Living Efficiently With Tom: Crawl Space Insulation
Thinking about making energy efficient home improvements? Home insulation is a classic homeowner example that comes to mind. Despite long-held aspirations, it was only recently that I tackled the project of insulating the crawlspace beneath my dining room. Cold floors during winter months finally convinced me it was time for insulation.
Choosing the Target
First there was the challenge of getting the large foam board panels home — they certainly wouldn’t fit in our small car. Finally, with a van rented for an unrelated home improvement project, I was able to get three of the 4-by-8 feet sheets home. Procrastination left them waiting in my attic (although, in theory, they helped a little just by lying on the floor up there) until they were featured in a recent interview on changes in energy efficiency tax credits with a local television station. With the added encouragement that they be installed before New Years to claim a 2010 tax credit, I was moved to action.
Getting Started
My first task was to tidy the space up. Fiberglass offers less insulation when it’s bunched up as some of this was. I needed to get the foam board snug against the joists to securely nail it into place and to reduce any air flow above the insulation, which the various scraps of wood and siding would prevent. A temporary solution came in the form of large quantities of duct tape held to the joists with equally large quantities of heavy-duty staples. Once in place, the foam board held the old fiberglass up.
Choosing Insulation
The insulation I chose was the most insulating rigid foam board I could find locally. It has a radiant barrier lining on one side which allowed it to face towards the conditioned room and reflect heat in or out, depending on the season. The other side has a moisture barrier to face outwards and limit dampness getting into and through the insulation, which could cause mold.
The 2-inch thick polyisocyanurate closed-cell foam is rated “R-12.” R values measure the insulation’s ability to resist heat flow. The higher the R value, the more effective the insulation is. The R-12 foam is a great deal more insulating than fiberglass batts and also controls air flow that might cause drafts. Added to the existing fiberglass between the joists — about 4 inches worth — this project easily exceeds the insulation value needed to qualify for a tax credit. It’s not a big credit, though. This was a pretty cheap project. It cost about $100, making it worth a whopping $30 credit on my 2010 income taxes. But hey, every little bit helps.
Missteps Along the Way
After cutting the foam board sheets to size, and maneuvering them into place (requiring the much appreciated assistance of my wife, who had to be called into the dust of the crawlspace), I had a bit of a learning experience as the nails affixing the first sheet began to pull through the foam board under the force of gravity. This was not entirely unexpected — I had tried to find long roofing nails for this project, as they have a plastic disc about an inch wide to prevent them from tearing through roofing materials, but I was unable to find roofing nails long enough to go through the 2-inch insulation and into the joists. My gamble with regular large-headed nails did not pay off.
While scrambling in the dust to keep the nails from tearing through the foam board, I happened upon a ready solution. There were plenty of scraps of relatively thin wood laying about that had previously been used in attempts to hold the old fiberglass insulation in place. Fortunately, the nails I had were long enough to go through small scraps of this wood, through the foam board and securely into the joists. We were back in business.
Once all three sheets were in place, some spray foam into gaps and vapor barrier tape on seams between the sheets and over nail holes ensured that everything was nice and snug to prevent outside air bypassing the insulation.
Mission complete.
I know a lot of instances where this is looked over. My wife and I were getting estimates on a new roof and an Indianapolis Roofing company pointed out that we were missing a lot of insulation. It explained a lot of the drafts we were feeling! Thanks, Peter
I just recently inspected a crawlspace on vancouver island canada. this crawl did have the foiled iinsulation throughout crawlspace ceiling and down sill plates..the house is only 9 yrs old and was a conditioned crawlspace before foil was installed. my concern is ,does this act as a vapour barrier trapping moist air between floor joist, rim joists and causing rot. this area cannot breath once this application has been done. if there is any moisture at all it cannot dry so will attack box ends or rim joists. if it was plastic vapour barrier we would recommend removal. as we live on the west coast we do have alot of humidity. your input would be welcome. thanks bart
The jury is not in on this one and cellulose and fibreglass manufacturers have been battling this one out for years. There are advantages to each approach, and at the end of the day the quality and skill of the installer matters more. I tend to lean toward cellulose if I'm not tearing the whole ceiling out.
Whatever system you use, an important aspect of the insulation working correctly in that location is the airtightness of your ceiling. A properly sealed, tight ceiling below the insulation is an important factor in controlling moisture and air wash in the open space above the insulation. When first isolated my house, I used these resources
http://en.wikipedia.org/wiki/Building_insulation
http://www.designdigs.net/loft-attic-ladders-stairs.html
I would recommend using spray foam. The problem that I had in my house was thremendous radiant heat gain during the summer months. Needless to say, it made an unbelievable difference.
I'm going a totally different direction. I would have recommended that you foam seal the entire crawlspace ceiling. R-Values assume no air leakage and the only air leakage proof insulation is foam insulation as it completely seals the entire crawlspace ceiling.
I'd recommend "closed cell" foam which is a dense low moisture absorbing material. It provides R-6 per inch so at 4 inches you'd have an R-24 insulation barrier. "The closed-cell nature of this foam provides for a highly effective air barrier, low moisture vapor permeability (often referred to as the "Perm" rating), and excellent resistance to water". (fomo.com) Closed cell foam also provides structural rigidity which will keep your floors from moving as much and they'll creak less. (disclosure-I don't sell this or any foam products)
As an IAQ expert I like that you'll be starving any existing mold you covered on the wood from the humidity water source it needs to grow so it will go dormant. The dense foam prevents additional mold spores, along with bacteria, from penetrating through so you'll have prevented any additional germs from penetrating into the wood ceiling. Germs need a food source to amplify and the cellulose in wood is steak for these guys.
Foam insulation solves the air penetration issues which compromise any other insulation choice. Here in the DC area, air penetration into the home from the mold infested crawlspaces has created many sick homes. Eliminating that germ source will improve the indoor air quality and the health of it's occupants. That's why I recommend this to my clients.
Your other choice is to tarp off the floor with 20 mil plastic and run it up the walls-usually 3 feet. Secure it with 2 X 4's and foam seal up to the ceiling making sure you fill the rim joist openings. Many companies add a dehumidifier which are energy hogs. You still have the mold which is living and reproducing in the wood ceiling so I don't like this alternative along with the energy consumption requirement.
You could have made the job much easier and achieved superior performance by using a reflective insulation product, foil or MPET/2 layers of poly bubble film/foil or MPET. They are available in rolls of 4' and 6' wide usually 125' long. With some aluminum foil tape to seal the seams, scissors and a staple gun, attaching the material to the face of the floor joists is relatively easy. When finished you have a reflective insulation that adds significant R-values to the insulation system and both a radon and vapor barrier that will stop moisture for migrating into the floor. I'd be a little concerned about the possible moisture in the fiberglass and would want to make sure the finish wouldn't result in trapping moisture in the system. Reflective insulation has been shown to have particular advantages over other types of insulation products when used for under floors, especially crawl spaces.
Looks like you made the right choice as far as insulating the floor, but I do agree with Harvey Sachs that you would normally try to bring the crawl space into the conditioned basement space if possible, but I see in the picture that you don't have a solid wall on at least one side. Good call on sealing the seams and edges of the foam board. I also agree with Scott Sudreth about the radiant barrier. It can only work as a radiant barrier when facing to an open space, but the foil faced foam is usually higher performance than the regular pink or blue board so it probably is a benefit that you've used it. In my home performance business I usually recommend removing the old fiberglass, installing 1" or more of rigid foam to the underside of the joists, taping all seams and sealing all edges, then dense pack the cavities with cellulose. This ensures full insulation contact with all surfaces and keeps any air from circulating inside the cavities.
Well this is a somewhat unconventional situation for various reasons, all stemming from the room's previous life as a screened-in porch, for the most part. It's under-floor, yet it's outside. There's no plumbing or duct work (I'd be better off if there were duct work... when we close the door into that room it's basically unconditioned space). It's also not closing off access (you can see the lattice work).
Scott, re: the batts: No, not really touching the underfloor, for the most part. They were all held in place with scraps of wood and chicken wire and were definitely not achieving anything resembling a vapor barrier. But as they weren't getting in the way of the foam board, and as they would continue to provide a bit of insulation, I left them in place after doing some tidying. The foam board, with sprayfoam and tape at edges and joints ought to drastically improve that.
Interesting question on the radiant barrier vs. vapor barrier up/down. I'd always been under the impression that the vapor barrier is best on the outside, to keep humidity out of the system (like putting Tyvek immediately under siding, outside of any insulation - - also why the company logos always face 'out'). Of course the radiant barrier is no good for conductive heat, but that'd be the case any way you do it.
You could have made the job much easier and achieved superior performance by using a reflective insulation product, foil or MPET/2 layers of poly bubble film/foil or MPET. They are available in rolls of 4' and 6' wide usually 125' long. With some aluminum foil tape to seal the seams, scissors and a staple gun, attaching the material to the face of the floor joists is relatively easy. When finished you have a reflective insulation that adds significant R-values to the insulation system and both a radon and vapor barrier that will stop moisture for migrating into the floor. I'd be a little concerned about the possible moisture in the fiberglass and would want to make sure the finish wouldn't result in trapping moisture in the system. Reflective insulation has been shown to have particular advantages over other types of insulation products when used for under floors, especially crawl spaces.
You could have made the job much easier and achieved superior performance by using a reflective insulation product, foil or MPET/2 layers of poly bubble film/foil or MPET. They are available in rolls of 4' and 6' wide usually 125' long. With some aluminum foil tape to seal the seams, scissors and a staple gun, attaching the material to the face of the floor joists is relatively easy. When finished you have a reflective insulation that adds significant R-values to the insulation system and both a radon and vapor barrier that will stop moisture for migrating into the floor. I'd be a little concerned about the possible moisture in the fiberglass and would want to make sure the finish wouldn't result in trapping moisture in the system. Reflective insulation has been shown to have particular advantages over other types of insulation products when used for under floors, especially crawl spaces.
A couple of things:
First of all overall your approach will probably be fine. However, with that said I thought i would throw out a few things. First of all your idea of getting a radiant barrier on the top side of the foam board is misleading. For a radiant barrier to work it can't touch surfaces. Once the reflective surface comes into contact with anything (your fiberglass batts)it can no longer act as a radiant barrier but will instead act as a conductor.
You being in Washington dc - probably means that your in a climate zone of 5 or higher. If that is true your vapor barrier must be on the warm side of the assembly. The photos show your insulation installed upside down with the vapor barrier facing down.
When I see batts installed paper side down i immediately wonder if its actually making contact with the floor your trying to insulate. Often we see the batts flush with the bottom of the floor joist but not making contact with the heated/cooled subfloor. If this were true it would mean that our building envelope is compromised. However, with that said the new foam at the bottom of the joists acts as a secondary air barrier and probably makes this a moot point.
My last point is maintenance. I see this approach used quite often as a retrofit measure in homes. The downside occurs when the home has a plumbing leak. Often the foam board is destroyed in finding the leak and not replaced properly. Overall you don't have any dealbreakers - i'm sure it will work fine. However, for the building science geeks out there be prepared to hear similar comments. :)
Wow, what a great article. It is informative and I love the part where you talk about the things that can go wrong when insulating crawl spaces. In fact, you have me thinking about whether or not we should look into that ourselves.
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Particularly where there are ducts in the crawl space, you might want to note two things (a) the large literature from Advanced Energy North Carolina on using perimeter insulation and converting the crawl space to a warm, closed, space, and (b) the importance in all crawl/basement insulation work of maintaining access for easy termite inspection.
