Interior insulation in the basement: protection against mold and energy loss


Unused cellar rooms often offer unimaginable potential as living space. However, before the basement can be used as a living or hobby room, an effective insulation is required. An interior insulation creates the necessary living environment, lowers the humidity in the basement and reduces heating costs in the long term. Compared to the external insulation, the effort is relatively low.

Interior insulation in the basement: less heating costs, more living comfort

Proper interior insulation creates new living space and improves the energy balance. Even an insulating layer of just a few centimeters can significantly reduce heat loss. Many insulation systems are already available at reasonable prices and can be easily retrofitted.

The advantages at a glance:

  • additional living space
  • no heat loss over the basement walls
  • no moisture and mold
  • warmer floors on the ground floor
  • no work on the ground

The inner insulation is associated with significantly less effort than an outer Perimeterdämmung, but also has some disadvantages. The dew point shifts inwards so that moisture and mildew can recur if improperly insulated. In addition, part of the living space is lost. The insulating materials are exposed to neither weather nor external pressure.

Vapor-tight and capillary-active insulation systems

For the internal insulation of the basement walls, various procedures are possible, which differ considerably in terms of cost. The most expensive but most effective solution is capillary-active insulation systems. These absorb the moisture and then release it to the room climate. So the living climate is optimally regulated and moisture damage is prevented. The insulating materials used are perforated calcium silicate, mineral foam or polyurethane panels.

Vapor-proof insulation systems are significantly cheaper, but they entail the risk of renewed moisture formation, especially in old buildings. For vapor-tight insulation systems, for example, polyurethane elements, plasterboard or calcium silicate boards are used. Panels made of polystyrene, mineral or rock wool are suitable for ceiling insulation.

For a complete basement insulation also windows and adjacent constructions must be considered. The insulation of the walls and basement ceiling can be continued via a flank insulation, in which 50 cm of the adjacent elements are also insulated.

In uninhabited basements, a pure ceiling insulation may be sufficient. This way, heat leaks can be effectively eliminated even without complete basement insulation. In the case of an exclusive insulation of the basement ceiling, the outer wall should be additionally insulated on the upper 50 cm in order to prevent thermal bridges.

Cellar insulation: effort and costs

The cost of a basement internal insulation varies depending on the material. A vapor-tight basement insulation can already be set up from about 40 EUR per square meter, a simple ceiling insulation from just 15 EUR. For a capillary-active insulation system, the costs are already around 100 - 130 EUR per square meter. However, the risk of future moisture damage is significantly lower.

Additional remedial measures can also increase costs, for example in the case of existing moisture damage. This is problematic especially in old buildings with insufficiently sealed walls. Here, an external renovation of the basement walls is necessary first, whereby it is advisable to combine them directly with a comprehensive external insulation. An alternative may be a chemically indexed sealing of the interior walls.

Interior insulation in the basement: protection against mold and energy loss

FAQ - 💬

❓ How do you insulate basement walls to prevent mold?

👉 The ideal Basement wall assembly to prevent mold growth:

  1. Install two inches of rigid insulation board directly against concrete. ...
  2. Frame an interior 2x4 stud wall at 24 inch centres, pressed tightly against the foam panels.
  3. Install mineral wool batts in the cavities.

❓ What is the best insulation to use on basement walls?

👉 Choosing the Best Insulation for Basement Walls and Ceiling If you are looking for a less expensive option that you can install yourself, then foam board or fiberglass will be the better options. If you want that air seal in your basement to make the space more comfortable, then spray foam is the way to go.

❓ How do you prevent heat loss in the basement?

👉 Your basement is the next to blame when looking at where your lost heat goes. Only 1% of lost heat goes through your basement's floor, but 20% is lost through your basement walls. The best solution for this is to provide more insulation around the walls, or finish the basement if it's cement.

❓ Is it better to insulate basement from inside or outside?

👉 Compared to exterior insulation, basements insulated on the inside provide superior comfort. Water intrusion, high humidity and condensation are the biggest issues/concerns when insulating basements. Mold is the result of a moisture laden basement. It's very simple; no moisture – no mold!

❓ Should you insulate interior basement walls?

👉 Basement walls should be insulated with non-water sensitive insulation that prevents interior air from contacting cold basement surfaces—the concrete structural elements and the rim joist framing.

❓ Is there mold proof insulation?

👉 Fiberglass insulation is constructed of tiny shards of glass that form pockets to trap air and help restrict the transfer of heat. Its naturally mold resistant in that the material itself is not a food source for mold.

❓ Is it worth insulating basement walls?

👉 Insulating your basement may seem like a project best suited for another day, but truthfully, insulating your basement walls can help improve comfort and reduce energy and maintenance costs to HVAC systems. It also allows for extra living space within a home, which can be invaluable.

❓ Do I need to insulate interior basement walls?

👉 Basement walls should be insulated with non-water sensitive insulation that prevents interior air from contacting cold basement surfaces—the concrete structural elements and the rim joist framing.

❓ What insulation should I use in my basement ceiling?

👉 Start with getting any moisture issues under control, then use water-resistant insulation like closed-cell spray foam or XPS foam board. Most homeowners opt for fiberglass, but fiberglass has the chance of trapping moisture.

❓ How do you insulate interior basement walls?

👉 0:595:08How to Insulate Your Basement: Part 3

❓ Is insulating a basement worth it?

👉 Insulating any part of your home is typically one of the best investments that you can make as a homeowner. The basement is an area where plenty of cold air resides, but adding basement insulation can stop any cold leaks, increase energy efficiency and reduce energy bills.

❓ Why insulate the exterior of my basement walls?

👉 By insulating the exterior of basement walls we consume less interior space and prevent exposing walls to the seasonal freeze/thaw cycle known as 'thermal shock' that can cause the cracking of foundations.

❓ How to build basement walls to prevent mold growth?

👉 The ideal Basement wall assembly to prevent mold growth: Install two inches of rigid insulation board directly against concrete. It is easiest to attach it to the wall with a couple of concrete nails or even some adhesive while you frame walls. Frame an interior 2x4 stud wall at 24 inch centres, pressed tightly against the foam panels.

❓ What are the benefits of thermal insulation in a basement?

👉 It also helps reduce the chance of interior moisture issues by raising the temperature of the first interior condensing surface, the concrete. Below is a thermal image of the basement descibed above with insulation on both sides.

❓ What type of insulation is used for basement walls?

👉 The below-grade portion of the insulation will be held in place by the backfill, but may require some fasteners to hold it in place during the process. Three types of insulation are used on the exterior of basement walls: rigid mineral wool boards, high-density polystyrene (Type IV) and polyurethane/polyisocyanurate boards.


Video Board: Basement Insulation: How to Insulate the Exterior and Interior of A Basement to Save Money, Energy