I have foil installed under the floor of my house. Is this an effective type of insulation?
Filed under Frequently Asked Questions.
May 8th, 2011
I have foil installed under the floor of my house. Is this an effective type of insulation?
Filed under Frequently Asked Questions.
May 8th, 2011
I have foil installed under the floor of my house. Is this an effective type of insulation?
Editor, May 8th, 2011 on 10:07 pm
Foils are a cheap and reasonably effective method of under floor insulation. They have been the industry standard for new buildings and retrofits for many years. Foils work in three ways:
Radiated heat from the floorboards is reflected back
The foil captures a cushion of still air which acts as an insulator
Draughts blowing up through the floor boards are eliminated
Foil products are usually stapled and strapped to the floor joists, and must be installed correctly to minimise any potential for air movement between the foil and the floor boards. Foils provide some protection from rising damp and provide adequate insulation from draughts and external air temperatures, provided the foil is intact and joins are taped securely to stop draughts.
Foils generally have a life of 15 years, but their performance can be seriously diminished if they are damaged. Some foils are easily ripped (cats and plumbers are two of the main culprits) and the insulating properties tend to reduce over time as the upward-facing surface loses its shine. However there are several foils under tradenames “Astrofoil” “Aircell” and “Silversark” that incorporate plastic membranes in their construction and are much tougher.
If the foil under your house is ripped or corroded, you might consider replacing it with a bulk insulation (such as fiberglass, polyester, or polystyrene). While these are more expensive, they are much more durable and are rated for at least 50 years. If you do decide to reinstall foil, then you must be extremely careful when stapling the foil. There have been several deaths from electrocution by DIY installers stapling through live cables. It will always be safer to disconnect power when you install under the house, but you will still need to check that the foil has not livened up (use a “volt stick” or multimeter) when the power is switched back on.