Rubble foundation - insulating

pmakulskiSeptember 12, 2005

I have a 110 year old house. I'm trying to make the basement more usable. It'll never by really usable because the joists are only 6'4", and the heating pipes run through the middle of all the rooms in the basement at about mid forehead level (I have the bumps to prove it).

The parging on the interior has some eflorescence, and where there are some exposed brick or stone, there is some surface crumbling. I had an engineer look at it a few years ago and he said all was fine. There is no noticable damp, no leaking, no mold.

I'd just like to put up some studwalls to make it look better, be easier to clean and to give me something to attach shelves to.

I have read that insulation on this type of foundation is best done on the exterior. But the house has issues on all sides that would make this extremely difficult (driveway, decks, porch, addition). So I'd like to put some insulation on the interior.

Is this a really bad idea? If so why. If not, any recommendations on how to go about it?

If insulating the inside accelerates the moisture wick, am I setting up for major repairs in 10 years? 50 years?


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Insulating the interior of a stone foundation allows frost to get into the foundation. This can loosen the stones and lead to big problems.

Your basement was not intended for living space, or for storing anything that could be subject to mildew. Enjoy it as a good place to store wine and vegetables.

    Bookmark   September 13, 2005 at 7:53AM
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I posted a similar question about two weeks ago, though my space is a crawl space.

One response I recieved was that by insulating the inside, you leave the foundation to freeze thaw cycles as the water that now enters the foundation cannot get wicked away as easily. This could lead to failure.

The down side is this is costing you energy to do this, the up side, you house has stayed in place for 110 years.

You are looking for space, I am looking to fix the wind tunnel that runs under my house. I am giving consideration to icynene in the floor joists, though I would prefer a conditioned space. I may at some point jack and hold the house and replace the foundation walls with concrete, that would fix the problem.

    Bookmark   September 13, 2005 at 7:54AM
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Hi Wianno.
I saw your original question. (Actually it showed up in a search engine which lead me to this forum in the first place.) I didn't think the situation was quite the same which is why I posted my question.

When you say my house will last 110 years, I hope you meant another 110 years :-)

So, it seems all fixes to these old foundations are either the wrong thing to do, or are extremely expensive. Insulate the inside - cheap in the short term, bad in the long term. Insulate on the outside $10k; replace the foundation $60k. Better to tear it down and start again. Moving is starting to look more attractive.

    Bookmark   September 13, 2005 at 11:58AM
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Actually, I don't think you should be so discouraged.

Insulating the exterior of a rubble foundation, is in my opinion, not a good plan for two reasons: first, because rubble foundations are very irregular on the exterior surface, I doubt it would be a workable idea anyway, and secondly, because rubble foundations are often put together with little mortar and therefore not freestanding like a poured or block one, excavating to expose the exterior might result in damage due to the loosening of the backfill.

And since you are reporting no dampness problems, it's probably safe to conclude that whatever methods used when your house was built are working well to protect your house from lateral water & moisture vapor movement through the surrounding soil. Since they didn't have advanced geo-textiles in those days, they used passive drainage techniques: french drains, tiling and coarse layers of backfill. All of these would be disturbed if you excavated.

It is understandable that you might want to capture some of this space and make it more usable, however, you may never be able to turn it into the kind of space one would find in a modern basement. And attempts to do so may do more harm than good.

If you want to save energy, insulate under your floor.

If you want to prevent rising moisture vapor from damaging the house and eliminate mustiness, install a good quality vapor retarder on the floor.

If you want to lower energy loss from your heat pipes, insulate them (though this will make the surrounding space colder).

If you want to reduce air infiltration due to wind and air pressure differentials, install a wind barrier (not vapor barrier) underneath the floor joists.

If you want to repair the crumbling parging on the interior, you can do so, though I would do it only in the summer when you could ventilate it.

If you want to make the space more light, then paint the surfaces with an appropriate (non-vapor blocking) paint.

If you want to store stuff, use free standing metal or plastic shelving.

All of these are fairly simple, even DIY, effective and low-cost (meaning, at most hundreds, not thousands of dollars) solutions to some of your concerns.

But, none of them will magically turn your space into a modern-style basement, for that you will have to move.


    Bookmark   September 13, 2005 at 2:40PM
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"But, none of them will magically turn your space into a modern-style basement, for that you will have to move."

OR, spend big bucks to upgrade the foundation.

    Bookmark   September 13, 2005 at 3:05PM
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One point made in my previous post about my crawl space was that if you cover the heat pipes and insulate the floors, you are essentially doing the same thing as insulating the inside of the foundation. You are removing all heat sources from the space and increasing the freezing of water between the stones. The example given was barns falling down due to the animals being removed (heat source)

Does NE1 have thoughts on this potential downside aspect of insulating a rubble foundation?

    Bookmark   September 13, 2005 at 3:23PM
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Fabulous answer Molly. Thanks for all the detail.

The "vapour retarder" on the floor is interesting. Do you mean the basement floor (as opposed to the basement ceiling).
I am getting some crumbling of the concrete on the basement floor. What type of product/technique were you referring to here?

    Bookmark   September 13, 2005 at 4:24PM
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By vapor barrier on the floor, I mean exactly that: on the floor of the cellar. There is a large amount of moisture rising up through the soil. Concrete poured directly on the soil or on a sand or gravel bed does very little to impede the upward flow.

The vapor retarder is a special plastic sheeting designed to be laid under poured floors. It can also be put under other kinds of floors, or even if you don't plan to walk on it, directly on the surface of the dirt of crawl spaces. Installation is pretty easy, except (and this is a big except) that you have to carefully seal it around the edges along the foundation. That's the time consuming part!

However since you report your basement doesn't smell musty, perhaps the concrete was poured in the near past, in which case there is a chance that you already have some kind of vapor barrier. Until relatively recently people used sheets of poly. Now there are better products. In the thread started by Wianno I put in a link to a product I have used, along with some information about the topic. I have a lot of other related links if you need more info.

I'm not entirely sure I buy the "don't insulate your rubble foundation or it will crack" argument. I think it would depend a great deal on your foundation, its depth, the type of backfill and the rigors of your climate. I have owned houses in northern New England with rubble foundations that were completely unheated for many years, with no apparent foundation damage. Plus the houses I tend to own have no central heat, hence no furnace or pipes in the basement (since they would freeze), with no signs of damage. I own rubble-foundationed barns that formerly had animals, and after two decades of no animals, no damage. Perhaps houses built in rigorous climates like mine are built to better withstand repeated freeze cycles.

I think the main difficulty is not the thermal barrier, but perhaps attempts to prevent water vapor from traveling through the foundation. Around here there a loads of proprietary "home improvement" companies offering promises of making your foundation watertight by various processes. I would never allow anyone to apply some kind of interior impervious coating, nor would I allow anyone to dig up the exterior and spray it (for the reasons I noted above), so I can't say if they work.

For me and my current 160-ish year old house, whatever I do has to be as simple and reversible as possible. I think older houses can get into big problems when we to apply modern construction standards and techniques to them. When they were built, people chose a working system developed over many years. Modern building techniques have evolved and nowadays houses are built differently, so not everything can be successfully exported backwards.


    Bookmark   September 14, 2005 at 9:42AM
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I have a 105yo house with a stone foundation. The basement is a walk-out, partially above ground. When I had the gas company come out last year, as part of an energy-saving program, they did a blower door test and air sealing.

The back wall of the foundation leaked cold air like a sieve. You could put a piece of tissue in front of it and watch it flutter around. So, they blew the expandable foam in most of the cracks, to seal the air flow.

Is this OK, or am I opening myself up for these foundation problems you are all talking about?

    Bookmark   September 14, 2005 at 3:13PM
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I think this is different than what most people are talking about. There isn't anything wrong with plugging holes in your foundation! They are talking about trapping moisture on your foundation when you insulate it. So basically you are making a sandwich with insulation and the foundation as bread and the water in the middle. if the water doesn't evaporate it could freeze causing problems.
You are not preventing moisture from wicking off your foundation by filling the holes. People fill foundation cracks/holes all the time. Just last year we had a huge stream of water peeing onto our basement floor during a huge rainstorm. We fixed it with some hydrolic cement.
I wouldn't worry about your situation. It is a bit different than what people are talking about in the thread.

    Bookmark   September 14, 2005 at 4:05PM
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My house was built in 1830 in Sackville, New Brunswick Canada. The stone basement still has a mud floor. The basement wall appears to be 2 stone walls separated by 1-2' and the void filled with rubble. There are many attempts at moisture control incl. painting the walls and joists. The basement is only 6' deep in the back half of the house and 5' in the front half. I replaced 130' of 8"x8" sills already and have sealed the basement around the top of the wall. My plan is to dig 1'+ in the basement, place 4" of gravel, then a vapour barrier, then another 2" of gravel. I may pour sections of concrete over time. I already have a sump pit and pump and I am going to grade my subgrade to the edge of the wall and around the house to the pit. Currently the water comes right up through the floor. Does anyone see a problem with extending by vapour barrier directly up the walls also. The basements only heat is from my ductwork. I have an air heat pump as well as a 140,000 BTU oil furnace. I believe this would be an inexpensive way to make the basement available for storage.

    Bookmark   October 10, 2005 at 12:22PM
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If your basement is below grade, things stored there through the summer will become very humid and mouldy, even with no water seeping in. Use it for wine and preserves, and winter storage of garden furniture, but nothing cloth, paper or wood during the winter.

    Bookmark   October 11, 2005 at 7:47AM
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Don;t put gravel against you vapor Retarder. It may poke holes in it. Use sand instead.

What I have read is cover the floor, not the wall. If water gets in the wall, you still need a way for it to get out. IMO, for walls, either put the vapor barrier outside, or leave it alone.

    Bookmark   October 12, 2005 at 1:31PM
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I own a house that has a rubble stone foundation built in the 1920's. In the 1970's a previous owner insulated and drywalled the basement. It has been a basement apartment ever since. I have not seen any problems with moisture or mould. The basement is toasty warm and very comfortable to spend time in. What should I do to continue to enjoy this living space ? Should I be doing some preventative maintenance to avoid any future problems?

    Bookmark   April 21, 2006 at 6:43PM
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A CMHC study on basements conducted in the 80's did not show any freeze-thaw issues created when insulated from the inside. I also have an old (100 years) house with a rubble foundation in a cold climate, and insulated it from the inside with 2" of XPS fastened with metal c-channels and tap-cons. No need for a vapour retarder, since the XPS acts like one, but you might want to tape the joints or caulk them. I installed drywall right against it anchored into the c-channels. Worked beautifully. It is now a nice warm dry useable space. No issues.

Good luck.

    Bookmark   May 21, 2009 at 12:59PM
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The frost argument is specious but interior insulation will cause the wall to be colder in winter and any moisture that passes from the inside through the insulation might condense on the wall (just like in a wood framed wall).

It is best to use spray-on closed-cell foam on the masonry wall.

Efflorescence on the wall indicates water has been passing from outside to inside bringing salts with it from the mortar.

    Bookmark   May 19, 2010 at 10:02PM
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There is no danger of freezing or frost damage to stone foundations that have been insulated from the inside. The weatherization industry has been insulating 10's of thousands of houses from the inside of foundations for at least 30 years, or more, without a single documented case of frost damage. Foundations are pushed inward from the hydraulic pressure of water-saturated earth pushing against the outside of foundations, not frost or freezing.
Neglecting to insulate foundations costs homeowners up to 25% more for heat than they should be paying. The moisture issues are solved by using sealed rigid foam boards on smooth surfaces or closed cell spray foam on stone surfaces. The best article that I've seen on this issue (insulating stone foundations) is here:

    Bookmark   May 15, 2013 at 12:23PM
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    Bookmark   May 15, 2013 at 4:07PM
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