Yet Another Insulation Question

[cdiggy]

Ok. I have been officially talked out of spray foam insulation for a bunch of different reasons including research on this site (thank you).
Seems like I can get 3 sheets of rmaxx foam board in the 2" variety for about 90 bucks so I am going with that. Problem is the ceiling ribs are hollow and 1 1/2" tall. I am debating whether filling them with SFI is a good idea.
The one over the drivers seat is about 6" wide and is steel, other than that they are just like the pic says. So.... What to do what to do. Fill with foam? Leave them hollow?
Btw i seemed to have spaced introducing myself so I guess this is me introducing myself (Doug)
Thanks!

 

[akrvbob]

I think the styrofoam is the perfect thing to use. What are your concerns about the ribs? That they are a 1/2 inch too short so you don't know how to attach the stryofoam? Sorry, I forget what you are in, is that a step-van?

The ultimate would be to get 1 1/2 in sheets of styrofoam and put it between the ribs, and then turn the 2 inch sheets the opposite direction and screw them into the ribs with the right sized sheet metal screw. that would give you 3 1/2 inches over the whole roof and 2 inches over the ribs.

But for most people in the Lower 48 that's unnecessary overkill. If you are in a really cold place you would be glad you did though!! It would also cost you a lot of headroom.

Leaving it hollow and running the sheets across the ribs will be easier and cheaper so if you can afford to lose the headroom that's a good way to go. To reduce heat in the summer you could lay some reflectix in the voids on top of the styrofoam so that there was an air gap between the roof and it. That would probably reduce heat coming in from the roof.
Bob

 

[cdiggy]

Yes. It is an 83 p30 Grumman Olson. Unfortunately I don't have enough head room for all of that. I was thinking of 1 1/2" for the voids and half inch over all of it but that will cost significantly more than using 2" and fill the half inch gap over top of the rib. I just didn't know whether filling the rib with foam would help keep the heat in or if it was a waste of time and money

 

[Almost There]

Yes. It is an 83 p30 Grumman Olson. Unfortunately I don't have enough head room for all of that. I was thinking of 1 1/2" for the voids and half inch over all of it but that will cost significantly more than using 2" and fill the half inch gap over top of the rib. I just didn't know whether filling the rib with foam would help keep the heat in or if it was a waste of time and money

Maybe use 1/2 foam over the ribs to give it 'some' insulation and then use the 2" between the ribs.

Either that or custom fit the 2" by cutting away a 1/2" to allow for the depth of the ribs where you need to.

 

[cdiggy]

That's what I was thinking. The 2" is $30 a sheet and 1 1/2" is $28. At first I was thinking 1 1/2 in between ribs and 1/2 over everything but it adds money. Guess I probably shouldn't skimp.

 

[Almost There]

What's the spacing between the ribs as compared to the size of the sheets.

I just realized you were talking about spraying the inside of the ribs with 'SFI' which I take to mean spray foam insulation...don't do it.

The ribs don't have enough access holes to do it well and I read that spraying in the sfi without enough room for it to fully expand is a 100% chance of it not expanding to it's full volume and therefore not curing. It's caustic when it isn't cured IIRC.

 

[akrvbob]

Putting the 2 inch between the ribs will work well. While not having anything over the ribs is less than ideal, it's no big deal. If it's 1/2 inch wide and there are 10 ribs, you are leaving a total of 5 inches un-insulated. It's better to cover it all but it certainly doesn't offset the great job you're doing of covering the rest.

A possible solution is to cut refelctix into narrow strips and put that over the ribs. It's not great but it will be fairly easy and cheap so it's better than nothing at all.
Bob

 

[Bdog1]

It's not that tuff to cut a channel in the 2" to accommodate the rib. Utility knife and some time.

 

[Van Go]

I have used a small router to cut channels in foam. Super fast.

 

[Luisafernandes]

Definitely do not use spray foam on the ribs! Just my opinion.
You say they're hollow but I don't see any holes you could possibly shove some foam pieces in. Would it be feasible to cut one hole big enough so you can fill the rib with the hard foam or other type of insulation (but not spray foam)? That could be a possibility.

 

[Reducto]

If you don't have a router or other suitable tool to cut the channel, cut the grooves at the ends of the foam pieces. That should be easier to do with a utility knife and straight edge.

Cut the foam so it's shaped like this:

_/¯¯¯¯¯¯¯¯\_
____________

Sized to fit between the ribs. At the joints fill in gaps with slivers of the stuff you're using, with foil tape over that. You can use spray glue to temporarily hold the foam in place then follow it up with some sort of wood screwed into the ribs.

I have multiple thin layers on my roof and it worked, but it squeaks like crazy.

 

[Belchfire]

Hi Cdiggy
Why were you talked out of spray foam?
Thanks

 

[One Awesome Inch]

Because it absorbs moisture leading to rust and / or mold.

 

[Belchfire]

Because it absorbs moisture leading to rust and / or mold.

Are we talking about closed cell spray insulation?
I thought it was waterproof

 

[One Awesome Inch]

I am not sure but I am not using any spray foam. I am no expert but I dont think its worth the risk. I plan to just crumble up regular white styrofoam and shove it in all holes I can find.

 

[cdiggy]

Hi Cdiggy
Why were you talked out of spray foam?
Thanks

Everything from water retention to shrinkage to being squeaky loud. I really think they have most of those issues solved now with newer products and delivery systems but it is expensive and until I use the stuff for myself I can't give it a bad rap. I know 'great stuff' is a decent product ( a friend of mine sealed holes to the outside of his house about 7 years ago and the stuff, even exposed to the weather was dry. The sun powderized the surface but it was dry) but I am not willing to use it. They say it works better if you mist some water before you spray for better expansion of the foam and that has been my experience too (I have used it to ship fragile items). If I had the extra money I would just spray it with the pro style 2 part stuff and call it a day. As it stands spray would cost me $1 a board foot and using the boards would cost me just north of $.50 a board foot. All that being said spray foam would probably do a much better job if it sprayed and acted like they say it does in the promotions.