ICF home with elevated radon
Folks,
Here’s my situation:
– 2150 SFT ICF ranch with full basement (partial walkout) in East-central Illinois with EIFS siding.
– Exhaust-only ventilation thru 3 bath fans (2 on the main floor plus one in the basement that we rarely use) and we can feel the fans struggling to get the air out due to tight ICF.
– Large windows on the pond-side that are double-paned but we can feel cold air drafts on the insides of the window sill sides. When I complained about this, the builder sent me some foam stoppers to install for the winter time which seems to help some.
– 2 adults and 3 children mostly using the main level, the basement just for recreation.
– Humidity issues in the basement during summer so I blocked-off some of the return registers on the main floor to force the HVAC to draw almost all of the return air from the basement so it gets dehumidified by the AC coils. This seems to work and so I left the blocks in place for the winter as well.
The issues:
– Misture condensation on the windows during winter.
– 3-day Radon test by a Radalink tester shows 6.3 pCI/l in the basement.
Questions:
1. Is negative pressure created by exhaust-only ventilation to blame for both of the issues? I am thinking if somehow positive pressure is introduced, there won’t be much infiltration from the outside at the window sills and it will also help keep radon not seep in in the first place.
2. Or does an HVAC in an exhaust-only ventilation setup somehow generated positive pressure by forcing air in thru leaks, cracks and such, and so that’s what’s causing the infiltration at the windows and radon thru the basement floor?
3. Any inexpensive way to measure the delta P?
4. Would adding a passive air inlet (say in the dryer closet) help with undesirable infiltration at the windows and radon/basement floor? Are these inlets really only one-way as the name suggests or do they let air to the outside as well? Don’t they have some minute dampers on them prevent the reverse flow?
5. Is an HVAC capable of sensing that the positive pressure has dropped and can it then automatically start off by bringing outside air in via an automatic damper controlled duct connected to the return duct?
6. I have also heard about HRVs. Are they capable of generating the desired slight positive pressure? IOW, can they be adjusted to bring in more air than what they let out? In the extreme case can I simply shutoff the exhaust side of the HRV? I realize they can’t keep up with the dryer and the central vac. We don’t have a kitchen exhaust.
TIA.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Venkat,
You need to deal with your high indoor humidity levels and your elevated radon levels.
Your next step on the radon issue is to perform a long-term test to confirm the results of your short-term test. For information on radon, I recommend this article: All About Radon.
The usual method of reducing indoor humidity levels in the winter is by operating a ventilation system. For more information on this issue, see Designing a Good Ventilation System.
Q. "Is negative pressure created by exhaust-only ventilation to blame for both of the issues?"
A. Probably not. First, you can verify the airflow through the exhaust fans using the credit card method described at the end of my article on ventilation systems. It's possible that the fans have convoluted ducts or undersized ducts. It's unlikely that your house is so tight that the fans can't find enough makeup air.
Q. "Does an HVAC in an exhaust-only ventilation setup somehow generated positive pressure by forcing air in thru leaks, cracks and such, and so that's what's causing the infiltration at the windows and radon thru the basement floor?"
A. Exhaust-only ventilation systems slightly depressurize a house, and pull in outdoor air through random cracks. The airflow through an exhaust-only ventilation system shouldn't be enough to affect your indoor radon levels.
Q. "Any inexpensive way to measure the delta P?"
A. No. You need a manometer. But you can inexpensively measure airflow with the tricks described in my article on ventilation.
Q. "Would adding a passive air inlet (say in the dryer closet) help with undesirable infiltration at the windows and radon/basement floor?"
A. No.
Q. "Are these inlets really only one-way as the name suggests or do they let air to the outside as well?"
A. They are not one-way. Air flows through them in both directions. Read my article.
Q. "Don't they have some minute dampers on them prevent the reverse flow?"
A. Some do, but the dampers are ineffective.
Q. "Is an HVAC capable of sensing that the positive pressure has dropped and can it then automatically start off by bringing outside air in via an automatic damper controlled duct connected to the return duct?"
A. No. But if you want to install a central-fan-integrated supply ventilation system, you can. Details are in my article.
Q. "I have also heard about HRVs. Are they capable of generating the desired slight positive pressure?"
A. If an HRV is properly installed, it will be a balanced system that neither pressurizes nor depressurizes the house.
Q. "Can HRVs be adjusted to bring in more air than what they let out?"
A. That is not recommended.
Martin,
Thanks so much for taking the time to answer my newbie questions.
I have read in some places that at least in winter/heating climates, a slight positive pressure is desired. I heard commercial buildings are usually setup for a slight positive pressure. So, I am curious as to why this isn't a recommended approach to take with HRVs for homes in winter climates. IOW, skewing an HRV to bring more air in than is let out. Just trying to understand the cons.
Thanks again,
venkat
Venkat,
You can choose whatever type of ventilation system you want. If you want a ventilation system that slightly pressurizes your house, install a central-fan-integrated supply ventilation system. They work just fine.
In general, it makes sense to try to avoid pressurizing or depressurizing your house (with respect to the outdoors) to any significant degree, which is why balanced ventilation systems are seen as the best approach.
However, ventilation air flow rates tend to be low (usually 50 cfm to 80 cfm), so the subject is often overblown. Considering the low air flow rates, it hardly matters whether you install an exhaust-only system, a supply-only system, or a balanced system. The choice is yours.
Martin,
Thanks for the advice. I think I am leaning towards getting an HRV that will draw from the 3 bathrooms (2 on the main level and 1 in the basement) and also one return from the basement area. The reason for the single return duct intake is to try and dilute any radon in the basement. I am planning to have the supply from the HRV released into the basement. Given that I have 2150 sq.ft. each floor, do you think I can get away with one HRV as opposed to one dedicated to each floor? I would appreciate any specific product recommendations. One feature I am looking for is the ability to trigger a boost of the HRV fans from any of the bathrooms so it can be triggered when any of those is in use. Once I have the HRV installed, we would cease to use the exhaust-only fans in the bathrooms, instead relying on the boosted HRV to ventilate while the bathrooms are in use.
Thanks,
venkat
Just to provide an update on where we are at and some questions as well.
1. Had a blower door test done and the number was 1.2 (forgot he units) but the Energy Auditor that did the test said the building is tight relative to non-ICF homes that he had seen.
2. Main label bath exhaust fans are doing about 41 to 56 CFM based on whether both are turned on at the same time or not. They connect to the same exhaust cap on the roof via insulated ducts in the attic.
3. A large section of the main level has 14-ft ceiling and there is moisture condensation on the inside edges of the ceiling where it meets the wall. A local insulation contractor sees issues with the insulation in the attic: knee-wall in the attic for the elevated ceiling is only insulated with fiberglass batts and the woods are exposed. Rest of the attic floor has about 14 inches of fiberglass blow-in insulation. He wanted to take out the knee-wall batts and spray 4 inches of Icynene Open Cell foam covering the woods and rest of the knee-wall. He is also proposing to add about 7 inches of cellulose to the fiberglass on the flat floors of the attic. A couple of questions:
a. Would adding cellulose on top on fiberglass cause any long term issues? Or should I have some truck come in and vacuum the whole thing of the fiberglass, add cellulose and then blow the fiberglass back on?
b. Best way to work with an Insulation contractor: Should I have a me trials and time contract or a turn-key contract, but I am afraid in the latter case, he will simply come down once he is out of the material he put in the bid, even when there's more work to be done?
4. Regarding Radon seepage into the basement: While a long-term test is the way to go, Wife is too concerned currently to wait and wants everything done to lower the short-term results we got. So I called a staff member of the team that originally built the house and he feels there's very likely a 12" x 12" pit where the trap for the bathtub goes into the ground, that's exposed to the pea gravel underneath the slab and further to the solid underneath the pea gravel (no vapor barrier between the soils and pea gravel apparently). I have bought a Safety Siren Radon detector and it's showing the highest reading at the wall adjacent to the bath tub head. A local company is sending a person to drill a hole thru a wall adjacent to the bathtub head and check out the area with a a snake Camera this Wednesday. Now if a pit is found which is highly likely, I am wondering what would be an appropriate material (currently thinking about concrete) to seal the pit with so that:
a. soil gases and moisture are at least mitigated to the same level as the rest of the basement slab and
b. the material won't damage the PVC pipes for the trap, drain, etc. and
c. not extremely difficult to break if the tub needs to be replaced in say 10 or 20 years and a new trap needs to be installed and connected to the drain now immersed in concrete or whatever material is used.
Once the pit is sealed, I will monitor the Radon levels and based on where they stand, I am thinking of having Radon Seal sealant applied to the entire basement floor (except wall areas of course).
I am also simultaneously investigating an appropriate HRV/ERV to ventilate the basement.
Many thanks in advance for any advice anyone can offer.
One other update I forgot to add: regarding the moisture level in the home, we see about 41% RH on the Hygrometer on the Refrigerator door in the kitchen. Given that the bath exhausts seem to be operating at 41-56 CFM, I am thinking applying sealant to the basement floor and addition of an HRV will result in controlling the humidity as well.
As mentioned in the previous post, we are planning to get the bathtub pit sealed to try to mitigate soil gases and moisture from coming in. Any tips on protecting the PVC pipes that constitute the trap and drain, I would be very grateful for...
Regarding the PVC pipes, would applying a can of closed-cell spray foam on the pipes about an inch thick before sealing the rest of the space with concrete be a prudent thing to do. TIA.
Venkat,
In your last three comments, you have asked a lot of questions -- more than I can easily answer.
If there is an open pit in your basement slab under your bathtub, the opening should be sealed to prevent soil gases from entering your basement.
Q. "Would adding cellulose on top on fiberglass cause any long term issues?"
A. No. It is a recommended method of improving the performance of fiberglass insulation installed on an attic floor.
Q. "Should I have some truck come in and vacuum the whole thing of the fiberglass, add cellulose and then blow the fiberglass back on?"
A. No. You want the cellulose to be on top of the fiberglass, not the other way around.
Never heard of building a home with a cut out in a slab for a tub trap.
You might have moisture coming up from the slab, who knows... best IMO is to get local help to check out your home, print out this thread and see what they say after looking over all the conditions you are describing.
Seal up your slab and add a radon system there are many companies that do so.. have the moisture mitigated by a pro which may not be a problem if the slab is pouring it in instead of occupants... Only you and someone local can really get this done... Use what you learn here and get calling locals.
Thanks so much for the replies/advice. The local company said if they find a pit, they are going to cover it with plexiglass that is silicone sealed down and around the drain pipe. According to them this is the preferred method because it seals just as well as concrete yet is removable if there should ever be a need in the future.
Thanks again for the replies earlier. Much appreciated.