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How to Insulate Your Basement

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W hether you plan on using the basement as a living space, turning it into an entertainment center or home office, or you don’t have any plans of the sort for it, insulation is still mandatory as it not only creates habitable conditions but helps lower cooling and heating costs throughout the year substantially by reducing heat loss. No matter how powerful your air conditioning system is you will still feel hot during summer without following the guidelines provided here and renovating the basement to benefit the whole building structure.

Did you know?
The basement is responsible for an estimated 30% of heat loss in buildings when not adequately insulated, so you can see why this is a matter of emergency in case it has not been performed from the get-go.

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What Causes Excess Basement Moisture

Air leaks and drafts are to account for most moisture entering a building, but with basements, especially which are made of concrete, a highly porous material, there’s the issue of their build that predisposes to humidity seeping in. This precise construction is what makes the basement feel damper after the snow thaws or when it rains, water entering through the floor and walls via vapor dispersion and capillary action.

The below-ground grade of the basement makes it cooler, during summer, the concrete build in basements without insulation becoming cold and vapor condensing on the walls, turning them wet, whereas during summer when humidity increases exponentially because of the weather, the vapors inside condense everywhere and the dampness sticks for months on end.

For this reason, before you actually move on with the actual insulation process, you must deal with blocking the water vapor and sealing any drafts that could cause you to trap wetness into the below-ground level once you insulate it, consequently compromising structural integrity as a result and providing perfect growing grounds for mold.

Check out the best dehumidifiers for basement to have an additional means to wick humidity as it appears, which strengthens the effectiveness of insulation, draft sealing, and water vapor blocking, ensuring this area of the residence won’t ever be at risk of mold development seeing how RH levels will stay within proper parameters.

Assessment Proceedings

Before you actually start with the insulation job, there is a task you must attend to, and that is evaluating the cellar for damages and problems. The issues you must look into during the assessment part are water leaks, dampness, radon, and cracks.

#1 – Leakage

Minor leaks can be rectified by simply patching the affected areas from the interior, sloping the grade to redirect water from the foundation, and setting up downspouts away from the building.

Major leaks require immediate correction as structural integrity is at stake if you do not handle them. These include constant leaks and waterlogging whenever it rains or when the snow melts and can be spotted quite easily. Adding a discharge system, outer insulation, waterproofing, these account for some viable solutions.

To handle the issue of water leaks, you can opt for sump pump installation as well, especially if you live in an area where heavy rains and snows are normality. Seeing how the sump pump is a measure to prevent flooding, you should install it in the basement regardless of any other factors as it is a safe means every building should have in check.

#2 – Moistness

Luckily, moistness is quite easy to spot as symptoms comprise staining, mold development, paint peeling, spalling, musty odors, and efflorescence on the finishes and groundwork. Minor moistness is quite easy to get rid of through proper ventilation, whereas major moistness can be fixed from the interior by installing and running a basement or a much more heavy-duty crawl space dehumidifier that tends to pull excess dampness from the air until RH levels normalize.

#3 – Radon

As the basement is in constant contact with the ground, radon levels can be dangerously high as the radioactive gas has its provenance from decaying uranium in the rocks and soil beneath the structure of the house. Aside from ventilation to circulate the air in the basement and ensure radon escapes from this space, you can install a sump well cover so that lower levels of radon seep inside the house, to begin with.

As radon is odorless, colorless, and tasteless, the only way to find out how severe levels are you need to perform a test. You can find single-use charcoal test kits and reusable digital radon test kits for this task.

#4 – Cracks

Regardless of how small or big the crack is, immediately pursue professional help to ascertain what type of structural repairs are needed to solve it. Cracks are not to be neglected as these could compromise the integrity of the whole building, so treat the matter with utmost urgency.

Inside vs. Outside Insulation

With basement insulation, you can either do it from the interior or the exterior. While outside insulation is the superior option, if money is an issue, interior insulation can suffice. Ideally, you should opt for a combination between the two, ensuring moisture issues and heat loss won’t be a problem caused by the below-ground level ever again.

PROS CONS
Interior Insulation
DIY level difficulty – doesn’t require you to hire a professional Obstructions can decrease its effectiveness
Can be performed regardless of the season Foundation walls can become even colder, which results in condense forming
Can be integrated with finish plans Moisture issues must be fixed before applying it
Cheaper option to go with
Exterior Insulation
Walls are easier to insulate from the outside Contraindicated to perform it during spring and winter
No interior space is lost Expert aid is recommended – costlier option
Frost won’t pervade the construction anymore If there are steps, fences, and trees around, your work is made all the more difficult
No more temperature fluctuations
Moisture and structural problems are simpler to spot and fix

Interior Insulation Proceedings

  • Make any renovation work is needed as we previously advised. Then, acquire and use a foam board that is of medium- or high-density, like extruded polystyrene.
  • You can actually take the simple route and seal it to the substructure via an adhesive that is placed around the board’s perimeter before you fasten it to the wall. Doing so actually serves as mold containment in case it grows backside the insulation you set in place.
  • On top, use wooden fixing strips as these are required to fasten the board to the wall. Nail the plaster cast to the strip that has previously been fixed to the concrete.
  • To diminish heat loss, position the insulant in overlaying layers, and fit it snugly at the edges. Use tape and caulk to close joists.
  • Before you finish, add 1/2” gypsum board to the wall to serve as protection.

Exterior Insulation Proceedings

  • With this procedure, you might need to install a discharge system and watertight the walls of the substructure, so beware that it is a lengthy and costly procedure. Professional installation is recommended.
  • First off, dig a ditch around the whole construction that is wide enough.
  • If the walls and discharge structure are in good shape, you can set it up 24” in the ground.
  • If you want, you can install a horizontal grip skirt to mitigate heat loss that comes from the surface, solving frost-related issues.
  • Clean the substructure surface, repair any damage you find, and fix deteriorated surfaces through replacement.
  • In case there is no discharge system, install one. For this, consult an expert.
  • Hire a builder to watertight everything and seal overlaps properly.
  • The materials you can use for exterior insulation include polyurethane boards, stiff material wool boards, and high-density styrofoam. Most commonly, people opt for high-density styrofoam for below-grade applications, whereas the wool board is generally used when there is a discharge system or the procedure is applied for the whole wall.
  • Measure and cut to the necessary height according to the project type you perform, and proceed to install it at one corner, with corners overlaying and sheets tightly sitting together.
  • Proceed to apply flashing to maintain the insulation in position so that water won’t gather behind it. Pitch wood flashing with a 3/4″ minimal protrude.
  • Apply layering from the top to approximately 12” beneath the soil surface to shield the insulation from any sort of damage, including that induced by sunlight. For this part of the project, you can use pressure-processed plywood or polymer-modified parging.
  • Refill the trench area and cover it with lawn, grass, or terrace stones.
  • Seal and coat any penetrations. Wrap insulation to finish the windows, and outline the doors with flashing. Lastly, insulate the header from the interior of the cellar.

Final Words

While not an easy procedure in the slightest, basement insulation is needed not only if you want to make this area livable, but for the purpose of preventing heat loss because you didn’t properly attend to it. Similar to crawl space encapsulation but considerably tougher in terms of difficulty, it isn’t something you should tread lightly, so beware that the importance of following through right is enormous and it requires skill that, if you lack, must require professional intervention.

Tobey Hunter
Tobey Hunter
Tobey is the editor-in-chief at Optima Institute, his prior experience as a niche product reviewer in air quality improvement systems helping shape his path to conduct thorough research toward selecting and analyzing products so that customers are satisfied with the provided recommendations. During his carrier, Tobey also gathered technical input that makes him well versed in understanding advancements in modern systems, helping readers in turn to better understand how modern devices help improve life quality.