Not all homes have crawlspaces but for those that do, it is important that they are considered when trying to manage the heating/insulation of your home.
There are two different approaches that can be used when dealing with a crawlspace.
A cold crawlspace
approach is designed to allow cold air and full ventilation through the crawlspace.
To insulate the home above, insulation is added to the ceiling of the crawlspace to help prevent the cold air in the crawlspace from moving up into the home. Ideally, the floor joist above the crawlspace will be 8 inches deep to allow for an R28 batt to fit into it. For 2x6 floor joists, a high density product can be used, which is a bit more expensive but will provide the necessary insulating R value. Batts are installed and strapped in place with a breathable material to ensure that moisture is not trapped between floors.If the floor of the crawlspace is concrete, there should not be any moisture issues; however if it is an exposed dirt floor, a ground seal should be installed to prevent overly moist air from permeating the batt insulation which causes it to lose its insulating properties as well as becoming heavy which makes it difficult to keep in place in the floor joist pocket. Ground seals can vary in price depending on how thick and elaborate a homeowner wants to get. For most basic situations, a 6mm poly is adequate to keep moist air at bay while not costing the homeowner a huge amount. Heavier and more elaborate options are available depending on the situation.
A warm crawlspace
approach is used when there is a source of heat or ignition located in the crawlspace.
In this situation, an insulated blanket or rigid insulation is fastened to the exterior walls of the crawlspace or even sprayfoam is applied to insulate the concrete. (If sprayfoam is used, it is important to use 2lb closed cell foam which forms its own vapour barrier. It is also important to note that sprayfoam and some rigid insulation products give off dangerous vapours if they are exposed to flame and fireproofing of them may be required. Alpine is one of the few companies that applies a fireproofing substrate to its foam in these instances.)
Exposed Joist ends are insulated with fibre glass batts and the vents to the crawlspace are closed off. A ground seal should also be applied in this design if there is an exposed dirt floor in order to eliminate the amount of cold moist air entering the space. No insulation should be added to the ceiling of the crawlspace as the heat in the crawlspace should be allowed to move upwards, keeping the floors above warmer.
While all new construction requires heated crawlspaces, cold crawlspaces also have their merits. It is essential that whichever design is utilized, that it is installed properly with the right components.
Often it is best to remove, old, wet, sagging insulation as it has lost its thermal properties and carries an odour that can permeate up into the living areas above.