Dover Projects How to Insulate Basement Rim Joists

Dover Projects How to Insulate Basement Rim Joists

Monday, November 24, 2008

How to Insulate Basement Rim Joists

Air Sealing and Insulating Basement Rim Joists

There are really two phases to weatherizing your home. First you air seal, then you insulate. What’s the difference? Well it’s just like when you dress for a winter day. You wear a sweater for «insulating», but that doesn’t do much to keep the wind from getting to you, so you wear an outer layer for «air sealing».

The main benefit of weatherizing the basement rim joists is air sealing. It’s not so much about insulating that area, so perhaps this article should be really be called «How to Air Seal Basement Rim Joists».

Stack Effect

All buildings are are subject to something called the «Stack effect «. When a building has openings, cracks, or ventilation at the top of the building, and similar ventilation at the bottom, there can be air movement either up or down, through the building (sometimes the «stack effect» is called the «chimney effect»). When the outside air is colder (denser) than the inside air, the flow goes out at the top, and in at the bottom. The reverse is true when the the outside air is warmer than the inside air. Here in the North, I care about the winter flow, which would be hot air leaving the top areas of my house, and cold air entering the lower areas.

Stack Effect In Action

One common area for air to come in, low on the house, is in the basement where your first floor meets the basement foundation walls. When you are in the basement looking up, you can see floor joists running across the basement ceiling. Capping those off around the perimeter of your house are rim joists. The sill plate is what those two pieces sit on. (Note: click on photos to enlarge them)

Sill Box Illustration

This is where a rigid foam insulation «sill box blockers» will be foamed in place, to air seal the small gaps where cold air can get in. Each gap is not much, but in total, around your entire basement, these little gaps can add up. (Note: You should also caulk or foam where the sill plate and foundation meet.)

If you can air seal the rim joists, or «sill boxes» (the floor joists, rim joist and sill plate form a box), you’ll go a long way in stopping air from entering the lower level of your house, reducing the stack effect, and thus reducing heat loss!

It’s a good idea to hire an energy auditor to test the tightness of your house with a blower door test. If you make the basement too tight, it is possible that you will interfere with the combustion air required by the furnace, boiler, or hot water heater. If these items can’t get enough air, and therefore can not work properly, they can produce deadly carbon monoxide.

Blower Door Test — Air Changes per Hour

I had a blower door test done by Energy Audits Unlimited. as I was interested in knowing how tight our house was before doing any air sealing or insulating. Turns out our house had .66 Natural Air Changes per Hour (ACH). That means that .66 of the total air in the house is exchanged every hour. I’ve read that anything lower than about .35 ACH can be too tight. I was surprised though, to find out that one internet source reported that most new homes had about 1.75 ACH. I always thought new homes would be tighter, apparently not, if air sealing is not a goal during construction.

Materials I Used

DOW, TUFF-R Commercial polyisocyanurate insulation with reflective/radiant barrier foil on both sides. It comes in 4′ x 8′ sheets and I used the 2″ thick stuff (R-Value: 13). Note from DOW: Local building codes may require a protective or thermal barrier. For more information, consult MSDS, call Dow at 1-866-583-BLUE (2583). This is because this insulation is flammable. UPDATE: Hindsight is always 20/20. It seems that Dow has a similar product called Thermax Heavy Duty Insulation, that does not require a «thermal barrier» for inside installation. Meaning you don’t have to cover with something like drywall. Well, you all can learn from my mistakes. Here’s a link to more about it. And here’s a link to all of their rigid foam insulation, so you can read and pick the right one.

From left to right: Gloves: Needed for most steps, especially mold removal, and spraying the «Great Stuff» which without gloves, will stay with you for days. Safety Glasses and Dusk Mask: Use them when cleaning and when working with the insulation, also wear the glasses when spraying the Great Stuff, Wipes: Used for minimal mold removal, Exterior/Interior Window and Door Caulk: Used to seal around sill boxes and foundation, High Temperature Caulk: Used to seal around my very hot steam pipes, which would melt the Great Stuff and perhaps the rigid insulation (not sure), so I cut around the pipes, then air sealed. Great Stuff Gaps and Cracks Filler: Used to seal around the insulation blocks, Great Stuff Big Gap Filler: Used for larger gaps (it expands more), Great Stuff Fireblock: Also used around steam pipes, but only after a first layers of the high temperature caulk, Drywall Saw: To cut the rigid insulation, T-Square: to measure and cut blocks.

Step 1: Removing Sill Box Debris

Mine where a mess with years of: unidentifiable junk, mortar, cobwebs, acorns, and so on. So I donned a N95 dust mask and got to work with a shop vac.

Step 2: Removing Mold

I had some white powdery sections on the wood. Nothing too bad, but enough that I didn’t want to cover it with the blocks. The first thing you learn about mold remediation, is to first correct the moisture problem. I didn’t have any any obvious leaks around the sill, but I have four basement windows that were leaky before I corrected that problem when we moved in. So I moved on to the next step, which is mold removal. After reading much conflicting information about whether or not to use bleach, or other dedicated mold remediation products, I decided to do what the EPA recommends. which basically says, «fix the moisture problem, then for hard surfaces, scrub with detergent and water and let it dry (wood is porous though, so there wasn’t a good way to remove all of it). I read that some professionals use sani-wipes. I used those, with gloves on, carefully containing the mold to a clean section of the wipe with continual folding and frequently tossing contaminated wipes, in order not to spread the spores further.

See those white specs on the floor joist (in the middle), just above the conduit pipe? That’s mold. I had some of that in the sill boxes too, but it wasn’t much.

Step 3: Sealing Potential Water Penetrations

I’m fairly sure my moisture was getting inside the basement from the basement windows, but to be on the safe side, I used caulk around all the joints/edges of the sill boxes after cleaning and removing the mold. I also did this in areas where the rim joist wood had cracks. I should also do this on the outside of the house, which I’ll do soon.

Step 4: Cutting the Rigid Insulation Blocks

I cut my rigid insulation with a drywall saw (shown in the materials photo above), but you could also rip these sheets with a table saw in 8 foot lengths, then cut the strips down to block size. I found that even with my 100 year old home, all of the blocks where almost the same size, so you won’t have to measure each block. Be sure to cut them about a 1/4 small on the sides. This is so you can have a good amount of space to spray the foam insulation into. The top and bottoms can be snug.

Step 5: Installing the Rigid Foam Blocks

Because I had just prior given the sill boxes a application of caulk, I also put a few dabs of caulk on the rim joist, to hold the insulation blocks in place prior to foaming. Push the blocks in place as snug up against the rim joist as you can get them.

Once you’ve got about 10 blocks in place, go ahead and start up a can of Great Stuff. You’ll find that once you start a can, you shouldn’t stop, as the spray tube will clog up. So get a bunch of blocks ready then apply the foam insulation. Be sure to also foam between the sill boxes, under the floor joist.

Great Stuff expands about 3 times it sizes as it sets, so don’t go overboard. Test it a few times to get the hang of it. Apply less than you want on final piece. You can always go back and add more if needed. And whatever you do, you MUST wear gloves. This stuff will stick with you for days. Wear goggles too. You don’t want this stuff in your eyes I’d recommend a few trial pieces first. My first few panels pushed out when the Great Stuff set. Not sure if I got some behind the panels or what.

Here’s the finished product. Perhaps the look is a bit space-aged for a 100 year old home, but it’s well worth it to be more «green» and save some green too. I increased the contrast of this photo a bit to show the sill insulation better. In doing so, I’ve made the ceiling look wet and leaky. It is not, it’s just a contrasty photo.

In previous winters I had so much cold air coming in at this location that my domestic water pipes froze (gray here). This year I’m hoping I’ve eliminated that problem.

Notes

I’ve read that it’s best not to simply stuff the sill boxes with fiberglass batts for two reasons: 1. Fiberglass batts alone, do not seal airflow, 2. They can become damp and thus moldy. I did though find an article recently that suggested to do as I did, but then in addition, add fiberglass batts, cut to fill each box flush with the foundation wall. Also, you can add rigid insulation to the other ends of your basement, but these are generally harder to cut long strips for, and I believe, they are less leaky.

Energy Auditor Who Showed Me How to Insulate Rim Joists, and Suggested it.

Energy Audits Unlimited Thanks to Paul Button for his initial input. I found Paul to be an excellent auditor.

Monday, November 24, 2008

How to Insulate Basement Rim Joists

Air Sealing and Insulating Basement Rim Joists

There are really two phases to weatherizing your home. First you air seal, then you insulate. What’s the difference? Well it’s just like when you dress for a winter day. You wear a sweater for «insulating», but that doesn’t do much to keep the wind from getting to you, so you wear an outer layer for «air sealing».

The main benefit of weatherizing the basement rim joists is air sealing. It’s not so much about insulating that area, so perhaps this article should be really be called «How to Air Seal Basement Rim Joists».

Stack Effect

All buildings are are subject to something called the «Stack effect «. When a building has openings, cracks, or ventilation at the top of the building, and similar ventilation at the bottom, there can be air movement either up or down, through the building (sometimes the «stack effect» is called the «chimney effect»). When the outside air is colder (denser) than the inside air, the flow goes out at the top, and in at the bottom. The reverse is true when the the outside air is warmer than the inside air. Here in the North, I care about the winter flow, which would be hot air leaving the top areas of my house, and cold air entering the lower areas.

Stack Effect In Action

One common area for air to come in, low on the house, is in the basement where your first floor meets the basement foundation walls. When you are in the basement looking up, you can see floor joists running across the basement ceiling. Capping those off around the perimeter of your house are rim joists. The sill plate is what those two pieces sit on. (Note: click on photos to enlarge them)

Sill Box Illustration

This is where a rigid foam insulation «sill box blockers» will be foamed in place, to air seal the small gaps where cold air can get in. Each gap is not much, but in total, around your entire basement, these little gaps can add up. (Note: You should also caulk or foam where the sill plate and foundation meet.)

If you can air seal the rim joists, or «sill boxes» (the floor joists, rim joist and sill plate form a box), you’ll go a long way in stopping air from entering the lower level of your house, reducing the stack effect, and thus reducing heat loss!

It’s a good idea to hire an energy auditor to test the tightness of your house with a blower door test. If you make the basement too tight, it is possible that you will interfere with the combustion air required by the furnace, boiler, or hot water heater. If these items can’t get enough air, and therefore can not work properly, they can produce deadly carbon monoxide.

Blower Door Test — Air Changes per Hour

I had a blower door test done by Energy Audits Unlimited. as I was interested in knowing how tight our house was before doing any air sealing or insulating. Turns out our house had .66 Natural Air Changes per Hour (ACH). That means that .66 of the total air in the house is exchanged every hour. I’ve read that anything lower than about .35 ACH can be too tight. I was surprised though, to find out that one internet source reported that most new homes had about 1.75 ACH. I always thought new homes would be tighter, apparently not, if air sealing is not a goal during construction.

Materials I Used

DOW, TUFF-R Commercial polyisocyanurate insulation with reflective/radiant barrier foil on both sides. It comes in 4′ x 8′ sheets and I used the 2″ thick stuff (R-Value: 13). Note from DOW: Local building codes may require a protective or thermal barrier. For more information, consult MSDS, call Dow at 1-866-583-BLUE (2583). This is because this insulation is flammable. UPDATE: Hindsight is always 20/20. It seems that Dow has a similar product called Thermax Heavy Duty Insulation, that does not require a «thermal barrier» for inside installation. Meaning you don’t have to cover with something like drywall. Well, you all can learn from my mistakes. Here’s a link to more about it. And here’s a link to all of their rigid foam insulation, so you can read and pick the right one.

From left to right: Gloves: Needed for most steps, especially mold removal, and spraying the «Great Stuff» which without gloves, will stay with you for days. Safety Glasses and Dusk Mask: Use them when cleaning and when working with the insulation, also wear the glasses when spraying the Great Stuff, Wipes: Used for minimal mold removal, Exterior/Interior Window and Door Caulk: Used to seal around sill boxes and foundation, High Temperature Caulk: Used to seal around my very hot steam pipes, which would melt the Great Stuff and perhaps the rigid insulation (not sure), so I cut around the pipes, then air sealed. Great Stuff Gaps and Cracks Filler: Used to seal around the insulation blocks, Great Stuff Big Gap Filler: Used for larger gaps (it expands more), Great Stuff Fireblock: Also used around steam pipes, but only after a first layers of the high temperature caulk, Drywall Saw: To cut the rigid insulation, T-Square: to measure and cut blocks.

Step 1: Removing Sill Box Debris

Mine where a mess with years of: unidentifiable junk, mortar, cobwebs, acorns, and so on. So I donned a N95 dust mask and got to work with a shop vac.

Step 2: Removing Mold

I had some white powdery sections on the wood. Nothing too bad, but enough that I didn’t want to cover it with the blocks. The first thing you learn about mold remediation, is to first correct the moisture problem. I didn’t have any any obvious leaks around the sill, but I have four basement windows that were leaky before I corrected that problem when we moved in. So I moved on to the next step, which is mold removal. After reading much conflicting information about whether or not to use bleach, or other dedicated mold remediation products, I decided to do what the EPA recommends. which basically says, «fix the moisture problem, then for hard surfaces, scrub with detergent and water and let it dry (wood is porous though, so there wasn’t a good way to remove all of it). I read that some professionals use sani-wipes. I used those, with gloves on, carefully containing the mold to a clean section of the wipe with continual folding and frequently tossing contaminated wipes, in order not to spread the spores further.

See those white specs on the floor joist (in the middle), just above the conduit pipe? That’s mold. I had some of that in the sill boxes too, but it wasn’t much.

Step 3: Sealing Potential Water Penetrations

I’m fairly sure my moisture was getting inside the basement from the basement windows, but to be on the safe side, I used caulk around all the joints/edges of the sill boxes after cleaning and removing the mold. I also did this in areas where the rim joist wood had cracks. I should also do this on the outside of the house, which I’ll do soon.

Step 4: Cutting the Rigid Insulation Blocks

I cut my rigid insulation with a drywall saw (shown in the materials photo above), but you could also rip these sheets with a table saw in 8 foot lengths, then cut the strips down to block size. I found that even with my 100 year old home, all of the blocks where almost the same size, so you won’t have to measure each block. Be sure to cut them about a 1/4 small on the sides. This is so you can have a good amount of space to spray the foam insulation into. The top and bottoms can be snug.

Step 5: Installing the Rigid Foam Blocks

Because I had just prior given the sill boxes a application of caulk, I also put a few dabs of caulk on the rim joist, to hold the insulation blocks in place prior to foaming. Push the blocks in place as snug up against the rim joist as you can get them.

Once you’ve got about 10 blocks in place, go ahead and start up a can of Great Stuff. You’ll find that once you start a can, you shouldn’t stop, as the spray tube will clog up. So get a bunch of blocks ready then apply the foam insulation. Be sure to also foam between the sill boxes, under the floor joist.

Great Stuff expands about 3 times it sizes as it sets, so don’t go overboard. Test it a few times to get the hang of it. Apply less than you want on final piece. You can always go back and add more if needed. And whatever you do, you MUST wear gloves. This stuff will stick with you for days. Wear goggles too. You don’t want this stuff in your eyes I’d recommend a few trial pieces first. My first few panels pushed out when the Great Stuff set. Not sure if I got some behind the panels or what.

Here’s the finished product. Perhaps the look is a bit space-aged for a 100 year old home, but it’s well worth it to be more «green» and save some green too. I increased the contrast of this photo a bit to show the sill insulation better. In doing so, I’ve made the ceiling look wet and leaky. It is not, it’s just a contrasty photo.

In previous winters I had so much cold air coming in at this location that my domestic water pipes froze (gray here). This year I’m hoping I’ve eliminated that problem.

Notes

I’ve read that it’s best not to simply stuff the sill boxes with fiberglass batts for two reasons: 1. Fiberglass batts alone, do not seal airflow, 2. They can become damp and thus moldy. I did though find an article recently that suggested to do as I did, but then in addition, add fiberglass batts, cut to fill each box flush with the foundation wall. Also, you can add rigid insulation to the other ends of your basement, but these are generally harder to cut long strips for, and I believe, they are less leaky.

Energy Auditor Who Showed Me How to Insulate Rim Joists, and Suggested it.

Energy Audits Unlimited Thanks to Paul Button for his initial input. I found Paul to be an excellent auditor.


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