There are a variety of underlayments used under wood floors, click-together floating floors, as well as carpet and tile.
Underlay can serve various functions like cushioning, sound deadening, leveling, uncoupling, and moisture resistance.
The following underlayments are relatively high in off-gassing (too high for me):
- Polyurethane foam
- Rubber (most SBR rubber)
- Vinyl (like Mass Loaded Vinyl)
- Most cork underlayments, except the ones listed here
This post goes over the best non-toxic low-VOC options.
This article contains affiliate links, upon purchase I earn a commission at no extra cost to you.
Paper Underlayments Used Under Wood Floors
Silicone Paper
Silicone paper is usually used under real solid hardwood floors, but it can also be used under engineered wood.
It is semi-permeable which is good, as you want your upper floors (over wood subfloors) to be breathable in almost all situations.
It meets perm ratings recommended by the National Wood Flooring Association.
Those extremely sensitive to chemicals have liked this product a lot.
If you just need something simple that is not providing sound dampening or levelling this will do the job.
Red Rosin Paper
Tried a true, Red Rosin is the old school underlayment paper used under real wood flooring. It’s extremely low in odor and even that dissipates rather quickly.
The extremely sensitive almost always do well with this, with only a few people mentioning that the undyed Rosin Paper was preferred.
Keep it simple and breathable.
Foam Underlayments for Click Together Floors
Basic Polyethylene Foam
For laminate, engineered, and other click-together floating floors I prefer the most basic polyethylene underlayment.
It’s very simple – it’s one of the safest plastics in terms of odors and off-gassing (it can be zero-VOC or super low VOC).
This provides some cushioning which is necessary under flooring types like laminate.
It’s not a complete vapor barrier (if it doesn’t have an attached polyethylene layer or foil layer), so it can breathe, which is great for upper-level floors. Plus, it’s very inexpensive.
This is the type of foam that comes pre-attached in some laminate lines. I find that very convenient.
A “2 in 1” will usually have polyethylene foam and a thin layer of plastic.
If you are looking for a vapor barrier, make sure it has one attached. The term 2 in 1 is rather confusing in this sense, as some are moisture-resistant and some have vapor barriers, but they are very thin.
Check with the flooring company and your contractor to make sure you have an appropriate vapor barrier, if one is required.
Cali Bamboo brand makes a good polyethylene underlay with foil as the vapor barrier, made for their floating floors. Antimicrobials are not listed in the description.
And Kahrs makes a polystyrene foam with 3 mil poly plastic for their engineered floors. They do mention it has mold-reducing properties so it might have an antimicrobial.
Polypropylene Foam
Polypropylene foam is another very safe plastic.
It’s not as breathable as polyethylene and I have only seen it advertised as being a vapor barrier or as having a vapor barrier (another plastic layer) attached to it.
It’s used for laminate, LVP an and engineered wood (mostly) when a vapor barrier is required.
It can be used under solid hardwood floors to provide cushioning and sound dampening.
If it’s labeled 3 in 1 like this Traffic Master opion, which usually means it’s cushioning, sound dampening, and a vapor barrier.
Floor Muffler has not tested their products with carpet. Their polypropylene underlayment is free of any added flame retardants they do list antimicrobials in the description.
They have a high acoustical rating, the one below can meet IIC up to (74) dB per ASTM E 492 / ASTM E 989, STC up to (73) dB per ASTM E 90.
Mohawk Silent Guard is STC 73, IIC 71.
EVA Foam
EVA foam is another low-VOC foam though it does sometimes contain phthalates.
Compared to polypropylene and polyethylene it does usually have slightly more of an odor.
EVA foam underlayment can be used under floating floors like engineered wood, laminate, bamboo, as well as carpet. That one says not to use with vinyl but check the description for each brand.
(Also at Home Depot).
Antimicrobials are not listed in the description.
IIC (Impact Sound Transmission Test) rating is 73, STC (Sound Transmission Class) is 72.
Felt Underlayment For Engineered Floors
Felt + Vapour Barrier
Quietwalk is felt and a vapor barrier made for under laminate and engineered wood as well as other floating floors like bamboo and luxury vinyl plank.
The felt and (polyethylene) plastic layers are quite safe even for many chemically sensitive folks.
It claims to be zero-VOC.
This one does contain Microban (Microban can refer to 6 chemicals, so this could be anything from silver to something more synthetic).
If you want it without antimicrobials, you can get Quietwalk from Green Building Supply.
Because this has a vapor barrier it’s meant for on top of a slab or basement floor.
If you do lay down laminate, engineered, or another organic-based click-together floor on a slab or basement you do need a vapor barrier.
However some mold preventative architects do not recommend putting down a vapor barrier on the slab like this. I explain this here.
Available on Amazon, Home Depot, and Walmart.
Natural Material Underlayment For Many Floor Types
Breathable Cork
Cork underlayment is one of the most expensive underlayments but it can be the purest.
It provides good cushioning and sound dampening as well as some leveling.
It can be used under engineered hardwood, laminate floors, hardwood flooring, and ceramic tiles.
There are at last two pure cork underlayments without any glue or binders. I list them in Substack in the Mold Preventative Flooring article.
In most brands out there, the small pieces of cork are usually pressed together with a polyurethane glue which I find to be quite strong in off-gassing, so I don’t personally use this underlayment.
Some brands are made with polyethylene as the binder, which is much better in terms of odor and off-gassing compared to polyurethane, but it does take away the vapor-open nature of cork.
Eco Cork Foam, says they use polyethylene as the main binder.
Like many underlayments, it does contain an undisclosed antimicrobial would could be problematic for some sensitive people.
They also recommended gluing the underlayment down.
There are many flooring types and brands that come with an already attached cork underlayment, which also almost always has polyurethane off-gassing.
1/2”(12mm) cork underlayment has STC 49 and IIC 48 sound ratings.
Pressed Wood Underlayment
This Steico product is a lot more unusual than the others. This is different from the old particle board underlayments. They claim it is more water-resistant than particleboard.
It’s a pressed wood product, but they don’t mention what kind of wax, oil, or glue is used to make it. They do claim it is zero-VOC and 100% natural.
It can be used under floating floors like LVT, laminate, and engineered wood, as well as hardwood floors.
It seems to be very good at sound dampening.
I’d be too worried about water damage during a spill personally.
Available on Amazon or Walmart.
Vapor Barrier for Over a Slab or Basement Floor
6 Mil Poly
6 mil polyethylene plastic, is a common vapor barrier for a slab. It does off-gas a little, though it’s minor.
I wouldn’t do this due to the reasons discussed in Substack. Though an alternative suggestion is included in the Substack article.
If cushioning is required it makes sense to buy a foam and vapor barrier in one.
Flooring with Attached Underlayment
Many click-together floors come with an attached underlayment. This really helps in simplifying things.
I like laminate floors with polyethylene foam backing attached, LVP with rubber or foam underlayment attached.
Some LVP comes with an EVA underlayment (which may contain phthalates).
Luxury Vinyl Plank (LVP) with a cork backing does not make sense to me in a basement, slab, or wet area since one of the main benefits of LVP is that it is waterproof and very mold-resistant.
Attached cork underlayments also tend to have more off-gassing. Though if that doesn’t bother you it is a great pre-attached underlayment for an upper floor.
Underlayment for Tile
I like the Schluter system under tile.
If you need zero-VOC acoustical control under tile Schluter DITRA-HEAT-DUO providers a ΔIIC contribution of 20.
Cork underlayment can also be used under tile.
Schulter has different membranes that I discuss more in the grout and thin-set post. They are made of a non-toxic very low odor plastic that even most chemically sensitive folks do well with.
Many acoustical underlayments for tiles are rubber or vinyl-based, and I would personally avoid those as they are one of the highest off-gassing products in a home.
For underlayment on a slab on grade or basement Cheryl Ciecko and I recommend a vapor open underlayment. There are only two I know of and they are listed in my book.
Photo Schulter membrane from Amazon.
You can also find Schulter products at Home Depot.
Underlayment for Carpet
The main healthy options are natural wool felt for wool carpet, polyethylene, EVA foam (though it does often contain phthalates), low-odor synthetic rubber, or built-in synthetic felt.
My carpet post goes into detail on underlayment for carpet.
Corinne Segura is an InterNACHI-certified Healthy Homes Inspector with certifications in Building Biology, Healthier Materials and Sustainable Buildings, and more. She has 10 years of experience helping others create healthy homes. You can book a consult here.
Join the top Substack on healing from MCS and mold!
John
What do you prefer for extremely sensitive (MCAS) people living in New England? Undyed rosin or silicone or regular rosin?
Corinne Segura, Building Biologist
it depends on your particular home and if you require some kind of vapor retarder in that installation not. And then for the extremely sensitive you will have to test both because there is no way to guess but I’d start with the silicone. You can also ask if you can do it without any.
John
Thanks. I bought both and will experiment.
John
Would cork be any better or the other two options just as good
Corinne Segura, Building Biologist
Cork has a very different function and a very different smell, and you would want to check the additives, like I talk about in the article.
Annette Poth
Our flooring contractor has used red rosin paper for years but is now recommending Wakol PU 280 – a liquid roll on polyurethane resin moisture barrier. What do you think of this product? WAKOL-PU-280
John
If rosin or silicone are under hardwood flooring then it likely won’t matter which is used as far as sensitivity correct? If can’t leach through the hardwood correct?
I bought both rosin and silicone. I’ve used rosin before and have not had any issues but was considering trying silicone since it’s supposedly safer. Suggestions thoughts?
Thanks greatly for what you do!
Corinne Segura, Building Biologist
If something is off-gassing, it will come up through the seams and the perimeter of the room.
Sally B
Hello, I would like to replace carpeting, in my 2002 built townhome, with engineered wood. I intend to do a floating floor. In the summer, there is more humidity in the basement, and I have a dehumidifier running down there during those months. So I am looking for suggestions for underlayment for the engineered wood. I would like a non toxic underlayment with fewer or zero vocs and no pfas. And if a moisture barrier is needed, will I have to be concerned with mold? I really am not sure where to start with options. Any help would be appreciated!
Thank you.
Sally
Corinne Segura, Building Biologist
It depends on the source of that humidity. The article on mold preventative flooring in substack talks about underlayments on slabs and in basements.
Yvonne
We’re installing 3¼” unfinished white oak flooring throughout our home on an island on the coast in Maine. The climate is humid in the summer and very cold in the winter. Our home is heated passively by sunlight, along with a masonry fireplace as our primary source of heat. We’re 100% solar-powered off grid with no backup heating system. The home is built on an exposed pier foundation. We leave for a few months in winter, so it gets very cold.
We’re looking for a non-toxic, breathable, and heat-storage/retaining layer we could install under the wood floors that are resilient to coastal humidity, seasonal cold, natural wood movement and water spills.
We’ve been considering STEICO standard wood fiber insulation board which we read provided a good thermal mass. You expressed concerns about their glues or additives as well as the impact from potential water damage in the event of a spill.
We’d appreciate any insights on what you would recommend considering our circumstances and goals for heat retention and a non-toxic flooring system.
Thank you!
Corinne Segura, Building Biologist
You’ll need a building science expert to comment on that as it’s a complex situation, it sounds like you may not have a properly detailed floor system, and I can’t get behind leaving a home unconditioned in the winter. but cork is likely the answer here.
Anne Flaherty
Thank you for all this info. I have referred back to your work si,ce pre pandemic! with that said, my eco friendly house renovations were stalled. Now financially I am in a challenging spot. So, not only seeking no voc and all natural materials, also seeking lowest price (functionality over rides beauty at this time). Due to a 25 year illness I am hyper chemically sensitive. Thankfully this is a 100 yo house so much has offgassed from years ago, or just was not voc. well, any advice on least expensive options is good. Once my 10×20 front room is properly floored (due to flood from many years ago, it is on the subfloor) I will be renting. Been in touch w Green Bldg Supply, also thanks for any guidance~!
james yang
Hello Corinne, thanks for this post. is ROBERTS-Silicone-Moisture-Barrier the silicon paper? comapring with Fortifiber Aquabar B,which one is better for health? It’s interesting if ROBERTS-Silicone-Moisture-Barrier is better bc I found Aquabar B is more expensive than ROBERTS Silicone Moisture Barrier.
james yang
And it says Aquabar passed CA1350, does it mean it’s ok for off gas?
John
Thank you for sharing this informative article.
Elana Streim
Hi Corinne,
Do you still recommend the Cali Bamboo brand polyethylene underlay with foil as the vapor barrier, made for their floating floors (link below)?
Do you know if it is VOC free?
I’m not seeing an MSDS sheet on it so wondering if that’s a red flag.
https://thegreendesigncenter.com/product/cali-complete-underlayment/
Corinne Segura, Building Biologist
The foil would block VOCs from the top side but I’m not sure if it’s officially 0-VOC. It might be. You can get a sample of it as well.
Ellie
hi Corinne
how do you feel about wax paper underlayment? I’m assuming there’s no with about vocs right? what about antimicrobials? thank you.
Ellie
Hi Corinne
we are getting hardwood floors installed and half way through i realized they are putting down an asphalt based underlayment (aquabar or similar brand-LSU 30-30-30). It claims that it produces no off-gassing, but it doesn’t feel health friendly to be putting down asphalt under the floor. I don’t see asphalt underlayment in your list, so just wondering what you think of it. Thank you!
Corinne Segura, Building Biologist
i don’t see how asphalt could have no off-gassing
Logan
Hi,
I have a partial inground basement (Split Level). Because we cannot install natural hardwood down there we are considering the Pergo Defense + engineered flooring. They have a recommended underlayment which contains a moisture barrier. Bases on this article it doesn’t sound like there is a great option when installing floors below grade. What underlayment would you most recommend?
Thank you!
Corinne Segura, Building Biologist
The mainstream opinion is to put down a vapor barrier and then the flooring. I would not do this. That opinion is outlined here https://corinnesegura.substack.com/p/mold-preventative-flooring
Lily
Hi Corinne.
I am looking into underlayments for Kahrs engineered floor. They have advised their Flex Silent becuse it is free of plasticizers, formaldehyde and heavy metals, solvent free and does not contain any other ozone-depleting substances. The material is PU + 90% made of raw materials (mineral filers, castor and rap seeds oil). Is PU going to off-gass and for how long? Or the floor lacquered coat would minimise this?
Would it be safe for a baby to sleep in that room a month after installation?
What is their most non-toxic underlayment in your opinion?
Thank you
Corinne Segura, Building Biologist
I can’t tell from that photo they have of it if it off-gasses.
Katharine
Hi Corinne,
I wasn’t sure where to ask this…but this post discusses vapor barriers, so I thought it might fit.
In your 15 pg checklist for before you buy/rent, you suggest we avoid improper vapor barriers.
What do you think of large areas of tile (extensive kitchen backsplash) on an exterior wall? How likely is this to cause mold?
(It’s a rental, so I can ask if the grout is breathable, but I don’t know if they’ll know the answer).
Thanks so much! 🙂
Lindsey
Hi Corrine,
Thanks so much for this. I’m considering getting your book to see what underlayment is good for under tile. Do you happen to know if those under layments can be used on a slab over 75%? That seems to be the cut off for a lot of materials.
Are they to prevent cracks then since they won’t stop vapor?
Thanks,
Lindsey
Lindsey Bottrell
75% RH
Kati
Hi Corinne,
Thank you for such a comprehensively researched article!
I was hoping to use cork underlayment under my engineered hardwood floor installation but didn’t realize there were so many things that could be hiding in most brands.
Is Thermacork the only heat pressed cork out there? I went on their website and it didn’t seem to me like it was made to be used as underlay.
Thanks in advance!
Corinne Segura, Building Biologist
yes that I know of and it’s too thick to be an underlay
DKI
Last update from Kahrs rep regarding their underlayments’ antimicrobrial properties:
“Antimicrobial properties are built-in to protect the ECO+ underlayment from mold, mildew and bacteria. Ultra-Fresh is not a sprayed-on component or treatment but is combined with the foam when it is still in a liquid state so it becomes a permanent part of the foam and will never “wear-off” or “leach out”.
COMBO consists of one layer of polystyrene beads layered between two sheets of polyethylene film only.”
Don’t know what “Ultra-Fresh” is in their Eco+ underlayment, but their Combo System doesnt have any added antimicrobrial treatments/chemicals. Hope this helps!
Corinne Segura, Building Biologist
Ultra Fresh is covered in my article about Microban’s chemicals. I’m actually in the same boat as you as im looking for a breathable underlayment for under enginnered wood flooring on an upper level apartment. There is one foam type in the carpet post that I’m not sure yet if it works under engineered, and then Im also look at basic polyethylene foam with no plastic layer and not yet found out how vapor permeable it is. Cork with a polyurethane binder I think would meet these specs but is too high offgassing even for me to use.
DKI
Thanks, I’ll check out the info on Ultra Fresh.
I am hoping that just one layer of polyethylene foam is breathable enough. I hope you find something that works!
I got another response from Karhs regarding their underlayments:
“Both underlayments [Combo and Eco+] are premium options to go underneath our wood. There could be no more than 10-12% of moisture content in the plywood subfloor.”
I will be talking to my local flooring co. that I found out supplies Kahrs as they would know all about potential moisture problems here. If they tell me anything about the best breathable underlayments for wood subfloors and engineered wood floors, will report back.
Corinne Segura, Building Biologist
Thanks yeah there are not that many that are breathable but I suspect there are more than the two I have found so far
DKI
Hi Corinne — in your experience or opinion, would QuietWalk Plus be suitable to place on a plywood subfloor as underlayment for engineered wood flooring in a relatively humid environment (55-70 depending on AC use)? I am concerned the vapor barrier will trap moisture and lead to mold. But I do like that QuietWalk Plus can help muffle sounds because installation will be on the 2nd floor.
Also, would you be concerned about the synthetic recycled fibers used in QuietWalk Plus? (“Recycled content — made from 95% post-industrial recycled fibers”)
Thanks for any insight!
Corinne Segura, Building Biologist
You’d have to ask them what the humidity range is for the underlayment. I am pretty sure that it can take that humidity but I would be worried there that if there is a spill with that humidity and being under a floor and blocked from the underside to drying by the plastic side of the underlayment that a spill would not be able to dry fast enough to not go moldy. This is not confirmed only my hunch there.
DKI
Thanks for the info on this. I talked to my contractor friend and he gave me the thumbs up on using the Roberts polyethylene foam as underlayment for Kahrs engineered wood flooring (floating) on a plywood subfloor.
I emailed Karhs about underlayments and they stated that I had to use one of theirs to meet the conditions of their warranty. I don’t like any of their underlayments they emailed to me (https://www.kahrs.com/globalassets/kahrs/consumer/documents/installation/us/kahrs_underlayment-digital-brochure-2022.pdf) — their underlayments either have antimicrobials added (Combo and Eco+) or are made of recycled rubber from tires (Quiet Stride 2.0). I also do not need a vapor barrier because it’s a 2nd story plywood subfloor situation, so I guess I’ll just void their warranty and get the less toxic, more breathable stuff for a fraction of the price at Home Depot or Amazon.
Kahrs also has this underlayment: https://www.kahrs.com/en/about-us/press-and-news/2023/kahrs-flex-silent/ but the Kahrs rep didnt mention it in her email. I havent seen it pop up for sale anywhere online when I searched.
I never knew there were so many different kinds of underlayments and options, so thanks for your article!
Corinne Segura, Building Biologist
hard no to rubber, and Im not sure what that second link is made of
DKI
Just to correct my earlier post — Kahrs’ combo underlayment does NOT contain added antimicrobial chemicals (per the Kahrs rep I emailed)
Kahrs technical support is awesome, btw!
Corinne Segura, Building Biologist
thanks!
Karin
So from your link to Roberts Serenity Foam polyethylene underlayment I have seen your opinion and from research I know it is inert, no VOC or off gassing . However when I asked company about PFAS they said it has PE’s due to being polyethylene. So does that mean it has PFAS or no and if so they don’t off gas? I know you recommend this so am just trying to understand. Hope its okay. I just need a cheap underlayment.
Corinne Segura, Building Biologist
PE means polyethylene. You may want to try asking again about PFAS.
Karin Kispert
Yes PFAS is exactly what I asked them about, and her response was “it contains PE’s because it is Polyethylene. So you use/like their product but haven’t checked into PFAS or is there not a reason to, meaning it won’t off Gass etc.
DKi
I think the Roberts rep was confused. PE is not a type of PFAS (and PFAS is not a type of PE). If PFAS where in PE, it would be a huge problem in CA where PFAS is banned from food packaging. (PE is used in a lot of food and bev packaging.) Also PE is itself water resistant so it would be weird if PFAS were intentionally added to it.
Meredith Turim
hi Corrine,
What do you recommend for sound barrier under hardwood floor to be nailed down ( plywood subfloor) I know you posted silcone paper but what if sound is needed too. thanks
Corinne Segura, Building Biologist
lots of options in this article
John
Hi
I am having UV treated hardwood put down. The store says they use a felt underpayment that helps keep down dust. I was going to ask them to go with Rosin paper due to your suggestions but what do you think about felt. Does it trap dust in or does it some how keep it out? I am super sensitive to dust so it’s important to know.
Thanks
John
I should mention the hardwood is on first floor so on top of plywood, not slab.
John
*not on concrete basement
Corinne Segura, Building Biologist
it sounds like they are trying to upsell you on the felt underlayment. though of course it’s thicker and is overall a better underlayment but I don’t see their reasoning with dust.
John
Thanks. I was going to go with rosin paper because it’s probably more natural and less chemicals right?
Corinne Segura, Building Biologist
you’d have to test it to make sure it’s ok for you (and better than felt for you)
Geri
Hi John,
Did you go with the Rosen paper? How did it do?
We are getting tongue and groove doug fir flooring, and wondering if the Rosin paper would be fine?
Thanks, G & E
Corinne Segura, Building Biologist
you have to test it out yourself, everyone’s sensitivities are different. It works for some and doesn’t work for others.
Abigail Harter
Hi Corinne,
I am having engineered wood flooring installed throughout the upper two floors of my house. The subfloor is chipboard which is standard here in the UK for new-build houses. My house was built in 2004 and that is considered a new-build. The flooring company can either glue it down or float it. The contractor said he uses a zero VOC adhesive called Zeromono by Vermeister made in Italy. It is a single-component silane terminated adhesive. This is from the company’s information: ‘Being certified EMICODE EC1PLUS, ZEROMONO may apply for the awarding of the EQ credit for Indoor
Environmental Quality – Low-Emitting Materials of the new international certification standard LEED v4.’ I am want to err on the side of caution so I have considered floating it and using Quiet Walk underlay so as to avoid adhesives altogether. The contractor is happy to float it and use Quiet Walk. Is there any drawbacks regarding floating it instead of glueing it or am I being too picky?
Corinne Segura, Building Biologist
Some of those types of glues are known to not cure and offgas within the timeframe that they should
Kate
Do you have a post for the best basement flooring you would recommend? Esp for a partially ground level basement, not too humid.
Corinne Segura, Building Biologist
I have a youtube video about it
sarah
Hi Corinne, I’m installing marmoleum in my apartment marmoleum in my apartment with cement subfloor. I am highly chemically sensitive, and more sensitive. I am unclear of what to use even after reading your article as I have a lot of brain fog from my health issues. What would you recommend for my situation for a vapor barrier.
Thank you so much!
sarah
I meant to say mold sensitive.
Corinne Segura, Building Biologist
it depends on the moisture content of your concrete, Marmoleum has a list of what you need below it depending on the moisture content
sarah
Hoe do you find out the moisture content?
Corinne Segura, Building Biologist
talk to a contractor for that they need to run a test then talk to Marmoleum
Abi Harter
Hi Corinne,
I live in the UK and my the ground floor of my townhouse and most modern houses here are concrete. I have never seen modern houses in the UK with basements. I wanted to install engineered wood flooring or marmoleum on the ground floor. My son and I are very sensitive to mould. In the British climate, I have to be very careful about mould. Do you think it would be ok to install this type of flooring on the ground floor (kitchen, front hall and dining room)? What type of underlayment would be best?
Corinne Segura, Building Biologist
personally i wouldn’t put down a vapor barrier but it is certainly the norm. you can see this article https://corinnesegura.substack.com/p/mold-preventative-flooring
sarah
So you don’t need a vapor barrier with marmolium over a cement floor? I’m confused..
Sophie
Hi Corinne,
I’m confused. Is polyurathane foam (high offgassing) the same as “urethane rebond” (Green Label Plus)? If they’re the same product, how can urethane rebond be considered eco-friendly, yet be high offgassing? Thank you.
Corinne Segura, Building Biologist
many of those cerifications don’t mean much. rebonded is polyurethane scraps glued together, it is relatively high in offgassing on the scale that I use to asses products and for people who are chemically sensitive.
Amanda
Hello Corinne
I am researching the underlayment for my radiant floor heating. Three options I have narrowed down are 1-diamond wire mesh with Ultraplan Easy, 2 – Blank Permat (fiberglass mesh, alkali resistant HDPE Mesh, polypropylene) with Mapei Granirapid and Ultra Flex2 thinnest, 3- Mapegaurd UM (polypropylene) with Mapei Granirapid and Kerabond/Keralastic System.
Any thoughts are greatly appreciated. Thank you in advance!
Corinne Segura, Building Biologist
It depends on how sensitive you are, all three underlayments – metal, fiberglass and polypropylene will be fine for most people. If you are in the most extremely sensitive group then metal is best and fiberglass is the worst. You also have to look at the VOC levels of the thinsets and grouts that go with each one and if you are sensitive also do a test but aim for 0-VOC with thinset and grout.
CJ
Hi Corinne, thank you for all your tips !
I’m a little confused .. i just purchased a 1950s house that is very well build with thick slab but we had to re-do some plumbing (old pipes got rusty) and thus jack hammer up some slab. The slab that was originally built had a thick layer of epoxy (like 1/8th of an inch) and the studs on that we removed show no signs of mold.
What should I do when we patch up the slab ? Leave it ‘raw’ ‘unsealed’? or paint it with something like drylock ? We will be placing back the stud frame on top of this slab. And then the rest of the floor will be tiled with porcelain tile.
Since this house has a big fat foundation and a thick slab and cinderblock walls is the slab not able to dry from the outside ? Leaving me able to seal up the slab with a layer ?
Is there an in-between product ? like a breathable system ?
What about buying a large hunk of beeswax to seal the slab . would that breathe ?
I’m asking because I’ve been sick from mold for 3 years from rentals prior to buying this house … and I am trying to get this done right.
Cheers
Corinne Segura, Building Biologist
you will need some building science advice there. its unusal for a thick slab to have an epoxy coating and if that was put down becase lots of moisture was drying up then you will need to keep that in mind. the slab can only dry inwards, it cannot dry down or to the sides. its best to keep it breathable, see https://corinnesegura.substack.com/p/mold-preventative-flooring
craig
I was wondering about the Eco Cork Foam underlayment, I was about to purchase it when I saw a comment about the Microban in the cork. In the product description i see “Ultra-Fresh® antimicrobial technology is infused into Eco Cork Foam for an added level of product protection against stain and odor causing mold and mildew.” Ultra-fresh is Microban, which has EDCs. Whats the deal with that, is it gonna effect me underneath my floor? And why is it on My Chemical-Free House site
Corinne Segura, Building Biologist
We don’t know what chemical/chemicals UltraFresh is. It’s not disclosed at all. Some of Microban’s antimicrobials are disclosed and their most popular one silver is not usually a concern for chemically sensitive folks. Others could be a concern even though they are blocked by the floor because they could offgas, depending on the chemical. but I have updated the article as that either wasn’t listed in 2020 or I missed it.
Patricia G
Hello,
I bought a condo and want to replace the 90’s dusty carpet with engineered hardwood. This is a concrete condo on the 8th floor, with electric baseboard heat. The contractor recommended Mirage flooring and I have some samples on order (maple and oak to try, with plywood core). For underpad, he recommended Good Neighbour Silencer XP 3.0. Becasue it is a condo, I can only replace carpet with hardwood if I use sound dampening underpad. This product is made of High-density IXPE foam and has vapour barrier and is antimicrobial. I am in the process of trying to find out what the antimicrobial substance is and obtaining a sample, but does this product seem like a good idea? I am extremely mould sensitive and live in the Pacific Northwest (Vancouver, Canada). I am also quite chemically sensitive due to a viral infection from 2020 which gave me emphysema, MCAS plus several new IgE allergies (dust mite, cladosporium, lanolin, limonene, linalool, etc). I am wary of generic “antimicrobial” due to horrible experiences with a product called Benefact.
https://goodneighbourunderlayment.com/product-details/silencer-xp-3-0/
Corinne Segura
IXPE should be fine, not likely any offgassing there. As for the antimicrobial, I don’t know what they are using. You will have to go by your own assessment, it won’t be like benefect but I don’t know what they would be using.
Dee
I am also looking to install floor in an upper level condo on concrete. Are the concerns about mold for slab and basement the same for a concrete building with multiple units?
Corinne Segura, Building Biologist
no, there is no moisture coming up in an upper level concrete floor. you can use flooring types like LVP that block moisture. i would still prefer not to have two layers that block moisure so that if water spills it doesnt get stuck between two layers
Dee
Thanks Corinne! So your preference is still for something vapor permeable, meaning no engineered wood, laminate or vinyl flooring? What about microcement instead of the insane expense of tiling or concrete polishing?
Corinne Segura, Building Biologist
you can use any flooring type, but i would prefer not to have both the floor and the underlayment and moisture blocking layer
Kat
I have mast cell activation syndrome and multiple chemical sensitivity . I am purchasing an older manufactured home (particle board subfloor) and we will be replacing all the floors. The crawl space has a vapor barrier over the dirt and a “belly wrap” above that. On the floor side of the belly wrap are the joists, insulation, and subfloor. Any idea if I need a vapor barrier as part of my underlayment? We are hoping to do a plywood floor sealed with Vermont naturals floor sealant. We will be putting this throughout the whole house , including bathrooms and kitchen. I keep reading conflicting info online about if a vapor barrier would be beneficial between the subfloor and plywood (finish floor) or not. My husband thinks we should use roofing paper but I am worried I’ll react to that. We have kids and pets if that makes a difference. Thank you, your website has been so helpful to me.
Corinne Segura
both a plastic barrier and a breathable underlayment like the ones in this post have the potential to cause moisture and mold problems so be sure to consult with Cheryl Ciekco or another building science expert.
pmfb
hi!!
we are nailing down pine boards for our bedroom flooring. the underlayment suggested was tar paper, and the flooring is already halfway down.
i did not see this option in your blog post; thoughts?
Corinne
I wouldn’t use that but I have two alternatives in the post
George C
Corrine – I am sending this link out to a bunch of people in my industry – wood flooring.
Corrine, really well done. You answer a problem three years ago that is only started in this trade article; https://hardwoodfloorsmag.com/2023/08/01/plastic-flooring-installed-on-top-of-wood/
pmfb – you are talking about 15lb asphalt-saturated felt paper. It works best BUT does have VOCs that show up in smaller areas; https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7435637/table/sensors-20-04099-t003/?report=objectonly (part of this study; https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7435637/#sec2dot3-sensors-20-04099)
Leah
We are in the same boat. Our contractor used „HWD-15“ underlays, which does seem to be certified as low emissions under California standards. I don’t see this mentioned in the post at all— have you heard of it? I really wish they had spoken to us first.
Corinne
this is the typical asphalt paper, the silicone paper and rosin paper are the better alternatives, especially for the chemically sensitive.
Jay
Hi! I came across this “Natural LVT SG” underlayment. This stuff makes some bold claims. It’s quite nice-feeling too. I got a small roll to check it out. It adds a degree of warmth, is relatively thick, and does not appear to give off any odor. What category do you think this falls under?
https:// naturalunderlayment.com/underlayments/natural-lvt-sg/
Eliza
Corinne, I’m desperate for help! We put an engineered hardwood on top of a cement subfloor with a QuietWalk barrier. I’m clearly very mold sensitive because the smell is oppressive and my allergies are on fire. I live in a pretty humid climate. What do we do? What floor can I put on cement subfloor that doesn’t require a vapor barrier? Thanks so much!
Jose Poloramos
A question regarding the sleeper system on a concrete slab. Would Rosin paper be placed over the slab, then the sleeper floor or would some other solution be better?
Corinne
you’d have to consult with a building science expert
Heather
What are your thoughts on the air gap underlayments? I’d like to put hardwood over an at/below grade concrete slab. Tile is way too cold for my climate and this is a cold room (and heated tile way too expensive), and carpet is a non-starter with my allergies (I just ripped out the carpet that was down there). I don’t do well with linoleums, laminates or LVP. I’ve seen contractors recommend some of the dimpled underlayments like Dampro or Dricore for preventing mold. Do you have any experience with them and the mold issue?
Corinne
not enough air movement under those for moisture to dry out says Cheryl ciecko.
Violetta Sur
My contractor purchased a waxed paper underlay. It doesn’t seem to smell at all but I wonder if it could possibly contain any PFAS or other chemicals, and if so would this even be a problem in a waxed underlay? It is similar to this: https://www.homedepot.ca/product/roberts-750-sq-ft-3-ft-x-250-ft-x-009-inch-waxed-paper-underlayment-for-wood-flooring/1000496301?eid=PS_GOOGLE_D23%20-%20E-Comm_GGL_Shopping_PLA_EN_Flooring_Flooring__PRODUCT_GROUP_pla-341957376360&gclid=CjwKCAjwvJyjBhApEiwAWz2nLYSgrjmjgjM39Vem9mv_QzNIXZ8m65tf2zGgd8HG0c4iLDI7UC8SvRoCUh4QAvD_BwE&gclsrc=aw.ds
What are your thoughts?
Violetta Sur
Is it generally considered a less “toxic” option for sensitive folks?
Corinne
yes
Kelley
Hi! Hemp Underlayment is challenging to get.
But i was wondering if this could work: hemp and jute canvas.
It would be going over wood, and under engineered wood (not glue down).
https://www.jerrysartarama.com/soho-urban-blanket-unprimed-no25-hemp-25oz-6yd-x-86in-86324a?gclid=CjwKCAiA-dCcBhBQEiwAeWidtQCvdE28oQ8ZbxwVGbYHwbU6xRz-mNEEggsg89o4PJwSNpAfIsF1jRoCo8QQAvD_BwE
Rene
Hi Corrine, I have a treated timber subfloor and I am trying to prevent any fumes from the subfloor entering inside the home. We are having engineered timber flooring laid over the subfloor. The glue we are using to secure the engineered timber is very good (A+ French interior air certified) European glue. This glue can also achieve a vapour barrier. If I apply it over my treated subfloor as a vapour barrier do you think this would be a good solution to prevent the subfloor offgasing inside the home? or will this cause mold issues if it is not a breathable layer between the subfloor and engineered timber? If so, is there another solution you could suggest? vapour barriers and mold is all new to me. Many thanks
Kavitha
Dear Corrine,
First of all, thank you so much for your thorough posts!! It is extremely helpful!! We have one question for you – is Aquabar safe as an underlayment? Thank you so much for sharing your advice and wisdom!
Thank you again,
Kavitha and Nicolas
Corinne
I wouldn’t use that over the options in this post
Emily
Hi! Any thoughts on COREtec’s new Soft Step underlayment, touted as being made from 100% recycled plastic bottles? I chatted with a rep on the website who said it is free of phtalates ad parabens, and the greenguard gold certification includes the underlayment. I just worry about adding more plastics.
Britney
Hi there! Do you have experience with Quietwalk Plus being used with nailed down engineered hardwood on a wood subfloor? We purchased it already to use under floating floors and have now decided to nail them down. Green Building Supply said that nail down is fine and so does the product. Just wondering why you mentioned it is best with floating floors. Thank you!
JY
Same question – Britney, what did you end up putting under the nail down floor? What floor did you pick out?
Michael
Hello there. There is so much information here. Thank you. I am wondering if you have anything to say about Absorba sound underlayment. It’s recycled rubber and I am a little wary about offgassing but flooring guy said don’t get foam because it compresses so much. Thank you for any thoughts. We are nailing the hardwood down on second floor over plywood.
Corinne
I would never use recycled rubber. See the post on Gym Flooring for details on rubber flooring.
Michael
Thanks so much Corrine. That’s awesome. We’ll shift to polypropylene.
Bri
For underlayment under a click and lock waterproof system, how much direct exposure would you really have to the antimicrobials in the underlayment? Does it leach through into the air? If you don’t have any known sensitivities to antimicrobials, how big a deal do you think they are? I’m trying to decide if the QuietWalk without the antimicrobials us worth the extra cost. (It would cost almost twice as much for the amount we need!) The regular kind It is still Green Guard Gold. Their blog lists their antimicrobial ingredient.as Polyphase 678 https://www.mpglobalproducts.com/blog/quietwalk-underlayment-includes-antimicrobial-pesticide-to-eliminate-mold-related-worries/
Corinne
Under a luxury vinyl plank floor I would say the risk is none.
Bri
Thanks for putting my mind at ease and helping me prioritize in my budget!
Julie Wilde
I am buying a 2750 s.f. concrete slab 1970s house on the east coast marsh. I am tearing out the original carpet that covers the entire interior and Ideally would like to replace it with wood flooring (or click lock engineered) for aesthetic purposes and comfort on joints as I have hip issues. I have always lived in older homes with gorgeous wood floors and can not stand comfortably on tile or carpet. I also have extreme sensitivities to chemicals and mildew. I believe that you said not to use a flooring that would require a moisture barrier on slab due to potential mold issues? If I insist on a wood (no vinyl) flooring for reasons stated above, could there be a solution for me?
Corinne
Talk to Cheryl Ciecko about building a sleeper system (which is not the common one you will see if you google it).
Julie Wilde
Thank you, Corinne. i appreciate your quick reply. I will try to contact Cheryl right away. If I can’t figure out a way to safely install wood over the concrete flooring, I may need to get out of my contract on the house a.s.a.p.! So glad I came across your article regarding moisture/mold problems in concrete flooring before it was too late!
Dianne Fradkin
Corrine,
I am desperate to find new flooring in my rental unit to replace carpeting that’s probably 20 years old.
I am very chemically sensitive and have tried bamboo and prestained hardwood, a box of each as a test, both of which I have been unable to tolerate.
After reading your article it seems tile would be best.
Which do you think would be least toxic and what underlayer would I use?
I would gladly schedule a 30 minute phone appointment but it seems that none are available for several months so I am asking for your help in this rather long email.
Thank you so much,
Dianne
Corinne
Hi Diane, I am doing email consultations if you would like to go through the options. I would also need to know what your subfloor is. https://app.acuityscheduling.com/schedule.php?owner=19257501&appointmentType=16364655
Gaye
When reading your info you recommend using a product that breathes for an underlayment on 2nd floor over wood. We are floating Engineered Hardwood over old vinyl tiles so should it still be a product that breathes? I am not wanting to trap in moisture! So I am wondering if the Robert’s Serenity polyethylene foam would be our best choice as it would provide some cushioning to dampen the clicking from a floating floor and you say it is also breathable.? Open to other suggestions that would also be good to use . Thanks. (I am not wanting anything with antimicrobials as I don’t want to be exposed to those chemicals.) ( Quietwalk from Green Building is not available in Canada right now.)
Thanks.
Corinne
Vinyl tiles are a complete vapour barrier so it doesn’t matter if your underlayment is breathable or not.
Tamilyn
I would be so grateful for any help. Im beside myself reading over and over again all of these floorings and your article. I just bought a mobile home w/crawl space lots of humidity at times. Current flooring vinyl top peeled off prob because of humidity. Which is the safer flooring for a lung condition and some water barrier protection LifeCore waterproof is only Floorscore certified best at blocking water, AquaGuard limestone engineered wood is greenguard gold, HydroShield HDW base core a Laminate is Greenguard Gold or Shaw Laminate OptiCore Board GreenGuard Gold buts also a Laminate. My only other options would be Cali Bamboo Geowood again limestone or Anorim Wise Wood. What out of all of these would be the best for lungs and health? Solid wood in humid mobile home I was told not the best, tile living off a train track also not good and I react to linoleum vinyl super bad. Can you please give me your thoughts begging please.
Akua
Hello Corrine, this post has been so interesting. I want to put LVP down on a tiled floor. No glue! I am in the UK. I want to know what the best thing to put down underneath is. Least off gassing and most resistant to mold. I live on the 8th floor of a high rise apartment block.. Thanks
Corinne
Hi Akua, I am also born on a wednesday. This post goes over the main options but also check the warranty as many have a preattached underlayment and the warranty can be voided by adding another underlayment.
Rachael Bonsignore
Hi Corrine. Have you found out anything about the possible toxicity of Iron Ply that is used under linoleum in the bathroom? It looks like a kind of thin plywood. It looks benign, but I started getting symptoms after it was installed- very loud ear ringing, chest or lung pain…Could be the wood itself I am reacting to, or something else in the house (a little bit of spray foam used recently or vinyl siding stored in house). I didn’t smell anything when I put a piece of it up to my nose, but I did smell a strong chemical smell on it after I soaked it in water for an hour or so.
Corinne
I haven’t seen that before, could you ask them what is in it?
Anne Robinson
Hi there-
Thanks so much for all this information.
We are using self-leveling concrete on our basement floor and then buying wool carpet with wool padding. Are there any concerns with self-leveling concrete?
I have looked all over the internet but have not found definitive information. The self leveling was our only option as redoing the floors entirely was beyond our budget and would have lowered the wall height. Should we air out for a long time after using the self-leveling concrete?
Corinne
Most of them are 0 VOC.
zuzana
Hi,
I bought recycled hardwood floor which I would like to lay in my basement apartment. What underlay would you recommend for the basement flat? I am confused about the vapour barier! The floor is concrete.
Many thanks,
Zuzana
Corinne
I personally would not put any type of wood over a concrete basement floor or slab on grade due to moisture. People do this, it’s the norm but mold is also the norm in buildings.
Candice
So you’re recommendation is to remove any existing plywood and use foam only underlayment, is that what I’m reading? I feel like this was vague in the blog but clarified more in comments. Thanks for the info
Corinne
You don’t usually put plywood down over concrete before installing your floor. It is done sometimes like if you want to put solid wood down but that other than that is not the norm.
Poon
Thank you so much Corrine for all the information. Would you suggest using Quietwalk plus under solid unfinished hardwood floors? Thanks.
Corinne
I would talk to your installer about that, since it’s mainly specified for floating floors.
Hawnes
Hi Corinne, thanks for the informative post.
I want to install linoleum upstairs. What would you recommend for either linoleum sheet vs. click as an underlayment?
Thanks.
Linda
Corinne,
Thank you for sharing this valuable healthy living information. You mentioned not to install flooring that requires a vapor barrier over a slab. I am having a concrete slab house built and am trying to be as green and non-toxic as possible. Mold terrifies me.
What type of floor that does not require a vapor barrier can be installed over a concrete slab? Also, is it possible to put a raised sub-floor to eliminate the need for a vapor barrier, if I can get the builder to do it?
Thank you,
Linda
Charlotte, NC
Corinne
Hi, polished concrete or tile or yes like you mention a “sleeper system” which is raised up. I would have Cheryl Ciecko detail that.
Linda
Thanks.
Tatum
Corinne,
Can you clarify doing polished concrete if you are under grade as I thought I read you recommend against sealing the slab (epoxy or other) due to ensuring it dried to the inside?
Wouldn’t polishing it prevent it from drying to the inside?
I appreciate the clarification as I’m trying to figure out our best flooring route for our finished walk-out basement. The north wall is completely under grade, while the west and east are partially under grade and the south wall is fully walk-out.
Blessings,
Tatum
Corinne
Polishing with (sodium/potassium/lithium) silicates is breathable according to the building science experts I work with.
Jonathan
Thank you so much Corinne, this is very helpful!
I called MP Global regarding Quietwalk and they said the use Polyphase 678 antimicrobial made by Troy (http://www.troycorp.com/product_view_Preservatives.asp?unitName=Preservatives&cat=products&sub=functions&ID=483) in their Quietwalk underlayment. The product info sheet (which I found doing a search since Troy requires an account) seems concerning. What are your thoughts?
Would something like FloorMuffler be a safer choice? https://www.floormuffler.com/products/floormuffler/
Thanks so much!
Corinne
Green Building Supply sells quietwalk without the antimicrobial.
Jonathan
Ahh yes, I forgot you mentioned that! Thanks!
Mariane Konstantaras
Corrine,
Is there any low tox or low voc liquid crack isolation or tape? We need to tile and was recommended by Andy pace as best to put ditra; but our home is 20 plus years and all contractors claim it is mostly cracked already and we should only put a liquid where needed. I can’t find anything that is asphalt free or low tox. Any suggestions?
Corinne Segura, Building Biologist
It’s not something I have published yet
Mariane K
Thank you! Looking forward to see. Andy Pace said from a human health perspective mapei mapelastic cI is fine. It’s quartz with rubber. That’s the better one I could find. If that’s going under the tile just on active cracks do you expect to have tons of Vocs? Or even any odor?