Are You Insulated?

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In general at ground level there are two different floor constructions to consider: suspended floors and solid floors. In the case of a solid floor then it will be necessary to relay the whole floor in order to install insulation. The expense of this will hardly be worth it unless the floor is in poor repair. Because of the insulating properties of the ground, insulation is only required at the edges of a solid floor. If a solid floor feels cold it is more likely to be the effect of the floor covering than cold coming up from below.

If you have suspended wooden floors, open and accessible from below, it is relatively easy to insulate even if you have to lie on your back to do it as I had to in our house. Mineral wool is the most commonly used material, although you may use rigid board insulants, and any loose fill insulant also works if you can easily construct a way of containing it. Mineral wool will more or less stay in position if cut slightly wider than the spacing. It can be held in position by chicken wire or light wire wound around nails zig-zagging back and forth between joists. Loose fill can be supported by netting or even rigid board insulants cut to size and held by nails.

If you can't insulate from below then you will have to consider whether it is worth insulating from above by taking up floorboards, fixing small laths to the bottom of each side of the joists, and laying rigid board insulation with loose fill on top. If a basement ceiling is preventing access, you can insulate finished ceilings by blowing cellulose into the ceiling cavity from below through access holes in the plaster.

Below Ground Insulation

Since the ground itself is a good insulator, only the walls just below the surface need help. If the wall is accessible from the outside, insulate by digging down about two feet below ground, allowing the brickwork to dry off before applying a coat of bitumen. You can then apply moisture-resistant insulation, such as polystyrene foam boards, to the outside of the wall below ground level. Choose a thickness of about 2-3" and finish off the top with granules, gravel, or similar material.

R-Values

The ability of insulation to block heat flow is measured by its R-value. The higher the R-value an insulating material has, the better its resistance to heat flow. Knowing the R-value per inch enables you to determine the ability of different types of insulation to block heat flow. For example, if a material has an R-value of 2 per inch, then 6 inches of it will give you a total R-value of 12. Some approximate R-Values are included below:

Common insulating materials

Cellulose fibers R-Value 3.7 per inch
Cellulose fiber insulation—made from processed waste paper, converted into fluff that can be placed by hand or sprayed. It is usually treated with borax (sodium tetraborate) for fire and insect resistance. Cellulose fiber insulation is most suitable for laying in roofspaces where it can be kept dry.

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