3 insulation questions, help needed(long)

jamesbodellAugust 25, 2005

Hi all, my 200 year old barn with a 1970's addition and one addition we just finished has insualation issues.

1. The original house sits on ledge and has about an 18 inch crawl space. There is lots of old rot under the house that has been fixed over the years with sistered boards. However, the original problem, which is water leaking under the house, is still there, and needs to be addressed once and for all. I plan to put in french drains on the oustside of the foundation, but need to know what best to do on the inside. The foundation is rubble (lose rocks) and so cannot easily be insulated with sheet product. Due to the rot, I do not want to put insualtion in the joists. However, last winter it was a wind tunnel under the house, so insulation is definitley needed. I was going to put down plastic on the ground and insulate the foundation, but that was before I realized it's rubble. What kinds of options do I have here?

2. The 1970 addition has insualtion falling from the joists and needs replacing. I intend to replace it with encapsulated insulation. However, should I include an additional vapor barrier of 6 mil plastic? If I staple it up under the joists, am I going to have a problem, or should I just put plastic on the ground?

Also, to my surprise, I noticed a heater in the crawl space (fins over the copper heating supply pipe). What was the thinking on that one? I know now why I had such a problem keeping the place warm last winter!

3. My new addition was insulated, but all my water pipes run through the space. I am thinking of putting insulation around the foundation walls and a vapor barrier on the floor. I am really concerned about freezing water pipes. I had the problem twice last year (before addition was added)

Any help on these issues would be greatly appreciated. I need to get a handle on this before the winter season is upon us!

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You have three and a half problems: interupting moisture and vapor rising from the soil to the underside of the floor and living space; preventing or retarding air infiltration through the rubble walls and up through floor joints or wall cracks; and creating a thermal barrier between the heated space and atmospheric temperatures. The half problem is preventing interior humidity from migrating through your walls and ceilings and getting stuck inside the walls, creating the possibility of rot and probably damaging exterior paint.

Are you discouraged, yet? I hope not!

Some forms of insulation/vapor barriers can control, or at least retard, two problems at once, but sometimes combination solutions don't do any one thing well, and you end up with less improvement than you hoped.

So, looking at the first problem: You know you have a problem with water entering the space under your floors from the soil. Exterior grading and french drains are the solution there for free water. You may also need to make some plan for periods of temporarily high ground water levels in the spring. Passive or gravitational (i.e. french) drains won't carry water away if they themselves are full. Temporary high water problems are usually solved by setting up some kind of sump pump to mechanically remove collected water and send it away from the house.

Gutters are a big part of soil water management around a house, but they need to be correctly installed and kept free of debris.

The last water issue is rising water vapor from the soil. This is blocked by laying a vapor impervious (or at least highly retardant) layer directly on the soil under the structure and securing it to the bottom of the exposed foundation. The securing part is quite a challenge in a rubble foundation! Rising soil moisture/vapor is, in my opinion, even more deleterious than episodic innudations, because it is so constant. But it can be substantially reduced with careful blocking. BTW, some people use poly sheets, but there are better, more longlasting and retarding products made especially for this purpose.

Some people do all this and still feel they need additional forced ventilation in the crawl space to keep the area dry. This technique is controversial as you can introduce moist atmospheric air which in turn collects on the cooler surfaces in the crawl space, recreating a problem.

Vapor barriers installed in the various insulation and infiltration layers are less successful at arresting the problem at the source, i.e. at ground level and can carry the adverse effects closer to the portions that can rot.

Now, on to air infiltration on the exposed sides of the foundation. I have rubble walls, too, and frankly despite a lot of experiments, despair at achieving a true infiltration barier on the foundation. Instead, I concentrate on an infiltration block as the lowest level underneath my floor joists. This is only an infiltration barrier, not a moisture barrier as I do not want to collect any moisture within the joist cavities There are various infiltration-only house textiles. This requires careful installation, with good sealing as you are trying to create a good wind barrier, and differential air pressure changes are constantly working to negate this.

The next layer above the infiltration barrier between the floor joists is a thermal barrier (insulation). I think the sheets of rigid foam are easiest to work with here and given the most R-value for the depth. I carefully friction-fit these in, but don't make my self crazy sealing them up, except near exterior walls, when I take some extra care to do so.

Lastlyy, you asked about wall insulation. Here the main principles are the same but in a somewhat different order as the source of moisture is the inside air which is humid due to plants, washing, showers, cooking and occupants' breath. You want to keep this moisture from migrating into your walls, so the vapor barrier should be as close to the interior surfaces as possible.

Then comes whatever thermal insulation you choose, followed by (assuming you can access the space) a good infiltration barrier to interrupt wind and air pressure driven drafts from the outside.

In climates where there is significant possiblity of high-wind driven rain penetration, a rain shield product is installed somewhere outboard of all of this, often in the sheathing/cladding assembly. It should *not* block water vapor only free moisture.

Where it becomes tricky is that in retrofitting you often don't have complete through-wall access so some of the layers can't be installed where they need to be. Furthermore, in retrofits, sealing is often hard because of access problems as well. And finally some of the commonly available insulation products are trying to do more than one task, putting vapor and/or infiltration barriers at a less than optimal postion, or are installed incorrectly.

In retrofits I think it is important to do as much as you can whenever you have a wall open, without taking the whole building back to the frames simply to insulate. I'd handle potential structure-damaging problems first (water under house); followed by infiltration barriers to keep heated air in and cold air out, then add insulation in what amounts and places it can be worked into other projects.

(What I mean here is not to suggest installing infiltration barriers, then taking them out later to install insulation; - I wouldn't do that if I could access the space at the same time. It's just that sometimes you have to make choices about what can be done in the time you have, with money avail., etc. I'm just suggesting a prioritization of projects, if you have to make a choice.)

I know this slightly cock-eyed from a purely energy conservation point of view, which stresses insulation first, and then infiltration blocking techniques, but it is what I do.

Finally, never underestimate the value of adding a new addition built from scratch. Assuming it is built to modern energy standards whatever former exterior wall space it connects to, is automatically very well-insulated!

There are other issues about insulation of walls and blocking upward air movement within them, but you didn't ask about that....!

Good luck and please don't despair when you compare what you can do in an old house with what can be achieved with modern ultra-tight building practices. I think in the long run, we may discover that old, somewhat air-leaky houses are better to live in than new ones which have very few air changes.


    Bookmark   August 26, 2005 at 12:57PM
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Wow, quite the response. Thanks. You mention products being available, do you have product names that you could suggest?

    Bookmark   August 28, 2005 at 11:20AM
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On the rubble foundation, could I lay plastic down on the dirt floor and spray the rubble foundation wall with some type of expanding insulation? Would a layer over the foundation create a problem here?

    Bookmark   August 28, 2005 at 11:26AM
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OK Molly, I have read and digested your sugestions. What I hear you say is poly sheets on the ground (you mentioned other products, what were they?), and a Tyvek type wind barrier stapled up to the joists with insulation between the joists?

Not sure what you suggest I use to cover the foundation. I was thinking a blow in expanding type insulation that can cover the rocks. Or are you suggesting a ploy sheet over the interior rubble foundation?

The wind barrier over a vapor barrier stapled to the underside of the joists is interesting as well, I had not thought about that. Only problem I see is the "loss" of the headroom I gain between the joists when under there, it's real tight.

    Bookmark   August 28, 2005 at 2:40PM
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Stone foundations can be damaged severely by freezing. This means that if you are going to insulate, you have to do it on the outside. Do not insulate so that the stone sits out in the cold. Frost will get in and break it apart.

When you see old barns totally falling down, it is usually because there are no animals in them to keep the foundations heated.

    Bookmark   August 29, 2005 at 7:07AM
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probably why I have seen these foam type insulations always applied to the outside of a foundation.

    Bookmark   August 31, 2005 at 10:32AM
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I don't think I was recommending wind barrier over vapor barrier under your joists. If I did, it was in error.

Moisture/vapor retarder sheets on the ground under the house.

Wind barrier stapled (or something) to the bottom of the floor joists.

Insulation between the floor joists. (As much as will fit.)

I wouldn't spray anything on the walls, except to try and patch a discrete hole (like where the electric line was punched, through) on the rubble walls. As Sharon said, anything sprayed (expanding foam, etc) has the possibility of damaging the stacking of the stones, causing settling and cracking. In some cases a careful re-pointing job might help, assuming your rubble wasn't dry laid in the first place. A dry laid rubble is helping to preserve your house from moisture and vapor being trapped under the house. Be very cautious about interrupting this cycle.

Don't worry about the wind whistling through the rubble under your floors. If you have carefully insulated and sealed between the floor joists and at the sills, that's the best you can do.

If you have pipes in this unheated space, re-route them before you block radiated heat from the structure with insulation. If you can't insulate the floor before winter, then, at least, insulate the pipes this year. But don't rely on pipe insulation in an otherwise unheated and insulated-from-the-living space area to keep the pipes from freezing.

If you want to google for moisture/vapor barrier products, you'll probably find what I was suggesting. If I have a moment I'll go down and see if I can a get a tradename for you.

Where are you?


    Bookmark   September 1, 2005 at 7:47PM
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Well, my rubble foundation IS dry laid.

I have almost given up on doing this myself, and do to the ledge and moisture problems I am having, am giving serious consideration to having icynene blown into the floor joist in the crawl space.

My research (www.icynene.com) suggests I will no longer need the moisture barrier on the ground (6mil plastic), wind break stapled to the joists (tyvek or equivalent) and insulation between the joists. And, this will go in a LOT faster.

In the segment of basement where water lines run, I will condition the space and put rigid foam on the walls and a moisture barrier on the floor. This is new construction, not rubble, and so will be much easier.

Does anyone have a comment on this approach?

    Bookmark   September 6, 2005 at 2:03PM
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Sorry, you'll still need a moisture barrier on the dirt floor to protect the sills and bottom edges of wooden joists, not to mention the wall cavities. Plus icynene is a blown in or expanded foam thing, isn't it?

That has a couple of problems that I can see: The first is that it will be a semi-permanent thing and not easily reversible. That means you'll have to dig at it if you need to run lines through or check on something in the joist cavities.

Secondly, I would think long and hard about it from an out-gassing point of view.

Third, its semi-permanence may be a problem if it reaches the end of its service life. When it's half-degraded, some later owner may curse the day it was installed.

The nice thing about a floor barrier, and wind barrier under the joists and foam insulation between them that I proposed is that is a reasonable DIY project and highly reversable, both for any maintence/inspection reasons and in case something better comes along.

Personally, I like things I can install and repair myself. It seems much more in keeping with how these houses were originally constructed.

I will try to get the name of the vapor barrier posted here tonight.


    Bookmark   September 6, 2005 at 6:08PM
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Here's the link to the manufacturer of the vapor retarder I have used.


This should get you to the manufacturer's page for the product and from there you can contact them and find a local supplier. I thought I'd have to search far and wide, but was surprised at how easy it was to get.

This higher-grade material is more expensive than ordinary poly but I think it is worth it.

I have a long set of bookmarked pages on this subject, so if you need more I can try to get some more info for you.

Here's a discussion that I started with when I was first looking into it. This link will take you to a series of articles. If you're lucky it will take you right to the vapor retarder article. If not, then put those words in the search box and find it that way. There is also info from this same source re french drains and trench drains, which you may find useful.


I am sorry it took me so long to get this info posted. I have a family member who is quite sick, so I am spending a lot of time going back and forth to the hospital.


    Bookmark   September 6, 2005 at 11:08PM
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Housekeeping: I was originaly skeptical about this stuff too. But the gas out I beleive is CO2, and only lasts 30 days. It biodegradable, and can be removed from a cavity with your bare hands. Animals can't burrow in it, and it contains no food quality for mold or mildew.

Wow, I should be the salesman. Anyway, it looks like a great product for me as the crawl space I am looking at is about 18-12 inches. I will not be able to get bats into these tight spaces, and the joists are 10 inches on center, which makes it harder to just push in. than standard 16 and 24 inch centers which the insulation is built to.

Molly, thanks for the info, I will give it some thought. Sorry to hear about your family member, I hope it work out for the best. Hospitals are the pits.

    Bookmark   September 7, 2005 at 7:44AM
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I just bought a one-room school house, renovated - save for the basement, which is fieldstone.

Am seriously thinking of having the headers and walls sprayed with foam insulation - but am now unsure even though the basement is dry - house was built on a knoll and there are no apparent water leakage issues anywhere.

A space of about one foot will be left open along the bottom of the walls for any potential leakage.

It sounds from reading a lot of these posts, however, that a stone foundation needs to "breathe", literally -

I wonder if I could obtain some advice on this subject.

Thanks a bunch!

    Bookmark   March 8, 2009 at 10:27PM
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