Last Updated: , Created: Friday, October 12th, 2001

Insulating an old house and more.

I don't often answer all the details of a long letter, especially not with the time constraints that we have on television. But Larry from Sydney Mines, Nova Scotia wrote such a coherent detailed letter about the 80 years old very cold home that he just bought that I thought I would just wade in -- so here it is.

Is blowing in cellulose insulation from the outside into the wall cavity the best way to go? Or should one rip out the old plaster? It is one of the best blow in insulations for wall cavities because it tends to block air drafts at the same time. However, if the wall cavity is already about half full or more of insulation, you probably won't succeed in blowing in much of anything as the old insulation tends to get in the way. Ripping out the old plaster does become necessary at when the insulation is poor and there are too many obstructions to do a good job of blowing in new stuff.

If I blow in insulation, is it necessary to put a vapour barrier on the wall? Yes and No. Do you like that? Yes, you need a vapour barrier wherever you have insulation. But two coats of oil paint is a vapour barrier, and an 80 year old home has at least 14 coats of paint already. So No, you don't need to add another one. So don't pull down all that plaster just to put in an unnecessary plastic sheet. But do work on all the air leaks around window frames, door frames, floor boards and electrical boxes.

If I blow in insulation now, and add siding later, would this cause a problem? Simply, NO. In fact you could add more insulation in the form of ridged foam insulation sheathing over the outside wall before the new siding when you get around to it.

What is the best way to seal drafts at the top of the foundation walls, currently plugged with fibreglass? You are right Larry that fibreglass by itself does not stop those drafts. Push the fibreglass back a bit from the surface and use it as a backer. Then either caulk over it, or shoot in the foam in a can to air seal that crack. 20% of all the cold air in the house comes through this crack between the concrete and the wood.

What is the best way to seal / insulate drafts around basement windows that are boarded up and serve no purpose? Treat them like walls. Weatherproofed on the outside, insulation of any kind in the middle, and a vapour barrier and protective coating on the inside.

For insulating the floor above the basement it is: staple and seal vapour barrier on the underside first and then insulation? Or insulation first and then held up with the vapour barrier? The rule is simple, the vapour barrier goes on the "Warm in Winter" side of the insulation. So in this case it goes up on the floor above before the insulation. But that is a lot of trouble with all the pipes, wires and blocking. Remember that a plywood floor, a vinyl or tile floor are all pretty good vapour barriers -- good enough for this job. I would only bother with that plastic squeezed into place and sealed all around if there was an old plank sub-floor and tongue and groove boards above, allowing relatively free air movement through the floor. How about leaving the floor alone and insulating the basement walls instead? That makes for a much more comfortable floor above, moisture control in the basement and no more freezing pipes.

The basement walls are cracked and water flows down on the inside from above as well as up from a couple of walls, then flows out the other side. The neighbours says it has always been like that, leave it be. I will be adding evestroughs next summer?.. Oops, I guess we won't be insulating those walls until we get the water stopped. You are right that controlling the water from the roof with rain gutters and downspouts that carry the water away from the house is a good first step. Check the landscaping too. Apparently the water is coming in high up on the wall, at least some of it, and that would be from surface run-off. Landscaping and raingutters can solve most basement water problems.

How does one seal old foundation wall cracks? We talked about this in the previous segment -- look up "concrete" "cracks" for details. But there is not much point in trying if there is a lake on the other side, it will just find new cracks. Solve the water problem before attempting to seal up wall cracks.

How do you cover over / seal crumbling, exposed foundation walls on the exterior of the foundation? Ahhh. Do you get the connection that all of that constantly flowing water is causing these walls to "spall"? The concrete gets saturated with water, then freezes. Solve the water problems first, or no patch will stick. Once it is going to stay dry, then brush off everything that is loose and apply a "parging", made for the job and available at all renovation stores. But stop the water first. Have fun Larry.


Keywords: Walls, Foundation, Vapour Barrier, Concrete, Drafts, Insulation

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