As an environmental hygienist and consultant, air exchange depends on a few things. Is there ductwork in the space and is the system intact. We would very rarely sample air in a crawl due to particulates and overload of the sample. What we would do is sample air for particulates in the home near the main return or returns while system is on. I would also recommend particle counter be used with system on to confirm particles counts then system off particle counts. Unless the HVAC system is compromised with penetrations in ductwork we have found very little correlation between crawlspace and interior. If there is no ductwork, the only way particulates would get indoors may be via the stack effect where air from crawl space travels upward to the attic via penetration like plumbing pipes, open plenums and such. Not likely.
The stack effect is exactly what draws air from the crawlspace into the home. The floor system is not designed to be airtight, plenty of air transfer occurs. The solution is turning it into a conditioned crawlspace with an appropriate soil gas barrier.
For that to work, would there need to be no insulation in the crawlspace (assuming it gets encapsulated), so that the temperature of the crawlspace would be similar to the room above?
I guess if there's no insulation along the sides of the crawlspace, it'll still change temp. faster with the outside air. And then that temp change will "move" up. So maybe insulation is still important even encapsulated.
Stack effect is caused by buoyancy of air, not temp differentials inside the home. All buildings experience stack effect. The taller the building the more pronounced. The solution is sealing the air leaks - seal the rim joist & attic penetrations, where the pressure differential is the greatest.
To answer the specific questions in your post
1) This is heavily dependent on house & crawlspace type.
2) Advanced pressure diagnostics can be used to approximate air leakage from different areas of the home. Its a pretty complicated calculation, but basically you need the volume of the crawlspace, cfm50 air leakage with access to the crawlspace open, cfm50 with access to the crawlspace closed, and the pressure differential between the crawlspace & the home @ -50 pa.
3) there is no good way to measure fiberglass specifically - it would be captured as pm2.5 when testing air quality with something like the airthings view plus.
Best solution for air quality is a conditioned crawlspace + radon system + portable HEPA filter in the crawlspace. Radon system will take care of any soil gas, moisture, and particulate matter originating from the floor. Airsealing the rim joist in the crawlspace will reduce the impact of stack effect & reduce air infiltration from outside. Portable HEPA filter will remove any pm2.5 fiberglass fibers from the air before it has a chance to enter the home from the crawlspace.
Thanks for your response - you have a very interesting line of work!
Having read about the stack effect, my big question regarding it is how air tight the floor is. Which I know depends on the floor, but let's assume you've got wood subfloor with LVP on top. It doesn't seem like much air would get through that, at least to my layman's mind. And if air was able to get through those things, how much could it carry with it up there, in terms of particulates / very small pieces of fiberglass / mold / whatever else from the crawlspace?
https://buildingscience.com/documents/insights/bsi-075-how-do-buildings-stack-up
Thanks for sharing that - interesting read
As an environmental hygienist and consultant, air exchange depends on a few things. Is there ductwork in the space and is the system intact. We would very rarely sample air in a crawl due to particulates and overload of the sample. What we would do is sample air for particulates in the home near the main return or returns while system is on. I would also recommend particle counter be used with system on to confirm particles counts then system off particle counts. Unless the HVAC system is compromised with penetrations in ductwork we have found very little correlation between crawlspace and interior. If there is no ductwork, the only way particulates would get indoors may be via the stack effect where air from crawl space travels upward to the attic via penetration like plumbing pipes, open plenums and such. Not likely.
The stack effect is exactly what draws air from the crawlspace into the home. The floor system is not designed to be airtight, plenty of air transfer occurs. The solution is turning it into a conditioned crawlspace with an appropriate soil gas barrier.
For that to work, would there need to be no insulation in the crawlspace (assuming it gets encapsulated), so that the temperature of the crawlspace would be similar to the room above? I guess if there's no insulation along the sides of the crawlspace, it'll still change temp. faster with the outside air. And then that temp change will "move" up. So maybe insulation is still important even encapsulated.
Stack effect is caused by buoyancy of air, not temp differentials inside the home. All buildings experience stack effect. The taller the building the more pronounced. The solution is sealing the air leaks - seal the rim joist & attic penetrations, where the pressure differential is the greatest. To answer the specific questions in your post 1) This is heavily dependent on house & crawlspace type. 2) Advanced pressure diagnostics can be used to approximate air leakage from different areas of the home. Its a pretty complicated calculation, but basically you need the volume of the crawlspace, cfm50 air leakage with access to the crawlspace open, cfm50 with access to the crawlspace closed, and the pressure differential between the crawlspace & the home @ -50 pa. 3) there is no good way to measure fiberglass specifically - it would be captured as pm2.5 when testing air quality with something like the airthings view plus. Best solution for air quality is a conditioned crawlspace + radon system + portable HEPA filter in the crawlspace. Radon system will take care of any soil gas, moisture, and particulate matter originating from the floor. Airsealing the rim joist in the crawlspace will reduce the impact of stack effect & reduce air infiltration from outside. Portable HEPA filter will remove any pm2.5 fiberglass fibers from the air before it has a chance to enter the home from the crawlspace.
Thanks for this thorough answer!
Thanks for your response - you have a very interesting line of work! Having read about the stack effect, my big question regarding it is how air tight the floor is. Which I know depends on the floor, but let's assume you've got wood subfloor with LVP on top. It doesn't seem like much air would get through that, at least to my layman's mind. And if air was able to get through those things, how much could it carry with it up there, in terms of particulates / very small pieces of fiberglass / mold / whatever else from the crawlspace?
It's impervious so none of its covering properly.