Our cottage in Gimli is over fifty years old and has had a couple of renovations in which the outside walls were insulated. I would like to completely insulate the cottage by doing the floor and ceiling. Do we need to install a vapour barrier next to the floorboards as well as insulate between the joists? Would it be better to build a wall around the perimeter crawl space and insulate it only?
In the attic there are several wooden cross pieces as well as pipes and electrical wires to contend with. How can you place the vapour barrier next to the ceiling tiles before installing the insulation? Is there another way of insulating the attic without putting down a vapour barrier?
Insulating an existing older building always poses a few challenges. One thing to keep in mind is that a proper continuous vapour barrier is ideal, but rarely achieved in a retro-fit situation. A good vapour barrier should be continuously sealed throughout the “building envelope”, from floor to ceiling. This is impossible to achieve if existing wall and floor sheathings are not removed. It appears that Dr. Goldberg is not planning to redo the wall and floor coverings, so we have to take this into consideration.
The best way to insulate underneath the cottage, in my opinion, is to ignore the floor altogether. Even if the floor is properly insulated and sealed it will be cool on very cold days. The preferable way to insulate under the building is to build knee walls to enclose the crawlspace. These can be insulated and a vapour barrier installed with the least amount of difficulty. This is only practical if there is enough ground clearance to work under the cottage. If the building is near grade, it may have to be raised before the insulating is done.
Firstly, the earth floor should be covered by a continuous polyethylene vapour barrier, which should be caulked to the wall vapour barrier. It has been discovered that 40-50% of the moisture in a house can come from an uninsulated crawlspace. Whenever insulation is increased, proper ventilation must also be added to prevent moisture damage. The crawlspace should have good air circulation when not being heated. This can be accomplished by adding vents with removable insulated covers, which can be opened in the summer to allow fresh air to force out any trapped moisture under the building.
Electric baseboard heaters can be installed under the floor to heat the crawlspace in the cool seasons. If the cottage has a furnace, ducts can be added under the floor for the same purpose. Heating this space will ensure that the floor above is warm and any water pipes present don’t freeze.
Insulating the attic may not be as cut and dried as the crawlspace. If there is no insulation present, a poly vapour barrier can be laid down directly over the ceiling sheathing and the ceiling joists. If obstructions are close to the ceiling, there should be little problem with covering these wires and vent pipes with poly before the insulation. Any framing that gets in the way can be caulked to the main vapour barrier with acoustical sealant.
Additional roof and soffit venting should be installed before insulating. Insulation stops should also be stapled to the rafters above the soffits to allow airflow from the new vents. Fiberglass batt insulation can be laid in between and above the ceiling joists or loosefill can be poured or blow in. Providing a continuous air/vapour barrier in the attic is important, but not as essential as ensuring the attic is well vented. Warm, moist air may get through a mediocre barrier, but it will do little damage if there is sufficient fresh cool air to force it out of the attic.
There are alternative foam insulations that can be installed that provide their own vapour barrier, but are more expensive than conventional insulation and can be equally difficult to install. These must be professionally applied and may not be available in all areas.