What to do about crawl space floor

[allinon72]

I have a new construction home with a large crawl space, gravel floor. Builder did a real half *** job leveling the gravel and putting down 6 mil plastic. I came back later and spray foamed the bare concrete walls…temperature, moisture and humidity are all fine, but I want to level out the floor put something substantial over the gravel. I use it for storage so it would be nice to have a flat floor with a thick plastic over it.

I see all the fully encapsulated crawl spaces,
completed by professionals, lined with white plastic (probably 20 mil) and it always looks like they put rigid insulation down on the ground, but Google seems to think that’s not advisable due to mold growth underneath. So do those companies do a vapor barrier first, then rigid foam, then a 20 mil plastic over that? Whats the best course of action? Debating if it’s worth it to tear out current vapor barrier, rake out and level the gravel, and implement the proper solution.

 

[Roert42]

I would either ignore the crawl space or concrete it in.

There are a lot of houses with dirt basements around here, but I wouldn’t use it to store anything valuable unless it was concreted.

 

[d.mcfarland]

Post a picture, would be very helpful in this situation.

 

[mike93lx]

No need to insulate the floor. Roughly level with a rake and then lay down thick plastic while taping all seams and sealing to the walls with a flexible sealant.

If the existing is overlapped, you can just tape it and add where needed.

Smooth is nice but not really necessary

 

[mm08822]

Existing ventilation/air flow would be good to know.....and, what if any, you plan to add.

What are the area dimensions?
Headroom?
How much height below grade?
Access?
Available help?
Any water seepage inward?


Years ago, I laid concrete in a small, narrow but long crawl space 3.5" headroom. No VB used, rigid insulation probably didn't even exist then, but it was open to be basement.

 

[mm08822]

I once insulated the first floor of a condo using a creeper in the crawl space. The floor was screeded decently to do that..

 

[mike93lx]

Existing ventilation/air flow

Hopefully zero to the exterior with the spray foam. It should be part of the conditioned envelope

 

[mm08822]

Hopefully zero to the exterior with the spray foam. It should be part of the conditioned envelope

depends what OP started with/modified since.

 

[PCustoms]

but I want to level out the floor put something substantial over the gravel. I use it for storage so it would be nice to have a flat floor with a thick plastic over it.

Up here we dig our crawl spaces at least 8' deep and level the floor out with concrete. Assuming drainage is OK works great for a large amount of dry storage.


I find it fascinating to see the effort and money that goes into management of moisture in a pretty useless space. I mean, I understand the need for it, but just don't get why in this day in age basements aren't more common

 

[mike93lx]

Up here we dig our crawl spaces at least 8' deep and level the floor out with concrete. Assuming drainage is OK works great for a large amount of dry storage.


I find it fascinating to see the effort and money that goes into management of moisture in a pretty useless space. I mean, I understand the need for it, but just don't get why in this day in age basements aren't more common

Because much of the country doesn't need to dig down far enough to justify an excavation, plus soils don't always drain well. My frost line is 1ft..pretty much scrape the organics, make a trench deep enough to form the footing and pour.

A basement in my area would be a pool if pumps aren't added or if the house isn't on a slope.

 

[Overboost44]

Up here we dig our crawl spaces at least 8' deep and level the floor out with concrete. Assuming drainage is OK works great for a large amount of dry storage.


I find it fascinating to see the effort and money that goes into management of moisture in a pretty useless space. I mean, I understand the need for it, but just don't get why in this day in age basements aren't more common

The reason we don't have basements is because we are on an island. Water table is too high. My problem is that my crawlspace is literally just that. It is about 2.5' deep. Terrible for getting under the house, but I can't imagine what someone would charge to make it deeper.

Some people have theirs encapsulated, but that is $12-15k. I have about a 6 mil liner that is not taped and is showing its age. When I build the garage, I have considered getting extra Stego 10 mil to lay down, tape and secure to the walls.

 

[mike93lx]

The reason we don't have basements is because we are on an island. Water table is too high. My problem is that my crawlspace is literally just that. It is about 2.5' deep. Terrible for getting under the house, but I can't imagine what someone would charge to make it deeper.

Some people have theirs encapsulated, but that is $12-15k. I have about a 6 mil liner that is not taped and is showing its age. When I build the garage, I have considered getting extra Stego 10 mil to lay down, tape and secure to the walls.

12-15k should do full encapsulation, wall insulation and probably dehumidification, based on what I've paid in VA for crawl space work. If it's that for just plastic, that's crazy pants or a monster house

 

[Overboost44]

12-15k should do full encapsulation, wall insulation and probably dehumidification, based on what I've paid in VA for crawl space work. If it's that for just plastic, that's crazy pants or a monster house

It would be full encapsulation and plenty of lighting. I could get a beach chair and watch TV in my neighbors crawl but his is a good 3'

 

[mike93lx]

It would be full encapsulation and plenty of lighting. I could get a beach chair and watch TV in my neighbors crawl but his is a good 3'

I just had a contractor do plastic in mine and I did the dehumidifier. The insulation still needs to get done at some point, but I doubt it would ever pay back

 

[Overboost44]

I just had a contractor do plastic in mine and I did the dehumidifier. The insulation still needs to get done at some point, but I doubt it would ever pay back

That's nice. Do you mean wall insulation or floor joist insulation? I have a good dehumidifier that is brand new. I just want that nice white poly under there. Then I have to seal off the air vents from the inside.

 

[mike93lx]

That's nice. Do you mean wall insulation or floor joist insulation? I have a good dehumidifier that is brand new. I just want that nice white poly under there. Then I have to seal off the air vents from the inside.

I currently have floor insulation but ideally it would be removed and replaced with wall insulation.

All exterior vents were sealed as part of the encapsulation on mine

 

[Overboost44]

I currently have floor insulation but ideally it would be removed and replaced with wall insulation.

All exterior vents were sealed as part of the encapsulation on mine

Mine seems to always be about at ground temp with the current setup. I know my neighbor had all of the floor insulation removed but I don't know if they put anything on the walls. It would certainly make sense to do that.

OP, I realize the above is OT but maybe it helps you. That said, I am obviously not an expert but I would rake it out level, replace with 15 mil and insulate the walls...or just wait for an expert to come along. I will be watching. @mike93lx sounds like he has a good plan.

 

[mm08822]

I currently have floor insulation but ideally it would be removed and replaced with wall insulation.

From what to what?

 

[mike93lx]

From what to what?

The insulation is in the first floor framing, separating the crawl and living space. The better place for insulation is the walls (what the OP has) and nothing in the floor framing. Then the crawl is fully inside the conditioned envelope

 

[mike93lx]

Mine seems to always be about at ground temp with the current setup. I know my neighbor had all of the floor insulation removed but I don't know if they put anything on the walls. It would certainly make sense to do that.

OP, I realize the above is OT but maybe it helps you. That said, I am obviously not an expert but I would rake it out level, replace with 15 mil and insulate the walls...or just wait for an expert to come along. I will be watching. @mike93lx sounds like he has a good plan.

I'm no expert, just did some research after buying a house with a crawl. They're almost always done improperly even today ("the house has to breathe!" and garbage like that).

Airseal, insulate and condition

@allinon72 if you will be going in and out for storage, I'd recommend putting either under or over the plastic to protect it and try to keep it clean. I wasn't good about dirt on a plumbing project and it both made the crawl less nice to move around in but also damaged the plastic in a few spots. I need to get under there to do some patching at some point. At rhe entrance, I laid down some extra double bubble insulation which has helped a lot with durability

 

[lmg]

I would either ignore the crawl space or concrete it in.

There are a lot of houses with dirt basements around here, but I wouldn’t use it to store anything valuable unless it was concreted.

Yes, concrete, and leave a creeper down there. Consider a lean concrete mud mat.

 

[twinfin]

If at all possible, pour a concrete slab in the crawl space. When I was having my house built back in 2017, my builder asked me if I wanted a slab under the house when he was preparing for the foundation pour. I decided to go for it and am glad that I did.

The first time you have to go under the house for some reason, you’ll be amazed at what a difference it makes being able to scoot from one end to the other on a creeper. It eliminates the possibility of rodents burrowing in underneath the foundation and keeps ground moisture and dirt out. The space will stay much cleaner too over time.



While you’re at it, have the electrician wire in some lights and buy a crappy old creeper at a garage sale and just leave it down there. If I ever build another house, I’d do it this way again.

 

[finn]

The insulation is in the first floor framing, separating the crawl and living space. The better place for insulation is the walls (what the OP has) and nothing in the floor framing. Then the crawl is fully inside the conditioned envelope

The insulation between the floor joists will become a soggy, moldy mess. Ask me how I know ( bought the house next door that had insulated floors and old school foundation vents. The warm moist summer air brought humidity into the cool crawl through the vents where it condensed on the now wringing wet insulation.

Better to insulate put down a thick vapor barrier directly on the dirt, or better a layer of clean well drained stone, tape the seams and wall joint, insulate the rim joist with foam, insulate the crawl walls with rigid foam, or preferably spray foam so the crawl is encapsulated..

Properly done, the floors will be warm.

 

[Miss the Pontiacs]

Concrete

 

[Ak Jim]

If at all possible, pour a concrete slab in the crawl space. When I was having my house built back in 2017, my builder asked me if I wanted a slab under the house when he was preparing for the foundation pour. I decided to go for it and am glad that I did.

The first time you have to go under the house for some reason, you’ll be amazed at what a difference it makes being able to scoot from one end to the other on a creeper. It eliminates the possibility of rodents burrowing in underneath the foundation and keeps ground moisture and dirt out. The space will stay much cleaner too over time.



While you’re at it, have the electrician wire in some lights and buy a crappy old creeper at a garage sale and just leave it down there. If I ever build another house, I’d do it this way again.

That’s looks really nice.

 

[mike93lx]

The insulation between the floor joists will become a soggy, moldy mess. Ask me how I know ( bought the house next door that had insulated floors and old school foundation vents. The warm moist summer air brought humidity into the cool crawl through the vents where it condensed on the now wringing wet insulation.

Better to insulate put down a thick vapor barrier directly on the dirt, or better a layer of clean well drained stone, tape the seams and wall joint, insulate the rim joist with foam, insulate the crawl walls with rigid foam, or preferably spray foam so the crawl is encapsulated..

Properly done, the floors will be warm.

My crawl is dehumidified and the vents are sealed. Without the dehumidifier though, yes, I can see problems forming.

 

[larry4406]

I did concrete slab with vapor barrier in the crawlspace for the kitchen extension.

Its conditioned via a tap off the HVAC system in the adjacent basement.

Perimeter walls of the crawl space and band board were spray foamed.

 

[mike93lx]

If I was building new with a crawl today, I'd definitely concrete it, but can't imagine trying to do that after the fact.

 

[allinon72]

Appreciate the concrete recommendations but at 600sq ft and basement access, that’s a total non starter. It would likely be 10-15k for my crawl space.

 

[driftpin]

In So. FL, few homes have basements. Those w/wood floor joists and whatever flooring do have a crawl space. I added lighting in one house, but most of the crawl space is dirt. There are vents of the side of the prevailing winds (east) and the opposite wall (west). Humidity in the summer is high, but I don't see any mold down there. The height to the underside of the floor joists is < 2.5'.

An attached 1-car garage was changed to a b.r./full bath w/permits. That has a concrete floor, lighting, and ventilation. I use a creeper there.

 

[CraigStu]

Mold was discovered in a house we were selling. My fault. I didn't know enough to make sure to keep the plastic taped and sealed. The official fix was mold encapsulation paint, good plastic well taped and sealed to the foundation and an additional vent in the block foundation. There were already vents on 3 sides but the new vent was a powered fan controlled by a humidistat. Not a dehumidifier, just a fan to promote extra circulation.

 

[mike93lx]

Mold was discovered in a house we were selling. My fault. I didn't know enough to make sure to keep the plastic taped and sealed. The official fix was mold encapsulation paint, good plastic well taped and sealed to the foundation and an additional vent in the block foundation. There were already vents on 3 sides but the new vent was a powered fan controlled by a humidistat. Not a dehumidifier, just a fan to promote extra circulation.

The last thing I'd want to do is **** in hot, humid air all summer. Moving air is better than stagnant, but getting the moisture out and keeping it out is much better

 

[Hank11]

OP, do you want to be able to walk around and store things in your crawlspace? If so, you’re gonna need more than plastic on the ground. Once you get it leveled and smooth out, you can put down heavy plastic and then lay some foam boards on top of that. Then add some plywood, OSB or some sort of hard smooth board to walk on. I wouldn’t do the entire floor that way, but you might be able to just lay down half a dozen sheets and have a good solid floor.

 

[Jackfre]

Forthose with moisture or other problems in crawl spaces Tjernlund make a nice crawl space ventilator.

 

[allinon72]

Perhaps I worded by original post poorly. I’m mainly asking what would provide a semi decent flat and somewhat durable floor. I’m not dragging floor jacks in there, I’m talking making it walkable for Christmas decorations storage retrieval. A solution that will not cause a problem that I don’t currently have …like I said it’s new construction, unvented and within the building envelope so I have no current environmental issues to address, as you would in many crawl spaces. I just don’t want to create one.

 

[PCustoms]

I’m talking making it walkable for Christmas decorations storage retrieval.

Well, it's a crawl space...

 

[mike93lx]

Perhaps I worded by original post poorly. I’m mainly asking what would provide a semi decent flat and somewhat durable floor. I’m not dragging floor jacks in there, I’m talking making it walkable for Christmas decorations storage retrieval. A solution that will not cause a problem that I don’t currently have …like I said it’s new construction, unvented and within the building envelope so I have no current environmental issues to address, as you would in many crawl spaces. I just don’t want to create one.

If you are regularly going in and out, something flexible on top of the plastic would be prudent, like astroturf, maybe.

 

[finn]

Mold was discovered in a house we were selling. My fault. I didn't know enough to make sure to keep the plastic taped and sealed. The official fix was mold encapsulation paint, good plastic well taped and sealed to the foundation and an additional vent in the block foundation. There were already vents on 3 sides but the new vent was a powered fan controlled by a humidistat. Not a dehumidifier, just a fan to promote extra circulation.

The vents are what allowed the mold to grow.

Warm air can hold a lot of moisture. When that warm humid air flows into the cooler air under the house, the humidity increases further, creating a perfect environment for mold to form.

You can’t ventilate your way out of that environment, unless perhaps you heat the crawl above the dew point. I don’t think you can even dehumidify that condition, as the open vents are continually admitting more warm humid air.

 

[Crashlandy]

I have a new construction home with a large crawl space, gravel floor. Builder did a real half *** job leveling the gravel and putting down 6 mil plastic. I came back later and spray foamed the bare concrete walls…temperature, moisture and humidity are all fine, but I want to level out the floor put something substantial over the gravel. I use it for storage so it would be nice to have a flat floor with a thick plastic over it.

I see all the fully encapsulated crawl spaces,
completed by professionals, lined with white plastic (probably 20 mil) and it always looks like they put rigid insulation down on the ground, but Google seems to think that’s not advisable due to mold growth underneath. So do those companies do a vapor barrier first, then rigid foam, then a 20 mil plastic over that? Whats the best course of action? Debating if it’s worth it to tear out current vapor barrier, rake out and level the gravel, and implement the proper solution.

I'm doing the encapsulation thing right now on a 100 year old crawl space. Found a pretty good deal on rubber stall mat to put down first. Then covering with StegoCrawl thick white plastic to control humidity from the ground. For the stand up area with foot traffic, I found some race-deck type interlocking tiles to go on top of the plastic. It's a Big job. Take a look at StegoCrawl.

 

[CraigStu]

The last thing I'd want to do is **** in hot, humid air all summer. Moving air is better than stagnant, but getting the moisture out and keeping it out is much better

Well of course you are correct. But this is what the licensed mitigation company did and what the buyers accepted so I was happy to get the problem solved and the house sold.