

As for the mold you mention, rigid foam against the foundation (I assume poured or concrete walls) actually allows a bit of drying to the inside, it is referred to as a vapor retarder. Any moisture that makes it in is easily handled by the dehumidifier, as long as it isn't a lot of liquid water.

Pictures will help

Bud


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## graymoment (Dec 16, 2017)

You can copy/paste the Google Photos link in my post to see photos. For whatever reason, when I a attempt to add photos the site won't save my post. Maybe because I'm a new user.

I do not see how spray foam under the subfloor wild allow the floor to be drafty/cold. The main benefit to that option seems to be that the floors would be air and vapor tight. 

My climate is fairly temperate... Coastal Southern California. I think that's part of the reason that none of the insulation companies I've talked to have ever heard of insulating the crawl space walls. Partly due to climate, and partly due to having mostly small crawl spaces and no basements anywhere.

All of the polyiso insulation installation videos I've seen talk about sealing the foam panels so no vapor or air can get in, so I'm not sure what you meant by allowing vapor to make it's way into the crawlspace. The whole idea of adding a vapor barrier is to eliminate as much of that as possible.
I think the water ingress is from


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## user_12345a (Nov 23, 2014)

when you only insulate the floor, you have a lot of thermal bridging through the joists and the floor still gets cold.

In humid weather with a vented crawlspace, you still get condensation and moisture issues on surfaces.

It's much better to seal off any dirt floors and insulate the walls with foam.

May need to run a dehumidifier down there in the summer, but it's cheaper than operating a house with a cold crawl space.

You may need to put a small source of heat in the winter.

It's a myth that walls that are not concrete need to "breath". In fact the air movement through the walls can cause condensation in the wall and rot. this is less of a factor in a crawl-space.

The tighter the wall is the fewer issues you have.

Problems come when walls are insulated and not sealed; the insulation reduces heat loss and makes the surfaces cold, so as air leaks out condensation forms.

The wall needs to have drying potential above ground on one side when you insulate however. Warm moist air from a conditioned space (this includes insulated crawl-spaces, it's like a mini-basement) can still leak and you can get water coming into the wall from outside.

The tar paper or house wrap is not perfect.

So whatever moisture that gets in can get out.

Rigid foam, being impermeable and much better at stopping airflow through walls than a plastic vapour barrier, makes it so drying potential is less important.

You must deal with any water penetration issues before you fix the crawlspace.

Unless your foundation has really major flaws, you can probably fix most issues by re-grading and having down-spouts drain far from the house.


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## graymoment (Dec 16, 2017)

user_12345a said:


> when you only insulate the floor, you have a lot of thermal bridging through the joists and the floor still gets cold.
> 
> In humid weather with a vented crawlspace, you still get condensation and moisture issues on surfaces.
> 
> ...


Everything you said makes a lot of sense. I thought about the thermal bridging of the floor joists, but assumed I would just have them insulate the joists as well if going the spray foam route. That would probably double the material costs, however.

Regarding the stem wall not needing to breathe to the inside of the crawlspace, do you have any source you can point me to on that? It's been my biggest concern. 

I appreciate the advice to address the water issue first. You're the second person to tell me that. My guess is it's a mix of grading and a few cracks in the foundation, but mostly the former. My thought is to run a French drain and install gutters. It's not obvious where the water comes in, but it happens after rains and I'll be enough to puddle in places. 

Any thoughts on running the foam board all the way to the ground vs a few inches off? Basement Systems, Inc seems to run to the ground, but I've seen other sources (Crawlspace Depot) advise being 3-4" up for termite inspection (not sure what that would achieve on a concrete wall).


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## Dave Sal (Dec 20, 2012)

Here's a link from Building Science that addresses crawl space insulation.

https://buildingscience.com/documents/information-sheets/crawlspace-insulation


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## graymoment (Dec 16, 2017)

Dave Sal said:


> Here's a link from Building Science that addresses crawl space insulation.
> 
> https://buildingscience.com/documents/information-sheets/crawlspace-insulation


I have read a lot of articles on buildingingscience.com, but had not read the information sheet you posted until seeing your comment. 

It seems the general consensus is to insulate the walls and encapsulate the floors. At least I have that part of the process decided. How to go about that is still unclear. 

Some decisions and questions that I need to address:


*Moisture in the pony walls.* It's unclear how I can both encapsulate the crawl space and allow the pony walls to remain dry. Whether I use polyiso foam board or batt insulation with a vapor barrier up the wall, I'm effectively sealing the wood behind the conditioned space, which (I presume) would create a ticking time bomb for the wood to rot and termites to eat it.
*Polyiso foam board vs batt insulation and poly vapor barrier?* It would seem that the foam board is the most expensive option, especially for the R-value. It would require 2" of polyiso foam board to equal the same R-value of of fiberglass or mineral wool batt insulation. The benefit of the foam board would be that it would allow me to insulate the concrete as well. I suppose I could put foam board on the concrete and batts in the pony wall.
*Drains inside vs outside the foundation wall?* It's not fun to work inside the crawl space, and it would require a sump pump and drain path to the outside, but the inside will allow me to trench all 4 walls without having to cut and repour concrete. That said, if I need to install a 6% grade vapor barrier around the exterior perimeter anyway, I'm halfway done with the doing the drains on the outside anyway. Maybe I just answered that question?


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## Nealtw (Jun 22, 2017)

I am not a fan of encapsulating but if you go that route, you treat the pony wall just as you would any basement wall, the space needs to be conditioned. And the bottom of the posts that will be below plastic can be wrapped with peal and stick. Plastic in pieces want to over lap 1 ft and be taped..
Up here vented or encapsulated crawlspaces get a 2" skim coat of concrete over the poly.

Take time to prove that all water issues are solved before moving ahead or you can buy lots of trouble.


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## graymoment (Dec 16, 2017)

Nealtw said:


> I am not a fan of encapsulating but if you go that route, you treat the pony wall just as you would any basement wall, the space needs to be conditioned. And the bottom of the posts that will be below plastic can be wrapped with peal and stick. Plastic in pieces want to over lap 1 ft and be taped..
> Up here vented or encapsulated crawlspaces get a 2" skim coat of concrete over the poly.
> 
> Take time to prove that all water issues are solved before moving ahead or you can buy lots of trouble.


Why are you not a fan of encapsulating crawl spaces? All of the building science I have read on crawl spaces seems to favor it over other methods, except when in areas with flood potential.

I keep getting the advice to make sure the water issues are solved before encapsulating, so I appreciate the additional confirmation there. Even though I'm freezing in the house and seem to care more about insulating and encapsulating for that reason, I understand that the moisture issue needs to be solved first.


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## Nealtw (Jun 22, 2017)

graymoment said:


> Why are you not a fan of encapsulating crawl spaces? All of the building science I have read on crawl spaces seems to favor it over other methods, except when in areas with flood potential.
> 
> I keep getting the advice to make sure the water issues are solved before encapsulating, so I appreciate the additional confirmation there. Even though I'm freezing in the house and seem to care more about insulating and encapsulating for that reason, I understand that the moisture issue needs to be solved first.


Is your HVAC system big enough to handle the extra cubic ft of the crawlspace.
If you have a flood of any kind, what is the plan for cleaning up the swimming pool under the house. Remember the drain and sump is not connected to the inside of the encapsulation. If the sump backs up and flood under the encapsulation, when will you know and what is the plan to clean that up.

Some experts will tell you that you don't need as much Hvac down there . As heat is expected to go up and heat the floor to be effective the heat would have to be directed to all areas of the sub floor.

If the Hvac is Tstat controlled from the living area how effective will it be for the crawlspace, will is actually change the temp of the floor?
I am not saying you should not do it. But how much more will it cost to raise the house so you can actually use the heated basement you are building?


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## user_12345a (Nov 23, 2014)

Encapsulating the crawl space moves the heat loss from through the floor which is hard to insulate and has thermal bridging to the crawlspace walls instead.

If the heating system is too small for an encapsulated crawl space, it's too small for a cold crawlspace with insulation under the floor.

The ground is above outdoor temp in winter. so a crawlspace with heat loss through the walls will cause less energy loss than a ventilated crawl space with heat loss through the floor, into the space.

With just floor insulation, a unheated, uninsulated crawlspace must be ventilated in winter to purge the moisture that leaks in through the foundation and floor. The ventilation makes the space very cold so it really jacks up the heating bills.

It's like having a cold attic, only there isn't sufficient space to get the R40+ needed and you have thermal bridging. Plus cold floors.

What u can do, r-value wise depends on your floor joists.



> Regarding the stem wall not needing to breathe to the inside of the crawlspace, do you have any source you can point me to on that? It's been my biggest concern.


I'm not familiar with the terminology you're using. by stem wall u must mean foundation wall.

I know the theory and so this is what I'm going to use to back up my statements with.

Foundations are made from poured concrete or brick.

Both can stay wet and be fine; they're always wet to varying degrees due to contact with the soil. Unless you have really good waterproofing on the outside.

Hydro-electric dams are made from concrete and last a century or more, always being in contact with water.

Do you know that concrete actually getting wet and drying harms it? The water picks up minerals as it moves through the concrete. As the water evaporates, the minerals are left behind.

The mineral deposited on the surface is referred to as efflorescence.

So having a foundation get wet and dry out to the inside actually isn't the greatest over several decades.

Drying potential is needed when you have a framed wall and other building materials at play.

The issue with ordinary exterior walls is that the moisture condenses and rots out building materials.

Any moisture that gets in has to get out somehow. You need one side with drying potential at least and the warm side air tight.

With concrete, water won't rot it out.

The basement or crawlspace wall, insulated conventionally with a vapour barrier and insulation can be more problematic on paper. while many foundations have been insulated this way - most with good water proofing and are fine, from a building science perspective it's a bad idea.

With a vapour barrier and insulation, you need drying potential so moisture that gets in from both sides (the barrier being imperfect) doesn't condense and reduce insulation r-value, rot out framing, etc.

But you have a vapour barrier on one side and a moist foundation on the other. The moisture has no where to go.

Putting foam on exterior walls with no ventilation in crawl space, dehumidifier for summer, tiny source of heat for winter reduces the risk of having issues.

When you have a total thermal break right on the concrete, you don't have to worry about condensation at all.


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## graymoment (Dec 16, 2017)

user_12345a said:


> Drying potential is needed when you have a framed wall and other building materials at play.
> 
> The issue with ordinary exterior walls is that the moisture condenses and rots out building materials.
> 
> ...


I mistyped and I can't edit my post. If you look at my previous posts you will see I meant the *wood framed pony wall*. 

As you stated, moisture will rot out building materials, and that's the part of this whole setup I can't seem to figure out. How to insulate the wood framed pony wall and encapsulate the entire crawl space, and not end up with moisture in the framing members? 

If you look at this video you'll see what I'm talking about. I'm not sure on the best approach with my setup.

I'm also not going to be able to fully encapsulate the dirt floor with over 50 posts down there, but I'll do my best. It'll involve a lot of taping and cutting of poly.


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## Nealtw (Jun 22, 2017)

Are you in an area that has radon gas? That should be tested for in case that has to be part of the plan.
I would run poly up the concrete wall and tape it at the top with butyl tape that will direct any wicked water from the concrete down. The moisture in the wood will be no different than the moisture in the house walls above. It will vent to the outside at the black paper is not sealed to the house.
2 ft wide strips of poly wrapped around the concrete part of the piers stuck with butyl tape cut the corners so the lower have lays on the ground. then the ground cover can be taped to it.


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## user_12345a (Nov 23, 2014)

Is the "pony wall" all above ground with concrete starting at the ground? 

What you're referring to they seem to call a cripple wall.

What's on the other side?

Presumably the exterior already has some drying potential. It will unless you have something impermeable on the outside. Drying potential you need on one side of exterior walls.

If it doesn't have good exterior drying potential, you have to look at something that provides a thermal break and but is moisture permeable.

Roxul board cut and put between the studs comes to mind.

Moisture can penetrate the wall from the outside due to rain, high humidity, etc; needs to come out somehow.


The type of wall you have can actually be insulated with batts and vapour barrier and be okay. Assuming it's all framed and above ground - concrete all below. Don't even need foam on that part.

The foundation below ground is best insulated with foam.


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## graymoment (Dec 16, 2017)

Nealtw said:


> Are you in an area that has radon gas? That should be tested for in case that has to be part of the plan.


I'm in zone 3, which is the lowest rated zone, so I should be pretty good there.



> The moisture in the wood will be no different than the moisture in the house walls above. It will vent to the outside at the black paper is not sealed to the house.


I don't believe that is true, as the exterior walls in the house can ventilate to the outside and the inside of the house. Vapor barriers between insulation and drywall is not a common practice where I am. 



> 2 ft wide strips of poly wrapped around the concrete part of the piers stuck with butyl tape cut the corners so the lower have lays on the ground. then the ground cover can be taped to it.


I'm a little worried about bringing the vapor barrier above the short (~4-5") concrete pads. I don't want to put the wood posts below the vapor barrier. Dry wood is the goal here.


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## Nealtw (Jun 22, 2017)

graymoment said:


> I'm in zone 3, which is the lowest rated zone, so I should be pretty good there.
> 
> 
> I don't believe that is true, as the exterior walls in the house can ventilate to the outside and the inside of the house. Vapor barriers between insulation and drywall is not a common practice where I am.
> ...


Paint in your house is a vapour barrier. And it looked like your sheeting was ship lap so your walls will breath. Just wrap the pier blocks up close to the wood. If you are correcting any moisture problems there will not be much moisture to deal with there.

The radon gas was just a thought, we don't have it here either.


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## user_12345a (Nov 23, 2014)

What kind of climate are you in? This will dictate best practices.

Interior plastic vapor barriers are used in cold climates to stop warm, moist indoor air from leaking through insulation and hitting cold surfaces, leading to condensation and rot. They stop moisture diffusion too but this is a minor issue.

The air leakage also reduces the r-value so they help with that.

A tight wall assembly is essential for batt insulation to work well, at a high r-value without leading to condensation and rot. The insulation makes the surfaces cold.

Dense pack cellulose is a different story; it stops most air movement so you don't have these issues.

Now with foam, it's a complete thermal and air break, not allowing moisture diffusion or air (with moisture) movement. And it works great in both cold and hot climates. The parts of the wall that can get exposed to moisture on both sides of the insulation have good drying potential -> lets say if moisture gets in from heavy rain hitting the exterior of a wall.

In super hot humid climates, when batts are used, the vapour/air barrier should be there but on the exterior side.

Just because vapour barriers aren't common where you are, doesn't mean walls need to "breath" or have drying potential on both sides. Just means that's what's done in your area/climate.

You only need drying potential on one side. Houses in northern climates are build with vapour barrier on warm side and a vapour-permeable but air tight and water proof membrane on the outside. ( to protect the structure from water and serve as a drainage plain. Helps with air-tightness too)

They don't rot out.

"Breath" is a word that should be stripped from the vocabulary when it comes to discussing wall assemblies.

"Breathing" = air movement. Air movement through a wall assembly is bad and what causes low insulation performance and condensation. Bad for air quality too, with air leaking through the building materials, bringing stuff in u don't want.

You want drying potential; you don't want it to "breath".


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## Nealtw (Jun 22, 2017)

user_12345a said:


> You want drying potential; you don't want it to "breath".


We do everything to stop air flow and we use the word breath as the normal expansion and contraction of the air with seasonal change. That is allowed to happen to the outside. It shouldn't be confused with leaking.


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## graymoment (Dec 16, 2017)

Nealtw said:


> Paint in your house is a vapour barrier. And it looked like your sheeting was ship lap so your walls will breath. Just wrap the pier blocks up close to the wood. If you are correcting any moisture problems there will not be much moisture to deal with there.
> 
> The radon gas was just a thought, we don't have it here either.


The paint in my house is latex, which according to buildingscience.com has 3.5-6.1 perms (dry cup), and some samples they have measured at 8-10 perms. It's not a vapor barrier.

My sheeting is stucco with 2 layers of 60 minute paper and open framing with Roxul mineral wool batt insulation. There is not insulation in the pony wall in the crawl space, which is one of the main decisions I have to make in this process:


How to insulate the crawl space walls
Where to run the vapor barrier to

For the insulation, I'm trying to adapt the information from this Building Science article. I'm having a difficult time adapting it as this seems to outline methods to use when doing new construction. I'm unable to add capillary breaks between the footing and the bottom plate, or the top plate. I'm also unclear why rigid insulation on the footing nees to be vapor semi-impermeable or vapor semi-permeable (foil facing or plastic facing not present). Especially if I'm adding a vapor barrier over it.


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## graymoment (Dec 16, 2017)

user_12345a said:


> What kind of climate are you in?


I live in coastal Southern California (Orange County). According to this map, I'm in climate zone 3.


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## Oso954 (Jun 23, 2012)

Insulate the floor to r19, don’t worry about the cripple wall. Keep the vents open year around.

Guys, it’s about 69f down there, low tonight is forecast to be 42f. Humidity is about 13. They are forecasting 74f and 43f tomorrow.
The last time it froze in December was 1998 when it hit 32 overnight.


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## graymoment (Dec 16, 2017)

Oso954 said:


> Insulate the floor to r19, don’t worry about the cripple wall. Keep the vents open year around.
> 
> Guys, it’s about 69f down there, low tonight is forecast to be 42f. Humidity is about 13. They are forecasting 74f and 43f tomorrow.
> The last time it froze in December was 1998 when it hit 32 overnight.


Humidity is low right now. Average relative humidity year-round is 65, and obviously higher in the summer months. Here's a chart. 

The fact that the crawl space is below grade means that it is always much colder in the crawl space than the outside, which means condensation in the summer is going to happen. Not as bad as many areas of the country, of course. 

That said, it's not really cheaper to insulate the subfloor than the crawl space walls, and it eliminates drafts. Because the soil is always moist, it makes sense to encapsulate. If I'm encapsulating the soil and insulating, why not condition the space? It's a legitimate question. If you have a logical reason to leave it open, I'm all ears, as I'm doing most of the work myself.


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## user_12345a (Nov 23, 2014)

In an area with low humidity year round, you can get away with a vented crawl. 

But if you get any winterish weather or even hot weather, it's important to note that batts in the floor don't have very good thermal performance. Unless you can do like R-30+.

Have you have been inside a house, either visiting or living and the room above the garage is always cold when you have a garage partially or fully recessed into the house?

That's why. The builders put R-19 or something and it never works right.

Get rid of the cold space, insulate where you can have a continuous thermal break and you get better results.

A fix is to spray foam and at least get decent r-value -> 




Maybe in southern california, if your climate is mild, you don't have to go to great lengths to insulate.

My mindset, i assume everyone is in a cold climate because i am.


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## graymoment (Dec 16, 2017)

user_12345a said:


> A fix is to spray foam and at least get decent r-value ->


I really like the closed cell spray foam method for insulation from so many angles other than getting to whatever you're covering in the event you need to access plumbing, electrical, subfloor, etc. I wish it was more common and less of a markup where I am. 

Maybe in southern california, if your climate is mild, you don't have to go to great lengths to insulate.



> My mindset, i assume everyone is in a cold climate because i am.


It seems that what works in more extreme climates just highlights the importance of those methods. It doesn't mean they aren't the best method in more temperate climates as well. There's just less pressure to do be as good with insulating.


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## Rich_SC (Feb 10, 2017)

I used closed cell spray foam on my crawlspace walls and the rim joist. Also totally encapsulated the dirt in the crawlspace and sealed all vents. It's now a stable temp and humidity and the big benefit is no more musty dusty smell. It's made a huge difference. 

After researching all the diy spray foam options the cheapest was actually eBay.


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