Installing rigid foam insulation on interior walls can improve energy efficiency, reduce heating and cooling costs, and minimize noise transmission, creating a more comfortable living environment. Proper installation involves safety precautions, precise measurement and cutting, thorough wall preparation, secure panel installation, and finishing touches for a polished insulation system. Foam board insulation is a product made from polystyrene and polyurethane used to insulate interiors from exterior temperatures. It is most often used to insulate areas of a st. and is installed between the studs that make up the wall and are often glued in place.
Rigid foam insulation is a good option for interior walls, as it provides numerous benefits such as improved energy efficiency, reduced heat loss, enhanced indoor comfort, and soundproofing. It is relatively easy to install yourself and can be placed on the inside of solid walls, wall studs, between cladding and the wall, or between wall cladding and the wall. To install foam board insulation, dry the area, remove excess debris, measure and cut the foam boards to fit the walls, drill mounting screws through the foam, or opt for an insulation.
Rigid-foam insulation is a more effective air barrier than batts or blown-in insulation, especially if the seams between sheets are carefully sealed with caulk, canned spray foam, or tape. Interior foam board is a well-tested method for improving thermal performance and comfort in a renovation. Adding the foam board to the walls will increase the R value of the wall by virtue of adding additional mass to the wall.
In mild climate zones, it is possible to put rigid foam on the exterior of your walls without worrying about moisture accumulation. Foam works as a thermal break if it is thick enough, continuous, and with all seams taped. Polyisocyanurate (polyiso) has the best R-value at 6.5 (after aging).
📹 Why Use RIGID Insulation board On basement walls
Basement Wall Insulation Using Rigid Foam Board FULL Article: …
📹 Simple trick to Exterior Insulation and Window Depth
Using Exterior Insulation on a Window without adding the thickness, Matt explains how Roxul helps achieve this detail.
If you value your life, cut this iso with a hand saw, measure for your cut, slice the iso on the back side of the sheet, slide your chalk line in that slice and snap the cut line, and make the cut with one the old handsaws you inherited. It will take an extra 30 seconds and you will be breathing easier than cutting by circ saw. Total hari kari with a circ saw. The dust created will not be airborne, spread out a sheet of poly below the sawhorses & dump the residue onto the poly and its easy clean up. Best Insulation value available.
maybe i’m missing something here, but they show an example of mold/mildew growing on the brick wall, and later show the installation of the rigid insulation. . . . . so what keeps mold/mildew from growing on the brick behind the rigid insulation. typically moisture can seep through the brick stone and mortar giving mold/mildew the moisture what it needs to grow, covering it with rigid insulation, gives it the darkness to better allow it to grow. I think this article glosses over additional necessities to keep mold/mildew from growing. I’m sure it’s important to put a vapor barrier on the inside like mentioned, but if water collects on the outside of the brick foundation of your home and there isn’t a vapor barrier on the outside, the moisture can soak into your foundation walls and any void gives mold/mildew the environment to grow. Are there any experts reading this who can provide a more comprehensive explanation?
Basement walls can only dry to the inside. So by putting up a foil faced insulation you are trapping moisture between the wall and foil insulation. This is a place for mold to form. Then if that mold gets through to the wood studs and back of the drywall it won’t be long before it’s causing havoc in the basement. From the reading I’ve done it is best to let the walls breathe. Use a EPS beaded foam glued to the walls. This lets some drying to the inside happen. Using metal studs would eliminate organic materials and a paperless drywall would also allow drying. This would make an assembly that can dry to the inside.
My old cinder block walls look like someone got real casual with alignment towards the top. Still, I’m considering putting foam boards where I can so they’re flat, and where the gaps are, to fill with spray foam. And then just create the stud wall an extra inch out. The extra gap between studs and foam board will just have to be filled in with more spray foam or rock wool.
Of course the coldest day of the year with 1″ of ice and 2″ of snow is when I go looking for home insulation articles.😂😂 Only to find your website and come to the realization that my crawl space insulation is woefully inadequate. It’s going to be a busy spring, I’ll be catching up on all your articles until then. Thanks for all the tips.
I have yet to find someone who addresses insulating poured concrete walls that aren’t perfectly flat. The builder of my home obviously didn’t pay much attention to properly tying the forms together in the middle of the height and all the walls appear bowed in, but are actually thicker in the middle, not warped. If I tried to put rigid insulation boards on these walls they would either be bowed as well, if they were flexible, cracked if they weren’t, or there would be gaps top and bottom so I could have a plumb wall. Gaps seems to be a recipe for moisture collection and mould growth, so how would I get around this?
If you are using those 1ftx1ft OSB boards with the closed cell “grid” layout for your floor (the grid is for airflow), would you put that down first with a small gap on the wallside and then put this tight to the panels? that way you have airflow from the floor to the wall in case there is moisture?
Hey guys really enjoy the articles. I have a 20′ x 16 shed / Office that I have A/C (I am in Florida) and I have 2″ x 4″ exterior wall what would you use to insulate the walls and roof areas. It sounds like the beat I am going to get is an R10 or R13 with either the spray foam or the Foam Board. Keep up the great articles. D
Best practices? Maybe if you left a gap at the bottom, top sides and then foamed them rather than adhesive. You got an R rating on that adhesive? You are also putting your vapor barrier to the inside of the foam which means the foam can hold moisture. If placed to the outside it keeps moisture back at the masonary layer. So install the panels right and get rid of that thermal bridging between panels.
Great article… 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 article and Go Blue!
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 website 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.
My basement has exist cmu with 1x furring 16″oc with paneling and likely no ext and int moisture barrier. How would you handle this situation: leave exist furring in place, apply 2″ polyico to furring, apply 1/2″ MR gyp board directly to polyico (which side?), etc? I thought about applying 3/4″ rigid insul between furring, possibly adding another 1″ rigid insul over furring and insul, applying vapor barrier overlapping 6″, then applying MR gyp board? Seems to be endless options and applications but I’m looking for best practice for old cmu basement walls and humid basement conditions. Also, if water penetrates into the block and contacts the polyico and drains to floor does this create problems as well? Thanks
Hi. Thx for the informative article 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
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.
Hi Rob, I love the poly idea on the interior and the benefits of it. I’d prefer to be able to have the ability to inspect in the remote future chance that the exterior water proof treatment fails or has an inadequately waterproofed area. My girlfriend bought a small cape Rome NY built in a hurry, post World War 2. The unvented crawl basement is humid and needs the dirt/rock sealed in the areas it is not dug out…on that, I wouldn’t worry about spay and I’d be able to crawl on it as opposed to a 15mil plastic sheet solution. Currently a large dehumidifier can barely keep it at 50% RH. The water table is high and aside from gutters, the cinder block exterior needs water proofing. What are your thoughts on spray polyurethane on the exterior from just under the siding, down to the “footing”? It seems like it would be waterproof and insulating and more durable over years of temperature cycling than the other typical coatings. It seems like like exterior inspection would be less likely to be required as far as accessibility is concerned.
I would like to isolate the walls of a small place where it will be to do some chores, a kind of workshop. All around the walls are made of brick and only one wall is made of yellow stone. What I was thinking of doing; -Stick on the wall directly XPS 260x60x3cm and then on top of the XPS OSB boards. What I do not know; -Collage, I know that there is a glue suitable for these cases, type of construction or industrial but safe ?! -The application of OSB, also on top? Do I drill the XPS and also the brick to put the OSB in? How? -Do I need to put frames between? -My biggest doubt is stability. Because later I wanted to hang some cabinets and shelves to put storage and tools!
Rob great the article, I am looking to refinish my basement the house had drainage & foundation issues which have been corrected. The basement walls are block wall with thoro-seal masonry coating on them. Would the ridged board or close cell spray foam you spoke of work in this situation? I have steel I-beams running vertical every 8′ around the perimeter of the basement.
Thank you! Can you affix this board under a metal fireplace base? That is, in my basement, I can see the underside of the wood burning fireplace that is located in the family room above it. I assume the metal will get warm when a fire is going. (I don’t use it.) The area is an alcove that will be turned into a closet. Should I keep the polyiso x” away from the metal? I was going to use .5″ polyiso in this area since it’s a closet. I don’t see how to attach a photo for clarity. Thank you!
I work at a door shop that has leftover polyurethane fiberglass pieces that are 1.75 inches thick. They are 1/8 inch thick of gel coated fiberglass on each side with 1.75 inches of polyurethane foam. They cut doors out for windows and I take home what’s left,because they just throw them in the trash. I’ve been there for 4.5 years and now Have 950 pieces now. 22″x 36″ and 22″x27.5″ pieces are all flat with no patterns. The R-value apparently is 7.5 according to Therma true . I am on on over 6 1/2 acre so I have room to store them. Just can’t quite figure out what to do with them for either an investment or projects.
Timely, I’m just moving into a house and need to do this! A question: To increase R value you mention building another wall over the ridgid board…would you do this directly on top of the foam board? I don’t really want to loose all the space of another wall…but I like the idea of a warmer better insulated space!
Poly Iso doesn’t like the cold. EPS and XPS will perform better in that regard. Also, a properly installed vapor barrier such as a plastic sheating that doesn’t have penetrations and is tightly sealed ….IS a vapor barrier. However, they get badly installed and demolished during the construction and afterwards and very often the construction methods make them non continuous anyway.
Can I build a sleeper floor on top of rigid foam board, fastening the sleeper floor through to foam board to the concrete? I’m building a subfloor in my garage in a sub zero climate. My plan is to also include foam board between the sleeper boards to be the thickness of the sleepers, then top with plywood. If so, can i shim between the bottom layer of rigid foam and the sleepers, as I would if the sleepers were just on a thin vapor barrier on top the concrete? Thanks for any feedback!
Hi rob, question for you We installed a interior french drain, did 10m vynile + 1.5 inch foam under. and installed a delta ms membrane on the interior wall that goes under the concrete (if water drip from interior wall it will go straight into the french drain. My question should we seal the upper delta ms with silicone + blue tape? We are going to use 2inch rigid foam on the wall for isolations
I heard you say the polyiso can go tight to the concrete floor. I just want to ensure there won’t be any wicking of water. I understand that John Manfield AP foil faced and R-Max R-Matte Plus 3 sold at the big box stores don’t have the fiberglass in them that was creating a moisture problem. Also, what happens if there are air gaps where the board doesn’t adhere fully to the poured concrete foundation wall? The polyiso I purchased was warped at the store and there are air gaps. I’m hoping that once the framing goes in front of it, it won’t be a problem.
Despite what this guy says….Polyiso is a terrible choice if you’re in a cold environment. Polyiso is good at keeping the cold in the house in hot areas. It’s VERY bad at keeping the heat in the house in cold areas. The R value you see advertised is based on its performance in warm weather. All of that goes down the drain in the cold.
Great article and information! Thanks a lot. My basement was already finished when I bought the house, but it’s only got the reflective fiberglass insulation between the studs, no XPS behind it. Most of my basement walls are about 30-50% above grade, and I don’t have any major moisture issues now. I’m about to start a basement remodel, so now is the time to replace with rigid board if I’m going to do so. What are your thoughts – start fresh or not to fix what isn’t broken?
Unfinished basements in new home construction, the concrete wall needs to be insulated now, and then sheet rocked for fire purposes. The rigid foam melts and smokes so it needs covering. Does the polyiso need it to. You said its more fire proof. Just wondering so the basement can be finished at a later time.
I am planning on a dimple mat on my concrete slab followed by a 2×4 wall 2″ off the foundation wall so that I can use closed-cell. Someone said I should take the dimple mat and wrap it up the wall 12″ in case any water gets through the foundation wall. Is going up the wall the 12″ even a good idea? Should the dimple mat go below the 2×4 wall? Thanks!