Under the Floor

[bubbaroski]

I am looking at a wood frame house. I may buy it. I looked under the house and saw the floor joists. My mobilehome that I presently live in has simular floor joists but they are covered with black plastic (belly wrap). Why does the wood frame not have plastic (belly wrap)? Does it need it? Thanks. Great site.

[Phelps]

I see what you mean. Good question you raised.

Mobile homes are meant to be moved anywhere, from Florida to upper Minnesota. The floors have to be insulated. And not only that...by sealing them with belly wrap the heat is trapped in the joist cavities so that the heat runs that are down there don't let heat escape through the duct to the outside, and, since they run wate rlines under there as well (often chased with the heat runs), they want to protect them from freezing..

Conventional houses usually don't have these issues. And by chance that plumbing runs ARE in the crawl space? Chances are the dwelling is somewheres that rarely ever gets a freeze. And insulating becomes a matter of choice and not so much that of necessity.

But it is adviseable, if you live where it is cold to want to insulate under there... When doing so, you must insulate so that any vapor barrier is on the house side of the joist and the insulation is below it. And you need to keep in mind that creatures love to get up in the insulation, if you insulate, so you must make sure that how you do it you guard against creatures from making a mess of it.

Where do you live?... and do other people around you have houses over crawl spaces (or up on pilings if by water)?

[HeadOfMax]

I have never seen that wrap used in houses, albeit I am in the city. My guess is that the wrap is either there to keep moisture out or as an added insulation.

[HeadOfMax]

Originally Posted by Phelps

I see what you mean. Good question you raised.

Mobile homes are meant to be moved anywhere, from Florida to upper Minnesota. The floors have to be insulated. And not only that...by sealing them with belly wrap the heat is trapped in the joist cavities so that the heat runs that are down there don't let heat escape through the duct to the outside, and, since they run wate rlines under there as well (often chased with the heat runs), they want to protect them from freezing..

Conventional houses usually don't have these issues. And by chance that plumbing runs ARE in the crawl space? Chances are the dwelling is somewheres that rarely ever gets a freeze. And insulating becomes a matter of choice and not so much that of necessity.

But it is adviseable, if you live where it is cold to want to insulate under there... When doing so, you must insulate so that any vapor barrier is on the house side of the joist and the insulation is below it. And you need to keep in mind that creatures love to get up in the insulation, if you insulate, so you must make sure that how you do it you guard against creatures from making a mess of it.

Where do you live?... and do other people around you have houses over crawl spaces (or up on pilings if by water)?

That was not there when I started typing.

[bubbaroski]

The house is in central Florida.

[bubbaroski]

Thanks Phelps. This helps.

[LazyPup]

Headof max was close with his answer. Mobile homes are manufactured at one point then intended to be moved for hundreds of miles before they are set up for final use.

Covering the underside of the floor joists aids in preventing insects from nesting or building cacoons in the joist cavities, then later being transported to another region where they would have an adverse effect on local agricutural crops. On some new mobile homes they actually have a letter affixed inside one of the windows that confirms the wrap was installed.

I have never seen the wrap installed on a site built home.

[bubbaroski]

Many thanks. Great site.