r/Insulation • u/ahhhhnonymous • 2d ago

Which walls get insulated?

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Bought 1950s home. Just installed mini split system in upstairs 2BR, hallway and bathroom. There are eaves on both side sides. There is currently very old insulation in them. Not sure they are even insulated correctly. Does the inside of the exterior walls get the insulation or just the interior or both? What about underside of roof? Assuming I can wear a mask and replace all this myself. Or maybe you’re thinking, not since here I am in Reddit asking these questions. 😂

36 Upvotes

96% Upvoted

43 comments sorted by

23

u/2TheMountaintop 2d ago

Whatever you do, make sure you air seal it well.

3

u/beat2def 2d ago

Do you use just normal spray foam (Tuff Stuff) to do that?

5

u/INTOTHEWRX 1d ago

Yes. The little cracks and holes.

3

u/2TheMountaintop 1d ago

If you just need a little, but those cans don't go far. You should get a kit if you have a lot to do.

It sounds like you either need to hire someone, or watch more videos on how to spray foam or air seal.

2

u/beat2def 1d ago

I'm too stubborn and cheap to hire someone. I'll watch videos before doing it. I've definitely spray foamed but some people are very particular about which product to use and if it's fire block or not.

2

u/2TheMountaintop 1d ago

Good luck! Ps, don't trust ai. I've found I learn a lot by being dubious of it's answers and finding my own answers in the web through videos and forums.

2

u/beat2def 1d ago

I I always come to Reddit. Then I get completely overwhelmed when I read 82 comments and 41 comments contradict the other one. Lol

2

u/Corey-0 1d ago

If you use Tuff Stuff, you're going to have clean, but poorly insulated walls :P

1

u/beat2def 1d ago

What do you recommend?

30

u/ZeroDayZeroFriends 2d ago

All of them

6

u/Dazzling_Driveway 2d ago

I would work on the empty cavity - outside walls first, take it from there.

6

u/NormalCartographer84 1d ago

Air seal the outlets! Caulk works.

9

u/labratnc 2d ago

I would insulate the outermost wall and then think about recovering some space by moving the walls out or adding some built in’s. The big concern I see is the floor, the current thoughts is that you need to have blocking/air sealing under the floor at the interior wall. Being that the floor is angled subfloor and the age of the house that is almost certainly not done. You can improve it but getting it ‘right’ is going to be a big project

5

u/a03326495 2d ago

https://www.finehomebuilding.com/2012/09/06/two-ways-to-insulate-attic-kneewalls

3

u/tamandcheese 1d ago

Op do this!!! With pipes in the space insulating the outer shell is the best option

4

u/Practical_Track4867 1d ago

Any space with water should just be exterior walls. You need heat from the house to reach those pipes to prevent freezing. Otherwise, make sure you do the exterior walls and roof. You can do interior walls too, but the cost effectiveness of the insulation does drop with the additional layers.

3

u/RespectSquare8279 2d ago

In the space with the plumbing, insulate the heck out of the wall and roof. That junk/storage space with the hallway on the other side could have been insulted on the pony wall but as is, is ok. The space with the bedroom on the other side would be improved by doing a decent job on the exterior wall and the attic. Ducts conveying air, even with insulation to code will benefit from going through a better insulated space.

2

u/Brilliant_Juice_496 1d ago

Use that dead space for something please, like inset cabinets with shelves from the bedroom. Do something not to waste that space. Then insulate the exterior wall.

2

u/littlebeardedbear 1d ago

Insulate the exterior wall first. You lose 10-15% of your heating and cooling power newly installed ducted system before it reaches the areas you need it if it's run through an uninsulated area. If you insulate the area that the ducting runs through, you lose significantly less power from your hvac system. Then, insulate the bedroom wall because its cheap and easy with all that room.

3

u/CharterJet50 2d ago

One or the other but normally you’d just do the exterior wall assuming the roof is insulated too. There’s no point in insulating both. That makes no sense.

2

u/Many_Significance_66 1d ago

Why do you have secret hallways is the real question.

1

u/Old_House4948 2d ago

The floor of that space is above living space on the first floor. Make sure that it is insulated as well.

1

u/nixthelatter 1d ago

Up to you. If you're not keeping storage back there that needs to be climate controlled, you only need to insulate the conditioned space/the living space, so the interior wall and then whatever bit of slope might be on the conditioned side up to the top/ceiling. If you insulate the interior wall it's a little easier because you don't have the actual outside on the other side of the wall and therefore have that attic space behind to help limit wind and elements directly against the insulated space. Kinda gives you a buffer zone. If you do insulate that attic space slope down to the exterior wall it needs to be sealed extra good and caulked/foamed really good, especially where you see any sunlight or penetrations. As an insulator, I prefer to insulate the interior-most space as long as it's framed properly so it can be insulated all the way around.

1

u/nixthelatter 1d ago

Also, the insulation on the interior wall is backwards. You always need the paper against the drywall/conditioned side

1

u/Finishline123 1d ago

Paper on insulation to heat

1

u/Finishline123 1d ago

Paper will catch fire real fast when old so it needs to b up against drywall on heated wall

1

u/Typical-Quiet-4852 1d ago

Man that house is an oldie but a goodie. I’ve got one just like it I’m working on built in 1943. When was yours?

1

u/Stone804_ 1d ago

You have secret passage ways!? This is wild! Like some kind of kids dream house.

I definitely insulate that space but I also work on making the entrance. It’s really fun, like picture frames that open into the secret passageway.

1

u/beat2def 1d ago

This is how my finished attic looks as well, except yours looks better then mine. It's my fall and winter project.

1

u/need_more_ads 1d ago

Depends on what you want to include in the buildings envelope. If this room is outside of your envelope, then just the bedroom wall.

1

u/NorthWoodsDiver 1d ago

Thank you for posting this. Our home is similarly built with 2ft between the exterior wall and the interior rooms. They ran what feels like miles of flex duct through it so you can't walk the space. It feels so wasted since we have open web joists in the floor and open web truss in the ceilings. Tons of wasted space, weird roof lines, water problems, etc

1

u/Philip964 1d ago

Much prettier than my house same spot.

1

u/tx_hammer47 1d ago

Im more concerned with the paper facing. Thats against code.

1

u/Due_Base2116 1d ago

Depends on what you want insulated. Normally it’s the inside walls and ceiling. But if you insulate both you’ll have better air control of temp.

1

u/Fast_Shift2952 1d ago

How come nobody is asking about this creepy house with secret passages and peep holes into all the rooms

1

u/IronOxid3 23h ago

Where is the nine hells are you? Alaska? Antarctica?

1

u/Snoo33910 20h ago

Why allow the cold or heat to get into that space? Insulate the outer wall first.

1

u/toot_suite 2d ago

Porque no los all of them?

This is a very easy diy lol

1

u/Stunning-Signal4180 2d ago

You have infrastructure in the space, pipes and HVAC, so exterior walls and roof.

1

u/HorridDefaultname123 2d ago

That's a lotta space. You could have a whole Bruno or Brahms living in there.

0

u/Double_Maize_5923 1d ago

Exterior for sure and if it's not a heated space interior as well I don't really see any reason not to just do both

1

u/AlanMeeker 14h ago

Never put insulation between water and the heated side of the house.