Insulation under floorboards/in crawlspace

[SarahFair]

Let me start out by stating I am in Georgia, hot and humid in the summer and sometimes cold and wet in the winter..

The insulation under one of the bedrooms is falling out and missing in most places.
It's gotten to the point the bedroom temperature is not consistent with the rest of the house.

Our house is around 120 years old, so while one of the former homeowners skirted the crawlspace with brick, it is not encapsulated, which will not be a top contender for the budget for a foreseeable future. (Should you encapsulate a historic home's crawlspace??)

What we currently have is some sort of batting, majority is yellow in color.
The dropping insulation is not exclusive to just this area, so we're going to replace as needed.

I'm guessing the insulation support rods are not long enough because the joists aren't exactly 24" apart in all areas, and with natural expansion and contraction
...not to leave out my youngest son's heavy walking (stomping :rolleyes:)...


What is going to be the best insulation to go back with?

[Gothichome]

Hello Sara, good to see your name up on the board. We had a rather long discussion on just this subject many years ago, can’t seem to find it. I also checked the building science site but could not find a direct answer to your question. Found this though.
https://www.buildingscience.com/documen ... insulation
How does the failing current bat insulation looking, wet and soggy or dry? If dry and there is no degradation to the floor or the joists I might be tempted to replace with the same.
As you may recall from previous posts confined damp is some thing to be vigorously avoided, the wood needs to be kept dry and able to expel any damp.

[SarahFair]

We went through last year and threw out all the wet or damaged insulation that had fallen out, but new pieces keep falling, which if in good condition we will reinstall.

We keep getting mixed answers on faced vs unfaced installation though.

One guy told us it will be termite bait, everywhere else says use faced as a moisture barrier.
The stuff under there currently is unfaced, so

[Gothichome]

Sara, wet batt insulation is a problem, did it get wet for condensation staying in the batt? I would lean to the unbacked insulation unless you can really get a good seal with means over lapping the backing and taping the edges, this only allows for moisture to evaporate up through the floor boards. Unbacked will allow moisture to escape both into the crawl space and via the floor boards. This brings up another question, is the crawl space vented in any way? If it’s a foundation wall then maybe the answer may be to insulate the the foundation walls instead of the floor. This would turn every thing into conditioned space. If on piers then I think your only option is the floors. But the question is raised, why is there moisture building up in the batt? It should absorb and expel moisture as the humidity changes.
Ron

[GibsonGM]

Is it a dirt or concrete floor in the crawl?

If dirt, you'll want to lay down at least 6mil poly as a 'floor', taping any seams with 3M Flashing tape. You can 'weigh down' the edges with 2x4s or bricks, if there is no way to seal them with the tape. You Don't want to VENT the crawl to the outside...this lets 80 degree, high humidity air enter a cooler space, where it will chill down and give off the moisture it's carrying to be absorbed up above the insulation!

If possible, you want the walls to be plastic lined, or better - foamboard insulated with taped seams. I did my last (modern) home in Maine that way, it is great - NO moisture down there, and the crawl stays WARM thus no moisture leaving the air ("conditioned space" tho not 70 in winter - more like 45-50F). "Encapsulation" doesn't have to be 100%, but it SHOULD be 'a reasonably tight job'. You may not be able to do this if you are somewhat open to the outside air.

It's about what is possible, cost etc. I'd MUCH rather see the above - a 'floor' of poly and insulated walls - than batts up above - that is where the humid air is moving to! It will migrate partially thru the insulation, then deposit its water. It is perfectly appropriate to do this on a vintage home, yes If you must use new batts in the floor, place the paper up in the bay toward the floor and let the pink show below it. In a pinch, you can get baling wire, or electric fence wire, and run some screws into floor joists and use the wire to hold up the insulation. Still using the poly below can help even if you are on piers, as long as outside (rain) water can't get onto it.

[Gothichome]

Gibson, I can see why Sara would be confused, you recommend vapour barrier and I recommend no vapour barrier. We do agree though that best practice would be perimeter insulation of some sort and making the crawl space part of the conditioned foot print.
My thoughts about non barriered insulating against the floor is it’s easier to let humidity freely come and go from the floor and joists allowing the wood to breath from both sides. Vapour barrier Against the floor in my view would would limit expelling of moisture only to the top surface of the floor boards.
I wonder if US parks has recommendations for this.
https://www.nps.gov/subjects/historicpr ... ndards.htm

Ron

[GibsonGM]

I can see the logic in 'come and go', Ron. I guess my approach would be that if you have it dry, and poly the floor (or concrete...), then it stays gone, LOL. I think some info from 'building science' might be of more use here, rather than anything directly related to old construction. It's the methods and materials - because many were simply not in existence then - at play here.

Hard to know what the right approach would be since we don't have any actual 'specs'/pics from her about what she's dealing with. If it's an enclosed space (she said brick - TOTALLY bricked in?), I really think 'sealing' the floor (as non airtight as a poly job would be) would be good, since the routes for moisture ingress are up from the ground and in thru vents/openings in the foundation structure. If one were to insulate the 'walls' of the crawl, with the floor open - would that not allow ground moisture to perk in and just hang out there? That was becoming an issue in my last home, 80s-built, concrete foundation but dirt floor crawl. Once I bricked up window openings (they used to 'vent' the space in summer, ugh), foam-board insulated the walls and rim joist, and put poly on the floor...moisture issues were solved, totally, measured with my hygrometer.

One way to observe this happening is to put a piece of poly down there flat, say 4'x4' piece, and come back in a week or 2...see if there's moisture accumulated under it. That would be going into the structure, if so. Mine certainly had that happening, 'telling' me it was the right way to go...I had a STREAM thru part of it when it rained (passing over bedrock). So I dug it down 8", put pea stone in, and then poly over that - problem solved. Each one is a little different. Even how much air volume is in there plays a part.

EDIT - I see now, you probably mean no vapor barrier on the INSULATION but ok on the floor, right?? The way I go at this is insulating the walls w/foamboard, NO insulation in the joists, for MAX. ability to pass vapor back & forth as you said. I think if I could get it good n dry, then no vapor barrier on the insulation would make sense if you're not insulating the walls...in my area (Maine) it's generally insulate one or the other, not both.

[nhguy]

I might suggest she go on Green Building Advisor's forum and post her question there. Martin Holliday that runs this as part of Fine Home Building is very knowledgeable. He can give a detailed plan to implement that will be effective in her region. They were helpful to me in my far northern region when we bought 8 years ago. Here's the link to the forum. https://www.greenbuildingadvisor.com/qa She'll have to create a free account then ask her question.

Let me start out by stating I am in Georgia, hot and humid in the summer and sometimes cold and wet in the winter..

The insulation under one of the bedrooms is falling out and missing in most places.
It's gotten to the point the bedroom temperature is not consistent with the rest of the house.

Our house is around 120 years old, so while one of the former homeowners skirted the crawlspace with brick, it is not encapsulated, which will not be a top contender for the budget for a foreseeable future. (Should you encapsulate a historic home's crawlspace??)

What we currently have is some sort of batting, majority is yellow in color.
The dropping insulation is not exclusive to just this area, so we're going to replace as needed.

I'm guessing the insulation support rods are not long enough because the joists aren't exactly 24" apart in all areas, and with natural expansion and contraction
...not to leave out my youngest son's heavy walking (stomping :rolleyes:)...


What is going to be the best insulation to go back with?

[Gothichome]

Gibson, glad you posted, it jogged my memo as to the building science write up on crawl spaces.
https://www.buildingscience.com/documen ... _resources
We had it in the reference section of the district. Some times I forget how much info we have collected over the years, some times I even forget we have a reference heading.
Ron

[GibsonGM]

Bit of a late reply here, but yes - good resource! It's not rocket science, but sometimes 'the rules' to moisture control can be confusing and easily shifted around, mentally. Once we understand how moisture works, that's probably 85% of the battle!