old house foundation insulation?

[pybyr]

hello all--

I'm the "keeper" of a circa 1830 VT farmhouse, with a cellar that's mostly unmortared stacked slate fieldstone below ground level, and then massive granite "curbing" from ground level up to the sills.

I don't dare insulate full depth, as frost would wrack the unmortared below-ground part pretty quickly if it didn't get some heat from the cellar to keep the surrounding soil from freezing (I have pretty heavy, poorly-drained soil)

So--- I could really stand to insulate the granite from ground to sills, but it's all too random to use something like foamboard,

Also, the unmortared fieldstone means that the cellar is sufficiently moist in the warmer months that I need to be really careful that any insulation cannot absorb or hold moisture against the sills (indeed, there are already places I need to brace or replace sills and joists)

spray foam has been suggested, but as far as I know, most of it then needs an additional layer of something to make it OK in terms of combustibility

any suggestions?

Thanks!

 

[begreen]

I don't mean to doubt your concerns, but how did the owners for the first century keep the foundation from wracking with frost if there was no central heating back then and no heat in the cellar? Or did they have a winter kitchen with fireplace in the cellar?

 

[fraxinus]

Last summer I had a very similar foundation from the mid 1800's sprayed on the inside with gunite concrete. Although this is not really insulation, it strengthened the foundation (the main purpose in having it done) and helped a great deal with air infiltration thus helping considerably with warmth. One caution: many foundations from this period were designed to allow water to enter where it would then be guided to a gravity cellar drain. Don't try to waterproof such foundations - the build up of water pressure on the outside could lead to a disaster. As for the danger of frost, its unlikely to be a problem if water is directed away from the foundation on the outside by proper land slope and gutters.

 

[velvetfoot]

Why not just insulate under the first floor?

 

[Highbeam]

When you say cellar do you mean basement? Is this a dirt floor crawlspace under the first floor or a living space with a slab? Do you have insulation in the cellar ceiling? If so, why bother with the cellar walls? If not, would it be easier to insulate the ceiling of the cellar? This to avoid water problems and you could use conventional insulation methods.

 

[WILDSOURDOUGH]

My two cents-
I would insulate the ceiling of the cellar, and leave the walls as they are- they have stood the test of time, and nothing 'modern' is going to improve them.

 

[Red Sun]

Although, it is likely that the floors are double planked where one set of boards runs perpendicular to the other set making the floor perhaps a solid 3-4" thick. With any carpeting on the first floor it is going to be difficult to add much more R value. The surest thing is to make temperature readings during the cold months to then isolate the cold spots (corners) and suitably insulate those places as needed.

Foam or introducing a synthetic/substrate is a non-traditional approach when the challenge is as much to maintain the integrity of the design regardless of its age. Back then, they may well have used hay, or, stacked wood in which case a fireplace could have served to dry the wood as much as retain heat... It was common to heat stones and move them to rooms or keep under the bed as the cold months lingered on.


I know of a person that set up a small corn stove in the basement and that served to heat the house quite well, although it served just as well to heat the stone lined wall. But there again, 150 years later a fire in the basement might not be suitable for the structure.