4 Rim Joist Insulation Things You Need to Know

This video will teach you four essential things about rim joist insulation in the basement or crawl space. Rim joist air sealing and insulation can help keep humidity down in the house during summer. It can also keep cold air out in the winter.
Four things you will learn about rim joist insulation from watching this video that are important for any homeowner to know:
1. How to identify the rim joist by learning some basics.
2. Why does paying attention to the rim joist area of your home actually matter?
3. Look for tell-tale signs of air leakage at the rim joist in YOUR home.
4. What type of insulation to use and how to properly air seal and insulate the rim joist.
Any unfinished basement area that allows access to the rim and band joist should be sealed and insulated to help lower energy costs and reduce summer humidity and winter drafts.
“Low-hanging fruit” are opportunities that cost the least and give you back the most. The best leaks to seal are near the bottom of your house (for example, the rim joist or a leaky basement window) and at the top (leaks at the ceiling due to penetrations like recessed lights and bath fans). These leaks are in the areas of the home where pressure is most significant, causing the leaks to do the most “damage.”
Sealing leaks in the neutral plane of the house (the halfway point) will not provide as much leakage reduction and likely would cost the most to accomplish.
Sealing leaks at the rim joist is significant and should be done where it is accessible, including above suspended ceiling tiles.
Treating the inaccessible portions of the rim joist is not recommended due to the high cost (drywall removal/obstruction removal) vs. actual return.
00:00 Introduction Eric Gans - Certified Energy Auditor
00:10 The Four Things I Want You to Know About Rim Joists
00:28 How to Identify the Rim Joist
01:14 Why Does the Rim Joist Matter?
01:49 How to Know if it Is a Problem at Your House
02:37 How to Properly Seal & Insulate the Rim Joist
03:16 A Tip About How to Prioritize Sealing a House
03:52 Concluding Thought
If you would like to learn more about my home performance company or get in touch, please visit www.hometrustremodeling.com or ericgans.com.
Unlock Your Home's Full Potential - Hometrust Remodeling, Your Trusted Partner in Maryland Home Performance

[@mjb995]

Thanks! Informative and to the point.

[@homeairleakagetest]

Glad it was helpful! Thanks for watching and for positive feedback. Much appreciated.

[@chuckhall5347]

I live in a temperate climate on the border of zone 5 and 4. On the last rim joist project I did I used caulk to seal the gaps then put in mineral wool bats. One reason is that mineral wool will let a small amount of condensation dissipate. Another reason is that homes in my area need periodic termite inspection and treatment. Mineral wool bats can be removed and put back.

[@homeairleakagetest]

This makes a lot of sense and I appreciate you sharing the information. Where do you anticipate condensation forming when you seal the rim joist? Thanks!

[@chuckhall5347]

@@homeairleakagetest On a day when it is below freezing outside and the basement air is warm, moisture could condense on the inside of the rim joist. I have not seen this, even before air sealing on any of the three houses I have done this project on so that part is a guess. Being able to remove mineral wool bats and put them back for termite inspection made the decision for me. Since I put the bats in my current house, I have removed a section and put it back twice. Once to repair a pipe that froze and once to fish a new wire into an outlet. I'll use mineral wool if I have any more projects like this. Caution: If you install mineral wool, wear a mask, wear gloves, keep your skin covered. I see people on youtube handling this stuff with bare hands and no mask but I found out that is a mistake.

[@homeairleakagetest]

​@@chuckhall5347 this makes sense to me, and I appreciate your thoughtful response. How did a pipe freeze if you sealed and insulated the area?

[@chuckhall5347]

@@homeairleakagetest The pipe ran through the wall to a hose bib in the garage. It had a shut off in the basement but I neglected to shut it off. We had a big cold snap on Christmas day and I found myself asking 'why do I hear water running running?'

[@homeairleakagetest]

@@chuckhall5347 Okay. Got it. I am a student of building science and I make mistakes, but since I do retrofitting, I have a little wiggle room because most of what I do is recommended by the local utility program guidelines and what I do typically always improves the situation, never makes it worse...in my mind, if you effectively seal and insulate the rim joist you are cutting off the contact point between inside and outside and you are "killing" the dew point possibility which is where the mold problem starts. You have to seal around each penetration through the joist and I would use foam if I were you. I did windows and doors and siding as well and there is a use for caulk, but for sealing up the cracks and crevices in the header areas - foam is superior. Anyways, all the best!!!

[@xx11xx54]

Would you seal the rim if only about 1/4 of it was accessible or is this more of a all or nothing fix

[@homeairleakagetest]

Every little bit helps!

[@bwsct]

What about using rigid foam in the rim joist area and sealing around the edges with canned foam? Just as affective or not? Cheaper?

[@homeairleakagetest]

One thing that was taught early that stuck with me is to seal the exact entry point for the best results. So, perhaps the best solution is to air seal the joist cracks and holes, then add the foam board (R19 in Maryland), and then add foam sealant to hold it in place/ for good measure. The foam sealant and R19 batt options are the most cost-effective, and that solution is also suitable for energy efficiency and comfort. Hope this helps.

[@pcatful]

I thought people were sealing the edges of the rigid foam to form an interior vapor barrier, to cut down moist warm air going behind the insulation and condensing when it reaches the cold surfaces. I agree that making a seal along the mudsill and foundation is good to reduce air from outside. @@homeairleakagetest

[@MisterSkizzels]

Thats what i did, cut the pink board to size, put it in the area, then put fire retardant spray foam around it. Works great.

[@Putin_Playbook_12345]

Would the closed cell foam on the rim joist create a place for mold to grow?

[@homeairleakagetest]

Hi geakin5458. IMO, no. The rim joist is not generally where I see mold when it is not sealed. Sealing the rim joist from the inside will keep the outside air from coming in, decreasing the chances. Keeping humidity out in summer and cold air in winter will improve indoor air quality and promote sustainability. Your rooms above the rim joist will also feel warmer in the winter because our feet are pretty sensitive so when cold air infiltrates the rim joist, we feel it and don't like it! There are so many benefits!

[@Putin_Playbook_12345]

@@homeairleakagetest I completely agree that sealing the inside of the joist will improve air quality inside. What I’m unsure about is would moisture buildup on the rim joist and promote mold? My rim joist is at or slightly below ground level, brick outside, basement-to-main floor interface.

[@homeairleakagetest]

@@Putin_Playbook_12345 Where do you imagine the mold growing? On the outside? If closed cell foam is sprayed, it will expand and fill the gaps. In theory, it should be airtight. I would love to hear any other expert opinions. Thanks!

[@pcatful]

Using closed cell insulation in many projects, I've not heard of mold being an issue. The reason closed-cell is used because it seals itself to the wood and protects the wood from moist inside air. It's similar to rigid foam that is backed by OSB. It acts as one piece without a place for mold inside. Furthermore it is forcing the dewpoint to the exterior. Nothing's perfect, but I have not heard of mold in that situation. Problems arise where air gaps are left due to improper application. @@homeairleakagetest

[@richardstewart4303]

Rim joist attic above outside walls should insulated to the wall plane R value, not the floor or ceiling planes.

[@homeairleakagetest]

Thanks for your input.

[@BruceGinkel]

Can seem them rim joists through them dang nostrils boss 😂😂😂 maybe use a higher camera angle lol. Informative content tho!

[@homeairleakagetest]

lol. Thanks for watching and thanks for the tip!!

[@pcatful]

I don't see why the air seal is sprayed on the wood joints except along the bottom at the concrete or mudsill joints. All you are doing on the sides and top is sealing from the next bay over and floor inside the house above. Sure it always helps to limit air movement into other framing areas, but these joints are not exposed to the outside any more than if you nailed two board together in the middle of your house and sprayed that joint. Seal along the joist-- you are literally sealing the basement from the basement air. Creating and sealing a vapor barrier on the rigid insulation between the inside and cool side of the insulation DOES make sense. If this is new construction, make a good air barrier on the OUTSIDE of the house from the foundation to the roof.

[@homeairleakagetest]

Hi, thanks for your contribution and for watching! In older houses that were not sealed during construction the rim and band joist is connected to the outside and should be sealed. It can be a source of air infiltration in both winter and summer. Sealing to the wood and then covering the header area with R19 is a cost-effective best practice in the Maryland climate zone. Using the cans of foam is the same concept as using closed-cell two-part spray foam. Spray foam seals and insulates in one shot, in the more conventional method, we seal the leaky parts to stop airflow and insulate with batts to resist heat transfer at the "weak" point. Watch this one if you want to see the problem with "x-ray" vision! kzbin.info/www/bejne/fWqUd5J9apWsfNE