Why Use RIGID Insulation board On basement walls

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Basement Wall Insulation Using Rigid Foam Board

Best practice for basement wall insulation [best insulating and vapor barrier system] is closed-cell foam, the second-best is using foam board, especially if you’re trying to save money. Using a rigid foam board creates a good vapor barrier along with an insulation layer that won’t promote mold growth. Rigid insulation board is also called Extruded Polystyrene (XPS) insulation.

Basement Insulation Vapor Barrier

The simplest way to prevent this water vapor from entering the space is to prevent air movement [moisture] into the basement by installing a vapor barrier. When properly installed, closed-cell foam (spray or rigid foam board) acts as a vapor barrier and insulates. [poly plastic and Kraft faced insulation is not a good solution for basement vapor barriers. ] The main goal for using rigid foam board against masonry walls is to prevent air vapor movement and mold growth, while it can be the only insulation used in a basement insulation system, it’s often supplemented by fiberglass insulation.

The BEST Rigid Board To Use

There are two types of rigid board commonly used.
Extruded Polystyrene (XPS) insulation board
Polyisocyanurate (Polyiso) insulation boar

Extruded Polystyrene (XPS) insulation foam boards deliver long-term stable thermal performance of R-5 per inch. Compared to spray foam, it’s harder to install in awkward areas (for example, in a tight space where a rim joist is close to another parallel joist). Rigid foam is also fussy to install if the rim joists has a lots of wiring and pipe penetrations. But its cheaper and a popular choice if you’re doing a DIY project.

Polyisocyanurate (Polyiso) is a closed-cell, rigid insulation foam board that is bonded to facers on both sides Polyiso is most commonly used due to its fire-retardant properties. Under normal fire conditions, XPS, melts and drips while polyiso, chars over.

The foil facing also helps with the limiting of any moisture travel. Polyiso is commonly used in roof, wall, ceiling and specialty applications within commercial and residential buildings of all types.

Relocate Any Wall Obstructions

Prior to installing polystyrene insulation boards on your masonry wall you need to make sure the wall is clear of pipes, electrical wires and other obstructions. If you do run into obstructions you can start and stop your rigid foam on either side of it and fill that area with spray foam.

Use Insulation Foam Boards [XPS or Polyiso]

Install 2″ insulation foam boards in a vertical orientation, tight to the floor and top of wall or joist bay. See How To Insulate A Rim Joist.

We ensure that the boards fit together using the factory joints, and then return later to tape all seams.

Prior to installing the next insulation board, we add a thick bead of adhesive in the edge groove.

We use DAP DynaGrip construction adhesive for Styrofoam products, and to adhere the boards to masonry walls. DynaGrip is a premium high strength adhesive for heavy interior/exterior construction and remodeling projects.

This multi-material adhesive delivers a powerful instant grab to hold the vertical insulation boards and creates a durable long-lasting adhesion. We apply a zig-zag pattern of 1/2″ bead directly to the wall and press the insulation board in place.

Seal Vertical Joints With Foil Tape

Tape all vertical seams using a foil tape compatible with the foam board. This type of tape has a durable backing, coated with an aggressive acrylic adhesive that offers excellent adhesion, and sealing properties.

Seal Top and Bottom Joints With Foam

Once all of the insulation foam boards are installed to the walls, and the vertical edges have been taped we then seal the top and bottom edge. Using a Pro Series spray gun applicator we completely fill all gaps, remaining penetrations, and any air leaks using DAP Touch ‘n Foam Polyurethane Foam Sealant.

This All-Purpose sealant is a 1-component polyurethane foam sealant that dispenses approved fire-block (ICC-ES ESR-1926) foam.

Seal the Rim Joist and Sill Plate Area

The rim joist is located above grade and for many years we treated it similar to the wall insulation above, by stuffing fiberglass batt insulation in the rim joist bays. This method is no longer recognized as best practice. .

Frame Basement Walls

Install basement walls up tight to the 2″polystyrene insulation boards. Fiberglass insulation can then be applied to the studs walls, to increase the basement insulating R-value.

[workinprogress]

your best practice is like listening to a step by step work instruction. I like it! Thumbs up

[Nick-gygc]

Great video... before even stumbling upon this I'm using the exact same method to insulate the basement by myself in my new home I'm building. I first tried using powder actuated nail fasteners to fasten the board to the masonry, but the nails kept bending or shooting through the board and ruined it. So I abandoned that and now am using construction adhesive. It's slower but it works like a champ. I will spray foam all the seems when I'm done. Fellow Wolverine here... Nice video and Go Blue!

[ladyploveroflife]

Great video. Here in Michigan we’ve been dealing with flooding this past year and I’m trying to find a new way to handle it without a repeat occurrence

[andrewsky]

Thanks for the video, Robert DeNiro. I am always amazed at the diversity of characters and roles that you are able to play!

[annbreckenridge]

I've lived in my house for 11 years, and I am finally getting to work on my basement. I cannot wait to insulate it! Thank you for this video and the one about insulating the rim joists.

[BetterwithBrubaker]

great info. my favorite part of your video method is no small talk, straight to the info.

[loulowe]

Hey Rob - Great video. I am an DIY'er and often have trouble finding any guidance from the big box stores. I really appreciate you sharing your expertise! Keep the videos coming! Thanks again!

[whatsthechannelnamex]

Ran this inside the underskirting on my mobile home and it's almost as warm under it than in the house. Excellent advice here. Still kept the heat tape on our water line though.

[erikellott]

What a great video. My wife and I were just talking about finishing the basement. Thank you for making this video.

[lisaruffin]

Awesome video. I am having my foam installed professionally, but you're helping me to learn.

[speerhere]

PSA: Couple of notes: 1. Never cut rigid insulation without a mask on. 2. Do not glue the rigid board directly to the concrete, you will end up with mold. The rigid needs to have a small drainage channel built into the system. Either use furring strips on the wall or if you are made of money buy something like the insofast product that has tiny grooves built-in similar to zip system plywood. I flip houses and have seen this mistake cause mold problems many times, especially with block walls.

[byron]

FINALLY... the video I've been searching for. WELL DONE 100%

[noskills]

Some good tips, have only taped over the joints before- might go into more detail on the next build 👍

[MrBrianDuga]

Some manuf of polyiso don't approve its use where it will come in contact with water. Also, if there's enough moisture in the wall and this is done, the water can migrate upwards towards the sill. If there's no capillary break (sill seal) and the sill isn't made of PT, then completely sealing from the inside can lead to a rotted sill. Better is a sump pump to manage water as it enters. Best is to control moisture from outside the concrete wall. I think also that I would use rigid foam up until a certain point and then switch to something that is vapor open at the rim joists (like rock-wool). Humidity entering from there could be managed with a dehumidifier.

[richardmckrell]

1st choice is exterior insulation, 2nd choice is interior closed cell spray.

[louisedevin]

Hi. Thx for the informative video and your expertise. I installed my rigid high performance aluminum sided foam insulation board behind an already framed wall. Now I want to insulate between the studs also. Can I cut another foam board and place it between the studs? Or do I have to use insulation batting? I prefer to use the foam board for moisture resistance but don’t know if that’s advisable…I know it’s more expensive and more work but I’m okay with spending more money and taking the time. I already bought the enough boards. I also have Owens Corning XPS insulating sheathing foam boards I could use. Thx for and advise or suggestions. Really appreciate

[stephensummerlot]

This video is AWSOME. Actually gives guidance

[guyh.]

I've often thought about this subject so thank you for the information. Now here's a question for you. What about during the summer? Where I live, the basement is amazing as it brings in the cooler temperature from the surrounding soil & makes it wonderful. How does that effect it?

[tomt]

I thought the best way to insulate basement masonry walls was to insulate the outside, keeping the masonry warm also.

[lmd]

Must you also put a vapor barrier plastic behind the foam board or is it not necessary?