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Insulating under a raised house

Posted by Drea (My Page) on
Fri, Oct 21, 05 at 19:15

I am the proud owner of a raised 70 year old, tongue and groove, cyprus home in Louisiana. Winter is coming such as it is. Gas central heat. Worrying about my gas bill that sky rockets in winter. I've had insulation blown in the attic. There is no insulation in the walls except for one of my newly remodeled master bath's exterior wall. Thought about having insulation blown in. TOO expensive. Half of my house has oak flooring over a pine subfloor. The other half is a pine subfloor with nothing over it. Very pretty, but VERY cold in the winter. I have 2x10 joists. I am trying to determine what is the best way to insulate. I've looked at Reflectix and the plastic encased figerglass insulation. R values are very different. I've read some of the postings here. I am uncertain what would be to my advantage, and if I need a vapor barrier. I will be doing the work myself. All my pipes run under the joists, yea. I've been under my house a number of times, and the crawl space is decent, just a little hard and dirty. Plan #1 was to use the Reflectix and staple it to the bottom of the joists. This would create a dead air space. Is this good or bad? Plan #2 is to use the plastic encased fiberglass about 9" thick and staple it to the bottom of the joists coming back with thin plastic stripping for additional support. I did not plan to use a plastic barrier. Also, I plan to use foam insulation around the wires that enter my house through the floor. What do I do with these wires when I insulate? I do have a number of cats who consider their home to be under my house. So, I must take this into consideration, as they like to sit on my pipes. Thanks for any input.

Follow-Up Postings:

RE: Insulating under a raised house

Either way, I don't think the cats will be pleased ......!

Does it ever freeze where you are? This would dictate what you did with your water and soil pipes. They definitely need to be on the "warm" side of any insulation.

If you did the plastic-encased fiberglass, would that surface be permanently exposed? And to what? If contained in a closed crawl space, it would be fine, I think, but if the space is not enclosed (and it sounds like it might not be since the cats can get in) I would be thinking about what could be mounted on the bottom side (towards earth) of the fiberglass to protect it. It would be a shame to have it vulnerable to varmints, inlcuding mice.

Can you concoct a hybrid: fiberglass between joists and something solid (reflictix or something else) attached the bottom of the joists?

Foam (I think you mean spray foam) is excellent around wire entry points. That alone can make a big difference. Wires in a 70 yo house should be fine just buried in the insulation, but for peace of mind and elimination of any future problems, I'd do a careful inspection of each one before encompassing it in insulation. Easier, and cheaper, to replace or repair now, than later.

Glad your house withstood all the bad weather you had earlier.


RE: Insulating under a raised house

Thanks Molly,
The underneath of my home is exposed to the elements, all of them. Rain water will pool under my house in some areas. I have dug a trench to help it escape. I had extra roofing felt, so I stapled it around the inseide of the most exposed sides (2). Helped a little, and since it is black, it didn't take away from the house. Cats being chased by dogs and an inconsiderate plumber have torn down parts of it.
Yes, we freeze in my area. Low 20s to mid teens, however we warm up to the 40s - 50s the same day. Last night was in the low 50s and my house is 68 in the middle of the day. Brrrrr. I get cold easily. As for my pipes, I have a variety: iron, PVC, and some kind of clay. Eventually, I will try to replace all the plumbing. Mice are not a problem beacause of the cats. But, I do have raccoons and opossums that frequent my home. How does styrofoam work as an insulator? Cost is a concern.
Your advice is greatly appreciated.

RE: Insulating under a raised house

Cost is always a consideration with older homes! LOL

And in LA, things may be even dicier this year.

I'd start at one of the big-box stores and price everything as a baseline. Comparing R-value for the $$ works, but you also have to factor in where and how you're going to use it. Combinations of materials work, too. Later this fall in a portion of my attic I plan to install a thinnish layer of unfaced fiberglass laid directly on the fragile, uneven keys of my old plaster. Above that I'll have insulating foam (what I think of as "rigid pink", but it may be another brand/product) sheets which give more R per inch than fiberglass and are easier to install, and to mouse-proof, in this particular situation. These two materials will completely fill the usable cavity space I have, without crushing, which would degrade the possible R-value.

You may also want to consider one of the infiltration barrier fabrics if your floors are leaky.

With your reported low winter temps (those temps would lead the local news with stories of a "warm spell" up here in January!), you will have to make sure your water pipes, and to some extent your waste pipes, are kept on the warm side of any insulation you put up, which would block heat from radiating downward and saving them from freezing up.

French drains will help re-direct surface water, and your totally open undercarriage is the only situation where I'd put a vapor barrier on the bottom side of the insulation/joist (as opposed to directly on the ground). It would be good to keep moisture from entering the interior of an insulated floor assembly. And add chicken wire if that's what it takes to excluded coons and possums. What about snakes, they always got in my Virginia house!

Good luck!


RE: Insulating under a raised house

I have a raised home ,in south la. is 8 feet high, my floors are plywood floors underneath.....also concrete paved under the house standing water issues...what would be the best way to insulate under floors and materials...

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