We have a manufactuered home on a block crawl space. The ceiling of the crawl space (floor of home) is insulated, but the walls of crawl space are not. There is no plastic sheeting on floor of crawl space, it is vented. The space is not conditioned. But is usually dry, due to sump pump in space. What is the best way to insulate the walls of the space? Should we try diy spray foam? Any ideas would be appreciated.

You could use the rigid insulation that comes in large sheets and cut that down and then use a construction adhesive to adhere the sheets to the block. Be sure to use the proper adhesive made for cement blocks. Do you have any vents in this crawlspace that open in warm weather? They do sell vents that open and close automatically that are triggered by temperature. This way if the vent is at an inconvenient place you don't have to crawl on your hands and knees to close it in colder weather.

Be sure that your water intake pipes are protected by the cold with heat tape plugged in. This is important even if you do insulate the crawl space.

I work for a manufactured home dealer and the homes we set on block crawl spaces here in Northern Ohio usually don't need insulated as the floor of the home usually has sufficient insulation. If you feel better insulating the crawl space, go right ahead but just make sure the vents are closed in the colder months. If you have a newer home (2000 or better) then the floor's own insulation should be sufficient. If earlier than 2000, the floors are not as insulated and doing the crawl space should solve your problem of cold floors. Also, while you're under there inspect the belly membrane under the home for any rips or tears. They sell special belly tape that needs a heat source (such as a hairdryer) to set the tape permanently onto the belly membrane. Just fixing the rips and tears can make a huge difference in the floors not being cold. They sell the special belly repair tape online at mobile home supply houses. It costs about $6 a 100' roll. Well worth the money. And if you are wondering - no, regular duct tape will not do the job as it will come away from the belly membrane material in about a week or less or not stick at all, so don't even bother with that avenue.

Thanks for the information. Yes the space is vented, and I guess I hadn't thought about closing the vents in the winter. We've had people in and out of there a lot lately (having city water put in) so I'll have my husband go down and close the vents. The existing insulation in the floor is intact and the membrane that holds it up is in really good shape. Should we insulate the walls of the crawls space? Or is this overkill?

Basically it would be overkill. Just close the vents and you should be fine. Also, don't forget about the heat tape on the water lines. You don't want the lines to freeze. Also, even if you do have the heat tape on the lines, I keep my cold water faucet in the kitchen at a tricke when the temp gets 10 degrees or lower. This way I don't have a frozen water line to thaw out (and that can be expensive to pay some one to come to your home to do).

Also, if you want to put down a layer of black plastic on the actual dirt of the crawlspace, you can buy 6 mil thick heavy black plastic at Lowe's or other DIY stores and put it down yourself. This would be for a vapor barrier and not insulation purposes.

Thank you. Ask away. I'm here to help you.

Can we order the polythylene frabric and belly tape online? I'm having problems finding it.

Modern building science advises to establish the building envelope at the slab/dirt floor and crawlspace/basement walls and seal up the vents completely all year, especially when there are HVAC ducts down there. There are some situations this may not make sense for existing homes but they are the exceptions not the rule.

The insulative sheathing that twink mentioned is a good product for this. Most crawls and even basements benefit from a dehumidifier during wet periods.

This GBA link to closed crawls actually questions the use of closed crawls but its still a great discussion that involves some important issues.

That was a good article. I bought a mobile home 6 summers and have shut it up for the last 4 winters but 2 springs ago and we had a little mold issue in a closet that backs onto the shower. This spring there was a little more mold there so I took the paneling off the back of the closet. Too my surprise there is a heat register in there under the tub! So I cleaned it up and also removed the tub surround and cleaned a small blue film behind it. So recently we had a musty smell and we have opened up the mobile home skirting in 2 places plus 2 vents. I am running fans and a dehumidifier. I notice less small after 2 days . I can see the dirt truning gray. I am planning on laying down 6ml black plastic on the ground and adding 2 vents for the summer plus repairing 3 holes in the underbelly where needed. We have styrofoam 2 inch behind the skirting and a rectangular blocks of that dark insulation along the ground. Does this sound like a good idea? If the heat is off all winter should I leave the vents open or closed?

Hard to know without seeing the situation but I would probably seal the under belly and seal the vents all year long. Run the dehumidifier as needed. The ground plastic is a goodt idea vented or not. I would look into sealing it to the skirting. There's a good link in the article I linked but you can get more info by researching sealed, insulated or unvented crawlspaces.