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Rumples
1957 Ranch Is Cold
Rumples

I have a 1957 ranch in Va, with a 3' tall crawlspace. Heat pump for heating and cooling; the floors are several degrees colder than the room temp. There is no insulation or moisture barrier under the hardwood floors or in the basement. The crawlspace is dry (I am at the top of slight hill.) I have been advised by two contractors that I have these options to improve comfort: put down a moisture barrier, to encapsulate the crawlspace, encapsulate the crawlspace and insulate the exterior crawlspace walls and to insulate under the floors. I have been advised that insulating under the floors first would not give me the comfort I am looking for. I like the idea of encapsulating and insulating the exterior crawlspace walls, but the price is high and I am not sure I will get my money back in energy savings. Suggestions are appreciated.

keith3267
Re: 1957 Ranch Is Cold
keith3267

Go into the crawl space and look at the area on top of the concrete blocks where the joists sit. Chances are that you have no insulation there. The joist that goes around the perimeter is called the rim joist and it is trough this rim joist where most of the heat radiating from the floor is lost.

The best way to insulate this joist is with a spray foam, but the cost will be high. It is not a DIY job and those spray can foams aren't formulated for this type of job. But you can use the spray can foam on all the seams to block air infiltration. Then use unfaced fiberglass batts or 2" thick (or greater) pieces of foam panels to insulate the rim joist.

This by itself may be all you need. This is one place where heat rising works in your favor. Heat radiated into the crawl space will rise up to the bottom of the floor. Usually air infiltrating through the rim joist will blow the warm air away and your floors will be cold. First sealing the rim joist, then insulating it to keep down the radiation losses from the edge will help a great deal.

But you will still have cold air circulating below the stratified air under the floor and that can increase your heat loss some even after the rim joist is sealed and insulated. You could encapsulate the whole crawl space to eliminate or reduce this loss. There are advantages and disadvantages. The biggest disadvantages are that you have a greater area for heat loss (the foundation walls) and possible increase in humidity in the crawl space. You may need to dehumidify the crawl space to protect your floors.

An alternative is to put a layer of insulation at the bottom of the joists so that only the area between the joists is encapsulated. You don't need very much as the dead air under the floor has about an R3 per inch (as opposed to R0.25/inch in a wall and 0 in a ceiling). The air under the floor is still where the air in the wall cavities will set up a circulation pattern. The air above the ceiling just rises out into the atmosphere.

Under the floor joists, you could just use heavy duty plastic to form an air barrier. This only works after the rim joists are sealed and insulated.

The disadvantage is that the crawl space will now be colder so you will need to protect your water pipes more. Putting insulation around the pipes may not be enough, you may have to use a heat tape first, then insulate. Heat tapes don't much energy though.

ordjen
Re: 1957 Ranch Is Cold
ordjen

When the crawlspace is encapsulated,it then becomes part of the house envelope and is conditioned air, being circulated by the house's heating and A/C system. Your floor becomes warmer because there is heat under it. Most heat loss is upwards, so there should not be a great penalty for the additional comfort.

keith3267
Re: 1957 Ranch Is Cold
keith3267
ordjen wrote:

When the crawlspace is encapsulated,it then becomes part of the house envelope and is conditioned air, being circulated by the house's heating and A/C system. Your floor becomes warmer because there is heat under it. Most heat loss is upwards, so there should not be a great penalty for the additional comfort.

Most heat loss is not upwards, that is a common myth. More heat is lost upwards, but not most heat. Heat radiates uniformly in all directions, but warm air rises so it is generally warmer up higher within an envelope.

Encapsulating the crawlspace increases the area that heat can be radiated from. Since the ground replaces the floor as the bottom radiator, the total increase in area that heat radiates from is the height of the crawl space times its linear outside dimension (2x length + 2x width).

Since you are adding the foundation walls to the radiating area, it is a good idea to insulate them, this includes sealing and insulating the rim joist as well. The ground will act like a huge heat sink so it too must be insulated.

Once the crawl space is incapsulated, the the earth under the crawl space has no where for water to evaporate and can become saturated with water (in some areas, not all). This might lead to the house settling further.

If I were you, I'd start with the rim joist and see how that works out first. You will get the most bang for the buck with this. Then decide whether insulating the bottoms of the joists or encapsulation is going to be worth the money.

Rumples
Re: 1957 Ranch Is Cold
Rumples

Thank all of y'all. A few notes which may or may not be relevant. Its a heat pump system with ducts in the attic. This was replaced before I moved in. The original system was oil with baseboard heat. We have shrink/swell soil which caused a lot of problems in the region this year due to a mild drought. I had some movement and plasterboard cracking, but was told my both an engineer and a foundation spe******t was normal and not to worry about.

Mastercarpentry
Re: 1957 Ranch Is Cold
Mastercarpentry
Rumples wrote:

We have shrink/swell soil....

That rules out encapsulation unless you somehow stabilize the soil's moisture content which is a nearly impossible task. Try doing the rim joists first, and seal those well.

If you need more, instead of poly under the joists I'd use Tyvek. Yes, tyvek passes air but it slows that down so much that here it is effectively equal to poly. Second is that poly holds moisture and again so does Tyvek, but the slight airflow with Tyvek will allow moisture to get out over time while poly won't. Moisture trapped there will mildew and mold plus it will soften the joists possibly inducing rot. Mobile homes have an under-sheet like poly and I've seen plenty of damage caused by that which is why I no longer recommend poly under floor joists. Restricted air movement is far better than none here and you won't notice enough difference to feel it in the floor.

Phil

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