Air sealing dryer vent (insulating basement) without setting house on fire

[Red Squirrel]

I'm insulating my basement, using spray foam for the areas that would be awkward to work with vapour barrier, and using roxul + plastic vapour barrier for the rest, and tying it all together as best as I can for maximum air tightness.

But what do I do for the dryer vent? I can't use plastic there as it will probably melt, and I probably should not use spray foam either? Is there some kind of foil based vapour barrier I can use?

Basically this is my setup, it's a really awkward way that pipe exits. (don't mind the other one that's just a bathroom vent, don't care too much about that one, it's the other one that exits behind the wall)






This is a view where I took out the partition wall just to make it easier to visualize:



The red is where the vapour barrier would go, the rest of the walls would then tie in with staples and tape.

So what would be the best product to use here that won't be affected by the heat of the dryer pipe? I know the Roxul batts will be fine, but still need some kind of air seal on the hot side.

 

[stormkroe]

Does your dryer melt the buttons on your shirt? Hehe, just put a thin layer of fiberglass in front of it, behind the poly if you're worried. Honestly, run your dryer as long as you want and put your hand on the duct.
But, just in case you don't know, DO NOT put screws into the duct for any reason. Clogging up the inside is a different matter and it will start a fire.

 

[Carson Dyle]

Who put the stupid wall there instead of six inches to the left?

If that's where your dryer goes, I'd think you could eliminate the solid duct almost completely. Is it necessary for code or some other reason?

 

[sdifox]

Use a form to leave a cutout for where the exaust goes, make it an inch bigger than the exaust. Spray your insulation, remove form then use this to fill in the gap.

http://www.touch-n-foam.com/firebreak.html

 

[NetWareHead]

Who put the stupid wall there instead of six inches to the left?

If that's where your dryer goes, I'd think you could eliminate the solid duct almost completely. Is it necessary for code or some other reason?

Flexible ducting catches more lint than solid ducting and its use should be minimized. I run solid ducting for as long of a length as possible and then make the connection to the dryer using a short run of flex.

 

[MagnusTheBrewer]

Maybe I'm misunderstanding what you said but, why would you put vapor barrier over batt insulation? You'd be trapping moisture in the wrong side.

 

[stormkroe]

Maybe I'm misunderstanding what you said but, why would you put vapor barrier over batt insulation? You'd be trapping moisture in the wrong side.

In Canadia, vapor barrier goes on the warm side. Just like a cold drink, moisture would collect on the poly if it were bordering the outside weather (on the cold side of the wall), this would cause the batting to be soaking wet for 8 months of the year. All natural mold wall fill filling!

 

[Carson Dyle]

Flexible ducting catches more lint than solid ducting and its use should be minimized. I run solid ducting for as long of a length as possible and then make the connection to the dryer using a short run of flex.

I doubt that three feet in his case is going to make any difference, and leaves him without a duct that ever has to be cleaned. The connection in my basement is at the ceiling, then there's a solid duct running about 15 feet to the outside wall, so requires about the same amount of flex duct as he'd need if he got rid of that piece in the wall.

* Edit *

Or... just bring the solid ducting outside the wall up above instead of trying to keep it inside the wall.

 

[Red Squirrel]

Who put the stupid wall there instead of six inches to the left?

If that's where your dryer goes, I'd think you could eliminate the solid duct almost completely. Is it necessary for code or some other reason?

Yeah not sure why they put the wall right up against where the vent exits or why the exit is even that far down. The solid duct is there as that part is going to be hidden so I don't want flexible duct inside walls, but solid is overall better anyway. I may even put more solid going from the dryer straight up, so that way I can push the dryer in and have access to both ends and just put a short flex line.

Use a form to leave a cutout for where the exaust goes, make it an inch bigger than the exaust. Spray your insulation, remove form then use this to fill in the gap.

http://www.touch-n-foam.com/firebreak.html

Touch-n-foam is what I'll be using (the system 400) but did not think of their fire retardant products, I think that may be an option for that section. Though I don't want to buy a whole setup just for that, so might just buy the cans then just do the part of the pipe that will touch vapour barrier, then do regular vapour barrier for rest. Since it's not a straight shoot out of the wall it makes it a bit more tricky.

Maybe I'm misunderstanding what you said but, why would you put vapor barrier over batt insulation? You'd be trapping moisture in the wrong side.

You want that to be on the inside, as it serves two purposes, preventing moisture, but also air sealing. So you want your air seal envelope to be on the inside and tie in with everything else. Ex: walls will tie in with rim joists, and so on. For rim joists and that general area I'll be using foam as it also acts as a vapour barrier. Then the foam will go all the way up to the top plate. If you put vapour barrier on the cold side you end up with condensation as the air inside the house is more moist than the cold air outside, and behind the insulation it will be cold.

 

[Carson Dyle]

Yeah not sure why they put the wall right up against where the vent exits or why the exit is even that far down. The solid duct is there as that part is going to be hidden so I don't want flexible duct inside walls, but solid is overall better anyway.

Unless you think it needs to be hidden inside the wall, just bring out of the wall up above.

 

[Red Squirrel]

Unless you think it needs to be hidden inside the wall, just bring out of the wall up above.

It is being brought out. It's the only way it can really go because that partition wall is in the way. Though now that I think about it, if I swap the exit points of both those vents it might make it easier, the other one is a bathroom fan, so I don't have to worry about what touches it. Then the other one is a straight shoot out so it will be easier to protect. I can do like sdifox said and use fire retardant foam around it.

 

[MagnusTheBrewer]

Yeah not sure why they put the wall right up against where the vent exits or why the exit is even that far down. The solid duct is there as that part is going to be hidden so I don't want flexible duct inside walls, but solid is overall better anyway. I may even put more solid going from the dryer straight up, so that way I can push the dryer in and have access to both ends and just put a short flex line.



Touch-n-foam is what I'll be using (the system 400) but did not think of their fire retardant products, I think that may be an option for that section. Though I don't want to buy a whole setup just for that, so might just buy the cans then just do the part of the pipe that will touch vapour barrier, then do regular vapour barrier for rest. Since it's not a straight shoot out of the wall it makes it a bit more tricky.



You want that to be on the inside, as it serves two purposes, preventing moisture, but also air sealing. So you want your air seal envelope to be on the inside and tie in with everything else. Ex: walls will tie in with rim joists, and so on. For rim joists and that general area I'll be using foam as it also acts as a vapour barrier. Then the foam will go all the way up to the top plate. If you put vapour barrier on the cold side you end up with condensation as the air inside the house is more moist than the cold air outside, and behind the insulation it will be cold.

I did some more research and the experts don't like batt insulation and vapor barrier in ANY combination on the walls of the basement. They ALL recommend either foam or rigid insulation.

 

[Red Squirrel]

I did some more research and the experts don't like batt insulation and vapor barrier in ANY combination on the walls of the basement. They ALL recommend either foam or rigid insulation.

There is a lot of misinformation out there on vapour barrier and air tightness in general. You want to air seal a space otherwise you're just going to leak air and negate the effects of the insulation. An ideal house is super airtight, and has controlled ventilation so that there is still some fresh air brought in. Ex: via an HRV system. That's mostly for your own health than the house's (so you're not breathing "stale" air) If your house is leaky then you'll always be cold and it will feel drafty as you're losing heat even if it's well insulated. Of course that also leads to condensation and other issues since you have warm air hitting very cold surfaces behind the insulation.

That's my problem on my main floor. I need to rip out the drywall and redo vapour barrier one day as I'm always freezing in my living room. The few sections I looked at due to other reasons I noticed it was a shoddy installation where they did not even use tape.

 

[stormkroe]

I did some more research and the experts don't like batt insulation and vapor barrier in ANY combination on the walls of the basement. They ALL recommend either foam or rigid insulation.

Which experts and why? That's quite contrary to national building code of canada, as well as alberta building cod.e

 

[MagnusTheBrewer]

Which experts and why? That's quite contrary to national building code of canada, as well as alberta building cod.e

Apparently,it's due to trapping moisture in the batt insulation causing mold. All I know about building codes in Canada is what I pick up from watching Mike Holmes who doesn't seem to think they're particularly stringent. My go-to for all things concerning construction is Tommy Silva and the TOH bunch.

 

[stormkroe]

Apparently,it's due to trapping moisture in the batt insulation causing mold. All I know about building codes in Canada is what I pick up from watching Mike Holmes who doesn't seem to think they're particularly stringent. My go-to for all things concerning construction is Tommy Silva and the TOH bunch.

Ahh. Mike Holmes is kind of a joke to real construction guys, he's actually just a plumber and does some pretty shoddy stuff (but also some way above code stuff).
Rule of thumb: You HAVE to have insulation on all exterior walls, and it has to be vapor barriered on the heated side. The air envelope keeps the insulation dry, though it doesn't get any more than atmospheric humidity, and the poly keeps it safe from the real moisture threat: heated living quarters.
Animals are gooey.

 

[Humpy]

Which experts and why? That's quite contrary to national building code of canada, as well as alberta building cod.e

Dr. Joseph Lstiburek is probably the main guy, he's a Canadian engineer that has studied this extensively. Plenty to read about, the jist is that batts are air permeable, and vapor barriers are imperfect enough to still allow water vapor into the wall via vapor drive.

 

[Red Squirrel]

Mike Holmes would solve this by just spray foaming the entire building envelope. But you also need a reality TV show budget for that. Though TBH if I was building a new house, that probably is what I would do. The foam acts as a vapour barrier and insulation in one and easier to tie it all together even with awkward areas. Thats why I'm doing a bit of both, spray foam for the rim joists and oddball corners, then tie it all in with batts and plastic as that is cheaper and still decently effective.

But yeah think tomorrow what I'll do is swap those two pipes around. If I make the dryer exit at the hole that is not behind the wall it will allow me to do a straight shoot into the wall making it much easier to deal with. Then I can frame a square around it and vapour barrier all the way to the square, then use that fire retardant spray foam for inside the square to tie it all together as a continuous seal. The other pipe is just an exhaust fan so I don't have to worry about heat, can just tie normal plastic to it with tuck tape.

 

[stormkroe]

Spray foam is only a vapor barrier if it's closed cell, which also makes it susceptible to cracking in older and (poorly built) new homes. The best insulation would be a combination of cellulose, spray foam, and fiber/mineral wool where needed.
As to the weakness of the vapor barrier itself, that is completely dependant on the installation. Drywallers aren't supposed to 'rotozip' walls with vapor barrier because they ruin it, but they all do. Otherwise, properly taped and sealed 6 mil poly is as water proof as it gets for a house, and the minuscule amount of humidity that might find its way through is negligible. That's why your siding system is supposed to breath. Batting is no more absorbent than spray foam, likely much less so. Without poly, your drywall will mold in most places in Canukistan, as well as not pass any inspection.
This is a great system that needs no improvement.

 

[Humpy]

This is a great system that needs no improvement.

The literature seems to indicate otherwise.

There are plenty of examples where widely accepted practice turned out to be wrong. Keep that in mind when considering alternatives or examining your own methods.

 

[Red Squirrel]

Spray foam is only a vapor barrier if it's closed cell, which also makes it susceptible to cracking in older and (poorly built) new homes. The best insulation would be a combination of cellulose, spray foam, and fiber/mineral wool where needed.
As to the weakness of the vapor barrier itself, that is completely dependant on the installation. Drywallers aren't supposed to 'rotozip' walls with vapor barrier because they ruin it, but they all do. Otherwise, properly taped and sealed 6 mil poly is as water proof as it gets for a house, and the minuscule amount of humidity that might find its way through is negligible. That's why your siding system is supposed to breath. Batting is no more absorbent than spray foam, likely much less so. Without poly, your drywall will mold in most places in Canukistan, as well as not pass any inspection.
This is a great system that needs no improvement.

Actually I was kind of wondering about long term quality of spray foam in new construction, as yeah things shift around. Does foam have a bit of a flex to it for minor movement? I think in older construction stuff probably shifted as much as it had to and there's probably less movement. But for new constructions I could definitely see it being an issue. Vapour barrier will at least have more play. A fully spray foamed house would work great for "exotic" structures though, like shipping containers, or building a large concrete dome, etc. Then you spray foam the hell out of that and make it like a foot thick. That's not going anywhere. Then you frame and drywall and don't need a vapour barrier since the foam acts as one. You need to do multiple layers if going that thick though.

I'm at the stage where I can foam the rim joists now, had lot of misc stuff to prep like removing some old insulation from rim joists and making any needed construction to build up foam in some places such as between top plate and foundation where there's too much distance. Basically doing all the rim joists and then carrying over the foam all the way to the top plate. Then the actual walls will be regular vapour barrier and batts.

As for the dryer pipe, ended up not swapping it with the fan one it as it was too hard to remove the fan one as that one is screwed in and the framing stops from being able to get a screw driver in there (the pipe was added before). So I'll just ensure the long part of the dryer pipe in the pic has insulation in the spots where it might touch the wood or vapour barrier. For where it comes out I'll probably just do the fire rated foam. I can probably just tape the vapour barrier from the rest of the wall to the foam, put a shit load of acoustic seal and should be good I think.

Also to show the importance of vapour barrier when I was pulling out the old insulation from rim joists (which has paper back, but was not taped) I was getting tons of sand and dust too. That's all crap being carried by air movement, which indicates heat loss.

 

[stormkroe]

Funny I just saw your post so soon. Open cell foam has tons of movement, like couch cushion almost, and incidentally a higher r per inch than closed, but then yoi have to vapor barrier it.
Closed cell has a very tiny amount of flex, I wouldn't count on it for anything helpful. The good thing is, you usually only use it in places that tend to be extremely rigid (like joist cavity end plates).
It's ridiculous to see how quickly vapor condenses on cold poly. In the winter, the builders poly the ceiling as soon as they can, then board it so they can blow in insulation and heat the building. Within minutes of turning the heater on, there is frost on the ceiling. I've actually been in a house that was pollied, boarded, and heated but the blow in wound up being late. As a result, the drywall started falling off the ceiling from moisture.
People in the south (like where I'm from), simply don't understand that moisture is trying to 'get out' of a home for most of the year in Canadia, vs. places like Georgia where it's humid outside and air-conditioned dry inside, it's trying to get in.

 

[Mr.IncrediblyBored]

What are your guys thoughts on XPS against the foundation in lieu of a vapor barrier? I'm currently finishing my basement and went with 1.5" rigid foam against the wall and then studs against that. I'm debating the need for any additional insulation or poly.

 

[Red Squirrel]

I think XPS is acceptable, just make sure to use tuck tape between all the seams. Though that does draw another issue, on it's own it does not have enough R value, so you'd want to put batts over it. That would then put the vapour barrier behind the batts. The R value of the foam might be enough to counter the moisture though. One thing some people do is do the floors and walls, that way you can seal the floors too, then you lay a plywood subfloor over the XPS. Everything is all taped together creating a nice sealed envelope.

I've also read elsewhere that rigid foam is not considered a vapour barrier, but first I hear of that myself so not sure how true it is, as even the shows like Holmes etc do sometimes use it.

 

[Humpy]

What are your guys thoughts on XPS against the foundation in lieu of a vapor barrier? I'm currently finishing my basement and went with 1.5" rigid foam against the wall and then studs against that. I'm debating the need for any additional insulation or poly.

You're going about it the best way.

In general, add the additional insulation in the stud bays, do not use poly.

https://buildingscience.com/documents/bareports/ba-0202-basement-insulation-systems/view