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Spur08

How to Insulate Between I-Beams/Joists?

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In doing various DIY project throughout my house, I've discovered cost-cutting/lazy work in certain areas.  I've addressed quite a few of them and I'm finally at a point (climate wise) where I can comfortable address this one.

 

There is a large attic space above my garage where the joists run across it into the house.  The problem I discovered is that there is no air block/barrier that is separating the unconditioned (at times, superheated) attic space from the joists into the house, above my office and below my gameroom.  It is of no coincidence that these are the absolute worst areas cooling/heating wise.  Below are a few pictures, there are probably 20 joists (10 or so gaps) where all the constructure workers did was stuff about 2 feet of batts.  Remove the batts, and that is what you see.  The gaps vary of having some ductwork in/crossing them or, sometimes, absolutely nothing but a back wall.  

 

I figure I have 2 approaches, buy some blow in insulation and fill these large gaps with the product or purchase some 2" rigid foam board to seal up the gaps.  Is any method better than the other R-value/efficiency-wise?   Any other factors or options to consider?

 

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Edited by Spur08

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Matt Risinger is an Austin home builder and he has a GREAT YouTube channel. He likes to make the entire attic "conditioned." Ie, no soffit or roof vents, and insulation right under the roof deck. That insulation is usually spray foam.

 

 

His channel has more vids covering the topic.

 

 

 

 

 

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I dont want to convert to complete spray foam insulation. Way too pricey and I dont think I would stay here long enough to make some money back. When I said foam insulation earlier, I meant foam board insulation.

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i agee with just blowing insulation in.  just shove the hose down the opening and just pull it back as you see it start to fill up.  For what you want to do it's a two man job.  Somebody needs to bee downstairs to load the insulation and also it will be a lot better if they can turn off blower between gap fills. Otherwise you will be trying to shove the hose in the opening as it is spraying out insulationa and you will never get it routed to the back of the opening before the insulation fills the gap.  Better to fill a gap, turn off machine, wggle tobe to the back of next hole and start the blower and pull back as it fills.  Repeat until the gaps are full.

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17 hours ago, Parliament said:

Matt Risinger is an Austin home builder and he has a GREAT YouTube channel. He likes to make the entire attic "conditioned." Ie, no soffit or roof vents, and insulation right under the roof deck. That insulation is usually spray foam.

 

 

 

His channel has more vids covering the topic.

 

 

 

 

 

For reference, I had a townhome about 8 years ago that I had to pull all the drywall off the walls and ceilings.  It had a flat roof that leaked horribly that I had replaced while also adding a 1" per 30"(iirc) slope from front to back of the place.(but I digress)

After the new roof was on I researched alternatives to re-insulate the place and decided upon Icynene open cell spray insulation.  It worked out quite well.  Not the cheapest alternative but with the air sealing properties as well as the decent R-factor the place seems quite energy efficient.(156 sheets of drywall later)

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i agee with just blowing insulation in.  just shove the hose down the opening and just pull it back as you see it start to fill up.  For what you want to do it's a two man job.  Somebody needs to bee downstairs to load the insulation and also it will be a lot better if they can turn off blower between gap fills. Otherwise you will be trying to shove the hose in the opening as it is spraying out insulationa and you will never get it routed to the back of the opening before the insulation fills the gap.  Better to fill a gap, turn off machine, wggle tobe to the back of next hole and start the blower and pull back as it fills.  Repeat until the gaps are full.
I'm leaning towards this. The only problem is there are some drip down areas where I think there might be electrical boxes or can lights, so things could get tricky there.

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6 minutes ago, Spur08 said:
3 hours ago, horn4life said:
i agee with just blowing insulation in.  just shove the hose down the opening and just pull it back as you see it start to fill up.  For what you want to do it's a two man job.  Somebody needs to bee downstairs to load the insulation and also it will be a lot better if they can turn off blower between gap fills. Otherwise you will be trying to shove the hose in the opening as it is spraying out insulationa and you will never get it routed to the back of the opening before the insulation fills the gap.  Better to fill a gap, turn off machine, wggle tobe to the back of next hole and start the blower and pull back as it fills.  Repeat until the gaps are full.

I'm leaning towards this. The only problem is there are some drip down areas where I think there might be electrical boxes or can lights, so things could get tricky there.

Your can lights need to be checked to see if they're IC compatible (insulation contact acceptable).

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I figured, but I cant access the back of the light in the crawl space. Maybe it says it on the inside housing?

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1 minute ago, Spur08 said:

I figured, but I cant access the back of the light in the crawl space. Maybe it says it on the inside housing?

should be a label inside the housing you can see.

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One item to consider with spray foam insulation directly under the deck is if a leak ever occurs, it is damn near impossible to determine the exact point of entry.  If you have any rotten decking that needs replacing, you will end up with a sizable gap in the insulation due to the removed spray foam.

Essentially consider it a minimum twice as expensive repair.  Could be more depending on where the damage is... chimney?  4x the cost.  Valley?  Prob. 3x.  Roof to wall joint (not a chimney), 3x.  Rake edge or eave (unsupported area) 3x.  Basic mid-field, maybe around a pipe penetration?  That's your cheap 2x cost.

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On 11/17/2019 at 12:09 AM, Jkwellborn said:

Doing that can void the warranty of your roof too.

 

Operative word is "can" but most likely there answer is no, your shingles warranty will not be void.

 

On 11/16/2019 at 11:19 PM, Parliament said:

Matt Risinger is an Austin home builder and he has a GREAT YouTube channel. He likes to make the entire attic "conditioned." Ie, no soffit or roof vents, and insulation right under the roof deck. That insulation is usually spray foam.

 

 

 

His channel has more vids covering the topic.

 

 

 

 

 

 

 

This is a terrible idea on an existing house unless you apply SFI to roof deck, inside of exterior walls, seal all openings, provide fresh air intake and COMPLETELY block off the un-A/C'd garage from the A/C'd house (which is exactly where his problem is).  Negative pressure is the enemy of SFI systems.  

OP needs to block off (simple draft stop) and batt insulate the un-air conditioned side of the draft stop where his garage hot humid air is getting into his insulated attic above his living area.  Keep the insulated A/C area completely separate from uninsulated, non-A/C area  

don't over think this  as you already had the right idea when you mentioned "air block" in your post  

Edited by deadshank

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Inadequate ventilation underneath the shingles can void your warranty. It’s most likely dependent on manufacturer and how much of a dick their claims department wants to be.

 

I don’t actually think it will hurt the shingles but it would be worth checking into before you did that.

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20 minutes ago, deadshank said:

Operative word is "can" but most likely there answer is no, your shingles warranty will not be void.

 

This is a terrible idea on an existing house unless you apply SFI to roof deck, inside of exterior walls, seal all openings, provide fresh air intake and COMPLETELY block off the un-A/C'd garage from the A/C'd house (which is exactly where his problem is).  Negative pressure is the enemy of SFI systems.  

OP needs to block off (simple draft stop) and batt insulate the un-air conditioned side of the draft stop where his garage hot humid air is getting into his insulated attic above his living area.  Keep the insulated A/C area completely separate from uninsulated, non-A/C area  

don't over think this  as you already had the right idea when you mentioned "air block" in your post  

Listen to this man. I'm sure he's fallen off a lot of roofs in his day.

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9 minutes ago, Jkwellborn said:

Inadequate ventilation underneath the shingles can void your warranty. It’s most likely dependent on manufacturer and how much of a dick their claims department wants to be.

 

I don’t actually think it will hurt the shingles but it would be worth checking into before you did that.

All shingle manufacturers have boiler plate "Inadequate ventilation" language in their warranties.  The shingle manufacturers' issue with ventilation inadequancies is NOT removing heat (or cold) from the attic but is about removing humidity.  With SFI, the building envelope becomes a non-venting system.

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3 minutes ago, Onboard 2.0 said:

Listen to this man. I'm sure he's fallen off a lot of roofs in his day.

Not yet but the day ain't over.  

Doing a mammoth re-roof with all new copper flashings, imported 2-piece clay tile, new copper gutters and downspouts, new balcony water proofing, yada, yada, yada.

SFI on underside of roof deck only.  Not on inside of wall sheathing.  Soffit vents and no roof exhaust vents.  Previous owner thought it was a great idea.   

No.  It wasn't.   Lots of moisture issues. 

Go all SFI everywhere or don't go at all. 

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OP needs to block off (simple draft stop) and batt insulate the un-air conditioned side of the draft stop where his garage hot humid air is getting into his insulated attic above his living area.  Keep the insulated A/C area completely separate from uninsulated, non-A/C area  
don't over think this  as you already had the right idea when you mentioned "air block" in your post  


This seems counterintuitive to me. Are you saying I should put batt insulation above the garage space (nonAC) after sealing with foam board or above the office (AC) space and then foam board seal?

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20 minutes ago, Spur08 said:


 

 


This seems counterintuitive to me. Are you saying I should put batt insulation above the garage space (nonAC) after sealing with foam board or above the office (AC) space and then foam board seal?

 

No.  Block the open areas where the non AC air from the garage is migrating between the joists and into the AC living area. Place the insulation on the non AC side of the blocking.  

 

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Just now, deadshank said:

No.  Block the open areas where the non AC air from the garage is migrating between the joists and into the AC living area. Place the insulation on the non AC side of the blocking.  

 

they have the individual cans of spray foam, i think it is orange but don't recall the brand they used.  only issue is to get to the cracks under those plywood planks as the individual can gun is not very good for long distances in tight spots unless you embody, are, stretch armstrong:

 

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No.  Block the open areas where the non AC air from the garage is migrating between the joists and into the AC living area. Place the insulation on the non AC side of the blocking.  
 


So basically just extend the walls up to the roof with insulation? Actually not a bad idea if that space is unusable anyway.

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So basically just extend the walls up to the roof with insulation panels? Actually not a bad idea if that space is unusable anyway.

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I'm leaning towards this. The only problem is there are some drip down areas where I think there might be electrical boxes or can lights, so things could get tricky there.


Can you crawl over to them? Do you need access to them? You could either cap them with something that rises higher than the blow in so you can find them, or just stuff the top of the gap with foam to plug it up if you don’t think you’ll ever need easy access. I don’t think electrical boxes are a problem as people insulate around them all the time. Can lights might be a different story though since they do get really hot. I’d definitely find someway to keep the insulation from piling up on them.

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Can you crawl over to them? Do you need access to them? You could either cap them with something that rises higher than the blow in so you can find them, or just stuff the top of the gap with foam to plug it up if you don’t think you’ll ever need easy access. I don’t think electrical boxes are a problem as people insulate around them all the time. Can lights might be a different story though since they do get really hot. I’d definitely find someway to keep the insulation from piling up on them.
I'm 6', 200#. Definitely not fitting.

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Coming back to this I didn't focus much on the lack of insulation being in the garage. I guess the answer as nearly is always the case is "it depends!"

Since they skimped in what I assume was supposed to fully insulated garage space the one thing I might do is make sure there is some sort of insulation in the wall between the garage and the house? Are the exterior garage walls insulated?  Garage door insulated? I'm guessing that no is the answer to at least one of those?  If the answer to these questions is yes then do the blow in AFTER CONFIRMING that if you do have exposed lighting housings that are IC rated.  

So by insulating the ceiling you are simply trying to block heat transfer? Correct? OF what may or may not be a well insulated garage.

Ultimately my decision making is what will work, and what's easiest/cheapest. I might simply go to home depot at buy some foam board and some mastic. Cut the foam to size to and seal off the garage from the house.  IF you have easy access, cutting the foam is pretty easy, especially if you but a duct knife (something I just discovered recently).  Odds are the one thing they did do is probably spaced the I-beams evenly so you may be able to cut a bunch to size and make quick work of it.  This is probably the easiest and cheapest.  If you want to more fully insulate the garage space, then blow shit in everywhere that won't burn the house down. And let the insulation block the air transfer.

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18 minutes ago, horn4life said:

Coming back to this I didn't focus much on the lack of insulation being in the garage. I guess the answer as nearly is always the case is "it depends!"

Since they skimped in what I assume was supposed to fully insulated garage space the one thing I might do is make sure there is some sort of insulation in the wall between the garage and the house? Are the exterior garage walls insulated?  Garage door insulated? I'm guessing that no is the answer to at least one of those?  If the answer to these questions is yes then do the blow in AFTER CONFIRMING that if you do have exposed lighting housings that are IC rated.  

So by insulating the ceiling you are simply trying to block heat transfer? Correct? OF what may or may not be a well insulated garage.

Ultimately my decision making is what will work, and what's easiest/cheapest. I might simply go to home depot at buy some foam board and some mastic. Cut the foam to size to and seal off the garage from the house.  IF you have easy access, cutting the foam is pretty easy, especially if you but a duct knife (something I just discovered recently).  Odds are the one thing they did do is probably spaced the I-beams evenly so you may be able to cut a bunch to size and make quick work of it.  This is probably the easiest and cheapest.  If you want to more fully insulate the garage space, then blow shit in everywhere that won't burn the house down. And let the insulation block the air transfer.

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Is your garage air conditioned?  If not then why would you want to insulate it?  

 

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If connected, uninsulated garage is open to insulated attic, is that airflow bad?

How is it different from soffit vents, ridge vents, etc.?

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Is your garage air conditioned?  If not then why would you want to insulate it?  
 
It is not. Neither the garage or the attic space directly above is conditioned.

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53 minutes ago, Spur08 said:
2 hours ago, deadshank said:
Is your garage air conditioned?  If not then why would you want to insulate it?  
 

It is not. Neither the garage or the attic space directly above is conditioned.

Then don't insulate it.  You'll just keep the hot air in in the summer.  Garages are hot in the summer because they are not air conditioned.

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Then don't insulate it.  You'll just keep the hot air in in the summer.  Garages are hot in the summer because they are not air conditioned.
Now you're confusing me. Upthread you mentioned to place insulation on the none AC side, then foam board, and leave the crawl space air gapped?

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3 minutes ago, Spur08 said:
7 minutes ago, deadshank said:
Then don't insulate it.  You'll just keep the hot air in in the summer.  Garages are hot in the summer because they are not air conditioned.

Now you're confusing me. Upthread you mentioned to place insulation on the none AC side, then foam board, and leave the crawl space air gapped?

Yes, I did.  You're insulating for the AC side of the equation which is in your house, not in the garage.

From the last post where I said don't insulate the garage I thought you were considering insulating the garage, too.  

I guess for applying batt insulation of the draft stop(s), it doesn't really matter where the insulation is placed as long as it is placed.  In keeping with what is already placed, the insulation in the attic is on the attic side.

 

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