Spray Foam Insulation Between Joists - Will The Foam Get Past The "X" Bridging? - Insulation - DIY Chatroom Home Improvement Forum
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Old 01-22-2020, 03:17 PM   #1
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Spray foam insulation between joists - will the foam get past the "X" bridging?


Hi all. The next step in my basement finishing project is to insulate between the ceiling joists. There is a wooden ceiling covering the joists that was put in some decades ago. Conveniently, I have some access to the area between the joists where I took out some old closets. I can easily step up on a ladder and see right down each of the joists.

Seems like a straight-forward insulation job with one hitch - in the middle of each space between the joists is an "X" shaped wooden support. Bridging, I think it's called?

Since it's X-shaped, there are cavities on any side of the bridging where something could pass through, but having never worked with spray foam insulation, I wanted to ask the group - will the spray foam just work its way past the bridging on its own? If not, can I work it past to the other side somehow? Would that be a huge pain in the ass?

Because of lead issues in the house, I really don't want to open up the other side of the ceiling.

Hopefully my question is clear. Below is a photo of the ceiling showing the exposed area where I plan to shoot the insulation from, if I can find a rental. Thanks all.

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Old 01-22-2020, 05:10 PM   #2
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Re: Spray foam insulation between joists - will the foam get past the "X" bridging?


I suspect you would do better with drilled holes to work in the other side.

But I have no experience.
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Old 01-23-2020, 09:46 AM   #3
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Re: Spray foam insulation between joists - will the foam get past the "X" bridging?


Just guessing from what i've seen in the videos. Spray foam starts to expand as soon as it is out of the nozzle. I don't think you can shoot it across the ceiling and expect to fill the space. I would guess it will not go through the bridgings. It may just get stuck there and become a bottleneck. I would also expect the spray foam to push the ceiling covering away from the joists. All in all, I think it will create a big mess. Spray foam also needs specific ambient temps to cure properly. Also applied in certain thicknesses. If you try to fill the whole space with one shot, the chemicals may not cure properly and end up with stink problem that won't go away. Probability is higher with blown in cellulose but again, I don't think you can shoot it across the whole ceiling. Even the walls, with gravity's help, require 2 holes, top and bottom.
If you can remove the wires and the drain, that would be the best way to add insulation. If not, I'd live with colder floor. Even a carpenter with some experience can handle those wires and the plumbing. Lead is not a concern as long as the material is not changed into a fine powder (such as sanding) and added into a coffee.
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Old 01-23-2020, 10:01 AM   #4
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Re: Spray foam insulation between joists - will the foam get past the "X" bridging?


Thanks all. I should have been more clear that the purpose of insulation in this case would primarily be to soundproof the finished basement space and create privacy between the new finished basement space (which includes a half bathroom) and upstairs living room.

I'm actually going to try passing through batt insulation this weekend using a broomstick or something. A bit janky, but batt insulation would mean less dust and fuss.
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Old 01-23-2020, 10:09 AM   #5
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Re: Spray foam insulation between joists - will the foam get past the "X" bridging?


Watch some videos of spray foam. As soon as that stuff hits those X supports, it will tend to accumulate and catch the subsequently sprayed foam. No way you are going to get much foam past that unless you can get the hose past the bridging.

Also, as @carpdad points out, spray foam is designed for a certain application thickness. Filling up a joist bay with foam in one shot is likely to leave lots of uncured foam, which doesn't just have the potential to stink, but can be hazardous.

Cellulose would be a better bet. Especially if you can sneak the hose past the bridging and work your way back from the farthest point, drawing the hose closer to you as you work. Or just cut out multiple holes and blow in cellulose in each area.
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Old 01-23-2020, 10:26 AM   #6
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Re: Spray foam insulation between joists - will the foam get past the "X" bridging?


The main concern with I have with using spray foam in a blind situation is that you run the risk of covering "improper" electrical connections.
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