Exterior insulation of basements walls

Pros of Basement Exterior Insulation

Exterior insulation of the basement walls is an effective and definitive way of correcting moisture problems.

To solve structural problems involving the foundation - water leakage, dampness and other moisture problems - you should insulate it from the exterior (and not from the interior). At the same time, exterior insulation makes foundation repair and waterproof much easier, and allows the installation of a foundation drainage system, if necessary.

Cons of Basement Exterior Insulation

There are costs and disadvantages of exterior insulation: digging a trench around the house can be costly and difficult, and collide with the weather, paved carports, trees, fences, electric lines, gas pipes, telephone and cable TV hook-ups…

Due to these cons, if there isn’t structural problems with the basement, you can try to solve the problem of moisture or coldness through other means: see, Solving the problem of cold basements without insulation

Another way of minimizing costs and problems is to adopt a partial depth insulation of the exterior basement walls.

Partial depth insulation of the exterior basement walls

In this method, the exterior basement insulation involve two pieces of insulation material: a vertical and an oblique one. The first (with 1 feet / 30 cm height or more) is installed below ground, against the outside wall of the basement; the second (with 2 feet / 60 cm or more) is installed under-ground, at the bottom of the first piece of insulation, with a convenient (20º/30º) oblique angle.

This method is suitable for basements without cracks, water leakage and dampness at its bottom, and if the ground isn't saturated with water. It's mainly a good method in dry and moderate-rain climates, where there is no problems with water-saturated soils.


Insulation materials

Common and recommended insulation materials include:

- Extrude expanded polystyrene (higher density type)
- High density polystyrene
- Foil-faced polyisocyanurate
- Rigid fiberglass (unsuitable for horizontal uses in partial depth insulation method.)


The R-value of the basement insulation materials

See on this matter: R-values for Basement Insulation

Exterior Basement Insulation Steps

The insulation of the exterior basement walls involves six major steps: 1) digging around the foundation, 2) sealing and damp-proofing the walls 3) installing the rigid insulation 4) installing a flashing 5) installing a protective covering on the exposed parts of insulation and 6) backfilling the excavated area with soil.

1 - Excavating around the foundation

The digging should go down to the limit of footings and not more. Be careful with pipes, electric lines, telephone hook-ups, etc. The width of the trench should be sufficient to work in it, though not bigger than the strictly necessary.

2 – Sealing and damp-proofing the walls

Clean the surface of the foundation. Repair holes, cracks and other damages, and allow repairs to dry. Penetrations should be sealed and removed.

Apply waterproofing – typically two coats of a waterproofing compound – all over the wall.

Check drainage tiles, repairing them if necessary. If there is no drainage system, it’s a good idea to install one.

3 - Installing the rigid insulation

Applying the insulation depends a lot of the materials and soil conditions. Follow the manufacturer’s instructions for installing.

Measure and cut the insulation board to the desired height (typically, from the top of the footings to the flashing…). Start at one corner and keep the insulation boards tightly glued to the wall.

Use the soil to held insulation in place, and also the flashing, fasteners and washers, at the top.

4 – Attaching a flashing to keep water from getting behind the insulation

The flashing allows the insulation to extend beyond the line of ground, protecting the insulation and the basement foundation from water. It also helps keep the insulation in place and provides a neat junction. Discuss its location and the type of flashing with an expert.

5 – Installing a protective covering on the exposed sections of insulation

The insulation should be protected from sunlight, lawn and garden tools, etc. A number of materials can provide that protection, including cement brick, grade plywood or treated siding of fiberglass panels, vinyl, aluminum…

6 – Backfilling the hole

Cover the drain tiles (made of perforated plastic pipe) with adequate clean gravel.

If possible, use free-draining soil if the existing is a poorly draining type. After backfilling the hole, ensure a proper run-off of rainwater. It’s important to provide drainage away from the insulation. See: Gutter, downspouts and surface drainage.
 

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