Insulating between Floor Joists/Under Baseboards

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Swampest

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Like many of us, I live in a house around 100 years old. This is our second winter. We are having issues with cold penetrating where the floor meets the wall. I took a few thermal imaging pictures and can see that’s exactly how we are losing heat/gaining cool.

We have batt insulation under the house. I am thinking about putting great stuff foam insulation under the baseboard gaps, crawling under the house and applying it between the floor joists and finally putting shoe molding down. Shoe molding will come in the future.



I have attached some pictures of what I am dealing with. Any suggestions would be greatly appreciated. Also, let me know if you think it’s a waste of time.
 

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Snoonyb

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While it's the assumed probability that the cold is intruding, from, that intersection, it may also be from another materials intersection.

In wood frame assembly, caulking is often used when walls are paced on wood platforms, but not aways, so that was my 1st thought, from your photos.
 

Swampest

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Seems like they missed the caulking job for sure. If I don't want to pull off the baseboards, do you think my idea of insulating from below would help?

Or are you saying putting down shoe molding/caulking would be the best solution.
 

Snoonyb

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You'd be insulating below the platform that the wall sets upon, and if you chose that, then I'd just pact more enfaced batt's in there.

If you caulk beneath the base, use a POLYSEAMSEAL or other flexible product, and then the shoe.

Because I'm a cheap old fart, I'd simply roll up some towels, and the critics who aren't helping on the mortgage, will not be frequent invites.
 

Swampest

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Appreciate the help.

I may try and do both. Insulate from underneath the house and us poly caulk at the baseboards. Really try and seal this place up.
 

Snoonyb

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Fix or not, the price was right.
 

bud16415

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They sell foam strip insulation that is round. I think it is called backer rod insulation. Comes rolled up. I would start with the 3/8 or 1/2 dia stuff and jam it under the baseboard and see how that works.

Welcome to the site.
 

BvilleBound

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First, Bud is right about starting with 'backer rod' on the top side. Backer rod is simply an inexpensive roll of circular foam - available in different diameters to match the gap you are trying to fill - that you press into a gap before you apply sealant. This is the correct way to fill a gap. Simply push the backer rod in, ~1/8" beyond the surface of the wall, then cover it with sealant, e.g. DAP 230. (DO NOT try to fill the interior gap with Great Stuff spray foam, which will stick to everything and create a real mess.) Backer rod and DAP 230 are available at Home Depot and Lowes, and many hardware stores.

I would do this first, which will should solve 90% of the problem. If you decide to do more in the crawl space, first apply the 'Window and Door' version of Great Stuff to seal any gaps / cracks. This version remains flexible after it cures, to avoid cracks and air leaks. Then pack a hunk of rock wool into the end of the joist bay, over the spary foam. Rock wool is much denser than fiberglass, molds a bit like clay and will stay where you put it. Wear gloves and a good 3M dust mask when you install it; the fibers are irritating like fiberglass and you don't want to breath them.

The next important insulation upgrade is probably in your attic. If you can see the tops of the joists, you definitely do not have enough insulation. Blown cellulose is the best option, and you can install it yourself if you are willing to crawl around in the attic and have a helper who can feed bales of cellulose into the blower. If you decide to upgrade you attic insulation, post another question on HouseRepairTalk and I can provide a bunch of tips.

I hope this is helpful.

Mark
 

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Backer rod sounds like a great solution. I am going to pick some 3/8" and 1/2" on the way home.

Would you suggest the R-15 rockwool? Would you match the height of the insulation all ready placed between the joist or just fill in a few inches?

We have an enclosed attic, so we can't access it.

Awesome suggestions guys. Defiantly going this route.
 

BvilleBound

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RE rockwool, that depends on your climate, how much you want to upgrade the insulation under your floor -- and the condition of existing insulation between the joists. If the existing insulation is old loose fiberglass, replacing it entirely with rockwool would be a significant improvement. Rock wool batts are available, e.g. from Home Depot, in a range of thicknesses to match the depth of your joists. Hold the batts in place with Simpson Strongtie insulation wire, which is also carried by Home Depot. Finally, if you live in an area with cold winters, you could screw panels of 1" polyiso foam board to the bottom of the joists. This will add R-6, break the 'thermal bridges' created by the (previously) exposed wood joists, and allow you to air-seal the floor. Use DAP 230 or HVAC mastic to seal the small gaps between the panels. Use the 'Window and Door' version of Great Stuff to seal the perimeter and larger gaps.

Four important notes on Great Stuff: (1) It cannot be applied if the temp is below ~50 degrees. You may need to wair till spring for that step. (2) The cured foam is very flammable and will ignite at just 240 degrees F -- which is significantly lower than the ignition temp for paper or wood. So NEVER install Great Stuff near any source of heat. (3) Great Stuff sticks to everything and no standard solvent will remove it. Wear gloves and eye protection when you install it. Never install it indoors unless you carefully tape and tarp off everything in the area. (4) If you do the crawlspace project, buy a $50 Great Stuff 'Pro' gun and use their pro cans. This will allow you to easily stop and start, without clogging the tube that comes with retail cans. Also buy a can of their 'gun cleaner' and use this when you stop for an extended period of time. I also found that you can attach a length of 3/8" clear nylon tube to the end of the Pro gun with a bit of masking tape. This will allow you to easily reach into remote joist bays. See the photo below:

1637335051056.png

If the existing insulation is in good shape, yes, simply pack a few inches of standard R-15 rock wool into the ends of the joist bays.

What did you mean by an "enclosed attic"? Is there an attic but it is not accessible? Or have the rafter walls already been insulated and finished?

I hope this is helpful,

Mark
 

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We are located in the Western Carolina mountains. Climate is normally mild but get lots of lows in the 20s the next 4 months.

The existing insulation is in great shape. So I will likely just try and pack a few inches of he R-15 as you recommend.

The sheet rock goes to the roof joists, which are insulated to my knowledge. So we don't actually have an attic.

Game plan.
1. Get 3/8" and 1/2" backer rod and go crazy and try to fill in gaps between the floor and base.
Wait a few days and go back with the thermal imaging cameras and see if it has helped.

If necessary, I will move on the phase 2

2. Use Great Stuff to fill the cracks at the end of the floor joists in crawl space when temperature is permitting. Should be able to do it this weekend before the final cold settles in.
3. Grab some R-15 and fill the end of the floor joists a few inches.

Hopefully this helps. I do believe it should.
 
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