Insulating crawl space

[allinon72]

Guys,

The majority of my house is situated on a basement, with the exception of the living room, which has a crawl space. The crawl space is vented to the outside and has no vapor barrier OR any insulation between the floor joists, making the room quite cold in comparison to the rest of the house. The crawl space has no water pipes in it, just HVAC.

What's the best way to take care of this? Install traditional insulation between the joists? Vapor barrier? Spray foam?

 

[5lima30]

Unfaced batts of insulation held up with pieces of wire between the floor joists is what I have in my house. Also make sure you have a vapor barrier down on the ground of the crawl space. YMMV.

 

[Mavawreck]

I work for a general contractor who specializes in high performance renovations and new homes - so color me biased. I like sealed crawl spaces. In most cases here in NC, they will yield a 8% +/- savings over a traditionally insulated home. Given you have no insulation and your duct work is most likely poorly insulated and unsealed (I say this because most of them are) you should see higher numbers.

Traditional floor insulation
Pros:
- Cheap
- You can do it yourself
Cons:
- It's difficult to install batts correctly, gravity is constantly working against you. Grade one insulation is consistent, unbunched yet without gaps. It needs to be split around wires and any other penetrations
- Fiberglass is not an air barrier. All penetrations and chases need to be sealed before installing batts to get the full thermal value. Who cares you might ask? It's amazing how quick your insulation becomes worthless when installed incorrectly. To the point it's almost not worth doing. So do it right. Think wool sweater on a windy day.
- Your duct work needs to be fully insulated (R8 whenever possible or better) and sealed. There are a couple of things going on here. One you are letting out conditioned air which should piss you off. Do you leave the window open when the AC is running? Probably not. Also you are going to be sucking air from the crawl space depending on where the leaks are, introducing all kinds of containmentants into your air and bypassing the filter. A lot of times the boots are uninsulated so you're pumping 60 degree air all summer through a piece of sheet metal with 90 degree air on the other side (at least in NC) and it starts condensing like a beer can in short order. Opposite is true in the winter. So thats introducing a lot of moisture into your crawl space and duct work.
- You need a vapor barrier, 6 mil at least and carry it 6" up the walls and around all columns.
- The insulation is going to fall, typically seems to stay up around 10 years
- Vented crawl spaces are a bad idea for several reasons, here in the south the air outside is moist, it hits the cool crawl space and reaches dew point. Promoting rot, mold, and lousy indoor air quality.

Sealed crawl space
Pros
- it's a better system
- More efficient, more durable, encourages a longer life for your home and improves indoor air quality.
- bringing the hvac system into conditioned space means it will be able to operate more efficiently. Duct leakage becomes less important - seal the supply side and go.
Cons
- it's expensive
- the market is flooded with morons claiming to seal crawl spaces that have no idea what they are doing or even a basic understanding of building sciences. If you go this route, make them test it and follow advanced energy's protocol (http://www.crawlspaces.org/)
- if you have any sort of natural combustion devices in the crawl space, do not seal it. (atmospherically venting furnace of water heater)

If you decide to go that route, you're welcome to send me a PM and I can send you a check list of things to make sure they complete.

 

[Mavawreck]

I also really do not like spray foam unless there is a really good reason for installing it. I've recommended it twice - once over a basement garage in a 60 year old home where the owners parked cars. We needed a high R value in a small amount of space. And in a 100 year old farm house with a vaulted second floor that code required I either vent the soffitts or install a air barrier. I always recommend air sealing prior to installing spray foam because it tends to expand quicker than it fills, meaning it commonly results in voids in the install. I would expect that to be the case in a difficult crawl space application. Make the contractor show you thermal images of the install and test the home before and after with a blower door.

I'm a jerk with contractors but I'm allowed to be because I am one myself. I don't ask anything of anyone else that I am not willing to do. So you can find people out there who will do it.

 

[Torque1st]

Thanks for the info and link Mavawreck.

I have the same situation as the OP and that living room typically runs at least 5°F different than the rest of the house. I have insulated the HVAC runs but the floor and register boots are uninsulated. I can't even get down in that crawlspace anymore due to age.

 

[allinon72]

I was under the impression that I should not seal up the crawl space because it would be a cold zone up against the warm zone of the house, which would create moisture. There are simply two vents at both ends of the crawl space...seems I could block those easily and seal the space but I'm worried about moisture.

The only thing in the crawl space is a single insulated flex duct and one uninsulated return duct.

What is the best way to attach a vapor barrier to the ground?

 

[cowboyjosh]

In Colorado I DO sometimes recommend closed cell spray foam in crawl spaces and the box sills and rim joist in basements. I also tell folks that your energy bill will never be $0, and every house looses heat and A/C. Sometimes when folks want the house to be tight, tight, tight, we have to caution them that too tight the furnace becomes oversized and then short cycles, etc. There can be allot of un-intended consequences of a house that is too tight.

 

[allinon72]

In Colorado I DO sometimes recommend closed cell spray foam in crawl spaces and the box sills and rim joist in basements. I also tell folks that your energy bill will never be $0, and every house looses heat and A/C. Sometimes when folks want the house to be tight, tight, tight, we have to caution them that too tight the furnace becomes oversized and then short cycles, etc. There can be allot of un-intended consequences of a house that is too tight.

Well Josh that sounds like the better problem to have, but I don't think I'm anywhere near that.

 

[wintermute]

Years ago I used a fully encapsulated fiberglass for my crawlspace. What's nice is that during installation, the amount of **** that falls in your face is greatly reduced. My crawlspace is vented, but I close up the vents in the winter and open them up for summer. The circulation in hot weather helps with cooling and vise-versa with closing it up for the cold weather.

 

[Mavawreck]

I was under the impression that I should not seal up the crawl space because it would be a cold zone up against the warm zone of the house, which would create moisture. There are simply two vents at both ends of the crawl space...seems I could block those easily and seal the space but I'm worried about moisture.

The only thing in the crawl space is a single insulated flex duct and one uninsulated return duct.

What is the best way to attach a vapor barrier to the ground?

The idea behind a sealed crawl space is that you are turning it into a conditioned space. Depending on the size, one or two supply vents should be added and the walls insulated with rigid insulation board. I'm not sure of code where you're at, but we insulated the walls with R10. It's involved but the end goal is pretty nice and very durable. We put in a dehumidifier too.

If you're just laying a vapor barrier, use long ground spikes and pound them in with a hammer. I've found the bent wire stakes rarely stay put and depending on the soil may not work at all. We spike it down (6d with washers, trying to find a link for you), shoot it into the wall with power shots 6" up (you could attach it to the wall other ways), and mastic the top edge if we are just laying a vapor for government weatherization.

 

[allinon72]

So what you are saying is I'm OK with closing the vents for the winter? I plan on laying down a vapor barrier as well.

Installing insulation between the joints would be a real *****.

 

[dirttracker18]

Maverick

Great to see someone with your MODERN understanding. Too many people just listen to the old contractors who tell them to just leave well enough alone or worse misguide them to something that either makes it worse or is just a waste of money.

I am no expert but I have spent a great deal of time researching this subject as I renovate my home. Living in Northern Ontario means I can save significant money by insulated and sealing properly. I wanted to be sure I spent the money in the right places. I am still learning and may lean on you for advice as I continue.

Hope you don't mind

 

[ZYA_LTR]

I too have a livingroom addition on a crawl, from what i remember, the "sealed basement" idea was what i was told to go with. i wanted to insulate the floor of the house and leave the crawl space vented. The contractor advised against, saying that by sealing the crawl, and installing a vapor barrier on the ground, and 6-12" up the walls, then insulating the walls/foundation with insulation, i would be essentially doing like other have described and making the crawl a "conditioned space" and seal the vents in winter, and open in summer, and that would be my best bet for crawlspace insulation. I think they were reccomending the ridgid foam board for insulating the foundation? I would have to find the quote they gave me. I would prefer the closed cell spray foam, but that **** is pricey!

 

[Air_Cooled_Nut]

Vented crawlspaces depends on the region, right? South Carolina is WAY different from Oregon (having lived in both places, I know).

Mavawreck, how much to have you insulate my crawl space

 

[JMURiz]

Good info to have...any ideas on the best solution to a 3-season room (a screened porch where the screen is replaced with windows and there are no heat vents)?

 

[DustynF]

So what you are saying is I'm OK with closing the vents for the winter? I plan on laying down a vapor barrier as well.

Installing insulation between the joints would be a real *****.

So I just did all this to my crawlspace after a lot of research and speaking with professionals, I sealed my space up totally. I first put a sump pump in the ground just in case water ever infiltrated. Second thing is buy a good quality vapor barrier. I bought a mid level 12 mil vapor barrier with seam tape, two sided tape and foundation pins. It took me two days to totally encapsulate the space. I noticed an immediate difference in the humidity level within the house.

I went back and forth on the insulations and like the other poster had said, there are many ways to improperly install insulation that renders it useless. I decided to have it sprayed with closed cell foam over the walls which were covered with the vapor barrier all the way to the sill plate. They also sprayed between the floor joists and the band board. The floors are no longer cold and the heater cycles are spaced further apart.

I sealed my vents up with rigid foam board then covered them with some galvanized metal plates to protect them.

If you are going to insulate yourself, I would definitely go with rock wool insulation. It will hold form and doesn't itch like fiberglass

I purchased my vapor barrier from these people: http://www.crawlspacevaporbarrier.net/Crawl-Space-Vapor-Barriers-_c_11.html

 

[allinon72]

On the subject of vapor barrier...I have a bit of an obstacle as there is the old concrete driveway and steps in the crawl space. How do I properly cover over that with the barrier?

 

[Mavawreck]

Shoot it into the walls with power shots if possible, or tape it up and cover the tape with mastic for when the tape fails. It is typically pretty stable if you attach it to the walls and columns, tape the seams with vinyl tape. I don't anchor the vapor barrier to the ground in fully sealed crawl spaces.

On basic vapor barriers we go 6mil, 10mil ladder reinforced on sealed spaces and double it up in high tread areas.

If you're at all concerned about humidity levels - get a humidity meter from your favorite home improvement store with a remote display. Probably cost you $30 or so and you can see what happens from the comfort of your living room. Buy two sensors and compare the inside to the outside to your crawl space. Which is what I did at my folks house - they have a 2300 sf one story ranch with 6 foot foundation walls on the back side. It was going to cost a fortune in materials, they have ok floor insulation and a decent vapor barrier. I sealed up all the duct work, insulated the register boots, and closed the foundation vents. We're just watching it for now.

If you're going through the trouble of laying a vapor barrier yourself, might as well lay a thick one. And if you're going to insulate, it's actually easier to attach it to the walls than it is the floors. Typically you have to leave a 3" inspection gap (3" from the first wood member) at the top per code, as mentioned you need an emergency drain. I prefer a drain to daylight as the sump pump is just another device to fail and another thing for homeowners to keep up with. It doesn't work in all applications though.

Is your crawl space connected to the basement in any way?

Another concern is radon, I do not know if your area is prone to issues or not. It's worth considering. Radon detectors are cheap, send it in after a year for analysis.

 

[allinon72]

We already have a radon mitigation system that was installed by the seller of the house so we're good there.

 

[6768rogues]

Our code does not allow for a sealed crawl space.
Vapor barrier should be placed on the ground.
Spray foam is best but the most expensive.
Bats can be used cost effectively but have to be supported.

 

[Mavawreck]

Our code does not allow for a sealed crawl space.
Vapor barrier should be placed on the ground.
Spray foam is best but the most expensive.
Bats can be used cost effectively but have to be supported.

1. I don't believe that. I have a harder time getting spray foam to pass with building inspectors than I do sealed crawl spaces. But then again this is the south.
2. It should be placed on the ground, it should also go wall to wall and then some
3. Spray foam is not the best, but it can be very good. Depends on the application. It often is expensive but not always the most expensive. I've had guys spray foam cheaper than I can blow fiberglass in walls.
4. Batts are typically cost effective, but even when they are supported, after a few years they almost always fall down. Isaac Newton, apples, head.... The insulation needs to be installed consistently against the floor to get full thermal value and even when supported it will droop. When put in horizontally it falls and vertically it sags. Bane of my existence next to the old lady and these lousy cars I drive

 

[DustynF]

I had closed cell under the house sprayed 2 inches thick and a garage (1000sqft)3-4 inches sprayed for 1300. I probably would still be under the house cutting bits and pieces for insulation.

 

[DustynF]

If you decide not to go with rock wool and do go with fiberglass batts make sure they are not faced. The paper makes great food for mold!

 

[allinon72]

I think I will be doing foamboard on the foundation walls with a vapor barrier.

Thanks everyone for the suggestions.

 

[Mavawreck]

Sounds good. On the foundation vents, block them off separately. Typically back them with a piece of thin gauge aluminum to stop rodents and then cut a separate piece of insulation to block them off.

 

[Air_Cooled_Nut]

So what about using Reflectix? Stapled and isn't supposed to mold.

 

[scotw]

When using foamboard on the foundation walls, which side of the vapor barrier do you put the foam?

 

[Mavawreck]

So what about using Reflectix? Stapled and isn't supposed to mold.

Where are you thinking? I use it to back knee wall insulation to prevent the batts from sagging. Staple it up and then seal the edges. Believe the R value is only like 4 and requires an air gap. Also use it on duct work that is too close to a wall for R8.

Vapor barrier goes against the wall, attach foam board over top, seal the foam board to the wall.

 

[Air_Cooled_Nut]

Where are you thinking?...

Click on the Reflectix in my post, it will take you to their site. I was thinking under the house.

 

[Torque1st]

Dust and particulates quickly render reflective 'insulation' worthless. There is lots of info on the web about it.

 

[CrawlSpaceMoisture]

On the subject of vapor barrier...I have a bit of an obstacle as there is the old concrete driveway and steps in the crawl space. How do I properly cover over that with the barrier?

Don't sweat it too much. If you're just putting poly on the floor - run it to the concrete or steps and stop it. Most codes I've seen recognize concrete as a 'vapor barrier' floor covering.

 

[John in OH]

Mavawreck,

Man, you are providing some GREAT info!! I'm new to the south and new to crawl spaces ... the house we bought a year or so ago is relatively new, but has a vented crawl space, fiberglass insulation between the floor joists and a sheet vapor barrier that, based on what you've said and what I've read, has been poorly installed ... just laid on the ground with no seam seals or wall seal. This all leads to some questions that I hope will add to rather than hijack the OP's posting ...

-- Can you provide a better description of these vapor barrier hold-down pins? How long, what gauge, spacing, etc?
-- What kind of tape should be used to tape the seams of the vinyl barrier? How wide and what can I ask for at the building supply house?
-- How do you attach the rigid foam board to the block walls? Nails or adhesive?
-- Is the 3" gap left at the top of the foam board for termite inspection?
-- Do you seal the vents on the inside or outside of the foundation?
-- What brand of dehumidifier do you recommend?

I want to attack this crawl space next spring and try to reduce the humidity as I've noticed some light mold on a few of the floor joists. I did buy a remote humidistat and the humidity in the crawl space can, at times, get up to 80% or so depending on the outside humidity and temperature!!