RE: 166 Year Old Stone House February 4, 2002

My wife and I are reworking this 166 year old stone house in Ontario. We are situated overlooking a lake so we are fairly high and a bit windy. The intent is to be well insulated and have the house exist for another 166 years.

We are heating with forced air oil, there is an air conditoner which is used a couple of days a year, there is an air exchanger (presently not working), the added on sun room is heated by wood and is our main evening TV, relaxing, reading room. The house is about 3500 sq.ft.

1- I have replaced 12 windows with Cayman (Brantford) windows and have three more large ones to do.
2- I have completetly repointed the entire outside of the house.
3- Our now project is to renovate inside starting with the upstairs bath room.

This typical stone house has walls about 2 feet thick with the usual rubble air space in the centre. I don't know how well the top is sealed as I cannot see this area. There is about a 2 1/2 inch air space between the inside stone surface and the lath and plaster interior walls. This air space is supposedly filled with Urea Formaldehyde Insulation. I believe, (and will verify when I gut the inside wall) that this UFFI is not existing in a lot of places because I notice condensation in some areas of the interior wall. Our UFFI is very sensitive to the touch and crumbles very easily. Also the window sills are very cold to the touch as are all the walls.

Question. I want to add insulation or reinsulate these wall, one at a time, to increase the insulating value and I certainly want to make sure that I do no future damage with inside wall condensation. Can you suggest a method to carry this out and what material should I use?

I'm thinking of gutting, insulating the air space with fibreglass batts, tack on some sort of breathable board, and covering with drywall.

Canada still does not like UFFI so its probably better to get rid of it at this time even though we find it a decent insulation with no affects, and all the experts feel it is completely safe.

I realize this question is a serious challenge as it incorporates the theories of condensation and drying.

We would like to start any time now and would really like your opinion on this and any related topics that we are bound to come up against.

...

John Straube replies:

The key from durablity point of view is to ensure a very airtight enclosure (including the attic), provide good ventilation for the interior, and reduce rain on the exterior. If you were to replace the UFFI with 2" of spray applied polurethane, it would give you a good air barrier and a good insulation. It would also provide plenty of R value. The problem is that you must open up significant areas at one time to ensure that it is economical for the guys to come and do this (they can do 1500 sq ft plus in a part day). Also, you need to be sure that you prepare penetrations like floors and partitions for their arrival.

If you insist on doing it yourself, you should consider how you will create the air barrier and the insulation layer. I would consider the use of a parge over the backside of the masonry to ensure it is kept smooth and airtight. There is a lot to worry about on the parge so that it does not crack etc., but it is not rocket science. You would need to use foam or something to seal the penetrations as before, but the foam can come from a simple can. Then you could install 4" batts between 3" studs to ensure that the wood is held back from the masonry and the space is tightly filled (denser fiberglass will likely do its job better). Finally finish with a painted drywall and seal the drywall whereever you can. Alternatively, buy the Styrofoam product that has rebates in the foam for a 1x2 strapping so that the foam presses tight to the smoothed masonry, Tapcons attach the strapping and foam to the masonry, and red tape is used to seal the joints before drywall is screwed over it.

I would then reinstate the air exchanger or install a fan while monitoring the indoor RH. One should also check that the basement rim joist area is sealed properly, and that the basement is dry.

Finally, repointing and working on exterior windowsill drips and eavestroughs will keep the masonry drier.

JS